ARTICLE IN PRESS

Building and Environment 44 (2009) 490– 501

Contents lists available at ScienceDirect

Building and Environment

0360-13

doi:10.1

� Corr

E-m

journal homepage: www.elsevier.com/locate/buildenv

Will future low-carbon schools in the UK have an overheating problem?

D.P. Jenkins �, A.D. Peacock, P.F.G. Banfill

Energy Academy, Heriot-Watt University, Edinburgh EH14 4AS, UK

a r t i c l e i n f o

Article history:

Received 14 December 2007

Received in revised form

15 April 2008

Accepted 16 April 2008

Keywords:

Schools

Carbon

Energy

Overheating

Climate

23/$ - see front matter & 2008 Elsevier Ltd. A

016/j.buildenv.2008.04.012

esponding author. Tel.: +441314514329.

ail address: D.P.Jenkins@hw.ac.uk (D.P. Jenkin

a b s t r a c t

Meeting thermal comfort and internal air quality standards for schools can be difficult for buildings

that, traditionally in the UK, have not used mechanical ventilation and air-conditioning. With a trend

towards increased internal gains, and climate change predicted to cause a significant rise in tempera-

tures, this issue becomes more problematic. Considering this within the context of low-carbon buildings

creates an added hurdle—can low-carbon schools be produced that will provide a comfortable teaching

environment in the future? Through a series of simulations on template school buildings, this study

highlights the effect that future small power and lighting energy use could have on reducing the

overheating of school teaching areas. The effect of a warming climate is also estimated, and the impact

that has on the internal temperatures of a school quantified. Introducing external shading and

increasing ventilation in classrooms can reduce overheating significantly but, for many cases, the risk

that the school building cannot cope with the overheating problem might still remain.

& 2008 Elsevier Ltd. All rights reserved.

1. Introduction

The thermal environment and air quality in schools isbecoming a growing concern [1,2]. With the UK climate predictedto experience further increases in temperature, and with internalheat gains in schools likely to change in the coming years,overheating in schools has potential to become even more of aproblem (as suggested in other studies [3]). The internalenvironment of classrooms, both in terms of the level ofoverheating [4] and the carbon dioxide concentrations [5], canhave a noticeable effect on the performance and comfort level ofthe occupants. A rise in temperature has been suggested to bedetrimental to occupant performance for various tasks (such asaddition, multiplication, reading, etc.) [4], whereas high carbondioxide concentrations in classrooms have been monitored andlinked to decreasing occupant productivity [6]. However, withsystems being installed to deal with these two issues, we alsoneed to look for solutions that will not have a negative impact onthe carbon footprint of the school. Mechanical ventilation hastraditionally not been used in UK schools, and air-conditioningsimilarly rare. The above factors, and growing concern andavailable data [7] regarding internal air quality, suggest that thissituation may have to change in the near future.

Tarbase [8] is a low-energy building refurbishment researchproject, funded by the Carbon Trust and EPSRC, which assessestechnologies applicable to existing UK buildings to produce a 50%

ll rights reserved.

s).

reduction in carbon emissions by the year 2030. Within this project,work is being carried out on the energy consumption of schoolbuildings. It has shown that, while carbon-saving measures can beproposed to meet the above aim (including insulation, end-useequipment and onsite generation measures), the systems that mightbe required to provide a suitable teaching environment in the futuremay cause school CO2 emissions to rise—that is, it is likely thatfuture school energy use will include ventilation or/and coolingsystems that are not currently present. This is an added carbonpenalty that must be accounted for. While this may be inevitable forsome cases, this study investigates changes (driven by a need forlow-carbon schools) that could be made to school buildings toreduce the overheating with building CO2 emissions in mind.

This topic is especially relevant as there is currently a majorrefurbishment and rebuilding programme being carried out forUK schools. The improvement in building fabric (in terms of lowerU-values) might be welcomed, but the effect that this will have onoverheating should not be ignored. Likewise, the changes inschool IT equipment and lighting will have a major impact on theoverheating problem—there is a current trend for increased ITequipment, particularly with electronic whiteboards being intro-duced in recent years. However, by taking a low-energy approachto end-use equipment, it is possible to minimise small power andlighting usage (by adopting low-carbon and energy-efficienttechnologies) and this will have the added bonus of decreasingthe overheating risk.

This paper uses building energy simulations to assess the effectof such strategies for typical schools in different parts of the UK.Modified climates for 2030 enable the future overheating risk inthese schools to be assessed.

ARTICLE IN PRESS

Table 2Formulae for estimating size of areas within school by pupil number (N)

Primary school Secondary school

Teaching areas: 100+2.6N 820+3.7N

of which sports hall n/a (570+0.35N)/2

of which assembly n/a (570+0.35N)/2

Storage 55+0.25N 165+0.4N

Dining/kitchen n/a 25+0.25N

Staff/admin 25+0.25N 50+0.3N

Total area 180+3.1N 1060+4.65N

Table 3Floor areas of the school variants

Primary school Secondary school

Pupil no. 150 1250

Staff no. 7 76

Floor area (m2)

Teaching (classroom) 480 4368

Sports n/a 504

Assembly n/a 504

Staff/admin 64 432

Storage 90 648

Toilets 36 240

Dining/kitchen n/a 342

Changing room n/a 168

Circulation 170 1992

D.P. Jenkins et al. / Building and Environment 44 (2009) 490–501 491

2. Design of assessed school buildings

The Tarbase project looks at several non-domestic ‘‘variants’’,i.e. virtual buildings that are considered to be indicative of aparticular sector, and several of these are schools. Two of theseschool variants, a primary and a secondary school, will be used inthis paper to demonstrate the problem of overheating.

The structure and fabric of the schools meet recent buildingregulations, to ensure that these buildings will still be in use in2030 (the current refurbishment/re-building programme ofschools will mean that older schools are likely to be demolishedor see change of use and so are not suitable for ascertaining futureenergy use). The internal activity (i.e. equipment, lighting andoccupants) is based on hourly profiles generated within theTarbase project.

There are several layout design issues for schools that arereflected in the chosen variants, including the use of an assemblyhall as a ‘‘hub’’, with this space doubling as a communal area anda circulation space. Corridor widths take into account wheelchairaccess requirements and classroom widths use the recommendedmaximum of 7–7.5 m [9] for suitable daylighting and viewingangle (for pupils viewing a board at the front of the classroom).With the different floor areas of the building relating to publishedrecommendations [10], the resulting buildings should be indica-tive of modern UK schools.

2.1. Primary school

The primary school variant is a simple one-storey building,with a construction in line with 2000 UK building regulations [11].The corresponding U-values are shown in Table 1.

With schools being divided into distinct zones of activitywithin the building (e.g. kitchens, assembly areas, teachingspaces, etc.), it is important to accurately represent these in theschool variants. This is achieved through recommended designdata [10]. Examples of ‘‘design formulae’’ used for defining theareas of these zones are shown in Table 2, where N is the numberof pupils present in the building.

The number of pupils and staff in each variant is based oncurrent building stock figures. The number of pupils in theprimary school variant is 150 (with seven staff present at anytime). This occupant number corresponds to 26% of the primaryschools in the UK [12] and is used with Table 2 to produce Table 3.

Fig. 1 is thus produced, showing the different zones within theprimary school variant. Note that internal subdivision of theteaching zones is not shown.

2.2. Secondary school

The process of Section 2.1 is repeated for the secondary school.There is slightly more diverse use of space, with specific zones for

Table 1Form of constructions and associated U-values for school variants

Construction

Walls Floor Roof

Primary school Brickwork,

mineral fibre,

blockwork,

plasterboard

Carpet, chipboard,

air, mineral fibre,

clinker, earth

Aluminium,

mineral fibre,

ceiling tile

Secondary school Brickwork, air,

mineral fibre,

blockwork,

plasterboard

Carpet, chipboard,

air, mineral fibre,

clinker, earth

Aluminium,

mineral fibre,

ceiling tile

dining, assembly and sports activities. The relevant constructiondetails and internal area information is shown in Tables 1–3. Thisbuilding is designed to meet 2004 building regulations [13].

The number of pupils is 1250 (with 76 staff present at any onetime). This occupant number corresponds to 35% of the secondaryschools in the UK [12].

Fig. 2 shows the plan and layout of the building. It should benoted that safety concerns mean that schools in the UK,particularly new build, are unlikely to exceed three storeys.

3. Internal activity of schools

When investigating overheating in a non-domestic building, it isvital to understand the temporal variation in gains generatedinternally to the building. The calculation of internal heat gainsdue to small power, lighting and occupants is detailed below. It isparticularly important to use a suitable temporal precision forthese variations so as to identify times of peak internaltemperature, i.e. when large internal gains coincide with large solarand external temperature gains. Hourly values were used inthis study.

U-values (W/m2 K)

Glazing Walls Floor Roof Glazing

Double-

glazed

0.56 0.25 0.22 2.75

Double-

glazed

0.51 0.25 0.22 2.75

ARTICLE IN PRESS

Teaching spaceStaffWCStorageCirculation area

21m

40m

7.5m

16m

8m8m

6m

7.5m

3m

6m

Store2

T3

T4

T1

T2

Store1

Staff

WC2

WC1Circ.

Fig. 1. Layout and plan of primary school variant.

D.P. Jenkins et al. / Building and Environment 44 (2009) 490–501492

3.1. Small power equipment

Previous work on office buildings by Tarbase [14,15] describesthe detailed bottom-up methodology used for defining smallpower equipment and associated heat gains in non-domesticbuildings. Hourly profiles are generated (based on the number ofitems of equipment, power ratings of equipment in differentmodes and their likely pattern of use over a day) to produce a totalequipment profile for a school day (defined here as being 9 a.m. to4 p.m.). This profile additionally includes standby loads during thenight. The number and type of equipment chosen are informed bya combination of empirical studies [16,17] and design [18]. It isassumed that, for non-cooking appliances/equipment, 100% of theelectrical usage is eventually converted into heat (i.e. an itemrated at 100 W will produce 100 W of heat). This heat gain is splitinto convective and radiant fractions using standard assumptions[18]. Small power equipment usage and resulting annual energyconsumption in the two variants are given in Table 4.

Internal heat gains from cooking are based on studies of schoolkitchen sizes [10,19]. For a given kitchen size, the likely electricityand gas usage (and internal gains from this) is estimated using thesame references as used for kitchen sizes. Typical extraction fans[20] are assumed which reduce heat gain from the kitchens (i.e.the total heat gain from the kitchen is not equal to 100% of theappliance energy usage). These fans, along with the energy usedby the respective kitchens, are given in Table 5. Also listed are therespective heat gains from the kitchen appliances, after account-ing for extraction fans (based on references for heat gains fromhooded appliances [18]). The calculations assume an operation inthe kitchen of 9 a.m. to 2 p.m.

3.2. Lighting

The lighting energy usage, and resulting heat gains, iscalculated using a previously formulated model [21]. Designilluminances are defined for the respective zones [18], typicallybetween 100 lx (for circulation zones and toilets) and 500 lx (forteaching spaces and staff zones). Lighting profiles are thusgenerated which, like the small power usage, provide anestimation of heat gain within the building. These are summarisedin Table 6.

3.3. Occupancy

The gains from occupants are based on sensible gains of 75 Wfor staff and 75% of this (i.e. 60 W) for children [22]. The occupantgains directly contribute to the building during occupancy hoursonly (i.e. 9 a.m. to 4 p.m.).

3.4. Heating

The simulations (Section 4) assume that heating will beapplied if, during 9 a.m. to 4 p.m., the area in question fallsbelow 19 1C [18]. This can have a small effect on cooling loadsduring the ‘‘changeover’’ between a heating and cooling season,with heat, from the heating system, stored for a short time by thethermal mass of the building fabric. This might add to the coolingload of the following day. The effect is usually small but isincluded in the building simulations.

ARTICLE IN PRESS

Teaching spaceStaffAssemblyChanging roomSports hallWCStorageDining/SocialCirculation area

16.5m

18m

15m

19m

28m 28m

14m

12m

10m

40m

26m

9m 8m6m

7m

4.5m

4m5m

Fig. 2. Layout and plan of secondary school variant.

D.P. Jenkins et al. / Building and Environment 44 (2009) 490–501 493

3.5. Ventilation and infiltration

The baseline infiltration rate is assumed to be 0.3 ach for bothschools. In addition to this, natural ventilation is assumed to occur(through window openings and vents) to meet building regulations(i.e. a maximum of 10 l/s [18]). The importance of this ventilationrate is discussed later. There is also additional mechanical ventilationin the kitchen (see Table 5) that, being solely for removing heat andodour from the kitchen, is assumed to have a negligible effect on theventilation rate of the classrooms.

3.6. Internal gain profile

The resultant internal gain profiles of a typical day in thedescribed schools are shown in Fig. 3 (for curves labelled 2005).

This information is used in the subsequent simulations, where thesame profile is assumed for every occupied day of the year.

4. Scenarios for simulation of internal temperatures

The dynamic building simulation software package ESP-r isused to estimate overheating in the buildings described inSections 2 and 3. Three scenarios are chosen for each building,in each of two climates, Edinburgh and London (hence sixscenarios in total). These are:

�

‘‘2005’’—2005 baseline energy use with 2005 climate; � ‘‘2005 new gains’’—2030 equipment and lighting with 2005

ARTICLE IN PRESS

Table 4Breakdown of small power energy usage in school variants

Primary school Secondary school

No. Annual (kWh) No. Annual (kWh)

PC 20 4625 255 58,973

Monitor 20 3124 255 39,837

Fax machine 1 132 4 528

Laser printer 5 825 35 5775

Scanner—active 1 38 7 268

Photocopier 2 2161 10 10,805

Server 1 767 2 1533

LAN 0 0 1 35

Public phone system 4 24 15 89

Vending machines—confectionery 0 0 1 149

Vending machines—chilled 0 0 1 526

Vending machines—drinks 0 0 2 3679

Coffee maker 1 806 4 3224

Kettle 1 780 5 3898

Hand dryer 4 526 15 1971

Fridge freezer 1 648 4 2593

Dishwasher 1 175 2 350

Microwave 1 131 5 657

Security camera 2 1402 6 4205

Shredder 1 35 3 105

Water dispenser 2 701 12 4205

Lift 0 0 2 3484

Extraction fans 1 375 1 4573

Electronic whiteboards 0 0 9 2106

D.P. Jenkins et al. / Building and Environment 44 (2009) 490–501494

climate; and

� ‘‘2030’’—2030 fabric refurbishments and 2030 climate (with

2030 equipment/lighting).

The assumptions for what constitutes 2030 small powerequipment/lighting, 2030 fabric changes and a 2030 climate arediscussed next, followed by the results of the simulations in thesubsequent section.

The problem of overheating is assumed to be confined toteaching spaces, with ‘‘office’’-type areas likely to have some formof air-conditioning if necessary and larger communal areas notbeing used with the same frequency. The temperature of 28 1C isoften used as a criterion for overheating, though this does notnecessarily define an ‘‘optimum’’ temperature for productivityand performance, with comfort in schools being slightly sub-jective [23]. Furthermore, if we look at work within the officesector (where more detailed studies exist), comfort temperaturecan vary significantly depending on external temperature [24].Overheating in schools, as defined by CIBSE Guide A [18], is said toexist if the temperature of 28 1C is exceeded for 1% of occupiedhours. Using an alternative definition in Building Bulletin 87 [25],the maximum number of hours at over 28 1C in teaching areas is80 h over a whole year.

The following assumptions are used for defining 2030 smallpower/lighting usage and for 2030 climate.

4.1. Changes in small power and lighting by 2030

It is assumed that IT equipment is likely to play an everincreasing role in educating children in schools. However, withadvances in the energy efficiency and cost of portable computing,the assumption (or, in fact, recommendation) given here is thateach pupil has an individual laptop (with a 15 W ‘‘on’’ powerrating [26]). Assuming that the laptops replace existing desktopcomputers, energy savings can still be made on IT equipment,despite an increase in the number of units. Such savings are aidedby energy management, with standby loads being eliminated andequipment programmed to switch off when not in use.

The savings that can be achieved from lighting usage are againtechnology-driven—replacing triphosphor fluorescent lightingwith light emitting diode (LED) based technology. The potentialefficacy of future LED lighting (i.e. lumens per electrical wattage,lm/W) is very high—conservatively estimated at 150 lm/W [27]compared to the current 70–100 lm/W of tubular fluorescentlights.

The result of these changes to small power and lighting istherefore significant, as shown in Table 7. The internal heat gainprofiles of Fig. 3 (labelled 2030) show a similar impact. These alsoinclude improvements to office equipment/appliances as detailedelsewhere [14,15]. Cooking energy usage is not considered in Table7, and is assumed not to change between 2005 and 2030. Fig. 3includes all internal heat gains, including occupant gains (whichare also assumed not to change between 2005 and 2030). Themid-day dip in 2030 gains is due to decreased activity over thelunch period (with laptops being put into low power modes). Such‘‘good practice’’ is assumed not to take place for the 2005equipment scenario.

4.2. Changes to building fabric by 2030

With heating consumption being significant in UK schools, it isassumed that there will be noticeable improvements to thebuilding fabric by the year 2030, mainly through improvedinsulation. The assumed change in U-value is shown in Table 8,with the existing mineral wool insulation (of the 2005 baseline)replaced with expanded polystyrene (EPS) in the roof and externalinsulation (again EPS) used with concrete render for the walls. Thewindows, already double-glazed, are not changed for the 2030scenario. The achieved U-values would reflect a very well-insulated school, and could perhaps be associated with a future‘‘low-energy’’ school.

4.3. Effect of 2030 climate

Existing climate data (hourly values) is used to describe thechosen locations of Edinburgh and London [28]. This is thenaltered using a published morphing algorithm [29] to account fora future warming climate. The mean annual external tempera-tures of the 2005 Edinburgh and London climates are 8.8 and11.4 1C, respectively. The corresponding values for the 2030versions of these locations are 9.6 and 12.4 1C, respectively.

5. Results

5.1. Primary school overheating

The six scenarios are now simulated for the primary school tocalculate the percentage of occupied hours, in the teaching areas,that exceed 28 1C. This assumes a typical school year (with termsof 3 January–24 March, 11 April–27 May, 6 June–21 July, 5September–21 October, 31 October–23 December—amounting to1421 occupied hours per year). An example of the output is shownin Fig. 4, giving the internal average teaching area temperaturewith external temperatures. The missing values refer to non-occupancy times.

It is clear that, even for the Edinburgh 2005 ‘‘current’’ climate,significant overheating is occurring in the teaching areas betweenMay and September. For all six scenarios, Fig. 5 shows thepercentage of occupied hours that are above 28 1C by month. Nooverheating at all is predicted outside April–September, and theschools are closed in August. There is a clear overheating problemin the summer, with all buildings showing significant periods over

ARTICLE IN PRESS

Table 5Kitchen energy usage in school building variants

Kitchen area (m2) Ventilation required (l/s) Fan(s) power (W) Average power consumption (W) Average heat gain (W)

Electric Gas Electric Gas

Primary school 11 193 385 711 3791 51 318

Secondary school 134 2345 4690 8658 46,178 618 3879

Table 6Lighting usage in school variants

Primary school Secondary school

Peak gain (W/m2) Energy use (kWh) Peak gain (W/m2) Energy use (kWh)

Teaching blocks 8.1 25,819 7.8 61,542

Assembly hall – – 9.9 20,514

Sports hall – – 16.5 34,190

Dining room – – 9.9 13,920

Changing room – – 8.5 5861

Total 8.1 25,819 8.5 320,653

0

5

10

15

20

25

30

00:00 02:00 04:00 06:00 08:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00Time

Inte

rnal

hea

t gai

n (W

/m2 )

2005 Primary2005 Secondary2030 Primary2030 Secondary

Fig. 3. Generated internal heat gain profiles for schools.

Table 7Comparison of 2005 and 2030 small power and lighting gains

2005 2030

Peak gain (W/m2) Energy use (MWh) Peak gain (W/m2) Energy use (MWh)

Primary school Small power 5.5 17.3 4.7 11.6

Lighting 8.1 16.0 3.8 5.4

Secondary school Small power 5.0 153.6 3.2 77.5

Lighting 8.5 184.4 4.0 61.9

D.P. Jenkins et al. / Building and Environment 44 (2009) 490–501 495

ARTICLE IN PRESS

Table 8Changes to building fabric U-values for the refurbished 2030 school variants

Existing U-values (W/m2 K) Suggested intervention Improved U-values (W/m2 K)

Walls Floor Roof Walls Floor Roof Walls Floor Roof

Primary school 0.56 0.25 0.22 External EPS (150 mm)

with concrete render

(13 mm)

Carpet, chipboard,

air, mineral fibre,

clinker, earth

Replace mineral

wool with EPS

0.15 0.25 0.17

Secondary school 0.51 0.25 0.22 External EPS (150 mm)

with concrete render

(13 mm)

Carpet, chipboard,

air, mineral fibre,

clinker, earth

Replace mineral

wool with EPS

0.14 0.25 0.17

-10

-5

0

5

10

15

20

25

30

35

40

01/01 31/01 02/03 01/04 01/05 31/05 30/06 30/07 29/08 28/09 28/10 27/11 27/12

Date (d/m)

Tem

pera

ture

(deg

C)

Internal averageExternal

28degC

Fig. 4. Internal teaching space and external temperatures for baseline 2005 primary school in Edinburgh.

0

10

20

30

40

50

60

70

80

90

100

Apr May Jun Jul Aug Sep

% o

f occ

upie

d ho

urs

that

teac

hing

are

a ex

ceed

s 28

degC

Edinburgh 2005Edinburgh new gainsEdinburgh 2030London 2005London new gainsLondon 2030

Fig. 5. Percentage of occupied hours in teaching spaces at over 28 1C by month for the primary school in six scenarios.

D.P. Jenkins et al. / Building and Environment 44 (2009) 490–501496

ARTICLE IN PRESS

D.P. Jenkins et al. / Building and Environment 44 (2009) 490–501 497

28 1C, especially during June and July (92–95% of the totaloverheating occurs in these 2 months for the Edinburgh climatescenarios and 72–85% for the London scenarios). Even the ‘‘best-case’’ solution of the ‘‘Edinburgh new gains’’ scenario indicatesthat such a building would overheat during the summer months.

Summarising this for the whole year produces Fig. 6. The effectof internal gains is quite significant for both climates. The resultssuggest that, for an Edinburgh school, internal gains might beresponsible for the majority of overheating, with a significant dropbetween the ‘‘Edinburgh 2005’’ and ‘‘Edinburgh new gains’’scenario (from 9% to 3% overheating). All six scenarios fail tomeet the CIBSE A guideline, of a permitted 1% of occupied hoursover 28 1C. However, the ‘‘Edinburgh new gains’’ and ‘‘Edinburgh2030’’ scenario do meet the BB87 guideline, of a permitted total80 occupied hours over 28 1C (equivalent to 5.6% of hours for thisstudy). The effect of climate change is still significant for the‘‘Edinburgh 2030’’ scenario, with a rise from 3% to 5% of hoursbeing over 28 1C.

The London scenarios show a much greater degree of over-heating throughout the year. All three scenarios fail to meet bothCIBSE and BB87 guidelines by some margin. Again reducing smallpower and lighting has a significant effect, suggesting thatregulating such energy use for schools would be a major step inreducing the risk of overheating. The effect of a 2030 climate ismore problematic than for Edinburgh, as London is predicted toexperience a greater temperature rise. So, although reducing smallpower and lighting gains has reduced overheating from 21% to 13%of occupied hours, the effect of a 2030 climate increases this to17%. It is unlikely that future regulations will allow this level ofoverheating in a teaching environment, suggesting the need forfurther passive or/and mechanical means of removing the heat.

5.2. Secondary school overheating

The calculations for the primary school are repeated for thesecondary school. Although the small power and lighting gains,per unit area, are slightly less for the secondary school (due to thegreater available floor area), the increased solar gain (due to thegreater glazing area to building volume ratio) and improvedbuilding insulation results in increased occurrence of overheating.This is demonstrated in Fig. 7, showing the month-by-month

0

5

10

15

20

25

Edinburgh2005

Edinburghnew gains

Edinburgh2030

% o

f occ

upie

d ho

urs

that

teac

hing

are

aex

ceed

s 28

degC

Fig. 6. Percentage of total occupied hours in teaching space

breakdown for overheating. Again the overheating is particularlyapparent during June and July (84–91% of the total overheatingoccurs in these 2 months for the Edinburgh climate scenarios and64–77% for the London scenarios). This raises the question ofwhether, to ensure an optimum performance, the school termtimes could be altered to reduce the number of days that theschool is in use over June and July.

As with the primary school, a large amount of overheating ispredicted for the summer months, and a slight extension to thepotential cooling season for the 2005 London climate, with a smallamount of overheating present in October. Taken over the entireyear, Fig. 8 shows the annual summary. The trends betweenscenarios are similar to the primary school simulations, but all sixscenarios fail to meet the overheating guidelines of CIBSE A andBB87.

These results indicate that either such a school would requirelarger window openings (or open for longer times) or, even morethan the primary school, would require further measures toproduce a more comfortable teaching environment. While all theabove simulations have assumed window openings playing amajor role in meeting the ventilation requirements for schools(and such buildings would be designed with this in mind), it canbe difficult to rely on such measures. In reality, it might bedifficult for windows to achieve the recommended 10 l/s/personventilation rate which, depending on the number of occupants ina given teaching space, can equate to several air changes per hour.Noise and other pollution from outside the building might oftenmake it undesirable to open windows wide (particularly for urbanschools). The conclusion is therefore that current schools could beill-equipped to deal with future overheating.

6. Further methods for reducing internal temperatures

Section 5 suggests that current design will not be able toprovide adequate temperatures in teaching spaces throughout theyear. Other measures, such as reducing solar gain and increasingventilation, will be needed to achieve comfort criteria. Toinvestigate these possibilities, the two final 2030 scenarios arenow amended with further measures.

London2005

Londonnew gains

London2030

s at over 28 1C for the primary school in six scenarios.

ARTICLE IN PRESS

0

10

20

30

40

50

60

70

80

90

100

Apr May Jun Jul Aug Sep Oct

% o

f occ

upie

d ho

urs

that

teac

hing

are

a ex

ceed

s 28

degC Edinburgh 2005

Edinburgh new gainsEdinburgh 2030London 2005London new gainsLondon 2030

Fig. 7. Percentage of occupied hours in teaching spaces at over 28 1C by month for the secondary school in six scenarios.

0

5

10

15

20

25

Edinburgh2005

Edinburghnew gains

Edinburgh2030

London2005

Londonnew gains

London2030

% o

f occ

upie

d ho

urs

that

teac

hing

area

exc

eeds

28d

egC

Fig. 8. Percentage of total occupied hours in teaching spaces at over 28 1C for the secondary school in six scenarios.

D.P. Jenkins et al. / Building and Environment 44 (2009) 490–501498

6.1. Shading

External shading is simulated for the school buildings byplacing horizontal shades above every window, with a width of0.8 m. The simulations are performed for the final 2030 scenariosonly (for both primary and secondary schools). The effect on agiven week is demonstrated for the warmest week in the 2030London scenario for the primary school in Fig. 9. A similar result isseen with the Edinburgh climate, though the temperaturesinvolved are somewhat lower. The difference is relatively small,as the width of the external shade is generally limited, due both tostructural issues and the need to allow daylight into the teachingspaces. It is possible that, as overheating becomes more of anissue in schools, daylight provision might be slightly compro-mised with a desire to increase external shading (though it should

be noted that, as well as being detrimental to daylight factors, thismeasure might increase the electrical lighting use, which in turnwould contribute to overheating). For the defined shading for thisscenario, while direct solar gain will be reduced at times of highsolar altitude, for large parts of the day the effect will be quitesmall. However, this does have the benefit of allowing ‘‘useful’’solar gain to contribute to the heating requirement of the buildingoutside the summer months.

The equivalent graph for the secondary school is shown inFig. 10. There is a slightly smaller reduction in temperaturecomponent to the primary school, possibly due to the fact that,although there is more glazing for the secondary school, the widthof the external shade is the same as the primary school and so,proportionally, it has less of an effect. However, with externalshades being a relatively cheap refurbishment, they could perform

ARTICLE IN PRESS

0

5

10

15

20

25

30

35

40

20/06 21/06 22/06 23/06 24/06

Teac

hing

spa

ce te

mpe

ratu

re (d

egC

)

2030 Londonwithout shading

2030 Londonwith shading

2030 Londonwith shadingand increasedventilation

Fig. 9. Effect of external shading and ventilation on temperatures of the primary

school for the warmest week of the 2030 London climate.

0

5

10

15

20

25

30

35

40

45

20/06 21/06 22/06 23/06 24/06

Teac

hing

spa

ce te

mpe

ratu

re (d

egC

)

2030 Londonwithoutshading2030 Londonwith shading

2030 Londonwith shadingand increasedventilation

Fig. 10. Effect of external shading and ventilation on temperatures of the

secondary school for the warmest week of the 2030 London climate.

D.P. Jenkins et al. / Building and Environment 44 (2009) 490–501 499

a role by reducing the overheating during clear sky/high solaraltitude conditions.

6.2. Mechanical ventilation

The baseline ventilation is 10 l/s/person throughout the entireschool building. This results in an average ventilation rate of1.9 ach in the primary school teaching spaces (when teachingvolume and pupil numbers are accounted for) and 1.5 ach in thesecondary school teaching spaces (this lower value is due to theteaching zone in the larger school including some corridor/communal area). While no specific mechanical system is beingproposed in this paper, the effect of doubling the ventilation airchange rate to 3.8 and 3 ach for the primary and secondary schoolsrespectively is instructive. Such an increase could not be achievedpassively, and other passive cooling techniques (such as boreholecooling and under-croft ventilation) might be more effective thanjust increasing the air change rates. This area is currently work-in-progress as part of the Tarbase project. The change is made to theteaching spaces only, with overheating in the non-teaching spaces

assumed to be less of a problem due to their low occupancy. Also,as this increase in ventilation is being used to deal withoverheating and not air quality, it is only applied during the‘‘overheating’’ months, i.e. April–October.

The effect of this increased ventilation, compared to the 2030scenarios with and without shading, is shown in Fig. 9 for theprimary school and Fig. 10 for the secondary school, for the sameworst-case overheating week of the year. As might be expected,with such a large increase in air change rates, the addedventilation reduces the peak temperatures considerably, typicallyby 3–5 1C compared to the 2030 scenario without either shadingor increased ventilation.

Over the course of the year, the combined effects of shadingand increased ventilation will have an obvious effect on over-heating. This is quantified in the next section.

6.3. Summary of further reductions

The effect of external shading and increased ventilation onoverheating is summarised in Fig. 11. Included in this graph arethe limits suggested by the two previous definitions of over-heating in schools (i.e. BB87 and CIBSE A). The effect of externalshading is relatively small, with a typical reduction of �1.5% in thepercentage of occupied hours in teaching spaces at temperaturesabove 28 1C. As mentioned in Section 6.1, external shades largerthan 0.8 m are assumed to be unsuitable for school buildings.However, the reduction in overheating might sometimes besignificant—the Edinburgh primary school is only marginallywithin the BB87 guidelines for the standard 2030 scenario, butthis limit is more comfortably met when shading is introduced.

The increased ventilation rate has a far greater effect, though itis likely that this measure would have a far greater capital cost.The Edinburgh primary school actually meets the CIBSE Aguidelines when increased ventilation is introduced (no morethan 1% of occupied hours over 28 1C)—the only scenario in theentire study to do so. The Edinburgh secondary school comesclose to this benchmark, while comfortably meeting the BB87requirement. The two London schools are still not meeting eitherbenchmark, emphasising the added overheating problem thatschools in the south of the UK might have in the future. The addedventilation has reduced overheating markedly, although it issuggested that further measures would be necessary to provide acomfortable teaching environment during the summer in London.

7. Discussion and conclusions

The risk of overheating in UK schools has been quantified bysimulating indicative buildings, as defined by the Tarbase project.The positive effect of a change in small power and lighting usagesuggests that applying limits to the power rating (and energyconsumption) of such technologies would be a prudent approachfor reducing overheating in schools, while simultaneously main-taining a low carbon footprint. However, the 2030 IT equipmentand lighting proposed here are low-carbon suggestions—they arenot necessarily the technologies that are currently being adopted.The authors suggest that this issue needs to be monitored, or elsebuildings currently being built (with current levels of smallpower/lighting use in mind) could end up being unsuitable forteaching in the coming decades. The situation is analogous to theoffice buildings built in the UK between the late 1960s and early1980s. These buildings, and the heating, cooling and ventilationsystems within, were not designed to cope with the sudden surgein IT equipment that was seen after the mid-1980s. As a result,such buildings have either been significantly refurbished (withextensive electrical air-conditioning), demolished, or remain in

ARTICLE IN PRESS

0

5

10

15

20

25

PrimarySchool

Edinburgh

PrimarySchoolLondon

SecondarySchool

Edinburgh

SecondarySchoolLondon

% o

f occ

upie

d ho

urs

that

teac

hing

are

aex

ceed

s 28

degC

2030scenario

With shadingWithincreasedventilation

BB87

CIBSE A

Fig. 11. Reduction in overheating for 2030 climates in school variants.

D.P. Jenkins et al. / Building and Environment 44 (2009) 490–501500

use but provide an uncomfortable working environment for theoccupants. The carbon penalty of both these situations (with air-conditioning being a major energy user in UK offices andsignificant embodied carbon involved with demolishing andrebuilding office blocks) is considerable. It is important thereforethat intelligent design and regulation is used to minimise thechances of the same problem occurring in schools, and a large partof this action should involve scrutinising IT growth.

The predicted change in climate by 2030 is likely to exacerbatethis problem, in terms of increasing the need for mechanicalventilation or cooling (to reduce internal temperatures). This islikely to have a significant effect across the UK, but particularly inthe south of the country. Building-related measures should beintroduced now into new-build schools to mitigate against sucheffects.

Two further measures were investigated, namely externalshading and increased ventilation in the teaching areas. Theformer is a low-impact but low-cost measure that might berecommended for new-build schools (though retro-fitting thisinto existing schools might be deemed to be not worth the cost/disruption). Increased ventilation can have a significant effect onpeak classroom temperatures, as well as the year-round over-heating. However, it should be noted that the ventilation ratesused (3–3.8 ach) are very high, and might provide problems inthemselves. It might be better advised to have a smaller increasein ventilation rate but coupled with some form of cooling (ideallypassive through ground-based heat exchangers). While this wouldbe a higher cost (and potentially a higher energy/carbon) measure,it would reduce the risk of classrooms being unable to cope with afuture overheating problem.

This study aims to highlight the problem of providing a low-carbon school that meets thermal comfort and internal air qualitycriteria. While this is a dilemma that exists now, future changes tothe way schools are used and the continuing change to the UKclimate will have a profound effect on how we deal with the issuein the coming decades.

Acknowledgements

Appreciation and thanks to JM Architects, Edinburgh, forassistance in specifying buildings. The Tarbase project is funded

by the UK Carbon Trust and EPSRC as part of the Carbon VisionBuildings programme (Grant no. GR/S94285/01).

References

[1] Karimipanah T, Awbi HB, Sandberg A, Blomqvist C. Investigation of air quality,comfort parameters and effectiveness for two floor-level air supply systems inclassrooms. Building and Environment 2007;42(2):647–55.

[2] Becker R, Goldberger I, Paciuk M. Improving energy performance of schoolbuildings while ensuring indoor air quality ventilation. Building andEnvironment 2007;42(9):3261–76.

[3] Chartered Institution of Building Services Engineers (CIBSE). Climate changeand the indoor environment: impacts and adaptation. CIBSE TechnicalMemorandum 36, 2005.

[4] Wargocki P, Wyon DP, Matysiak B, Irgens S. The effects of classroom airtemperature and outdoor air supply rate on the performance of school workby children. In: Proceedings of indoor air 2005, Beijing, the 10th internationalconference on indoor air quality and climate, vol. 1(1), 2005, p. 368–72.

[5] Griffiths M, Eftekhari M. Control of CO2 in a naturally-ventilated classroom.Energy and Buildings 2008;40(4):556–60.

[6] Fisk WJ. Health and productivity gains from better indoor environments andtheir relationship with building energy efficiency. Annual Review of Energyand the Environment 2000;25(1):537–66.

[7] Kukadia V, Ajiboye P, White M. Ventilation and indoor air quality in schools.BRE Information Paper 6/05, BRE 2005.

[8] Peacock A, Banfill PF, Newborough M, Kane D, Turan S, Jenkins D, et al.Reducing CO2 emissions through refurbishment of UK housing. EuropeanCouncil for an Energy Efficient Economy (ECEEE) 2007 Summer Study, Coted’Azur, France, 4–9 June 2007.

[9] Architectural Press Metric Handbook, 2nd ed. Butterworth, 2005 [chapter 28].[10] Building Bulletin 98. Briefing framework for secondary school projects. UK

Government Department for Education and Skills, 2005.[11] 2000 UK Building Regulations, Part L. Office of the Deputy Prime Minister,

2000.[12] National Statistics of Education. UK Government Department of Education

and Skills, 2004.[13] 2004 UK Building Regulations, Part L. Office of the Deputy Prime Minister,

2004.[14] Jenkins D, Peacock A, Liu Y. Climatic and internal factors affecting future UK

office heating and cooling energy consumptions. Energy and Buildings2008;40(5):874–81.

[15] Jenkins D, Peacock A, Newborough M. Assessing the potential for reducingcarbon emissions in offices. In: World Renewable Energy Congress (WREC) IX,Florence, August 2006.

[16] Mortimer ND, Ashley A, Moody CAC, Rix JHR, Moss SA. Carbon dioxide savingsin the commercial building sector. Energy Policy 1998;26(8):615–24.

[17] ICT in Schools Survey 2004. UK Government Department of Education andSkills, 2004.

[18] Chartered Institution of Building Services Engineers (CIBSE). EnvironmentalDesign, CIBSE Guide A, 2006.

[19] Jones PG, Turner RN, Browne DWJ, Illingworth PJ. Energy benchmarks forpublic sector buildings in northern Ireland. CIBSE Conference Paper, Dublin./http://www.cibse.org/pdfs/energy_benchmarks.pdfS; 2000.

ARTICLE IN PRESS

D.P. Jenkins et al. / Building and Environment 44 (2009) 490–501 501

[20] Chartered Institution of Building Services Engineers (CIBSE). Ventilation andair-conditioning. CIBSE Guide B2, 2006.

[21] Jenkins DP, Newborough M. An approach for estimating the carbon emissionsassociated with office lighting with a daylight contribution. Applied Energy2007;84(6):608–22.

[22] American Society of Heating Refrigeration and Air-conditioning Engineers(ASHRAE). Fundamentals handbook, Chapter 30. Non-residential cooling andheating load calculations, 2005.

[23] Corgnati SP, Filippi M, Viazzo S. Perception of the thermal environment inhigh school and university classrooms: subjective preferences and thermalcomfort. Building and Environment 2007;42(2):951–9.

[24] Nicol F, Humphreys M. Maximum temperatures in European office buildingsto avoid heat discomfort. Solar Energy 2007;81(3):295–304.

[25] Building Bulletin 87. Guidelines for environmental design in schools. UKGovernment Department for Education and Skills, 2003.

[26] Low-power Zonbu notebook (15 W average power rating). /http://www.zonbu.com/device/notebook.htmS.

[27] Steigerwald DA, Bhat JC, Collins D, Fletcher RM, Holcomb MO, Ludowise MJ,et al. Illumination with solid state lighting technology. IEEE Journal onSelected Topics in Quantum Electronics 2002;8(2):310–20.

[28] CIBSE/Met Office Hourly Weather Data. Chartered Institution of BuildingServices Engineers/UK Meteorological Office, October 2005.

[29] Belcher SE, Hacker JN, Powell DS. Constructing design weather data for futureclimates. Building Services Engineering Research and Technology2005;26(1):49–61.