cover v3.3 3/5/06 16:04 Page 1 sign for i s l shading control · 2013-04-18 · Solar shading of buildings(4) gives detailed advice on solar control. BRE Trust Report FB9: Summertime

Design for improved solarshading control

The Chartered Institution of Building Services Engineers222 Balham High Road, London SW12 9BS+ 44 (0)20 8675 5211www.cibse.org

Desig

n for improved solar shadin

g con

trolTM

37

Engineering a sustainablebuilt environment

TM37: 2006

cover v3.3 3/5/06 16:04 Page 1

Design for improved solarshading control

CIBSE TM37

Engineering a sustainablebuilt environment

The Chartered Institution of Building Services Engineers222 Balham High Road, London SW12 9BS

Darren Love, darren.love@

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The rights of publication or translation are reserved.

No part of this publication may be reproduced, stored in aretrieval system or transmitted in any form or by any meanswithout the prior permission of the Institution.

© April 2006 The Chartered Institution of Building ServicesEngineers London

Registered charity number 278104

ISBN-10: 1-903287-57-XISBN-13: 978-1-903287-57-6

This document is based on the best knowledge available atthe time of publication. However no responsibility of anykind for any injury, death, loss, damage or delay howevercaused resulting from the use of these recommendations canbe accepted by the Chartered Institution of Building ServicesEngineers, the authors or others involved in its publication.In adopting these recommendations for use each adopter bydoing so agrees to accept full responsibility for any personalinjury, death, loss, damage or delay arising out of or inconnection with their use by or on behalf of such adopterirrespective of the cause or reason therefore and agrees todefend, indemnify and hold harmless the CharteredInstitution of Building Services Engineers, the authors andothers involved in their publication from any and all liabilityarising out of or in connection with such use as aforesaidand irrespective of any negligence on the part of thoseindemnified.

Typeset by CIBSE Publications

Printed in Great Britain by Hobbs the Printers Ltd., Totton,Hampshire, SO40 3WX

Cover illustration: The Lowry, Salford, England; MichaelWilford & Partners, architects; photograph © BRE

Note from the publisherThis publication is primarily intended to provide guidance to those responsible for thedesign, installation, commissioning, operation and maintenance of building services. It isnot intended to be exhaustive or definitive and it will be necessary for users of the guidancegiven to exercise their own professional judgement when deciding whether to abide by ordepart from it.

Printed on 100% recycled paper comprising at least 80%post-consumer waste

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ForewordAvoiding overheating due to solar gain is a key design requirement to minimise the use ofmechanical cooling and reduce energy consumption by cooling systems. Good low energydesign will seek to minimise the effect of excessive solar gains in summer by appropriateorientation, massing and selection of the building façade. However, additional measuresmay still be required to provide solar shading to the building to reduce solar gains and theassociated risk of overheating.

This publication provides guidance on the design of facades to incorporate appropriatelevels of solar shading, and gives information on some of the design options available. Theguidance in this CIBSE TM demonstrates how designers can address the issue of solar gain,ensuring that the building is able to benefit from solar gains when appropriate withoutsuffering problems of excessive gains in summer.

Under Part L of the 2006 Building Regulations for England and Wales, there is now anexplicit requirement to limit heat gains to buildings. This will involve assessing designs ofnaturally ventilated buildings to ensure that they will not suffer from overheating insummer. This TM provides guidance on meeting the requirements, but will be of far widerrelevance to CIBSE members. The physical laws which underlie the theory of solar heatingapply outside England and Wales, and so the guidance will be valuable to engineers seekingto address the issue wherever the sun may shine. The document also enables designers andfacilities managers to quantify casual heat gains from lighting and other equipment in thebuilding.

The development of the TM was undertaken by Paul Littlefair of BRE, supported bycolleagues at Faber Maunsell and BRE. The author also benefited from the input of theTM37 Steering Group, whose members were drawn from the industry, to try to ensure thatthe guidance is practical and relates to the systems available in practice. CIBSE is gratefulto the members of the TM37 Steering Group and the companies which they represent fortheir contribution to the development of the guidance.

This TM also represents one of the last CIBSE publications to be funded through theDepartment of Trade and Industry (DTI) Partners in Innovation scheme. This schemesupported a number of CIBSE publications from its inception in the mid-1990’s until itsrecent closure. CIBSE acknowledges the support of DTI for this publication. CIBSE alsoacknowledges the support of the Office of the Deputy Prime Minister (ODPM) in thoseaspects of the TM relating to the application of the guidance in support of the requirementsof the Building Regulation in England and Wales

Dr Hywel DaviesChairman, TM37 Steering Group

Acknowledgements

The work leading to the production of this publication and its associated CD-ROM wascarried out as a Partners in Innovation project (ref. STBF/004/00043C). The fundingprovided by the Department of Trade and Industry (DTI) is gratefully acknowledged.

This document is published with the consent of the DTI, but the views expressed are notnecessarily accepted or endorsed by the Department.

Principal authorPaul Littlefair (BRE)

ContributorsQuinten Babcock (FaberMaunsell)Hilary Graves (BRE)Anna Holding (FaberMaunsell)Antonia Jansz (BRE) José Ortiz (BRE)


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TM37 Steering GroupHywel Davies (CIBSE) (Chairman) Steve Birtles (Louver-Lite Ltd.)Peter Braybrook (Levolux A.T. Ltd.)Paul Compton (Colt International Ltd.)Andy Dyer (Verosol)George Henderson (WS Atkins, for DTI)Steve Irving (Faber Maunsell)Alexandra Wilson (Arup)Rick Wilberforce (Pilkington plc)

EditorKen Butcher

CIBSE Research ManagerHywel Davies

CIBSE Publishing ManagerJacqueline Balian

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Contents1 Introduction

1.1 The purpose of this document1.2 Principles of solar overheating control1.3 Other sources of information

2 Requirements of the Building Regulations2.1 Approved Document L2A (2006): buildings other than dwellings2.2 Approved Document L1A (2006): dwellings

3 Solar control techniques3.1 Introduction3.2 Shading measures3.3 Control of solar shading

4 Quantifying solar control performance4.1 Glazing4.2 Blinds and shutters alone4.3 Solar protection devices combined with glazing4.4 Derivation of the effective g-value4.5 Combinations of glazing and shading

5 Calculating gains5.1 Calculating solar gains5.2 Calculating internal gains

6 Examples of gain calculation6.1 Open-plan office6.2 Bedsitting room6.3 Industrial unit

References

Bibliography

Appendix A: Standard casual gains for different types of space

Index

1111

223

3345

66667

10

111214

18181920

21

22

23

29


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1

1 Introduction

1.1 The purpose of this document

Sunlight is often welcome in buildings but the sun canalso have negative impacts: excessive solar gain can lead tooverheating in summer or high air conditioning loads.Glare can also cause problems, particularly in interiorswith computer screens. In most buildings, careful designis required so the benefits of sunlight and daylight can beenjoyed while any problems are effectively controlled.

This document deals with the issue of solar overheatingand the way it can be avoided by appropriate buildingdesign.

In the UK, the control of overheating is a requirement ofthe Workplace (Health, Safety and Welfare) Regulations1992(1), which state that ‘[d]uring working hours, thetemperature in all workplaces inside buildings shall bereasonable’. However the regulations do not specify aparticular maximum temperature.

The Building Regulations Part L (2006 edition)(2,3)

include a requirement to limit the effects of solar gains insummer. This covers both new dwellings (ApprovedDocument L1A(2)) and new buildings that are notdwellings (Approved Document L2A(3)) in England andWales. In Scotland the Building (Scotland) Regulations2004* and the supporting guidance provided in Section 6of the Technical Handbooks apply, and in NorthernIreland Part F (Conservation of fuel and power) of theBuilding Regulations (Northern Ireland) applies.

This document provides additional explanation of thesolar overheating guidance in Approved Document L2A.It has been endorsed for this purpose by the Office of theDeputy Prime Minister (ODPM).

1.2 Principles of solar overheating control

Solar overheating can be reduced or avoided by thefollowing techniques:

— Planning the layout of buildings and rooms to maximisethe benefits of sunlight and minimise the disadvantages:

where possible, have main facades of buildingsfacing north and south. This makes shading easierand allows use of winter solar gain where thiswould be beneficial. Spaces where overheatingwould be critical can be placed on the north side ofbuildings.

— Limiting window area: solar heat gain is roughlyproportional to the window area. However,reducing window area can also limit daylight andrestrict the view out.

— Solar shading: this may include external, internalor mid-pane shading devices, or solar controlglazing. It is described in detail in section 3.

— Thermal mass: an exposed heavyweight structure,with a long response time, will tend to absorb heat,resulting in lower peak temperatures on hot days.However, this will also need appropriate night-time venting and acoustic requirements to betaken into account.

— Good ventilation: a reasonable level of ventilationwill always be required in buildings to maintainindoor air quality. The ability to switch to a muchhigher air change rate can be a very effective wayto control solar overheating. This can be achievedby wind driven ventilation through conventionalwindows, particularly if cross ventilation ispossible; by use of the solar heat itself throughstack effects, venting hot air out at high level; andby mechanical ventilation(3).

— Reducing internal gains: for example, by specifyingenergy efficient equipment, lamps and luminaires,or controls to switch off lighting and other equip-ment when it is not required. Occupancy levelsand small power loads will be dictated by theintended use of the space, and this will need to beagreed between the client and the design team.

— Mechanical cooling or air conditioning.

1.3 Other sources of information

This document is intended to be read in conjunction withother industry guidance on building design. In Englandand Wales, Building Regulations Approved DocumentL2A(3) is the primary source of guidance on compliancewith the regulations. In Scotland and Northern Irelandprovisions are given in the relevant Technical Handbooksand Technical Booklets, respectively. BRE Report BR364:Solar shading of buildings(4) gives detailed advice on solarcontrol. BRE Trust Report FB9: Summertime solarperformance of windows with shading devices(5) gives

Design for improved solar shading control

* At the time of publication, the Scottish Executive is consideringproposals for amending the energy standards in the Building (Scotland)Regulations 2004 and the supporting guidance provided in Section 6 ofthe Technical Handbooks


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2 Design for improved solar shading control

information on how to calculate the solar control perform-ance of glazing with and without blinds and externalshading. The British Blind and Shutter Association hasalso published guidance on the different shading typesand giving a list of suppliers(6).

For offices and similar side-lit buildings, the BREEnvironmental Design Guide(7) includes tables that show theimpact of window area (and other design parameters) onpeak temperatures, and other useful design guidance.

2 Requirements of the Building Regulations

Part L of the Building Regulations for England and Wales(coming into effect on 6 April 2006) includes arequirement ‘limiting heat gains and losses throughthermal elements and other parts of the building fabric’.Approved Document L2A(3) gives guidance on meetingthis requirement in England and Wales.

At the time of publication the Scottish Executive isconsidering proposals for amending regulations under theBuilding (Scotland) Regulations 2004 and the associatedguidance on ways to comply with the building regulationsin Scotland. In Northern Ireland, Part F (Conservation offuel and power) of the Building Regulations (NorthernIreland) and the associated guidance applies.

2.1 Approved Document L2A (2006):buildings other than dwellings

Approved Document L2A* (ADL2A) covers new non-domestic buildings and large non-domestic extensions(with floor area greater than 100 m2 and greater than 25%of the floor area of the existing building). The solar gainsrequirement does not apply to small extensions or otherwork being carried out in existing buildings. It applies tooccupied, naturally ventilated spaces so as to avoid theretrofit of cooling systems in naturally ventilatedbuildings that overheat.

Some buildings have stacks (Figure 2.1), or atria, to driveair movement. The guidance does not apply to themunless they are occupied. If an atrium, for example,contains a reception area or restaurant where people workfor a substantial part of the day, then it is an occupiedspace. Spaces that are only occupied on a temporary basis,such as circulation spaces, do not count as occupied.

Generally, the following activity areas would not count asoccupied and no calculation would be required:bathrooms, changing facilities, circulation areas (unlessthey contain permanent workstations as described above),IT equipment areas (without desk-based staff), perform-ance areas (stages), plant rooms, public circulation areas(unless staff members are permanently working there),

storage areas which only occasionally have someoneworking in them, tea making areas used for only a fewminutes each time, toilets.

ADL2A describes three possible design strategies:

— appropriate combination of window size andorientation

— solar protection through shading and other solarcontrol measures (Figure 2.2)

— using thermal capacity with night ventilation.

For school buildings in England and Wales, BuildingBulletin 101(8) specifies the overheating criterion andprovides guidance on methods to achieve compliance.

For other building types the AD gives two specific ways tocomply with the requirement in a space:

— limit solar and internal casual gain

— show that the space will not overheat.

These are alternatives, so only one of them need be used todemonstrate compliance for a particular space.

Figure 2.1 Ventilation stacks at the BRE Environmental Building

Figure 2.2 Brise soleil at the Scottish Office building, Edinburgh

* For England and Wales, the text of Approved Document L2A(3),including the legal technical requirements, can be viewed on the website ofthe Office of the Deputy Prime Minister (ODPM) (www.odpm.gov.uk).Requirements for Scotland are published by the Scottish BuildingStandards Agency (www.sbsa.gov.uk) and for Northern Ireland by theDepartment of Finance and Personnel (www.buildingregulationsni.gov.uk).

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Solar control techniques 3

2.1.1 Limiting gains

One way to comply is to show that the combined solar andinternal casual gain on peak summer days (corrected forgeographical location) would not be greater than 35 W perm2 of floor area in each occupied space. The basis for thisguidance was CIBSE AM10: Natural ventilation in non-domestic buildings(9), which states that good practice naturalventilation design should be able to cope with30–40 W·m–2 of total heat gains.

Gains are averaged over a 07:30–17:30 BST time period.The solar gains are given as the entry for July in the tableof design irradiances in Table 2.30 of the 2006 edition ofCIBSE Guide A(10).

Section 5 of this document explains how to carry out thecalculation of gains.

2.1.2 Overheating calculation

Compliance is also possible by showing that the operativetemperature in the space does not exceed an agreedthreshold for more than a reasonable number of occupiedhours per annum. An exact definition of what constitutesoverheating is not given in the AD. The thresholdtemperature, and the maximum number of hours that it isto be exceeded, depend on the activities within the space.The 2006 edition of CIBSE Guide A(10) contains someguidance on this issue.

This is intended to provide a completely flexible method.It could be used, for example, in spaces with night coolingand thermal mass, or where innovative natural ventilationtechniques, such as stack effects in tall spaces, are used.The AD does not specify a calculation procedure except tostate that the building be tested against the CIBSE DesignSummer Year(11) appropriate to the building location. Anyreputable calculation technique could be used.

2.2 Approved Document L1A (2006):dwellings

The 2006 Approved Document L1A(2) for England andWales also contains a requirement to limit the effects ofsolar gains in summer. The requirement applies to all newdwellings, even those where full air conditioning orcomfort cooling is already planned. It does not apply toextensions or work in existing dwellings.

The Approved Document explains that ‘provision shouldbe made to limit internal temperature rise due to excessivesolar gains. This can be done by an appropriate combi-nation of window size and orientation, solar protectionthrough shading and other solar control measures,ventilation (day and night) and high thermal capacity.’

Appendix P of SAP 2005(12) contains a procedure thatenables the designer to check on the likelihood of solaroverheating. The method takes into account the followingfactors:

(a) heat gains through windows

(b) internal gains from lighting, appliances, cookingand people

(c) gains from hot water storage, distribution andconsumption

(d) heat loss through the fabric

(e) natural ventilation

(f) average external temperatures (depending onlocation within the UK)

(g) thermal capacity of the building.

The calculation does not include solar gains through thefabric. In practice these may offset some of the heat lossesthrough the fabric, particularly through roofs which maybe fully exposed to the sun. As thermally separatedconservatories are exempt from the solar overheatingprovisions of Part L, they are not included in thecalculation.

The calculation gives a threshold internal temperature Tin degrees C. The methodology then classifies thelikelihood of high internal temperatures in hot weatherinto four different bands. The four overheating bands are:

— not significant: T < 20.5 °C

— slight: 20.5 °C <__ T < 22.0 °C

— medium: 22.0 °C <__ T < 23.5 °C

— high: T >= 23.5 °C

Dwellings which are in the first three bands are viewed ascomplying with the solar gain provisions of the 2006Building Regulations Part L1A.

The calculation attached to the SAP gives an overall figurefor the entire dwelling. This is reasonable because inmany cases people leave internal doors open during theday. In some dwellings there may be a potential risk oflocalised overheating, however, for example in a smallroom with large south facing windows.

Further information about techniques to avoid over-heating in dwellings can be found in Reducing overheating— a designer’s guide(13).

3 Solar control techniques

3.1 Introduction

Compared to the alternative of installing air conditioning,solar shading can be a highly cost effective way to controloverheating. A BRE study(14) estimated that installing airconditioning in a typical 1960s open plan office wouldrequire an extra 55 kW·h·m–2 per year, resulting in overallrunning costs for the air conditioning of £15 per m2 peryear.

The same study showed that comfort could be achieved atzero cooling energy consumption, with a combination ofsolar shading (either mid-pane or external) and night-timeventilation. The extra cost of such measures will usuallybe substantially less than that of installing cooling. Thecalculations also showed that, even in a building wherecooling had already been fitted, the shading could pay foritself in less than five years.


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Solar shading can be particularly effective as part of apackage of passive measures to limit overheating. Theseinclude night-time ventilation and the use of moreefficient equipment and lighting controls to limit internalheat gains. Solar shading is of particular value in suchsituations because it can reduce the swings in temperaturethat can occur on sunny days.

Selecting the correct form of solar control is important.Sometimes energy and cost savings can be less thanexpected because the solar control system blocks incomingdaylight, increasing the use of electric lighting. Some fixedsystems can obstruct useful solar gain in the winter,increasing heating needs. However some kinds of blindcan reduce heat loss through the window to some extent.Also, some types of shading can impede natural venti-lation. BRE Report BR364: Solar shading of buildings(4)

contains detailed advice.

This document concentrates on the thermal aspects ofsolar shading. Glare is also an important issue for manybuilding occupants, and glare control is a legalrequirement where workers regularly use display screenequipment. Glare can be caused by the bright sky or byreflections from buildings outside, but most commonly bydirect sunlight. If direct sunlight causes glare, transparentshading devices such as tinted glazing usually do not helpmuch because the sun is so bright.Translucent shading,such as a thin light coloured fabric blind, gives someprotection but may itself become uncomfortably brightunder sunlight. Opaque shading is best. Various BREpublications(15,16) give guidance on glare control. Often thebest option is to control overheating using one technique,e.g. an external shade or solar control glazing, and providea separate system to reduce glare, e.g. internal blinds.

3.2 Shading measures

3.2.1 External shading

The most effective way to control overheating is toprevent sunlight from reaching the window. Externalshading is particularly appropriate for heavily glazedbuildings where solar heat gain would otherwise be amajor concern.

Simple overhangs can be highly effective at blocking highangle summer sun. They work particularly well on southfacing windows. In brise soleil form (Figure 2.2), they canbe fixed to an existing façade. They do not hinder openingof the windows and a full view out is retained.

The light shelf is a form of overhang installed part way upa window, typically just above an occupant’s head height.Extra daylight can enter the space by reflection from thetop of the shelf, passing through the glazing above it.Having an internal shelf as well as an external one helpscontrol glare for the occupants.

In a range of building types, an awning can be anattractive, and simply installed, way of providing aretractable overhang (Figure 3.1).

The extent of solar protection depends on the ratio of theprojection of the overhang (or brise soleil or awning) tothe height of the window. A ratio of 1:1 gives good

protection in summer but an overhang projecting by onlyhalf the window height will help, particularly on a south-facing window.

A variety of external blinds are available(6) and theseprovide more flexibility in use than a light shelf oroverhang. External horizontal slatted blinds and othertypes of external controllable louvre have the lowestshading coefficient of any system. External roller blinds(Figure 3.2) can also be retrofitted. Where the outwardview is important, retractable blinds with occupantcontrol are the best option. An open-weave fabric blindcan give a view out even when lowered, though may allowglare from the sun.

When designing external shading, access for windowcleaning should be planned.

3.2.2 Glazing and films

A wide variety of solar control glasses are available andthey have been extensively used in commercial buildings.There are two main types: absorbing glasses, which are

Figure 3.1 Awnings shading windows at the Royal Albert Hall, London(photo courtesy Deans Blinds and Awnings Ltd.)

Figure 3.2 Roller blinds used for external shading (photo courtesy JamesRobertshaw Ltd)

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Solar control techniques 5

body tinted, and reflective glasses, which have a specialcoating. Reflective glasses are usually slightly better atrejecting incoming solar gain. Absorbing glass heats upmore when sunlight falls upon it and some of this heat canreach the inside of the building.

Solar control films can be easily added onto flat glazing.Although less durable than glazing, they are easy toretrofit into existing buildings.

As with fixed systems, both glazing and solar films willreduce useful winter solar gain and daylight. A USstudy(17) suggests that if the light transmittance of thewindow is less than around 35%, then people start to findthe view out dull (see also reference 18).

Advanced glazing is now available that can control over-heating while admitting reasonable levels of daylight. Theglass has a spectrally selective coating that reflects infraredradiation while admitting visible light. The coating alsoreduces heat loss in winter in the same way as aconventional low emissivity glass. Some forms of solarcontrol film also have this type of coating.

Where the façade is being refurbished, one option is toreduce window area. Insulated cladding panels areavailable that can match the appearance of glazed units.Daylight and view out will be reduced, but so will heatloss in winter.

3.2.3 Mid-pane blinds

In double glazed units, mid-pane blinds can be anunobtrusive way to help control solar heat gain. Generallythe solar performance of a mid-pane blind will beintermediate between that of an external and an internalsystem. In a sealed unit, a mid-pane blind will get dirtyless quickly than an external or internal blind. Variousoptions are available(6) to allow mid-pane blinds to becontrolled from the inside of the building.

3.2.4 Internal blinds

Internal systems can contribute towards solar heat controlbut tend to be less effective than their external or mid-pane counterparts. Incoming solar gain can be absorbedby the shading device and convected or re-radiated intothe interior. Fabrics with a solar reflecting coating or ametallised finish on the reverse will help reflect this solarheat and offer improved solar shading performancecompared to conventional fabrics. Thus systems thatincorporate reflective materials usually have lower heattransmittances.

Reflective roller blinds (Figure 3.3) look similar to aheavy-duty window film. They can give good rejection ofsolar gain but, unlike conventional window films, can bewithdrawn when daylight and solar radiation are required.Opaque types are available and also those that aretransparent and darken, but do not obscure, the view. Thetransparent types will not completely control glare fromthe sun and the opaque types are better if this is aproblem.

Fabric roller blinds are also available with a metallisedbacking which helps to reflect solar heat. The performanceof internal shading systems with reflective properties may

be reduced where tinted glazing or window film is used,since heat reflected by the shading could be absorbed orreflected back in by the glazing.

3.3 Control of solar shading

In most buildings the need for shading changesthroughout the year. It can vary according to:

— seasonal requirements: overheating is a problem insummer, but winter solar heat gain can bewelcome;

— daily weather: on dull days there is often little needfor shading devices;

— occupant requirements: for some activities peopleneed extra privacy, or extra control of glare.

For all these reasons adjustable shading is often the bestoption. However it has the disadvantages of being morecostly and harder to maintain as moving parts can fail.

Where only seasonal requirements change, it is possible touse fixed shading which varies its performance fromwinter to summer, by means of its geometry. An exampleis an overhang or light shelf, which blocks high-anglesummer sun but lets through low-angle winter sun.

If adjustable shading is used it should be easy to control.The choice of manual or automatic control should dependon the needs of the space. In buildings such as officespeople expect to control the shading themselves, and tendto resent automatic shading. In spaces such as atria,entrance halls, airport buildings, swimming pools andsports halls buildings, users do not expect to control theshading and automatic control will normally be best.

Manual controls should be easy to find, reach and operate.Ideally they should be self-explanatory otherwise theoccupants need to be instructed in their use. Controlsshould operate quickly and give feedback to users.

If control is automatic then manual override should beconsidered, e.g. for blackout purposes. Sometimes acombination of manual and automatic control is best. ABRE Information Paper(19) explores the various options.

Figure 3.3 Reflective window film blind (photo courtesy Reflex-Rol(UK))


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4 Quantifying solar control performance

4.1 Glazing

The determination of luminous and solar characteristicsof glazing is the subject of BS EN 410(20).

When radiation impinges on a glass surface, it will betransmitted, reflected or absorbed, depending on the glassand on the angle of incidence of the light. In BS EN 410,the characteristics of glazing are determined for quasi-parallel light at near-normal radiation incidence. Glassmanufacturers can supply graphs of transmittance andreflectance as a function of angle of incidence, which canbe used to predict the performance of the glass at differentseasons and times of day.

The general characteristics of glazing defined in BS EN410 are as follows:

— the spectral transmittance, !("), and spectralreflectance, #("), at a given wavelength (") in therange 300–2500 nm

— the light transmittance, !v, and the light reflec-tance, #v, for illuminant D65 (daylight)

— the solar direct transmittance, !e , and the solardirect reflectance, #e

— the total solar energy transmittance (solar factor), g

— the ultraviolet transmittance, !UV

— the general colour rendering index Ra.

The solar direct transmittance is one of the mostimportant factors for thermal comfort.

The solar direct transmittance, !e , of a single sheet ofglazing is calculated using the following formula:

(4.1)

where S" is the relative spectral distribution of the solarradiation, ! (") is the spectral transmittance of the glazingand $" is the wavelength interval (nm).

In the case of multiple glazing, the spectral transmittance,! ("), has to be calculated using a separate formula for thecombination of glazing sheets.

From the point of view of shading for thermal comfort thetotal solar energy transmittance is the most relevant factoras it includes the secondary heat transfer from the glazingto the inside. The total solar energy transmittance (g) iscalculated as the sum of the solar direct transmittance (!e)and the secondary heat transfer factor (qi) of the glazingtowards the inside. (qi results from heat transfer byconvection and long wave infrared radiation of that partof the incident solar radiation which has been absorbed bythe glazing.) So the g-value represents the total amount of

!

! " "

"

"

"

"

"

enm

nm

nm

nm==

=

%

%

S

S

( ) $

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300

2500

300

2500

solar energy entering the room, divided by the solarenergy incident on the window.

4.2 Blinds and shutters alone

There are two British Standards: BS EN 14500: Blindsand shutters. Thermal and visual comfort. Test methods(21) andBS EN 14501: Blinds and shutters. Thermal and visualcomfort. Assessment of performances(22).

BS EN 14500 gives experimental methods for measuringproperties of blinds. The characteristics measured arenormal/hemispherical solar and light transmittance andnormal/hemispherical solar and light reflectance of thetwo sides of the sample, as defined in BS EN 14501.

Other properties of a blind defined in BS EN 14501include openness coefficient (C), which is the relative areaof the openings in a fabric seen under a given incidence.This applies only to woven fabrics.

The ability of a solar protection device to protect personsand surroundings from direct irradiation (which isimportant for thermal comfort) is measured by thedirect–direct solar transmittance of the device, !e

nn. Blindscan be classified in a class range 0–4 by the value of !e

nn,where class 0 designates !e

nn>0.2 and class 4 designates!e

nn<0.02.

4.3 Solar protection devices combined with glazing

For solar protection devices combined with glazing, draftEuropean Standard prEN 13363-2(23) gives a referencemethod for the calculation of solar and light transmit-tance. The basis of the calculation is that the combinationof glazing and solar protection consists of a series of solidlayers separated by air or gas-filled spaces.

The standard also includes a method for determining theequivalent solar and light optical characteristics forlouvres or horizontal slatted blinds. In these calculationsit is assumed that (1) the louvres or blinds are adjusted toeliminate direct transmittance of the solar beam, (2) thatthe reflectance and transmittance are diffuse, and (3) thatthe slats are perpendicular to the solar beam. Therefore,the calculated direct and diffuse radiation factors willdepend on the angle of the sun.

As in BS EN 410(20), the total solar energy transmittance(g) is calculated as the sum of the solar direct trans-mittance (!e) and the secondary heat transfer factor (qi).The secondary heat transfer factor is the sum of thethermal radiation factor, the convection factor and theventilation factor, all of which are defined in prEN 13363-2(23). The rigorous method defined in prEN 13363-2 canbe used for any combination of blinds and glazing.

The total solar energy transmittance (g) can also bedefined as the ratio between the total solar energy trans-mitted into a room through a window and the incidentsolar energy on the window and can be determined for awindow plus blind combination using the methods givenin BS EN 13363-1(24) (a simplified method compared withprEN 13363-2(23)) or ISO/DIS 15099(25). These methodsare described, with examples, in section 4.5.2.

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Quantifying solar control performance 7

CIBSE Guide A: Environmental design(10) gives guidance onshading calculation. It concentrates on solar gain factorswith and without shading with a view to assessing thepeak cooling load and, hence, the size of cooling plantrequired in a building.

CIBSE Guide A describes the CIBSE Simple (dynamic)Model (also known as the admittance method) forcalculating solar gain. Guide A defines mean solar gainfactors and instantaneous cyclic solar gain factors. Thelatter gains are the variations in gain with timethroughout the day and usually lag the solar intensity bybetween zero and two hours, depending on the surfacefactors of the building, i.e. the solar gain factors will bedifferent for lightweight and heavyweight buildings.

For example, the mean solar gain factor at the air node isdefined as:

Mean solar gain at air node per m2 of glazing–Sa = ———————————————————Mean solar intensity incident on glazed façade

Appendix 5.A4 of Guide A(10) shows the derivation of solargain factors. In Table 5.7 of Guide A, solar gain factors aregiven for a number of generic glazing/blind combinations.

Table 5.7 of Guide A also gives are short-wave and long-wave shading coefficients. Shading coefficients arecalculated as follows:

Solar gain through subject glass and blind at direct normal incidence

Sc = ——————————————————–Solar gain through reference glass

at direct normal incidence

where the solar gain through reference glass at directnormal incidence is 0.87.

Shading coefficients can take three forms:

— short-wave shading coefficient (solar direct trans-mittance divided by 0.87)

— long-wave shading coefficient (the fraction of thesolar absorptance that is re-radiated and con-tributes to the total transmittance divided by 0.87)

— total shading coefficient (total solar transmittancedivided by 0.87).

When values of shading coefficients are quoted it isimportant to know the basis on which they werecalculated.

BRE has defined an ‘effective g-value’ for the shadingperformance of a window with shading device asfollows(5):

Solar gain in period of potentialoverheating through window ( with shading device )

Effective g-value = ——————————————Solar gain through unshaded,

unglazed aperture for the ( same period )The period from May–August has been chosen as the basisfor the calculation of solar protection. The whole 24 hours

have been taken rather than a typical working day, as thisgives general results for the full range of building typeswhich can be used in admittance calculations.

Solar overheating is most likely to occur on clear dayswith uninterrupted sun. CIBSE Guide A(10) gives theradiation available on those days (i.e. the 2.5 percentile ofradiation availability) and these values have been used asthe basis for calculation, together with the sun positionsfor that period and a model of the radiance of the sky.

This enables data to be calculated to allow for the differentamounts of radiation received from different directions.The data can then be coupled with the angular transmit-tance of the shading device and window to give an overallvalue of shading performance.

However, this inevitably means that for most shadingdevices the value of the effective g-value will vary with theorientation of the window and its slope (i.e. vertical,horizontal or tilted). To simplify things slightly, the datahave been averaged so that east- and west-facing windowsgive the same value; for UK weather conditions this leadsto only a very small error.

4.4 Derivation of the effective g-value

Data for the effective g-value are given in detail in BRETrust Report FB9: Summertime solar performance of windowswith shading devices(5). This includes data for other systemtypes such as vertical louvres (internal and external), mid-coloured blinds, vertical fins, deep window reveals andexternal obstructions. The tables below give some of thedata for the most common system types.

4.4.1 Glazing

For glazing and window films, the effective g-value can befound by multiplying the normal incidence g-value (ortotal solar transmittance) for the glazing or glazing filmcombination by the factors given in Table 4.1. The factorsare less than 1 because the glazing rejects more solar gainwhen the sun is incident at an oblique angle(26,27).

For example, the effective g-value of a south-facing doubleglazed unit with 6 mm conventional low emissivity glass(SnO2 coating) (e.g. Pilkington K glass) would be thenormal incidence g-value (0.68) times 0.817 = 0.56.

Where single glazing is used, the effective g-value shouldbe multiplied by an additional correction factor of 1.02. Soa west-facing sheet of clear 4 mm single glass would havean effective g-value of 0.86 & 0.923 & 1.02 = 0.81.

For triple glazing, the effective g-value should bemultiplied by 0.98.

4.4.2 Overhangs

Where an overhang or light shelf is fitted, the effective g-value for the glazing should be multiplied by an additionalfactor to allow for the solar gain blocked by the externaldevice, as shown in section 4.5.


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Tables 4.2 to Table 4.5 give these correction factors forsimple overhangs of different sizes. The tables applywhere the overhang is next to the top of the window(Figure 4.2). In each table, ‘depth’ means the projection ofthe overhang measured from, and normal to, the plane ofthe glass. Factors for intermediate depth/window heightratios, or window width/window height ratios, can beestimated by interpolation.

Where the overhang is at least twice as wide as thewindow, Table 4.3 can be used regardless of the windowheight and width. Where the overhang width is less thantwice the window width (or equal to it) the appropriatetable should be used depending on the width/height ratioof the window. This is because extra solar gain canpenetrate around the sides of the overhang.

The tables apply where the overhang is next to the top ofthe window. If there is a significant distance between thebottom of the overhang and the top of the window, thetables cannot be used. If the overhang projects below thetop of the window like a canopy (Figure 4.2) the tablescould be used with H as the vertical distance between thebottom of the overhang and the bottom of the window.This would give conservative answers, provided the totalarea of the window is used in the calculation of solar gain.

For a light shelf, with a window below the overhang and awindow above, the tables can be used for the windowbelow it. The window above the overhang should beassumed unshaded.

4.4.3 Horizontal external louvres

For horizontal external louvres the transmittance willdepend on the angle of the louvre as well as its colour. InTables 4.6 and 4.7 below, the louvre is assumed to havethin, opaque slats of width equal to their vertical spacing,with louvre angle measured in degrees from the horizontal(Figure 4.3). A positive angle means that the outside edge

Table 4.1 Factors to convert normal incidence g-value to effective g-value, for double glazing

Glazing type Glazing coating Factor for stated orientation of window

N NE/NW E/W SE/SW S Horiz.

Ultra-low emissivity glass Double silver 0.737 0.822 0.866 0.808 0.727 0.842(' ! 0.05), absorbing electro-chromic

Absorbing grey or green — 0.778 0.858 0.897 0.853 0.778 0.879

Very low emissivity glass Single silver 0.791 0.869 0.905 0.865 0.793 0.889(0.05<' ! 0.1)

Standard low emissivity glass SnO2, SnO2/SiO2, 0.81 0.884 0.918 0.885 0.817 0.904(K glass) (0.1<' ! 0.2), anti- SiO (anti-reflection reflection glass glass)

Clear glass — 0.818 0.891 0.923 0.893 0.828 0.911

Solar control glass with high a-Si/SiO2 0.825 0.897 0.927 0.9 0.837 0.916emissivity (' >0.5), solar transmittance greater than light transmittance

Reflective solar control glass Titanium oxide 0.845 0.911 0.938 0.917 0.862 0.929with low absorptance and high emissivity, self-cleaning glass

Solar control glass TiN, stainless steel, 0.884 0.938 0.957 0.946 0.907 0.951(transmittance <0.5) with inter- a-Simediate emissivity (0.2<' ! 0.5)

Windowheight (H)

Windowwidth (W)

Overhangdepth (D)measuredfrom planeof glass

Figure 4.1 Overhang dimensions

Effective windowheight H

Overhangdepth D

Figure 4.2 For a canopy-type overhang,the effective window height is taken asthe vertical distance from the windowsill to the lower edge of the canopy

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Quantifying solar control performance 9

of the louvre is lower than the inside edge (this will givethe best shading). Table 4.6 gives basic data for a lightcoloured louvre (reflectance = 0.6) and Table 4.7 for adark coloured louvre (reflectance = 0.1).

The data should not be used on their own and need to becombined with data for the glazing as shown in section4.5. This procedure also requires absorptance data for thelouvres. For the dark ones, the absorptance can be taken as(1 – g) (reflectance = 0). For the light-coloured louvres,the absorptances are given in Table 4.8.

Table 4.2 Correction factors for very wide overhangs (where overhang isat least twice as wide as the window, or where window width andoverhang width are at least five times the window height)

Ratio D / H* Correction factor for stated window orientation

N NE/NW E/W SE/SW S

0.2 0.919 0.893 0.875 0.83 0.7670.4 0.846 0.797 0.76 0.671 0.5450.6 0.785 0.716 0.661 0.537 0.382

0.8 0.734 0.649 0.579 0.433 0.3241 0.692 0.594 0.512 0.36 0.3011.2 0.657 0.549 0.459 0.312 0.285

* D is depth of overhang measured from glass and H is height of window

Table 4.3 Correction factors for wide windows (where the window widthand overhang width are twice the window height)


N NE/NW E/W SE/SW S

0.2 0.928 0.902 0.88 0.837 0.780.4 0.877 0.824 0.776 0.694 0.5920.6 0.841 0.764 0.689 0.578 0.459

0.8 0.816 0.72 0.619 0.495 0.4141 0.798 0.686 0.563 0.444 0.3981.2 0.784 0.661 0.519 0.416 0.388


Table 4.4 Correction factors for square windows (where the windowwidth and overhang width are equal to the window height)


N NE/NW E/W SE/SW S

0.2 0.937 0.91 0.885 0.843 0.7940.4 0.9 0.849 0.792 0.715 0.6360.6 0.877 0.811 0.717 0.617 0.531

0.8 0.861 0.786 0.658 0.552 0.4971 0.85 0.77 0.611 0.518 0.4861.2 0.842 0.759 0.574 0.503 0.479


Table 4.5 Correction factors for narrow windows (where the windowwidth and overhang width are half the window height)


N NE/NW E/W SE/SW S

0.2 0.949 0.924 0.895 0.856 0.7940.4 0.926 0.89 0.821 0.756 0.6360.6 0.912 0.873 0.767 0.685 0.531

0.8 0.903 0.864 0.727 0.643 0.4971 0.897 0.858 0.694 0.625 0.4861.2 0.892 0.854 0.669 0.619 0.479


Figure 4.3 Louvre cross sectionfor external louvres

Slat angle

Outside

Louvrespacing

Louvrewidth

Table 4.6 Basic effective g-value for light-coloured horizontal louvres (reflectance = 0.6)

Slat angle to Effective g-value for stated window orientationhorizontal N NE/NW E/W SE/SW S

–30 0.573 0.642 0.680 0.644 0.471–15 0.635 0.666 0.660 0.544 0.408

0 (horizontal) 0.619 0.598 0.556 0.434 0.365

15 0.547 0.486 0.431 0.339 0.31530 0.451 0.373 0.319 0.264 0.26145 0.340 0.266 0.223 0.197 0.19960 0.224 0.168 0.140 0.129 0.132

Table 4.7 Basic effective g-value for dark-coloured horizontal louvres (reflectance = 0.1)


–30 0.491 0.564 0.602 0.540 0.302–15 0.549 0.580 0.567 0.414 0.249

0 (horizontal) 0.526 0.500 0.447 0.298 0.226

15 0.450 0.380 0.317 0.212 0.19630 0.358 0.273 0.214 0.157 0.16245 0.259 0.181 0.137 0.114 0.12460 0.163 0.107 0.080 0.074 0.083

Table 4.8 Absorption factors ((B) for light-coloured horizontal louvres (reflectance = 0.6)


–30 0.279 0.249 0.227 0.260 0.392–15 0.269 0.253 0.255 0.333 0.430

0 (horizontal) 0.288 0.295 0.317 0.393 0.438

15 0.322 0.347 0.374 0.425 0.43530 0.352 0.383 0.407 0.432 0.42745 0.374 0.401 0.418 0.424 0.41660 0.386 0.405 0.415 0.413 0.407


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4.4.4 Internal and mid-pane blinds

For roller or other types of fabric blinds, blind transmit-tance can be assumed isotropic and the effective g-valuewill equal the manufacturer’s normal incidence transmit-tance value for the product. This does not includeradiation that is absorbed by the blind and then warms theroom; this is treated separately (see next section). Thus ablind with a dark coloured side facing the outside mighthave a lower transmittance when looked at on its own, butcould result in more heat gain in the room because of thisabsorbed radiation. The calculations in section 4.5 requirethe absorptance of the blind which should also beavailable from the manufacturer; in the case of a blindwith a solar reflective coating, or lighter colour on itsreverse, the absorptance is the absorptance of the sidefacing the outside.

For horizontal slatted blinds the transmittance willdepend on the slat angle as well as on the colour of theblind. In Tables 4.9 and 4.10 below, slat angle is measuredin degrees from the horizontal. A positive slat angle meansthat the outside edge of the slat is lower than the insideedge (this will give the best shading). Table 4.9 give basicdata for a light-coloured blind (slat reflectance = 0.6) andTable 4.8 for a dark-coloured one (slat reflectance = 0.1).

The blind is assumed to have thin curved slats of width25 mm and vertical spacing 20 mm. The data can be usedfor blinds with larger or smaller slats provided the ratio ofslat width to slat spacing remains similar (this is true formost blind types).

The data should not be used on their own and need to becombined with data for the glazing as shown in section4.5. The data can be used for internal, external or mid-pane blinds provided the correct equation in section 4.5 isused. This procedure also requires absorptance data forthe blinds. For dark-coloured blinds, the absorptance canbe taken as (1 – g) (reflectance = 0). For light-colouredblinds, the absorptances are given in Table 4.11.

4.5 Combinations of glazing and shading

For combinations of shading and glazing devices, thefollowing approaches can be used.

4.5.1 External shading and glazing

The overall effective g-value is equal to the effective g-value for the glazing, multiplied by that for the shadingalone. This assumes all the heat absorbed by the externalshading is removed and that radiation reflected by theglazing is not redirected back in by the shading device.This method is appropriate for an overhang or fin whichis not in close proximity to the glazing (not an externalblind in the plane of the window, see below).

For example, the effective g-value of an unshaded south-facing double glazed unit with conventional low emissiv-ity glass is 0.56 (see section 4.4.1). Assuming a squarewindow, with an overhang of depth 0.6 times the windowdimension, the overhang would give a g-value correctionof 0.531 (Table 4.5). The overall effective g-value would be0.56 & 0.531 = 0.30.

4.5.2 Glazing and shading (blinds)

The total solar energy transmittance (g) can also bedefined as the ratio between the total solar energy trans-mitted into a room through a window and the incidentsolar energy on the window and can be determined for awindow plus blind combination using the methods givenin BS EN 13363-1(24).

4.5.2.1 Glazing with external blind

The effective g-value for a glazing and external blindcombination (gtot) is given by:

gtot = (gb & g)+ (b () / )2) + gb (1 – g) () / )1) (4.1)

where g is the effective g-value of the glazing, gb is theeffective g-value of the blind alone, (b is the absorptivityof the blind (given by (b = 1 – gb – #b , where #b is thesolar reflectance of the blind), ) is the heat transfercoefficient (W·m–2·K–1), and )1 and )2 are notionalparameters which are mathematically fitted (W·m–2·K–1).

The heat transfer coefficient is given by:

Table 4.9 Basic effective g-value for light-coloured horizontal slattedblinds (blinds alone) (slat reflectance = 0.6)


–30 0.498 0.569 0.609 0.568 0.388–15 0.566 0.598 0.590 0.463 0.347

0 (horizontal) 0.549 0.526 0.480 0.359 0.315

15 0.470 0.406 0.351 0.279 0.27030 0.368 0.292 0.246 0.217 0.21845 0.261 0.197 0.168 0.159 0.16160 0.161 0.122 0.105 0.100 0.101

Table 4.10 Basic effective g-value for dark-coloured horizontal slattedblinds (blinds alone) (slat reflectance = 0.1)


–30 0.409 0.484 0.524 0.457 0.226–15 0.474 0.507 0.492 0.331 0.204

0 (horizontal) 0.451 0.423 0.367 0.225 0.189

15 0.367 0.296 0.233 0.158 0.15930 0.268 0.187 0.138 0.115 0.12545 0.173 0.108 0.081 0.079 0.08860 0.095 0.059 0.046 0.046 0.052

Table 4.11 Absorption factors ((B) for light-coloured horizontal slattedblinds (reflectance = 0.6)


–30 0.324 0.286 0.265 0.305 0.441–15 0.300 0.283 0.293 0.387 0.463

0 (horizontal) 0.316 0.332 0.365 0.446 0.464

15 0.358 0.396 0.431 0.469 0.46130 0.396 0.437 0.461 0.466 0.45245 0.422 0.450 0.460 0.452 0.44060 0.429 0.440 0.442 0.435 0.428

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Calculating gains 11

1! = ———————————– (4.2)

(1 / U) + (1 / !1) + (1 / !2 )

where U is the overall thermal transmittance of the glazing(W·m–2·K–1), and !1 and !2 take the values 6 W·m–2·K–1

and 18 W·m–2·K–1 respectively.

For example, consider a south-facing window with con-ventional low emissivity glass (g = 0.56) covered by anexternal blind of fairly dark, open weave fabric having thefollowing properties:

— transmittance: gb = 0.2

— reflectance: "b = 0.3

— absorptivity: #b = 0.5

The window U-value is assumed to be 2 W·m–2·K–1.

From equation 4.2:

! = 1 / (0.5 + 0.167 + 0.055) = 1.385 W·m–2·K–1

Therefore, from equation 4.1:

gtot = (0.2 $ 0.56) + 0.5 (1.385 / 18)

+ 0.2 ( 1 – 0.56) $ (1.385 / 6) = 0.17

4.5.2.2 Glazing with internal blind

The total solar energy transmittance (gtot) for a glazing andinternal blind combination is given by:

gtot = g (1 – g "b – #b (! / !2)) (4.3)

and the heat transfer coefficient is given by:

1! = ——————— (4.4)

(1 / U) + (1 / !2 )

where !2 takes the value 18 W·m–2·K–1.

For example, for the south-facing window (g = 0.56) andblind considered in section 4.5.2.1:

! = 1 / (0.5 + 0.055) = 1.8 W·m–2·K–1

Hence, from equation 4.3:

gtot = 0.56 [1 – (0.56 $ 0.3) – 0.5 (1.8 / 18)] = 0.44

A more reflective blind would perform better and thedifference between the effective g-values for the internaland external blinds would be reduced.

4.5.2.3 Glazing with mid-pane blind

The effective g-value (gtot) for a blind between two glasspanes (i.e. a mid-pane shading device) is given by:

gtot = (gb $ g) + g [#b + (1 – g) "b ] (! / !3 ) (4.5)

where !3 is a notional parameter which is mathematicallyfitted (W·m–2·K–1).

The heat transfer coefficient is given by:

1! = ——————— (4.6)

(1 / U) + (1 / !3)

where !3 takes the value 3 W·m–2·K–1.

For example, for the same south-facing window (g = 0.56)and blind considered in sections 4.5.2.1 and 4.5.2.2:

! = 1 / (0.5 + 0.33) = 1.2 W·m–2·K–1

Hence, from equation 4.5:

gtot = (0.2 $ 0.56) + 0.56 [0.5 + (1 – 0.56 ) 0.3] (1.2 / 3)

= 0.25

4.5.3 External shading, glazing and blinds

Assuming the external shading is an overhang or fin thatis not in close proximity to the glazing, the approach is asfollows:

(1) Calculate the effective g-value for the glazing plusblind.

(2) Multiply this value by the effective g-value correc-tion for the external shading.

For the example of a square south-facing ‘K glass’ doubleglazed window with an internal blind (section 4.5.2.2), theeffective g-value for the glazing plus blind was 0.44. Withan overhang of depth 0.6 times the window dimension, theoverhang would give a g-value correction of 0.531(Table4.5). Therefore the overall effective g-value would be0.44 $ 0.531 = 0.23.

This approach works well with a roughly isotropic blindsuch as a roller blind. With a combination of overhangand venetian blind, or fin plus open vertical slat blind, themethod will tend to overestimate the shading effect of thecombination, particularly for reflective blinds in an openposition. BRE Report FB9: Summertime solar performance ofwindows with shading devices(5) gives additional guidance.

5 Calculating gainsThis section explains how to calculate the gains per unitfloor area, which forms one of the ways to comply with thesolar gains requirement of Approved Document L2A(3).This involves adding together the average solar gains for an07:30–17:30 BST time period (equivalent to 06:30–16:30solar time), and the internal casual gains (people, lightingand equipment) for the same period. The sum of thesenumbers is then compared with the recommended limit of35 W·m–2.

In assessing compliance with the requirement inApproved Document L2A, an allowance for geographicallocation can be made. This corrects for the influence ofoutdoor air temperature in determining whether abuilding is likely to overheat. In cooler locations it wouldbe possible to have higher solar and internal gains for thesame internal temperature. More of the gains will be


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removed through ventilation and conduction if theexternal temperature is lower.

Table 5.1 gives correction factors which allow for thiseffect. They are based on simulations of example buildingsin different locations. The correction factors wereobtained by calculating the gains (solar plus internal)which would give the same degree of summertime comfortin the stated location as in the same building in theLondon area (Bracknell) with 35 W·m–2 gains. This levelof gains was divided by 35 W·m–2 to obtain the correctionfactor.

For example in Manchester, 41 W·m–2 of gains (solar plusinternal) would give the same level of comfort (aftercorrection for adaptive effects) in a standard building as inthe same building in the London area with 35 W·m–2

gains. The correction factor is 41/35 = 1.17.

To assess compliance with the limiting gains guidance inApproved Document L2A, the sum of the solar andinternal gains is divided by the appropriate correctionfactor in Table 5.1. Suppose a space in a building in westWales (Aberporth) has a total solar plus internal gain of43 W·m–2. The relevant correction factor is 1.31. Thetemperature corrected gains are 43/ 1.31 = 32.8 W·m–2. Asthis is less than 35 W·m–2, this space would comply withthe limiting gains requirement in Part L.

This correction should not be applied if the gains are to beused in a calculation method, for example a thermalmodelling program, which already allows for the influenceof external temperature or geographical location.

5.1 Calculating solar gains

5.1.1 Basic equation

The solar load per unit floor area in a space is given by:

*sl = (1 / Ap) + (Ag ,s geff) (5.1)

where *sl is the solar load per unit floor area in a space(W·m–2), Ap is the perimeter zone floor area (m2) (seesection 5.1.2), Ag is the net area of glazing in each elementin the perimeter zone (wall or roof) (m2), ,s is the externalsolar radiation for the particular orientation of opening(W·m–2 of glazing) (see section 5.1.3) and geff is theeffective g-value of the window and blind (see section5.1.4).

The summation sign indicates summation over theglazing areas on each façade and in the roof bounding thespace in question.

The net area of glazing does not include window frames.For conventional windows it is the area of glass alone. Ifthe detailed type of window is not known, the net area ofglazing can be calculated by multiplying the overallaperture area by 0.8 for vertical windows and by 0.7 forrooflights.

Display windows are exempted from the solar gainsprovisions of Approved Document L2A(3). So for thepurposes of showing compliance with the BuildingRegulations Part L only, the area of display windows canbe omitted from Ag. The definition of display windows isgiven in ADL2A. (In practice solar gains from displayglazing can be significant and should be borne in mindwhen considering more general occupant comfort issues).

5.1.2 Perimeter zones

The calculation of solar load is averaged over a perimeterarea, each point in which is within 6 metres on plan froma window wall or rooflight. Figures 5.1 to 5.3 illustratehow the perimeter area is computed. Secondary windowwalls that do not have openable windows or vents do notcount towards generating the perimeter zone. This is toprevent the anomaly whereby a small fixed secondarywindow can increase the area of the perimeter zone andreduce the calculated solar load, without contributing tothe ventilation of the space. Secondary windows withopening windows or vents can contribute to the perimeterzone because they can aid cross ventilation.

In a space lit by a set of rooflights, all the space can countas a perimeter zone provided that the rooflights areopenable or roof vents are provided.

Figure 5.3 shows how the perimeter zone and its area arefound for side lit spaces.

In the shallow room, Figure 5.2(b), some points are lessthan six metres from both window walls, but these pointsare not counted twice; the perimeter area is the same asthe room area.

When calculating the solar load, all windows androoflights within the perimeter zone are included.

5.1.3 External solar gains on the window

The solar gain on the outside of the window (,s) is givenin Table 5.2. This is the external irradiances for a peakJuly day (irradiances exceeded 2.5% of the time) averagedover daytime hours 07:30–17:30 BST (06:30–16:30 solartime). These are derived from Table 2.30 of CIBSE GuideA(10) (2006 edition). To simplify the calculation and the

Table 5.1 Correction factors for geographical location

Location Correction factor

Aberdeen 1.33Aberporth 1.31Aughton 1.25Belfast 1.31

Birmingham 1.14Bournemouth 1.14Bristol 1.09Cardiff 1.18

Edinburgh 1.32Exeter 1.15Glasgow 1.26Jersey 1.20

Lerwick 1.37London 1.00Manchester 1.17Nottingham 1.15

Plymouth 1.25Stornoway 1.37

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tables in section 5.1.4, the values for the east and westfacades have been averaged together.

The values quoted in Table 5.2 are for unobstructedwindows with a ground albedo of 0.2. The BRE TrustReport Summertime performance of windows with shadingdevices(5) describes a method to allow for continuousobstructions opposite windows. These can significantlyreduce the amount of solar radiation received, especiallyby east and west facing windows.

20 m

10 m

Perimeter zone

(zone area = 6 " 20 = 120 m2)

6 m

20 m

10 m

Perimeter zone

(zone area = 6 " 14 = 84 m2)6 m

6 m8 m

(a)

(b)Figures 5.1 Perimeter zones in a room lit from one side: (a) only the sixmetre deep strip next to the window wall counts as the perimeter zone;.(b) where the windows only occupy a limited part of the window wall, theperimeter strip within six metres of the windows is taken as theperimeter zone

20 m

15 m

Perimeter zone 6 m

6 m

Perimeter zone

(zone area = 2 " 6 " 20 = 240 m2)

20 m

10 mPerimeter zone

(zone area = 10 " 20 = 200 m2)

(a)

(b)

Figures 5.2 Perimeter zones in a room with windows in opposite walls:(a) deep room in which the interior area more than 6 metres from bothwindow walls does not count towards the perimeter zone; (b) shallowroom in which all the interior area counts as the perimeter zone

20 m

15 m

Perimeter zone

Perimeter zone

(zone area = (2 " 6 " 20) + (3 " 6) = 258 m2)

(a)

20 m

15 m

Perimeter zone

(b)

6 m

6 m6 m

6 m

6 m

6 m

6 m Perimeter zone

(zone area = (2 " 6 " 20) + (2 " 3 " 6) = 276 m2)

Figures 5.3 Perimeter zones in rooms with (a) three and (b) four windowwalls; for adjacent window walls, points near the corner of the room arenot counted twice in assessing the area of the perimeter zone

Table 5.2 Solar gain on outside of window

Orientation Solar gain on outside of window, ,s / W·m–2

London Manchester Edinburgh

North 124 127 125

NE/NW 203 206 198

East/West 319 332 326

SE/SW 367 395 404

South 355 391 413

Horizontal 655 672 647


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5.1.4 Allowing for fixed and moveable shading

To obtain the solar gain penetrating into the space, theexternal solar radiation ,s is multiplied by the effective g-value of the window (including shading if provided), geff .

For fixed shading, geff is found using the method describedin sections 4.4 and 4.5.

For moveable shading, geff is found from the weightedaverage of the effective g-value for the window with themoveable shading in place geff (down) and the value with thewindow without the moveable shading geff (up), dependingon the fraction of time the shading is in place fdown. Thus:

geff = fdown geff (down) + (1 – fdown) geff (up) (5.2)

where fdown is the fraction of time that the shading is inplace, geff (down) is the effective g-value for the window withthe moveable shading in place and geff (up) is the effective g-value without the moveable shading.

Values of fdown are given in Table 5.3.

The values in Table 5.3 are calculated on the followingbasis. If the solar radiation on the outside of the windowexceeds 200 W·m–2, the shading is assumed to be in placeon 60% of occasions for occupant control, 90% ofoccasions for automatic control with occupant override,and 100% of occasions for fully automatic control. If the

solar radiation on the outside of the window is less than200 W·m–2 the shading is assumed to be in place on 20% ofoccasions for manual control, and automatic control withmanual override. This is because people might want theblinds down for privacy or to control glare from the sky, ormay just have forgotten to raise them. Fully automaticcontrol is assumed to remove the shading on all occasionswhen the external radiation is below the target 200 W·m–2

(in most spaces, occupants will normally prefer to havesome form of override(19)).

As an example, Table 5.4 gives values of weighted averagegeff for glazing with and without a typical blind oftransmittance 0.2 and reflectance 0.4(10). Values for othertypes of glazing and blinds can be found using the methodabove.

For industrial type rooflights the effective g-value ismultiplied by a further correction of 0.71. This comprisesfactors for dirt on the rooflights (0.8) plus internalabsorption in the sides of the rooflight (0.89).

5.2 Calculating internal gains

In assessing tendency to overheat, Approved DocumentL2A(3) includes internal casual gains from people,equipment and lighting. These are added together to givethe total internal casual gain, then added to the solar gain(section 5.1 above) before being compared with the35 W·m–2 guidance figure.

TM37 gives two ways to estimate these internal gains:

(a) take a standard figure in W·m–2 for people,equipment and lighting; or

(b) calculate the gains from people, equipment andlighting based on the likely occupancy and use ofthe space.

Method (b) enables the designer to allow for the benefits ofmeasures to reduce the effect of gains such as the use ofenergy efficient equipment, or localised extract fans toremove heat before it warms up the space.

It is possible to use a combination of the two approaches.So if the lighting system has been finalised but the likely

Table 5.3 Fraction of time shading in place on peak radiation days in July

Orientation Fraction of time shading in place, fdown

Occupant Automatic Fully automatic control control with control

occupantoverride

North 0.20 0.20 0.00

NE/NW 0.43 0.59 0.56

East/West 0.53 0.77 0.81

SE/SW 0.55 0.81 0.87

South 0.58 0.86 0.95

Horizontal 0.60 0.90 1.00

Table 5.4 Weighted average values of geff for standard 6 mm hard coat low emissivity double glazing with andwithout blinds

Type of glazing and blind Value of geff for stated glazing orientation (from outside to inside) North NE/NW E/W SE/SW South Horiz.

Low-e/clear (no blind) 0.55 0.60 0.62 0.60 0.56 0.61

Occupant control:— low-e/clear, internal blind 0.52 0.53 0.53 0.51 0.47 0.51— low-e/clear, mid-pane blind 0.49 0.45 0.43 0.41 0.37 0.40— low-e/clear, external blind 0.47 0.41 0.38 0.36 0.33 0.35

Automatic control with occupant override:— low-e/clear, internal blind 0.52 0.50 0.48 0.46 0.43 0.46— low-e/clear, midpane blind 0.49 0.40 0.34 0.32 0.28 0.29— low-e/clear, external blind 0.47 0.35 0.28 0.25 0.22 0.21

Fully automatic control:— low-e/clear, internal blind 0.55 0.51 0.48 0.45 0.42 0.44— low-e/clear, mid-pane blind 0.55 0.41 0.33 0.30 0.26 0.26— low-e/clear, external blind 0.55 0.36 0.26 0.23 0.18 0.17

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occupancy and equipment loads in the space have not yetbeen decided, the actual gain for lighting can be calculatedand added to standard gains for people and equipment.

5.2.1 Use of standard tables based on activity schedules

Appendix A gives standard casual gains in W·m–2 for awide range of buildings and space types, based on theactivity schedules in SBEM (Simplified Building EnergyModel), the standard tool for assessing compliance withthe Building Regulations Part L2A.

Sometimes a single large area contains a number ofdifferent activities. For example a retail space may containa chilled sales area or an electrical sales area as well as ageneral sales area. If the whole of the space is ventilated inthe same way, then for the purposes of this document anarea-weighted average of the different levels of heat gaincan be taken. If there is special additional ventilation ofthe areas with greater heat gain, then the heat gains for theactivity in the rest of the space can be taken for the wholeof the perimeter area.

Values are given for people, equipment, general lightingand display lighting. The general lighting values are takenfrom the standard illuminances in SBEM, multiplied by3.75 W·m–2 per 100 lux (office, industrial and storagespaces), or 5.2 W·m–2 per 100 lux (other spaces). Displaylighting values are typical loadings for the types of spacein question. For both general and display lighting, theactual lighting power density can be used instead if this isknown.

If the space is daylit and appropriate lighting controls arefitted (see section 5.2.4), the contribution from generallighting can be assumed to be zero on peak summer days,since it can be assumed to be turned off. However displaylighting would not normally be turned off under thesecircumstances so its contribution should be included.

5.2.2 Detailed method: occupant gains

If the likely occupancy of the space is known, a moredetailed analysis of the heat gains from people into thespace can be carried out. Table 5.5 gives the sensible heatgains per person when undertaking particular types ofactivity; these are taken from data in the 1999 edition ofCIBSE Guide A(28) for heatwave conditions (i.e. 26 °C

ambient temperature). People also give out latent heat inthe form of moisture, but this has not been included.Under heatwave conditions this is assumed to be removedfrom the building by ventilation rather than condensingwithin the space and consequently giving up its heat.

The appropriate figure in Table 5.5 is then divided by theaverage number of square metres per person in theperimeter zone on peak summer days. This is notnecessarily the same as the number of square metres perworkstation or desk; this should be modified according tothe probability that people will be present in the space ona hot summer working day. Many buildings have lowerthan average occupancy in summer, but some (for examplehotels in resorts) may have higher than average occupancy.The occupancy density also needs to be modified by theproportion of the 07:30–17:30 period that compriseworking hours.

Thus:

Heat gain from people = (heat emission per occupant ÷ workstation density)& probability people are present & working hours per person / 10

For example in an office there might be an average of10 m2 per workstation. However on a summer’s day insome types of office only half the people might be present,giving 20 m2 per person. This would result in heat gainsduring working hours of 65/20 = 3.25 W·m–2. If eachperson is typically in the space for 8 hours per day, thisgives an average heat gain of 3.25 & 8 /10 = 2.6 W·m–2.These figures should be modified for the anticipated useof the building and the type of work involved.

5.2.3 Detailed method: equipment gains

If the type of equipment to be installed in a space isknown, a detailed calculation of the equipment gains inthe space can be undertaken. This is carried out bysumming the average power gains to the space, during an07:30–17:30 period, from each piece of equipment in theperimeter zone, and dividing by the floor area of theperimeter zone.

The average power gain from a piece of equipment isgiven by:

Average power gain = power consumed by equipment& fraction of heat that enters space& daily probability equipment will be switched on& hours equipment in use / 10

The daily probability that equipment would be switchedon is that appropriate to a working day in summer. Ifequipment is associated with a particular person (e.g.personal computers (PCs)), the probability it would beswitched on can be assumed to be equal to the probabilitythat person is in the space on that particular day (see 5.2.2above).

Often all the heat generated by the equipment will end upin the space. However if there is localised mechanicalventilation or passive venting of particular equipment,most of the heat generated will usually be extracted. For

Table 5.5 Heat emission from typical occupants under heatwave conditions.

Activity Sensible heat gain per person under heatwave conditions / W

Seated, inactive 59

Seated, light work 63

Seated moderate work (e.g. office) 65

Standing, light work, walking (e.g. retail) 66

Light bench work 71

Medium bench work 85

Heavy work 105

Moderate dancing 85


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the purposes of the Approved Document L2A calculation,heat gains from equipment for which there is localisedmechanical ventilation may be discounted.

5.2.3.1 Office equipment

Office equipment is normally labelled with a maximumwattage, but usually the average power consumed is muchless than this. Table 5.6 gives typical average powerconsumptions for office equipment of various types. Thesevalues are taken from CIBSE Guide A(10) and a detailedAmerican study(29).

Some equipment, e.g. PCs, have ‘standby’ and ‘sleep’ modesduring which they consume less power. The powerconsumed by such equipment is given by:

Power consumed = (fraction of time in full operation & power infull operation) + (fraction of time in standby mode & power instandby mode) + (fraction of time in sleep mode & power in sleepmode)

Usually the power consumed in sleep mode is very lowand can be taken as zero.

5.2.3.2 Household equipment

Table 5.7 gives typical power consumptions for householdequipment. The data have been taken from the Market

Transformation Programme website(30) and from a detailedAmerican study(31). The right hand column gives averagedaily power consumption in residential rooms, accordingto their estimated usage during 07:30–17:30 on a hotsummer’s day. In different applications (for examplepublic houses and restaurants) much heavier appliance usecan be expected during the day. The overall wattage overan 07:30–17:30 period can in these cases be estimatedfrom:

Power consumed = [(hours in full operation & power in full operation)+ (hours in standby mode & power in standby mode) ] / 10

Data for some appliances are given in kW·h per operatingcycle. These are given in Table 5.8. To obtain the averagewatts over a 07:30–17:30 time period, the kW·h per cycleare multiplied by the number of cycles during that period,and by 100. The third column gives examples for a typicalresidential setting, based on the usage patterns in thesecond column. It assumes for example that on a really hotday, people will not cook or use a tumble drier ordishwasher during the daytime. In other types of space,e.g. hotels, public houses, restaurants and communal areasof residential buildings, energy use may be much moreintensive, and a best estimate of the likely number ofcycles should be used instead. Data have been taken fromthe Market Transformation Programme website(30), whichgives values for other ratings of equipment too. Only aselection have been reproduced here.

Table 5.6 Average power consumptions for office equipment(10,29)

Type of equipment Power consumed / W

Full Standby Average when operation mode switched on

Desktop PC (without 55 25 50monitor)

Laptop PC 15 3 6

CRT monitors:— 15 inch 61 19 40— 17 inch 90 9 50— 19 inch 104 13 58— 21 inch 135 14 73

LCD monitors:— 15 inch 12 3 7— 17 inch 17 5 11— 20 inch 32 9 20

Printers:— dot matrix 50 25 30— impact 37 17 19— inkjet 43 13 15— small desktop laser 130 10 22— desktop laser 215 35 53— small office laser 320 70 115— large office laser 550 125 200

Copiers:— desktop 400 20 53— office 1100 300 350

Fax machine 30 15 16

Scanner 25 15 16

Table 5.7 Average power consumptions for domestic equipment(30,31)

Type of equipment Power consumed / W

Full Standby Average onoperation mode residential

summer day*

Televisions:— CRT (small) 45 3 11— CRT (large) 90 7 24— plasma screen (large) 400 1 81— LCD (up to 60 cm diag.) 50 1 11— digital light projection 130 1 27

Digital TV adapter box 9 7 8

Video recorder 17 6 7

DVD player 17 4 5

Component stereo 44 3 11

Compact stereo 22 10 12

Microwave oven 1390 4 9

Refrigerators:— A-rated 16 — 16— C-rated 31 — 31

Freezers:— chest (A-rated) 24 — 24— chest (C-rated) 36 — 36— upright (A-rated) 24 — 24— upright (C-rated) 41 — 41

Fridge-freezers:— A-rated 36 — 36— C-rated 60 — 60

* 07:30–17:30

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5.2.3.3 Other equipment

Many interiors have specialist equipment for whichaverage power consumptions may be obtainable from themanufacturer. CIBSE Guide A(10) contains data for a widerange of commercial cooking equipment.

5.2.4 Detailed method: lighting gains

For the purposes of estimating heat gain, lighting can bedivided into two types: general and display lighting. In

many daylit spaces, general lighting will often be switchedoff on sunny summer days. The contribution of generallighting to casual heat gains can be assumed to be zero ifthere is enough daylight in the space, and if appropriatelighting controls are fitted.

5.2.4.1 Availability of daylight in the space

The perimeter zone counts as a daylit space if the windowarea is at least 20% of the internal area of the window wall.If it is a rooflit space it counts as daylit if the rooflight areais at least 10% of the floor area. In each case the normallight transmittance of the glazing should be at least 70%or, if the light transmittance is below 70%, the requiredglazing area is to be increased proportionately.

Alternatively the perimeter zone counts as daylit if it hasan average daylight factor of at least 2%. References 32–34explain how to calculate the average daylight factor.

For a shaded space to remain daylit under peak sunnyconditions, the shading provided should be of a typewhich can allow some daylight to enter when the shadingis in place. Examples include overhangs, light shelves,light coloured venetian blinds or louvres, diffusing fabricshades with transmittance of 0.1 or higher, or with onlypartial coverage of the window.

5.2.4.2 Lighting controls

Lighting controls should be daylight linked, so that thelighting can be switched off when there is ample daylightin the space. Suitable lighting controls include(35):

— photoelectric switching

— photoelectric dimming

— localised occupant controlled switching ordimming; in localised control the closest distancefrom a switch to all the luminaires it controlsshould be 6 m, or twice the mounting height of theluminaire above the floor if this is greater.

Controls that do not respond to daylight, such as presencedetection or time switching, do not count unless they arecoupled with one of the forms of control listed above.

Table 5.8 Energy consumption per cycle for typical domestic equipment

Type of equipment Energy Typical no. Average powerconsumed of cycles in emitted inper cycle residential residential/ kW·h summer day* summer day*

/ W

Kettle 0.11 2 22

Washing machines[1]:— A-rated (60 °C wash) 0.94 0 0— A-rated (40 °C wash) 0.56 1 56— C-rated (60 °C wash) 1.23 0 0— C-rated (40 °C wash) 0.74 1 74

Condenser tumble driers[2]:— A-rated 1.84 0 0— C-rated 2.45 0 0

Dishwashers[1]:— A-rated (65 °C wash) 1.00 0 0— A-rated (55 °C wash) 0.70 0 0— C-rated (65 °C wash) 1.32 0 0— C-rated (55 °C wash) 0.92 0 0

Ovens (electric or gas):— A-rated 0.97 0 0— C-rated 1.37 0 0

Hobs:— electric 0.725 0 0— gas 1.00 0 0

* 07:30–17:30

Notes:[1] For externally vented driers, heat is assumed to be vented outside the

space and therefore casual gains can be ignored.

[2] The figures include heat in waste water that would in practice bepiped outside the space, so therefore represent worst case values asfar as internal gains are concerned.

Table 5.9 Measured energy distribution for fluorescent fittings having four 70 W lamps(36)

Type of fitting Energy distribution / %

Mounting Schematic Description Upwards Downwards

Recessed Open 38 62

Louvre 45 55

Prismatic or opal diffuser 53 47

Surface Open 12 88

Enclosed prismatic or opal 22 78

Enclosed prismatic on metal 6 94spine


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If the perimeter zone is not daylit or if appropriatelighting controls are not fitted, the contribution of generallighting to internal gains should be added in. Forsuspended, wall mounted or portable fittings this is thecircuit power (in W·m–2) of the lighting in the space,including ballasts and other control gear. If the circuitpower is not known it can be found by multiplying thedesign illuminance in the space by 0.0375 for office,storage and industrial spaces, or by 0.052 for all otherspaces.

If the space has recessed or surface mounted fittings belowa false ceiling, some of the heat from the lamps will go intothe ceiling void rather than into the space itself. In thesecases the circuit power should be multiplied by the‘downwards’ factor in Table 5.9 to give the heat gain intothe occupied space. Alternatively manufacturer’s data forthe particular light fitting can be used.

5.2.4.3 Display lighting

Display lighting will normally be left on during occupiedhours and should therefore be added to the total heatgains. The circuit watts from the display lighting(including portable and track mounted lighting) in theperimeter zone are summed and then divided by the floorarea of that zone.

6 Examples of gain calculation

6.1 Open-plan office

Solar and internal gains are to be calculated in the officeshown in Figure 6.1. The office is in Liverpool, so weatherdata for Manchester can be used.

The office is 15 metres deep, and lit from two sides. Theperimeter zone is taken as the area within six metres ofeach window wall. This covers a floor area of 240 m2.

6.1.1 Solar gains

The office is lit by two bands of windows, four facingnorth and four facing south. The windows have standardlow emissivity glass. Each set of windows is 16 m wide and

1.8 m high, but only 80% of this is glass. This gives a glassarea of 16 & 1.8 & 0.8 = 23 m2 on each side of the room.

The solar gain is given by equation 5.1, i.e:

*sl = (1 / Ap) + (Ag ,s geff)

Here the summation sign indicates summation over theglazing areas on the north and south façades.

The perimeter zone floor area (Ap) is 240 m2 and the netarea of glazing (Ag) is 23 m2 on each side. From Table 5.2,the external solar radiation for each orientation of opening(,s) is 127 W·m–2 on the north side and 391 W·m–2 on thesouth side.

The windows are to be fitted with internal venetian blindsunder occupant control. Therefore, from Table 5.4, therelevant values for the effective g-value (geff ) are 0.52 forthe north side and 0.47 for the south side.

Thus the overall solar gain is:

*sl = (1/240) [(23 & 127 & 0.52) + (23 & 391 & 0.47)]

= 23.9 W·m–2.

6.1.2 Occupant gains

There are expected to be 20 workstations within the entireperimeter zone. Adapting the method in section 5.2.2gives:

Heat gain from people (W) =(heat emission per occupant & number of workstations)& probability people are present& hours per person is present / 10

From Table 5.5, the heat gain per occupant is 65 W. Eachperson will typically be in the office space for 6 hours perday. The occupants are generally office based, but on a hotsummer’s day around a quarter of them might be on leave,giving a probability of presence of 0.75. The overall heatgain is therefore:

Heat gain = 65 & 20 & 0.75 & 6/10 = 585 W.

The heat gain per unit area is found by dividing this bythe area of the perimeter zone:

Occupant heat gain per unit area = 585/240

= 2.4 W·m–2.

6.1.3 Equipment gains

From section 5.2.3, the average power gain from a piece ofequipment is given by:

Average power gain = power consumed by equipment& fraction of heat that enters space& daily probability equipment will be switched on& hours equipment in use / 10

The expected types of equipment in the space and theirpower gains are given in Table 6.1. Extra mechanical

20 m

15 m

Perimeter zone 6 m

6 m

Perimeter zone

(zone area = 2 " 6 " 20 = 240 m2)

Figure 6.1 Example 6.1: open-plan office

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ventilation is not provided for any of the equipment so allthe heat is assumed to enter the space (the printers andcopier are assumed to be used only intermittently so thatthere is no requirement to locate them outside the space).

Each person is assumed to switch on their own PC andmonitor, and inkjet printer if they have one, if they are inthe space that day. However they are assumed to leave thisequipment on if they leave the space for a short while, sothe 8 hours this equipment is left on is greater than the6 hours that each person is present in the space.

The total power used is found by adding up the right handcolumn. Dividing this by the area of the perimeter zonegives 1490/240 = 6.2 W·m–2.

6.1.4 Lighting gains

The perimeter zone counts as a daylit space. The glazingarea is 41% of the area of the internal window wall, greaterthan the 20% rule of thumb. The lighting is to be providedwith integrated controls with photocell control plusmanual override using infrared switching. This would beexpected to be switched off on sunny summer days, so thecontribution of lighting to internal gains can be taken tobe zero.

6.1.5 Overall gains

Summarising, for the office space the total gains are:

— solar: 23.9 W·m–2

— occupant: 2.4 W·m–2

— equipment: 6.2 W·m–2.

This gives a total solar plus internal gain of 32.5 W·m–2.For comparison with the guidance in ApprovedDocument L2A(3), this can be divided by the correctionfactor of 1.17, given in Table 5.1, to give a temperaturecorrected gain of 27.8 W·m–2. This is less than the35 W·m–2 recommended as a maximum in the ApprovedDocument, so the space can be said to comply with thesolar gain requirements of Part L.

6.2 Bedsitting room

Figure 6.2 is a plan of a bedsitting room, part of studentaccommodation in London. The room is lit by patio doors

Examples of gain calculation 19

onto a small balcony and faces south west. It includes asmall kitchenette area.

Since the room is a maximum of 6 metres deep, all of it isassumed to lie within the perimeter zone. This gives aroom area of (5 & 5) + (1.5 & 1) = 26.5 m2. The en-suitebathroom is not included in the room area as it isseparately ventilated.

6.2.1 Solar gains

The patio doors have a total glass area of 3.8 m2. Adaptingequation 5.1, the solar gain is given by:

*sl = (1 / Ap) (Ag ,s geff )

Since there is only one window wall, there is no need forsummation. The room floor area (Ap) is 26.5 m2. The netarea of glazing (Ag) is 3.8 m2. From Table 5.2, the externalsolar radiation (,s) is 367 W·m2 for south west facingglazing.

The windows are fitted with curtains but these are notexpected to be drawn during the day. The window is ofclear low emissivity glass, giving an effective g-value (geff)for the window and blind of 0.60 (Table 5.4). However on

Table 6.1 Example 6.1: expected equipment use in example office space

Equipment No. in perimeter Average power Probability Hours per day Total averagezone, N consumed when switched on, f switched on, H power used

on, P (Table 5.6) (= N P f H / 10)

PCs 20 50 0.75 8 600

CRT monitor (17--) 20 50 0.75 8 600

Inkjet printer 10 15 0.75 8 90

Laser printer 1 115 1 10 115

Scanner 1 16 1 10 16

Small copier 1 53 1 10 53

Fax machine 1 16 1 10 16

Total: 1490

5 m

5 m

6 m

1.5 m

En-suite bathroom

Bedsitting room

Balcony

Figure 6.2 Example 6.2: bedsitting room


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all floors but the top floor there will be additional shadingfrom the balcony above. Additional correction factors foroverhangs such as balconies are given in section 4.4.2. Inthis case Table 4.4 applies since the window is approxi-mately square. The depth of the overhang is 1.2 m and theheight of the window is 2.4 m, so the depth/height ratiofor is 0.5. By interpolation, for a south west facing window,the additional correction factor is 0.666, giving an overallg-value for window plus overhang of 0.40.

Thus the overall solar gain for the lower floors is

*sl = (1/26.5) (3.8 & 367 & 0.40) = 21.1 W·m–2.

On the top floor:

*sl = (1/26.5) (3.8 & 367 & 0.60) = 31.6 W·m–2.

6.2.2 Occupant gains

The room is designed for single occupancy. On an averageday the occupant might be expected to be out most of thetime, but from an overheating point of view the mostimportant conditions are those when the occupant ispresent and therefore able to experience potentially hightemperatures. Accordingly weekend occupation, with theoccupant being present 70% of the time, could be taken asthe basis for calculation. During this period the occupantcould be expected to be doing moderate work, with a heatgain of 65 W.

The average heat gain over the 07:30–17:30 time period:

Heat gain = 65 & 0.7 = 45.5 W

Hence:

Occupant heat gain per unit area = 45.5/26.5

= 1.7 W·m–2.

6.2.3 Equipment gains

The equipment listed in Table 6.2 is assumed to be in thespace. In a residential space the easiest way to estimate theaverage internal gains is to use the values in the righthand columns of Tables 5.7 and 5.8.

The total heat gain due to equipment is 103 W. Thisequates to 103/26.5 = 3.9 W·m–2 of floor area.

6.2.4 Lighting gains

The bedsitting room counts as a daylit space. The glazingarea is 29% of the area of the internal window wall, greaterthan the 20% rule of thumb. The lighting is to be providedby local manual switching. This would be expected to beswitched off on sunny summer days, so the contribution oflighting to internal gains can be taken to be zero.

6.2.5 Overall gains

Summarising, for the bedsitting room on the lower floors,the total gains are:

— solar: 21.1 W·m–2

— occupants: 1.7 W·m–2


This gives a total solar plus internal gain of 26.7 W·m–2.No correction is made for location since the building is inthe London area. The total gain is less than the 35 W·m–2

recommended as a maximum in Approved DocumentL2A, so the space can be said to comply with the solargain requirements of Part L.

On the upper floor the solar gain is higher because there isno balcony above to shade the window. The total gainswould be

— solar: 31.6 W·m–2



This gives a total solar plus internal gain of 37.2 W·m–2.This is more than 35 W·m–2, so this space has not beenshown to comply with the solar gain requirements of PartL. The space could be made to comply by adding anoverhang above the window, similar in size to the balconybelow. Alternatively a full overheating calculation couldbe carried out to investigate whether the operativetemperature in the space exceeds an agreed threshold formore than a reasonable number of occupied hours perannum.

6.3 Industrial unit

Figure 6.3 is a plan of a process space in a speculativeindustrial unit in Newcastle with a shed-type roof. Thespace has eight strips of rooflights each 6 m & 1 m.

6.3.1 Solar gains

Adapting equation 5.1, the solar gain is given by:

*sl = (1 / Ap) (Ag ,s geff )

Summation is not necessary as the space is lit only byrooflights. Since all the space is within 6 metres of arooflight, the whole floor area counts as perimeter zone,therefore the perimeter zone floor area (Ap) is 500 m2.

The overall area of rooflights is 48 m2, but 20% of this isframing. Therefore, the net glazed area (Ag) is 48 & 0.8 =38.4 m2.

Table 6.2 Example 6.2: equipment gains inbedsitting room

Equipment Average heat gain* / W

Small television 11

Video recorder 7

Laptop 6

Stereo 11

Microwave oven 9

Kettle 22

Fridge freezer (A-rated) 36

Total: 103

* over period 07:30–17:30

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References 21

From Table 5.2, using Edinburgh data, the external solarradiation for the orientation of opening (,s) is 647 W·m–2

of glazing.

The normal incidence g-value of the rooflight is 0.64. Thisis multiplied by the appropriate factor given in Table 4.1to obtain the effective g-value. As optical data for therooflight material are not available, the value for clearglass of 0.911 is used, plus an extra correction of 0.98because the rooflight is triple skinned (see section 4.4.1).This gives an effective g-value (geff ) of 0.57. This is thenmultiplied by the additional rooflight correction (for dirtand internal absorption) of 0.71.

Thus the overall solar gain is:

*sl = (1/500) (38.4 & 647 & 0.57 & 0.71)

= 20.1 W·m–2

6.3.2 Occupant and equipment gains

Since the industrial unit is a speculative one, theoccupancy and equipment gains cannot be predicted indetail. Therefore the standard values for this type of spacehave been taken. From Table A.2 in Appendix A, they aregiven as 1.7 W·m–2 for occupant gains, and 50 W·m–2 fromindustrial process equipment.

The rooflight glazing area (38.4 m2) is under 10% of theroof area which is the rule of thumb value for a daylitspace. However the space can be shown(32–34) to have anaverage daylight factor of 2.2%, above the 2% required todefine it as daylit. Photoelectric dimming of fluorescentlamps is to be provided, so the lighting can be assumed tobe switched off during sunny summer days, and lightinggains can therefore be discounted.

6.3.3 Overall gains

For the industrial unit, the total gains are

— solar: 20.1 W·m–2


— equipment: 50 W·m–2.

This gives a total solar plus internal gain of 71.4 W·m–2.This may be corrected for external temperature bydividing by the factor of 1.32 for Edinburgh from Table5.1, to give 71.4/1.32 = 54.1 W·m–2. This is more than the35 W·m–2 recommended as a maximum in ApprovedDocument L2A, so compliance with the solar gainrequirements of Part L have not been demonstrated. A fulloverheating calculation could be carried out to investigatewhether the operative temperature in the space exceeds anagreed threshold for more than a reasonable number ofoccupied hours per annum, but with an equipment gain of50 W·m–2, high summertime temperatures can beexpected.

If it were fairly certain that the space is to be used forindustrial processes with high internal gains, oneapproach would be to install cooling and treat the space asair conditioned for the purpose of Part L. If the actual useof the building is uncertain, a way to proceed would be todesignate the space as a workshop at this stage. Thiswould give equipment loads of 5 W·m–2, and overall loadsof 25.1 W·m–2 (19.0 W·m–2 when corrected for externaltemperature), less than the recommended 35 W·m–2. If itbecame clear later on that the space was to be used forindustrial process, then compliance with Part L could bereviewed at the fit-out stage.

References1 Health and Safety (Workplace) Regulations 1992. Guidance on

regulations (London: Her Majesty’s Stationery Office) (1992)

2 Conservation of fuel and power in new dwellings The BuildingRegulations 2000 Approved Document L1A (London:NBS/RIBA Enterprises) (2006) (available from www.odpm.gov.uk)

3 Conservation of fuel and power in new buildings other than dwellingsApproved Document L2A (London: NBS/RIBA Enterprises)(2006) (available from www.odpm.gov.uk)

4 Littlefair P J Solar shading of buildings BRE Report BR 364(Garston: BRE) (1999)

5 Littlefair P J Summertime solar performance of windows withshading devices BRE Trust Report FB9 (Garston: BRE) (2005)

6 Blinds and shutters buyers guide 2004/5 (Tamworth: British Blindand Shutter Association) (2003)

7 Environmental design guide BRE Report BR 345 (Garston: BRE)(1998)

8 Ventilation of school buildings DfES School Building and DesignUnit Building Bulletin 101 (London: Department forEducation and Skills) (to be published 2006)

9 Natural ventilation in non-domestic buildings CIBSE ApplicationsManual AM10 (London: Chartered Institution of BuildingServices Engineers) (2005)

10 Environmental design CIBSE Guide A (London: CharteredInstitution of Building Services Engineers) (2006)

11 CIBSE/Met Office Hourly Weather Data — Design Summer Years(London: Chartered Institution of Building ServicesEngineers) (2005)

12 The Government’s Standard Assessment Procedure for Energy Ratingof Dwellings (Garston: BRE) (2005) (available fromhttp://projects.bre.co.uk/sap2005/)

13 Reducing overheating: a designer’s guide Energy Efficiency BestPractice in Housing CE129 (London: Energy Saving Trust)(2005)

25 m

20 m

Figure 6.3 Example 6.3: industrial space


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14 Comfort without air conditioning in refurbished offices — anassessment of possibilities New Practice Case Study NPCS118(The Carbon Trust) (2000) (available from thecarbontrust.co.uk)

15 Littlefair P J Daylighting design for display-screen equipment BREInformation Paper IP10/95 (Garston: BRE) (1995)

16 Littlefair P J Retrofitting solar shading BRE Information PaperIP11/02 (Garston: BRE) (2002)

17 Boyce P, Eklund N, Mangum S, Saalfield M S and Tang LMinimum acceptable transmittance of glazing Ltg. Res. Technol.27 (3) 145–152 (1995)

18 Cuttle C Subjective assessments of the appearance of specialperformance glazing in offices Ltg. Res. Technol. 11 (3) 140–149(1979)

19 Littlefair P J Controlling solar shading BRE Information PaperIP12/02 (Garston: BRE) (2002)

20 BS EN 410: 1998: Glass in building. Determination of luminousand solar characteristics of glazing (London: British StandardsInstitution) (1998)

21 BS EN 14500: Blinds and shutters. Thermal and visual comfort.Performance characteristics and classification (London: BritishStandards Institution) (2005)

22 BS EN 14501: 2005: Blinds and shutters. Thermal and visualcomfort. Performance characteristics and classification (London:British Standards Institution) (2005)

23 prEN 13363-2: Solar protection devices combined with glazing.Calculation of solar and light transmittance. Part 2. Referencemethod (draft for comment 02/105506) (London: BritishStandards Institution) (2002)

24 BS EN 13363-1: 2003: Solar protection devices combined withglazing. Calculation of solar and light transmittance. Simplifiedmethod (London: British Standards Institution) (2003)

25 ISO/DIS 15099: Thermal performance of windows, doors andshading devices. Detailed calculations (Geneva: InternationalStandards Organisation)

26 Karlsson J and Roos A Modelling the angular behaviour of thetotal solar energy transmittance of windows Solar Energy 68493–497 (2000)

27 Roos A et al. Angular dependent optical properties of low-eand solar control windows — simulations versus measurementsSolar Energy 69 (supplement) 15–26 (2000)

28 Environmental design CIBSE Guide A (London: CharteredInstitution of Building Services Engineers) (1999)

29 Roth K W, Goldstein F and Kleinman J Energy Consumption byOffice and Telecommunications Equipment in CommercialBuildings: Volume I: Energy Consumption Baseline (Springfield,VA: U.S. Department of Commerce National TechnicalInformation Service) (2002) (available from http://www.eere.doe.gov/buildings/info/documents/pdfs/office_telecom-vol1_final.pdf)

30 Market Transformation Programme (www.mtprog.com)

31 Rosen K and Meier A Energy Use of U.S. ConsumerElectronics at the End of the 20th Century Proc. 2ndInternational Conf. Energy Efficiency in Household Appliances andLighting, 27–29 September 2000, Naples, Italy (Rome: Associationof Italian Energy Economics) (available from http://eetd.lbl.gov/EA/Reports/46212/)

32 Daylighting and window design CIBSE Lighting Guide LG10(London: Chartered Institution of Building ServicesEngineers) (1999)

33 BS 8206: Part 2: 1992: Code of Practice for daylighting (LondonBritish Standards Institution) (1992)

34 Bell J and Burt W Designing buildings for daylight BRE ReportBR 288 (Garston:BRE) (1995)

35 Selecting lighting controls BRE Digest 498 (Garston:BRE) (to bepublished 2006)

36 Bedocs L and Hewitt H Lighting and the thermal environ-ment J. Inst. Heating and Ventilating Eng. 37 217–231 (January1970)

BibliographyAnello M, Parker D, Sherwin J, Richards K Measured impact of advancedwindows on cooling energy use Publication FSEC-PF364-01 (Cocoa, FL:Florida Solar Energy Centre) (2001) (www.fsec.ucf.edu)

Aydinli S, Kaase H, Scartezzini J-L, Michel L, Kischkoweit-Lopin M,Wienold J, Apian-Bennewitz P Measurement of photometriccharacteristics of daylighting systems Proc. Daylighting ’98 (Ottawa,Canada: Natural Resources Canada) (1998) (www.nrcan.gc.ca)

Crawley D, Lawrie L, Pedersen C, Liesen R, Fisher D, Strand R, TaylorR, Winkelmann F, Buhl W, Huang J, Erdem E EnergyPlus: A newgeneration Building Energy Simulation Program Proc. Renewable andAdvanced Energy Systems for the 21st Century, Hawaii (New York NY:American Society of Mechanical Engineers) (1999)

Display screen equipment work. Health and Safety (Display Screen)Regulations 1992. Guidance on regulations (London: Her Majesty’sStationery Office) (1992)

Dubois M-C A simple chart to design shading devices considering thewindow solar angle dependent properties Proc Eurosun 2000, Denmark(International Solar Energy Society) (2000) (www.ises.org)

Dubois M-C A method to define shading devices considering the idealtotal solar energy transmittance Proc Eurosun 2000, Denmark(International Solar Energy Society) (2000) (www.ises.org)

Energy efficiency in buildings CIBSE Guide F (London:CharteredInstitution of Building Services Engineers) (2004)

Energy Star Office Equipment Product Specification, Attachment A (WashingtonDC: US Environmental Protection Agency) (www.energystar.gov)

Energy use in offices Energy Consumption Guide ECG019 (The CarbonTrust) (www.thecarbontrust.co.uk)

Fundamentals ASHRAE handbook (Atlanta GA: American Society ofHeating, Refrigeration and Air-conditioning Engineers) (2001)

Goetzberger A, Wirth H, Bühler C New selective components fordaylighting Proc. Eurosun 98 (International Solar Energy Society) (1998)(www.ises.org)

Goulding J R, Lewis J O and Steemers T C Energy in architecture(London: Batsford) (1992)

Goulding J R, Lewis J O and Steemers T C Energy conscious design(London: Batsford) (1992)

Harrison S, van Wonderen S Evaluation of Solar Heat Gain Coefficientfor solar-control glazings and shading devices ASHRAE Trans. 104(1)(1998)

Källblad K A method to estimate the shading of solar radiation; theoryand implementation in a computer program Proc. Building Simulation’99, Kyoto, Japan (International Building Performance SimulationAssociation) (1999) (www.ibpsa.org)

Karllson J, Rubin M, Roos A Evaluation of predictive models for theangle-dependent total solar energy transmittance of glazing materialsSolar Energy 71(1) (2001)

Klems J, Warner J, Kelley G A new method for predicting the Solar HeatGain of Complex Fenestration Systems ASHRAE Solar Heat Gain Project548 – RP. Final Report LBL-36995 (Atlanta: GA: American Society ofHeating, Refrigeration and Air-conditioning Engineers) (1995)

Knight I and Dunn G Evaluation of heat gains in UK officeenvironments Proc. CIBSE/ASHRAE Conf., Edinburgh, 2003 (2003)

Komor P Space cooling demands from office plug loads ASHRAE J.39(12) 41–44 (December 1997)

22 Design for improved solar shading controlD

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Laboratories ch. 14 in ASHRAE Handbook: Applications (Atlanta GA:American Society of Heating, Refrigerating and Air-conditioningEngineers) (1995)

Managing energy use — Minimising office equipment and air conditioning costsGood Practice Guide GPG118 (available from www.thecarbontrust.co.uk/energy/)

Managing for a better environment — reducing the running costs and impact ofoffice equipment Good Practice Guide GPG276 (available fromwww.thecarbontrust.co.uk/energy/)

McCluney R Advanced fenestration and daylighting systems Proc.Daylighting ’98 (Ottawa, Canada: Natural Resources Canada) (1998)(www.nrcan.gc.ca)

McCluney R Fenestration Solar Gain Analysis Publication FSEC-GP-65(Cocoa FL: Florida Solar Energy Centre) (1996) (www.fsec.ucf.edu)

Papamichael K, Hitchcock R, Ehrlich C, Carroll B New tools for theevaluation of daylighting strategies and Technologies Proc. Daylighting ’98(Ottawa, Canada: Natural Resources Canada) (1998) (www.nrcan.gc.ca)

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Wallenten P, Kvist H, Dubois M-C Parasol-LTH: a user-friendly computertool to predict the energy performance of shading devices (Lund, Sweden:Lund University) (2001)

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Wilkins C K, Kosonen R and Laine T An analysis of office equipmentload factors ASHRAE J. 33(9) 38–44 (September 1991)

Appendix A: Standard casual gains for different types of space

This appendix gives standard casual gains in W·m–2 for awide range of buildings and space types. These are basedon the activity schedules in the Simplified BuildingEnergy Model (SBEM), the standard tool for assessingcompliance with the Building Regulations Part L2A.However, the heat gains from people have been modifiedbecause they will generally be lower under heat waveconditions. If it is warm inside the building, people willgive off less sensible heat and more latent heat (throughperspiration). Latent heat has not been included in the

gains here, because in a naturally ventilated building on ahot day water vapour is assumed not to condense withinthe space but be ventilated to the outside.

For some spaces (mainly in colleges of further education)the values for June have been used because SBEM assumesthese spaces will be unoccupied in July. The definitions ofthe different types of space are given in Table A.1.Standard casual gains are given in Table A.2.

Table A.1 Definition of types of space

Type of space Definition

A&E consulting/treatment/work areas For all A&E consulting/treatment/work areas, occupied and conditioned 24 hours a day.

Baggage reclaim area The area within an airport where baggage is reclaimed from conveyor belts.

Bedroom An area specifically used for sleeping.

Cell (police/prison) A secure room which accommodates one or more people.

Cellular office Enclosed office space for up to four people, commonly of low density.

Check-in area Area within an airport where travellers check in for their flight, containing check-in desks and conveyer belt.

Classroom For areas used for teaching/seminars that are not lecture theatres.

Common room/staff room/lounge An area for relaxing, taking breaks or meeting in a non-work capacity. May contain some hot drink facilities.

Consulting room An area used specifically for medical consultation, often containing a desk and also a consultation couch.

Consulting/treatment areas For all clinic consulting and treatment areas.

Diagnostic imaging For areas which contain diagnostic imaging equipment (such as MRI and CT scanners). This category shouldbe used for any associated plant areas where people work.

Dining room An area, usually containing a table and chairs, which is primarily used for eating a meal.

Display area An area where display lighting is used to illuminate items.

Dry sports hall An area where indoor sports can be played, generally with high ceilings.

Eating/drinking area An area specifically designed for eating and drinking. For areas where food and drink may be consumed butwhere this is not the specific function of the area, use ‘common/staff room’.

Fitness studio An area used for exercising/dance, usually with high person density but with no machines.

Fitness suite/gym An area used for exercise, containing machines.

Food preparation area An area where food is prepared by staff for others, such as a kitchen.

Hall/lecture theatre/assembly area An area that can accommodate a large number of seated people, often with fixed seating.

High density IT work space High density desk-based work space with correspondingly dense IT provision.

Table continues


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Table A.1 Definition of space types — continued

Type of space Definition

Hydrotherapy pool hall The area in which the hydrotherapy pool is contained.

Ice rink An area which contains an ice rink.

Industrial process area An area for practical work on a large scale, involving large machinery.

Intensive care/high dependency For all intensive care and high dependency wards such as baby care.

Kitchen The area within the dwelling where food is prepared.

Laboratory An area often containing fume cupboards and a gas supply. Normally containing benches for working ratherthan tables.

Laundry An area used only for washing and/or drying clothes using washing machines and/or tumble dryers. This doesnot include an individual washing machine within another space (e.g. a food preparation area).

Lounge An area which is used primarily for relaxing, normally containing seating and a television.

Meeting room An area specifically used for people to have meetings, not for everyday desk working. For everyday deskworking areas refer to the appropriate office category.

Offices (hospitals) For all office areas in hospitals which are occupied predominantly 5 days a week. For ward offices or officesoccupied 7 days a week refer to ‘Ward offices’.

Open plan office Shared office space for more than four people. Commonly of higher density than a cellular office.

Operating theatre An operating suite.

Patient accommodation (wards) For all areas containing beds which accommodate either single or multiple patients except for intensive careand high dependency wards.

Physiotherapy studio For all physiotherapy areas

Reception An area often containing a reception desk and reception staff. Normally found immediately inside the mainfront entrance or inside other entrances to a building or building storeys.

Sales area — chilled A sales area designed to accommodate a considerable quantity of refrigerators/freezers such as a supermarketor food hall.

Sales area — electrical Sales areas designed to accommodate considerable electrical equipment loads such as lighting sales areas andIT/TV/hi-fi sales areas.

Sales area — general All sales areas that do not have a large concentration of refrigerators/freezers or electrical appliances.

Security check area For the security areas of an airport containing equipment such as X-ray machines.

Swimming pool The area in which a swimming pool is contained.

Waiting room Enclosed waiting areas with seating.

Ward common room/staff room/lounge Areas for relaxing, taking breaks or meeting in a non-work capacity which may be occupied 7 days a week.This category can be used for patient/relative day rooms and lounges as well as staff rooms and commonrooms.

Ward offices For all ward office areas and any other offices which may be occupied 7 days a week.

Warehouse sales area — chilled All warehouse sized sales areas designed to accommodate a considerable quantity of refrigerators/freezers suchas a hypermarket.

Warehouse sales area — electrical All warehouse sized sales areas designed to accommodate considerable electrical equipment loads such as IT

sales.

Warehouse sales area — general All warehouse sized sales area which do not contain a large concentration of refrigerators/fridges or electricalappliances.

Warehouse storage Large (warehouse sized) storage areas (unchilled).

Workshop — small scale An area for sedentary/light practical work. Often containing some machinery.

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Table A.2 Standard casual gains in different building and space types

Building type Space type Occupant Equipment Lighting Display lightinggain / W·m–2 gain / W·m–2 gain / W·m–2 gain / W·m–2

Airport terminals Baggage reclaim area 17.8 10.0 10.4 0Cellular office 4.0 9.5 18.8 0Check-in area 16.5 15.0 26.0 0Common room/staff room/lounge 1.6 5.0 7.8 0Display area 0.1 1.9 10.4 22Eating/drinking area 9.0 19.0 7.8 0Food preparation area 5.2 25.8 26.0 0High density IT work space 11.1 30.0 11.3 0Meeting room 5.2 4.0 11.3 0Open plan office 6.3 14.3 18.8 0Public circulation areas 13.2 5.0 10.4 0Reception 3.4 4.8 10.4 9Sales area — chilled 6.3 25.0 41.6 10Sales area — general 6.0 4.8 31.2 10Security check area 16.5 20.0 10.4 0Waiting room 6.2 4.8 10.4 0

Bus station/railway station/ Cellular office 3.2 9.5 18.8 0seaport terminal Eating/drinking area 6.6 20.0 7.8 0

Food preparation area 4.1 25.9 26.0 0Meeting room 2.3 4.3 11.3 0Open plan office 5.1 14.3 18.8 0Public circulation areas 6.4 5.0 10.4 0Reception 4.4 4.8 10.4 9Waiting room 5.6 5.0 10.4 0

Community/day centre Cellular office 3.4 9.5 18.8 0Common room/staff room/lounge 0.8 3.5 7.8 0Consulting room 1.5 8.1 26.0 0Dry sports hall 1.4 1.7 15.6 0Eating/drinking area 2.8 14.3 7.8 0Food preparation area 1.4 19.4 26.0 0Hall/lecture theatre/assembly area 9.8 1.6 15.6 0Meeting room 3.8 4.1 11.3 0Open plan office 5.4 14.3 18.8 0Reception 2.5 4.5 10.4 9Waiting room 3.8 4.1 10.4 0Workshop — small scale 0.0 3.8 18.8 0

Crown and County Courts Cell (police/prison) 1.9 5.0 5.2 0Cellular office 3.5 9.5 18.8 0Eating/drinking area 3.7 18.1 7.8 0Food preparation area 3.5 25.9 26.0 0Hall/lecture theatre/assembly area 10.6 1.6 15.6 0Meeting room 4.2 4.1 11.3 0Open plan office 5.5 14.3 18.8 0Reception 6.0 5.0 10.4 9

Dwelling Bedroom 0.1 0.8 5.2 0Dining room 0.1 1.0 7.8 0Kitchen 0.1 6.5 15.6 0Lounge 0.0 0.3 7.8 0

Emergency services Bedroom 0.6 0.8 4.2 0Cell (police/prison) 0.7 1.0 5.2 0Cellular office 4.0 10.0 18.8 0Common room/staff room/lounge 1.2 5.0 7.8 0Dry sports hall 0.4 1.7 15.6 0Eating/drinking area 5.2 19.1 7.8 0Food preparation area 3.7 25.9 26.0 0Meeting room 2.8 4.3 11.3 0Open plan office 6.3 15.0 18.8 0Reception 6.5 5.0 10.4 9Workshop — small scale 0.0 5.0 18.8 0

Further education/universities Bedroom 0.6 1.2 4.2 0Cellular office 3.4 9.5 18.8 0Classroom 25.6 4.8 11.3 0Common room/staff room/lounge 1.0 5.0 7.8 0Consulting room 0.4 8.6 26.0 0Dry sports hall 3.2 1.9 15.6 0Eating/drinking area 8.2 15.3 7.8 0Fitness suite/gym 11.4 14.3 7.8 0

Table continues

Appendix A: Standard casual gains for different types of space 25D

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Table A.2 Standard casual gains in different building and space types — continued


Further education/universities Food preparation area 4.1 20.7 26.0 0(continued) Hall/lecture theatre/assembly area 24.4 1.9 15.6 0

High density IT work space 8.4 28.6 11.3 0Laboratory 7.0 9.2 41.6 0Laundry 0.3 29.5 15.6 0Meeting room 9.8 4.8 11.3 0Open plan office 5.4 14.3 18.8 0Reception 1.6 4.8 10.4 9Swimming pool 9.1 2.0 15.6 0Waiting room 1.0 4.3 10.4 0Workshop — small scale 0.0 4.8 18.8 0

Hospital A&E consulting/treatment/work areas 5.0 10.0 26.0 1Bedroom 0.6 0.8 4.2 0Classroom 13.0 4.1 11.3 0Common room/staff room/lounge 2.8 5.0 7.8 0Consulting/treatment areas 4.2 10.0 26.0 1Diagnostic imaging 7.3 50.0 15.6 1Eating/drinking area 7.4 20.0 7.8 0Food preparation area 7.1 27.2 26.0 0Hall/lecture theatre/assembly area 13.0 1.6 15.6 0Hydrotherapy pool hall 1.6 2.0 15.6 0Intensive care/high dependency 11.4 25.0 20.8 0Laboratory 7.8 9.7 41.6 0Laundry 2.1 47.5 15.6 0Meeting room 4.4 4.3 11.3 0Offices 6.0 15.0 18.8 0Operating theatre 17.0 15.0 26.0 1Patient accommodation (wards) 4.4 10.0 20.8 0Physiotherapy studio 11.0 1.7 7.8 0Reception 6.3 5.0 10.4 9Waiting room 9.3 5.0 10.4 0Ward common room/staff room/lounge 2.8 5.0 7.8 0Ward offices 6.5 15.0 18.8 0

Hotel Bedroom 0.1 0.8 4.2 0Cellular office 3.6 10.0 18.8 0Common room/staff room/lounge 0.2 4.1 7.8 0Display area 0.1 2.0 10.4 22Dry sports hall 2.2 1.9 15.6 0Eating/drinking area 4.1 14.3 7.8 0Fitness suite/gym 7.6 14.3 7.8 0Food preparation area 5.6 27.2 26.0 0Hall/lecture theatre/assembly area 6.1 1.5 15.6 0Laundry 0.9 47.5 15.6 0Meeting room 9.1 4.3 11.3 0Open plan office 5.6 15.0 18.8 0Reception 6.9 5.0 10.4 9Swimming pool 6.7 2.0 15.6 0

Industrial process building Cellular office 3.8 10.0 18.8 0Common room/staff room/lounge 0.8 3.5 7.8 0Eating/drinking area 2.4 7.7 7.8 0Food preparation area 3.1 25.9 26.0 0Industrial process area 1.3 50.0 37.5 0Laboratory 7.7 9.7 41.6 0Meeting room 2.9 4.5 11.3 0Open plan office 5.9 15.0 18.8 0Reception 2.9 4.5 10.4 9Warehouse storage 0.3 2.0 11.3 0Workshop — small scale 0.0 5.0 18.8 0

Office Fitness suite/gym 7.6 15.0 7.8 0High density IT work space 9.3 30.6 11.3 0Meeting room 4.2 4.1 11.3 0Open plan office 6.0 15.0 18.8 0Reception 5.9 4.8 10.4 9

Primary health care buildings Cellular office 3.8 10.0 18.8 0Consulting room 4.2 10.0 26.0 1Open plan office 6.0 15.0 18.8 0Reception 6.1 5.0 10.4 9Waiting room 10.9 5.0 10.4 0

Table continues

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Appendix A: Standard casual gains for different types of space 27



Primary school Cellular office 3.2 9.1 18.8 0Classroom 22.8 4.5 11.3 0Common room/staff room/lounge 0.8 4.4 7.8 0Dry sports hall 2.6 1.4 15.6 0Eating/drinking area 2.5 8.6 7.8 0Food preparation area 2.5 16.9 26.0 0Meeting room 9.1 4.5 11.3 0Open plan office 5.0 13.6 18.8 0Reception 1.0 4.5 10.4 9Swimming pool 5.2 2.0 15.6 0

Prisons Cell (police/prison) 1.1 1.0 5.2 0Cellular office 3.6 10.0 18.8 0Classroom 10.6 4.5 11.3 0Common room/staff room/lounge 1.4 4.6 7.8 0Consulting room 0.4 8.6 26.0 0Dry sports hall 0.9 1.6 15.6 0Eating/drinking area 3.6 10.5 7.8 0Fitness suite/gym 2.9 12.2 7.8 0Hall/lecture theatre/assembly area 10.6 1.8 15.6 0Laundry 0.8 45.2 15.6 0Meeting room 4.2 4.5 11.3 0Open plan office 5.6 15.0 18.8 0Reception 1.6 4.8 10.4 9Waiting room 1.1 4.3 10.4 0Workshop — small scale 0.0 3.1 18.8 0

Restaurant/public house Cellular office 3.1 9.5 18.8 0Eating/drinking area 6.3 20.0 7.8 0Food preparation area 5.8 27.2 26.0 0Open plan office 4.9 14.3 18.8 0

Retail Cellular office 3.6 9.5 18.8 0Common room/staff room/lounge 0.4 3.1 7.8 0Display area 0.1 1.9 10.4 22Eating/drinking area 5.7 17.2 7.8 0Food preparation area 3.6 23.3 26.0 0Meeting room 5.9 4.8 11.3 0Open plan office 5.7 14.3 18.8 0Public circulation areas 5.3 4.3 10.4 0Sales area — chilled 2.8 25.0 41.6 10Sales area — electrical 3.0 47.6 31.2 10Sales area — general 2.8 4.8 31.2 10Workshop — small scale 4.2 4.8 18.8 0

Retail warehouses Cellular office 4.1 10.0 18.8 0Common room/staff room/lounge 0.6 5.0 7.8 0Display area 0.1 2.0 10.4 22Eating/drinking area 4.4 20.0 7.8 0Food preparation area 2.7 27.2 26.0 0Meeting room 2.6 5.0 11.3 0Open plan office 6.4 15.0 18.8 0Warehouse sales area — chilled 1.7 10.0 41.6 5Warehouse sales area — electrical 1.7 15.0 31.2 5Warehouse sales area — general 1.7 2.0 31.2 5Workshop — small scale 0.0 5.0 18.8 0

Secondary school Cellular office 3.1 10.0 18.8 0Classroom 23.9 5.0 11.3 0Common room/staff room/lounge 0.8 4.4 7.8 0Dry sports hall 3.4 2.0 15.6 0Eating/drinking area 3.5 19.1 7.8 0Food preparation area 3.6 25.9 26.0 0Hall/lecture theatre/assembly area 23.9 2.0 15.6 0High density IT work space 3.1 12.7 11.3 0Laboratory 12.5 9.7 41.6 0Meeting room 9.6 5.0 11.3 0Open plan office 4.9 15.0 18.8 0Reception 1.5 4.3 10.4 9Swimming pool 6.7 2.0 15.6 0Workshop — small scale 0.0 4.8 18.8 0

Table continues


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Social clubs Cellular office 0.9 7.6 18.8 0Dry sports hall 1.5 1.7 15.6 0Eating/drinking area 2.2 8.6 7.8 0Fitness suite/gym 5.1 12.9 7.8 0Food preparation area 1.3 11.7 26.0 0Hall/lecture theatre/assembly area 6.1 1.5 15.6 0Meeting room 1.0 3.8 11.3 0Open plan office 1.3 11.4 18.8 0Reception 0.5 3.8 10.4 9Workshop — small scale 0.0 3.8 18.8 0

Sports centre/leisure centre Cellular office 3.1 10.0 18.8 0Common room/staff room/lounge 0.8 3.5 7.8 0Dry sports hall 2.4 1.7 15.6 0Eating/drinking area 2.9 14.3 7.8 0Fitness studio 7.9 1.7 7.8 0Fitness suite/gym 10.5 15.0 7.8 0Food preparation area 1.8 24.6 26.0 0Hall/lecture theatre/assembly area 11.0 1.7 15.6 0Ice rink 6.4 1.5 10.4 0Laundry 0.7 34.0 15.6 0Meeting room 4.4 4.3 11.3 0Open plan office 4.9 15.0 18.8 0Reception 4.0 4.8 10.4 9Swimming pool 12.5 2.8 15.6 0

Sports ground arena Cellular office 2.6 9.5 18.8 0Common room/staff room/lounge 0.8 3.5 7.8 0Display area 0.1 1.9 10.4 22Dry sports hall 2.4 1.7 15.6 0Eating/drinking area 2.9 14.3 7.8 0Fitness studio 7.9 1.7 7.8 0Fitness suite/gym 10.5 15.0 7.8 0Food preparation area 1.8 24.6 26.0 0Hall/lecture theatre/assembly area 11.0 1.7 15.6 0Meeting room 1.7 3.7 11.3 0Open plan office 4.0 14.3 18.8 0Sales area — general 4.6 4.8 31.2 10Workshop — small scale 0.0 4.8 18.8 0

Telephone exchanges Cellular office 3.5 9.5 18.8 0Common room/staff room/lounge 0.8 3.5 7.8 0High density IT work space 8.5 28.6 11.3 0Open plan office 5.5 14.3 18.8 0Reception 1.6 4.5 10.4 9

Theatres/cinemas/music halls/ Cellular office 1.8 8.6 18.8 0auditoria Display area 0.1 1.4 10.4 22

Eating/drinking area 2.0 9.6 7.8 0Food preparation area 1.2 13.0 26.0 0Hall/lecture theatre/assembly area 6.8 1.7 15.6 0Meeting room 2.6 4.1 11.3 0Open plan office 2.8 12.9 18.8 0Public circulation areas 1.2 2.9 10.4 0Reception 1.9 3.8 10.4 9Workshop — small scale 0.0 4.1 18.8 0

Warehouse and storage Cellular office 3.6 9.5 18.8 0Common room/staff room/lounge 0.8 3.1 7.8 0Eating/drinking area 4.9 19.1 7.8 0Food preparation area 5.3 25.9 26.0 0High density IT work space 8.9 28.6 11.3 0Meeting room 4.5 4.3 11.3 0Open plan office 5.7 14.3 18.8 0Reception 1.6 4.8 10.4 9Warehouse storage 0.5 2.0 11.3 0Workshop — small scale 0.0 4.8 18.8 0

Workshops/maintenance depot Cellular office 3.8 10.0 18.8 0Open plan office 5.9 15.0 18.8 0Warehouse storage 0.3 2.0 11.3 0Workshop — small scale 0.0 5.1 18.8 0

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Indexadjustable shading 5admittance method 7airport terminals, casual gains 25Approved Document L2A 2, 12, 14atria 2auditoria, casual gains 28awnings 4

blindsexternal 4, 10–11heat transfer of absorbed radiation 10internal 5, 10, 11mid-pane 5performance 6–7, 10–11brise soleil 4

BS EN 13363 6BS EN 14500 6BS EN 14501 6BS EN 410 6Building Regulations (Northern Ireland) 1, 2Building Regulations Part L 2006 1, 2Building (Scotland) Regulations 2004 1, 2bus stations, casual gains 25

casual heat gains see internal casual heat gainschanging facilities 2cinemas, casual gains 28circulation spaces 2community centres, casual gains 25control methods 5costs 3court buildings, casual gains 25

day centres, casual gains 25design criteria 3design strategies 2display lighting, internal heat gains 18, 25–28display windows 12domestic appliances, internal heat gains

16–17, 20, 25domestic buildings see dwellingsdouble glazing 7, 8, 14dwellings

casual gains 25overheating calculation 3

educational buildings, casual gains 25–26, 27effective g-value

definition 7calculation 7–10

emergency services buildings, casual gains 25equipment, internal heat gains 15–17

sample calculations 18–19, 20, 21standard casual gains by building type

25–28European standards 6external blinds 4

performance 10–11external louvres 4, 6, 8–9external shading 4

performance 7–9, 10–11

fabric blinds 4, 5, 6, 10

geographical location, allowance for 11–12glare 4glazing

coatings 5, 8effective g-value 7, 8, 10–11

glazing (continued)heat gain calculation 12–14heat transfer of absorbed radiation 6mid-pane blinds 5multiple glazing 6orientation, effect of 7, 8, 10performance 6–7, 8, 10–11solar control films 5solar control glasses 4–5window area reduction 5window film 5

g-valuedefinition 6, 10calculation 7–10

healthcare buildings, casual gains 26heat gains

internal casual gains 14–18sample calculations 18–19, 20, 21standard casual gains by building type

23–28overheating risk 3solar gains 6–7, 11–14sample calculations 18–21

heat transfer coefficient 10–11hospitals, casual gains 26hotels, casual gains 26household equipment, internal heat gains

16–17, 20, 25

industrial buildingscasual gains 26sample calculation 20–21

internal blinds 5performance 10, 11

internal casual heat gainscalculation 14–18sample calculations 18–19, 20, 21standard casual gains by building type

23–28ISO/DIS 15099 6IT equipment areas 2

legislation 1, 2leisure centres, casual gains 28light shelves 4

effective g-value 7–8lighting, internal heat gains 17–18

sample calculations 19, 20standard casual gains by building type

25–28long-wave shading coefficient 7louvres 4, 6, 8–9

mean solar gain factor 7mid-pane blinds 5, 10, 11multiple glazing 6, 7, 8, 14

non-domestic buildings 2–3

occupants, internal heat gains 15sample calculations 18, 20, 21standard casual gains by building type

25–28occupied spaces, definition 2office equipment, internal heat gains 15–16,

26sample calculations 18–19

officescasual gains 26sample calculation 18–19

Index 29

orientation, building, correction factors 7, 8, 9, 10

overhangs 4effective g-value 7–8projection ratio 4, 8

overheating calculation 3see also heat gains

performance, quantifying 6–11plant rooms 2prisons, casual gains 27public houses, casual gains 27

railway stations, casual gains 25reflective roller blinds 5residential buildings

casual gains 25overheating calculation 3sample heat gain calculation 19–20

restaurants, casual gains 27retail buildings, casual gains 27roller blinds 4, 5, 10rooflights 12, 17

heat gain calculation 14, 20–21

school buildingscasual gains 27overheating criteria 2

shading coefficients 7shops, casual gains 27shortwave shading coefficient 7shutters 6Simple (dynamic) Model 7slatted blinds 4, 6, 10social clubs, casual gains 28solar control films 5solar control glasses 4–5solar direct transmittance 6solar gain calculation 6–7, 11–14

sample calculations 18–21solar gain factors 7sports arenas, casual gains 28sports centres, casual gains 28stack ventilation 2stages (performance areas) 2standards 3, 6storage areas 2

telephone exchanges, casual gains 28temperature limits 3theatres, casual gains 28toilets 2total shading coefficient 7total solar energy transmittance

calculation 7–10definition 6, 10

transmittance, glazing 6transport buildings, casual gains 25triple glazing 7

ventilation stacks 2

warehouses, casual gains 27, 28window film 5windows see glazingWorkplace (Health, Safety and Welfare)

Regulations 1992 1workshops, casual gains 28


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Documents

cover v3.3 3/5/06 16:04 Page 1 sign for i s l shading control · 2013-04-18 · Solar shading of buildings(4) gives detailed advice on solar control. BRE Trust Report FB9: Summertime