TM36: Climate Change and Indoor Environment: Impacts and Adaptation

63 Pages·2005·2.768 MB·English

by  Chartered Institution Of Building Services Engineers Staff

Climate change and the indoor
environment: impacts and adaptation
CIBSE TM36: 2005
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.
©February 2005 The Chartered Institution of Building Services
Engineers London
Registered charity number 278104
ISBN1 903287 50 2
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time of publication. However no responsibility of any kind for
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Contents
Summary 1
1 Introduction 3
2 The climate scenarios 4
2.1 UKCIP02 scenarios 4
2.2 Use of the UKCIP02 scenarios for environmental design 6
2.3 UKCIP02 climate changes for UK sites 6
3 Performance indicators 6
3.1 ‘Overheating’ criteria 6
3.2 Energy usage 10
4 What does the future look like? 10
4.1 Temperatures in future climate 10
4.2 Space heating 11
4.3 Risk of summertime overheating 13
4.4 Comfort cooling 14
4.5 Performance of air conditioning systems 14
5 Case studies:detailed assessment of existing building types 15
5.1 Introduction 15
5.2 Dwellings 16
5.3 Offices 17
5.4 Schools 17
5.5 Other locations:Manchester and Edinburgh 17
5.6 Other emissions scenarios 17
5.7 Ventilation control for the advanced naturally ventilated buildings 18
6 Adaptation strategies 19
6.1 Dwellings 20
6.2 Offices 23
6.3 Schools 24
7 Conclusions 25
7.1 Passive measures 26
7.2 Mechanical cooling 27
7.3 Final conclusions 28
References 28
Annex: data sheets for case studies 29
D1 19th century house 30
D2–D4New-build house 32
D5 1960s flat 36
D6 New-build flat 38
O1 Naturally ventilated 1960s office 40
O2 Modern mixed-mode office 42
O3 Mechanically ventilated high thermal mass office 44
O4 Advanced naturally ventilated office 46
O5 Fully air conditioned office 48
S1 1960s school 50
S2 Advanced naturally ventilated school 52
3
Climate change and the indoor environment:
impacts and adaptation
1 Introduction — To what extent will passive measures be able to
improve summertime thermal comfort and amelio-
rate the increased propensity for overheating?
This publication addresses the issue of how climate
change in the UK over the 21st century may affect — How effective will different approaches to comfort
summertime thermal comfort in buildings and the energy cooling be under the changing climate?
use of associated heating, ventilation and air conditioning
— What are the energy use implications of the
(HVAC) systems.
various strategies?
There is compelling scientific evidence that our climate is
changing and it is probable that average annual tempera- These questions are addressed here by quantitative assess-
tures will increase by several degrees during this century. ment of the effect of climate change on building and HVAC
Changes in climate will impact upon the energy used for system performance, measured by the frequency of
heating and cooling in buildings, may cause overheating overheating, energy consumption and carbon emissions.
in naturally ventilated buildings and affect the ability of The risks posed by climate change to these performance
low energy cooling systems to provide comfortable measures are assessed in two ways. First, properties of the
conditions. Many buildings, particularly dwellings, are future climate are examined to provide an initial, qualita-
designed to last for several decades and longer; consid- tive, assessment. Secondly, dynamic thermal modelling is
eration of climate change issues is therefore necessary now used to make quantitative assessments of case study
to ensure the longevity of the building stock. Not to do so buildings drawn from three generic building types:
will result in a generation of buildings that are likely to dwellings, offices, and schools. The case study buildings
become obsolete within their useful lifetime, or require are chosen to illustrate the response of different HVAC
costly and difficult retrofits. Designing for the anticipated strategies, including manually operated natural ventila-
future climate is therefore very much a current issue. tion, full mechanical air conditioning, and passive and low
Until now, however, there has been little information energy methods.
available regarding the magnitude of these effects.
An important aspect of the study was to analyse the
While mechanical air conditioning is an obvious tech- performance of design features that successfully cool
nological solution to adapt to the warming climate, this buildings without mechanical means, e.g. the control of
route is undesirable for two reasons. First, inclusion, solar radiation and ventilation, or the use of thermal
retrofitting and maintenance of air conditioning in many storage. A number of approaches currently used in the UK
buildings is likely to be beyond the bounds of economic and other parts of the world were applied to the case study
viability. This is particularly important in the domestic buildings and tested under present and future climates.
sector in which the very young, old or physically infirm Novel techniques such as embodying phase change
are likely to suffer greatest harm from thermal discomfort materials within the building fabric were not considered,
and heat stress. Secondly, and perhaps more fundamen- because the objective was to examine what can be done
tally, use of air conditioning has the potential to increase with existing technology. Similarly it was assumed that
significantly the energy burden of, and consequently the there will not be significant changes in modes of building
greenhouse gas emissions from, a building, thereby use, including internal heat gains and occupation patterns,
exacerbating the problem for which the adaptation is over the time periods considered.
needed.
Following this introduction, the structure of the docu-
It is estimated that buildings account for approximately ment is as follows:
45% of total energy consumption in the UK(1) and 41%
across the European Community(2). There is, therefore, — Section 2: describes the climate change scenarios
used and the method used to produce design
considerable potential to reduce emissions through good
weather years for projected future climates.
practice in building design and methods of use, e.g. by up
to 50% for new buildings and following major refurbish- — Section 3: discusses design targets for thermal
ment(2). performance and energy use.
This publication aims to address these issues by providing — Section 4: describes some of the general impli-
guidance on measures to ensure summertime thermal cations of the climate changes on the performance
comfort in UK buildings without incurring excessive of different types of building based on the charac-
energy use. There are a number of key questions: teristics of the future weather years.
— To what extent will climate change increase the — Section 5: forms the core of the document and
occurrence of summertime thermal discomfort and presents the results of the dynamic thermal
‘overheating’? modelling of the case study buildings.
4 Climate change and the indoor environment: impacts and adaptation
— Section 6: considers further strategies and remedial ranging from one relatively intensive in fossil fuel use and
options for those buildings where limitations to greenhouse gases emissions, to one in which sustainability
performance have been identified. is given high priority on a global level and fossil fuel use
decreases.
— Section 7: presents the conclusions.
— Annex: contains the data sheets for the case study Figure 2.1 shows the predicted changes in atmospheric
buildings and the results of thermal modelling. carbon dioxide over the coming century under each of the
scenarios. These changes in atmospheric composition are
computed independently of the climate models. They
2 The climate scenarios form the input ‘forcing’ to the climate models, which then
aim to calculate the resulting future climates . Note that
even under the Low Emissions (Global Sustainability)
2.1 UKCIP02 scenarios scenario, atmospheric carbon dioxide continues to
increase until around the middle of the century due to the
projected timescale to phase out fossil fuel use. In the
In 1998 the United Kingdom Climate Impacts Programme
scenarios it is therefore anticipated that there will be an
(UKCIP) released the first set of comprehensive climate
appreciable level of climate change over the course of the
change scenarios for the United Kingdom. This was done
century even if substantial efforts are made now to reduce
in recognition of the need to make quantitative assess-
greenhouse gas emissions.
ments of the possible impacts of climate change. These
scenarios were subsequently updated in 2002 as the
‘UKCIP02’ scenarios(3). (A further update is expected in 2.1.2 The global climate model
2007/8.) The principal changes in the 2002 scenarios are
that (a) they make use of the more recent Met Office Predictions for global temperature change in UKCIP02
global climate model (HadCM3) and (b) they contain were obtained in the following way. First, the global
information from a regional model (HadRM3) embedded climate model was run for the period from 1860 (a
within the global climate model with a resolution of nominal pre-industrial starting point) until 1990 using
50 km. The scenarios are being widely used to assess the observed changes in greenhouse gases and other natural
possible impacts of climate change on the UK (see forcings of climate change such as volcanoes. The data for
www.ukcip.org). the thirty-year period 1960–1990 were averaged to form
the ‘baseline’ climate. Next, the global climate model was
It is likely that the scenarios will be further refined and run forward until 2100 for each of the four emissions
developed in the future, but at present they represent the scenarios. Values of global average temperature in the runs
are shown in Figure 2.2. Finally, these data were averaged
best available information on the likely course of climate
over three 30-year timeslices: the 2020s, 2050s and 2080s
change in the UK over the 21st century. Some types of
climate scenario are excluded, e.g. sudden or gradual 1000 1000
cooling of the northern hemisphere due to changes in the
m
Gulf Stream. However, these types of climate change are p 900 A1F1 900
p
considered to be of very low probability within the next n / 800 800
100 years and lie outside the range of scenarios presently o
being considered in climate change impacts adaptation ntrati 700 A2 700
and planning. The following is a brief outline of how the e
c
scenarios were produced; full details are available in on 600 B2 600
c
Hulme et al.(3) e
d 500 B1 500
xi
o
di 400 400
2.1.1 Emissions scenarios n
o
b
ar 300 300
The basis for the UKCIP02 climate scenarios is a set of C
four ‘storylines’ for greenhouse gas emissions, which are 200 200
taken from the Intergovernmental Panel on Climate 1960 1980 2000 2020 2040 2060 2080 2100
Change (IPCC) SRES emissions scenarios. Each storyline
Figure 2.1 Global carbon dioxide increases (reproduced from UKCIP02
represents a possible future, as described in Table 2.1, Scientific Report(1); Crown copyright)
Table 2.1 Characteristics of the UKCIP emissions scenarios (from tables A.2 and A.3 of the UKCIP02 report(3))
UKCIP02 climate change IPCC SRES UKCIP socio-economic Description
scenario emissions storyline scenario title
Low Emissions B1 Global Sustainability Clean and efficient technologies; reduction in material use;
global solutions to economic, social and environmental
sustainability; improved equity; population peaks mid-
century
Medium-Low Emissions B2 Local Stewardship Local solutions to sustainability; continuously increasing
population
Medium-High Emissions A2 National Enterprise Self-reliance; preservation of local identities; continuously
increasing population; economic growth on regional scales
High Emissions A1F1 World Markets Very rapid economic growth; population peaks mid-
century; social, cultural and economic convergence among
regions; market mechanisms dominate.
4 Climate change and the indoor environment: impacts and adaptation
— Section 6: considers further strategies and remedial ranging from one relatively intensive in fossil fuel use and
options for those buildings where limitations to greenhouse gases emissions, to one in which sustainability
performance have been identified. is given high priority on a global level and fossil fuel use
decreases.
— Section 7: presents the conclusions.
— Annex: contains the data sheets for the case study Figure 2.1 shows the predicted changes in atmospheric
buildings and the results of thermal modelling. carbon dioxide over the coming century under each of the
scenarios. These changes in atmospheric composition are
computed independently of the climate models. They
2 The climate scenarios form the input ‘forcing’ to the climate models, which then
aim to calculate the resulting future climates . Note that
even under the Low Emissions (Global Sustainability)
2.1 UKCIP02 scenarios scenario, atmospheric carbon dioxide continues to
increase until around the middle of the century due to the
projected timescale to phase out fossil fuel use. In the
In 1998 the United Kingdom Climate Impacts Programme
scenarios it is therefore anticipated that there will be an
(UKCIP) released the first set of comprehensive climate
appreciable level of climate change over the course of the
change scenarios for the United Kingdom. This was done
century even if substantial efforts are made now to reduce
in recognition of the need to make quantitative assess-
greenhouse gas emissions.
ments of the possible impacts of climate change. These
scenarios were subsequently updated in 2002 as the
‘UKCIP02’ scenarios(3). (A further update is expected in 2.1.2 The global climate model
2007/8.) The principal changes in the 2002 scenarios are
that (a) they make use of the more recent Met Office Predictions for global temperature change in UKCIP02
global climate model (HadCM3) and (b) they contain were obtained in the following way. First, the global
information from a regional model (HadRM3) embedded climate model was run for the period from 1860 (a
within the global climate model with a resolution of nominal pre-industrial starting point) until 1990 using
50 km. The scenarios are being widely used to assess the observed changes in greenhouse gases and other natural
possible impacts of climate change on the UK (see forcings of climate change such as volcanoes. The data for
www.ukcip.org). the thirty-year period 1960–1990 were averaged to form
the ‘baseline’ climate. Next, the global climate model was
It is likely that the scenarios will be further refined and run forward until 2100 for each of the four emissions
developed in the future, but at present they represent the scenarios. Values of global average temperature in the runs
are shown in Figure 2.2. Finally, these data were averaged
best available information on the likely course of climate
over three 30-year timeslices: the 2020s, 2050s and 2080s
change in the UK over the 21st century. Some types of
climate scenario are excluded, e.g. sudden or gradual 1000 1000
cooling of the northern hemisphere due to changes in the
m
Gulf Stream. However, these types of climate change are p 900 A1F1 900
p
considered to be of very low probability within the next n / 800 800
100 years and lie outside the range of scenarios presently o
being considered in climate change impacts adaptation ntrati 700 A2 700
and planning. The following is a brief outline of how the e
c
scenarios were produced; full details are available in on 600 B2 600
c
Hulme et al.(3) e
d 500 B1 500
xi
o
di 400 400
2.1.1 Emissions scenarios n
o
b
ar 300 300
The basis for the UKCIP02 climate scenarios is a set of C
four ‘storylines’ for greenhouse gas emissions, which are 200 200
taken from the Intergovernmental Panel on Climate 1960 1980 2000 2020 2040 2060 2080 2100
Change (IPCC) SRES emissions scenarios. Each storyline
Figure 2.1 Global carbon dioxide increases (reproduced from UKCIP02
represents a possible future, as described in Table 2.1, Scientific Report(1); Crown copyright)
Table 2.1 Characteristics of the UKCIP emissions scenarios (from tables A.2 and A.3 of the UKCIP02 report(3))
UKCIP02 climate change IPCC SRES UKCIP socio-economic Description
scenario emissions storyline scenario title
Low Emissions B1 Global Sustainability Clean and efficient technologies; reduction in material use;
global solutions to economic, social and environmental
sustainability; improved equity; population peaks mid-
century
Medium-Low Emissions B2 Local Stewardship Local solutions to sustainability; continuously increasing
population
Medium-High Emissions A2 National Enterprise Self-reliance; preservation of local identities; continuously
increasing population; economic growth on regional scales
High Emissions A1F1 World Markets Very rapid economic growth; population peaks mid-
century; social, cultural and economic convergence among
regions; market mechanisms dominate.
The climate scenarios 5
6
Observations High
e / K 4 AA21F1 nario
g e Medium-high
n B2 c
ha B1 s s
c n
ure 2 ssio Medium-low
at mi 2080s
er E 2050s
mp 0 Low 2020s
e
T
0 0·2 0·4 0·6 0·8 1·0 1·2
-2
1850 1900 1950 2000 2050 2100 Figure 2.3 The range of climate scaling factors in the UKCIP02 scenarios
Figure 2.2 Predictions of annual average temperature in the UKCIP02
Low scenario 2080s similar to that in the High scenario
global climate model runs (Crown copyright)
2050s.
corresponding to the periods 2011–2040, 2041–2070 and
2071–2100, respectively.
2.1.3 The regional climate model
The four emissions scenarios and three timeslices in The size of the computational grid boxes for the global
UKCIP02 make a total of twelve climate examples to climate model (HadCM3) is approximately 300 km over
consider. Dealing with the complete set of scenarios is the UK. This spatial resolution is too coarse to resolve the
therefore a considerable undertaking. However, the geographical variations due to factors such as topography
scenarios are mathematically linked and the differences
and coastline morphology. To produce such information, a
between them are proportional. The proportionality is
‘regional climate model’ (HadRM3), covering only the UK
given by a ‘climate scaling factor’ (CSF), which is defined and part of northern Europe was used.
as the ratio of the global average temperature change in a
scenario relative to that in the Medium-High 2080s
The regional model takes boundary conditions from the
scenario (the CSF is called the ‘pattern scaling factor’ in global climate model and the size of the computational
UKCIP02).
grid boxes was approximately 50 km. Running the
regional climate model is computationally intensive,
The scenarios are listed in Table 2.2 in order of increasing
requiring several months of ‘super-computer’ power. For
average global temperature change and CSF. The CSFvalues this reason only a limited number of model runs were
in this table may be used to relate the climate changes
made. All the regional detail in the UKCIP02 scenarios is
under a given scenario to those in the Medium-High
based on regional model runs for the Medium-High
Emissions 2080s scenario which has a CSF of 1.0. A
Emissions scenario 2080s and the baseline 1961–1990
graphical comparison of CSFs is shown in Figure 2.3. It can
climate. Results for the present day climate were then
be seen that in the 2020s the level of climate change in the
subtracted from the 2080s results, giving the change in the
four emissions scenarios is similar, which is because the
climate parameters across the UK on a 50 km grid. The
levels of CO in the atmosphere are similar at this time
2 philosophy adopted in UKCIP02 is that the geographical
(Figure 2.1). By the 2050s timeslice, however, the four
variations in climate changes across the UK are the same
scenarios are starting to diverge, with differences being
for all scenarios but vary in magnitude in direct propor-
quite appreciable by the 2080s timeslice. For example in
tion to the global average temperature change. To obtain
the 2080s the climate scaling factor associated with the
regional climate changes for the other scenarios and
High Emissions scenario is around twice that of the Low
timeslices, the changes for the Medium-High Emissions
Emissions scenario. Figure 2.3 also indicates that the
climate scaling factor of different scenarios is similar at scenarios are simply multiplied by the CSFvalues given in
Table 2.2. This method is called ‘pattern scaling’.
different timeslices. For example, the level or warming in
the Low Emissions scenarios 2080s is similar to that in the
The resulting UKCIP02 climate scenarios contain
Medium-High scenario 2050s, and that in the Medium-
monthly averaged values of climate variables recorded on
Table 2.2 UKCIP02 scenarios ranked by magnitude of global average the 50km computational grid. The variables available are:
temperature change and the derived climate scaling factor (CSF)
— temperature (daily average, maximum and mini-
Average global Climate Emissions scenario Timeslice
mum dry-bulb)
temp. change scaling
relative to factor (CSF) — total precipitation
1960–1990
— snowfall rate
0.79 0.24 Low 2020s
0.88 0.27 Medium-Low 2020s — 10m wind speed
0.88 0.27 Medium-High 2020s
— relative and specific humidity
0.94 0.29 High 2020s
1.4 0.43 Low 2050s — total cloud in the longwave radiation band
1.6 0.50 Medium-Low 2050s
— net surface long and shortwave radiation
1.9 0.57 Medium-High 2050s
— total downward shortwave radiation
2.0 0.61 Low 2080s
2.2 0.68 High 2050s
— soil moisture content
2.3 0.71 Medium-Low 2080s
— mean sea-level pressure
3.3 1.0 Medium-High 2080s
3.9 1.18 High 2080s — surface latent heat flux.
6 Climate change and the indoor environment: impacts and adaptation
2.1.4 Uncertainties in the UKCIP02 scenarios This is the baseline climate onto which the UKCIP02
changes are applied*. Figure 2.4 shows the baseline
The climate projections in the UKCIP02 scenarios are monthly mean values of some important climate variables
subject to a number of uncertainties beyond the uncertain- in the 1980s for London, Manchester and Edinburgh. As
ties in the emissions scenarios. A discussion of these expected, London is slightly warmer than Manchester,
uncertainties is given by Jenkins and Lowe(5). An important which is in turn slightly warmer than Edinburgh. The
point to recognise is that the UKCIP02 scenarios were three locations received comparable solar irradiance.
based on just one climate modelling framework, that of
the Hadley Centre. Other climate models in other Figure 2.5 (see page 8) shows the changes to the monthly
countries would yield somewhat different rates and mean values of a number of key variables taken from
patterns of climate change for the UK. However, the UKCIP02 for the 2080s Medium-High Emissions
Hadley Centre model is one of the best validated models scenario. The changes for other scenarios may be obtained
in the world and the UKCIP02 scenarios are the climate by multiplying these changes by the CSF values, shown in
change scenarios approved for use by the Department of Figure 2.3. The greatest changes are in temperature,
Environment, Food and Rural Affairs (DEFRA). particularly in summer and in London. There are also
appreciable increases in solar irradiance in summer
(principally due to reduced cloud cover). Air moisture
2.2 Use of the UKCIP02 scenarios
content increases in winter and decreases in late summer
for environmental design and autumn, but relative humidity is reduced in all
seasons due to the increase in temperature, decreasing
quite sharply in summer. Average wind speeds show
Not all of the variables contained in the UKCIP02
smaller magnitude changes, typically less than 5%,
scenarios correspond directly to those needed for
increasing in winter and decreasing in summer.
environmental design, but relevant parameters may be
derived. More fundamentally, while the scenarios contain
values for changes in monthly averaged values of climate
variables, environmental design and HVAC system sizing 3 Performance indicators
need information regarding extremes and hour-to-hour
variability. This type of information is typically not In order to assess the impacts of climate change discussed
directly available from climate models. This is a common in section 1, performance indicators are defined, based on:
problem in climate change impacts assessment known as
— the level of summertime thermal performance
‘temporal downscaling’. An additional problem, ‘spatial
downscaling’, is that while the UKCIP02 scenarios data — associated changes in energy consumption and
are at relatively high resolution, the grid box containing carbon emissions.
the location of the building may not be truly repre-
sentative of local microclimate effects such as unresolved These two aspects are discussed below.
topography, local land use and urban heat island effects.
The weather data were collected at airports and so have a
3.1 Summertime thermal
local microclimate characteristic of an urban area. For
example, London (Heathrow) has a maximum ‘heat performance
island’ of about 5 K, which compares with a maximum
heat island in central London of about 6K. Summertime thermal performance is usually measured
against a criterion expressed in terms of a benchmark
To address the spatial and temporal downscaling problems temperature that should not be exceeded for a designated
use is made here of the temporal and spatial information number of hours or percentage of the year. The bench-
contained in the CIBSE/Met Office weather years for mark temperature is usually related to a temperature at
London, Manchester and Edinburgh(4). All these weather which occupants begin to feel thermal discomfort,
years have been combined with the UKCIP02 scenarios although may be related to other factors, such as produc-
for monthly climate changes for the three sites, thereby tivity or health. When the benchmark temperature is
producing synthetic future weather years. The future exceeded, the building is said to have ‘overheated’ and if
weather years contain the diurnal variations and vari- this occurs for more than the designated amount of time,
ability of the present day, and the microclimate of an the building is said to suffer from ‘overheating’.
urban area, but the average climatic properties (e.g. daily Consequently the design target is called an ‘overheating
average temperature, solar irradiance, wind speed etc.) of criterion’.
the UKCIP02 scenarios. This method is referred to here as
‘morphing’ as it involves shifting and stretching the In the UK, there is no universally agreed overheating
present-day weather time series to produce new weather criterion for buildings with the exception of schools(7), to
time series with the required monthly climate statistics. which standard Building Regulations Approved Document
The full details of the method used here are described in L2 now refers(8). Other countries, e.g. Germany(9), have
Belcher et al.(6) fixed standards for overheating in offices. In the UK,
thermal performance targets for offices and many other
buildings types are decided upon on a project-by-project
2.3 UKCIP02 climate changes for
basis, through discussion between the design team, the
London, Manchester and client, and the other building stakeholders.
Edinburgh
*The CIBSE/Met Office data, which cover the period 1976–1995 and are
used here as the base period, are about 0.3 K higher than the UKCIP02
The CIBSE/Met Office weather years span 1976–1995, and
base period, which is 1961–1990. Hence the ‘morphing’ here leads to a
may be considered here to constitute a ‘1980s’ timeslice. slight exaggeration of the climate change.
6 Climate change and the indoor environment: impacts and adaptation
2.1.4 Uncertainties in the UKCIP02 scenarios This is the baseline climate onto which the UKCIP02
changes are applied*. Figure 2.4 shows the baseline
The climate projections in the UKCIP02 scenarios are monthly mean values of some important climate variables
subject to a number of uncertainties beyond the uncertain- in the 1980s for London, Manchester and Edinburgh. As
ties in the emissions scenarios. A discussion of these expected, London is slightly warmer than Manchester,
uncertainties is given by Jenkins and Lowe(5). An important which is in turn slightly warmer than Edinburgh. The
point to recognise is that the UKCIP02 scenarios were three locations received comparable solar irradiance.
based on just one climate modelling framework, that of
the Hadley Centre. Other climate models in other Figure 2.5 (see page 8) shows the changes to the monthly
countries would yield somewhat different rates and mean values of a number of key variables taken from
patterns of climate change for the UK. However, the UKCIP02 for the 2080s Medium-High Emissions
Hadley Centre model is one of the best validated models scenario. The changes for other scenarios may be obtained
in the world and the UKCIP02 scenarios are the climate by multiplying these changes by the CSF values, shown in
change scenarios approved for use by the Department of Figure 2.3. The greatest changes are in temperature,
Environment, Food and Rural Affairs (DEFRA). particularly in summer and in London. There are also
appreciable increases in solar irradiance in summer
(principally due to reduced cloud cover). Air moisture
2.2 Use of the UKCIP02 scenarios
content increases in winter and decreases in late summer
for environmental design and autumn, but relative humidity is reduced in all
seasons due to the increase in temperature, decreasing
quite sharply in summer. Average wind speeds show
Not all of the variables contained in the UKCIP02
smaller magnitude changes, typically less than 5%,
scenarios correspond directly to those needed for
increasing in winter and decreasing in summer.
environmental design, but relevant parameters may be
derived. More fundamentally, while the scenarios contain
values for changes in monthly averaged values of climate
variables, environmental design and HVAC system sizing 3 Performance indicators
need information regarding extremes and hour-to-hour
variability. This type of information is typically not In order to assess the impacts of climate change discussed
directly available from climate models. This is a common in section 1, performance indicators are defined, based on:
problem in climate change impacts assessment known as
— the level of summertime thermal performance
‘temporal downscaling’. An additional problem, ‘spatial
downscaling’, is that while the UKCIP02 scenarios data — associated changes in energy consumption and
are at relatively high resolution, the grid box containing carbon emissions.
the location of the building may not be truly repre-
sentative of local microclimate effects such as unresolved These two aspects are discussed below.
topography, local land use and urban heat island effects.
The weather data were collected at airports and so have a
3.1 Summertime thermal
local microclimate characteristic of an urban area. For
example, London (Heathrow) has a maximum ‘heat performance
island’ of about 5 K, which compares with a maximum
heat island in central London of about 6K. Summertime thermal performance is usually measured
against a criterion expressed in terms of a benchmark
To address the spatial and temporal downscaling problems temperature that should not be exceeded for a designated
use is made here of the temporal and spatial information number of hours or percentage of the year. The bench-
contained in the CIBSE/Met Office weather years for mark temperature is usually related to a temperature at
London, Manchester and Edinburgh(4). All these weather which occupants begin to feel thermal discomfort,
years have been combined with the UKCIP02 scenarios although may be related to other factors, such as produc-
for monthly climate changes for the three sites, thereby tivity or health. When the benchmark temperature is
producing synthetic future weather years. The future exceeded, the building is said to have ‘overheated’ and if
weather years contain the diurnal variations and vari- this occurs for more than the designated amount of time,
ability of the present day, and the microclimate of an the building is said to suffer from ‘overheating’.
urban area, but the average climatic properties (e.g. daily Consequently the design target is called an ‘overheating
average temperature, solar irradiance, wind speed etc.) of criterion’.
the UKCIP02 scenarios. This method is referred to here as
‘morphing’ as it involves shifting and stretching the In the UK, there is no universally agreed overheating
present-day weather time series to produce new weather criterion for buildings with the exception of schools(7), to
time series with the required monthly climate statistics. which standard Building Regulations Approved Document
The full details of the method used here are described in L2 now refers(8). Other countries, e.g. Germany(9), have
Belcher et al.(6) fixed standards for overheating in offices. In the UK,
thermal performance targets for offices and many other
buildings types are decided upon on a project-by-project
2.3 UKCIP02 climate changes for
basis, through discussion between the design team, the
London, Manchester and client, and the other building stakeholders.
Edinburgh
*The CIBSE/Met Office data, which cover the period 1976–1995 and are
used here as the base period, are about 0.3 K higher than the UKCIP02
The CIBSE/Met Office weather years span 1976–1995, and
base period, which is 1961–1990. Hence the ‘morphing’ here leads to a
may be considered here to constitute a ‘1980s’ timeslice. slight exaggeration of the climate change.
Performance indicators 7
30 30
°e / C 25 LMoanndcohnester °e / C 25 LMoanndcohnester
ur Edinburgh ur Edinburgh
at at
er 20 er 20
p p
m m
m te 15 m te 15
u u
m m
10 10
xi ni
ma mi
y 5 y 5
ail ail
D D
0 0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
(a) (b)
30 250
C London London
°
e temperature / 221505 MEdainnbchuergsther olar shortwave nce / (W/m)2 210500 MEdainnbchuergsther
averag 10 erage sirradia100
aily 5 Av 50
D
0 0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
(c) (d)
Figure 2.4 Average ‘baseline’ climate of the CIBSE/Met Office ‘1980s’ period; (a) daily maximum temperature, (b) daily minimum temperature,
(c) daily average temperature, (d) solar shortwave irradiance
For the present study, thermal performance benchmark The benchmark temperatures for each of the buildings are
temperatures have been chosen for the case study building given in Table 3.1. They are discussed further below.
types. The temperature thresholds are based on thermal
comfort models, which are discussed in section 3.1.1
3.1.1 Adaptive and deterministic thermal
below. It should be noted, however, that the temperature
comfort models
thresholds are only intended to be illustrative and are not
advocated here as being universally appropriate.
The majority of research on thermal comfort in buildings
In each case, two temperature thresholds have been has taken one of two approaches to the specification of
defined: a lower temperature threshold, which is taken to comfort conditions:
indicate when occupants will start to feel ‘warm’, and a
(a) deterministic methods (e.g. Fanger(10)), which relate
higher threshold temperature, which is taken to indicate
given space conditions, e.g. in terms of tempera-
when occupants will start to feel ‘hot’. Using two tempera-
ture, humidity and air speed, and given clothing
ture benchmarks is helpful, as it is likely that occurrences
of either intense periods of hot conditions or more and activity levels, to the likely level of occupant
prolonged periods of warm conditions can have an equally comfort
detrimental impact on building users. In section 5, the
(b) adaptive methods (e.g. Brager and de Dear(11)), that
percentage of occupied hours that the two threshold
are empirically based on the outcomes of occu-
temperatures are exceeded are displayed graphically so
pancy surveys, and aim to capture the variation in
that an assessment can be made of the degree to which the
building is predicted to overheat. However, to define a comfort expectations with different climates.
fixed measure of ‘overheating’, an exceedance of more
than 1% of occupied hours in a year over the higher Typically, the level of thermal discomfort in both types of
temperature benchmark has been adopted to indicate a model is expressed as the ‘percentage of persons dis-
failure of the building to control overheating risk. satisfied’ (PPD).
Table 3.1 Benchmark temperatures and overheating criteria
Building type ‘Warm’ threshold ‘Hot’ threshold Overheating criterion
temperature / °C temperature / °C
Dwellings:
— living areas 25 °C 28 °C 1% occupied hours over 28 °C
— bedrooms 21 °C 25 °C 1% occupied hours over 25 °C
Offices 25 °C 28 °C 1% occupied hours over 28 °C
Schools 25 °C 28 °C 1% occupied hours over 28 °C