Design Guide Part 4: General
requirements for HVAC systems
RIBA Stages 3 - 7
2016 V1.0 Green Cover
Phillip Hunt (EST) Phillip.hunt@uea.ac.uk
Estates & Buildings Division, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ
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Contents
1
Introduction .................................................................................................................... 5
Prior Reading .......................................................................................................... 5
Purpose of the UEA Design Guide .......................................................................... 5
Purpose of This Section of the Design Guide .......................................................... 5
Interpretation........................................................................................................... 5
Structure of this Part of the Design Guide ............................................................... 6
2
Requirements for All HVAC Systems ............................................................................. 8
Introduction ............................................................................................................. 8
Key Principles and Requirements ........................................................................... 8
Building Heating, Cooling and Ventilation Load Assessment .................................. 9
Introduction ...................................................................................................... 9
Key principles and requirements ...................................................................... 9
Preferred materials, technology and solutions................................................ 10
Suggested schematics ................................................................................... 10
Applicable standards and best practice guides .............................................. 10
Integration with the Campus’s Building Management System (BMS) .................... 10
Testing, Commissioning and Documentation ........................................................ 10
Testing and Commissioning ........................................................................... 10
Documentation............................................................................................... 11
3
Heating ........................................................................................................................ 12
Introduction ........................................................................................................... 12
District Heating System (DHS) .............................................................................. 12
Introduction .................................................................................................... 12
Key Principles and Requirements .................................................................. 13
Preferred materials, technology and solutions................................................ 14
Suggested schematics ................................................................................... 17
Applicable standards and best practice guides .............................................. 17
District Heating System Integration (Building Connection) with Space Heating and
Domestic Hot Water Systems .......................................................................................... 18
Introduction .................................................................................................... 18
Key principles and requirements .................................................................... 19
Preferred materials, technology and solutions................................................ 21
Suggested schematics ................................................................................... 23
Applicable standards and best practice guides .............................................. 23
Alternative Heat Sources – Renewable Energy Systems ...................................... 24
Introduction .................................................................................................... 24
Key principles and requirements .................................................................... 24
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Preferred materials, technology and solutions................................................ 24
Relevant drawings and schematics ................................................................ 25
Applicable standards and best practice guides .............................................. 25
Alternative Heat Sources – Gas Heat Sources and Infrastructure ......................... 25
Introduction .................................................................................................... 25
Key principles and requirements .................................................................... 26
Preferred materials, technology and solutions................................................ 26
Relevant drawings and schematics ................................................................ 28
Applicable standards and best practice guides .............................................. 29
Space Heating Circuit Design and Emitter Sizing .................................................. 29
Introduction .................................................................................................... 29
Key principles and requirements .................................................................... 29
Preferred materials, technology and solutions................................................ 30
Relevant drawings and schematics ................................................................ 35
Applicable standards and best practice guides .............................................. 35
Domestic Hot Water System (DHWS) Design ....................................................... 35
Introduction .................................................................................................... 35
Key principles and requirements .................................................................... 35
Preferred materials, technology and solutions................................................ 36
Relevant drawings and schematics .............................................................................. 40
Applicable standards and best practice guides .............................................. 40
4
TermoDeck System Design and Control ...................................................................... 41
General Description .............................................................................................. 41
UEA Control Concept............................................................................................ 41
Heat Sources for TermoDeck Installations ............................................................ 42
Air Handling Unit Requirements for TermoDeck Installations ................................ 42
General requirements .................................................................................... 42
Supply Side Requirements............................................................................. 42
Extract Side Requirements ............................................................................ 43
5
Comfort Cooling Using Chilled Water and/or Refrigerant Gas ...................................... 44
Introduction ........................................................................................................... 44
District Cooling System (DCS) .............................................................................. 44
Introduction .................................................................................................... 44
DCS Infrastructure ......................................................................................... 44
Key principles and requirements .................................................................... 45
Preferred materials, technology and solutions................................................ 46
Suggested schematics ................................................................................... 49
Applicable standards and best practice guides .............................................. 49
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District Cooling System Integration (Building Connection) with Space Cooling
Systems .......................................................................................................................... 50
Introduction .................................................................................................... 50
Key principles and requirements .................................................................... 50
Preferred materials, technology and solutions................................................ 51
Suggested schematics ................................................................................... 54
Applicable standards and best practice guides .............................................. 54
Alternative Cooling Technologies .......................................................................... 54
Introduction .................................................................................................... 54
Key principles and requirements .................................................................... 55
Preferred materials, technology and solutions................................................ 55
Relevant drawings and schematics ................................................................ 56
Applicable standards and best practice guides .............................................. 56
Space Cooling Circuit Design and Emitter Sizing (for Chilled Water) .................... 56
Introduction .................................................................................................... 56
Key principles and requirements .................................................................... 57
Preferred materials, technology and solutions................................................ 57
Relevant drawings and schematics ................................................................ 61
Applicable standards and best practice guides .............................................. 61
6
Ventilation Including Fresh Air Cooling......................................................................... 62
Introduction ........................................................................................................... 62
Key Principles and Requirements ......................................................................... 62
Preferred Materials, Technology and Solutions ..................................................... 63
Natural ventilation .......................................................................................... 63
Mixed mode (hybrid) ...................................................................................... 64
Mechanical ventilation, fresh air cooling and ground coupled passive cooling 64
Phase change ventilation ............................................................................... 65
Displacement ventilation ................................................................................ 65
BMS integration ............................................................................................. 65
Relevant Drawings and Schematics ...................................................................... 65
Applicable Standards and Best Practice ............................................................... 65
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1 Introduction
Prior Reading
It is imperative for readers of this document to first refer to the introductory Part entitled:
‘Design Guide Part 1: Principles and overview’.
Part 1 gives vital information and context that apply to all projects.
In addition to Part 1, readers may need to refer to Part 3: Philosophies and Criteria for
Heating, Cooling, Ventilation and Light in Buildings. Part 3 gives important information about
design criteria for different types of buildings as well as the preferred strategies for meeting
them; Parts 1 and 3 are intended for use at RIBA Preparation and Brief stage (RIBA Stage
11) to the Concept Design Stage (RIBA Stage 2).
Purpose of the UEA Design Guide
The Design Guide (as a whole) is written for employees of the UEA, architects and external
consultants and contractors. The purpose of the Guide is to act as a briefing document to
give designers an overview of the design requirements, constraints and challenges
presented by the UEA’s specialist needs. It applies to all new-build and refurbishment
projects controlling quality in the production of designs, specifications and the subsequent
performance of buildings.
The Design Guide aims to discuss strategic matters and does not provide an exhaustive
treatment of statutory or best practice design and compliance requirements; its primary
purpose is to establish a starting point for design briefs. It is the responsibility of readers/duty
holders to ensure subsequent designs are complete, compliant and able to meet the final
approved brief when measured in use.
Purpose of this
this Part of the Design Guide
This Part of the Design Guide is written for designers and specifiers of heating, cooling and
ventilation strategies and systems from the Developed Design Stage (RIBA Stage 3) to
when the building is in use (RIBA Stage 7).
Interpretation
Interpretation
Any part of the Design Guide may be referenced in project contractual documentation in
order for the UEA to control quality. The following interpretations apply:
Enforced requirements; the use of the word(s) ‘shall’, ‘are required’, ‘is required’ ‘must’ or
‘will be’ denotes a requirement that is non-negotiable and shall be used as the basis for
designs, technical submissions and/or activities. If such a statement conflicts with a statutory
obligation then a report to the Head of Engineering and Infrastructure shall be produced
highlighting the conflict, for his or her final decision regarding compliance.
1
http://www.ribaplanofwork.com
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Requirements needing confirmation; the use of the word ‘may’ denotes a negotiable
requirement or indication of a solution, where innovation and further calculation, design and
discussion may be required to arrive at an optimised solution.
Quality; the Design Guide aims to arrive at the UEA’s highest design aspirations and
standards. It may be that, at the UEA’s sole discretion, solutions are value engineered during
subsequent design iterations. Designers are encouraged to consider where value
engineering may result in an improved financial performance should funding constraints
occur.
Currency of third party documents; where superseded standards and regulatory
documents are referred to in the text, the reader shall apply current versions and disregard
superseded versions.
Proof; where the word ‘proof’ is used e.g. ‘proof is required’, a written report or installation
certificate must be produced for approval depending on context.
Approval and proof; all designs shall be approved by the UEA. Approval shall be
interpreted as meaning written approval from either the UEA’s appointed approving authority
or by the Head of Engineering and Infrastructure where no other approving authority is
appointed. Approvals shall be sought prior to design decision points or installation activities
(depending on context) and shall be made in writing. Where approvals are sought, a written
technical submission shall accompany the request setting out, with proof (e.g. calculations,
drawings), the case for the approval. The purpose of the approval process is to ensure
designs meet the strategic requirements of the UEA.
The obligations owed by external architects, consultants and contractors to UEA and their
liabilities to UEA is not in any way diminished or otherwise reduced by the approval process.
UEA is not taking over the roles and duties of the external architects; consultants and
contractors who will remain fully and totally responsible for the design and/or works carried
out by them or on their behalf by their staff; agents; sub-consultants or sub-contractors.
Structure of this Part of the Design Guide
The separate sections are as follows:
Section 1:
Introduction; prior reading, purpose and interpretation
Section 2:
Requirements for all HVAC Systems; applies to all sections in this
document including general principles, details of heat, cooling and ventilation
load assessment, the campus’s building management systems,
commissioning protocols, etc.
Section 3:
Heating; space, water and process requirements covering the hydraulic
elements of heating systems as well as gas infrastructure and heating.
Section 4:
TermoDeck heating; configuration with air handling plant and control
Section 5:
Comfort cooling using chilled water and/or refrigerant gas; space and
process requirements.
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Section 6:
Ventilation including fresh air cooling; air handling plant, natural and
mixed mode ventilation.
Each Section includes the following sub-headings:
•
Introduction
•
Key principles and requirements
•
Preferred material, technology and solutions; this section describes how the key
principles and requirements might be met
•
Suggested schematics
•
Applicable standards and best practice guides
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2 Requirements for All HVAC Systems
Introduction
The principles and requirements detailed below are of strategic importance and apply to all
HVAC systems, mainly with regard to environmental performance and cost efficiency.
Key Principles and Requirements
•
Most new build projects and refurbishments shall be subject to the targets of a
BREEAM2 standard usually established at RIBA Stage 1.
•
Heating and cooling systems shall be connected to the district systems where
technically and commercially feasible.
•
Integration with the district heating and cooling system shall be by means of a
gasketed plate heating exchanger (PHE).
•
Variable volume strategies are preferred.
•
The zone control strategy shall carefully consider the geometry of individual spaces
and the needs of the users.
•
Heat loss and gain shall be modelled by a recognised dynamic simulation application
using current and future weather data sets3 using Dry Resultant Temperature (tc) as
the preferred temperature index4.
•
Emitter sizes shall be calculated, on a zone by zone (or room by room) basis, using a
recognised methodology and not by using ‘standard’ tables based on floor area.
•
Heating and cooling circuit temperature differences (∆T’s) shall be high as detailed
below.
•
Pressure loss in pipe and duct systems shall be low (as detailed below) to minimise
annual pumping energy requirements but a consideration shall also me made
regarding thermal losses which may increase from unnecessary over sizing.
•
Low return temperatures are required to ensure district heating system (DHS) losses
are minimised and central boiler plant can operated in condensing mode. High return
temperatures are required for the district cooling system (DCS).
•
Thermal losses from pipe systems shall be carefully considered to ensure gains from
internal pipework do not create an overheating problem and systems are energy
efficient. Insulation thicknesses are greater than those required for Approved
Documents and second tier documents.
2
Building Research Establishment Environmental Assessment Model
Future CIBSE TRY/DSY Hourly Weather Data Set Norwich – Product Code WM08NOR
4 As described in CIBSE Guide B
3
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•
All systems shall have enough sensors to allow full monitoring and control of the
system and shall be integrated with the campuses Trend BMS system. Schematics
are provided showing the location and type of sensors.
•
Heating hydraulic pipe systems and components shall meet the UEA’s requirements
with regards to pipe material and jointing methods.
•
Hydraulic systems shall be dosed and maintained with the UEA’s preferred treatment
regime to ensure long life, reliability & efficiency.
•
All systems shall be tested and commissioned according to bespoke protocols
agreed with the Head of Engineering and Infrastructure. All systems will be subject to
a seasonal commissioning protocol.
•
Performance in use (PIU) standards shall be determined as part of the design
process to ensure targets are met for safety, reliability, compliance, efficiency and
other specific elements of the design brief.
Building Heating,
Heating, Cooling and Ventilation
Ventilation Load Assessment
Assessment
Introduction
A quality assessment of a building’s heating, cooling and ventilation load underpins energy
efficient design in terms of minimising HVAC system energy requirements. This section
describes the UEA’s requirement for such exercises.
Key principles and requirements
Heat loss & gain and ventilation (and infiltration) shall be modelled by a recognised dynamic
simulation application using current and future weather data sets5 using Dry Resultant
Temperature (tc) as the preferred temperature index6. The UEA or a member of the
consultant team will supply operational data for the building such as occupancy profiles,
heating times and temperatures, U-Values, infiltration & ventilation rates etc. Hot water loads
shall also be assessed according to profiles supplied by the UEA consultant team.
An hourly load model for space heating and cooling, hot water and ventilation shall be
developed allowing the risk of discomfort/undersupply to be understood for current and
future conditions for 40 years from the date of commissioning.
As a general rule for heating, having calculated the winter design day building heat loss (in
kW) using the method described above, an additional allowance for error and building warm
up of 15% should be allowed for. If the heat requirement for the domestic hot water service
(DHWS) does not exceed this 15% allowance then no extra sizing allowance for the heating
system shall be made for the DHWS and it will be provided by means of an instantaneous
plate heat exchanger (notwithstanding that this approach is technically and financially
feasible).
5
6
Future CIBSE TRY/DSY Hourly Weather Data Set Norwich – Product Code WM08NOR
As described in CIBSE Guide B
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As a general rule for cooling, a 10% addition shall be allowed for error and rapid cooling of
space.
Preferred materials, technology and solutions
If a dynamic modelling exercise is deemed too onerous for the project by the Head of
Engineering and Infrastructure, (e.g. when designing a heating system extension for a small
space), the design day heat loss can be assessed using a methodology approved by the UK
government that complies with the requirement of BS EN 12831 Heating systems in
buildings. Method for calculation of the design heat load or use the steady state heat loss
methodology set out in CIBSE Guide A7.
In such cases an assessment of the design day cooling load can be made using one of the
methods described in CIBSE8 Guide A.
Suggested schematics
NA
Applicable standards and best practice guides
Building Research Establishment Environmental Assessment Model
Future CIBSE TRY/DSY Hourly Weather Data Set Norwich – Product Code WM08NOR
CIBSE Guide B Heating, ventilation, air conditioning and refrigeration
BS EN 12831 Heating systems in buildings. Method for calculation of the design heat load
CIBSE Guide A Environmental design
Integration with the Campus’s
ampus’s Building Management System (BMS)
The campus is controlled and monitored by a Trend building management system connected
to all buildings and significant items of plant. Part 5 of the Guide gives detailed guidance
regarding the requirements for any new BMS developments or modification to existing
systems.
Testing, Commissioning and Documentation
Testing and Commissioning
The UEA recognises that the design aspirations for any development work can be realised
or lost at the testing and commissioning stage. Testing and commissioning often takes place
during the final stages of a project when time pressures are greatest, potentially resulting in
systems that perform poorly when in use.
7
8
CIBSE Guide A
Chartered Institute of Building Services Engineers
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A commissioning agent will be appointed early in the design process to follow the design and
construction throughout the project, reporting on a regular basis on issues that could affect
the reliable and efficient running of building services and the subsequent impacts on comfort
and safety. The commissioning agents will then fully test and approve the systems and
monitor performance during the first year of occupation. Commissioning reports shall be
issued at handover and 12 months later.
In order to ensure that sufficient time for commissioning is built into the development
schedule, the following procedures must be allowed for:
•
A bespoke commissioning protocol shall be produced, basing its detail on existing
best practice commissioning codes and guides (e.g. CIBSE and/or BSRIA).
•
Seasonal commissioning may be a requirement of the brief depending on the scale
of the project.
•
System performance shall be measured in use to ensure the agreed design
parameters are met and where they aren’t, to gain an understanding of how to make
improvements for the future and to adjust final invoice values accordingly.
Documentation
The UEA requires as built drawings and Building Information Modelling (BIM) models to be
made available within the timescales determined at the project brief stage. BIM Level 2, 6D
shall be the protocol applied and achieved. Record drawings shall be made available in 2D
and 3D in Revit and dwg file formats. Retentions will not be released until all contractual
obligations have been met and in some cases a damages claim may be the result of late
submission.
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3 Heating
Introduction
The sections below describe the UEA’s preferred solutions for space and hot water heating
systems. This document does not provide information for specialist heating systems (such
as process heat for research purposes) and in such cases a bespoke brief and subsequent
design shall be produced. Information regarding comfort criteria and preferred approaches to
heating can be found in Part 3 of the Guide: Design criteria for heating, cooling, ventilation
and light in buildings.
Having read this Part of the Guide (Part 4), it is expected that designers contact a member of
the UEA’s Engineering and Infrastructure team to discuss its contents and to ensure that no
ambiguity exists, before designs are developed.
District Heating System (DHS)
Introduction
Where technically and financially feasible, all heat at the UEA shall be provided by the
DHS. A standard finance model shall be supplied by the Head of Engineering and
Infrastructure upon which the decision shall be made.
The UEA utilises a DHS to provide heating and primary hot water to a large number of
buildings on the campus. The system utilises a combination of combined heat and
power engines with conventional condensing gas fired low temperature hot water boilers
(with oil standby) to provide this heat source; the total heat output is c25 MW.
The water is pumped from two energy centres to the individual buildings in a flow and
return arrangement via a combination of service ducts and the university’s raised
walkways.
The system flow temperature is weather compensated and varies seasonally from 70°C
in the summer to a maximum possible of 98°C in the winter and at an operating pressure
of between 2.5 and 4.5 bar(g). The typical operating temperature is c85°C.
The system operates using a variable flow pumping arrangement which varies the flow
volume to meet the sum of individual building flow demands. The design philosophy of
the system is to obtain the greatest possible difference between the flow and return
temperatures, leading to low return water temperatures and so maximising the pumping
and thermal efficiency of the combined heat and power system and the condensing gas
boilers. Minimising return temperatures is generally achieved by the use of two port
control valves as described in detail below. Bypass should not be fitted within the system
unless special circumstances exist.
The system utilises a building management control system (Trend) to monitor the
system pressure differential between the flow and return at the two extremities of the site
and adjusts the DHS pump speed to maintain 0.7 bar(g) at these locations.
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Key Principles
Principles and Requirements
Any work to develop new sections of the DHS and to repair or alter the existing system shall
consider the following key principles and requirements, which are discussed in detail below:
•
Diversity of demand shall be considered to ensure DHS pipes are not oversized.
Where multiple domestic spaces are to be connected to the system the diversity
factor shall be calculated using the Danish Standard DS 439.
•
The DHS and building secondary circuits shall employ a variable volume strategy
with dynamic balancing valves.
•
All components shall be capable of withstanding 105 ºC and 6 bar (g) as a normal
operating condition.
•
Components in contact with the DHS fluid shall be manufactured from carbon steel
although stainless steel is also permitted for smaller pipe diameters.
•
Return temperatures shall be maintained below 50 ºC (as measured on the primary
side of the PHE) for new buildings and 60 ºC for existing heating systems to ensure
thermal losses and annual pumping energy are minimised.
•
Pressure loss in the DHS shall be minimised to reduce annual pumping energy pressure loss shall not exceed 200 Pa/m. Flow velocities shall not exceed those in
Table 3 of CIBSE’s Heat Networks: Code of Practice for the UK9.
•
Insulation and pipe casing shall ensure thermal losses are minimised and the degree
of waterproofness meets the needs of the installation.
•
Expansion and mechanical support shall be adequate and for existing pipework,
improved where necessary.
•
Bypasses at the ends of index runs maybe required to maintain flow temperatures at
times of low use. Fixed bypasses shall be avoided – the flow shall be less than 1% of
the branch peak demand at all times and limited by means of a differential pressure
control valve.
•
An automatic leak surveillance system shall be included.
•
The system shall be adequately protected against corrosion using the prescribed
treatment regime.
•
Old services that are no longer in use shall be removed as part of any works
programme.
An assessment of any existing pipework’s vulnerability and mechanical strength shall be
carried out before installation. Where necessary, additional mechanical protection shall be
provided. Bend, tees and branches should be of a size and design to minimise resistance to
water flow. Elbows and very small radius bend shall only be acceptable when no other
alternative is available.
9
CIBSE Heat Networks: Code of Practice for the UK
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Preferred materials, technology and solutions
Diversity of demand and pipe sizing; in order to ensure DHS pipes are not oversized the
diversity of demand shall be considered for the types of building being supplied by the DHS.
Generally speaking the Danish Standard DS 439:200910 is recommended for sizing
residential buildings but it’s suitability for use must be determined considering the type of
building being modelled.
An example of DHS pipe sizing (not including a diversity factor) is as follows: having
calculated building heat loss (in kW) using the method described above in Section 2.2, an
additional allowance for error and building warm up of 15% should be made.
If the heat requirement for the DHWS does not exceed this 15% allowance then no extra
sizing allowance shall be made for the DHWS and it will be provided by means of an
instantaneous PHE. If the hot water heat requirement is expected to exceed the building
heat loss by more than 15% then a feasibility study shall be undertaken to determine
whether an instantaneous supply can be supported by the DHS or whether hot water storage
is required.
Pipe and insulation; in the ground, in ducts and in free air and up to the point where the
DHS is within a plant room enclosure, pipe work shall meet the standards given it Table 1:
Table 1
Description
Stress analysis, design and
installation
Standard
EN 1394111
Preinsulated steel pipe
Steel pipe nominal diameter
BS EN 25312
EN ISO 670813
Steel valve assemblies
Fitting assemblies
Joint assemblies
BS EN 48814
BS EN 44815.
BS EN 48916
Notes
Use for existing sections of
pipe that may need
improved support as well as
for new installations
Series 2 insulation thickness
Pipes shall be sized to the
‘DN’ standard
10
DS 439:2009 Code of practice for domestic water supply
BS EN 13941:2009+A1:2010 Design and installation of preinsulatred bonded systems for district
heating
12 BS EN 253:2009+A1:2013 District heating pipes. Preinsulated bonded pipe systems for directly
buried hot water networks. Pipe assembly of steel service pipe, polyurethane thermal insulation and
outer casing of polyethylene.
13 EN ISO 6708:1995 Pipework components – Definition and selection of DN (nominal size)
14 BS EN 488:2003 District heating pipes. Preinsulated bonded pipe systems for directly buried hot
water networks. Steel valve assembly for steel service pipes, polyurethane thermal insulation and
outer casing of polyethylene.
15 BS EN 448:2009 District heating pipes. Preinsulated bonded pipe systems for directly buried hot
water networks. Fitting assemblies of steel service pipes, polyurethane thermal insulation and outer
casing of polyethylene
16 BS EN 489:2009 District heating pipes. Preinsulated bonded pipe systems for directly buried hot
water networks. Joint assembly for steel service pipes, polyurethane thermal insulation and outer
casing of polyethylene
11
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Leak detection system
BS EN 1441917
Pressure loss of main lines
Pressure loss of network
branches
≤ 100 Pa/m
≤ 250 Pa/m
Must be automatic and
connected to BMS
The existing DHS is imperial and so a method joining DN to imperial pipe sizes must be
approved, in advance, by the Head of Engineering and Infrastructure.
DHS shall be designed and installed according to the manufacturers requirements.
Where pipework is external to the building and not possible to construct using pre-insulated
pipe to BS EN 253, e.g. sections negotiating tight turns, then short sections may be insulated
in an alternative manner and jacketed with Polyisobutylene (PIB), glued and sealed at
overlaps using the manufacturer’s proprietary adhesive – such sections shall be approved.
In such circumstances the steel pipe shall meet the heat loss pipe requirements of BS EN
253.
The whole installation shall provide a completely weatherproof finish. Where subject to
possible damage, the insulation will be protected using chicken wire wrap or other
mechanical means. The use of trace heating shall be avoided and should only be used as a
last resort and with the permission of the Head of Engineering and Infrastructure.
Polymer pipe systems shall not be used unless they can be shown, in advance of
installation, to meet the requirements for temperature, pressure and long term survivability.
A stress analysis complying with EN 13941 shall be undertaken for all new DHS installations
to ensure sufficient expansion capability is included in the design. A finished report shall be
made available for approval.
For pipes below ground polyethylene (PE) casing shall be used and the casing joints shall
be fusion welded. For above ground high density PE (HDPE) casing shall be used (because
it is UV stable) with joints of the heat shrink type.
Square stabbings shall not be used unless for venting and draining purposes.
Pipework within plant rooms up to the final isolation valve (shown in Schematic DG 4.3a)
shall either be steel barrel to EN 1025518 with malleable fittings to EN 1024219. Yellow
metals shall not be used except for dezincification resistant brass (DRZ). Pipe insulation in
plant rooms shall result in not more than 10 W/m heat loss.
Valves; pipework up to and including 50mm to include ball types valves, 65mm and above
to be butterfly with geared action and stainless steel disc. Valves shall be suitable for a
continuous operating temperature of 105 °C. Isolating valves shall be approved by the UEA.
17
BS EN 14419:2009 District heating pipes. Preinsulated bonded pipe systems for directly buried hot
water networks. Surveillance systems
18 BS EN 10255:2004 Non-alloy steel tubes suitable for welding and threading. Technical delivery
conditions
19 BS EN 10242:1995 Threaded pipe fittings in malleable cast iron
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Double isolation of all buildings/installations from the district heating main is required for
safety. Globe valves shall be used for double isolation with a bleed pipe in between isolated
with a butterfly or ball valve depending on size. Lugged valves shall be used. All valves shall
be fitted with valve labels, which shall be cross referenced with the record drawings/BIM.
Sufficient space must be allowed for maintaining valves (not just operating them) this point
being particularly important in valve pits.
The method of installation and general workmanship shall be in accordance with TR/20 Part
One20.
Pumps; circulating pumps under normal circumstances are not required within the district
heating system. When it is felt necessary to install circulation pumps within the district
heating system, approval must be gained from the Head of Engineering and Infrastructure.
In such cases pumps should be close coupled in line circulation and controlled by inverter
controllers connected to the BMS system to ensure maximum efficiency. A duty and
standby arrangement shall be provided.
System protection; the general procedures set out in CIBSE’s AM14 Non-domestic hot
water heating systems21 shall be followed with regards flushing and assessment of the need
for chemical cleaning (the flushing and cleaning regime shall be approved at the design
stage) but with the exception of the water treatment chemical recommended by CIBSE; the
regime described below shall be adopted.
The UEA’s dosing regime is a combination of molybdate, nitrite, azolzes and biocide. The
dose rate shall be in accordance with the supplier’s instructions and also sufficient so that,
following circulation for at least 48 hours after dosing, the reserve molybdate level is greater
than 300 ppm/l as measured as MoO4 and the nitrite reserve level is greater than 525 ppm/l
measured as NaNO2. A biocide shall be added to all new system fluid at the manufacturers’
recommended dosing rate.
Other control limits are:
•
pH 8.5 to 9.2
•
Biological activity TVC at 22 °C ≤ 10,000 cfu/ml AND pseudomonas < 1000
cfu/100ml at 30 °C AND sulphate reducing bacteria absent
•
Total hardness < 30 ppm
•
Total copper < 1.0 ppm
•
Total iron < 6.0 ppm
•
Soluble iron < 3.0 ppm
•
Particulate matter < 30 mg/l as measured at pumps in circulating water
Trenching; Schematic DG 4.3c gives details of trench requirements the preferred
trench/valve pit cross section and pipe depth and spacings. DHS pipework shall meet the
requirements shown in DG4.3c. Warning tape shall be laid 200mm above DHS pipes.
Spacing between DHS pipes and existing apparatus shall meet the requirements of the
20 HVCA Installation and testing of pipework systems. Part One Low Temperature Hot Water Heating
published
21 CIBSE AM14 Non-domestic hot water heating systems
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existing apparatus. Newly installed pipeowork shall comply with the principles within the
Joint Utilities Guidelines on the Positioning of Underground Utilities Apparatus for New
Development Sites22.
Testing and commissioning; testing of pipework shall be in accordance with EN13941 and
the relevant project class. Balancing and commissioning of the system shall be as
recommended in the CIBSE Commissioning Code W ‘water distribution systems’23. A
bespoke commissioning protocol shall be developed for each project which the Head of
Engineering and Infrastructure must approve before the commissioning exercise takes
place. Refilling of the district heating main shall be completed with freshwater, chemically
treated to the same standard as the existing district heating supply. Existing district heating
system water shall not be used to fill new sections of the main unless approved in advance
by the Engineering & Infrastructure Manager. Pressure testing of the system shall be to 1½
times the working pressure.
Commissioning procedures shall be witnessed and approved by a member of the
Engineering and Infrastructure Team (E&IT).
The Estates and Building Division Central Boiler House Manager shall be informed prior to
any new system being brought into operation and shall be involved in the reinstatement
process as slugs of cold water entering the district heating main can have a detrimental
effect.
Suggested
Suggested schematics
Schematic DG 4.3a & DG4.3c
Some isolators, DOCs and air valves are not shown for simplicity – locations of these items
shall be discussed with the Head of Engineering and Infrastructure when producing bespoke
designs.
Applicable standards
standards and best practice guides
CIBSE Heat Networks: Code of Practice for the UK
DS 439:2009 Code of practice for domestic water supply
BS EN 13941:2009+A1:2010 Design and installation of preinsulatred bonded systems for
district heating
BS EN 253:2009+A1:2013 District heating pipes. Preinsulated bonded pipe systems for
directly buried hot water networks. Pipe assembly of steel service pipe, polyurethane thermal
insulation and outer casing of polyethylene.
EN ISO 6708:1995 Pipework components – Definition and selection of DN (nominal size)
22
National Joint Utilities Group Guidelines on the Positioning of Underground Utilities Apparatus for
New Development Sites
23 CIBSE Commissioning Code W – Water Systems
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BS EN 488:2003 District heating pipes. Preinsulated bonded pipe systems for directly buried
hot water networks. Steel valve assembly for steel service pipes, polyurethane thermal
insulation and outer casing of polyethylene.
BS EN 448:2009 District heating pipes. Preinsulated bonded pipe systems for directly buried
hot water networks. Fitting assemblies of steel service pipes, polyurethane thermal insulation
and outer casing of polyethylene
BS EN 489:2009 District heating pipes. Preinsulated bonded pipe systems for directly buried
hot water networks. Joint assembly for steel service pipes, polyurethane thermal insulation
and outer casing of polyethylene
BS EN 14419:2009 District heating pipes. Preinsulated bonded pipe systems for directly
buried hot water networks. Surveillance systems
BS EN 10255:2004 Non-alloy steel tubes suitable for welding and threading. Technical
delivery conditions
BS EN 10242:1995 Threaded pipe fittings in malleable cast iron
HVCA Installation and testing of pipework systems. Part One Low Temperature Hot Water
Heating published
CIBSE AM14 Non-domestic hot water heating systems
National Joint Utilities Group Guidelines on the Positioning of Underground Utilities
Apparatus for New Development Sites
CIBSE Commissioning Code W – Water Systems
District Heating System Integration (Building Connection) with Space
Heating and Domestic Hot Water Systems
Introduction
This section discusses the preferred method of integrating heating and hot water systems
with the DHS whereas other sections cover separately the DHS itself (before the integration)
and heating and hot water systems that occur after the integration. As discussed previously,
all new and existing buildings shall be connected to the district heating system when
technically and commercially feasible. Even for existing buildings that are currently being
supplied by the DHS, this section may help identify previous approaches to integration that
need modification to improve performance.
Notwithstanding the previous paragraph, there may be circumstances where an alternative
heat source produces a benefit even though a DHS connection is feasible. For example, a
building with a high space and hot water load, such as a sports facility, may benefit from an
air source heat pump (ASHP) system because the cost of upgrading the DHS infrastructure
to meet the combined load is high. The DHS without upgrade may be able to meet the DHW
and space heating load and the ASHP system may be able to meet the pool heating load. In
this example both a DHS connection and an ASHP system might be the optimised solution.
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Designers shall consider alternative heat sources and how they might produce an
operational benefit to the campus’s energy infrastructure as a whole. Section 3.3 and 3.4
below discuss the requirements of alternative heat sources.
Key principles and requirements
The design requirements for integrating building heating systems with the DHS are:
Technical and commercial feasibility: where technically and commercially feasible, all
heat at the UEA shall be provided by the DHS.
DHS pipe sizing; for information on DHS configuration please see Section 3.1.3 above.
Plate heat exchanger separation; the use of two gasketed plate heat exchangers (PHE) is
required to hydraulically separate the primary DHS and secondary building systems whilst
providing a means of heating the building when one PHE is being serviced. Two PHE’s also
allow modulation to match heat supply with load. Each PHE shall be sized for half the peak
design load (and with reference to the principles set out in CIBSE’s Heat Networks: Code of
Practice for the UK24) with a pressure drop not exceeding 25 kPa.
Each PHE shall be provided with a 2 port return temperature limiting valve and dynamic
balancing valve on the primary side. The control algorithm for the return temperature control
valve shall recognise the logarithmic flow response of a PHE to pressure.
Pressure transmitters shall be located immediately adjacent to the PHE on primary and
secondary flow and return pipes so that the level of fouling can be determined. Each
connection shall have an isolating valve.
PHE’s with connections up to DN shall be provided with screw connections, those DN65 and
above shall have flanged connections. PHE’s shall be mounted on a concrete plinth.
Oversizing of PHE’s is to be avoided - they should closely match the peak heat loss
requirement as set out in Section 2.2 above.
Where more than 1 PHE is installed and where space is sufficient, the PHE’s shall be
balanced using a reverse return arrangement. Where space is insufficient, balancing shall be
by means of double regulating valves with an orifice plate (and self-sealing test points).
PHE’s shall be located at ground level to reduce DHS pump pressure requirements.
Minimise DHS return temperatures for space heating and DHW systems; as discussed
above, DHS return temperatures shall, as measured adjacent to the PHE on the primary
side, are less than 50 ºC at all times for new buildings (using the plate optimisation control
solutions detailed below) and less than 60 ºC when connecting existing heating systems – a
discussion of how this can be achieved is included in the sections on space heating and
DHW systems below. This approach minimises energy loss from the DHS and ensures the
centralised heating plant can operate in condensing mode which increases efficiency greatly.
It is the UEA’s preference to produce hot water instantaneously by means of a PHE
integration with the DHS. Schematic DG 4.3b (link) shows an instantaneous arrangement as
24
CIBSE Heat Networks: Code of Practice for the UK
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well as a stored HW configuration which may, in some cases, be required. Hot Water
requirements are discussed further below in Section 3.6.
Secondary system flow and return temperatures for new heating systems shall not exceed
those stated in Table 2 of CIBSE’s Heat networks: Code of Practice for the UK as follows:
Table 2
Circuit
Radiators
Fan-coil units
Air handling unit
Underfloor heating
Domestic hot water service
(DHWS) instantaneous heat
exchanger on load
DHWS cylinder with coil
Secondary Flow Temp (ºC)
Max 70
Max 60
Max 70
See Note 1
See Note 2
Secondary Return Temp (ºC)
Max 40
Max 40
Max 40
See Note 1
Max 25 ºC for 10 ºC cold feed
temperature
See Note 3
DHWS calorifier with external
PHE
See Note 4
Max 45 ºC when heating up from
cold at 10 °C
Max 25 ºC for 10 ºC cold feed
temperature
Note 1: Underfloor heating systems will typically operate with floor temperatures below 35 ºC
and typically flow temperatures of 45 ºC which is advantageous for heat networks as this will
result in low return temperatures.
Note 2: A minimum flow temperature of 65 °C is typical and will be determined by the
required hot water delivery temperature which is typically set to 55 °C. Lower hot water
delivery temperatures may be acceptable provided the volume of water is small and the
Legionella risk can be controlled and this may allow the use of lower flow temperatures.
Note 3: Hot water storage involves a Legionella risk and the stored temperature is normally
above 55 °C. For acceptable heat up times a minimum flow temperature of 70 °C is typical.
The return temperature will generally be higher than for instantaneous heat exchangers as
heat from cold rarely occurs and so higher heat losses will result.
Note 4: A central hot water calorifier would normally be designed to store water at 60 °C and
with a minimum recirculation temperature of 55 °C. Typically a flow temperature of 70 °C or
higher would be needed.
Use split headers; split header systems shall be used in preference to low loss headers to
ensure good temperature and flow control.
Control, metering and monitoring; Schematic DG 4.3a indicates sensor types and
locations. All sensors will be connected ultimately to the campus-wide Trend BMS system.
Heat meters are required and shall be manufactured in accordance with the Measuring
Instruments Directive (MID004) and be Class 2 accuracy as described in Section 3.2.3
below.
The integration pipe work shall include orifice plates (with self-sealing test points) at strategic
locations to ensure flow rates can be measured to ensure the system can be commissioned
fully and accurately. Orifice plates shall be configured with a double regulation valve.
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Preferred materials, technology and solutions
Pipe systems; DHS primary pipe material shall be steel or stainless steel only and able to
withstand temperatures of 105 ºC and 6 bar(g). Pipe systems shall meet the following
requirements:
Table 3
≤ DN80:
The use of threaded joints in steel barrel to
EN 1025525 with malleable fittings to EN
1024226 is acceptable.
≥ DN100 and all concealed pipework
The use of crimped joints in stainless steel
is acceptable up to 3” (seals must able with
meet the temperature and pressure
requirements).
Pipes must be steel (DN specification) and
welded with welds tested to EN 13941 as a
minimum.
Yellow metals shall not be used between the DHS supply pipes and PHE’s with the exception
of DZR.
Pipe insulation; insulation thickness shall be the same thickness and type as the insulation
on the DHS supply pipes or not less than 40mm phenolic foam insulation. All valves and
fittings shall be insulated. Pipe supports shall be thermally isolating. All insulation shall be
Class ‘O’ British Standard BS47627 fire resistant and shall be installed as generally detailed
by the manufacturer.
Valves and fittings; pipework up to and including 50mm to include ball types valves, 65mm
and above to be butterfly with geared action. Valves should be suitable for an operating
temperature of 105°C. Isolating valves must be approved. Where two isolating valves are to
be positioned within a system, a spool section is required between valves. Lugged valves
shall be used. All valves should be fitted with valve labels, which should be cross referenced
with commissioning records and drawings. Globe valves shall not be used in the main flow
but can be used on low flow branches such as test points.
Dirt and air separation; a dirt and air separator with sufficient low velocity zones and a
baffle (with bleed valve) below the automatic air valve shall be installed before the PHE.
Differential pressure control valve; in order to ensure the DHS remains balanced under
dynamic pressure conditions a Samson differential pressure control valve shall be provided
for each PHE and be located within the building plant room and should be positioned as
close to the district heating connection position as is possible.
Heat meters; Heat meters for DHS integrations shall be compliant with the UK
Government’s Renewable Heat Incentive (RHI) Scheme and be ultrasonic. Meters shall
25
BS EN 10255:2004 Non-alloy steel tubes suitable for welding and threading. Technical delivery
conditions
26 BS EN 10242:1995 Threaded pipe fittings in malleable cast iron
27 BS 476 Fire tests on building materials and structures
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conform to MID (Measuring Instruments Directive) Class 2 accuracy requirements within
EN143428 and
•
comply with the relevant requirements set out in Annex I to the 2004 Measuring
Instruments Directive (MID)100 (2004/22/EC)29
•
comply with the specific requirements listed in Annex MI-004 of the MID
•
fall within accuracy Class 2 as defined in Annex MI-004101
To comply with the specific requirements in Annex MI-004 of the MID, all heat meters used
shall comprise:
•
A flow sensor (or meter) - a meter which determines the volume of fluid which has
passed through a pipe within a given time period
•
A matched pair of temperature sensors two temperature sensors that are calibrated
together as a pair to make sure the temperature difference between the input and
output of the system is measured to the stated accuracy level. For all types of
temperature sensors we must be assured that they meet the RHI requirements. See
13.17 for information regarding externally mounted (strap-on) temperature sensors.
•
A calculator/digital integrator (though in some systems a Building Management
System may take the place of the integrator) – a device which uses the information
provided by the flow meter and the matched pair of temperature sensors to calculate
the heat energy being transferred.
Heat meters shall be tag sealed in the installation and must be tamper proof i.e. sealed in
such a way that the flow and return temperature sensors cannot be swapped around nor the
integrator opened. The flow meter component shall be configured with local isolating valves
and a spool section so it can be removed for calibrating.
An additional requirement is that the meter shall be installed in either the flow or return pipe
(depending on how the flow meter is calibrated) and with sufficient ‘before and after’ pipe
length dimensions as described by the manufacturer.
Metrs shall be configured to send temperature and flow rate data every 15 minutes via the
BMS using the M-Buss protocol described in EN 1375730 to the UEA’s Trend database.
System protection; the general procedures set out in CIBSE’s AM14 Non-domestic hot
water heating systems31 shall be followed with regards flushing and assessment of the need
for chemical cleaning (the flushing and cleaning regime shall be approved at the design
stage) but with the exception of the water treatment chemical recommended by CIBSE; the
regime described below shall be adopted.
The UEA’s dosing regime is a combination of molybdate, nitrite, azolzes and biocide. The
dose rate shall be in accordance with the supplier’s instructions and also sufficient so that,
following circulation for at least 48 hours after dosing, the reserve molybdate level is greater
than 300 ppm/l as measured as MoO4 and the nitrite reserve level is greater than 525 ppm/l
28
BS EN 1434 Parts 1-6
Measuring Instruments Directive 2004/22/EC
30 EN 13757 Parts 1-5
31 CIBSE AM14 Non-domestic hot water heating systems
29
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measured as NaNO2. A biocide shall be added to all new system fluid at the manufacturers
recommended dosing rate.
Other control limits are:
•
pH 8.5 to 9.2
•
Biological activity TVC at 22 °C ≤ 10,000 cfu/ml AND pseudomonas < 1000
cfu/100ml at 30 °C AND sulphate reducing bacteria absent
•
Total hardness < 30 ppm
•
Total copper < 1.0 ppm
•
Total iron < 6.0 ppm
•
Soluble iron < 3.0 ppm
•
Particulate matter < 30 mg/l as measured at pumps in circulating water
Testing and Commissioning; Testing, balancing and commissioning of the system shall be
as recommended in the CIBSE Commissioning Code W ‘water distribution systems’32. A
bespoke commissioning protocol shall be developed for each project which the Head of
Engineering and Infrastructure must approve before the commissioning exercise takes
place. Pressure testing of the system shall be to 1½ times the working pressure.
Commissioning procedures shall be witnessed and approved by a member of the
Engineering and Infrastructure Team (E&IT).
Suggested schematics
Schematic DG 4.3a
Some isolators, DOCs and air valves are not shown for simplicity – locations of these items
shall be discussed with the Head of Engineering and Infrastructure when producing bespoke
designs.
Applicable standards and best practice guides
CIBSE Heat Networks: Code of Practice for the UK
BS EN 10255:2004 Non-alloy steel tubes suitable for welding and threading. Technical
delivery conditions
BS EN 10242:1995 Threaded pipe fittings in malleable cast iron
BS EN 1434 Parts 1-6
Measuring Instruments Directive 2004/22/EC
EN 13757 Parts 1-5
32
CIBSE Commissioning Code W – Water Systems
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CIBSE Commissioning Code W – Water Systems
Alternative Heat Sources – Renewable Energy Systems
Systems
Introduction
Where a connection to the DHS proves to be unfeasible for all or part of the load, an
alternative source of heat shall be considered in preference to the use of natural gas. This
section discusses the decision making process and requirements for renewable energy heat
sources. Gas heat sources are discussed in Section 3.4.
Key principles and requirements
Systems providing heat as an alternative to the DHS shall address the following principles
and requirements:
•
The design/sizing process shall use proprietary/approved software applications to
size the systems using an hourly simulation process to ensure they are safe, reliable
and efficient and will meet the requirements of the brief.
•
Whole life cost analysis shall be used following a detailed assessment of
maintenance costs to determine the optimum alternative heat solution. The cost
analysis methodology shall be approved.
•
For renewable sources of heat, the installation requirements of the Microgeneration
Installation Standards (MIS) published by the Microgeneration Certification Scheme33
shall be used (regardless of the output of the system) for the relevant technology
unless a different standard is approved.
•
Renewable energy system products are required to be certified by the
Microgeneration Certification Scheme (MCS).
Preferred materials, technology and solutions
Solar hot water (SHW); SHW is a preferred technology using either heat pipe type
evacuated tubes or flat plate collectors; direct evacuated tubes shall not be used.
Air source heat (and cooling) pumps (ASHP); ASHP systems may be considered where
their deployment will result in inherently high COP34s such as when heating leisure pool
water or very low flow temperature heating systems such as underfloor heating. Heat pumps
using natural refrigerants (e.g. CO2 are preferred).
Ground source heat (and cooling) pumps (GSHP); GSHP systems may be considered
where their deployment will result in inherently high COPs such as when heating leisure pool
33
http://www.microgenerationcertification.org/
34
Coefficient of Performance
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water or very low flow temperature heating systems such as underfloor heating. Heat pumps
using natural refrigerants (e.g. CO2 are preferred).
Biomass heating; Biomass heating may be considered for existing buildings with higher
flow temperature heating systems, where this is sufficient space and where the provision of
a flue is feasible.
Relevant drawings and schematics
Schematics will be provided by the Head of Engineering and Infrastructure for the renewable
systems on a case by case basis.
Applicable standards and best practice guides
The table below details standards and information sources for microgeneration systems
Table 4
Solar Hot Water Systems
MIS 3001 Solar Heating Standard
MCS 024 Solar Domestic Hot Water Energy Calculation
Thermal Solar Performance Energy Calculator
MCS 012 Important Information
Biomass Systems
MIS 3004 Biomass Standard
Heat Pump Systems
MIS 3005 Heat Pump Standard (Mandatory from 26/3/2016)
MCS 021 Heat Emitter Guide
MIS 3005 Heat Pump Standard
MCS 021 Heat Emitter Guide
MCS 022 Supplementary Information Ground loop sizing tables
Supplementary Tables of Heat Emitter Outputs
MGD 002 Guidance for MIS 3005
Alternative Heat
Heat Sources – Gas Heat Sources and Infrastructure
Introduction
Where a connection to the DHS proves to be unfeasible for all or part of the load and where
a renewable energy system is not economically or technically feasible, natural gas shall be
considered as the primary source of heat. An assessment of the campus’s gas infrastructure
shall be required to ensure a natural gas boiler is technically and economically feasible. This
section discusses the requirements for natural gas systems.
The University’s gas infrastructure operates at 2 pressures. From the main intake position at
the far north east corner of the campus, the gas main is run at a working pressure of 300
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mbar. Within the gas meter room adjacent to the boiler house the supply splits, to serve the
gas boilers and engines and the main site infrastructure is metered and stepped down to a
supply pressure of 33 mbar.
High pressure supplies feed the following buildings:
1. Health and Community Centre
2. SportsPark
3. Security Lodge
4. Energy Centre 1
5. INTO Building
These supplies have been fitted with the appropriate govenors and safety devices and
deliver gas to the buildings at 21 mbar.
The gas supply to the inner site leaves the gas meter room below ground and crosses
Chancellor’s Drive before splitting to form a ring circuit. The majority of the gas installation has
been replaced, removing spun cast pipework and installing Medium Density Polyethylene
(MDPE) yellow gas pipes. There are however, sections of steel pipe still in use and may still
be sections of cast iron main which remains undetected.
An AutoCAD drawing detailing the campus infrastructure at its currently known state is
available on request.
Key principles and requirements
When connecting to the gas infrastructure, the following items shall be incorporated.
•
Secondary metering shall be provided in all buildings for all significant loads
•
The supply pressure shall be suitable for the size of the load
•
Pipes shall be sized to minimise pressure loss
•
System safety and reliability shall be assured
Where connections are made to the high pressure infrastructure main, the system shall be
fitted with slam shut or similar safety devises and pressure relief devises where appropriate.
Purge and test points should be provided on both primary and secondary sides of the system
and in locations that enable all sub circuits to be tested without loss of service.
Preferred materials, technology and solutions
Boilers; SEDBUK A rated, modulating boilers with stainless steel heat exchangers shall be
used.
Gas absorption heat pumps; shall be considered for suitable applications.
Pipework; pipework should be fit for the purpose it is intended and shall be sized to the
most economic size, balancing system pressure drop with pipe size. Within buildings the
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pipes shall be sized to accommodate a pressure drop of 1 mbar from the meter to the
furthest appliance/connection.
Pipework laid directly into the ground shall be Medium Density Polyethylene (MDPE) yellow
pipe electrofusion welded at a depth suitable for the respective ground cover.
Warning tape shall be installed in all instances 200mm above the pipe. Within buildings
pipework shall be either:
•
Mild steel tube with malleable fittings
•
Stainless steel press fit with seals made of the appropriate material
•
Copper tube to EN 105735 R250 with appropriate compression or solder fittings
Supports and fixings shall be designed for the purpose and should support the pipework
evenly throughout its length allowing minimal deflection. In general, pipework supports should
be installed in accordance with TR/20 Part 936 installation and testing of pipework systems
published by Heating and Ventilating Contractors Association.
Valves; isolating valves shall be of the butterfly plug or ball type suitable for natural gas
manufactured to EN 33137 and suitable for the pipe size as follows:
•
Up to and including 65mm - 2½” plug or ball type valves shall be used
•
For valves 65mm and larger - lugged butterfly valves shall be used with nitrile liner
Isolating valves shall be approved. Where valves are installed using a threaded joint these
shall be tapered to BS2138.
All valves shall be fitted with valve labels and cross referenced with commissioning and BIM
information.
Safety devices: where deemed necessary or as a requirement of the code of practice,
natural gas certified safety devices shall be utilised. Where automatic solenoid valves are
utilised, a manual reset facility shall be provided even where the valve has automatic reset
facility. Where manual reset valves are utilised, suitable access and labels must be provided.
Where laboratories are provided with gas taps and gas proving system is required. Where
connection to the high pressure main is made, slam shut valves shall be installed to protect
the down-stream system from over pressure.
Governors; Governors shall be provided at the intake positions of all buildings connected to
the infrastructure. In addition to this governors shall be provided whenever a step down in
pressure is required or where the gas main serving an appliance is at risk of fluctuating gas
35
BS EN 1057 Copper and copper alloys. Seamless, round copper tubes for water and gas in
sanitary and heating applications
36 HVCA TR/20 Installation and testing of pipework systems. Part 9 – Natural gas
37 BS EN 331 Manually operated ball valves and closed bottom taper plug valves for gas installations
for buildings
38 BS 21 Specification for pipe threads for tubes and fittings where pressure-tight joints are made on
the threads (metric dimensions)
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pressures beyond the acceptable range for the appliance. Governors shall be manufactured
to meet BS EN 8839 (Class A Group 2).
Gas metering; As a minimum, metering shall be provided at the main intake position of any
building connected to the gas infrastructure or prior to any item of plant connected to the gas
infrastructure. All significant loads shall be metered separately. A metering scheme shall be
presented to the Head of Engineering and Infrastructure for approval.
Sub metering within the building shall be provided to meet the 90% requirement of Part L of
the Building Regulations. Meters shall be suitable for natural gas and shall produce a pulsed
signal for remote monitoring by the campus’s Trend Building Management System as
described in Part 5 of the Guide.
Heating Metering; gas heat sources providing heat to systems that are also connected to
the DHS shall be metering using a MID 004 heat meter with Class 2 accuracy as described
in Section 3.2.3
System protection; the general procedures set out in CIBSE’s AM14 Non-domestic hot
water heating systems40 shall be followed with regards flushing and assessment of the need
for chemical cleaning (the flushing and cleaning regime shall be approved at the design
stage) but with the exception of the water treatment chemical recommended by CIBSE; the
regime described below shall be adopted.
The UEA’s dosing regime is a combination of molybdate, nitrite, azolzes and biocide. The
dose rate shall be in accordance with the supplier’s instructions and also sufficient so that,
following circulation for at least 48 hours after dosing, the reserve molybdate level is greater
than 300 ppm/l as measured as MoO4 and the nitrite reserve level is greater than 525 ppm/l
measured as NaNO2. A biocide shall be added to all new system fluid at the manufacturers’
recommended dosing rate.
Other control limits are:
•
pH 8.5 to 9.2
•
Biological activity TVC at 22 °C ≤ 10,000 cfu/ml AND pseudomonas < 1000
cfu/100ml at 30 °C AND sulphate reducing bacteria absent
•
Total hardness < 30 ppm
•
Total copper < 1.0 ppm
•
Total iron < 6.0 ppm
•
Soluble iron < 3.0 ppm
•
Particulate matter < 30 mg/l as measured at pumps in circulating water
Relevant drawings and schematics
NA
39 BS EN 88 Pressure regulators and associated safety devices for gas appliances. Pressure
regulators for inlet pressures up to and including 50 kPa
40 CIBSE AM14 Non-domestic hot water heating systems
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Applicable standards and best practice guides
BS EN 1057 Copper and copper alloys. Seamless, round copper tubes for water and gas in
sanitary and heating applications
HVCA TR/20 Installation and testing of pipework systems. Part 9 – Natural gas
BS EN 331 Manually operated ball valves and closed bottom taper plug valves for gas
installations for buildings
BS 21 Specification for pipe threads for tubes and fittings where pressure-tight joints are
made on the threads (metric dimensions)
BS EN 88 Pressure regulators and associated safety devices for gas appliances. Pressure
regulators for inlet pressures up to and including 50 kPa
CIBSE AM14 Non-domestic hot water heating systems
Space Heating Circuit Design and Emitter Sizing
Introduction
This section describes the UEA’s preferences for space heating circuit design, whereas DHS
design and methods of integrating heating and hot water systems with the DHS, are covered
in the sections above.
Information about the UEA’s preferred design philosophies and comfort criteria can be found
in Part 3 of the Guide: Design Philosophies and Criteria for Heating, Cooling, Ventilation and
Light in Buildings. This section on heating circuit design provides guidance for designers at a
more advanced stage of the design development process (RIBA Stages 3 -7).
Having arrived at an accurate assessment of a building’s load profile, as described in
Section 2.2 above, this section gives details regarding the UEA’s requirements for space
heating systems.
Key principles and requirements
•
Emitters shall not be oversized.
•
Heating circuits shall be separated from the DHS by means of a PHE and be
pressurised.
•
Hydraulic circuit temperature differences (∆T’s) shall be as high, as described below,
to reduce pumping energy requirements.
•
Pressure loss in pipe systems shall be 100 – 250 Pa/m to minimise pumping energy
requirements.
•
Shared risers shall be used in preference to single risers where long horizontal runs
are likely to increase losses and lead to overheating of spaces.
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•
Hydraulic heating system return temperatures shall be as low, as described below, to
reduce DHS network losses and to ensure condensing mode can be achieved in gas
plant.
•
Pipe insulation thicknesses greater than those required by Approved Documents and
second tier documents shall ensure summer overheating doesn’t occur in high
performance buildings and that pipe systems are efficient.
•
Space heating circuits shall be weather compensated where emitter type allows and
variable volume in all cases.
•
The zoning scheme shall consider the requirements of individual spaces and their
occupants including building geometry, etc.
•
Heat metering must consider the needs of the Energy Efficiency Directive and allow
communication with the campus’s BMS system.
•
Heating systems shall be adequately protected from corrosion and adequately
supported.
Preferred materials, technology and solutions
Emitter sizing; emitters shall be sized to meet the building/zone/space design day heat loss
with an oversizing factor of 0.15 (15%) to account for error and allow rapid warm-up of
space.
PHE separation; PHE’s are described in Section 3.2.2.
Hydraulic circuit temperatures; DHS return temperatures, as measured adjacent to the
PHE on the primary side, shall be less than 50 ºC at all times for new buildings (using the
plate optimisation control solutions detailed below) and less than 60 ºC when connecting
existing heating systems; 60 ºC can often be achieved in existing buildings because emitter
systems are often oversized. When re-working an existing emitter system a feasibility study
should be undertaken to determine the lowest return temperature possible whilst remaining
within the comfort criteria of the space. The results of the feasibility study shall be approved
by the Head of Engineering and Infrastructure.
The measures described minimise energy loss from the DHS while also ensuring the
centralised heating plant can operate in condensing mode which increases efficiency greatly.
Secondary system flow and return temperatures shall not exceed those stated in Table 6 of
CIBSE’s Heat networks: Code of Practice for the UK41 as follows:
Table 6
Circuit
Radiators
Fan-coil units
Air handling unit
Underfloor heating
41
Secondary Flow Temp (ºC)
Max 70
Max 60
Max 70
See Note 1
Secondary Return Temp (ºC)
Max 40
Max 40
Max 40
See Note 1
CIBSE Heat Networks: Code of Practice for the UK
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Note 1: Underfloor heating systems will typically operate with floor temperatures below 35 ºC
and typically flow temperatures of 45 ºC which is advantageous for heat networks as this will
result in low return temperatures.
Heating circuits shall be weather compensated notwithstanding that weather compensation
fits with the system design philosophy.
Electrical efficiency; pressure loss shall be 100 – 250 Pa/m with swept bends and full bore
valves and fittings being used to minimise pressure loss in pipe runs that have flow for a high
percentage of the heating season/year. For pipes that have flow for a lesser percentage of
the year, designing to 350 Pa/m may be justified on the grounds that smaller pipe diameters
have lower thermal losses.
Variable speed pumps shall be employed notwithstanding that they fit with the system
design philosophy. Pumps serving index circuits and/or significant emitters i.e. an AHU
battery, a radiator zone, an UFH zone, shall be controlled by a differential pressure signal
generated at the end of the circuit.
Thermal efficiency; thermal losses shall be minimised by employing the following
measures:
•
Pipe insulation thickness shall ensure heat lost from heating system pipework does
not exceed 15% of the building heat loss and that summer overheating is avoided.
Reducing pipe heat losses by 10% compared to the values given in BS 542242 shall
be the basis for the first design iteration. Experience, according to CIBSE’s Heat
networks: Code of Practice for the UK, is that 40mm of phenolic foam insulation may
be required.
•
Shared risers shall be used in preference to single risers to minimise long horizontal
runs – especially in corridors.
•
All valves and fittings shall be insulated and with thermally insulating pipe supports.
•
Communal spaces, where actively heated, shall be provided with good temperature
control.
•
Pipes shall not be oversized and shall be sized in consideration of diversified
demands. Consideration shall also be given to the possibility that peak demands may
only occur for short periods at the limits of index runs and so exceeding the 250 Pa/m
limit may be acceptable.
All insulation shall be Class ‘O’ British Standard BS 47643 fire resistant. Where pipework is
external to the building it shall meet the requirements of DHS pipework as described in
Section 3.1 and shall be provided with a heat meter of the type described in Section 3.1 at
the point at which is leaves and enters the thermal envelope so that losses external to
buildings can be metred.
42
BS 5422:2009 Method for specifying thermal insulating materials for pipes, tanks, vessels, ductwork
and equipment operating within the temperature range -40°C to +700°C
43 BS 476 Fire tests on building materials and structures
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For internal pipework, the tables below give the insulation requirements that shall be met.
The required insulation thickness may impact on depth of ceiling voids so early discussions
with the architect should be help to ensure sufficient depth is allowed for.
Table 7 - Maximum pipe heat loss rates
Nominal Pipe Diameter
15
22
28
35
W/m
8.1
8.2
9.1
10.2
Table 8 - Minimum insulation thicknesses
Outside pipe diameter
15
22
28
35
Minimum thickness of
insulation for λ = 0.040W/mK
(typical for mineral wool)
mm
40
50
50
50
Minimum thickness of
insulation for λ = 0.021 W/mK
(typical for phenolic foam)
mm
15
15
15
20
Insulation for PHE’s shall not exceed 50 W per m² of casing surface area (assuming an
average PHE surface temperature of 60 ºC and a plant room air temperature of 18 ºC). This
equates to a U Value of 1.2 W/m² K.
All valves and fittings shall be insulated with pipe supports using rigid, low conductivity
supports to maintain insulation quality integrity.
Zone control strategy; the zoning strategy shall address the needs of the users of
individual spaces and the building’s geometry (e.g. patterns of solar gain). The strategy must
be discussed and approved.
Smaller rooms not controlled directly via the BMS shall be provided with thermostatic
radiator valves (TRV’s).
Actuated windows should be interlocked with zone controls to ensure heat loss through
infiltration is minimised although reference should be made to the ventilation strategy to
ensure an acceptable level of fresh air is available to occupants.
Emitter Control; each significant emitter shall be controlled by means of:
•
Appropriate thermostatic control i.e. air temperature sensors for convective emitters
and black bulb sensors for radiant emitters.
•
A two port control valve with a modulating actuator shall act as a zone valve as well
as a valve that ensures the emitter doesn’t pass significant quantities of heat to the
return pipe – it shall act upon a temperature signal in the return pipe positioned
immediately adjacent to the emitter. The valve shall be set-up so that is passes very
low volumes as a minimum to ensure the return temperature can be effectively
monitored, that thermal response times are minimised and inhibitor chemicals stay in
circulation. The valve opens fully when the thermostat calls for heat Schematic
DG4.3a gives details of this arrangement.
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•
A differential pressure control valve (DPCV) or pressure independent control valve
(PICV) with flow setting capability to ensure the system remains balanced under
dynamic conditions and to enable the flow rate to be accurately set during balancing
& commissioning exercises.
•
An orifice plate with self-sealing test points with an accuracy of ±5% or better for flow
setting during commissioning exercises.
•
A flushing bypass and strainer shall be fitted to emitters deemed by the UEA to be at
risk of fouling e.g. fan coil units and AHU heater batteries.
N.B it is possible to combine the two port control valve, the DPCV and the commissioning
arrangements in the same valve arrangement by using proprietary valves designed for the
purpose.
All radiators shall be provided with TRV’s. All TRV’s shall include a non-user settable
temperature limiter set to 22 °C but shall allow users to reduce the temperature at their
discretion.
The UEA can assist with the development of the BMS algorithms required for the control
functions described above. These algorithms shall address the specific qualities of individual
emitter types e.g. the flow rate through heat exchangers responds logarithmically to pressure
whereas radiator index circuits respond in a linear fashion.
Pipe systems; pipe systems on the building secondary side of the PHE shall be suitable for
operating temperatures of -30 ºC to 98 ºC without loss of 20 year survivability and shall be
warrantied for 20 years. Carbon steel tube with press fittings is not acceptable but stainless
steel tube with press fittings using butyl rubber seals is the preferred method and shall be
used on to pipes up and including DN80 where pipes are accessible, threaded barrel to BS
EN 10255:200444 with malleable fittings to BS EN 10242:199545 may also be used.
For larger pipes and those that that are concealed, welded pipes shall be used. Pipe
systems shall be provided with a 20 year warranty.
Compression fittings with brass olives on stainless steel tube are acceptable whereas
copper olives are not – notwithstanding that this approach meets the warranty conditions of
the warranty provider. Where copper tube is joined to stainless steel tube, a brass fitting
shall be used to separate the dissimilar metals.
Valves; where balancing valves are installed within circuits that have been oversized for
future use, these shall be line size and not sized to the initial design flow rate. Valve types
for pipe sizes are generally as follows:
Pipe sizes > 65mm use butterfly with stainless steel disc and lugged
Pipe sizes < 65mm lever type ball operated.
44
BS EN 10255:2004 Non-alloy steel tubes suitable for welding and threading. Technical delivery
conditions
45
BS EN 10242:1995 Threaded pipe fittings in malleable cast iron
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Where branches are connected to a main riser or distribution system, isolation of the
branch must be provided. All valves should be fitted with valve labels, which should be
cross referenced with commissioning records and drawings.
System protection; The general procedures set out in CIBSE’s AM14 Non-domestic hot
water systems shall be followed with regards flushing and assessment of the need for
chemical cleaning but with the exception of the water treatment chemical recommended by
CIBSE. Each separate system shall including a dosing pot.
The UEA’s dosing regime is a combination of molybdate, nitrite, azolzes and biocide. The
dose rate shall be in accordance with the supplier’s instructions and also sufficient so that,
following circulation for at least 48 hours after dosing, the reserve molybdate level is greater
than 300 ppm/l as measured as MoO4 and the nitrite reserve level is greater than 525 ppm/l
measured as NaNO2. A biocide shall be added to all new system fluid at the manufacturers
recommended dosing rate.
Other control limits are:
•
pH 8.5 to 9.2
•
Biological activity TVC at 22 °C ≤ 10,000 cfu/ml AND pseudomonas < 1000
cfu/100ml at 30 °C AND sulphate reducing bacteria absent
•
Total hardness < 30 ppm
•
Total copper < 1.0 ppm
•
Total iron < 6.0 ppm
•
Soluble iron < 3.0 ppm
•
Particulate matter < 30 mg/l as measured at pumps in circulating water
The cleaning and protection plan shall be discussed and agreed with the Head of
Engineering and Infrastructure prior to the actions being taken.
Heat metering; heat metering must consider the statutory requirements of the Energy
Efficiency Directive (as it applies to the metering and billing of district heating and communal
hot water systems)46 as well as the needs of the building user for billing for specific spaces.
Heat meters shall communicate with the campus’s BMS system using the M-Buss Protocol
described in EN 1434-3:199747. The heat metering strategy for space heating systems shall
be developed in consideration of the need for heat metering as part of the DHS integration
arrangement as described in Secion 3.1 of this document.
Testing and commissioning; Balancing and commissioning of the system shall generally
be as recommended in the CIBSE Commissioning Code W ‘water distribution systems’48. A
bespoke commissioning protocol shall be developed for each project that shall be approved
prior to the commissioning exercise taking place. Pressure testing of the system shall be to
1½ times the working pressure.
46
https://www.gov.uk/government/consultations/implementing-the-energy-efficiency-directivemetering-and-billing-of-heating-and-cooling
47 BS EN 1434-3:2008. Heat Meters. Data exchange and interfaces
48 CIBSE Commissioning Code W – Water Systems
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Relevant drawings and schematics
Schematic DG 4.3a
Some isolators, DOCs and air valves are not shown for simplicity – locations of these items
shall be discussed with the Head of Engineering and Infrastructure when producing bespoke
designs.
Applicable standards and best practice guides
CIBSE Heat Networks: Code of Practice for the UK
BS 5422:2009 Method for specifying thermal insulating materials for pipes, tanks, vessels,
ductwork and equipment operating within the temperature range -40°C to +700°C
BS 476 Fire tests on building materials and structures
BS EN 10255:2004 Non-alloy steel tubes suitable for welding and threading. Technical
delivery conditions
BS EN 10242:1995 Threaded pipe fittings in malleable cast iron
BS EN 1434-3:2008. Heat Meters. Data exchange and interfaces
CIBSE Commissioning Code W – Water Systems
Domestic
Domestic Hot Water System
System (DHWS) Design
Introduction
DHWS design is influenced by the specialist requirements of the DHS, the site’s constraints
with regards to maximum daily water demand as well as the need for safety and efficiency.
The sections below guide the designer through the decision making processes and the
requirements for the provision of hot water.
Key principles and requirements
•
DHWS design shall be based on an accurate, hourly assessment of load as
described in Section 2.2 above.
•
The DHS is the preferred source of heat for the provision of hot water when
technically and commercially feasible.
•
The preferred method of generating hot water is by means of a PHE either
instantaneously or for direct heating a hot water store.
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•
Hot water provision must consider the constraints imposed by the campus’s
infrastructure with regards pressure and flow rate and so may need to be supplied by
a boosted supply from a cold water cistern.
•
Health and safety risk, such the need for bacterial control and the need to prevent
scalding, shall be based on the level of risk as determined by bespoke risk analysis.
•
Heat loss from primary, building secondary and DHW secondary pipes shall be
controlled by insulation levels that exceed statutory requirements.
•
Electrical efficiency shall be maximised by best practice circuit design & control and
the selection of efficient solutions and products.
•
All hot water storage vessels shall be provided with an immersion heaters and all
instantaneous hot water systems provided with an inline electric heater. Electrical
back-up systems shall be sized to maintain the hot water service in the event of
failure of the DHS.
Preferred materials, technology and solutions
The sections below describe how the principles and requirements described above shall be
interpreted when designing DHWSs.
Heat sources for DHWS; a report on the feasibility of meeting a DHWS load from the DHS
shall consider the following:
For new buildings, is it cost effective (on a whole life basis) to extend the DHS to meet the
DHWS demand and if so, can the DHS support the flow rates required for an instantaneous
supply? This will normally be considered at the same time as considering the space heating
loads. The study shall calculate the whole life cost using an approved methodology.
DHS pipes, as described in Section 3.1 above shall be pre-insulated (Class 2 insulation as
defined in EN 253) mild-steel with a branch pressure loss not exceeding 250 Pa/m. Having
calculated building heat loss (in kW) using the method described above in Section 2.1, an
additional allowance for error and building warm up of 15% should be made.
If the heat requirement for the DHWS does not exceed this 15% allowance then no extra
DHS pipe sizing allowance shall be made for the HWS and it will be provided preferably by
means of an instantaneous PHE. If the hot water heat requirement is expected to exceed the
building heat loss by more than 15% then the feasibility study shall determine whether an
instantaneous supply can be supported by the DHS or whether hot water storage is required.
Where a DHS connection is not feasible, as decided by the Head of Engineering and
Infrastructure, alternative heat sources shall be considered as discussed in Section 3.3 & 3.4
above. For small, remote and intermittent DHWS requirements, electrical point of use units
are acceptable. The legionella risk assessment shall consider whether point of use units can
be controlled by timers that switch the units off when the building is not in use and where
safe to do so timers shall be used.
PHE hot water generation; PHEs are the preferred method of hot water generation
because they provide low return temperatures (for both instantaneous and stored systems)
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and can improve hygiene. Where hot water generation is mission critical, there shall be 2
PHEs installed in parallel, each sized for 100% of the peak demand, so that a DHWS can be
maintained while the other remains in use.
PHEs shall be sized to give low return temperatures to the DHS as detailed in Table 9 of
CIBSE’s Heat Networks: Code of Practice for the UK49 as follows:
Table 9
Circuit
Domestic hot water service
(DHWS) instantaneous heat
exchanger on load
DHWS cylinder with coil
Secondary Flow Temp (ºC)
See Note 2
Secondary Return Temp (ºC)
Max 25 ºC for 10 ºC cold feed
temperature
See Note 3
DHWS calorifier with external
PHE
See Note 4
Max 45 ºC when heating up from
cold at 10 °C
Max 25 ºC for 10 ºC cold feed
temperature
Note 2: A minimum flow temperature of 65 °C is typical and will be determined by the
required hot water delivery temperature which is typically set to 55 °C. Lower hot water
delivery temperatures may be acceptable provided the volume of water is small and the
Legionella risk can be controlled and this may allow the use of lower flow temperatures.
Note 3: Hot water storage involves a Legionella risk and the stored temperature is normally
above 55 °C. For acceptable heat up times a minimum flow temperature of 70 °C is typical.
The return temperature will generally be higher than for instantaneous heat exchangers as
heat from cold rarely occurs and so higher heat losses will result.
Note 4: A central hot water calorifier would normally be designed to store water at 60 °C and
with a minimum recirculation temperature of 55 °C. Typically a flow temperature of 70 °C or
higher would be needed.
Cold water constraints; the site is constrained to some degree in terms of maximum daily
demand and so it may be preferable to meet significant hot water peak loads from stored
cold water rather than directly from the mains cold water supply. For most residential, office
and teaching spaces, stored cold water is not required as long as the site’s cold water
infrastructure can meet the pressure and flow requirement. A direct supply without storage to
an instantaneous PHE is the UEA’s preferred approach. Where a break tank is required the
volume should be minimised and it must be provided with automatic flushing valves as per
the Schematic DG 4.3b
Thermal efficiency; thermal losses in the DHWS primary and secondary pipe system shall
be by means of insulation requirements as follows:
Table 10 Maximum pipe heat loss rate
Outside Pipe Diameter
15
22
28
35
49
W/m
8.1
8.2
9.1
10.2
CIBSE Heat Networks: Code of Practice for the UK
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Table 11 Minimum insulation thicknesses
Outside pipe diameter
15
22
28
35
Minimum thickness of
insulation for λ = 0.040W/mK
(typical for mineral wool)
mm
40
50
50
50
Minimum thickness of
insulation for λ = 0.021 W/mK
(typical for phenolic foam)
mm
15
15
15
20
Note: these heat loss rates are approximately 10% of those given in Table 15 of BS5422 and
the required insulation thickness may impact on depth of ceiling voids so early discussions
with the architect should be help to ensure sufficient depth is allowed for.
All valves and fittings shall be insulated with pipe supports using rigid, low conductivity
supports to maintain insulation quality integrity.
Insulation for PHE’s shall not exceed 50 W per m² of casing surface area assuming an
average PHE surface temperature of 60 ºC and a plant room air temperature of 18 ºC. This
equates to a U Value of 1.2 W/m².K.
Electrical efficiency; where an instantaneous supply is provided by a PHE, designs should
consider bypassing the PHE (in the DHWS secondary circuit) when no heat is required – see
Schematic DG 4.3b for details. This approach minimises pumping energy, as long as a
variable speed pump is used, because PHE’s have a relatively high pressure loss and so
bypassing the PHE when no heat is required can save a significant amount of energy on an
annual basis. It may be important to regularly purge the PHE during periods of low use to
ensure bacterial growth can be controlled and so the legionella control strategy shall
consider this.
DHWS secondary circuits should be designed so that pressure loss does not exceed 250
Pa/m. The legionella control strategy should consider whether it’s safe to turn off DHWS
secondary circulators when the building is not in use e.g. overnight for office spaces and
during student holidays for residential buildings.
As a general rule the pressure loss of any DHWS PHE should not exceed 25 kPa.
Hot water safety; all components in contact with mains cold water (Category 1 Fluids50) and
heated water (Category 2 Fluids) shall be WRAS51 approved. Legionella control shall be
effected on a risk basis following a bespoke risk analysis by a member of the Legionella
Control Association52. The UEA’s approach is to put in place very effective control measures
that are risk based rather than attempting to comply by following each and every paragraph
of the health and safety guidance, such as those detailed in L853, which may be
unnecessarily onerous and wasteful of resources.
DHWS shall be designed from the outset to be hygienic rather than relying on excessive
flushing which is wasteful of resources. All new systems shall be of a flow and return type.
The use of total loss systems require approval even during refurbishments of existing
buildings.
50
As described by WRAS’s Water Regulations Guide
Water Regulations Advisory Scheme
52 http://www.legionellacontrol.org.uk/
53 Health and Safety Executive L8 The control of legionella bacteria in water systems
51
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There shall be only one circulation pump and not a run and standby arrangement. A spare
pump of the same make and model should be located next to the installed pump to allow for
quick replacement if the installed pump fails.
The destratification pumps shall run if the temperature between the top sensor (T3) and the
low sensor (T1) is greater than 5°C.
Thermostatic Mixing Valves (TMVs) shall be fitted to hot water outlets serving occupants
deemed to be at a high risk of scalding (and shall be accredited to a level of safety required
for the level of scald risk that exists). A scald risk assessment shall be undertaken and the
decision regarding the use of TMVs shall be approved. Where TMVs are not used a hazard
sign warning of very hot water shall be affixed in a location immediately adjacent to each
outlet. TMVs shall be easily accessible for servicing.
Expansions vessels serving DHS shall be fitted with a proprietary flow through valve and a
flushing and sampling point. All hot water storage vessels shall have an electric
immersion heater and a direct sampling point.
Pipe and fitting materials; pipe systems for DHWS shall be supplied with a 20 year
warranty and shall utilise stainless steel and/or copper tube. Copper tube shall not be
directly pressed to stainless steel tube and where a connection is necessary a brass or DZR
fitting shall be used to separate them. Where compression fittings are made onto stainless
tube they shall be done so using brass olives notwithstanding that these methods are in
compliance with the warranty conditions.
Valves; valves shall be of the following type:
Pipe sizes > 65mm use butterfly.
Pipe sizes < 65mm lever type ball operated.
All valves shall be fitted with valve labels which should be cross referenced with
commissioning records and BIM. For insulation requirements please see the section above
on thermal efficiency. All valves for mains cold and heated water shall be insulated.
Water meters; a WRAS approved water meter or sub-meter shall be provided for each
significant consumer. All meters shall emit a pulse signal and be connected to the BMS.
BMS; all meters, pressures and temperature sensors as well as all automatic flushing valves
are to be linked to the BMS to facilitate automatic pasteurisation. The number and location of
temperature sensors, meters and valves is shown on the schematic DG4.3b.
Water softening; for systems without thermal storage an inline electrolytic anode system
with controller shall be used. For systems with thermal storage an ion exchange resin
softener shall be used.
Resilience – all hot water systems shall be provided with a electric back-up heater of the
immersion or inline type according to application.
Testing & commissioning; a bespoke protocol shall be developed and approved for each
testing and commissioning exercise. Special consideration shall be given to any phased
occupation of buildings so that the potential for stagnation (and the resulting microbial
growth) are minimised.
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Any new or re-worked water system shall, as a minimum, be flushed and disinfection (as
specified in BS EN 80654 and BS 8558:201155) before being brought into use. The building
commissioning process shall take into account the size and complexity of the water system.
Water turnover should also be consider at commissioning stage. If water turnover is
anticipated to be low initially, it may be advisable not to commission certain parts of the
system, such as cold water storage tanks, until the building is ready for occupation. This will
ensure flushing during low use periods will draw directly on the mains supply rather than
intermediate storage. The supplier of any component to be bypassed should be consulted
regarding whether it needs to be filled or can remain empty until it is brought into use.
If there are prolonged periods between pressure testing using water and full occupation of
the development, a procedure should be adopted to maintain water quality in the system.
Weekly flushing should be implemented to reduce stagnation and the potential for microbial
growth, and keep temperatures below 20°C.
In larger systems where there is expected to be a long period of time from filling to
occupation which cannot be avoided, continuous dosing with an appropriate concentration of
biocide can be considered as soon as the system is filled combined with a regular flushing at
all outlets to control the potential accumulation of biofilm.
Relevant drawings and schematics
Schematic DG 4.3b
Some isolators, DOCs and air valves are not shown for simplicity – locations of these items
shall be discussed with the Head of Engineering and Infrastructure when producing bespoke
designs.
Applicable standards and best practice guides
CIBSE Heat Networks: Code of Practice for the UK
As described by WRAS’s Water Regulations Guide
Water Regulations Advisory Scheme
Health and Safety Executive L8 The control of legionella bacteria in water systems
BS EN 806 All Parts Specifications for installations inside buildings conveying water for
human consumption
BS 8558:2001 Guide to the design, installation, testing and maintenance of services
supplying water for domestic use within buildings and their curtilages. Complementary
guidance to BS EN 806
54
BS EN 806 All Parts Specifications for installations inside buildings conveying water for human
consumption
55 BS 8558:2001 Guide to the design, installation, testing and maintenance of services supplying
water for domestic use within buildings and their curtilages. Complementary guidance to BS EN 806
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4 TermoDeck System Design and Control
General Description
Where the building concept, as established at RIBA stage 2, has determined that a low energy
TermoDeck building is to be built the following design parameters shall be adopted.
TermoDeck is a low energy method of construction which utilises the building’s thermal
mass to store thermal energy during periods of off peak demand and release this energy
back into the building during periods of peak demand. An additional benefit is that night time
and fresh air cooling strategies (as defined in CIBSE’s KS03: Sustainable low energy
cooling, an overview56) can be employed to reduce active cooling loads.
Within a TermoDeck building the floor slabs are manufactured with a number of ventilation
cores through which air is passed from mechanical ventilation plant to the space. Ventilation
plant is configured with heat/cold recovery to influence the fresh air temperature prior to its
introduction to the system. The design of a TermoDeck system should be by TermoDeck
with the controls strategy being instructed and approved by the Head of Engineering and
Infrastructure and Head of Energy and Utilities.
This section of the Guide describes the system and materials associated with the heating
pipework installation and the special requirements of air handling units.
UEA Control Concept
The control of TermoDeck buildings is very complicated and the UEA has many years’
experience in managing the controls of these buildings. The UEA control strategy shall be
used to control any TermoDeck buildings.
The UEA control concept is to operate the system with reference to the concrete slab
temperature. Two air temperature sensors for each zone should be installed and situated as
close as possible (approximately 25mm) from the underside surface of the concrete ceiling,
between the second and third passes. The strategy is to maintain the slab temperature
within an adjustable band, above and below a set point.
Fresh air cooling is provided by the outside air when it is cooler than the slab by at least 2 ºC,
by operating the fans, without heat recovery.
During periods of normal operation, the fans are run to provide ventilation air. If the slab is
below the set point the ventilation system is run in heat recovery mode. If the slab is above
the set point the ventilation is run in fresh air mode, without recovery. If the outside air
temperature is 3 ºC above the building extract temperature the heat recovery is used to heat
the incoming air. A larger dead band is used at night to try and force heating to happen
during the occupied periods when fans are running for ventilation.
Each zone (e.g. each storey of the building) shall have a control damper to limit nuisance
energy migration through the building.
56
CIBSE KS03 Sustainable low energy cooling – an overview
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Heat Sources for TermoDeck Installations
It is the UEA’s preference to connect TermoDeck buildings to the DHS and district cooling
system (DCS) where necessary. The DHS and DCS are described in Sections 3.1 and 5.2
respectively. A feasibility study shall be produced for all new connections to the DHS and
DCS with a final decision being made by the Head of Engineering and Infrastructure and the
Head of Energy and Utilities.
Where a connection to a centralised system is not feasible, an alternative heat source shall
be decided upon as described in Sections 3.3 (renewables) and 3.4 (gas).
Air Handling Unit Requirements for TermoDeck Installations
General requirements
•
Fans and thermal wheels to be speed-controlled via inverters.
•
Inlet and Exhaust dampers to shut tight when fans are off.
•
Configuration to enable re-circulation without route through thermal wheel. Supply fan
may be able to be used solo in this mode.
•
Inlet and exhaust configured to eliminate short-circuiting between them.
•
Exposed duct routes on roofs to be avoided.
Supply
Supply Side
Side Requirements
Requirements
Face velocity :
2.0 m/s max.
Frost coil:
Not always necessary. Minimal re-circulation can be used below 3ºC
depending upon configuration of mixing dampers.
Heat recovery:
75% minimum. Thermal pack with self-purge section preferred as
manufactured by ELE (or equal) and approved.
Recirculation
Damper:
Heating or cooling
coils:
Fan:
Capable of tight shut off.
Low-pressure drops required. Typical sizing to be based on 13ºC lift
(14-27ºC) at 100% fan duty in full fresh air day mode and 15ºC lift (2035ºC) at 85% fan duty in recirculation night mode.
Plug type (no fan casing) preferred, with direct drive and backward
curved aerofoil blades.
76% minimum efficiency suggested for impeller and casing.
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88% minimum efficiency suggested for motor, drive and inverter
combined.
67% minimum efficiency suggested for total fan system including
inverter.
Total fan pressure no more than 800 Pa
Filters designed and maintained for low-pressure drop; EU7/8.
Extract Side
Side Requirements
Face velocity:
2.0 m/s max.
Recirculation
Damper:
Capable of tight shut off.
Heat recovery:
As supply (see above).
Fan:
Plug type (no fan casing) preferred, with direct drive and backward
curved aerofoil blades.
76% minimum efficiency suggested for impeller.
88% minimum efficiency suggested for combined motor and inverter
efficiency.
67% minimum efficiency suggested for total fan system including
inverter.
Total fan pressure no more than 530 Pa.
Filters:
Designed and maintained for low-pressure drop; EU7/8.
Notes:
The above specifications combine to limit the Specific Fan Power to
1.2 W/I/s (supply side) and 0.8 W/I/s (extract side), so that it adheres
to CIBSE code B2 2001 section 4.4.4 and Part L2A of the Building
Regulation amendments of 2006, as defined in sections 10.2 & 10.3 of
the second-tier document ‘Non-Domestic Heating Cooling and
Ventilation Compliance Guide’. For AHU’s with heat recovery, a
combined SFP of 2.5 W/I/s can achieve Part L2A compliance.
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5 Comfort Cooling Using Chilled Water and/or
Refrigerant Gas
Introduction
The sections below describe the UEA’s preferred solutions for comfort space cooling
systems i.e. mechanical systems utilising chilled water and/or refrigerant gas. This document
does not provide information for specialist cooling systems (such as process heat for
research purposes) and in such cases a bespoke brief and subsequent design shall be
produced. Information regarding comfort criteria and preferred approaches to cooling can be
found in Part 3 of the Guide: Design criteria for heating, cooling, ventilation and light in
buildings.
Having read this Part (Part 4) of the Guide it is expected that designers contact a member of
the UEA’s Engineering and Infrastructure team to discuss its contents and to ensure that no
ambiguity exists, before designs are developed.
District Cooling System (DCS)
Introduction
Where feasible, all cooling at the UEA shall be provided by the DCS. A feasibility study
shall be produced for all new connections to the DCS to ensure a connection is technically
and economically feasible. A standard finance model shall be provided for the study to
ensure all cash flows and risks are measured. A final decision shall be made by the Head of
Engineering and Infrastructure and the Head of Energy and Utilities.
Notwithstanding the previous paragraph, there may be circumstances where an alternative
cooling source produces a benefit even though a DCS connection is feasible. For example, a
building with a space cooling load, such as a sports facility, may benefit from an air source
heat pump (ASHP) system because the cost of upgrading the DCS infrastructure to meet the
combined load is high. The DCS without upgrade may be able to meet the summer baseload
with the ASHP system meeting peaks. In this example both a DCS connection and an ASHP
system might be the optimised solution.
Designers should consider alternative cooling sources and how they can produce an
operational benefit to the campus’s energy infrastructure as a whole. Section 5.3 discusses
the requirements of alternative cooling sources.
DCS Infrastructure
The UEA utilises DCS to provide cooling to a large number of buildings on the campus. The
system utilises a combination of combined heat and power engines (with LTHW boilers to
provide back-up) to provide heat to a 1 MW th absorption chiller. Additional cooling is
provided by 3 packaged chillers also connected to the DCS which are located at the faculties
of Chemistry, Biology & LGMAC and with a total thermal capacity of 830 kW.
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The chilled water is pumped from Energy Centre 1 to the individual buildings in a flow and
return arrangement via a combination of service ducts and the university’s raised walkways.
The system design flow temperature is 6 °C with a return of around 14 °C and at an
operating pressure of between 2.5 and 4.5 bar(g).
The system operates
DCS. Maximising return temperatures is generally achieved by the use of two port control
valves as described in detail below. Bypass should NOT be fitted within the system unless
special circumstances exist.
The system utilises a building management control system (Trend) to monitor the system
pressure differential between the flow and return at the two extremities of the site and
adjusts the control pump speed to maintain 0.7 bar at these locations.
Key principles and requirements
Any work to develop new sections of the DCS and to repair or alter the existing system shall
consider the following key principles and requirements, which are discussed in further detail
below:
•
Diversity of demand shall be considered to ensure DCS pipes are not oversized.
•
The DCS and building secondary circuits shall employ a variable volume strategy
with dynamic balancing valves.
•
Return temperatures on the DCS are controlled by means of a 2 port control valve.
•
All building integrations shall use a plate heat exchanger.
•
All components shall be capable of withstanding -30 to 60 ºC and 6 bar as a normal
operating condition.
•
Components in contact with the DCS fluid shall be manufactured from carbon steel
although stainless steel is also permitted for smaller pipe diameters. Polymer pipe
systems may be considered if their long terms suitability can be guaranteed.
•
Flow temperatures from centralised chilling plant are 6 ºC with design return
temperatures of 12 ºC but returns of 15 ºC are preferred.
•
Chilled beams are the preferred emitter for DCS connections because they give a
higher return temperature. Using the return from air handling units (in cascade)
should be considered for the supply of chilled beams.
•
Systems with heat recovery and a free cooling function are preferred.
•
Pressure loss in the DCS must be minimised to reduce annual pumping energy.
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•
Insulation and pipe casing shall ensure thermal losses are minimised, are
impermeable to vapour and the degree of waterproofness meets the needs of the
installation.
•
Expansion and mechanical support shall be adequate and for existing pipework,
improved where necessary.
•
Bypasses at the ends of index runs maybe required to maintain flow temperatures at
times of low use. Fixed bypasses shall be avoided – the flow shall be less than 1% of
the branch peak demand at all times and limited by means of a differential pressure
control valve.
•
An automatic leak surveillance system shall be included.
•
The system shall be adequately protected against internal corrosion and freezing
using a prescribed treatment regime.
•
Old services that are no longer in used shall be removed as part of any works
programme.
•
Double isolation from the DCS is required for safety.
A stress analysis complying with EN 13941 shall be undertaken for all new DCS installations
to ensure sufficient expansion capability is included in the design.
Preferred materials, technology and solutions
Heat gain and diversity; heat gain and cooling load profiles shall be assessed using the
methodology set out in Section 2.2.
Pipe and insulation; in the ground, in ducts and in free air and up to the point where the
DCS is within a plant room enclosure, pipe work shall meet the standards given in Table 12:
Table 12
Description
Stress analysis, design and
installation
Preinsulated steel pipe
Steel pipe nominal diameter
Standard
EN 1394157
BS EN 25358
EN ISO 670859
Notes
Use for existing sections of
pipe that may need
improved support as well as
for new installations
Series 1 insulation thickness
Pipes shall be sized to the
‘DN’ standard
57
BS EN 13941:2009+A1:2010 Design and installation of preinsulatred bonded systems for district
heating
58 BS EN 253:2009+A1:2013 District heating pipes. Preinsulated bonded pipe systems for directly
buried hot water networks. Pipe assembly of steel service pipe, polyurethane thermal insulation and
outer casing of polyethylene.
59 EN ISO 6708:1995 Pipework components – Definition and selection of DN (nominal size)
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Steel valve assemblies
Fitting assemblies
Joint assemblies
Leak detection system
BS EN 48860
BS EN 44861.
BS EN 48962
BS EN 1441963
Pressure loss of main lines
Pressure loss of network
branches
≤ 100 Pa/m
≤ 250 Pa/m
Must be automatic and
connected to BMS
The existing DCS is imperial and so a method joining DN to imperial pipe sizes must be
approved, in advance, by the Head of Engineering and Infrastructure.
DCS shall be designed and installed according to the manufacturers requirements.
Where pipework is external to the building and not possible to construct using pre-insulated
pipe to BS EN 253, e.g. sections negotiating tight turns, then short sections may be insulated
in an alternative manner and jacketed with Polyisobutylene (PIB), glued and sealed at
overlaps using the manufacturer’s proprietary adhesive – such sections shall be approved.
In such circumstances the steel pipe shall meet the heat loss pipe requirements of BS EN
253.
The whole installation shall provide a completely weatherproof finish. Where subject to
possible damage, the insulation will be protected using chicken wire wrap or other
mechanical means. The use of trace heating shall be avoided and should only be used as a
last resort and with the permission of the Head of Engineering and Infrastructure.
Polymer pipe systems shall not be used unless they can be shown, at an early stage od
design, to meet the requirements for temperature, pressure and long term survivability.
A stress analysis complying with EN 13941 shall be undertaken for all new DCS installations
to ensure sufficient expansion capability is included in the design. A finished report shall be
made available for approval.
For pipes below ground, polyethylene (PE) casing shall be used and the casing joints shall
be fusion welded. For above ground high density PE (HDPE) casing shall be used (because
it is UV stable) with joints of the heat shrink type although fusion welding is preferred.
Square stabbings shall not be used unless for venting and draining purposes.
60
BS EN 488:2003 District heating pipes. Preinsulated bonded pipe systems for directly buried hot
water networks. Steel valve assembly for steel service pipes, polyurethane thermal insulation and
outer casing of polyethylene.
61 BS EN 448:2009 District heating pipes. Preinsulated bonded pipe systems for directly buried hot
water networks. Fitting assemblies of steel service pipes, polyurethane thermal insulation and outer
casing of polyethylene
62 BS EN 489:2009 District heating pipes. Preinsulated bonded pipe systems for directly buried hot
water networks. Joint assembly for steel service pipes, polyurethane thermal insulation and outer
casing of polyethylene
63 BS EN 14419:2009 District heating pipes. Preinsulated bonded pipe systems for directly buried hot
water networks. Surveillance systems
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Pipework within plant rooms up to the final isolation valve (shown in Schematic DG 4.5a)
shall either be steel barrel to EN 1025564 with malleable fittings to EN 1024265. Yellow
metals shall not be used except for dezincification resistant brass (DRZ). Pipe insulation in
plant rooms shall result in not more than 10 W/m heat loss.
Valves; pipework up to and including 50mm to include ball types valves, 65mm and above
to be butterfly with geared action. Globe valves shall only be used on pipe routes away from
the main flow such as sampling points. Valves should be suitable for an operating in the
presence of monoethylene glycol. Isolating valves must be approved by UEA. Where two
isolating valves are to be positioned within a system, a spool section is required between
valves. Lugged valves shall be used. All valves should be fitted with valve labels, which
should be cross referenced with the record drawings/BIM.
The method of installation and general workmanship should be in accordance with the
HVCA’s TR/20 Part 966.
Pumps; circulating pumps under normal circumstances are not required within the district
cooling system. When it is felt necessary to install circulation pumps within the district
cooling system, approval must be gained from the Head of Engineering and Infrastructure.
In such cases pumps should be close coupled in line circulation and controlled by inverter
controllers connected to the BMS system to ensure maximum efficiency.
System protection; The general procedures set out in CIBSE’s AM14 Non-domestic hot
water systems67 shall be followed with regards flushing and assessment of the need for
chemical cleaning but with the exception of the water treatment chemical recommended by
CIBSE.
The UEA’s dosing regime is a combination of molybdate, nitrite, azolzes and biocide. The
dose rate shall be in accordance with the supplier’s instructions and also sufficient so that,
following circulation for at least 48 hours after dosing, the reserve molybdate level is greater
than 300 ppm/l as measured as MoO4 and the nitrite reserve level is greater than 525 ppm/l
measured as NaNO2. A biocide shall be added to all new system fluid at the manufacturers
recommended dosing rate.
Other control limits are:
•
pH 8.5 to 9.2
•
Biological activity TVC at 22 °C ≤ 10,000 cfu/ml AND pseudomonas < 1000
cfu/100ml at 30 °C AND sulphate reducing bacteria absent
•
Total hardness < 30 ppm
•
Total copper < 1.0 ppm
•
Total iron < 6.0 ppm
•
Soluble iron < 3.0 ppm
64
BS EN 10255:2004 Non-alloy steel tubes suitable for welding and threading. Technical delivery
conditions
65 BS EN 10242:1995 Threaded pipe fittings in malleable cast iron
66 HVCA TR/20 Installation and testing of pipework systems. Part seven - Condenser and cooling
water
67 CIBSE AM14 Non-domestic hot water heating systems
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•
Particulate matter < 30 mg/l as measured at pumps in circulating water
•
Freeze protection to -12 °C using monoethylene glycol68
Testing & commissioning; Testing and commissioning of the system shall generally be as
recommended in the CIBSE Commissioning Code W ‘water distribution systems’69. A
bespoke commissioning protocol shall be developed for each project that the Head of
Engineering and Infrastructure shall approve before the commissioning exercise takes place.
Pressure testing of the system shall be to 1½ times the working pressure.
Commissioning procedures shall be witnessed and approved by a member of the
Engineering and Infrastructure Team (E&IT).
Refilling of the district cooling main shall be completed with freshwater, chemically treated to
the same Standard as the existing district cooling supply. Existing district cooling system
water shall not be used to fill new sections of the main unless approved in advance by the
Engineering & Infrastructure Manager.
The Estates and Building Division Central Boiler House Manager shall be informed prior to
any new system being brought into operation and shall be involved in the reinstatement
process as slugs of cold water entering the district cooling main can have a detrimental
effect.
Suggested schematics
Schematic DG 4.5a
Some isolators, DOCs and air valves are not shown for simplicity – locations of these items
shall be discussed with the Head of Engineering and Infrastructure when producing bespoke
designs.
Applicable standards and best practice guides
BS EN 13941:2009+A1:2010 Design and installation of preinsulatred bonded systems for
district heating
BS EN 253:2009+A1:2013 District heating pipes. Preinsulated bonded pipe systems for
directly buried hot water networks. Pipe assembly of steel service pipe, polyurethane thermal
insulation and outer casing of polyethylene.
EN ISO 6708:1995 Pipework components – Definition and selection of DN (nominal size)
BS EN 488:2003 District heating pipes. Preinsulated bonded pipe systems for directly buried
hot water networks. Steel valve assembly for steel service pipes, polyurethane thermal
insulation and outer casing of polyethylene.
BS EN 448:2009 District heating pipes. Preinsulated bonded pipe systems for directly buried
hot water networks. Fitting assemblies of steel service pipes, polyurethane thermal insulation
and outer casing of polyethylene
69
CIBSE Commissioning Code W – Water Systems
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BS EN 489:2009 District heating pipes. Preinsulated bonded pipe systems for directly buried
hot water networks. Joint assembly for steel service pipes, polyurethane thermal insulation
and outer casing of polyethylene
BS EN 14419:2009 District heating pipes. Preinsulated bonded pipe systems for directly
buried hot water networks. Surveillance systems
BS EN 10255:2004 Non-alloy steel tubes suitable for welding and threading. Technical
delivery conditions
BS EN 10242:1995 Threaded pipe fittings in malleable cast iron
HVCA TR/20 Installation and testing of pipework systems. Part seven - Condenser and
cooling water
CIBSE Commissioning Code W – Water Systems
District Cooling System Integration (Building Connection) with Space
Cooling Systems
Introduction
This section discusses the preferred method of integrating space cooling systems with the
DCS whereas other sections cover separately the DCS itself (before the integration) and
space cooling systems that occur after the integration. As discussed previously, all new and
existing buildings shall be connected to the DCS when technically and commercially
feasible. Even for existing buildings that are currently being supplied by the DCS, this
section may help identify previous approaches to integration that need modification to
improve performance.
Notwithstanding the previous paragraph, there may be circumstances where an alternative
cooling source produces a benefit even though a DCS connection is feasible. For example, a
building with a space cooling load, such as a sports facility, may benefit from an air source
heat pump (ASHP) system because the cost of upgrading the DCS infrastructure to meet the
combined load is high. The DCS without upgrade may be able to meet the summer baseload
with the ASHP system meeting peaks. In this example both a DCS connection and an ASHP
system might be the optimised solution.
Designers should consider alternative cooling sources and how they can produce an
operational benefit to the campus’s energy infrastructure as a whole. Section 5.3 discusses
the requirements of alternative cooling sources.
Key principles and requirements
•
Buildings connected to the DCS shall be separated by a PHE.
•
Pressure and thermal losses and shall be minimised.
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•
Return temperatures shall be maintained at a high temperature using two port,
modulating control valves.
•
The system shall stay in balance under dynamic conditions using pressure
independent control valves.
•
System fluid shall provide adequate protection against corrosion and freezing and
shall be maintained free from dirt and air.
•
All systems shall be controlled by the campus’s building management system and be
adequately metered.
•
Pipe and insulation materials shall meet the requirements of this Guide.
•
Systems shall be provided with sufficient valves, orifice plates and self-sealing test
ports for effective commissioning.
Preferred materials, technology and solutions
The design requirements for integrating building cooling systems with the district cooling
system (DCS) are:
Integration pipe sizing; for more information on DCS configuration please see Section
5.1.3 above. DCS pipes up to the PHE shall be pre-insulated steel with a pressure loss not
exceeding 200 Pa/m. Having calculated building heat gain (in kW) using the method
described above in Section 2.2 an additional allowance for error and building cool down of
10% should be made.
Plate heat exchanger separation; two gasketed plate heat exchangers (PHE) shall be
used for connections over 250 kWth. A single PHE is adequate for smaller connections.
Pressure transmitters shall be located immediately adjacent to the PHE on primary and
secondary flow and return pipes so that the level of fouling can be determined. Each
connection shall have an isolating valve.
Where 2 PHE’s are required, each PHE shall be sized for half the peak design load. All
cooling PHE’s shall have a pressure drop not exceeding 50 kPa. PHEs using a close
temperature approach of not more than 1 °C shall be used. Each PHE shall be provided with
a 2 port return temperature limiting valve and dynamic balancing valve on the primary side.
The control algorithm for the return temperature control valve shall recognise the logarithmic
flow response of a PHE to pressure.
PHE’s with connections up to DN 50 shall be provided with screw connections, those DN65
and above shall have flanged connections. PHE’s shall be mounted on a concrete plinth.
Oversizing of PHE’s is to be avoided - they should closely match the peak heat gain
requirement as set out in Section 2.2 above.
Where more than 1 PHE is installed and where space is sufficient, the PHE’s shall be
balanced using a reverse return arrangement. Where space is insufficient, balancing shall be
by means of double regulating valves with an orifice plate (and self-sealing test points).
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Use split headers; split header systems shall be used in preference to low loss headers to
ensure good temperature and flow control.
Control and monitoring; Schematic DG 4.5a indicates sensor types and locations. All
sensors will be connected ultimately to the campus-wide Trend BMS system.
The integration pipe work shall include orifice plates (with self-sealing test points) at strategic
locations to ensure flow rates can be measured to ensure the system can be commissioned
fully and accurately.
Pipe systems; DCS primary pipe material shall be steel or stainless steel only and able to
withstand temperatures of 60 ºC and 6 bar(g). Pipe systems shall meet the following
requirements:
Table 13
≤ DN80:
The use of threaded joints in steel barrel to
EN 1025570 with malleable fittings to EN
1024271 is acceptable.
≥ DN100 and all concealed pipework
The use of crimped joints in stainless steel
is acceptable up to 3” (seals must able with
meet the temperature and pressure
requirements).
Pipes must be steel (DN specification) and
welded with welds tested to EN 13941 as a
minimum.
No yellow metals shall be included between the DCS supply pipes and PHE’s.
Pipe insulation; insulation thickness shall be the same thickness as the insulation on the D
CS supply pipes or not less than 20mm phenolic foam insulation or equivalent. All valves
and fittings shall be insulated. Pipe supports must be thermally isolating. All insulation shall
be Class ‘O’ British Standard BS47672 fire resistant and shall be installed as generally
detailed by the manufacturer.
Valves and fittings; pipework up to and including 50mm to include ball types valves, 65mm
and above to be butterfly with geared action. Valves should be suitable for an operating
temperature of -20°C. Isolating valves must be approved by UEA. Where two isolating valves
are to be positioned within a system, a spool section is required between valves. Lugged
valves shall be used. All valves should be fitted with valve labels, which should be cross
referenced with commissioning records and drawings. Globe valves shall not be used in the
main flow but can be used on low flow branches such as test points.
Dirt and air separation; a dirt and air separator with sufficient low velocity zones and a
baffle (with bleed valve) below the automatic air valve shall be installed before the PHE.
Differential pressure control valve; in order to ensure the DCS remains balanced under
dynamic pressure conditions a Samson differential pressure control valve shall be provided
70
BS EN 10255:2004 Non-alloy steel tubes suitable for welding and threading. Technical delivery
conditions
71 BS EN 10242:1995 Threaded pipe fittings in malleable cast iron
72 BS 476 Fire tests on building materials and structures
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for each PHE and be located within the building plant room and should be positioned as
close to the district cooling connection position as is possible.
Heat meters; A heat metering strategy shall be developed that considers the need for:
•
Billing of consumers
•
Measuring system efficiency
•
Compliance – meeting the requirements of the Energy Efficiency Directive (as it
applies to the metering and billing of district heating and communal hot water
systems)73
Heat meters for DCS integrations must be compliant with the UK Governments Renewable
Heat Incentive (RHI) Scheme. Meters must conform to MID (Measuring Instruments
Directive) Class 2 accuracy requirements within EN143474 and
•
comply with the relevant requirements set out in Annex I to the 2004 Measuring
Instruments Directive (MID)100 (2004/22/EC75)
•
comply with the specific requirements listed in Annex MI-004 of the MID
•
fall within accuracy Class 2 as defined in Annex MI-004101
To comply with the specific requirements in Annex MI-004 of the MID, all heat meters used
must comprise:
•
An ultrasonic flow sensor (or meter) - a meter which determines the volume of fluid
which has passed through a pipe within a given time period
•
A matched pair of temperature sensors two temperature sensors that are calibrated
together as a pair to make sure the temperature difference between the input and
output of the system is measured to the stated accuracy level. For all types of
temperature sensors we must be assured that they meet the RHI requirements. See
13.17 for information regarding externally mounted (strap-on) temperature sensors.
•
A calculator/digital integrator (though in some systems a Building Management
System may take the place of the integrator) – a device which uses the information
provided by the flow meter and the matched pair of temperature sensors to calculate
the heat energy being transferred.
Heat meters must be tag sealed in the installation and must be tamper proof i.e. sealed in
such a way that the flow and return temperature sensors cannot be swapped around.
An additional requirement is that the meter is installed in either the flow or return pipe (return
is more common) and with sufficient ‘before and after’ pipe length dimensions as described
by the manufacturer.
73
https://www.gov.uk/government/consultations/implementing-the-energy-efficiency-directivemetering-and-billing-of-heating-and-cooling
74 EN1434 Parts 1-6
75 Measuring Instruments Directive 2004/22/EC
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Meters shall be configured to send temperature and flow rate data via the BMS using the MBuss protocol described in EN 1434-3:199776.
Testing and Commissioning; Testing and commissioning of the system shall generally be
as recommended in the CIBSE Commissioning Code W ‘water distribution systems’77. A
bespoke commissioning protocol shall be developed for each project which the Head of
Engineering and Infrastructure must approve before the commissioning exercise takes
place. Pressure testing of the system shall be to 1½ times the working pressure.
Commissioning procedures shall be witnessed and approved by a member of the
Engineering and Infrastructure Team (E&IT).
Suggested schematics
Schematic DG 5.3a
Some isolators, DOCs and air valves are not shown for simplicity – locations of these items
shall be discussed with the Head of Engineering and Infrastructure when producing bespoke
designs.
Applicable standards and best practice guides
BS EN 10255:2004 Non-alloy steel tubes suitable for welding and threading. Technical
delivery conditions
BS EN 10242:1995 Threaded pipe fittings in malleable cast iron
BS 476 Fire tests on building materials and structures
https://www.gov.uk/government/consultations/implementing-the-energy-efficiency-directivemetering-and-billing-of-heating-and-cooling
EN1434 Parts 1-6
Measuring Instruments Directive 2004/22/EC
EN 1434-3 Parts 1-6
CIBSE Commissioning Code W – Water Systems
Alternative Cooling Technologies
Introduction
Where a connection to the DCS proves unfeasible, a local cooling system shall be designed.
76
77
EN 1434-3 Parts 1-6
CIBSE Commissioning Code W – Water Systems
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Key principles and requirements
The following principles and requirements apply to alternative cooling technologies:
•
Air conditioning systems must have a Seasonal Energy Efficiency Ratio78 (SEER) of
at least those detailed in Table 33 of the Non-Domestic Building Services
Compliance Guide 201379
•
Air conditioning systems shall use a refrigerant with a global warming potential
(GWP) of less than 5.
•
Ammonia shall not be used as a refrigerant except for specialist process cooling
applications and with the authority of the Head of Engineering and Infrastructure.
•
Cooling systems shall be sized using the methods set out in Section 2.2 of this
document.
•
All compressors, pumps and fans shall be inverter speed controlled.
•
Systems with free cooling capability and heat recovery are preferred.
•
Waste heat from refrigeration process shall be recovered where possible.
Preferred materials, technology and solutions
Direct and indirect adiabatic cooling; adiabatic (evaporative) cooling shall be considered
in preference to the use of chillers and split units.
Chillers; where their products meet the requirements of this Guide, they shall be sourced
from Airdale International Air conditioning Ltd. The general design requirements for chillers
are that systems shall be designed for flow and return temperatures of 7/15 °C
The feasibility of using chilled water free cooling or condenser water/chilled water heat
recovery should be studied using a finance and risk model supplied by the UEA.
Split Units; where their products meet the requirements of this Guide, they shall be sourced
from Mitsubishi Electric Europe BV.
Refrigeration pipework; shall be designed and installed in accordance with the following
standards and guides:
•
BS EN 378 Parts 1 – 4 Refrigerating Systems and Heat Pumps – Safety and
Environmental Requirements80.
78
As defined by BS EN 14511 Part 3 Air conditioners, liquid chilling packages and heat pumps with
electrically driven compressors for space heating and cooling. Test methods
79 HM Government Non Domestic Building Services Compliance Guide 2013
80 BS EN 378 Parts 1-4 Refrigerating systems and heat pumps. Safety and environmental
requirements.
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•
Institute of Refrigeration Code of Practice for Refrigerating System utilising group A1
and A1 Refrigerants81.
•
HVCA Guide to Good Practice Commercial and Light Industrial Refrigeration
Insulation should be applied to suction pipelines to minimise condensation. Liquid lines
should be insulated to prevent heat pick-up if passing through high temperature areas.
Hot gas lines should be separated from each other and insulated. Insulation material
should conform to the relevant Building Fire Regulations BS 476 part 7 class ‘O’.
Chilled water pipework; see Section 5.2.3 for chilled water pipework requirements.
Testing and commissioning; testing and commissioning of the pipework systems shall
be as detailed in the HVCA a Guide to Good Practice – Commercial and Light Industrial
Refrigeration82.
Relevant drawings and schematics
NA
Applicable standards and best practice guides
As defined by BS EN 14511 Part 3 Air conditioners, liquid chilling packages and heat
pumps with electrically driven compressors for space heating and cooling. Test methods
HM Government Non Domestic Building Services Compliance Guide 2013
BS EN 378 Parts 1-4 Refrigerating systems and heat pumps. Safety and environmental
requirements.
Institute of Refrigeration A1 Refrigerant (HFC) Code of Practice
HVCA a Guide to Good Practice – Commercial and Light Industrial Refrigeration.
Space Cooling Circuit Design and Emitter Sizing (for Chilled Water)
Introduction
This section describes the UEA’s preferences for space cooling distribution circuit design
whereas DCS design and methods of connecting buildings to it are covered in the sections
above.
Information about the UEA’s preferred design philosophies and comfort criteria can be found
in Part 3 of the Guide: Design Philosophies and Criteria for Heating, Cooling, Ventilation and
Light in Buildings. This Part of the Guide (Part 4) on cooling circuit design, considers
information for designers at a more advanced stage of the design development process
(RIBA Stages 3 -7).
81
82
Institute of Refrigeration A1 Refrigerant (HFC) Code of Practice
HVCA a Guide to Good Practice – Commercial and Light Industrial Refrigeration.
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Having arrived at an accurate assessment of a building’s load profile, as described in
Section 2.2 above, this section gives details regarding the UEA’s requirements for space
cooling systems.
Key principles and requirements
•
The building services design shall be developed in conjunction with the architect so
that passive solutions are integrated into the building in order manage heat e.g. using
shading to reduce solar gain, the use of thermal mass, etc.
•
Emitters shall not be oversized; they shall be sized for the heat gain of the space +
10% for rapid cooling of the space.
•
Cooling circuits shall be separated from the DCS by means of a PHE and be
pressurised.
•
Hydraulic circuit temperature differences (∆T’s) shall be as high as possible, as
described below, to reduce pumping energy requirements.
•
Pressure loss in pipe systems shall be 100 – 250 Pa/m to minimise pumping energy
requirements.
•
Hydraulic cooling system return temperatures shall be maintained at 15 °C using 2
port control valves.
•
Space cooling circuits shall be weather compensated where emitter type allows and
variable volume in all cases.
•
The zoning scheme shall consider the requirements of individual spaces, building
geometry, etc.
•
Metering must consider the needs of the Energy Efficiency Directive and allow
communication with the campus’s BMS system.
•
Cooling circuits and emitters shall be adequately protected from corrosion and
freezing.
Preferred materials, technology and solutions
Emitter sizing; emitters shall be sized to meet the building design day heat gain with an
oversizing factor of 0.10 (10%) to account for error and allow rapid cool-down of space.
PHE separation; 2 gasketed PHE’s shall be used to separate the DCS from space cooling
secondary circuits in applications above 250 kWth and a single PHE used for smaller
applications as described above in Section 5.2.2. PHE’s shall be sized according to the
design heat gain of the building + 10%. Pressure drop across cooling PHEs shall be 50 kPa.
Insulation requirements for PHE’s are described below.
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Hydraulic circuit temperatures; the DCS return design temperature, as measured adjacent
to the PHE on the primary side, is 15 ºC for new buildings using the plate optimisation
control solutions detailed below. For existing buildings, 12- 14 ºC is acceptable and can
often be achieved in existing buildings because emitter systems are often oversized. When
re-working an existing emitter system a feasibility study should be undertaken to determine
the highest return temperature possible whilst remaining within the comfort criteria of the
space. The results of the feasibility study shall be approved by the Head of Engineering and
Infrastructure. These measures minimise energy loss and pumping energy requirements
associated with the DCS.
Secondary system flow and return design temperatures shall use those set out in the table
below as a starting point.
Table 14
Circuit
New Buildings
Secondary Flow
Temp (ºC)
AHU Coils
Radiant Panels
Fan Coils
Chilled Beams
6-7
15-18
6-7
15-18
Secondary
Return Temp
(ºC)
11-12
18-21
11-12
18-21
Existing Buildings
Secondary Flow
Secondary
Temp (ºC)
Return Temp
(ºC)
6-7
15.5
15-18
18-21
6-7
15.5
15-18
18-21
Cooling circuits shall be weather compensated notwithstanding that weather compensation
fits with the system design philosophy.
Electrical efficiency; pressure loss shall be 100 – 250 Pa/m with swept bends and full bore
valves and fittings being used to minimise pressure loss in pipe runs that have flow for a high
percentage of the heating season/year. For pipes that have flow for a lesser percentage of
the year, designing to 350 Pa/m may be justified.
Variable speed pumps shall be employed notwithstanding that they fit with the system
design philosophy. Pumps serving index circuits and/or significant emitters i.e. an AHU
battery, a chilled beam or radiant panel zone, shall be controlled by a differential pressure
signal generated at the end of the circuit.
Thermal efficiency; thermal gains shall be minimised by employing the following measures:
•
The total cooling system heat gain shall be less than 1% of the total average annual
cooling load.
•
The maximum recommended pipe heat gains given in Table 40 of the Non-Domestic
Building Services Compliance Guide shall be adopted.
•
All valves and fittings shall be insulated with thermally insulating pipe supports.
•
Communal spaces, where actively cooled, shall be provided with good temperature
control.
•
Pipes shall not be oversized and shall be sized in consideration of diversified
demands. Consideration shall also be given to the possibility that peak demands may
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only occur for short periods at the limits of index runs and so exceeding the 250 Pa/m
limit may be acceptable.
All insulation shall be Class ‘O’ British Standard BS 47683 fire resistant and vapour
impermeable. Where pipework is external to the building, or within external ducts the
insulation shall meet the requirements of pipework for the DCS as described in Section 5.1
above. The use of trace heating shall be avoided and should only be used as a last resort
and with the permission of the Head of Engineering and Infrastructure.
The required insulation thickness may impact on depth of ceiling voids so early discussions
with the architect should be help to ensure sufficient depth is allowed for.
Heat gain for PHE’s shall not exceed 50 W per m² of casing surface area (assuming an
average PHE surface temperature of 12 ºC and a plant room air temperature of 18 ºC).
All valves and fittings shall be insulated with pipe supports using rigid, low conductivity
supports to maintain insulation quality integrity.
Zone control strategy; the zoning strategy must address the needs of the users of individual
spaces and the building’s geometry (e.g. patterns of solar gain). The strategy must be
discussed and agreed with the Head of Engineering and Infrastructure.
Actuated windows should be interlocked with zone controls to ensure heat gain through
infiltration is minimised although reference should be made to the ventilation strategy to
ensure an acceptable level of fresh air is available to occupants. Please note that
requirements for actuated windows, particularly to do this noise emissions, are described in
other parts of this guide.
Emitter Control; each significant emitter shall be controlled by means of:
83
•
Appropriate thermostatic control e.g. dew point sensors for radiant/convective ceiling
panels.
•
A two port control valve with a modulating actuator shall act as a zone valve as well
as a valve that ensures the emitter doesn’t pass significant quantities of cold to the
return pipe – it shall act upon a temperature signal in the return pipe positioned
immediately adjacent to the emitter. The valve shall be set-up so that is passes very
low volumes as a minimum to ensure the return temperature can be effectively
monitored, that thermal response times are minimised and inhibitor chemicals remain
in circulation. The valve opens fully when the thermostat calls for cooling Schematic
DG 5.3a gives details of this arrangement.
•
A differential pressure control valve (DPCV) or pressure independent control valve
(PICV) with flow setting capability to ensure the system remains balanced under
dynamic conditions and to enable the flow rate to be accurately set during balancing
& commissioning exercises. This valve shall be protected by a strainer.
•
An orifice plate with self-sealing test points with an accuracy of ±5% or better for flow
setting during commissioning exercises.
BS 476 Fire tests on building materials and structures
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The UEA can assist with the development of the BMS algorithms required for the control
functions described above. These algorithms shall address the specific qualities of individual
emitter types e.g. the flow rate through heat exchangers responds logarithmically to pressure
whereas radiator index circuits respond in a linear fashion.
Pipe systems; pipe systems on the building secondary side of the PHE shall be suitable for
operating temperatures of -30 ºC to 60 ºC without loss of 20 year survivability. Carbon steel
tube with press fittings is not acceptable. Threaded steel barrel to EN 1025584 with malleable
fittings to EN 1024285 may be used but stainless steel tube with press fittings using butyl
rubber seals is the preferred approach to pipes up to DN 80 where pipes are accessible. For
larger pipes and those that are inaccessible, welding is required. Pipe systems shall be
provided with a 20 year warranty.
Compression fittings with brass olives on stainless steel tube are acceptable whereas
copper olives are not. Where copper tube is joined to stainless steel tube a brass fitting shall
be used to separate the dissimilar metals notwithstanding that this arrangement is
acceptable under the terms of the warranty.
Valves; where balancing valves are installed within circuits that have been oversized for
future use, these shall be line size and not sized to the initial design flow rate. Valve types
for pipe sizes are generally as follows:
Pipe sizes > 65mm use butterfly.
Pipe sizes < 65mm lever type ball operated.
Where branches are connected to a main riser or distribution system, isolation of the
branch must be provided. All valves shall be approved by the UEA, fitted with valve labels
which should be cross referenced with commissioning records and drawings and BIM.
System protection; The general procedures set out in CIBSE’s AM14 Non-domestic hot
water systems86 shall be followed with regards flushing and assessment of the need for
chemical cleaning but with the exception of the water treatment chemical recommended by
CIBSE.
The UEA’s dosing regime is a combination of molybdate, nitrite, azolzes and biocide. The
dose rate shall be in accordance with the supplier’s instructions and also sufficient so that,
following circulation for at least 48 hours after dosing, the reserve molybdate level is greater
than 300 ppm/l as measured as MoO4 and the nitrite reserve level is greater than 525 ppm/l
measured as NaNO2. A biocide shall be added to all new system fluid at the manufacturers’
recommended dosing rate.
Other control limits are:
•
Monoethylene glycol antifreeze protection to -12°C
•
pH 8.5 to 9.2
84
BS EN 10255:2004 Non-alloy steel tubes suitable for welding and threading. Technical delivery
conditions
85 EN 10242:1995 Threaded pipe fittings in malleable cast iron
86 CIBSE AM14 Non-domestic hot water heating systems
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•
Biological activity TVC at 22 °C ≤ 10,000 cfu/ml AND pseudomonas < 1000
cfu/100ml at 30 °C AND sulphate reducing bacteria absent
•
Total hardness < 30 ppm
•
Total copper < 1.0 ppm
•
Total iron < 6.0 ppm
•
Soluble iron < 3.0 ppm
•
Particulate matter < 30 mg/l as measured at pumps in circulating water
The cleaning and protection plan shall be discussed and agreed with the Head of
Engineering and Infrastructure prior to the actions being taken.
Heat metering; heat metering must consider the statutory requirements of the Energy
Efficiency Directive87 (as it applies to the metering and billing of district heating and
communal hot water systems) as well as the needs of the building user for billing for specific
spaces.
Cooling meters shall communicate with the campus’s BMS system using the M-Buss
Protocol described in EN 1434-3:199788. The cooling metering strategy for space cooling
systems shall be developed in consideration of the need for cooling metering as part of the
DCS integration arrangement as described in Secion 3.5 of this document.
Testing and Commissioning; Balancing and commissioning of the system shall generally
be as recommended in the CIBSE Commissioning Code W ‘water distribution systems’89. A
bespoke commissioning protocol shall be developed for each project which the Head of
Engineering and Infrastructure must approve before the commissioning exercise takes
place. Pressure testing of the system shall be to 1½ times the working pressure.
Relevant drawings and schematics
Schematic DG 5.3a
Some isolators, DOCs and air valves are not shown for simplicity – locations of these items
shall be discussed with the Head of Engineering and Infrastructure when producing bespoke
designs.
Applicable standards and best practice guides
BS 476 Fire tests on building materials and structures
BS EN 10255:2004 Non-alloy steel tubes suitable for welding and threading. Technical
delivery conditions
EN 10242:1995 Threaded pipe fittings in malleable cast iron
87
See https://www.gov.uk/government/consultations/implementing-the-energy-efficiency-directivemetering-and-billing-of-heating-and-cooling
88 EN 13757 Parts 1-5
89 CIBSE Commissioning Code W – Water Systems
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CIBSE AM14 Non-domestic hot water heating systems
See https://www.gov.uk/government/consultations/implementing-the-energy-efficiencydirective-metering-and-billing-of-heating-and-cooling
EN 13757 Parts 1-5
CIBSE Commissioning Code W – Water Systems
6 Ventilation Including
Including Fresh
Fresh Air Cooling
Introduction
The sections below describe the UEA’s preferred solutions for ventilation systems including
those that are designed to produce a space cooling effect using outside air i.e. without
mechanical cooling. Ventilation systems referred to in this Guide are defined as ‘a
combination of components required to provide air treatment in which temperature, fresh air
required for respiration or combustion and air cleanliness are controlled’. Information
regarding comfort criteria, ventilation rates, (etc.) and preferred approaches to ventilation
can be found in Part 3 of the Guide: Design criteria for heating, cooling, ventilation and light
in buildings.
‘This document does not provide information for specialist ventilation systems (e.g. for
research purposes) or for systems required only in unusual circumstances (e.g. smoke
vents). In such cases a bespoke brief and subsequent design shall be produced.
Having read this Part of the Guide (Part 4) it is expected that designers contact a member of
the UEA’s Engineering and Infrastructure team to discuss its contents and to ensure that no
ambiguity exists, before designs are developed.
Key Principles and Requirements
•
Ventilation systems shall comply with the requirements set out in Part 3 of the Guide:
Design criteria for heating, cooling, ventilation and light in buildings as well as
statutory requirements.
•
Ventilation of people, plant and spaces shall be achieved using the least amount of
primary energy, including the use of occupancy sensing control strategies and low
energy filter media.
•
When considering whether mechanical cooling or fresh air cooling is the best
approach, a detailed hourly model shall be used to determine the optimum solution –
the UEA has a standard model for investigating this.
•
Where heat and cooling is achieved using ventilation air (i.e. heat and cooling
batteries), AHU’s shall be designed to recirculate.
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•
Specific fan power shall meet the recommendations of the Non Domestic Building
Services Compliance Guide90 for full and part load.
•
The UEA’s preferred approaches to ventilation (as described below) shall be
explored as the starting point for designs.
•
Ventilation systems shall be controlled and monitored by the BMS using the sensor
types and locations set out in the schematics detailed below.
•
AHU’s shall have either thermal wheel or reciprocating plate type heat recovery with
summer bypasses that shall have a minimum efficiency of 85%
•
Intake and extract locations shall consider building features such as openable
windows and doors, so that extract air cannot be reinducted back into buildings.
•
The impact of noise shall be considered especially with regards to actuated windows.
•
Intake locations shall consider sources of pollution.
•
A zoning strategy shall be developed to ensure the optimum ventilation strategy is
employed for each space. For example, natural ventilation may meet the
requirements of atria with mixed mode being required for spaces with a more
constant occupation profile.
Preferred Materials, Technology and Solutions
The desire of the University is to use low energy systems where possible to meet the
ventilation and overheating requirements. The building services design must be developed in
conjunction with the architect so that passive solutions are integrated into the building in
order manage heat e.g. using shading to reduce solar gain, the use of thermal mass and
phase change materials, where appropriate, to attenuate extremes of temperature.
Natural ventilation
In keeping with the principles detailed above, the UEA prefers passive ventilation systems
for spaces where comfort can be guaranteed using this approach. Controllability must be
assured in consideration of the following points:
•
Occupants opening windows in the winter causing unnecessary heat loss
•
Good dispersal of fresh air though deep plan spaces without localised cooling effects
•
Maintaining a secure environment if, for example, the strategy requires windows and
doors to be left open.
•
Wind speed and direction sensors may be used to determine when actuated
windows are opened.
In consideration of these points and if space and geometry allow, natural stack type
ventilation may be preferred.
90
Non Domestic Building Services Compliance Guide
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With regards fresh air cooling using natural ventilation (NV), a simple approach that works
well at the UEA is to have actuated windows at the top and bottom of buildings in atria and
other connected parts of the building. The BMS is employed to open the windows (subject to
security constraints) to allow cooling of the building when the temperature of outside air
allows it to be used effectively.
Natural ventilation has been shown to be very effective at delivering comfort while returning
very good whole life value for money91 although the energy efficiency of this approach
maybe poor compared to mixed mode ventilation due to the lack of heat recovery.
Mixed mode (hybrid)
The UEA’s preference for heating and cooling spaces is by means of wet systems with
emitters in the actual space (e.g. radiators for heating and chilled beams for cooling) as
discussed in Part 3 of the Guide - Design criteria for heating, cooling, ventilation and light in
buildings In light of this preference, mixed mode ventilation is very applicable at the UEA
with NV meeting base load requirements and mechanical ventilation meeting peak loads.
Mixed mode designs shall be based on a zoning strategy. Another consideration, depending
on the type of space, is which type of hybrid system to employ given the two main types as
described in the following paragraphs92:
Contingency design; a contingency based design allows both systems to be used as a
back-up to the other depending on the circumstance; both systems are designed for peak
load. The mechanical system shall incorporate occupancy sensing ventilation
notwithstanding that it fits with the heating and cooling strategy. This approach has a higher
capital cost but lower risk regarding comfort conditions. A benefit of this approach is that
during the winter, the mechanical plant can operate in heat recovery mode and so avoiding
the main problem with NV.
Complimentary design; a complimentary design is one where each system (NV and
mechanical) do not meet peak load but act together or in changeover mode to meet all load
conditions. In this design an occupancy sensing control strategy (such as CO2 sensing)
determines the switching point of the mechanical plant with an override enabling fresh air
cooling when conditions allow. Heat recovery shall be provided for the mechanical element
of the strategy.
This decision regarding which type of system to use will be made according to cost and the
risk of comfort not being achieved but it is likely that a contingency strategy delivers the best
whole life performance because heat recovery can be employed in the winter. A final
decision regarding which design approach to develop shall be made by the Head of
Engineering and Infrastructure.
Mechanical ventilation,
ventilation, fresh air cooling and ground coupled passive cooling
All mechanical ventilation systems shall have heat recovery with summer bypass built in. For
systems with heating and cooling batteries, recirculation shall also be provided for.
Requirements for air handling units are shown in the Schematic DG 4.6a.
91
As discussed in: HYBRID VENTILATION – THE BEST VENTILATION CONCEPT FOR FUTURE
SCHOOL BUILDINGS? CIBSE Technical Symposium 2013 (available from CIBSE Knowledge Portal).
92 As discussed in CIBSE’s KS3 Sustainable low energy cooling, an overview
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Fresh air cooling shall be considered and modelled to ensure that it produces a genuine
energy saving when compared to mechanical cooling i.e. that the specific fan power used for
fresh air cooling using less energy than a mechanical cooling system based on its COP.
Phase change ventilation
ventilation
Phase change materials may be used in air handling units.
Displacement venti
ventilation
entilation
This system provides effective mechanical ventilation as well as cooling. It is particularly
energy efficient and is the UEA’s preferred approach for lecture theatres.
BMS integration
Please see Schematic DG 4.6a for details of how the BMS systems shall be integrated into
air handling units.
Relevant Drawings and Schematics
Schematic DG 4.6a
Applicable Standards
Standards and Best Practice
Non Domestic Building Services Compliance Guide
As discussed in: HYBRID VENTILATION – THE BEST VENTILATION CONCEPT FOR
FUTURE SCHOOL BUILDINGS? CIBSE Technical Symposium 2013 (available from CIBSE
Knowledge Portal).
CIBSE KS3 Sustainable low energy cooling, an overview
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