Guide to Low Energy Shading · G u i d e t o L o w E n e r g y S h a d i n g 02.13.1 Solar shading...

Guide to LowEnergy Shading

Using blinds, awnings and shutters to save energy andenhance thermal and visual comfort in buildings

April 2013Issue 1

G u i d e t o L o w E n e r g y S h a d i n g

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Solar shading is now an accepted energy saving measure in the Green Deal.Correctly specified, installed and operated solar shading will reduce the energyconsumption of buildings.

Solar shading has an important role to play whether the requirement is to; savewanted heat, reject unwanted heat, harvest natural light, reduce capital buildcosts, cut carbon emissions, reduce embodied carbon, provide a more produc-tive and comfortable environment, meet compliance or a combination of thesebenefits.

This guide will clearly highlight what must be considered in the specification anduse of a solar shading system and the requirements that you should seek fromyour chosen solar shading specialist.

Dave BushIvonne Ortega NavaBBSA Technical Working Group

CONTRIBUTORS

Wouter Beck (Verozo)Steve Birtles (BBSA)Dave Bush (BBSA)Andrew Chalk (BBSA)Dick Dolmans (ES-SO)Gonzague Dutoo (SNFPSA)Anders Hall (Svenska Solskyddsförbundet)Richard Keen (BBSA)Hervé Lamy (SNFPSA)Ivonne Ortega Nava (BBSA)Olli Seppänen (REHVA)Cassie Sutherland (BBSA)

© British Blind and Shutter Association, 2013. All rights reserved. No part of this publication may be reproduced in any formwithout the express written permission on the British Blind and Shutter Association.

BBSA, PO Box 232, Stowmarket, Suffolk, IP14 9AR - [email protected] www.bbsa.org.uk


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Section Subject Page Number

1 Introduction 1

1.1 Energy saving in buildings 1

1.2 Why do we need shading? 2

1.3 What is energy efficient shading? 2

1.4 What is the most efficient form of shading? 3

1.5 Why is it that it is not possible to give blinds an A-Grating 3

1.6 What is solar gain? 4

1.7 What is U-value? 4

1.8 What is g-value? 4

1.9 What is Tv? 5

1.1 Data and calculation tools 5

1.11 What types of shading should you choose? 6

1.12 Commercial building cooling savings 6

1.13 Domestic building energy saving 7

1.14 Refurbishment 7

1.15 PassivHaus and near zero energy buildings 8

1.16 Double Skinned Façades 8

1.17 Automation 8

1.18 Why is solar shading often not considered? - the needfor behavioural change 9

1.19 As a final thought – Could energy efficient shadinghave prevented the global credit crisis?

10

2 Conclusions 10

3 AppendicesA What is solar gain? 11

B Behavioural change 14

C Check list of requirements for solar controlmanagement 15

D U-value calculations 19

F G-value calculations 20

G Commercial building shading costs benefit analysis 22

H Comparison of energy saving technologies fordomestic buildings 23

I Summer solar gain 25

J Types of automated control 26

K Fuel poverty and energy efficient shading 29

L Productivity and internal environment 30

M Double skinned facades 32

N Control of light 34

4 Standards 36

5 References 36

6 Photograph Credits 37

7 Glossary 37


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1.0 INTRODUCTIONShading devices have been used for centuries to help make the internalenvironments of buildings more comfortable. Buildings in hot climates typicallyhave small windows, overhangs or are orientated to minimise heat gain in thesummer. The basic science is common sense, but in the UK the use of thisscience is not common practice.

Solar shading is a proven energy saving technology, all that is needed is abetter understanding of how to maximise those benefits. It is estimated that ifthe equipment that is already installed in our buildings is used efficiently thenbuilding energy costs could be reduced by as much as 10%. A zero costsolution, simply involving behavioural change, which is explored further inAppendix B.

For commercial and public buildings solar shading can have a positive impact onheating, cooling, lighting and glazing systems. To meet the economic andenvironmental imperatives of building design and refurbishment a holisticapproach is a prerequisite. So solar shading must be considered and specified atthe beginning of a project, not at the end when it’s too late to reap the realbenefits.

For dwellings, blinds, awnings and shutters can help save precious heat in thewinter and keep homes cooler in summer.

To assess the shading that is required for any building it is necessary to have abasic understanding of the different effects of the sun’s radiation. The purposeof this guide is to explain how solar shading can be used to save energy. Solarshading can control the radiation of the sun, a variable force that changesconstantly throughout the day, the seasons and is typically unpredictable.

As it is not possible to forecast the exact impact of the weather on a building,shading has to be dynamic to react to constant changes. Consequently there isnot a simple one-size-fits-all solution and so this guide does not provide specificproduct solutions. That advice should be sought from your chosen supplier fromyour check list of requirements - see Appendix C.

1.1 Energy Saving in Buildings

As buildings account for almost 40% of the total primary energy use in Europe,pressure has grown to make them more energy efficient. The savings potentialis huge. It is not rare today to have buildings that consume a total energy ofmore than 250 kWh/m² per annum, whereas state-of-the-art technology inmodern buildings shows figures wellbelow 100 kWh/m² per annum. Toassess the energy performance ofbuildings, the UK government uses twosoftware tools, the StandardAssessment Procedure (SAP) fordwellings and the Simplified BuildingEnergy Model (SBEM) for non-dwellings. Both tools are used todemonstrate compliance with theBuilding Regulations that are derivedfrom the European Energy Performanceof Buildings Directive, but do notcurrently allow adequate credit forsolar shading measures.

Limiting the effectsof solar gain insummer can beachieved by anappropriatecombination ofwindow size andorientation, solarprotection throughshading and othersolar controlmeasures,ventilation (dayand night) and highthermal capacity”BuildingRegulations PartL1A

Energy efficientshading is the

balance betweencontrolling light andheat and reducingenergy demand.Weather conditionsare dynamic andglazing static.Automated shadingis the solution.

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Several countries are also working on legislation limiting maximum energy useto 50 kWh/m² per annum by the year 2015 or shortly after, some 20% oftypical current levels. At the same time, Passive and Active House technology isgaining market share and the European Parliament has stated that all newbuildings should be near zero energy from 2019 onwards. The UK hascommitted to introducing zero carbon standards for all new buildings from 2016for homes and 2019 for non-domestic buildings to assist with reducing energydemand by 20% as part of the 20/20/20 obligation. The Green Deal is designedto help deliver these objectives.

1.2 Why do we need shading?

Controlling the entry of solar heat and light has a considerable effect on theenergy needs of a building. It is a keyelement for improving the energyefficiency and daylight management ofexisting buildings and optimising the low-energy designs of new buildings. Thisproven technology is still under-utilisedalthough it provides a major impact on thereduction of energy consumption of thebuilt environment whilst improving thethermal and visual comfort of theoccupants.

However, solar shading is only oneelement of the building’s envelope, alongwith glazing, window frames, walls, roofsand floors. We think of energy saving asinsulation. Solar shading is the insulationof the transparent parts of a building, thatis the glazing.

Indeed, solar protection devices enable adjustment of the properties of windowsand façades to weather conditions and, most importantly, the needs of theoccupants. Proper management of these systems can maximise the solar heatgains in winter, so reducing the heating loads, and minimise these heat gains insummer, so reducing the cooling loads, while at the same time providing goodvisual comfort to the occupants.

1.3 What is energy efficient shading?

Solar shading is a broad term used to cover all the techniques to limit the entryof excessive solar energy. These range from shading using trees, fixed awningsor brise soleil to fully automated blinds and shutters. On the other side, solarshading can be also effectively used in winter to keep heat in as it improves thethermal transmittance of glazing. Shading acts as an insulator. Weatherconditions, light and heat, change constantly in the course of one day. That iswhy, in the context of this guide, there is some emphasis on automatedsystems so that the optimum benefits can be obtained.

In order to make the correct choice in terms of products and façademanagement when designing a new building or preparing works to an existingone, it is necessary to take into consideration all of the characteristics of solarprotection devices. Shading products have an impact on the insulation level ofthe façade, its solar heat transmittance and its light transmittance. As aconsequence it is necessary to find the best balance between all thesecharacteristics depending on the building properties, its location and orientation.

“Solar shading isthe insulation ofthe transparentparts of a building.”Dick Dolmans,ES-SO

Shading canreduce heat

gain, reduce heatloss, control lightand provide visualcomfort.


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This guide is intended to give the basic knowledge to understand how solarshading characteristics are evaluated and what physical properties are involvedin the transmission of the solar radiation. It is based on calculation methodstaken from European standards.

Examples of simulations showing the impact of solar shading on the energyloads of buildings are shown in Appendix D.

1.4 What is the most energy efficient form of shading?

There is not a simple answer to this question.

We need to permit heat gain in the winter and limit it in the summer. The sungives us both light and heat and controlling one element will affect the other.

We need to control when we do not get enough light and when we get toomuch. Similarly we need control over too much or too little heat. It alsodepends whether the building is commercial or domestic. With dwellings themain energy cost is heating whereas in commercial buildings it is cooling andlighting.

As the sun moves the problems are different throughout the day and theychange throughout the year. Windows facing east will have different problemsto those facing south which will be different to those on other façades.

Different types of glass and frames will have differentperformance when shading is added.

The size of the window and the amount of glazed areawill also affect the calculation and it should be notedthat selection of the right colour of any shadingdevice is an energy as well as a design decision.

Different parts of the country have different weatherpatterns and thus different shading needs. And finallywe can never be certain when the sun will shine andwhen it will not. As an energy source it is erratic.

That is why there is not a ‘one size fits all’ perfectsolution. To select the most appropriate shading foryour requirements use Appendix C to prioritise yourneeds.

1.5 Why is it not possible to give blinds an A-G rating?

Providing clear energy ratings has been very effective in improving the energyconsumption of many products such as whitegoods so why not for shading?

The performance figures for solar shading shouldbe calculated to European Standards (SeeAppendix D). This is a relatively complexcalculation method but that is, ironically, the easypart. What is needed is how the shading willperform in conjunction with the different types ofglazing, the orientation of the building and itsspecific location. A simple rating system to coverall of the variables is very difficult to achieve.

Performance willnot only depend

on the type ofshading but alsolocation, the surfacearea and type ofglass, the building’sorientation andmany other factors.

Selecting theright colour of a

shading system isan energy as wellas a designdecision.

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1.6 What is Solar Gain?

To understand solar gain we need to understand how the sun’s rays work. Thesun’s rays are actually cold and they convert to heat when they are absorbed byan object. The sun’s radiation is transmitted in two types of waves, theshortwaves which are mostly light and the longwaves which are mostly heat.

Glass allows most of the shortwave radiation (light) to pass through it but willnot transmit most of the longwave (heat). So the sun’s rays pass through theglazing as shortwave, hit objects in the room such as walls, furniture etc whichabsorb the radiation and radiate it back as longwave heat. That heat cannotpass back through the glass as this is an opaque object and so it becomestrapped in the building. This is the same effect that happens in the atmosphereand it is called the Greenhouse effect.

Blinds, awnings and shutters can help prevent excessive solar gain by blockingsome of the incoming shortwave solar radiation.

External blinds and shutters are very effective at this as they prevent theradiation from even reaching the window as the heat stays outside. However,internal blinds can also reduce solar gain. This is especially true of fabrics thathave a reflective coating facing the window which will reject some of theincoming shortwave radiation, therefore not allowing it to be absorbed andturned into heat. A more detailed assessment of the effects of solar gain isshown in Appendix A.

In summary, solar gain determines the thermal and visual performance of solarshading devices. There are three key measures that assess this performance;U-value, g-value and Tv which will be briefly described in the followingparagraphs.

1.7 What is U-value?

U-value is a measure of thermaltransmittance which is the ability of amaterial to transfer heat. All components of abuilding have U-values for example masonry,insulation materials, plasterboard andwindows. The lower the value, the lower theheat loss through the material. Therefore amaterial with a low U-value is a goodinsulator. The U-value of glazing is alwaysimproved by installing blinds or shutters. Adetailed explanation is shown in Appendix E.

For energy calculations it is necessary to takethe figure for the combination of the glassand shading and not just the shading alone.

1.8 What is g-value?

Also called solar factor, g-value is the measure of the total energy passingthrough the glazing when exposed to solar radiation. It is the sum of twovalues: the solar transmittance, Ts, and the secondary internal heat transferfactor Qi. In other words, this measure represents the heat gains. When theg-value of the glazing is combined with the value of the shading, this is the gtot

value.

KEYPERFORMANCEMEASURES OFSOLAR SHADINGDEVICES

U-value is ameasure of thermaltransmittancewhich is the abilityof a material totransfer heat.

g-value is themeasure of thetotal energypassing throughthe glazing whenexposed to solarradiation.

Tv is the fraction ofvisible lighttransmittedthrough theshading material

These values mustbe alwaysmeasured inconjunction withthe glazing.

Blinds andshutters can

prevent excessivesolar gain byblocking some of theincoming shortwavesolar radiation andretain heat whennecessary. This iswhy it is importantto know the gtot andthe U-values. TheU-value of glazing isalways improved bythe installation ofblinds or shutters.


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The lower the value, the lower the heat gain.The value of gtot is between 0 and 1, where 0equates to no radiation being transmitted intothe room and 1 means all radiation istransmitted. So a gtot of 0.25 (75% heatrejection) reduces heat gain three times moreeffectively than a gtot of 0.75 (25% heatrejection). External shading helps to reducegtot values and has much more impact on gtot

than internal shading.For energy calculations it is necessary to takethe figure for the combination of the glass andshading and not just the shading alone. Adetailed assessment is shown in Appendix F.

1.9 What is light transmittance (Tv)?

This measure refers to the fraction of visiblelight transmitted into a room. As with the g-value we have to consider the measure of theglass in combination with the shading device.The value is between 0 and 1, where 1 meansno light is transmitted and 0 means all visiblelight is transmitted. A Tv value of 0.25 means25% of light is transmitted. See Appendix Afor more information.

1.10 Data and calculation tools

When using data it is essential to ensure thatthe calculations methods are correct. TheBritish Blind & Shutter Association (BBSA), inconjunction with partners in the EuropeanSolar Shading Organisation (ES-SO), havedeveloped a database of solar shadingmaterials, the Shade Specifier Database.

This database includes independently validated energy performance data ofblind and shutter fabrics and materials to European standards. The databasecalculates the energy performance of blind and shutter products when used incombination with reference (typical) glazing defined in the European StandardsEN 13363-1 and EN 14501. All calculations are performed in accordance withthe relevant European standards.

This process used by the Shade Specifier Database is identical to that used bythe glazing industry database1 and is a robust and effective way of ensuring theintegrity of the database2.

Outputs include:

● Total solar energy transmittance, gtot (amount of heat gain)● Visible transmittance, Tv (amount of light)● Thermal transmittance, U-value (amount of heat loss)

A detailed assessment of the calculation methods and data required is shown inAppendix D.

The science ofshading is simple

- to keep the heatout in summer andkeep it in during thewinter. However,calculating theeffects is not sosimple, make surethat the data youare using is correct.

gtot - It is themeasure of the

total energytransmittance of theglazing incombination with theblind when exposedto solar radiation.

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1.11 What types of shading should you choose?

There are many reasons for needing shading and there has to be a balance ofthose requirements. Designing for optimum energy saving is unlikely to producethe most satisfactory solution.

For example, one of the most effective energy saving solutions is an externalblackout roller blind. On the database this will probably show one of the bestgtot performances, better than 0.05, and good U-values as well but would itwork in practice? Almost certainly not withno vision through and no light transmissionresulting in extra energy cost for lighting, anextreme example but it shows the need forbalance and practical selection.

So it is not a matter of what is the bestsolution it is what is best for the building andwindows that it is to be applied to. Thecreation of a checklist of the requirements isnecessary and an example is shown inAppendix C.

The completion of this list may come to theconclusion of several scientific studies fromFrauhofer Institut für Bauphysik3 amongothers, that ideally a window requires bothinternal and external shading.

1.12 Commercial building cooling savings

Typically for commercial buildings cooling costs are more significant thanheating costs and so this is where the greatest energy savings can be achieved.

Selection of solar shading should always be one of the first steps in the designof HVAC systems. Shading makes it possible to prevent extra solar heat fromentering the building and so avoid the need for additional cooling to remove thisheat, which costs precious energy. This is particularly important whenconsidering highly insulated and airtight buildings which try to comply withnearly-zero energy requirements.

In winter time when the shading israised the free heat from the sun isvery welcome to reduce the building’sheating costs.

Appendix G shows a cost benefitanalysis from computer simulations ofa typical office building using solarglass without shading compared todouble low-e glass with shading. Notonly is the capital cost lower but thereis a continuing payback from reducedrunning costs. In fact effectiveshading allows highly glazed buildingsto be built respecting the latest

building regulations that would not be met without it.

Significant productivity performance improvements can also be achieved with acontrolled internal environment and an analysis can be seen in Appendix L.

The Green Deal isa government

initiative that seeksto improve theenergy efficiency ofexisting buildings.Solar shading is arecognised energyefficient measurewithin the GreenDeal.

“Selection of solarshading shouldalways be one ofthe first steps inthe design of HVACsystems.”Olli Seppannen,REHVA


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1.13 Domestic building energy saving

Typically domestic buildings do not have mechanical cooling so the greatestenergy savings will come from heat retention. Unacceptably high temperaturesin summer that would prevent staff from functioning in a commercial buildingare accepted in a domestic building, although the space would be mostunbearable. That is why we live with it rather than paying for a cooling system.Shading therefore provides a more comfortable environment.

Moreover, approximately 27% of the UK’s carbon dioxide emissions come fromdomestic buildings4, so improving the energy efficiency of the UK’s housingstock by improving heat retention will significantly reduce national CO2

emissions.

There are many differenttechnologies available to improvethe energy efficiency and thereforereduce the annual energy bills ofdomestic buildings, and shading isone of them.

Appendix H shows a comparison ofsome of the popular energyefficiency measures and the relativecost benefits. The annual savingand payback period from installingblinds is very similar to those forother insulating products.

1.14 Refurbishment

It is estimated that 75% of the existing building stock was constructed before1980. Whilst by 2020 all new buildings are expected to be “nearly zero energy”only 1-1.5% are replaced every year5. The Green Deal seeks to improve theenergy efficiency of existing buildings.

In both new build and renovation, more insulation of the opaque (solid) parts ofthe building envelope is what is normally thought of first. While reducing airleaks is also important as is effective ventilation, what is often overlooked is theserious risk of overheating in summer.

Of all the building components the windows are typically one of the weakestelements. While weather conditions and the position of the sun variescontinuously windows are static. Shading reduces or eliminates the need foractive cooling in summer conditions by controlling the amount of solar energyentering through the windows. Correctly managed solar shading also allowsharvesting of free solar energy in the winter season and offers additionalinsulation to the transparent parts of the building structure which helps toreduce heat loss in cool weather.

Solar shading will also manage and control daylight admittance, reduce glareand improve visual comfort. According to the Building Regulations Part L whenseeking to limit solar gains the provision of adequate level of daylight needsspecial attention. One effective way to control the light entrance throughwindows is by using blinds. For more details see Appendix N.

Effective shadingallows highly

glazed buildings tobe built respectingthe latest buildingregulations thatwould not be metwithout it.

As around 75% ofthe existing

building stock wasconstructed before1980, the GreenDeal seeks toimprove the energyefficiency of thesebuildings

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1.15 PassivHaus and near zero energy buildings

The development of the PassivHaus concept has created requirements forshading that are not normally considered in UK design.

The principle of high levels of insulation and large areas of glazing to maximisewinter heat gains has the opposite effect in the spring and summer whenexcessive heat gain becomes a serious concern. In theory this could be reducedby a passive fixed system to reduce high angle peak solar gain. In reality thiswould only solve part of the problem. Even in mid-July low angle early morninggains will also be an issue. In other summer months where the sun angle islower there is more of a problem as the high level of insulation to retain heat inwinter performs the same way in spring and summer - so causing overheating.

In these buildings shading has to be externaland to be most effective needs to be moveableallowing to be lowered for cooling and raised forheating depending on the season. Several post-occupancy studies of high performancebuildings report high temperatures as one ofthe most frequent problems6. These types ofbuildings still need external, moveable shadingin order to prevent overheating. For moreinformation see the videos from the BBSA/BRESolar Shading Conference: Hannes Gertsmann– BVST (Austria) about Solar Control inPassivhaus and Peter Foldjberg – Velux(Denmark) Solar Control in Active House.

1.16 Double Skin Façades

For extensive commercial renovation thatincludes the replacement of the glazingconsideration should be given to a doubleskinned façade incorporating shading withinthe building envelope. This is an effectiveoption that has the benefits of an externalshading system by utilising the naturalventilation created within the façade. Thedesign of The Shard in London was onlypossible with effective automated shadingwithin the façade that enabled a gtot figureof 0.12 (88% heat rejection). A detailed description can be found at Appendix Mof this Guidance or in REHVA Guidebook No 127.

1.17 Automation

The energy saving benefits of solar shading will only be achieved if the systemis controlled to react to changing outdoor conditions. The most effective way,especially for commercial buildings, is an automatically controlled system. Itwill then work correctly even if the occupant is absent and it will react to theenvironmental conditions without needing the attention of the user ensuringthat the energy balance of the building is maintained. Control can be achievedwith simple stand-alone systems or large scale systems integrated into thebuilding or home management system.

Whilst a solar shading system should maximise energy savings and improveinternal comfort it should also accommodate the varying wishes of the

The principle ofhigh levels of

insulation and largeareas of glazing tomaximise winterheat gains has theopposite effect insummer whenexcessive heat gainbecomes a seriousconcern. Blinds orshutters can be asolution.

“The currentdevelopment inbuilding energyefficiency towardsnearly-zero energybuildingsrepresents anumber of newchallenges todesign andconstruction ofbuildings. One ofthe majorchallenges is theincreased need forcooling in thesehighly insulatedand airtightbuildings”.Per Heiselberg,Aalborg University,Denmark


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occupants. External shading should also be secure from damage from highwinds or extreme weather conditions, in both cases this is easily achieved withautomation.

Adequate time and attention should be paid to the selection of an automatedsystem and a description of the control options is shown in Appendix J.

1.18 Why is shading often not considered? The need forbehavioural change

Behavioural change is a key part ofthe UK strategy to reach ourenvironmental and energy savingtargets.

With energy prices increasing andset to increase further in the futurethe only way for home owners andbusinesses to save money onenergy is to change the way we useit - that is behavioural change.When energy was cheap andplentiful there was not theimperative to consider how energywas used and how it could be saved.

Blinds and shutters are still thought of as the decoration at the window butshould be considered as part of an energy saving strategy. A building’s energyconsumption can be reduced by up to 10% just through behavioural changetherefore at no extra cost.

By adopting best practice on shading building users and owners can quicklyrealise how they will save energy and money. To save energy it is vital that theuser understands the reason for the measures that are being taken to realisethe full benefits.

Blinds and shutters can work to save energy irrespective of the season. In thesummer they can reduce heat gain and in winter they can reduce heat lostthrough window systems.

Advice on understanding and communicating the benefits is shown in AppendixB.

1.19 As a final thought – Could energy efficient shading haveprevented the global credit crisis?

Not quite, but as the case study in Appendix K shows fuel poverty was thetrigger that started it and inadequate attention to the need for shading was oneof the issues.

Fanciful? As the UK’s own energy reserves decline and we become increasinglyreliant on others for our energy sources the need to reduce consumption is asnecessary today in the UK as it was then in Arizona.

The conclusion ofseveral scientific

studies is thatideally a windowshould have bothinternal and externalshading.

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2.0 CONCLUSIONIn order for blinds, awnings and shutters to improve the comfort and energyperformance of buildings they need to be correctly specified, installed and used.Automation will ensure the chosen solar shading devices provide the optimumbenefit but manual systems can also be highly effective.

When considering the performance of a solar shading system it is important toremember:

● Blinds and shutters must be always be considered in combination withglazing to determine energy saving calculations

● Blinds and shutters should be considered at the design stage of thebuilding as they will affect other building services

Solar shading can have a direct impact on the type, size and cost of:

● Glazing● Lighting● Heating systems● Cooling systems

Consequently solar shading needs to be considered at an early stage of thedesign.

Solar shading systems can be installed external or internal to the building orwithin the glazing itself. In each position the performance characteristics will bedifferent. Similarly the type of glazing, colour, material, fitting and position ofthe blind will all affect performance.

With the ever increasing costs of energy and stricter control on building designand use solar shading has an important part to play in managing the energycosts as well as thermal and visual comfort of a building’s occupants.

The solutions available are many and varied so expert advice should be soughtfrom an accredited specialist.

“Zero carbonhomes from 2016may eliminatearound one milliontonnes of carbondioxide per year by2050 but this onlyrepresentsaround 6% of totalcarbon dioxideemissions from allhomes. If we wantto hit the UK'scurrent target of60% emissionscuts we need to berefurbishing somehalf a millionhomes per year toa standardof 70% emissionsreduction.”Dr Paul Ruyssevelt,Cameo


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3.0 APPENDICESAPPENDIX A WHAT IS SOLAR GAIN?

This Appendix shows some keyinformation concerning the differenttypes of radiation that have to beconsidered in the performance of solarprotection devices and the position ofthe sun. It also shows how a materialbehaves when it is affected by suchradiation.

The solar irradiance depends on theposition of the sun in the sky, whichcan vary throughout the year andduring the day. Figure 1 shows thesun’s position in winter is lower than insummer. This gives an opportunity ofharvesting large amounts of irradianceduring the day through glazing incolder months.

Types of radiation

People are exposed to a large variety of radiation that can be natural orartificial. Radiation has differing wavelengths. The “power” of a radiation isrepresented by its irradiance in W/m². For a given wavelength, it is calledspectral irradiance given in W/m²nm. Figure 2 gives the distribution of variouselectromagnetic radiation depending of its wavelength. Based on its wavelength radiation can be divided in two types:

· The solar radiation (solar gain) with a wavelength between 280 nm to2,500 nm that is subdivided into three parts: UV, visible and shortwaveinfrared. This radiation is emitted by the sun.

· The longwave infrared with wavelength between 2500 nm to 10,000 nm

that is due to the temperature level of a material (e.g. a heater or anywarm surface). This radiation is in the infrared spectrum which is in theinvisible range.

Solar radiation

The sun produces an enormous amount of energy (66 million W/m²) which istransmitted to the earth through radiation. Only a fraction of this energy

Figure 1. Position of the sun atdifferent seasons

When consideringa solar

protection device, itis necessary todivide the globalincident radiationinto three parts:Ultraviolet, Visibleand shortwaveinfrared.

Figure 2. Classification of various electromagnetic radiation depending oftheir wavelength

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3.0 APPENDICES reaches the atmosphere (around 1,300W/m²). Approximately 15% of thisradiation is then absorbed by theatmosphere and emitted in all directionsin the form of diffuse radiation. Around6% is reflected back into the space. Theremaining part (79%) is directlytransmitted to the ground through theatmosphere - see Figure 3.

As a consequence, the energy of solarradiation hitting the ground is muchlower than at the outer limit of theatmosphere. It is generally consideredthat the energy reaching the groundwhen there is a clear blue sky is around1,000 W/m².

When considering a solar protectiondevice, it is necessary to distinguish thethree parts involved in the solar radiation-see Figure 4.

·Ultraviolet (UV): from 250 nm to 380nm. These rays are invisible to the humaneye and may be dangerous in case ofoverexposure. They age materials anddamage surfaces and colours.·Visible (Tv): from 380 nm (violet) to 780nm (red). These rays are LIGHT and aredetected by your eyes and enable thesight of shapes, relief and colours.·Shortwave infrared (IR): from 780 nm to2,500 nm, these rays are invisible but arefelt as HEAT.

When the sun irradiates a surface(glazing, fabric or a venetian blind slatfor example), incident radiation splitsinto three parts as well (Figure 5):

· A part which is transmittedthrough the material. It ischaracterised by the

transmittance τ· A part which is reflected by the

material. It is characterised by

the reflectance ρ· A part which is absorbed by the

material which is characterised by the absorptance α

so that τ + ρ + α = 100%

Figure 5. Behaviour of radiation incontact with material

When the sunirradiates a

surface (glazing,fabric or a slat forexample), incidentradiation splits intothree parts:transmittance,reflectance andabsortance. Thesevalues are assessedfor solar gain andvisible light todetermine thethermal and visualproperties of theglazing combinedwith a shadingdevice.

Figure 3. Solar Radiation

Figure 4. Spectral irradiance at thesea level for the solar spectrum


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These three values are specific to a material and are affected by the type ofmaterial (fabric, metal, glass etc) the density or openness and the colour. Italso depends on the wavelength of the solar radiation. This is measured in alaboratory and as the amount of reflection and transmission will vary throughthe solar spectrum it is measured at 5 nanometer (nm) increments from 260 to2,500 nm.

The three values for solar gain (that is heat) are taken from the data for thecomplete solar spectrum from 250-2,500 nanometers and are defined as:

Ts - Solar TransmissionRs - Solar ReflectionAs - Solar Absorption

The three values for visible light are taken from the data for the visible part ofthe solar spectrum from 380-780 nanometers and are defined as:

Tv - Visible TransmissionRv - Visible ReflectionAv - Visible Absorption

These material properties are then used in calculations which combine thematerial data of the blinds, awnings or shutters with glazing data - seeAppendix D.

A more detailed assessment of the methods and calculations can be found inSolar Shading for Low Energy Buildings8. These characteristics are measured inaccordance with the European Standard EN 14500 Blinds and shutters - thermaland visual comfort - Test and calculation methods.

The solar radiancealso depends on

the position of thesun in the sky,which can varythroughout the yearand during the day.

1402.13.1


APPENDIX B BEHAVIOURAL CHANGE

Summer cooling with blinds and shutters

In hotter climates such as those found in southern Europe it is normal for theblinds or shutter to be closed in early morning and then later in the day theroom is a cool refuge from the afternoon sun. It is a natural, efficient method ofcooling a room without using energy.

The best way of minimising heat from the sun is to use nature and plant treesoutside your windows. In the summer the leaves shade, like the shutter, and inautumn the loss of leaves will allow the sun to penetrate and provide somenatural winter heating even when temperatures outside are lower. Efficient,effective, and a virtually no cost and a positive environmental solution.

In the UK it also gets hot in the summer. Traditionally we have preferred largeareas of glass that need air-conditioning to cool the resulting heat gain in officesor fans in our homes rather than utilising passive cooling methods such asnatural shading.

Using your new or existing blinds and shutters to the BBSA best practice onshading will work in the same way as the shutters and trees – a simple way tosave energy.

Winter heat saving with blinds and shutters

A significant amount of heat can be lost from a building through its windowsespecially during the cold winter months. Also, in the winter you want tomaximise heat gains from the low angle sun. Blinds and shutters can work toreduce the amount of heat lost as they can also be raised to maximise the solarenergy entering the building.

In commercial buildings this can mean that less heating is required in themorning to get the building to a comfortable temperature. In domestic buildingsthis means you can spend less money on your heating bills. You just need tooperate the blinds and shutters effectively. To achieve this, follow the bestpractice guide recommended by the BBSA.

The BBSA best practice on using solarshading to maximise energy savings

Summer

● Close the blinds at night onthe east-south elevations toprotect from early morningheat gains

● Open the blinds at night onthe west and north-westelevations to assist night timecooling

● Close the blinds after thesun goes down to retain heat

● On sunny days open theblinds during the daytime tomaximise heat gain from thewinter sun and close blinds atnight.

Winter

Blinds in unoccupied rooms should always be closed.

To save energyyou just need to

operate the blindsand shutterseffectively. Toachieve this, followthe best practiceguide recommendedby the BBSA.


1502.13.1

APPENDIX C CHECK LIST OF REQUIREMENTS FOR SOLAR CONTROL MANAGEMENT

What do you expect the blinds or shutters on your project to achieve? Do youknow all the benefits that blinds and shutters could provide for you? Which aremore important for you?

You may not be able to achieve all your requirements with only one solution.The following list highlights some of the benefits. Classify them in terms of howimportant they are in your daily life or specific projects.

FunctionDegree of Importance

High Medium Low

BUILDING CONTROLControl of solar gainLight level controlRetain heat in winterReject solar gains in summerInterface with building or homemanagement systemMaster override of automated system andwind overrideShading when area is unoccupiedAutomatic control of primary heat gainNight heat retentionMinimal reduction of light levels on dulldaysGood natural light levelsLight shelf to diffuse and spread lightHeating benefit from low angle winter sunControl of energy costsArt gallery lux level controlUSER CONTROLGlare control for visual comfortVDU screen glare controlEase of operationVisual perception, allowing external visionPrivacy during daylightPrivacy during night timeManual override of automatic controlREGULATIONS AND STANDARDSCompliance with Building RegulationsCompliance with energy performancesoftware (SAP and SBEM)Local authority planning

Solar shadinghas many

functions so makesure you prioritiseyour needs.

1602.13.1


Blinds and shutters can perform many functions. This list is intended to helpyou to identify the issues rather than direct you to specific options. It is unlikelythat a single product will achieve every requirement and for many situationstwo shading systems may be required. So prioritise your needs and check themagainst the products you have selected.

Solar shading hasseveral

functions such asbuilding control,user control, tocomply withregulations andstandards,aesthetics, buildinglifecycle costs.Therefore, it isimportant that theuser prioritises theirneeds to select themost appropriateproduct.

FunctionDegree of Importance

High Medium Low

REGULATIONS AND STANDARDSEnergy performance and energy auditsHelp to reduce carbon emissions inbuildingsAESTHETICSCo-ordination with the decorationSame solution for every elevationSymmetry of appearance of externalshading (elevational consistency)Internal symmetryDecorative featureBUILDING LIFECYCLE COSTSManageable maintenance costsLong design lifeOTHER FUNCTIONS AND NEEDSBlackoutDim out for projection and AV equipmentExternal shade area for sitting underRooflight shadingAdvertising signFlame retardant materialsPrevent UV fading of furniture anddecoration


1702.13.1

APPENDIX D DATA AND CALCULATION TOOLS

The British Blind and Shutter Association (BBSA) in conjunction with partners inthe European Solar Shading Association (ES-SO) have developed a database ofshading materials. The Shade Specifier database includes independentlyvalidated energy performance data of blind and shutter fabrics and materialsmeasured to European standards. A user friendly calculation tool has beendesigned to be similar to the one used by the glass and glazing federationexcept that it combines shading with glazing.

The database enables thecalculation of the performance ofshading products in combinationwith the glazing (this combinationis known as ‘complex glazing’). Ittakes the data for the glass andthe shading to enable thecalculation for the actualcombinations of gtot and U-valuesof glass and blinds or shutters.

Although there is a value for theblind without glass, this is not theway a blind is used. The correctuse should combine the values of

the glass and the blind resulting in a gtot. You need to know the performancewhen the products are combined and that will give a different figure dependingon where the blind is fitted - internal, mid-pane or external. Furthermore thecombination of the glass such as single, double, triple and which pane and onwhich side a low-e or other coating is applied will all have a bearing too.

For each of the myriad of combinations the performance will be different. It isnot a simple calculation which is why we need the Shade Specifier database.

The output figures from the databaseallow a comparison of the benefits inenergy saving. However, to calculatefigures for performance it is necessary tobuild a model of your building to test thedifferent options. This can be done withcomputer simulation tools to create avirtual building and will enable you tocalculate all of the energy effectsincluding how one product can affectanother. For example, the amount bywhich improving the shading can reducethe need for cooling or whether toomuch shading could increase lighting costs.

The BBSA has developed a simple calculation system called Monergy Calculator9

so that you can get an indication of the effect that blinds and shutters can haveon the heating and cooling requirement of your building. This has beenconstructed using a simplified building energy model to predict energy, carbonand financial savings for a typical domestic dwelling and a typical office building.

To access to the Monergy calculation tool, follow the the link:www.monergy.org.uk

Although there isa value for the

blind without glass,this is not the way ablind is used. Thecorrect use shouldcombine the valuesof the glass and theblind resulting in agtot. This will give adifferent gtot figurefor every type ofglazing combination.

1802.13.1


To predict the energy performance of a building with and without solar shadingreference (typical) buildings are used. Within the Monergy calculation tool,many aspects are considered such as:

● Dimensions of the building● Occupancy schedules● Weather data● U-values of building components (roof, external and internal walls,

ground and internal floors and windows)● Transmission of heat loss● Ventilation heat loss● Solar gain● Internal gains● Utilisation factor● Gain utilisation factor for heating● Loss utilisation factor for cooling● Space heating requirement● Space cooling requirement● Day and night profiles during a complete year

The model takes the data from the outputs of the Shade Specifier database andapplies them to the reference glazing combinations from EN 13363-1 and EN14501.

A calculation tool for office buildings Textinergie® has also been developed bythe French Association of Blind and Shutter Manufacturers, SNFPSA. It can beseen at: www.textinergie.org

Standard Glazing U-value g-value

EN 14501 A. Clear single glass 5.8 0.85

EN 14501 B. Clear double glass 2.9 0.76

EN 14501 C. Heat control glazing 1.2 0.59

EN 14501 D. Solar control doubleglazing 1.1 0.32

EN 13363-1 Triple glazing 2 0.65

EN 13363-1 Double clear glazingwith low-emissivity 1.6 0.7

An holisticapproach to

energy shadingmeans solarshading should beconsidered at theplanning stage.


1902.13.1

APPENDIX E U-VALUE CALCULATIONS

U-value is a measure of thermal transmittance which is the ability of a materialto transfer heat. The U-value indicates the ability of a material to retain heat.This is particularly useful in winter.

Many components of a building have U-values for example masonry, insulationmaterials, plasterboard, metals and windows. It is expressed as Watts permetre square Celsius W/(m2 oC) or Watts per metre square Kelvin W/(m2K) forexample the U-value of a standard double glazed window is 2.9 W/(m2K).

Heat transfer through windows

Heat is transferred (lost) through a window by four main mechanisms:

1. Conduction – direct loss ofheat through the window tothe outside

2. Convection – heat lossthrough the warm room airreaching the colder surfaceof the glass

3. Radiation – the coldersurface of the glassabsorbing the infraredradiation and therefore heatfrom the room

4. Air leakage – heat lostthrough cracks in the frameor from around ill-fittingglass

Therefore the U-value that is needed is the value for the combination of glassand blind or shutter. There is a value for the blind fabric without glass but thatis not the way a blind is used. You need to know the performance when theproducts are combined and that will give a different figure depending on wherethe blind is fitted, internal, mid-pane or external. In addition, the type ofglazing - whether it is single, double, triple and which pane and on which side alow-e or other coating is applied will also affect the U-value.

Single glazing Doubleglazing

Solar controlglazing

GlassAlone

U=5.8W/(m2K)

U=2.9W/(m2K)

U=1.1W/(m2K)

Internalblindand

glass

High airpermeability 4 2.4 1

Average airpermeability 3.5 2.2 1

Low airpermeability 3.2 2.1 1

The U-value ofglazing is

always improvedwith shading.

U-value is ameasure of

thermaltransmittance whichis the ability of amaterial to transferheat. The U-valueindicates the abilityof a material toretain heat. This isparticularly useful inwinter.

Figure 6. Heat transfer through windows

2002.13.1


However, whatever the U-value of the glazing combination it will always beimproved with a blind or shutter as in the examples in Figure 7 which showsthat in all cases the U-value of glazing is improved reducing the amount of heatlost in cold weather. An example of an average air permeability blind would bean internal blind that has no openness factor and peripheral gaps of between20mm and 80mm between the blind and the window frame.

The example alsoshows that the effectof the blind or shutteris more pronouncedwhen it is combinedwith a window with lowenergy performancefor example singleglazing or firstgeneration doubleglazing. An internal

blind with average air permeability can reduce the heat loss through single glazing by almost 40%. The reason for needing to know the figures for a

combination of blind and glazing rather than just the blind is illustrated bythe same blind with solar control glazing which heat loss using a blind is less attypically 11% than the glass alone. That is still a significant improvement andas you would expect the total U-value of the solar control glass with a blind issignificantly better (lower U-value) than the single glazed system.

CIBSE Guide A10 quotes that a conventional roller blind (unsealed) would have aU-value of 2.53 W/(m²K) when installed on double glazing. If the same blindwas installed with a cassette, casing or channels on the same double glazingthen the U-value would be improved by 25% to 1.9W/(m²K).

A product such as an external insulated shutter which is fully sealed is likely togive a lower U-value and be more effective in reducing winter heat loss than aninternal solution.

EN standard 1312511 provides the methods and formulae for calculating valuesand for more information this is analysed in “Solar Shading for Low EnergyBuildings”12. U-Values for blinds combined with glass can be found on the ShadeSpecifier Database, see Appendix D.

APPENDIX F G-VALUE CALCULATIONS

The g-value, also called solar factor, is the total solar energy transmittancethrough a building element. It is the sum of the solar transmittance, Ts, and thesecondary internal heat transfer factor Qi. The latter term arising fromabsorption of solar radiation in the glazing and subsequent re-radiation atthermal wavelengths to both the outside and the inside of the enclosure. Thesymbol g is the solar factor of the glazing alone while gtot is the solar factor ofthe combination of a glazing and a solar protection device - see Figure 8.

0

1

2

3

4

5

U-v

alue

(W/m

2 K)

Shade with average permeabilityUnshaded

Single glazing Double glazing Solar controlglazing

The effect of theblind or shutter is

more pronouncedwhen the windowhas low energyperformance forexample singleglazing or firstgeneration doubleglazing.

Figure 7. U-value of blinds combined withdifferent types of glazing


2102.13.1

The g-value of glazing alone is determined by the calculation method given inEN 410. There are two methods for the calculation of the gtot of a blind andglass combination (also known as complex glazing) either a simplified methodgiven by EN 13363-1 or a detailed method given in EN 13363-2.

The simplified method is considered adequate for basic energy calculations andis the one used in the database described in Appendix D.

So why do we need these calculation methods? Surely if we know theperformance of a piece of glass and the performance of a piece of material if weadd the two together that will give the result? Unfortunately it does not workthat way. To have an accurate calculation, it is necessary to combine theproperties of the glazing with the blinds at the same time.

The reason is the solar radiation travels through the window and the blind(Figure 9). The sun’s rays are absorbed by objects and converted to heat. Thisheat cannot entirely pass back through the solid glass because most of the heatbecomes trapped between the two panes and some is absorbed by the panes ofglass. That heat is also transferred by convection and some is re-radiated backthrough the second pane into the room, some remains trapped and some isradiated through the first pane to the outside. Convection is when heattransfers from one hotter material to a colder one, that is for example if youtouch a hot kettle the heat flow from the hot kettle to your colder hand is byconvection (Figure 10).

That is why we need the database to calculate the way this energy is reflectedand transmitted. The simplified formulae for the calculations for external,internal and mid- pane blinds are specified in EN13363-1 and analysed in SolarShading for Low Energy Buildings13.

The g-value, alsocalled solar

factor, is the totalsolar energytransmittancethrough a buildingelement. The symbolg is the solar factorof the glazing alonewhile gtot is the solarfactor of thecombination of aglazing and a solarprotection device.

Figure 8. g-value

Figure 9. Solar energy properties

2202.13.1


Although there is a value for the blind without glass, this is not the way a blindis used. The correct use should combine the values of the glass and the blindresulting in a gtot. You need to know the performance when the products arecombined and that will give a different figure depending on where the blind isfitted, internal, mid-pane or external and what the combination of the glass issingle, double, triple and which pane and on which side a low-e or other coatingis applied. For each of the myriad of combinations the figure is different. It isnot a simple calculation which is why we need the database.

The industry standard for gtot comparisons is reference glazing C from EN 14501which is for double glazing with low-e glass as this is the minimum level ofglazing for a new build design.

APPENDIX G COMMERCIAL BUILDING SHADING COST BENEFITANALYSIS

Correctly specified blinds and shutters can significantly reduce the capital andenergy running costs of HVAC systems. Comparisons of HVAC, lighting, glazingand shading systems is not straightforward as the systems all interact with oneanother and a positive design benefit for one could be a negative for another.

Therefore an holistic approach is essential. It is precisely this holisticrequirement which means that solar shading should be considered at theplanning phase of a building or building refurbishment. Solar controlmanagement via blinds and shutters should be a building servicesconsideration.

Computer simulations carried out by REHVA and ES-SO considered a modeloffice under two different scenarios:

1. solar control glazing installed

2. low-e glazing and automated external venetian blinds installed (controlled bya seasonal programme)

The table below shows a comparison of the two model scenarios underAmsterdam’s climate conditions. The same models were carried out forStockholm and Madrid climate conditions. These cities also showed a paybackfor the capital cost of the solar shading of less than a year. The results forAmsterdam are demonstrated as this city has similar weather conditions to

The performanceof the blinds

products ismeasured incombination withglazing. That willgive a differentfigure depending onwhere the blind isfitted, internal, mid-pane or external andthe type of the glass-single, double,triple- and whichpane and on whichside a low-e or othercoating is applied. Itis not a simplecalculation which iswhy we need thedatabase.

Figure 10. Solar radiation travels through a window and interacts withdifferent layers


2302.13.1

parts of the UK. The other cities are in Solar Shading for Low EnergyBuildings14.

The data table shows that overall there is a zero payback period for the solarshading. This is because the investment required for the shading is lower thanthe investment for the advanced solar control glazing and HVAC costs. Thisdemonstrates that shading represents an investment rather than a cost. Asignificant benefit is achieved through a reduction in running costs (lighting,cooling and heating). In the Amsterdam model a reduction of 20% is seenbetween the office without shading and the office with window blinds installed15.

When a building has a glazing percentage, greater than 50-60% it requires noextra investment to install solar shading. This is because significant savings willbe achieved through reduced running costs from lighting, cooling and heatingand a smaller HVAC system can be specified saving additional capitalinvestment (Figure 11).

Amsterdam Solar control glazing Low-e glazing withsolar shading

Investmentcost Quantity Unit Cost

(¤) Quantity Unit Cost(¤)

Difference(¤)

HVAC 1490 W 1729 1053 W 1423 306Solar shading 6.48 m2 6.48 m2 626 -626

Glazing 6.48 m2 791 6.48 m2 441 350

Totalinvestment

2519 2490 30

Recurring costLighting 99 W 10 91 W 9 1Cooling 404 m2 20 292 m2 14 6

Heating 447 m2 22 372 m2 19 3

Totalrecurring/year

52 42

Simple payback period (years) 0

This graphshows theamount ofinvestmentrequired toinstall shadingcompared witha base case ofinvestment forHVAC and solarcontrol ofglazing.

Figure 11. Investment cost of shading compared to a HVAC

Based on the cost-benefit analysis

presented in thissection, blinds arepaid for by theenergy savings inless than a year.Blinds and shuttersshould then beconsidered as aninvestment ratherthan a cost.

2402.13.1


APPENDIX H COMPARISON OF ENERGY SAVINGTECHNOLOGIES FOR DOMESTIC BUILDINGS

There are many different technologies available to improve the energyefficiency and therefore reduce the annual energy bills of domestic buildings.This appendix concentrates on options that reduce the amount of heating ahome requires and compares energy saving rates of different domestictechnologies.

Technologies in this category include: loft insulation, cavity wall insulation,double glazing and blinds and shutters. All of these products will improve thethermal performance of a building by reducing the amount of heat lostthrough the building elements such as walls, roofs and windows. The EnergySaving Trust estimates that 18% of all heat loss is through windows 33%,through walls and 26% through the roof16.

The table below compares the installed cost, annual savings, payback periodand CO2 savings associated with a range of domestic heat loss reducingproducts. The values are all based on a three bedroom semi-detached housewith single glazing.

The graph below (Figure 12) shows the payback time for the initial productinvestment against the amount of money the product will save the householdon heating bills each year. The size of the circles represents the initial cost ofthe product with the larger the circle the higher the initial cost.

It is clear that low e-double glazing is the most expensive of the productsconsidered and therefore has the longest payback period. Loft insulation (0 -270mm) shows the shortest payback period, highest annual saving and hasa low initial cost.

Technology Saving/year(£)

Installed(£)

Payback(years)

CO2

savings/year(kg)

Roller blind 96 500 5 478

Cavity wallinsulation 140 500 4 560

Loft Insulation0-270mm 180 300 2 730

Loft Insulation100-270mm 25 300 12 110

Single glazing todouble glazing 170 2500 15 680

Blinds installed onsingle glazed

windows arecompetitive with theother domesticenergy savingproducts.

Source: Energy Saving Trust and British Blind and Shutters Association


2502.13.1

The graph also shows that blinds installed on single glazed windows arecompetitive with the other domestic energy saving products. The blinds have apayback time of 5 years and can save up to £96 per year on heating bills.

The graph in Figure 13 shows that glazing with blinds has a lower U-value thanthe window alone for both single and double glazing. As the U-value is themeasure that represents the heat losses through materials, for instancewindows, the lower the value, the lower the heat loss. Therefore, in all casesblinds improve the insulation properties of glazing.

APPENDIX I SUMMER SOLAR GAIN

Traditionally air conditioning has not been used in domestic buildings that havetended to have smaller glazed areas than commercial properties and there hasbeen more tolerance of excessive heat. The development of large glazed areasin the conservatory market has created areas where the heat gains areintolerable without shading with blinds. The use of fans or introduction ofcooling is the least energy efficient option and, as with commercial buildings,the use of shading with blinds and shutters should be the first consideration.

In addition, the regulatory requirement for energy efficiency and nearly zerocarbon emission buildings has resulted in a drive for more highly insulated andairtight dwellings, in both new build and retrofit. Highly insulated and airtight

Loft insulation0-270 mm

Cavity wallinsulation

Roller Blind

Single glazingin double

Loft insulation100-270 mm

Payback (years)

2 4 6 10 12 14 16 180

50

100

150

200

Sav

ing

/ye

ar (

£/

y)

8

Figure 12. Comparison of different energy efficient measures

U-value (W/m2K)

0 2 4 6

Glass and blind

Glass alone

Single glazing

Double glazing

8

2.1

2.9

3.5

5.8

Fig 13. Glazing and shading=better insulation

The developmentof large glazed

areas in theconservatory markethas created areaswhere the heat gainsare intolerablewithout shading withblinds.

“Overheating maybecome an issuewhere crossventilation is notachievable inlightweight, airtighthouses with little orno solar shading”NHBC Foundation

2602.13.1


low and zero carbon homes, oftendesigned with large areas of glazing,mechanical ventilation and/orcommunal heating systems have thepotential to overheat throughout theyear, not just in the summer monthsor in heatwaves.

In rural and suburban locations itmay be easy to use naturalventilation (e.g. window opening) tohelp cool dwellings, but in urban anddeep-urban locations it is often notpossible to do this. Thus, overheating

may become an issue where cross ventilation is not achievable in lightweight,airtight houses with little or no solar shading17.

For effective energy savings, blinds and shutters have to be always combinedwith glazing and considered at the building design stage. If shading is notconsidered when the area and type of glazing are decided it is likely that thebuilding will require a larger than necessary heating and cooling system.

APPENDIX J TYPES OF AUTOMATED CONTROL

The benefits of a solar shading system in terms of energy savings, improvedindoor and visual comfort and the best use of natural daylight can only be fullyrealised if the system is automatically controlled. It will then work optimallyeven when the occupant is absent reacting to the climatic conditions withoutrequiring any attention which is important to maximise the energy savingbenefits. A study by the Building Research Establishment18 showed thatautomatically controlled shading will give an extra 3% of total building CO2

savings compared with manual or fixed shading systems.

Automated solar shading can operate on timers and with light and heat sensorsthat ensure the shading is operating in themost energy efficient way.

There are control systems to suit singleblinds, groups of blinds or whole buildingmanagement systems. Yet even basic “plugand play” single blind systems have energy-smart functions. Whilst the inputs such aswind, temperature or timer controls aresimple their settings will ensure that theshading is in place to control heat loss andgain.

For multiple windows there are twosolutions. Basic systems can be expandedto enable multiple controls as a stand-alone solution or there are systemsthat link into the building management controls.

The stand-alone is a cost effective solution for domestic or smaller commercialinstallations where all of the control functions are available except for aninterface with other building control functions.

All of the systems require sensors that will track the actual climatic conditionsaround the building. The most frequently used sensors are wind, outdoor

Keep it simplewhen designing

automated systems

All of the systemsrequire sensors

that will track theactual climaticconditions aroundthe building. Themost frequentlyused sensors arewind, outdoortemperature, rain,indoor temperatureand occupancydetector.


2702.13.1

temperature, rain, indoortemperature and occupancydetector.

Simple interfaces are available saywith the fire alarm but to maximiseenergy efficiency an holisticapproach to control is essential bylinking all of the building servicesco-ordinating lighting, heating,cooling and shading (Figure 14).That is why Home Automation fordomestic dwellings and BMS(Building Management System) forcommercial properties that functionwith a “bus” system. A bus is anetwork where all devices are attached directly to a line and all signals passthrough all of the devices.

Each device has a unique identity and can recognise those signals that areintended for it. The market offers arange of solutions but the most commonare KNX and LON, all of these are basedon an “open” data transfer language thatis non-proprietary and allows differentsuppliers to connect to the “bus”.

This allows the user to create a controlstrategy for the priorities of theirparticular requirements. The possibilitiesare almost limitless but early contactbetween the system designer and thesupplier of the shading system isessential so that the full benefits can bereaped. Today, computer technology andadvanced software offer vast possibilitiesto interconnect systems in a building.

However, that does not necessarily mean better energy efficiency or usersatisfaction. It is easy to make the daily use of the system more complicatedthan needed19.

Before designing a system it is recommended that basic questions areconsidered:

1) What functions do we really need?2) Why do we need them?3) How would we use them?4) Will it meet the needs of the user?5) Will it assist with building regulation compliance?

A building services engineer and solar shading consultant will be helpful while agood dose of common sense may be of assistance.

A carefullydesignedautomatic

control allow tomanage glare,personal settings,energy use as wellas the interactionbetween solarshading, lighting,heating, ventilatingand cooling.

2802.13.1


A BRE studyshowed that

automaticallycontrolled shadingwill provide anextra 3% of CO2savings comparedto fixed shadingsystems.

Figure 14. Automated systems


2902.13.1

APPENDIX K FUEL POVERTY AND ENERGY EFFICIENT SHADING

According to the paper “Adapting of Refrigeration Thinking for Survival in aRapidly Changing World”20 written by Professor Susan Roaf and presented atthe International Congress of Refrigeration 2011, issues of social equity mustdrive change as it becomes evident that solutions that are affordable only for aminority may cause market instability and financial crisis. This paper suggeststhrough a series of case studies that one way of adding value to a product is toapply a “whole system thinking” approach by: spreading the contextualboundaries of their operation, addressing a broader group of stakeholders at thedesign stage, and using design to extract more from less meaning a moreeffective system and fit for purpose in the building sector.

She highlighted that in a case study of Arizona in April 2007, it showed that anincrease of fuel prices to more than double (from $65 to $147) affected a hugeamount of Americans living a standard lifestyle. For instance, if they had to payaround $70,000 a year for mortgages, health, insurance, food, energy, creditcard bills among other expenses, with the increase in energy prices the annualincome required jumped to $90,000.

Arizona was a state dominated byhouse developers who not onlyincreased square feet per house from1,500 to 4,000, but also did notinclude any insulation or shading in ahot desert climate. This meant ahigher demand for cooling and as aconsequence higher costs. At the sametime, people needed to drive and copewith that higher cost of energy, so themortgage was the first thing that wasnot paid. At the beginning, this onlyaffected the poor but then the effectincreased up the social scale and thenaffected other states and finally led toa global financial crisis.

This case study demonstrates that if only house developers had built smallerhomes with thermal storage and insulation, shading, solar hot water systems,smaller air conditioning systems with cleaner refrigerants and somephotovoltaics, then people would have been able to cool their houses moreefficiently and pay their mortgages. Thus, the solution according to Susan Roafis to rethink the whole system and build a better network between HVACmanufacturers and house builders to produce low carbon, energy secure homesthat cost the same overall but represent a paradigm shift for the industry. Quitesimply, an holistic approach to building services design that must includeshading.

In summary, could energy efficient shading have prevented the global financialcrisis? Obviously not, but its omission may have contributed to the cause of theproblem. As the case study above shows fuel poverty was the trigger thatstarted it and inadequate attention to the need for shading was one of theissues. As traditional energy sources deplete and the costs escalate the need toreduce the need for power is as necessary today in the UK as it was then inArizona.

“The solution is torethink the wholesystem and build abetter networkbetween refrigerantmanufacturers andhouse builders toproduce a lowcarbon, energysecure homes thatcost the sameoverall but representa paradigm shift forthe industry.”Prof Susan Roaf

3002.13.1


APPENDIX L PRODUCTIVITY & INTERNAL ENVIRONMENT

A good quality internal environment typically has a positive effect onproductivity. It is widely acknowledged that the visual and thermal comfort ofan internal environment will affect people’s relative comfort and therefore howthey work within it. This can be true in schools, offices, factories and any otherbuilding where the efforts of the employees can be affected by anuncomfortable working environment21. Research from the University ofCalifornia in Los Angeles found that employees of companies voluntarilyadopting environmental practices and standards are 16% more productive thanthe average worker22.

Thermal Comfort

Working in a comfortable temperature in a building can have a significantimpact on employee productivity. However, building designers often do notconsider thermal comfort as a priority and believe that it is more important toreduce construction and operating costs. But when the whole lifetime of abuilding is assessed it is clear that employee’s salaries and associated costs aresignificantly higher than building operating costs.

The flow chart below (Figure 15) shows that 80% of the total operating cost ofa building is used for salary and employee related costs. Increases inproductivity will reduce the costs in this section due to increased efficiency andalso reduced absenteeism.

If productivity is increased by 1% in an organisation this equates to 0.8% of thetotal operating expense. This 0.8% is more than the total cost of energy for theorganisation which is typically between 0.3-0.6% of the total costs.

This shows that relatively minor productivity increases have a large economicimpact and provide a valid case for organisations to invest in improving the

Total Operating Expense100%

Salary & EmployeeRelated Cost

80%

MiscellaneousCosts10%

Building RelatedCosts10%

Operation &Maintenance

3%

ConstructionCost7%

Energy0.3 - 0.6%

Electricity0.2 - 0.4%

Heating0.1 - 0.2%

Relatively minorincreases in

productivity canhave a largeeconomic impact.

Figure 15. Total operating cost in an organisation


3102.13.1

quality of their indoor environments23. Issues associated with incorrect indoorthermal conditions in a workplace include:

● High indoor temperatures increasing the prevalence of sick buildingsyndrome, symptoms of which include sensory irritations of eyes, noseand throat; neurotoxic and general health problems24.

● High temperatures in classrooms which are harmful to performance ofschool work. In a controlled Danish study the performance of schooltasks was found to be better at 20oC than 25oC25 and declines astemperature rises.

● Lower temperatures reduce the dexterity of hands and may affect theperformance of manual tasks26.

This graph shows theoptimum temperaturerange for productivity foroffice based work. Itshows that the idealrange is between 20-24oC27. Above and belowthese temperatures thereis a sharp drop inproductivity as peoplebecome too hot or cold,uncomfortable and find itdifficult to concentrate28

(Figure 16)

Productivity drops by more than 1% for every degree that the temperature isoutside of the optimum range. The impact of this fall in productivity will besignificant to the organisation. The costs of an effective solar shading system tohelp prevent such drops in productivity through temperature variation istypically a fraction of the lost productivity cost.

The example in the table below shows potential productivity losses for anaverage office worker can be as much as £10 per day if the temperature is just7 degrees above the optimum.

That offers a different perspective on the seemingly capital expensive option ofexternal shading for building control coupled with internal shading for usercontrol. The capital payback is quick and the ongoing running costs for coolingare negligible. Where internal shading is the only option the payback on the

“Windows shall befitted with asuitable system ofadjustable coveringto attenuate thedaylight that fallson theworkstation.”The Health &Safety (DisplayScreen EquipmentRegulations) 1992.

Unshadedwindows could

be costing as muchas £20 per day inlost productivity forevery window.

Figure 16. Optimum temperature range forproductivity level

No.Windows

No.Employees Temp

Lostproductivity

(day)

Lostproductivity

(year)

1 2 26° £6 £1,500

1 2 28° £11 £2,750

1 2 30° £17 £4,250

4 8 30° £80 £17,000

3202.13.1


additional investment in the most effective shading instead of the basic isquickly recovered. The added value of a comfortable workforce is a bonus.

Visual Comfort

People prefer natural daylight to artificial lighting in buildings. It is clear thatvisual contact with the outside world affects people’s state of mind and it isproven that it will increase productivity as people will feel happier29. Bymaximising the use of daylight without glare and providing daylight responsivelighting control a productivity benefit of 3.75% was found in a workplace30.Adjustable shading to reflect and direct natural light will also have a significanteffect in improving visual comfort and reducing lighting costs.

Solar Shading and the Impact of Productivity

Solar shading can provide a cost-effective and simple solution to improvingindoor thermal and visual comfort. Through blocking solar radiation externaland internal blinds can reduce the build up of heat gains within a building,thereby increasing comfort and productivity for the occupants and reducing theneed for air-conditioning. Blinds and shutters will also help to reduce heat lossin the winter.

Shading can also reduce glare in buildings. Correctly specified and operatedblinds and shutters provide the user with the ability to reduce glare, control theamount of natural light and solar gain entering a building.

APPENDIX M DOUBLE SKINNED FAÇADES (DSF)

What is a double skinned façade?

A double skin system consists of an external glazing, a ventilated cavity and aninternal glazing. There are two types:

1. Naturally ventilated façades, composed of an external single layer ofglass and an internal double glazing unit. The cavity between the twoskins is naturally ventilated with outdoor air, which comes up throughthe base of the glazing and returns to the outside at the top.

2. Mechanically ventilated façades, composed of an external insulatingglazing unit and an internal single layer of glass. The cavity betweenthe two skins is ventilated with return room air which is extracted fromthe room at the base of the glazing and returned to the air-handlingunit at the top31.

What are the issues with a normally glazed façade?

The main issues that can be overcome with a shaded DSF:

● Excessive heating demand during the winter● Overheating of the building and/or high cooling requirements during the

summer● A difference in surface temperature of external walls results in

discomfort for the occupant placed near the façade i.e. draughts andasymmetric radiation.

● Compliance with the 2010 Building Regulations for England and Waleswhich set a Target Emissions Rate which must be achieved for buildings

Blinds in DoubleSkinned façades

resolve the issue ofinterruption of theexternal appearanceof the clean glazinglines and removesany weatherprotection concerns.

Blinds andshutters will not

only improve thequality of an indoorenvironment andthereforeproductivity but theywill also reduce theenergy costs of anorganisation throughreduced heating andcooling requirementand reduced use ofartificial lighting.


3302.13.1

to comply. In Part L of the regulations Criterion 3 contains guidance forbuildings to limit the effects of solar gains in summer32.

What is the importance of Shading in a Double Skinned Façade?

Glass is a static element in a building. Static against the dynamics of theweather, particularly in the UK, and static in the face of dynamic buildingloading and use, as the number and needs of the people inside will changeconstantly.

Shading is an established technology that is not normally associated withenergy efficiency and its benefits generally are not fully appreciated. gtot figuresfor shading between the façade are improved by the natural ventilation withinthe façade. That enables fully glazed areas that would not otherwise beachievable within the requirements of the regulations with systems typicallyrejecting better than 88% of the solar gain.

The Proof of the Shading in a Double Skinned Façade (DSF)

The REHVA Guidebook How to integrate solar shading in sustainable buildings33

shows that when the correct ventilation strategy is used, a blind placed betweenthe outer and inner glazing of a DSF will have a similar effect in solar energyreduction as an external blind. This resolves the issue of interruption of theexternal appearance of the clean glazing lines and removes any weatherprotection concerns therefore enabling the shading systems to be fullyfunctional throughout the year.

The graph below shows that a DSF with integral blinds has almost the same netcooling demand as a standard façade with an external shading system. It alsoillustrates that a traditional façade with a standard internal blind typically has amuch higher cooling demand. However, whilst the DSF shading providesbuilding control the addition of an internal blind for user control would reducethe cooling demand still further.

In summary, some of the benefits of integrating blinds into DSF are:

● Allows large full height glazing to be used● Reduces energy consumption by helping to control heat gain in the

summer and heat loss in the winter● Makes a static element dynamic● Improves the internal environment leading to higher productivity● Allows for natural light to be harvested but glare controlled● Improves acoustic properties● Assists with building regulation compliance

Figure 17. Double Skinned Façades

0 10 20 30

Traditional cladding with exteriorshading device

40

17.8

19.8

39.2

50

Annual net cooling demand (kWh/m2a)

DSF natural ventilation andintegral shading

Traditional cladding with interiorshading device

A double skinsystem consists

of an externalglazing, a ventilatedcavity and aninternal glazing.Overheating andexcessive lighttransmittance can beovercome by shadeddouble skinnedfaçades.

3402.13.1


APPENDIX N CONTROL OF LIGHT

Solar control management by blinds and shutters can harvest natural lightwhich can help reduce the use of artificial lighting. This is one of the biggestuses of electricity in commercial buildings. In a typical office building 30-40% ofelectric energy is spent on lighting34.

Blinds and shutters are important enablers of daylight as they regulate the flowof both direct solar radiation and diffuse radiation. The illuminance, or whatmost commonly call brightness is measured in lux. Illuminance levels by directsunlight in summer are as high as 100,000 lux. For a general office environment(tasks such as computer work, writing, drawing) a recommended lux level is500. Direct sunlight can cause glare. Thus attenuating and diffusing theincoming light reduces the chances of glare and brings light deeper into thespace. This function is performed especially well by internal blinds35.

Lux can be measured by a Luxometer which quantifies only Visible Light (Tv).They are typically deployed within the room/building or more frequently severalbeing deployed within the same room to assess different light levels in thevarious parts of the room.

Some important factors that impact on the quantity of light are Visible LightTransmittance (Tvis) and Openness Coefficient (CO). The Visible LightTransmittance determines the total amount of brightness and glare that willpass through the fabric of the blind. The openness coefficient is the ratiobetween the area of opening in the fabric and the total area of the fabric. This isrelated to the number and size of the holes in the fabric. Therefore theopenness coefficient is an indicator of the amount of visible light transmittanceand of the degree of visibility through a fabric. Both factors are typicallyexpressed as a percentage.

When a blind has a lower openness coefficient there is typically less visible lighttransmittance and therefore glare is reduced when the blind is closed. As theopenness value increases so does the possibility of glare, however daylightlevels and through vision are increased. But reducing the openness coefficientof a fabric does not necessarily mean that the light entering through the fabricis the level required for all ocuppants.

Colour is another factor to consider when selecting for light control. Lightercolours are more reflective with lower heat gains and higher visual lighttransmistance, illuminating the interior but surface brightness can be too muchfor visual comfort. Darker colours provide a better outside view and glare freeenvironments making them more ideal for viewing computer and TV screens butabsorb more light and thus heat.

It is often assumed that light can be separated from heat in the context of solarradiation. This creates the illusion that you can have light without heat. This isincorrect, light is latent heat. Visible light (shortwave) that enters the room andis neither reflected out nor transmitted through will be absorbed and then re-radiated as (longwave) heat.

Appendix A showed that the visible light figure is calculated the part of the solarspectrum that is light (250-780 nanometers) is used. When heat gain iscalculated it includes the part of the spectrum that is light (250-2,500nm) aswell as the part that is heat. That is because light that is not reflected willbecome heat when it reaches a surface.

Solar controlmanagement by

blinds and shutterscan harvest naturallight which can helpreduce the use ofartificial lighting.


3502.13.1

Part L of the Building Regulations places emphasis on the control of light andconserve energy use. It is stated that to limit solar gains attention should bepaid to the provision of adequate levels of daylight. Although there is not anspecific minimum requirement of daylight, reducing windows areas can increasethe use of artificial light. Thus, suitable solar shading is needed to control thenatural light entering into the buildings.

Blinds andshutters are

important enablersof daylight as theyregulate the flow ofboth direct solarradiation anddiffuse radiation.

3602.13.1


4.0 STANDARDS

● EN 410 – Glass in buildings. Determination of luminous and solar characteristics of glazing

● EN13125:2001 Shutters and blinds – additional thermal resistance- allocation of a class ofair permeability to a product.

● EN 13363-1 – Solar protection devices combined with glazing. Calculation of solar and lighttransmittance. Simplified method.

● EN 13363-2 – Solar protection devices combined with glazing. Calculation of solar and lighttransmittance. Detailed calculation method.

● EN 13125 - Shutters and blinds - Additional thermal resistance - Allocation of a class of airpermeability to a product

● EN13561 External blinds - Performance requirements including safety

● EN13659 Shutters – Performance requirements including safety

● EN 14500 - Blinds and shutters - Thermal and visual comfort - Test and calculationmethods

● EN 14501 - Blinds and shutters - Thermal and visual comfort - Performance characteristicsand classification

5.0 REFERENCES1 Windows Database: http://www.windat.org/2 British Blind and Shutter Association, Shade Specifier Database, 20083 REHVA Guidebook No 12 “Solar Shading – How to integrate solar shading in sustainable buildings”, 2012, www.rehva.euPp. 41 or refer to the Fraunhofer Institute: http://www.fraunhofer.de/de/en.html4 UK Green Building Council, Key Statistic, 2008, http://www.ukgbc.org/content/key-statistics-05 Pout C.H, MacKenzie F and Bettle R, Carbon dioxide emissions from nondomestic buildings: 2000 and beyond: BR442. CRC Ltd,London, 20026 Heiselberg Per, Ventilative Cooling track, Rehva Journal, 2013, p.97 Rehva Guidebook No 12, op. Cit.8 European Solar-Shading Organisation (ES-SO), Solar Shading or Low Energy Buildings, www.es-so.com9 British Blind and Shutter Association, Blind and Shutter Monergy - Energy Saving Calculator, 201310 CIBSE Guide A – Environmental Design11 EN13125:2001 Shutters and blinds – additional thermal resistance- allocation of a class of air permeability to a product.12 European Solar-Shading Organisation (ES-SO), opc. Cit.13 European Solar-Shading Organisation (ES-SO), opc. Cit.14 European Solar-Shading Organisation (ES-SO), opc. Cit.15 Rehva Guidebook No 12, op. Cit., Pp. 3916 Energy Saving Trust, Our calculations, http://www.energysavingtrust.org.uk/Energy-Saving-Trust/Our-calculations#insulation17 NHBC Foundation, Overheating in new homes, 201218 Littlefair Paul, Ortiz Jose and Das Bhaumic Claire, The Energy Effects of Controlling Solar Shading, BRE, Somfy.19 Rehva Guidebook No 12, op. Cit., Pp. 46-5320 Roof Susan, “Adapting of Refrigeration Thinking for Survival in a Rapidly Changing Worlds” in International Congress ofRefrigeration, 201121 Heshcong L., Windows and Offices: A study of office worker performance and the indoor environment. Report prepared for theCalifornia Energy Commission, 2003a.22 Heschong L.,Windows and Classrooms: A Study of Student Performance and the indoor environment. Report prepared for theCalifornian Energy Commission, 2003b.23 Rehva guidebook No 6 “Indoor Climate and Productivity in Offices”24 Wargocki P. and Wyon D. The performance of schoolwork by children is affected by classroom air quality and temperature.Proceedings of Healthy Buildings Congress 2006a, Lisbon Portugal.25 Wargocki P. and Wyon D., Research report on effects of HVAC on student performance. ASHRAE journal 2006b 48: pp 22-2826 Rehva Guidebook No 12, op. Cit.27 Seppanen O. and Fisk W., Some quantitative relations between indoor environmental quality and work performance or health.ASHRAE Research journal V12 No 4, 2006a28 Seppanen O. and Fisk W. and Lei Q.H., Room temperature and productivity in office work. Proceedings of Healthy BuildingCongress 2006b. Lisbon, Portugal. Vol 1, 2006, pp 243-24729 Heshcong L., 2003a, op. Cit.30 CMU, Guidelines for High Performance Buildings, 2004http://www.bristolite.com/interfaces/media/Carenegie%20Mellon%20University%20Daylighting%20Study%202004.pdf31 Rehva Guidebook No 12, op. Cit., Pp. 5732 Rehva Guidebook No 12, op. Cit., Pp. 5833 Rehva Guidebook No 12, op. Cit., Pp. 5934 Wargocki P., 2006a Op. Cit.35 Rehva Guidebook No 12, op. Cit., Pp. 14-15

6.0 PHOTOGRAPH CREDITS

The product photographs used in this publication have been reprinted with kind permission fromBBSA members:Decora Blind Systems, Deans Blinds & Awnings, Eclipse Blind Systems, Flamingo Blinds & Fabrics,Louvolite, Luxaflex, Pentel Contracts Ltd, James Robertshaw & Son (1954) and Torbay Blinds.


3702.13.1

7.0 GLOSSARY

Air permeabilityThe unintended leakage of air through gaps and cracks in the external envelope of a building.

ConductionThe transfer of heat between substances that are in direct contact with each other.

ConvectionIt is the transfer of the heat in fluid or air, caused by the movement of the heated air of fluid itself.In a building escape, warm air rises and cold air settles to create a convection loop

GlareThe conduction of vision in which there is discomfort or a reduction in the ability to see significantobjects, due to an unusable distribution or range of luminance.

Nanometers (nm)Measurement of the sun’s wave length.

Solar GainIt refers to the solar radiation that enters to the building through the glazing and hits objectsconverting it to heat. This reduces the need to artificially heat the space.

RadiationEmission or transfer of energy in the form of electromagnetic waves or particles transferring energyfrom a warm body to a cold body without heating the air in between.

g-valueThe measure of the total energy passing through the glazing when exposed to solar radiation.

gtot

The measure of the total energy transmittance of the glazing in combination with the blind whenexposed to solar radiation. It is also called Solar Factor.

LuxThe amount of illumination on a surface.

Light Transmittance (Tv)The fraction of visible light transmitted through the shading material.

Natural VentilationThe supply of adequate fresh air to spaced within a home through windows , trickle ventilators etc.Removal of air may take place by natural or mechanical means.

Solar gainsThe build up of heat within a building from direct sunlight.

Solar Transmittance (Ts)

This gives the fraction of the solar energy transmitted through the fabric. A low value means thatthe fabric performs well at reducing solar energy transmission.

Solar Reflectance (Rs)The fraction of solar energy reflected by the fabric. A high value means that the fabric performs wellat reflecting solar energy.

Shading Coefficient (SC)Ratio of solar gain passing through a window unit (gtot) to the solar energy which passes through3mm float glass (0.87). Expressed as a value between 0 and 1.

Shading Factor (Fc)This is the ratio of solar factor of the combined glazing and solar shade (gtot) to that of the glazingalone.

Qi

It results from heat transfer by convection and longwave infra-red radiation of that part of theincident solar radiation which has been absorbed by the glazing. It is the absorbed heat that will notgo back through the glass.

3802.13.1


Whilst every care has been taken in the production of this Guide to Low Energy Shading, the BBSAand its contributors cannot be held responsible for any errors or omissions. This guide will be

subject to regular updates. To ensure you have the current version see www.shadespecifier.org.uk

Standard Assessment Procedure (SAP)A software that calculates the energy performance of dwellings. It has been developed by theBuilding Research Establishment (BRE) for the Department of Energy and Climate Chance (DECC).SAP assess the cost per year to provide a home with heating, lighting and hot water and presentsthe cost per square metre of floor area.

Simplified Building Energy Model (SBEM)A software that calculated the energy performance of buildings that are not dwellings. It wasdeveloped by the Building Research Establishment (BRE) for the Department of Communities andLocal Government (DCLG). SBEM estimated the amount of CO2 emissions produced by the buildingper square metre of floor rather than the cost.

U-valueA measure of thermal transmittance which is the ability of a material to transfer heat.


3902.13.1

4002.13.1


© British Blind and Shutter Association, 2013. All rights reserved. No part of this publication may be reproduced in any formwithout the express written permission on the British Blind and Shutter Association.

BBSA, PO Box 232, Stowmarket, Suffolk, IP14 9AR - [email protected] www.bbsa.org.uk

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