OPTIMAL WALLING SOLUTIONS FOR ENERGY EFFICIENT HOMES IN SA
Specifying the Minimal Thermal
Performances for External Walling
Presented by:
Howard Harris, Technical Director, WSP Energy Management
October 2010
FINAL REPORT
Independent Study
The Development of a Rational Basis for:
 The Selection of Thermal Mass and Thermal
Insulation in Walling
 Deemed-to-Satisfy (DTS) Requirements
for Walling in the SANS 204 Standard
Prepared by: WSP Energy Africa
Authors: Prof. D. Holm, H.C. Harris, W. Burton
On Behalf of: ClayBrick.org (Clay Brick Association)
National Standards and Regulations
Energy Efficiency in Buildings
Global Energy Efficiency Rules
 Increased thermal resistance
requirements of walling systems
SANS 204 - A World’s First
 Rational basis for the selection
of appropriate thermal capacity
or thermal mass to improve
energy efficiency of buildings
National Standards and Regulations
Energy Efficiency in Buildings
CR Method
 Documented building physics
assist regulators and designers
in achieving energy efficiency
 Pioneered by National Building
Research Council, early ‘80’s
 Computer technology used to
develop DTS requirements for
thermal capacity and thermal
resistance
Regulations
Energy Efficiency in Buildings
SANS 10-400
Part XA standard
SANS 204
First of a series of standards
intended to support the recent
amendment to national
Building Regulations, which
are intended to build
sustainability into South
African building construction.
Specifies the design requirements for energy efficiency in
buildings and of services in
buildings with natural
environmental control and
artificial ventilation or air
conditioning systems.
Thermal Mass Performs
Empirical Testing in Australia ~ Thermal Lag
Source: Think Brick
Australia
Regulations
Energy Efficiency in Buildings
Amplitude Reduction of Maxima and Minima
Regulations
Energy Efficiency in Buildings
Source: Think Brick
Australia
Project Methodology
CR Method:
 Theories used to develop selection of thermal mass
and thermal resistance in walling
 Results compared with building Energy Simulation
methods and Life Cycle Cost evaluations
Aim:
 To provide financial justification for specifying amount
of active thermal capacity necessary for optimal
occupancy comfort, across varying climatic regions of
South Africa.
Project Methodology
DTS Rules Developed in SANS 204
 Ensures optimal energy efficiency in walling systems
Active Thermal Capacity
 Design tool facilitates appropriate selection of thermal mass
and thermal resistance
SANS 204
Deemed-to-Satisfy Rule for Energy Efficiency in Walling
 Facilitates reaching national energy reduction
targets by 2015
 Buildings in RSA classified under Occupancy in
SANS 10400 for National Building Regulations
 Regional climate classification borrowed from
CSIR papers (1970)
 Occupancy classes referenced in SANS 204 and
initial DTS walling solutions based on
Building Code of Australia
SANS 204
Minimum Total R-Values
Construction Surface Densities less than 180 kg/m2
Climatic Zones
Minimum Total R-Value
1&6
2.2
2, 3, 4 & 5
1.9
Minimum Total R-Value for Surface Densities Greater than 180 kg/m2 = 0.4
Minimum Thermal Capacity & Resistance CR Product, in Hours, for External Walling
Occupancy Group / Climate Zone
1
2
3
4
5
6
Residential E1-3,H1-5
100
80
80
100
60
100
Office & Institutional A1-4,C1-2,B1-3,G1
80
80
90
80
80
80
Retail F1-3,J3
80
120
120
90
80
120
SANS 204
External Walls
 Complete walling system from outer skin to interior skin
excl. glazing.
 Glazing included in SANS 204-2 and SANS 204-3.
 Interstitial condensation occurs in walling systems not
able to accommodate moisture migration.
 Vapour barriers and appropriate construction materials,
incl. insulation important for thermal efficiency in climate
zones with damp and high relative humidity.
 Thermal resistance added to external walling with high
thermal capacity to be placed between layers e.g. in the
cavity of a masonry wall.
 Thermal resistance not be added to internal face of walls
with high thermal capacity.
SANS 204 Deemed-to-Satisfy Rule
Energy Efficiency in Walling
 Outlines rational basis for set of rules to be
applied for local climatic conditions
 Energy efficiency to be acceptable to DME
 Proposals to satisfy the National Compulsory
Specifications Regulator are set out in
SANS 10-400XA
National Building Regulations and Standards
Effect Constitutional
Requirements
Constructed in
line with World
Trade Organisation
Agreements
Functional
Regulations
Environment not
harmful to health
Performance based
regulations
Hot water to be
50% heated by nonelectrical energy
Environment protected
for benefit of present
and future generations
Nordic structure
Prevention of pollution
Ecological sustainable
development
Not specific product
standards
Buildings designed
and constructed to be
energy efficient
Energy Efficiency in Walling
South Africa

RSA National Building Regulations include
requirements for energy efficiency and sustainability

SANS 10-400XA provides for compliance with these
regulations

Accepted Routes to Compliance:
- Performance requirements by competent person
- Deemed-to-Satisfy provisions
- Reference building method
Energy Efficiency in Walling
South Africa
 DTS walling solutions in SANS 10-400 XA show minimal
movement towards energy efficiency or sustainability
 Proposals for SANS 204 are not compulsory
The Challenge:
 To develop sustainable and energy efficient walling systems
 Enable state sponsored housing to meet SANS 204
(or similar level walling) thermal performance
SANS 10-400 XA Rules:
 Insufficient to reach 2015 RSA Energy Strategy energy reduction
targets
Regulatory Framework
Energy Efficiency in Buildings
ACT 106 – Building Standards & Regulations
National Building Regulations
SA National Standard 10-400 X
Sustainability Energy subsection XA
Commercial, Retail &
Institutional Buildings
by Rational Design by
a competent person.
DTS requirements as
per SANS 204 for
Residential, Hospital &
Other Buildings
Equivalent Performance
to Reference building to
SANS 204 for
Residential, Hospital etc.
National Building Regulations
Compliance with SANS 10-400 XA
Routes to Compliance for Walling:
DTS Requirements for Residential and Hospitals
 Walls have prescriptive requirements
 Other aspects in terms of SANS 204
Performance Requirements for Energy Usage & Demand
 Design by Competent Person
 Offices, Shopping Centres, Institutional Buildings only
 Table 1 & 2 requirements are met
Reference Building Method an Alternative to SANS 204 DTS
 Model the deemed-to-satisfy – find the energy usage & demand
 Develop more energy efficient alternative
SANS 204 & SANS 104 00 PART XA
Overview of Responsibilities
Roles and Responsibilities:
 Architectural design
 Building Services Design
 Energy Modelling
 Compliance and Verification
Three Compliance Paths:
 DTS: Building envelope and components method
 Rational Design: Energy usage method
 Rational Design: Reference building method
Architect Responsibility
Building Envelope
DTS Provisions Relevant to Building Architecture:






Town Planning
Site Orientation
Building Orientation
Shading
Building Sealing
Building Design
– Floors, Walls, Ceilings and Roofs
– External Glazing (Fenestration)
– Roof Lights
 Accounted for in specifications and drawings
MEP Engineer Responsibilities
Building Services
DTS Provisions Relevant to Building Services Systems:
 Lighting
 Hot Water Services
 Vertical Transportation
 Heating, Ventilation & Air Conditioning
 Installed Equipment
•
DTS provisions accounted for in
specifications and drawings
Modelled Compliance Methods
Building Modelling
 Fabric Performance
 Operating Hours
 Weather (Location)
 Occupancy &
Internal Heat Gains
Modelled Compliance Methods
Services Modelling
 Air & Water-side Design
 Heating & Cooling Equipment
 Controls
Performance Requirements
Building Performance Dictated by Climate Zone & Occupancy
Energy Use
kWh/m²/year
Peak
demand
VA/m²
Entertainment
and public
assembly
390-440
80-90
Theatrical and
indoor sport
390-440
80-90
Places of
Instruction
390-440
75-85
Worship
110-125
75-85
Large Shop
(incl malls)
240-260
85-95
Offices
185-210
85-95
Hotels
585-650
85-95
Building Type
 Buildings within hot interior
(climate zone 3) have largest
energy use allowance
 Buildings in temperate coastal
areas (climate zone 4) have
lowest energy use allowance
 Residential building
performance requirements not
set out
 Scope for rational design uses
the reference building
SANS 204 in Context
Green Building Markets
Number of Buildings
BCA Minimum Performance
Typical Practice
The Majority
75%
Illegal Practise
Green Star
Top 25% of Market
Innovators Risk Takers
Best Practise ~ Green Buildings
Operation of Regulations
SANS 10 - 400XA Timeline
General Principles and Requirements
– Dictate date of implementation and responsibilities
– Effective 12 months from date of gazetting for projects
completed thereafter
Designs within 6 months of Gazetting;
– Owners to advise Local Authority
– Up to 12 months to complete project
Energy Provisions
– Responsibility of Competent Person appointed by building Owner
via Forms 1, 2, 3 and 4
Building Inspections
–
To be performed by Local Authority
Thermal Design
Influence of Walling
Walling and Elements of Building Shell:
 Can influence thermal comfort and energy usage of perimeter zone
 Insignificant influence on interior zone
 Modeling supports notion that exterior walls are important
determinant of energy efficiency of exterior zone
Important Specification Rules:
 Specification of walling and building shell not to be influenced by
size of building
 Shell serves energy efficiency of perimeter zone.
 Buildings with natural ventilation should comprise of perimeter
zone spaces, i.e rooms with external windows and walling.
Requirements for Energy Efficient Walling Systems
Determinants of Walling Systems in any Climate:
 Occupancy Type
- Occupation Density
- Levels of Activity
- Heat Generation

Comfort Requirements
– as per levels of comfort compliance
e.g. 80% range +/- 3.5K in naturally ventilated buildings
Requirements for an Energy Efficient Walling System
Clusters of Occupancy Groups:

Based on Determinants of Walling Systems & Classification
of Buildings in National Building Regulations:
- Residential
- Office and Institutional (combined)
- Retail
Acceptable Ranges of Human Comfort
Building Type
Acceptability
Formulae
Range
Air Conditioned
90%
Tn=18,9+0,225ET*outdoor
±1,2K
Air Conditioned
80%
Tn=18,9+0,225ET*outdoor
±2,5K
Naturally Ventilated
90%
Naturally Ventilated
80%
Tn=18,9+0,225ET*outdoor
±3,5K
Unique South African Climate
Thermal Neutrality
 Optimum thermal neutrality temperature
- Exists for all climatic regions
- Related to mean temperatures of local climate.
TnNV80%=18,9°C+0,225ET*outdoor
 Validity limits 17,8°C < Tn < 29,5°C
- Tn is the neutrality temperature
- ET* is New Effective Temperature. i.e.
Considers air temperature and relative humidity.
Unique South African Climate
Thermal Neutrality

For any regional climate and occupancy group, a
range of temperatures satisfies users of buildings.

Fluctuations in daily and seasonal temperature
swings acceptable for minimising heating or cooling
energy and costs.

Daily fluctuations in temperature within comfort
range for many RSA locations much of the year
Unique SA Climate & Thermal Neutrality
Adaptive Indoor Comfort Targets
Building Envelope Effects
 Building Envelope
contains windows,
shading and walls,
which can bring
comfort or lead to
overheating or
overcooling.
 Overheating in
summer to increase in
South Africa with global
warming aggravated by
urban heat islanding.
Building Envelope Effects
 Overcooling evident in most small RSA residences.
 Building Envelope’s insulation determines conductive,
radiative and convective heat losses or gains.
 Denoted by Thermal Resistance - R = m2K/W.
Building Envelope Effects
Thermal Mass
 Directly or indirectly exposed indoor air is called
Thermal Capacity i.e. C = kJ/kg.K
 Indoor thermal mass called active thermal mass interacts
with indoor air by heating or cooling.
 Air has thermal mass of only 1,2kJ/m3K, whereas;
Brickwork = 1360kJ/m3K and Concrete = 1764kJ/m3K.
 Such materials have strong impact on indoor air
temperatures, which is why much air movement is needed
to heat or cool heavy structures.
 Air leakage can sometimes annul benefits of C and R.
Design Influences
Building Shell Envelope-to-Volume Ratio
 As house sizes decrease surface-to-volume ratio increases
 To retain same indoor climate additional 28% envelope
insulation and commensurate thermal mass is required
 Thermal performance of freestanding housing poor
compared to duplexes or row houses
Design Influences
Perimeter to Floor Area Ratio

Reduction of floor area increased perimeter to floor
area ratio.

Unwanted heat gains/losses via floor increased
with thermal mass effect reduced. Countered with
perimeter insulation.

Thermal performance of freestanding housing
model compared to multi-story buildings.
Aspect

Deviations in excess of 15° from true North can
add 50% to heating energy.
What is the CR Product?
How much?
 CR product is Thermal Capacity of a wall multiplied
by the Thermal Resistance i.e. C x R
 Required levels of C and R set out in SANS 204 for
climatic regions of RSA
Optimal Thermal Capacity & Resistance Product
by Region and Occupancy (kJ/m2K)
Region
1
2
3
4
5
6
Residential
100
80
80
100
60
90
Office & Institutional
80
80
100
100
80
80
Retail
80
80
120
80
60
100
Rational Design
Correct Correct
Level ofLevel
Thermal
of Thermal
Resistance
Resistance
& Capacity
& Capacity
of Walling
of
Walling
 Basis for rational approach to correct level of thermal
resistance and thermal capacity found in application of CR
Method
 CR Method links degree of modulation and fluctuating
internal temperatures with various levels of thermal
resistance and thermal capacity
 Fluctuation expressed as a ratio of the internal
temperature amplitude versus outside diurnal temperature
fluctuation
Rational Design
Correct Level of Thermal Resistance & Capacity of
Walling
 Temperature fluctuations in a building can be reduced by
improving thermal efficiency of the shell
 Building can then operate at lower energy intensity levels.
 CR Method provides CR constant measured in units of time
 Indicates minimum required combinations of thermal mass
and thermal resistance to maintain temperature fluctuations
within the comfort temperature.
Internal Temperature
Effects of Low Mass
Correlation for CR Product & Energy Usage
 Correlation of CR Product to Energy Usage using
various walling systems exceeds 90% in most cases.
 CR Method used to construct either a Rational Design
Tool or a simple DTS rule for walling.
 Establishes minimum thermal mass and thermal
resistance combination requirements, for use in SANS
204, as means of achieving sustainability in buildings
 Guidance to future development of SANS10-400XA in
direction of CR Product or Active Thermal Capacity
given by research outcomes.
Closing Thoughts
 Unique RSA climate presents opportunity for using
thermal mass in buildings to achieve lower energy usage
 Use of high mass building elements traditional in RSA
 National Building Regulations references lower standard
of thermal performance as indicated by thermal
resistance – next 2 years.
 Lack of affordability restraining development of energy
efficient walling energy in subsidy housing sector
Closing Thoughts
 No reason why rest of building stock should be given free
reign to continue building without sustainable walling
systems
 Future development of SANS10-400XA in direction of CR
Product or Active thermal capacity given by research
outcomes.
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