APPLICATION GUIDE AG 16/2002
Variable-flow water systems
Design, installation and commissioning
guidance
By Arnold Teekaram and Anu Palmer
Supported by
PREFACE
There are significant benefits to variable speed pumping in terms of
both energy cost and capital cost. The main energy savings derive
from the pump law relationship which indicates that (for a system
with fixed resistance) halving the flow rate would reduce the pump
power to roughly one eighth its previous value. This theoretical
saving is however unlikely to be achieved on an actual variable flow
installation because of the following:
• Changes in the system resistance as valves close
• Reduction in the pump efficiency as the system characteristics
change
• Variable speed drive losses.
Capital cost saving opportunities are likely to arise from the potential
diversity of load during pipe and pump sizing.
Constant flow heating and chilled water systems are generally well
understood by designers and commissioning specialists. The
commissioning procedure involves setting up systems to achieve fixed
flow rate parameters. Most of the valves used for commissioning are
manually adjusted during commissioning, and three-port valves are
used to modulate flow rate and hence heat transfer across coils.
There are significant differences in systems where pump speed is
allowed to vary. Some of the valves used may be self-acting types
responding to changes in pressure. Control of heat transfer is more
likely to be achieved through the use of two-port valves which need
to be able to shut off against the system pressures. Inevitably, the
designer and commissioning specialist must take into account part
load conditions as part of commissioning and system proving.
For these reasons, many of the commissioning procedures laid down
in the BSRIA Application Guide AG 2/89.3: Commissioning Water
1
Systems - Application Principles are not applicable to systems with
variable speed pumps. This Guide is therefore aimed at these specific
types of system. The format of the Guide is the same as the
aforementioned Commissioning Water System AG 2/89.3 in that
guidance is split into three parts: The Design of Commissionable
Systems, The Installation of Commissionable Systems and
Commissioning Procedures. Cross reference is made to other BSRIA
commissioning guides as appropriate, although every effort has been
made to make this guide a standalone document.
It is hoped that the introduction of this guide, and other supporting
guidance on variable speed applications, will encourage their
implementation on a wider scale. This will hopefully result in a
realisation of the significant energy saving potential that such systems
have to offer. The recommendations given in this document are for
guidance only.
VARIABLE-FLOW WATER SYSTEMS
© BSRIA AG 16/2002
CONTENTS
DEFINITIONS
vi
LIST OF SYMBOLS
viii
PART A: THE DESIGN OF COMMISSIONABLE SYSTEMS
1
1
INTRODUCTION
1
1.1 General
1.2 Commissioning information
1
1
PIPEWORK SYSTEM DESIGN
4
2.1
2.2
2.3
2.4
2.5
2.6
2.7
4
4
5
8
9
9
9
2
3
4
5
6
7
Self-balancing arrangements
Flow velocities
Pump selection
Inverter drives
System cleanliness
Venting
Access
FLOW MEASUREMENT AND REGULATING DEVICES
11
3.1 Regulating valves
3.2 Flow measurement devices
3.3 Flow measurement/regulating/isolating devices
11
12
12
GUIDELINES FOR COMPONENT SELECTION AND
APPLICATION
20
4.1 Flow measurement/regulation options
4.2 Selection criteria
20
22
SPECIFYING FLOW RATES AND TOLERANCES
24
5.1 Accuracy of flow measurements
24
DESIGN CONSIDERATIONS
25
6.1
6.2
6.3
6.4
25
26
30
30
Return temperature and demand in variable volume systems
Pressure distribution
Benefits and design considerations
Design considerations
EXAMPLE OF VARIABLE FLOW SYSTEM DESIGNS
33
7.1 The Bodle-Orchard circuit
7.2 Boiler house circuit
7.3 Sub-circuits and branches
33
38
40
PART B: THE INSTALLATION OF COMMISSIONABLE
SYSTEMS
45
1
MANAGEMENT
45
1.1 General
1.2 Organisation and planning
45
45
PIPEWORK INSTALLATION PROCEDURES
47
2.1
2.2
2.3
2.4
47
47
48
53
2
Good housekeeping
Good workmanship
Good pipework arrangements
Adequate accessibility
VARIABLE-FLOW WATER SYSTEMS
© BSRIA AG 16/2002
CONTENTS
3
INSTALLATION OF VARIABLE SPEED DRIVES
54
4
INSTALLATION INSPECTIONS
56
PART C: COMMISSIONING OF VARIABLE FLOW
HYDRONIC SYSTEMS
57
1
INTRODUCTION
57
2
CONSTANT VOLUME COMMISSIONING PROCEDURES
59
2.1 Least favoured and most favoured circuits
2.2 Proportional balancing
2.3 Balancing of branches and risers
59
59
61
SYSTEM COMPONENTS COMMISSIONING PROCEDURES
62
3.1
3.2
3.3
3.4
62
63
64
3
3.5
3.6
3.7
3.8
3.9
3.10
3.11
3.12
4
Inverter-driven pumps
DPCV in sub-circuits controlling single loads
DPCV in sub-circuits controlling serveral loads
Primary constant volume circuit serving a secondary
circuit
Primary variable serving constant-volume secondary flow
Variable volume served by variable primary flow
Variable primary serving a variable secondary at different
temperatures
Use of differential pressure control valve across a single
control valve
Combination valves in sub-circuits
Two-port valves
Thermostatic radiator valves
Variable speed drives
VARIABLE FLOW COMMISSIONING PROCEDURES
64
66
67
68
69
70
70
71
71
72
4.1 Case study
72
4.2 Commissioning procedure
74
4.3 Information to be recorded in final commissioning report 78
5
HYDRONIC VARIABLE FLOW COMMISSIONING
PROBLEMS
REFERENCES
80
82
TABLES
Table 1: Recommended range of water velocities (CIBSE Guide,
Volume C, 2000).
Table 2: Valves and flow measurement devices.
Table 3: Typical flow rate accuracies for flow measurement devices
VARIABLE-FLOW WATER SYSTEMS
© BSRIA AG 16/2002
4
11
24
FIGURES
Figure 1: Fixed-speed pump performance characteristics
Figure 2: Variable-speed pump performance characteristics
Figure 3: An example of a double regulating valve
Figure 4: Examples of fixed-orifice fittings
Figure 5: Examples of variable-orifice double regulating valves
Figure 6: Typical fixed-orifice double regulating valve
Figure 7: Cartridge type constant flow regulator
Figure 8: An adjustable flow controller
Figure 9: Typical differential pressure control valve
Figure 10: Combination valve
Figure 11: The arrangement of a combination valve
Figure 12: Relationship between flow rate and pressure drop for a
combination valve
Figure 13: Practical construction of a combination valve
Figure 14: Pipework schematic showing valve locations
Figure 15: Return temperature variation in heating systems
Figure 16: Return temperature variation in chilled water systems
Figure 17: Pressure distance diagram
Figure 18: Pressure distance diagram
Figure 19: Pressure-distance diagram
Figure 20: Bodle-Orchard circuit for a variable-volume heating system
Figure 21: Bodle-Orchard circuit for a primary/secondary variable-volume
heating system
Figure 22: Schematic of sub-circuits
Figure 23: Schematic of injection sub-circuit
Figure 24: Performance of a radiator as a function of the return
temperature of the radiator
Figure 25: Control of minimum flow through boilers
Figure 26: Installation of self acting differential pressure control valve
Figure 27: Differential pressure control valve located at the bottom
of a riser
Figure 28: Differential pressure control valve on floor branch
Figure 29: Use of reverse acting bypass valve
Figure 30: Two-port isolating valve in branch with differential pressure
control valve
Figure 31: Installation of a combination valve
Figure 32: Least favoured and most favoured circuits
Figure 33: Schematic of sub-circuit
Figure 34: Commissioning of a differential pressure control valve with
single load in sub-circuit
Figure 35: The Commissioning of a differential pressure control valve with
several loads in a sub-circuit
Figure 36: A secondary variable-volume circuit with a constant primary
circuit
Figure 37: A secondary constant-volume circuit with a variable primary
circuit
Figure 38: A secondary variable-volume circuit with a variable primary
circuit
Figure 39: A pump arrangement in a secondary circuit
Figure 40: The arrangement of a differential pressure control valve across
a control valve
Figure 41: Commissioning a combination valve
Figure 42: A system diagram detailing the configurations for three typical
circuits
Figure 43: A commissioning network diagram
6
7
11
12
13
13
14
15
16
17
17
18
19
21
25
26
27
28
29
34
35
36
37
39
42
50
50
51
51
52
52
59
60
63
64
65
66
67
68
69
70
73
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INTRODUCTION
INTRODUCTION
A1
A1
PART A: THE DESIGN OF COMMISSIONABLE SYSTEMS
1
1.1
GENERAL
INTRODUCTION
As soon as possible, and no later than upon entering the scheme design
stage, the designer should pay attention to the strategy for
commissioning the scheme, and the level of commissioning expertise
required. The designer should ask themself the following questions:
•
Is external commissioning expertise required in support of the design
role?
•
Will the services sub-contractor have the capability in-house to carry
out commissioning?
•
Will the services sub-contractor have commissioning expertise
available during the installation?
In consideration of these aspects, the designer should advise if a
commissioning specialist is required, and when that specialist should be
appointed. The degree to which the designer influences decisions on
these matters and advises the project management team will greatly affect
the commissionability of the built systems.
1.2
COMMISSIONING
INFORMATION
To enable a water distribution system to be successfully commissioned,
the designer must provide adequate information, documented in the
form of drawings, schedules and specifications. The technical
requirements of the commissioning works should be developed by the
designer to define clearly:
•
The scope of the works, in other words the systems to be
commissioned, their functions and duration of operation and an
explanation of their operational inter-relationships with other
engineering services systems.
•
The setting out of the responsibilities of the various parties (client,
design team, main or managing contractor, installation contractor
and commissioning specialist). BSRIA Technical Memorandum
TM 1/88: Commissioning HVAC Systems, Division of Responsibilities2,
gives guidance on this subject.
•
The technical specification of the commissioning work, for example:
− the standards (for example relevant parts of CIBSE Codes and
BSRIA guides) to which the works should be carried out
− the tolerances for regulation and test results
− the reporting procedures required
− the witnessing procedures to be observed.
•
Design drawings showing the layout of the system in relation to the
building form and, if required, other engineering services.
VARIABLE-FLOW WATER SYSTEMS
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A1
INTRODUCTION
•
Schematic diagrams clearly illustrating the design intent and
including all the design information required to commission the
system. For example:
Water flow rates and system
pressures
Terminal branches
Branches
Mains
Sizes
Pipes
Valves
Flow measurement devices
Locations
Isolating valves
Regulating valves
Differential pressure control valves
Control valves
Flow measurement devices
Differential pressure sensors
Constant flow controllers
Automatic flow controller
Reference Identification
Terminal units
Isolating valves
Regulating valves
Differential pressure control valves
Control valves
Flow measurement devices
Constant flow controllers
Automatic flow controller
The reference identification should be unique to each individual
component to permit cross referencing and to enable a component to be
identified in correspondence and telephone discussions.
If the schematics are prepared at the same time as the design drawings,
potential difficulties in regulation may often be revealed and rectified
prior to installation.
•
Schedules of major plant, equipment and components, crossreferenced to the design drawings and schematic diagrams.
•
Additional design information required for commissioning which
may not be available until after the appointment of the building
services installer may include:
− electrical wiring diagrams of associated plant and equipment
− control system diagrams
− pump performance curves
− regulating valve calibration data, based upon calculated pipework
head losses.
2
VARIABLE-FLOW WATER SYSTEMS
© BSRIA AG 16/2002
INTRODUCTION
A1
The specification of management requirements must be related to
specific contractual conditions. Although the designer will strongly
influence whether the commissioning specialist is to be employed by the
main, managing or installing contractor, it is the latter who will specify:
•
Forms of contract
•
programme constraints
•
•
resource levels
method statements
•
quality assurance procedures
•
•
insurance requirements
site establishment details
•
compliance with site safety and industrial relations protocol
•
bonds, warranties and guarantees.
The different sources of project information required to fully specify
commissioning should not, however, preclude the early appointment of a
commissioning specialist. The specialist could be appointed on a
consultant basis during the design phase, converting to a contractor later.
VARIABLE-FLOW WATER SYSTEMS
© BSRIA AG 16/2002
3
MANAGEMENT
MANAGEMENT
B1
B1
PART B: THE INSTALLATION OF COMMISSIONABLE
SYSTEMS
1
MANAGEMENT
1.1
GENERAL
The installer’s responsibility is to provide a water installation which
meets the specified requirements. To achieve this, properly managed
resources must be allocated to the process of constructing a
commissionable system.
The tendering or appointed installer must carefully study the
enquiry/contract documents to determine precisely the project
requirements. The installer should ask himself the following questions:
•
Is the installer called upon to install only?
•
Does the installer have to commission the system and, if so, has the
installer got the resources in-house or will a specialist need to be
appointed?
•
Has a commissioning specialist been appointed by the designer or
client?
•
Is the installer aware of the commissioning specialist’s duties and
requirements during the system construction?
The designer/project team will have been responsible for establishing the
commissioning strategy. The system installer must understand the
strategy in order to meet the designer’s requirements and enable the
commissioning process to proceed.
1.2
ORGANISATION
AND PLANNING
Where the installer is responsible for commissioning, the installer should
select and instruct the commissioning specialist at the earliest possible
stage to ensure that commissioning expertise is available in the planning
and programming of the commissioning tasks.
Together, they should:
•
Establish effective lines of communication between the
commissioning specialist and other parties involved
•
Produce a set of working drawings that show the detailed provisions
for incorporating the commissioning facilities. These drawings must
also show the details of required temporary facilities
•
Review the contract documents to determine the requirements for
commissioning, taking nothing for granted and seeking clarification
where necessary
•
Produce a realistic programme which incorporates the
commissioning activities, phased and fully integrated with the main
installation and construction programmes
•
Regularly review the programme during installation to establish the
effect of modifications and delays on the planned static completion
and power-on dates and any other dates critical to the
commissioning activities
Acquire all the information specified in Section A1.2 from the
designer
•
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B1
MANAGEMENT
•
Obtain from equipment suppliers and manufacturers their latest
information for all items supplied. Standard details which are not
modified to suit the particular project should always be treated with
caution. Manufacturer’s literature should be checked for any
installation requirements additional to those specified
•
Progressively record as-installed information on at least two sets of
installation drawings – one clean set to facilitate the production of
the record drawings and operating/maintenance documentation, and
one site set for use by the commissioning specialist
•
Establish systematic site control procedures to assist the progressive
monitoring of the standard of the pipework installation practices
maintained on site (see Section B2)
Prepare co-ordinated ceiling plans illustrating access panel
requirements
Establish an equipment and materials procurement procedure which
incorporates an effective means of checking each and every delivered
item against specified requirements
•
•
•
46
Retain all documents and literature provided with each delivered
item of equipment for use by the commissioning engineer (and for
inclusion in the operating and maintenance manuals).
VARIABLE-FLOW WATER SYSTEMS
© BSRIA AG 16/2002
INTRODUCTION
INTRODUCTION
C1
C1
PART C: COMMISSIONING OF VARIABLE FLOW
HYDRONIC SYSTEMS
1
INTRODUCTION
Effective commissioning of variable flow hydronic systems for heating
and chilled water distribution is essential if they are to provide good
controllability for the heating and cooling loads they serve. Traditionally
the majority of building services applications, systems have been designed
with fixed speed primary/secondary pumps to provide constant-volume
flow with the application of three-port valves for controlling the loads in
the sub-circuits. Arrangement of these valves in the sub-circuits can be
such that the circuit is either a diverting, mixing or an injection circuit.
For these circuits, operation of the circulating pumps is always at constant
speed irrespective of whether the system is operating at full load or part
load conditions. The main commissioning procedure for constant
volume systems is therefore generally one of water balancing where the
flows are proportionally balanced in the respective branches to satisfy the
particular requirements of the system. Control and balancing are
maintained at part load, but there are no savings from reduced pumping
unless the heating is switched off in summer or the designer had provided
smaller pumps for the summer duty.
In variable-flow hydronic systems, reducing pump speed or staging of
pumps with boilers and chillers to suit part-load conditions is an energy
efficient method of control. These systems were developed as an
alternative to constant volume systems because of the potential pump
energy savings to be derived by varying the flows to match the diversity
on load requirements. There is also the additional benefit from reduced
pipe heat losses due to low return water temperatures that two-way valve
systems give on part load compared to the higher return temperatures
with three-way valve control.
For such systems, components such as differential pressure controllers,
inverter driven pumps, two-port control valves, combination valves,
automatic variable volume limiter, constant flow controllers, orifice plates
and pressure-tapped double regulating valves etc must be correctly
installed and specified as an integral part of the design to maintain
dynamic control and flow stability and to allow easy commissioning. In
two-port valve systems one method of balancing and commissioning that
makes life easy is to use differential pressure control valves, as these valves
can perform a dual duty of maximum volume control and differential
pressure control. Once a sub-circuit has been commissioned the
differential pressure control effectively prevents the flow and balance in
the sub-circuit being affected by other sub-circuits.
The main purpose of the commissioning procedure will therefore be to
ensure that the system is proportionally balanced to give design flows
under design (full load) conditions in the same way as constant volume
systems are balanced and that the components provide the desired control
in response to changes in the system demand.
The following sections of this document provide guidance on
commissioning procedures for variable flow hydronic systems and their
components.
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© BSRIA AG 16/2002
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C1
INTRODUCTION
Section 2 briefly describes the basic principles of conventional
commissioning procedures for constant volume systems. These have
been fully described in other publications to which the reader is referred
and only the main points are summarised here. These include: basics of
proportional balancing, procedures for identifying the least favoured and
most favoured circuits and balancing of branches and risers.
Section 3 gives guidance on commissioning of individual system
components such as pumps, differential pressure controllers in subcircuits controlling single and multiple loads, combination valves, twoport valves, thermostatic radiator valves and variable speed drives.
For the purpose of describing the commissioning procedure for variable
flow hydronic systems, a case study is given in section 4 which describes
the commissioning process on an actual project. A diagram is included
to detail briefly the system layout and a brief description of controls
operation is also included prior to a detailed step by step commissioning
procedure. The commissioning procedure employed is then translated
into a generic commissioning flowchart for variable flow hydronic
systems.
Section 5 of the document begins by highlighting typical commissioning
problems associated with variable-speed pumping systems and the
corrective measures that can be taken.
58
VARIABLE-FLOW WATER SYSTEMS
© BSRIA AG 16/2002