Environmental Performance Toolkit for Gl

26 Pages·2004·0.908 MB·English

by  Cibse

Environmental performance toolkit
for glazed façades
CIBSE TM35: 2004
The Chartered Institution of Building Services Engineers
222 Balham High Road, London SW12 9BS
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without the prior permission of the Institution.
©November 2004 The Chartered Institution of Building
Services Engineers London
Registered charity number 278104
ISBN1 903287 53 7
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time of publication. However no responsibility of any kind for
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Printed on 100%recycled paper comprising at least 80%
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Foreword
The publication is based on a 2-year Partners-in-Innovation (PII) project sponsored by
the Department of Trade and Industry, that conducted a comprehensive study on the
overall performance of highly glazed façades. Their performances are represented by
various performance indicators for different aspects of the façade characteristics,
including:
— heat transfer characteristics
— solar energy penetration and solar shading
— condensation risk
— occupant visual comfort, including daylight availability and visual engagement
— acoustic attenuation properties
— estimated manufacturing/installation costs.
A total of 37 different façade systems were analysed to cover the different glazing systems
available in the market today, such as basic double glazed systems, advanced triple glazed
systems, ventilation double skinned curtain walls, and shading solutions like external
overhangs, louvres, fins, internal or interstitial blinds, etc.
The chief objective of this publication is to provide those with an interest in buildings
(e.g. developers, planners, surveyors, architects, engineers etc) with a better under-
standing of the glazed façade. It will serve as a reference guide for the design of energy-
efficient and occupant-friendly glazed building envelope. Furthermore, the accompanying
software tool ‘Façade Selector’ will allow users quickly and easily to identify façade
configurations suitable for their applications, hence expediting the building design
process.
Based on the results of the analyses on the 37 façade options (see Appendix), the best
performers in the different criteria are:
(1) Lowest peak cooling load: reflective solar control double glazed units
(2) Lowest peak heating load: high performance structural triple glazed units
(3) Highest average daylight factor: full-height hard coat low emissivity double glazed
units
(4) Lowest installation cost:historic clear float double glazed units
It is important to note that best performance in one criterion generally does not equate to
a good performance in another criterion. For instance, best performers in daylight
penetration and visual engagement tend to suffer in terms of cooling energy and capacity
requirements. Therefore, to achieve a system that will perform well thermally and
visually, it would frequently mean significantly higher capital costs incurred in installing
systems such as ventilated double skin façades and advanced spectrally-selective low
emissivity glazing. The use of electric lighting controls to take advantage of high daylight
available can help reduce cooling, as well as lighting energy requirements.
Kai Lim
Principal author
Acknowledgements
The work leading to the production of this publication was carried out as a Partners in
Innovation project co-ordinated by FaberMaunsell. The funding provided by the
Department of Trade and Industry is gratefully acknowledged. The contributions of the
other project partners are also gratefully acknowledged.
Foreword
The publication is based on a 2-year Partners-in-Innovation (PII) project sponsored by
the Department of Trade and Industry, that conducted a comprehensive study on the
overall performance of highly glazed façades. Their performances are represented by
various performance indicators for different aspects of the façade characteristics,
including:
— heat transfer characteristics
— solar energy penetration and solar shading
— condensation risk
— occupant visual comfort, including daylight availability and visual engagement
— acoustic attenuation properties
— estimated manufacturing/installation costs.
A total of 37 different façade systems were analysed to cover the different glazing systems
available in the market today, such as basic double glazed systems, advanced triple glazed
systems, ventilation double skinned curtain walls, and shading solutions like external
overhangs, louvres, fins, internal or interstitial blinds, etc.
The chief objective of this publication is to provide those with an interest in buildings
(e.g. developers, planners, surveyors, architects, engineers etc) with a better under-
standing of the glazed façade. It will serve as a reference guide for the design of energy-
efficient and occupant-friendly glazed building envelope. Furthermore, the accompanying
software tool ‘Façade Selector’ will allow users quickly and easily to identify façade
configurations suitable for their applications, hence expediting the building design
process.
Based on the results of the analyses on the 37 façade options (see Appendix), the best
performers in the different criteria are:
(1) Lowest peak cooling load: reflective solar control double glazed units
(2) Lowest peak heating load: high performance structural triple glazed units
(3) Highest average daylight factor: full-height hard coat low emissivity double glazed
units
(4) Lowest installation cost:historic clear float double glazed units
It is important to note that best performance in one criterion generally does not equate to
a good performance in another criterion. For instance, best performers in daylight
penetration and visual engagement tend to suffer in terms of cooling energy and capacity
requirements. Therefore, to achieve a system that will perform well thermally and
visually, it would frequently mean significantly higher capital costs incurred in installing
systems such as ventilated double skin façades and advanced spectrally-selective low
emissivity glazing. The use of electric lighting controls to take advantage of high daylight
available can help reduce cooling, as well as lighting energy requirements.
Kai Lim
Principal author
Acknowledgements
The work leading to the production of this publication was carried out as a Partners in
Innovation project co-ordinated by FaberMaunsell. The funding provided by the
Department of Trade and Industry is gratefully acknowledged. The contributions of the
other project partners are also gratefully acknowledged.
TM35 Project Steering Group
The project partners and their representatives on the steering group were as follows:
FaberMaunsell Ltd K Lim, A Wilson, S Law, S Irving
Building Sciences Ltd S Borland
CIBSE H Davis, M Holmes
Colt Group Limited R Buck
Department of Trade and Industry G Henderson
Parry Bowen Limited J Taylor
Pilkington plc R Wilberforce
Schüco International S Cottee
Sheppard Robson B Keenan
Stanhope plc M Knowles
Taylor Woodrow plc R Fry
Turner & Townsend Group C Jones
Principal author
Kai Lim (FaberMaunsell)
Project team
The analysis and software development work that provided the information on which this
document is based were carried out by:
Kai Lim (FaberMaunsell)
Simon Law (FaberMaunsell)
Nigel Banks (FaberMaunsell)
Christopher Pountney (FaberMaunsell)
Chris Jones (Turner & Townsend Group)
Editor
Ken Butcher
CIBSE Editorial Manager
Ken Butcher
CIBSE Research Manager
Hywel Davies
CIBSE Publishing Manager
Jacqueline Balian
Note from the publisher
This publication is primarily intended to provide guidance to those responsible for the
design, installation, commissioning, operation and maintenance of building services. It is
not intended to be exhaustive or definitive and it will be necessary for users of the
guidance given to exercise their own professional judgement when deciding whether to
abide by or depart from it.
14 Environmental performance toolkit for glazed façades
South west facing office (no lighting control)
120 600
Peak cooling Cost per m2
(W/m2) facade
100 500
2m)
s / (W/ 80 400 )£/m2
oad 60 300 s / (
g l ost
n 40 200 C
oli
o
C
20 100
0 0
Option 08 Option 09 Option 12
Figure 40 Selection of suitable south-west facing façades
South west facing office (with lighting control)
120 600
Figure 38 Façade Selector: estimated costs/cost indices comparison chart Peak cooling Cost per m2
(W/m2) facade
100 500
East facing office 2m)
100 P(Wea/mk c2)ooling Afavcetroarge daylight 10 s / (W/ 80 400 £/m)2
2s / (W/m) 8600 86 e DF ooling load 6400 320000 Costs / (
ad ag C 20 100
oling lo 40 4 Aver 0 Option 03 Option 08 Option 09 Option 12 0
Co 20 2 Figure 41 Selection of suitable south-west facing façades (using lighting
control
0 0
Option 08 Option 31 Option 34
Figure 39 Selection of suitable east facing façades adequate lighting controls are operated, not only is the
peak cooling load in the office spaces reduced (comparing
— peak cooling loads of 80 W/m2or less
Options 08, 09 and 12 in Figures 40 and 41), but other
— average daylight factor of 2.0 or greater. façade options may become feasible due to the reduced
peak loads (in this case, option 03: body tinted 3200 mm
In this case, only three options will meet the requirements double glazed unit).
instead of the five identified for the south-facing façade.
Note that these extra comparison charts are not provided
In another instance, the requirements are as follows: by the analysis window of the Façade Selector, but are
produced independently, based on data provided in the
(a) south-west facing offices
individual performance summary reports.
(b) peak cooling loads of 110 W/m2 or less (suitable
for, say, fan coil systems)
3.4 Conclusions
(c) façade costs below £600/m2.
Too often, designers seek a ‘one size fits all’ solution to the
Figure 40 shows the façades that will meet these require-
design of highly glazed façades, hoping to find a single
ments.
façade solution that meets all requirements (low energy
usage for heating and cooling, maximum daylight penetra-
These façades correspond to (in order of peak cooling
tion and visual comfort for occupants, cost, etc). However,
loads):
it is not as simple as that.
(1) Option 09: reflective solar control 3200 mm
double glazed unit Hence, it is hoped that TM35: Environmental performance
toolkit for glazed façadeswill give designers a greater insight
(2) Option 08: high performance solar control
into glazed façade design, and a better understanding into
3200mm double glazed unit
the underlying interactions of the different performance
(3) Option 12: hard coat low-e 1/ rd height double criteria that define the façade system.
3
glazed unit.
However, should it be decided that more energy savings
References
can be made through lighting control, i.e. switching
electrical lighting off when daylight levels are sufficient
1 Conservation of fuel and power in buildings The Building
(400 lux on working plane or higher), the selection would
Regulations 2000 Approved Document L2 (London:The
look like that shown in Figure 41. This shows that when Stationery Office) (2002)
References 15
2 Environmental design CIBSE Guide A (London: Chartered 8 The visual environment for display screen use CIBSE Lighting
Institution of Building Services Engineers) (1999) Guide LG3 plus addendum LG3: 2001 (London: Chartered
Institution of Building Services Engineers) (1996/2001)
3 Fundamentals ASHRAE Handbook (Atlanta, GA: American
Society of Heating, Refrigerating and Air-Conditioning 9 BS 8233: 1999: Sound insulation and noise reduction for buildings
Engineers, Inc.) (2001) (London: British Standards Institution) (1999)
4 Code for lighting (London: Society of Light and Lighting) 10 BS EN ISO 140-3: 1995: Acoustics. Measurement of sound
(2004) insulation in buildings and of building elements. Laboratory
measurement of airborne sound insulation of building elements
5 Best practice in the specification for offices (London: British
(London: British Standards Institution) (1995)
Council of Offices) (2000)
11 BS EN ISO 717-2: 1997: Acoustics. Rating of sound insulation in
6 A Yates, R Baldwin, N Howard and S Rao BREEAM 98 for
buildings and of building elements. Impact sound insulation
offices(Garston: Building Research Establishment) (1998)
(London: British Standards Institution) (1997)
7 Daylighting and window designCIBSE Lighting Guide LG10
(London: Chartered Institution of Building Services
Engineers) (1999)
Contents
1 Introduction 1
2 Building environmental performance criteria 1
2.1 Identifying performance criteria 1
2.2 Heat transfer 1
2.3 Solar heat gains and solar shading 2
2.4 Condensation risks 5
2.5 Occupants’ visual comfort 5
2.6 Acoustic performance 9
2.7 Capital costs 10
3 Thermal modelling and the Façade Selector 11
3.1 External and internal design conditions 11
3.2 The Façade Selector 11
3.3 Additional performance comparisons 13
3.4 Conclusions 14
References 14
Appendix: Façade classification matrix 16
1
Environmental performance toolkit
for glazed façades
1 Introduction decisions. Consequently, the efficiency of the design
process should be improved, since the amount of bespoke
analysis being repeated time and again in different design
Highly glazed façades are becoming an increasingly
offices should be substantially reduced.
common feature in the present day urban landscape due to
the versatility, transparency and physical beauty of glass.
Other benefits of this publication include:
This trend, however, introduces several challenges to
designers as they attempt to balance the visual and — Environmental: Work carried as part of the develop-
aesthetic benefits that glass provides against the environ- ment of the amendments to Part L of the Building
mental performance of the building envelope. This is Regulations in 2002 indicated that although only
because highly glazed buildings tend to increase solar heat about 2.5% of UK buildings are greater in area
gains in the internal spaces. Even though this might be than 2500 m2, they are responsible for 43% of the
deemed beneficial in the form of passive heating in colder energy consumed in the non-domestic building
climates, the growing trend of increasing casual loads in sector. It is such buildings where advanced façades
office buildings also means that there is an increasing predominate, and so improvements in their design
need for cooling throughout the year. will improve heating, cooling and lighting per-
formance and have a disproportionately large
The need for a balanced design strategy is further impact on national CO emissions.
2
accentuated by the increasing complexity in the design of
— Human factors: Better façade design will improve
highly glazed façades and the growing emphasis on
internal comfort standards to the increased well-
environmental responsibility of buildings, enforced by
being of occupants, thereby directly enhancing
Building Regulations Approved Document L2 (ADL2)(1).
productivity and business performance.
Increasing environmental awareness has led to demands — Financial: By improving façade performance, the
for increasingly efficient buildings with a view to value of the building as a capital asset will be
achieving sustainable societies. The concept of sustain- enhanced, and running costs potentially reduced
ability is to meet the needs of today’s society such that the with more efficient use of energy.
capabilities of future populations to meet their needs are
not impaired. Achieving this requires the conservation of
finite resources, which, on a larger scale, can be seen as the
2 Building environmental
need to conserve the global environment.
performance criteria
At present, there are very few consistent data on the
overall performance of the building façade, and there is
still considerable misunderstanding in the industry as to 2.1 Identifying performance criteria
the critical parameters that influence façade performance.
Discussions with architects and designers about advanced The criteria that define the performance of a glazed facade
façades showed that the performance was looked at purely include:
from the perspective of the glazing, and ignored crucial
— heat transfer
factors such as frame and edge technologies, and of the
façade design as a whole. The reason for this is that the — solar heat gains and solar shading
data readily available to the industry are related to com-
— condensation risks
ponents rather than complete façade systems.
— occupant visual comfort
This publication aims to improve the building design by
— acoustic performance
better informing designers and clients about the impacts
of their glazed façade design choices via a comprehensive — capital costs.
database of the environmental performances of existing
and advanced glazed façades. This will be especially
beneficial for designers at the early stage of design, when 2.2 Heat transfer
irreversible decisions about the treatment of elevations are
often made. This will improve the quality of design, The total thermal transmittance, or the U-value, of a
reduce energy demand for heating, cooling and lighting glazed façade is one of the most important, but yet most
and improve occupant comfort. misunderstood, concepts in building envelope design. It
determines the thermal conduction performance of the
By investing in a comprehensive analysis of different envelope, and indirectly influences the strength of
generic façade treatments, both basic and advanced, potential cold downdraughts off highly glazed façades
industry will have robust data on which to base its design during winter conditions.
1
Environmental performance toolkit
for glazed façades
1 Introduction decisions. Consequently, the efficiency of the design
process should be improved, since the amount of bespoke
analysis being repeated time and again in different design
Highly glazed façades are becoming an increasingly
offices should be substantially reduced.
common feature in the present day urban landscape due to
the versatility, transparency and physical beauty of glass.
Other benefits of this publication include:
This trend, however, introduces several challenges to
designers as they attempt to balance the visual and — Environmental: Work carried as part of the develop-
aesthetic benefits that glass provides against the environ- ment of the amendments to Part L of the Building
mental performance of the building envelope. This is Regulations in 2002 indicated that although only
because highly glazed buildings tend to increase solar heat about 2.5% of UK buildings are greater in area
gains in the internal spaces. Even though this might be than 2500 m2, they are responsible for 43% of the
deemed beneficial in the form of passive heating in colder energy consumed in the non-domestic building
climates, the growing trend of increasing casual loads in sector. It is such buildings where advanced façades
office buildings also means that there is an increasing predominate, and so improvements in their design
need for cooling throughout the year. will improve heating, cooling and lighting per-
formance and have a disproportionately large
The need for a balanced design strategy is further impact on national CO emissions.
2
accentuated by the increasing complexity in the design of
— Human factors: Better façade design will improve
highly glazed façades and the growing emphasis on
internal comfort standards to the increased well-
environmental responsibility of buildings, enforced by
being of occupants, thereby directly enhancing
Building Regulations Approved Document L2 (ADL2)(1).
productivity and business performance.
Increasing environmental awareness has led to demands — Financial: By improving façade performance, the
for increasingly efficient buildings with a view to value of the building as a capital asset will be
achieving sustainable societies. The concept of sustain- enhanced, and running costs potentially reduced
ability is to meet the needs of today’s society such that the with more efficient use of energy.
capabilities of future populations to meet their needs are
not impaired. Achieving this requires the conservation of
finite resources, which, on a larger scale, can be seen as the
2 Building environmental
need to conserve the global environment.
performance criteria
At present, there are very few consistent data on the
overall performance of the building façade, and there is
still considerable misunderstanding in the industry as to 2.1 Identifying performance criteria
the critical parameters that influence façade performance.
Discussions with architects and designers about advanced The criteria that define the performance of a glazed facade
façades showed that the performance was looked at purely include:
from the perspective of the glazing, and ignored crucial
— heat transfer
factors such as frame and edge technologies, and of the
façade design as a whole. The reason for this is that the — solar heat gains and solar shading
data readily available to the industry are related to com-
— condensation risks
ponents rather than complete façade systems.
— occupant visual comfort
This publication aims to improve the building design by
— acoustic performance
better informing designers and clients about the impacts
of their glazed façade design choices via a comprehensive — capital costs.
database of the environmental performances of existing
and advanced glazed façades. This will be especially
beneficial for designers at the early stage of design, when 2.2 Heat transfer
irreversible decisions about the treatment of elevations are
often made. This will improve the quality of design, The total thermal transmittance, or the U-value, of a
reduce energy demand for heating, cooling and lighting glazed façade is one of the most important, but yet most
and improve occupant comfort. misunderstood, concepts in building envelope design. It
determines the thermal conduction performance of the
By investing in a comprehensive analysis of different envelope, and indirectly influences the strength of
generic façade treatments, both basic and advanced, potential cold downdraughts off highly glazed façades
industry will have robust data on which to base its design during winter conditions.