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The main energy consumption in the UK is not from cars or from planes. 40% of our energy use is for buildings mainly for heating and cooling. Efficient use of sunscreening can reduce that amount considerably.

The Shade Specifier project developed by our Trade Association, BBSA, shows that efficient solar shading can reduce consumption by over 15% where air conditioning is used and up to 10% in domestic buildings. Even a  saving of just 5% would reduce total UK energy consumption by 2%. If we could achieve that it would contribute significantly to the Governments target of 20% cut in energy use by 2020.

This is not just an issue that can be solved by incorporating into new buildings. It is estimated that in Europe we replace little more than 1% of our housing stock annually and less than 2% of our commercial buildings so it would take nearly 100 years unless we attend to existing buildings.

Clearly where a BMS system is provided the solar shading should be included and it will ensure that it performs to the optimum level. It can monitor the building requirements and react to changing climate conditions.

It can also be programmed to provide different levels of control around a building. Not only can it follow the sun path it can also allow individual override. But it could be very "Big Brother" if the needs of the users start to affect the minimum levels of control and other areas need to have closed blinds to compensate.

Fanciful - maybe but the needs of the user must not be overlooked in any control system.

Blinds that start to operate during a presentation just at the time when the MD reaches the punch line will not be appreciated.

Overrides are essential if the system is to be accepted by the user but the balance of how this is achieved and the effect that it will have on the system is the key to control design. 

Allow in the design for figures that are slightly less than optimum performance. Local isolation from auto control with reversion to auto at the end of the day will ensure that only those areas where the user has a problem will be outside of the BMS control. In reality how likely is it that more than 5% of the users will consciously opt out? Even if they do it is likely that they will manually adjust to the shading position.

Education is vital - a clear understanding of the reasons for the automatic shading will ensure its acceptance and mitigate some of the “control” effect.

Do not forget that the most important consideration in all control systems needs to be the User.

Whilst the range of options is extensive orientation of the building can influence the selection.

On south elevations, horizontal blinds are the most effective; vertical drop roller blinds and projecting awnings are also perfectly suited. On east and west elevations vertical louvres can be adjusted to the angle of sun, yet still allow outward vision. External roller blinds with a mesh material also allow visual perception of the outside. Horizontal Venetian blinds can be adjusted to maintain light levels.

Projecting external fixed louvres will intercept high angle sun but should be combined with an internal blind to control low angle sun and low intensity gain. They will also allow heating from low angle winter solar gain. They are most appropriate for south elevations.

Vertical drop blinds are more effective on east/west elevations than projecting awnings or brise soleil. 

It is unlikely that any one system will satisfy all of the needs for screening a window. A combination of external shading for primary heat reduction and internal blinds for privacy, light and secondary heat gain control is almost certainly the most cost effective solution available to the designer.


Comfort, privacy, ventilation and light control – Naturally.

Check list of requirements for blinds.

It may seem an obvious question, but apart from shading the window and looking good what do you expect the blinds on your project to achieve?

Building Control

Control of solar gain

Light level control

Interface with building or home management system

Master override of automated system and wind override

Shading when area is unoccupied

Automatic control of primary heat gain

Night heat retention

Minimal reduction of light levels on dull days

Good natural light levels

Light shelf to diffuse and spread light

Heating benefit from low angle winter sun

Control of energy costs

Art gallery lux level control

Security

User control

Glare control for visual comfort

VDU screen glare control

Ease of operation

Visual perception, allowing external vision

Privacy during daylight

Privacy during night time

Manual override of automatic control

Regulations and Standards

Compliance with the Building Regulations and SAP Codes

Local authority planning

Energy Performance and Energy Audits

Aesthetics

Co-ordination with the decoration

Same solution for every elevation

Symmetry of appearance of external shading

Internal symmetry

Decorative feature

Preventing UV fading of furniture and decoration

Building Lifecycle Costs

Manageable maintenance costs

Long design life

Other functions and needs

Blackout

Dim out for film projection

External shaded area for sitting under

Rooflight shading

Advertising sign

Flame retardant materials

Blinds can perform many functions. This list is intended to help you to identify the issues rather than direct you to specific options. It is unlikely that a single product will achieve every requirement and for many situations two shading systems may be required. So prioritise your needs and check them against the products that you have selected.

At Hallmark we believe that energy saving is not a matter of green credentials or saving the planet although that may well be the result. It is common sense economics, for as energy costs rise, any effective means of reducing cooling costs should be assessed.

We hope that we have highlighted some of the issues for you to consider. It is our belief that efficient shading should be used to complement rather than dominate design.

However our ideal solution is clearly not appropriate to all design and whilst natural ventilation may be appropriate for some buildings we believe that the main function of shading should be to reduce cooling loads, rather than replacing air-conditioning. With glass we believe that sensible shading solutions can enhance rather than reduce the glazing. The latest amendments to the building regulations do not mean the end of the fully glazed building if shading is incorporated in facade design.

In the UK we have a cultural issue, we do not believe that the sun is a problem – the market for external screening is far larger in cooler Scandinavia than here – but clearly that will begin to change.

Finally do not forget the requirements of the user and also their need to understand the reasons for the shading system and its benefits. Systems will only work if used as designed.

Holistic design of glazing, shading, lighting and controls is essential.

Energy savings demonstrated by Building Modelling software

Computer simulation programmes have now advanced so that it is now possible to predict the operational cost of a building before construction commences. Using a simulation programme enables the designer or services engineer to predict the energy savings that can be achieved with effective shading.

With a culture in the UK of assuming that shading is a decorative feature the extent of those savings is not widely appreciated. They can be substantial.

Working with IES one of the leading modelling companies in building performance software our trade association BBSA has simulated comparative figures on a typical commercial and a typical domestic building with different shading combinations. The Shade Specifier programme shows the savings in terms of cost and emissions as the following example of an output screen.

The programme does not just calculate the benefits of shading alone it shows the results from within a virtual environment of the effect of shading when combined with other building elements such as lighting and cooling systems. It also demonstrates the effect on glare of the various options (visual comfort) and can show temperature (thermal comfort). The inputs, shown below, allow changes to location, building type and orientation as well as glass and blind types. However, the vast number of permutations of the different combinations means that it is not possible to demonstrate more than representative examples.

This does though give a very clear indication of savings as although your building may not be the same size or have the same area of glazing the results will be in proportion.

The programme in its present form is available for use within our industry and is continuing in its development. In particular an independently verified database of the performance figures of manufacturer’s materials will be available in January 2010 by the BBSA to coincide with the launch of the project to the wider market. We would be pleased to demonstrate the programme in the meantime.

Glare Control

Glare is defined as “the condition of vision in which there is discomfort or a reduction in the ability to see significant objects, or both, due to an unsuitable distribution or range of luminance”.

To minimize glare the light has to be diffused or spread. To diffuse is to spread the light source so that an even light is produced. If the light intensity is too high it needs to be reduced.

The function of the window blind is to spread and reflect the light to produce an even broad light source. That is rather than a direct beam from the sun or say a light bulb.

If a light source (a bulb) is more noticeable than the objects that it is illuminating then the source is producing glare. Diffusers are used to minimise glare so less light is needed to see well (thus saving energy in the process). We always see better in the absence of glare. Window blinds are diffusers of light from the sun.

Glare can be a cause of eye strain among computer users and the need to provide window coverings to protect them from screen glare is a requirement of the Health and Safety Display Screen Equipment Regulations 1996. Control of glare is also a comfort requirement of EU standard 14500 that identifies 2 levels of control. One is protection for occupier visual comfort (you can see clearly without being affected by direct sunlight in your eyes) and the higher level of control is for screen glare. A more detailed explanation can be found in the guidance note below.

What measure should I look for when specifying a blind to control glare?

An adjustable solid horizontal louvre blind can be adjusted to enable the correct level of light.

For a fabric blind the amount of transmitted visible light Tv is the figure not the openness factor (Of). That is the measure of the actual percentage of transmitted light and needs to be 0.05 or less. Darker colours are more effective than light ones and a white material needs to be very dense to be suitable and a mesh of 1% openness is unlikely to be lower than 0.08.

A darker colour though will not be as effective for heat rejection and a really dense or blackout material could increase the need for lighting or make the environment oppressive thus reducing productivity. A very careful balance is needed and two fabrics may be needed to cater for all needs.

There are many expressions that are used in describing shading that sound similar and it is essential for comparison that the right figure is used. The development of the more exacting definitions in European Standards has added to the problem. The following are a selection of the most common.

Energy labelling 

Introduced to conform to an EU directive on the Energy Performance of Buildings, it requires public and private commercial buildings over 1000m sq to be rated for energy efficiency and be assessed for an energy performance certificate. The intention is for buildings over 250m sq to be included by 2016.

Energy Performance Certificate

When energy labelling is enacted, certificates must be available to prospective purchasers or tenants of commercial buildings. They must show reference values and a carbon dioxide indicator. They might also include an asset and an operational rating, which would show how efficiently a property is being managed.

Fr factor

This is a formula to calculate the protection from solar gain for a person sitting under an awning. It is described in EN14501 4.5.

FU factor

The unshaded factor used in ASHRE calculations.

g eff (effective G value) 

The g value assumes that the sun will be opposite the window, whereas in reality it is often at an oblique angle, when less radiation will be transmitted depending on time of day and month and orientation of the window. The effective g value adjusts the g value to give a more accurate figure. It has been developed by BRE and the calculator is available on CD-Rom with their report “Summertime Solar Performance of windows with shading devices.”

g Value (total solar transmittance) Gtot

This is the fraction of the solar radiation that passes through the window and shading. It is the figure for the actual combination of blind and glass type to be used (unlike SC which is the combination of the blind and clear glass). It includes that which is transmitted through the blind and glass, the amount that is absorbed and then (as the blind/glass heats up) is re-radiated, convected or conducted into the room. It is the figure to use for comparison of products

Glare 

Is defined as “the condition of vision in which there is discomfort or a reduction in the ability to see significant objects, or both, due to an unsuitable distribution or range of luminance."

Lux Level

Is the measurement of light intensity.

Nanometers (nm) 

Are the measurement of the suns wavelength. The shortest, Ultra Violet, are 250-380 nm. Visible rays (light) are short wave 380 -780 nm. Infra red are long wave, 780 -2500 nm, and are heat.

O/F Openness factor 

Normally applied to fabric, it is the proportion of the area of an open weave cloth that is not covered by the cloth (the holes in it). Typically 3,5,7 and 10% are available.

Rs Solar reflectance 

The solar reflectance corresponds to the amount of solar radiation, that is reflected by the blind material. It is a figure for the performance of the material alone for use in calculations to combine it with glazing to get actual effects

SC Shading Co-efficient

This was the most used of all terms but has now mostly been replaced by Gtot. It is a figure for the total solar energy passing into the room. It adjusts the figure for the blind to allow for the effect of clear glazing. The shading effect of clear glass is that only 87% of the solar energy passes through it (the remaining 13% is either reflected or absorbed and radiated back out). Thus a material with SHGC figure of .60 = SC .52.( .6 x .87) The lower the S.C. figure the more effective the system.

Short wave shading co-efficient/Long wave shading co-efficient

The short wave S.C. is the proportion of direct transmission. The long wave S.C. is the proportion of the absorbed energy that is re-radiated. The shading co-efficient S.C. is the two added together.

SHGC - Solar Heat Gain Co-efficient

Is a figure for the total solar energy passing into the room. It does not make the adjustment for clear glazing of the shading co-efficient figure. To compare multiply by the adjustment 0.87 ie SHGC .60 = SC .52. The lower the figure the more effective the system.

Solar disc

EU speak for the sun (EN14501 5.1)

Stack effect 

One way to ventilate a building that is hotter or colder on the inside than outside, is to use what is known as "stack effect". Because of the temperature difference, the air inside the building is either more or less dense than the air outside. If there is an opening high in the building and another low in the building, a natural flow will be caused. If the air in the building is warmer than the outside, this warmer air will float out the top opening, being replaced with Convective Flow due to Stack Effect with cooler air from outside coming in from the bottom. The effect is used in naturally ventilated buildings.

Ts Solar transmittance 

The solar transmittance corresponds to the amount of solar radiation that is transmitted through the blind material. It is a figure the performance of the material alone for use in calculations to combine it with glazing to get actual effects.

Total Solar Energy

The total transmittance and reflectance figure of the glazing or glazing/shade combination.

Transparent External Closure

EU speak for glass

Tv Visible Transmittance 

Is a figure for light (short wave) rather than heat (long wave). It is the amount of visible solar energy that is allowed to pass through a glazing system. It is related to the amount of glare a person receives through a glazing system.

It is directly influenced by the openness factor and the colour.

It is calculated by dividing the amount of visible light that penetrates the fabric by the amount that hits the fabric:
        Amount of visible light penetrating the fabric
T v = ___________________________________
        Amount of visible light hitting the fabric

Visible Light

The transmittance and reflectance for light passing the glazing or glazing/shade combination.

Organisations concerned with shading calculations

ASHRE American Society of Heating, Refrigerating and Air Conditioning Engineers
BBSA British Blind and Shutter Association
BRE Building Research Establishment
CEN European Committee for Standardisation
CIBSE Chartered Institute of Building Services Engineers
ES-SO European Solar Shading Organisation

For an accurate assessment of building cooling requirements factors other than solar gain must also be considered. An holistic approach to building services design is vital co-ordinating the requirements of lighting glazing shading and control.

Heat gain in the building will be affected by the density of the building fabric and the area of glass. A building with a large area of glass and curtain walling will attract much more gain than an insulated brick building with smaller windows.

Room size will have a bearing as a large shallow room with a large area of glass will have a greater need for solar control than a small deep room with half height windows.

Heat will also be generated by the occupants, their office equipment and the lighting.

Shading is the insulation of the transparent parts

Main shading terms - an explanation of the technical terms.

Other causes of heat gain to consider

The G value is the measure for rejecting heat gains in the same way that the U value is the measure for retaining heat.

For an accurate assessment of the performance of a glazing system the figure to use is Gtot, that is the figure for the glazing with shading. The position of the shading, that is internal external or mid pane, will affect the Gtot figure as will the type of glass, that is single, double, low e or special surfaces.

It is defined as the measure of the total energy transmission of the glazing in combination with the blind when exposed to solar radiation.

It demonstrates clearly how effective and essential shading is for energy calculations.

It is difficult to achieve a G value of better than 0.27 for glazing alone and a  glazing system can be A+ rated for energy performance with a G value of more than 0.27 whereas even with single glazing an external blind in the shading position that on its own would have a G value of 0.87 can achieve 3 times more heat rejection at 0.09 than the most high performing glass and a closed blind almost 10 times more effective at 0.03.

Shading will always improve the G Value of a glazing system.

The validated Gtot values for Hallmark products can be found on the BBSA database. Shading is the insulation of the transparent parts.

The whole picture of Sick Building Syndrome indicates two deep seated problems. One is actually stress related, the feeling of lack of control over working conditions and surroundings. The other is that most symptoms occur in buildings that are sealed and have mechanical ventilation or air conditioning and special glasses.

The issue of control can be usually be addressed with internal shading by allowing the occupier the ability to adjust in their own area. This problem of environmental control has led to the development of fabric ranges specifically designed for the contract market that allow staff to determine the degree of light filtration by operating their internal window blinds.

The addition of dynamic external screening is the natural alternative to the need for sealed buildings and expenditure on cooling plant. Automatic external blinds that operate on solar sensors can be designed to reduce solar heat gain to provide a comfortable working environment and still be configured to allow user local override adjustment of the controls. As the building does not have to be sealed further control is enabled by the use of opening windows for natural ventilation.


External sunscreening for primary heat rejection combined with internal blinds for privacy and individual control- The natural healthy solution.

Solar gain refers to the increase in temperature in a space, object or structure that results from solar radiation. Sunlight is made up from ultraviolet, visible and infrared wavelengths.

Nanometers (nm) are the units used to measure the suns wavelength. The shortest, Ultra Violet, are 250-380 nm. Visible rays (light) are short wave 380 -780 nm. Infra red are long wave, 780 -2500 nm (also known as heat.)

Objects that are struck by sunlight absorb the shorter radiation (light) and then re-radiate as longer infrared wavelengths (heat).

This affects the glazing because when the rays go through glass, the glass is more transparent to the shorter wavelengths and opaque to long wave. So  the longer infrared wavelength will not pass back through the glass heating up the room causing solar gain.

Similarly where the radiation is absorbed by the internal shading system some is transmitted back into the room and some is trapped between the blind and glass. Unless it is vented with an air flow (from mechanical ventilation or an open window) it will heat the blind which will become a radiator.

An external shading system is the most effective in reducing solar gain as it is converted into long wave heat when it hits the blind. Most that is transmitted through or absorbed by the blind will then not pass through the glass and is trapped as hot air between blind and glass. As hot air rises it is then dissipated above the blind by natural convection (It rises and draws cooler air up between blind and glass.)

EFFECTIVE SHADING IS THE CONTROL STRATEGY THAT LIMITS THE EFFECTS OF SOLAR GAIN

Radiation enters as short-wave

Converts to long-wave when it hits objects and cannot leave through the glass

The need to shield office equipment screens from direct sunlight and glare can lead to the use of materials or glasses that create a confined environment. Endeavouring to combine all requirements into one solution will inevitably result in an unsatisfactory compromise. An external view with the ability to close it off for limited periods can usually only be achieved by allowing control by the individual.

Thus automated control by a centralised system can be resented by the users.

By separating the requirement of the need for building control and the needs of the individual an acceptable system can be achieved with two solutions. Internal blinds allow the user to determine their individual control and privacy whilst the external symmetry is maintained by the shielding of the external sunscreens.

Research has shown that working in artificial light causes lethargy and irritation, therefore affecting productivity.

Natural lighting has an uplifting effect; sunlight affects our mood, appetite and energy levels. It helps produce vitamins C and D (linked to alleviating depression and minimising the chances of developing several types of cancer.) Sunlight also suppresses the development of melatonin, a naturally occurring hormone which helps us sleep. When it is dark a small part of the brain called the pineal gland produces melatonin, when it is light the melatonin production is suppressed therefore helping us to wake up. Natural sunlight has also been said to improve conditions such as SAD (Seasonal Affective Disorder.) To put this into perspective, ordinary light bulbs in an office would give out 320-500 lux, in comparison, even on an overcast day natural light gives out about 1000 lux.

A light level of 500 lux is suitable for visual comfort in the workplace. Sunscreening such as a light shelf blind that allows light control will improve the natural lighting whilst still screening the working area.

 Shading should not be considered in isolation it is essential to integrate with lighting and other building services for a balanced internal environment.

NO SUNLIGHT = LETHARGY AND TIREDNESS

Internal blinds for individual control - External blinds for Solar Screening

The importance of user education.

User education is important, it is pointless designing an energy efficient system if the user does not understand it. The following was included in the staff manual describing an external shading system that had user override.

Yes the sun does shine in the UK

When you go on holiday to say Italy or Spain you close the shutters on your hotel window in the early morning and then later in the day the room is a cool refuge from the afternoon sun. It is a natural, efficient method of cooling a room without using energy.

In the UK it also gets hot in the summer. Honest it does. Except that we have traditionally preferred large areas of glass that need air-conditioning to cool the resulting heat gain in offices.

To meet the Governments target of complying with the Kyoto accord and 2020 target (Europe 20-20-20 Strategy) of 20% renewables 20% greenhouse gas reduction and 20% improvement in energy efficiency adequate solar shading is now a requirement of the Building Regulations and must be considered to meet the higher standards of building energy use that Kyoto and EU regulations now demand.

You may or may not agree with Government targets but it is difficult to argue against unnecessary waste. So if there is a cheaper way of keeping the office cool it deserves to be considered.

Going back to your holiday – the shutters work because they solve the problem before it becomes one. They stop the solar gain before it reaches the glass and is transmitted into the room.

The best way of minimising heat gains is to use nature and plant trees outside the office windows. In the summer the leaves shade, like the shutter, and in autumn the loss of leaves will allow the sun to penetrate and provide some natural heating when temperatures outside are lower. Totally efficient it does not cost a penny.

Needless to say it is not practical on a multi storey building, so yours has been designed with external shading that emulates nature. It is automatically controlled to react to solar sensors so that the ideal climate and working conditions can be maintained.  Perfect - when the sun shines the blinds come down and if it gets cloudy after a time delay they open providing better light levels for you to work in.

Except – it’s a bit big brother. For example it will not be appreciated by the MD if, in the middle of his motivating the troops message, just as he reaches the punch line the blinds start to operate and destroy the impact of the moment. It could also be a nuisance to lesser mortals. So a facility has been included to allow you to override the blinds in your area. Use it sensibly. If you want to isolate an area from the system it will help the balance of the building if you keep the blinds in the 45 degree open shading position rather than raising them.

Better still internal blinds have been provided to assist with computer screen glare and to give you the ability to control your own area. But as they are much less effective in controlling heat gains the balance of the building will work best if the automated system is allowed to operate.  The external appearance of the building will be better if it is evenly balanced.

So whilst you can alter the system do it with consideration. When you need to change it adjust the internal rather than the external blinds. Not only is it energy efficient you will probably feel more comfortable if you do.

The Psychological effects to consider

Visual perception of heat can have an effect on the comfort of the individual. If the eyes can see the sun the instruction to the brain is that it is hot. A building temperature that would otherwise be deemed as comfortable would be perceived as hotter by the user if generated by solar (radiant) heat.

Buyer "This sample blind that your fitters have just installed really makes the room feel cooler"

Rep "I would like to think so but it does not work that quickly it is partly because you cannot see the sun but that is also a valid reason for purchase"

This differential must be considered when assessing comfort. Thus a sunscreen that prevents a direct view of the sun such as an angled venetian blind will appear to the user to be far more effective than say a tinted glass or solar film that has a comparable shading co-efficient.

The ability to see out is also important for working comfort as it gives a psychological boost to occupants of the building who subconsciously need to track the subtle changes in the progress of the daytime. Brighter views other than the enclosed zones of the office and being able to see changes in the weather and light outside also uplift the spirit. The ability of the user to adjust the screening is an essential requirement.

Internal blinds for control

of visual perception

Thermal comfort and natural ventilation

A comfortable environment leads to a productive workforce. Cost savings in efficient operation will be achieved in a building designed for staff comfort.

The human body adapts itself to its surroundings maintaining constant internal temperature by thermal regulation. In the cold, muscular activity will be required to release internal warmth or wrapping up in layers of clothing will conserve body warmth. In hot temperatures movement is reduced so conserving stored energy. Any excess calories are eliminated by sweating (which evaporates in the heat) or by moisture in exhaled breath.

Thus thermal comfort basically relies on heat exchange and hygrometrics between the body and the environment. To avoid the need for the body to expend energy in this way correct temperature, an ideal level of humidity and a light air movement are necessary for thermal comfort and efficient working conditions. Whilst sunscreening will have the most significant effect natural ventilation is also important. As an example a temperature of 30 °C with a breeze moving at a rate of 1m per second would feel the same as 26 °C if the air was still.

Clearly this should not be taken to extremes!

Productivity in an office will drop 1% for every degree above the comfort threshold of 26 °C. Effective shading that maintains this comfort level will thus have a significant impact on the highest cost item in any office – the performance of the employees.

Sunscreening that allows air circulation combined with natural ventilation can significantly improve the thermal comfort of the user and is healthier than  a sealed air conditioned environment.

What are the reasons for using fixed rather than moveable external blinds?

Fixed external louvres became popular on commercial buildings because the calculations (prior to 2010) in Part L of the Building Regulations have been biased in favour of fixed sunscreening.

The logic is that if the blinds are fixed the building will function as designed whereas if the system is moveable it could be disabled by the user to the detriment of the energy balance of the building.

So why would anyone knowingly retract a blind system if the sun was shining? Not too likely but they could isolate it off season if the benefit had not been explained to them. Education is the key, but no matter how diligently building manuals are prepared, when the link from designer/contractor to user is lost the appreciation of the importance of the sunscreening system can be forgotten.

So although fixed louvres may not always be as effective as moveable they have the certainty that they will always function.

Dynamic Shading

Whilst there may be situations where fixed shading is preferable it is not the most energy efficient solution. As the regulations have correctly increased the requirement for insulation this has created overheating even in some winter months. Unless designed as a light shelf fixed shading can also impact on lighting costs

A significant adjustment was applied to the benefit of dynamic moveable shading in the last revision of the regulations. As energy costs rise behavioural change and understanding will ensure that dynamic shading solutions will become the accepted solution.

When is horizontal fixed shading not practical?
To be effective a horizontal system has to project at least half of the drop of the glazing. On large glazed areas this is often not practical for a combination of structural and aesthetic reasons.

Unless combined with additional solar protection they are not as effective on east or west facing elevations where sun angles are lower. 

The bias of the building regulations toward fixed shading produced many designs that have a token short projection at the window head which is fine as a decorative feature but has limited benefit in reducing solar gain.

Although fixed shading will always function as designed it should combine with internal shading for user control.

External blinds stop most of the solar gain before it reaches the glass. Of the part that is not reflected and is either absorbed by the blind or transmitted through it, most does not penetrate the glass. Instead as most of the transmitted energy will be converted into long wave radiation (heat) it is trapped between the blind and the glass. Because hot air rises natural convection draws it up and away.

With an internal blind, film or special glass when the suns rays pass through the blind/glass they convert into heat in the same way but because the have changed wavelength most cannot be reflected back out. So the heat becomes trapped between the blind and the glass. Some is reflected out but most is absorbed and then as the glass, space and blind heat up it re-radiates back into the room.

If the blind is fitted mid-pane the secondary glazing will further trap some of that absorbed energy. Venting the space between blind and glass will dissipate some of that especially in a mid pane situation where cooler air can be introduced at cill level with the hot air rising by natural convection at the head to draw in the cooler air.

Shading fitted mid pane in a double skin façade is especially suited to multi storey buildings. With this design the outer façade is open at the top and bottom enabling natural convection. It is possible to achieve Gtot figures that are nearly as good as external blinds. The design of the Shard was only possible with effective automated shading within the façade achieving a Gtot of 0.12.

As a guide if an internal blind in the shading position fitted behind a south facing clear double glazed unit rejects 65% of the heat gain the same combination with the material fitted outside would reject 91% with a Gtot of 0.09

What would be a perfect shading solution?

A double skin façade with three shading devices to a window. It would seem to be an expensive option, but it does have cost advantages when compared to an all glass façade, with just an internal blind and air-conditioning. Whilst there are capital cost advantages, the main benefit is that shading is achieved with minimal energy cost and winter heating costs are lower.

Benefits:

Uninterrupted all glass façade that meets tighter building regulations

Primary solar control with an external grade blind

External venetian blinds and fixed louvres function mid pane with almost as good shading figures as they would achieve if mounted externally but with the benefit of protection from the elements and ease of maintenance access.

Fixed louvres are also an access walkway for maintenance and cleaning.

Positioned below ceiling level they function as a light shelf.

Internal mesh roller blind – visual perception, control of screen glare and user control.

Internal glazing at normal cill height, with better insulation from denser building structure, giving lower energy loss in winter.

Natural ventilation and air change from openable internal windows.

It is certainly good for the glass and shading supplier, it has a clean glass façade for the designer, high energy rating for the developer and lower energy costs for the occupier. But above all it ticks rather a lot of boxes for the comfort of the most important (and in any lifecycle calculation the most expensive) building component - the occupiers staff.

Remember back to that Club 18-30 holiday you locked the outside shutters on your room to stop midnight raiders from next door. You collapsed to bed in the early hours and woke in mid afternoon. You slept well because the room was cool – Why? Because the shutters had prevented the heat gain before it reached the glass and so it was cooler inside than out.

But the UK temperatures are not as hot as Spain! Not quite but we still spend a fortune on unnecessary energy to keep cool. Why, you ask, when we could solve the problem with external shading? Use prevention rather than cure.

If shading is so beneficial why does it not get specified? 

Most UK architects do not like the idea of external shading cluttering the clean lines of their design. Solar Glass is the answer except that a glass with a low U vlaue to retain heat in the winter does the same in the summer. The G value is usually not less than 0.27 that is up to 3 times less effective than external shading and thus needs energy consuming mechanical cooling.

What should happen is that the products are combined so that blinds allow greater use of glass and enable cost savings so that the air change is not at peak load!

So my architect is keen on energy efficiency and wants external shading why now will he have a problem?

He needs to get the agreement of his building services engineer. But traditionally shading is not part of his remit so he does not normally consider it. For a holistic approach the answer is that solar shading is and should be part of the building services package.

So shading is in the services and my architect and engineer are in favour. The Quantity Surveyor is happy because the capital cost is lower than predicted - so why not?

The developers’ financier - Unless the building is air conditioned his estate agent will tell him that it is difficult to let. Natural ventilation and energy efficiency are benefits to the running costs of the tenant not the developer/landlord so why bother. Even though the fitting of external blinds will be less than the additional capital spend on a/c equipment the marketing benefit to the letting agent has been seen to be more important. That is changing with a realisation that buildings with low energy performance will become difficult to let and will require expensive upgrades or become redundant. The financial benefit of designing for energy efficiency and the risk of not doing so is now being appreciated. See WGBC report.

The reality is that the capital cost of external shading is much less than 5 years running costs of air conditioning* let alone the savings on capital costs.

The business case for energy efficient buildings will eventually force change

*BRE report Summertime performance of windows with shading devices.2005

Whether you are concerned or not about climate change the most important factor affecting energy needs in the UK is that our generating capacity has been reduced to meet carbon reduction targets and will continue to decline in 2014 and beyond will soon decline and for the user it will cost significantly more.

Power blackouts were predicted by a House of Commons select committee chairman as long ago as 2008 and the probability is increasing as the alternatives of renewables are failing to make up the shortfall. The attached comment from the House of Commons select committee chairman confirms that power blackouts can be expected in the near future if action is not taken

This will affect peak time cooling more than heating as, whist energy for heating uses gas and electricity, energy for cooling is mostly supplied by electricity.

As the attached information sheets show shading can have a significant benefit in reducing cooling costs.

Buildings use 40% of generated energy- effective shading can reduce that by as much as 15%

The following is a list of standards that are most relevant to window blinds. Standards that relate to test methods or have some reference to blinds are in the second list.

Standards relating to blinds:

EN 13120:2004

Internal blinds - Performance requirements including safety

EN 13363-1:2003

Solar protection devices combined with glazing - Calculation of solar and light transmittance - Part 1: Simplified method

EN 13363-2:2002

Solar protection devices combined with glazing - Calculation of solar and light transmittance -

Part 2: Reference method

EN 13561:2004

External blinds - Performance requirements including safety

EN 14501:2005

Blinds and shutters - Thermal and visual comfort - Performance characteristics and classification

BS 5867: Part 2: 1980

Fabrics for curtains and drapes - Part 2. Flammability requirements

Standards for test methods or that have some references to blinds and shutters:

EN 410:1998

Glass in building - Determination of luminous and solar characteristics of glazing

EN 1522:1999

Windows, doors, shutters and blinds - Bullet resistance – Requirements and classification

EN 1523:1999

Windows, doors, shutters and blinds - Bullet resistance – Test method.

EN 1932:2001

External blinds and shutters – Resistance to wind loads – Method of testing

EN 1933:2001

External blinds – Resistance to load due to water accumulation – Test method.

EN 12045:2000

Shutters and blinds power operated – Safety in use – Measurement of the transmitted force.

EN 12194:2000

Shutters, external and internal blinds – Misuse – Test methods.

EN 12216:2002

Shutters, external blinds, internal blinds - Terminology, glossary and definitions

EN 12635:2002

Industrial, commercial and garage doors and gates - Installation and use

EN 12833:2001

Skylight and conservatory roller shutters – Resistance to snow load – Test method.

EN 12835:2001

Airtight shutters – Air permeability test.

EN 13125:2001

Shutters and blinds – Additional thermal resistance – Allocation of a class of air permeability to a product.

EN 13330:2002

Shutters - Hard body impact - Test method

EN 13527:2000

Shutters and blinds – Measurement of operating force – Test methods.

EN 13659:2004

Shutters - Performance requirements including safety

EN 14201:2004

Blinds and Shutters - Resistance to repeated operations (mechanical endurance) - Methods of testing.

EN 14202:2004

Blinds and shutters - Suitability for use of tubular and square motorizations - Requirements and test methods

EN 14203:2004

Blinds and shutters - Capability for use of gears with crank handle - Requirements and test methods

EN 14500:2002

Blinds and shutters - Thermal and visual comfort - Test methods

EN 14759:2005

Shutters - Acoustic insulation relative to airborne sound - Expression of performance

BS 5867 Part 1:1980

Fabrics for curtains and drapes - Part 1. General requirements

Energy performance of Buildings Directive

This is the main EU directive that dictates UK policy. It is the requirements of this directive and the subsequent monitoring of that performance that is the driver of UK energy policy.

Part L, SAP codes, HIPs, EPCs Carbon Trading and many other regulations and initiatives are all part of our need to comply with this directive.

The political need to be green and climate change aware has to some extent disguised the underlying strategic planning that requires more efficient use of our resources. In truth it is the declining availability of our sources of power and the resulting reliance on potentially unreliable foreign sources that is the true motivator of these policies.

Although energy issues are now high on the political agenda this is a more recent trend and for the user it is only since the middle of 2007 that steep rises in the cost of energy have begun to be noticeable

Until the revision of Part L of the Building Regulations in October 2010 sun screening was generally not  recognised for the benefits that it has to offer quite simply because there has not been the will of the user to look at ways to conserve energy.  As energy costs have become more significant to the economy this is now changing. Buildings in Europe consume 40% of our total energy usage mainly for heating and cooling. In excess of 15% of that could be saved in the UK with efficient shading. In particular because a significant part of that is air-conditioning costs and whilst more efficient plant will make a contribution reducing the load will be more effective.

Shading is proven technology that can contribute significantly to energy cost reductions throughout the EU to help meet the targets. Awareness is increasing, our trade association BBSA www.bbsa.org.uk is a member of ES-SO the European Solar Shading Organisation www.es-so.com that is active in lobbying the European parliament and member governments to promote an understanding of the benefits that effective shading can contribute to reducing energy consumption.

The Recast (Revision)of the EPBD was ratified by the EU Parliament in July 2010.

Key provisions of the Directive are:

• Minimum requirements for the energy performance of all new buildings

• Minimum requirements for the energy performance of large existing buildings subject to a major renovation

• Energy certification of all buildings, with frequently visited buildings providing public services to prominently display a Display Energy Certificate

• Regular, mandatory inspection of boilers and air conditioning systems in buildings

Energy Performance Certificates

EPC’s are part of the Energy Performance of Buildings Directive (EPBD) EPC’s are a new requirement providing information on the energy efficiency of a building. The owner or landlord of the property is responsible for providing the EPC to the buyer or tenant when selling or letting.

The property industry has now recognised that the value of a building and its rental stream will be affected by this rating. Whereas in the past the running cost of the building in particular that for cooling and heating were a problem for the tenant there is now a realisation that a prestige site will only retain that description if it is energy efficient.

To improve the rating of existing buildings attention is being given to the efficiency of the cooling system and possible replacement. Consideration should also be given to reducing the load with more efficient solar shading as this may be a far more cost effective way of achieving the target figure.

The requirements are:

 From 6th April 2008 an EPC is required when selling, letting or constructing a commercial building with a total floor area of more than 10,000m2

 From 1st July 2008 the threshold is reduced to 2,500m2

 From 1st October 2008 an EPC will be required for any commercial building when it is let, sold, or constructed. All public buildings over 1,000m2 will have to display an EPC from this date.

BREEAM - Building Research Establishment Environmetal Assessment Method

This is a standard that was designed to improve both the health of the building occupants and reduce the amount of external environmental pollution. It is not in itself a standard of energy efficiency of a building although higher credits are awarded for more efficient designs.

When it was introduced in 1990 energy costs were not a significant issue and points to reach the target for compliance are awarded to meet a variety of objectives. The assessment separates into Global effects - carbon emissions acid rain and ozone depletion and Neighbourhood effects -  the indoor effects on the occupants and the outdoor effects on its neighbours.

As an example compliance by the builder with the Considerate Contractor Scheme will gain credit toward minimising the environmental impact of the building on its neighbourhood.

From the outset the method was conceived to be one that would evolve and improve and it has developed significantly since its introduction. The benefits of external shading as detailed in the Energy Performance of Buildings directive are not considered for credits. There is ongoing discussion between the trade associations (ES-SO and BBSA) with BRE to rectify this.

As energy costs rise still further we expect that to change in the future with the realisation that preventing the need for the cost of cooling by shading is more energy efficient.

Energy Efficient Solar Shading