The fundamentals of solar gain in buildings

Author: StuartD Date: 28|09|11

Understanding the basics behind how the sun's rays work and the impact they have on buildings

Solar gain in buildings refers to the build up and increase of heat in a room or area and persons and objects. Cloud cover in the sky along with abosorption in the atmosphere affect the amount of energy reaching the earths surface and subsequent solar gain in a building along with the shading device employed at the windows.

The sun's rays affect buildings because:

The sun's energy enters the earths atmosphere as shortwave radiation
Glazing is virtually transparent to these shortwave radiation and subseqeuntly the suns energy easily passes through these transparent areas in buildings
When inside a building, the sun's energy is absorbed by fixtures, fittings, furnishings and people
It is then re-radiated as infra-red (heat) rays which are at a different, longer wavelength
These longer wavelengths cannot pass through glazing and therefore remain trapped in the building, causing it to heat up

The above process is often referred to as the greenhouse effect.

Exterior blinds provide a barrier between the glazing and suns energy, blocking it from reaching the glass and therefore preventing overheating caused by solar gain. Single pane glazing, still installed on much of the older building stock in the UK admits 87% of the suns 'heat' energy which will remain trapped inside the building causing it to warm up. With exterior blinds this figure can be cut by more than 90% resulting in improved indoor thermal comfort with minimal or no need for costly air conditioning and the resultant CO2 emissions.

Exterior blinds provide a natural cooling solution to natures free gift of vast amounts of solar energy.

StuartD
replied on 01|10|11

Peter - A very valid comment. In fact a study into solar shading by REHVA, the European Heating and Ventilation Association, suggests that both internal and external shading would be needed at the same time, external primarily for heat control, internal mostly for light control, resulting in improved indoor conditions and savings on the cooling load and the heating energy needs, in turn reducing the environmental footprint of a building over its life cycle.
As you have quite rightly pointed out no two applications are the same and every application requires a specialist to discuss and understand the clients needs, putting together a specific solution (system, fabric, control configuration etc) to meet with the clients requirements.

Peter Matthews
replied on 30|09|11

Whilst you make a very good point there Stuart, I think that there is also a very strong case for internal blinds as well, especially where privacy, light translucency and reduction in sound reverberation are required for complex shaped roofs, as well as those situations where outward opening roof vents, windows and doors limit the possibilities of exterior blinds.

Of course this is also subject to the exact type of glazing and the volume of air enclosed within the structure, as well as the extent of ventilation, number of people within the space and the extent of air changes per hour.

As always, there is no black and white answer for every application. It takes an expert to listen to the client’s needs and assess the situation correctly before providing the best solution.

Having said that; when considering very large areas of fixed roof glazing, particularly where commercial applications are concerned, exterior roof blinds are often the ideal solution, so I suppose that this is just a long comment agreeing with you!

The Greenhouse Effect

Twitter: @WeLoveEB - Thanks for the mention @SkyblueCreation Graphics look wicked and getting plenty of attention! If you hadn't guessed we love exterior blinds