Dynamic shading is not just the decoration at the window. It is the tool to harness and benefit from the energy of the sun. It is both a beneficial free energy source and a cause of discomfort.
The Sun gives us the natural light that we need, it is a source of free heat and is the tonic that motivates and helps keep us healthy.
But it is a variable force needing dynamic control and solutions that need to consider all of those varying effects to optimise the energy saving and user wellbeing benefits.
Shading is the insulation of the weakest part of a building, the glazing. It is proven technology that we did not need to think about when energy was cheap.
What is sustainable shading? The windows are the weak point in energy efficient building design. They can gain too much energy in summer and lose too much in winter.
Shading is a sustainable solution that can control that solar gain in summer, be raised to maximise it and lowered to reduce heat loss in winter.
A study by the Austrian Association, BVST, showed that an external Venetian blind will save around 8.5 tonnes of CO2 over its life cycle - and creates only 150 kg of CO2 from production to disposal!
This means that it saves nearly 60 times its CO2 emissions footprint over a 20-year life!
These enormous savings come from three elements:
Firstly, in summer the Venetian blind reduces the solar heat very effectively, so that mechanical cooling (with correspondingly high CO2 emissions) is not necessary, as well as complying with the construction technology for housing regulations.
Secondly, in cold weather during the day it is raised and allows in the sun's warming rays into the interior, and during the night in the closed position, reduces heat losses. In a zero-energy building that reduces its heating cost by 20% or more.
And thirdly with this sunscreen it enables the maximum use of natural daylight can be harvested as a free energy light source - that can, for example, reduce the power required for lighting in offices and schools by up to 80%!
The report clearly demonstrates the importance of shading in sustainable building design. There can be few other elements that can match this performance.
Studies are continuing on other types of blinds and shutters but are likely to be similar for other external products and a multiple of the energy used in their lifecycle for internal shading.
Our Techtonic PV Rooflight system is even more energy efficient as its PV collector produces the power to operate it, a true Nega energy solution.
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The marketing trend for outside liveability is an attractive message. The natural habitat for humans has been in the open air and it is only in the last century that we have moved to work inside. Merging the inside with the outside reconnects us with our natural way of living.
Liveability and biophilic design (connecting with nature) are as we need to reconnect with the natural environment that our bodies are designed for. It is only in the last century that we are spending more time inside than out and many issues of health and well being are linked to this change of lifestyle.
Opening up the living area with large folding or sliding doors is an attractive solution. But without considering shading there are potential problems.
A large area of south facing glazing will need a low U value otherwise it will lose heat in winter. That will then need external shading (go to "gtot what is it?" for an explanation) which ideally is vertically dropped in front of the window. That though needs guides which are not wanted and if the doors fold out probably cannot be used when they are open.
If the compromise on heat rejection is internal blinds, they also cannot have guides to control them as that would be a restriction on the open plan. So on a hot sunny day we open the doors but we do not want to overheat the room, so we drop the blind but they will blow around.
If they are manual they cannot be chain or cord operated as there is not anywhere to fit child safety devices so motorised will probably be necessary.
But we are not going to have the doors open all of the time so when we go out the room overheats as even on sunny winter days the Gtot will not be low enough with internal blinds.
That then leaves the option of an external foldaway awning except that it needs to be planned as part of the design as the structure needs to be able to take the load. If the doors concertina out there is also the problem of clearance for the arms so it may have to be bracketed higher to clear them and with a single storey structure that certainly has to be planned for in the design.
Outdoor liveability is an attractive prospect but do not overlook the shading.
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Maximising the use of daylight can bring energy saving as well as user health and comfort benefits.
The energy issue is relatively simple. Energy as daylight provided by the sun is free energy providing that controlling it does not cost more than it saves in artificial lighting
Working in artificial light causes lethargy and irritation which affects productivity and wellbeing.
Natural daylight has an uplifting effect; sunlight creates vitamins in the body and suppresses the development of melanin, a natural occurring hormone, generated by the body, which is produced to tell you when it is time to sleep. The passing of time throughout the day, linked to light levels and stimulation through the eye, trigger the production of this hormone. When the eye sees sunlight melanin is suppressed. Good natural light also supports health through various other mechanisms including regulating sleeping rhythms.
So daylight has the potential to provide the necessary light levels for a
productive, stimulating environment, while reducing reliance on electric lighting.
Blinds such as the Lumax light shelf blind will provide the ability to control and maximise the daylight whilst enabling the user to adjust the shading for their visual comfort.
A report from the World Green Building Council (read report) identifies that benefits of views outside are also closely connected with the provision of daylight.
Ideally views should be aesthetically pleasing, and there is good evidence that shows the benefits to occupants are particularly strong if the view features nature. This is an example of ‘biophilia’, a phrase that describes a relationship between nature and humans, which suggests that because humans are intrinsically “of nature” we need contact with the natural environment to sustain our health and wellbeing.
Biophilic design will grow in importance with greater realisation of the impact of today’s working environment as urbanisation continues apace and we risk becoming further divorced from nature in our day to day lives. The benefits on physical and mental health are becoming increasingly well understood, with a significant body of evidence supporting this view.
The window is our view on the world and shading that controls the energy of the sun whilst maintaining that connection to nature is crucial to a comfortable productive working environment.
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Providing clear energy ratings has been very effective in improving the energy consumption of many products such as white goods so why not for shading?
A simple rating system to cover all of the variables can be difficult to achieve. What is ideally needed is how the shading will perform in conjunction with the different types of glazing, the orientation of the building and its specific location. To show of that that on a single label would be complex.
The purpose of A-G ratings though is to provide an easily understood label to provide a simple comparison of product in an example situation. The A-G rating for tyres for example does not assume a performance level it is just a measure that means that the tyre with the highest rating will perform best however the vehicle is driven.
BVST the German Trade Association working with the German laboratory Ift Rosenheim has developed a simple rating system for shading products combined with glazing. This shows the cooling energy benefit in summer and the heating energy saving in winter.
Shading will always improve the performance of glazing in many instances substantially. The labels highlight that external shading is the first line of defence for summer cooling and internal shading for winter heat saving. They show that if the performance of the shading is considered before selecting the glass a more cost effective glazing solution is the likely outcome.
The example labels for our Trojan external blind with standard first generation
double glazing show an A rating whereas the best performing solar glass can only
achieve a D.
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Introduced by the Government to encourage householders and businesses to invest in energy saving measures the complexity of the offering has resulted in a rather slow uptake.
In practice the main uptake has been by Housing Associations and Local Authorities and for the commercial building sector the financing was not competitive.
That said the concept was right as our buildings consume over 40% of the energy that we use upgrading our stock of housing would make an impact on our energy needs.
As part of the exercise it was essential that the benefits could be measured to ensure a return on the investment. That was achieved with a publicly available standard for each of the measures.
There is standard for shading that is blinds and shutters in the standard PAS2030. Our trade industry publication “A Guide to Low Energy Shading” is referenced in the standard as a source of advice on the measures that will save energy.
These are highlighted in the guidance on this website
Saving on energy costs is important but the higher cost in any business is its employees. That can be as high as 90% of the total so a 1% saving on that cost will have far more impact on the bottom line than a 10% saving in energy costs.
The World Green Council Report highlights the issues and benefits that can accrue from staff comfort and well being and health. Many are obvious if you take the time to think about it not least that an indoor working environment has only been developed over the last century. The natural environment for humans is outside and many of the issues of health and well being are connected to our need to be part of the outside world.
Health and sickness are just a part of the picture the report also shows how improvements to staff comfort can be rewarded with really significant gains in productivity and performance as shown on the chart taken from the report.
The windows in a building are the connection to the outside and the power of the sun and nature to activate our body clocks. We need the sun and the light and heat that it gives us but it needs to be controlled. Too little and we become lethargic and unproductive, too much and we cannot work productively.
Design to connect with nature is identified as Biophilia. Shading is the control mechanism that should be the first consideration in Biophilic Design as it is the enabler and solution for many of the issues identified in the report.
And it will save on the energy costs as well
What drives green building – conducive to healthy, productive occupiers – is quite simple:
1. Good design (such as passive solutions, shading, and natural ventilation
Summary of evidence
Indoor Air Quality: The health and productivity benefits of good indoor air quality (IAQ) are well established. This can be indicated by low concentrations of CO2 and pollutants, and high ventilation rates. It would be unwise to suggest that the results of individual studies, even meta-analyses, are automatically replicable for any organisation. However, with this important caveat, a comprehensive body of research can be drawn on to suggest that productivity improvements of 8-11% are not uncommon as a result of better air quality.
Thermal comfort: This is very closely related to IAQ, and indeed separating out the benefits is difficult. However, the relationship is clear, with research demonstrating that thermal comfort has a significant impact on workplace satisfaction. Suggesting a general rule about the size of productivity gains is not a robust exercise because of the importance of specific circumstances and the lack of comparability between studies. However, studies consistently show that even modest degrees of personal control over thermal comfort can return single digit improvements in productivity. The importance of personal control applies to other factors too, including lighting.
Daylighting & lighting: Good lighting is crucial for occupant satisfaction, and our understanding of the health and wellbeing benefits of light is growing all the time. It can be difficult to separate out the benefits of daylight – greater nearer a window, of course – from the benefits of views out of the window. Several studies in the last decade have estimated productivity gains as a result of proximity to windows, with experts now thinking that the views out are probably the more significant factor, particularly where the view offers a connection to nature.
Biophilia: The rise of biophilia, the suggestion that we have an instinctive bond to nature, is a growing theme in the research. A growing scientific understanding of biophilic design, and the positive impact of green space and nature on (particularly) mental health, has implications for those involved in office design and fit-out, developers and urban planners alike.
Health,Users in control: Putting trust in the occupier and putting them at the centre of design, including personal control over their indoor environment, can reap rewards in terms of satisfaction, productivity and energy performance. This encourages users to work with the grain of their building and vice versa. There is also evidence that occupants are more forgiving and willing to work in a greater range of temperatures in a ‘green building’.
Maximising daylight: This is not without challenges (solar gain, glare etc) but daylight has the potential to provide the necessary light levels for a productive, stimulating environment, while reducing reliance on electric lighting. This just cannot be done in offices with a very deep floor plate,
which is a challenge to the status quo in many markets. However, electricity use for some lighting is inevitable, and further innovations in low carbon lighting design will be crucial.
Passive design…up to a point: Where the benefits of fresh air and good thermal comfort can be provided by natural ventilation and passive design (or mixed mode systems), there is a clear win-win for occupier and energy use. In many regions of the world, there is probably scope for passive techniques to be used more frequently than at present. However, we have to recognise that
in some climates, high outside temperature (both in the day and at night) and humidity simply make some conditioning of air inevitable.
Overheating in a passive house? This a design concept that is not just for housing but also for commercial buildings. The objective is to create a building that creates the energy it needs and uses virtually no external energy. That demands sustainable solutions.
However, several post-occupancy studies of these high performance buildings report high temperatures when shading has been overlooked as the most frequent problem. So why is that and how do you solve it?
As the cheapest energy is the energy that you do not need, the design maximises the insulation and seals it to prevent heat loss.
To minimise the energy need for heating the system utilises free energy from the sun on bright winter days. That is done by having large areas of south facing glazing designed with low U values that allow the gain in and then trap it inside the building.
That is fine in winter but in summer the glass still acts as a heat collector and without shading overheating is inevitable and not just in summer, on bright winter days the design can be so efficient it can overheat then as well.
Shading has to be external and dynamic.
External as it has to be intercepted before it reaches the glass and moveable so that it will allow the heat gain when it is needed and prevent it when it is not. For internal comfort the Gtot value needs to be a minimum of 0.15 and preferably better than 0.10. (Gtot is the measure of the solar gain of the shading and glazing system combined.)
In the UK with decades of cheap energy we have not had to consider external shading or even how the sun actually works as we have solved the problem with air-conditioning or fans but think back to the days before mechanical cooling every shop in those old photos of the High Street had a shop blind to keep their produce cool. So external shading is up to date technology but a traditional solution utilising basic science.
We attach links to more information on the principals of shading including a video from our trade association BBSA.
In a highly insulated structure the glazing is normally the weakest part. Shading is the insulation of the windows and must be properly considered at the design stage.
External shading is also a sustainable solution as in its lifetime it saves, in cooling energy that would otherwise be needed, a multiple (as much as over 50 times) of the energy that it uses throughout its lifecycle
Trojan external Venetian blinds and Hemera external roller blinds are essential components in a Passive House design.
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The Glass & Glazing Federation has developed a rating system for glass the BRFC label.
As heat loss in winter has a greater cost than removing heat gain in summer the rating system has been designed to encourage the development of the best glass for retaining heat that is to have a low U value.
In that respect it has been really successful in encouraging the development of glazing systems (the complete window not just the glass) that has significantly improved the performance. If you consider that U values for single glazing are 5.7 and for first generation double glazing 2.9 we are now getting figures of 0.8 and even down to 0.6 may be possible. The A-G rating system has had to have A+ added to quantify this improvement. The industry is now suggesting triple glazing as the ultimate solution.
The low emissivity film that is normally fitted to the inside of the outer pane in simple terms is designed to reflect back into the room any heat that is in the room that would otherwise be conducted through the glass . The glazing is designed to admit as much solar gain as possible so that in winter months it is a source of free heating energy.
So what is the problem with that?
To achieve the A+ rating U value the combination of glass will not have a g value. That is it must not be able to reject heat gain from the sun as it is designed to gain as much as possible and then keep it in. That is fine on a cold day but will cause overheating on most other days.
Any internal shading will also be less effective in heat rejection than with standard glass as the effect of the blind will be countered by the glass which will be trying to keep it in.
In fact the additional benefit of a triple glazed system will probably not regain the additional cost in energy saving throughout its lifecycle, 50% more glass does not mean 50% better it is nearer to 5%. If fitted to standard spacing frame it actually has a worse performance than a good double unit as to be effective it has to have a deeper, heavier and more expensive frame.
Taking glass to extreme levels of heat retention will inevitably lead to overheating not just in the summer but on sunny winter days.
A low permeability blind such as the Ebony or Hemera 103R with good performing double glazing will match the performance far more cost effectively and will have the added benefit that the blind can be adjusted and it can be raised on sunny winter days to gain from the free solar energy. Glass cannot do that.
Also consumers should be wary of claims for A+ performing glass. The rating system applies to the complete window including frame and seals not the glass alone. That needs a very well designed frame tested to a very high standard of low permeability (leakage).
There are more triple glazed windows in Scandinavia where the winters are far colder than in UK yet they have more external than internal shading even though their summers are cooler. If you fit A+ Glazing you will probably overheat and need external shading.