Members of the UK Green
Achilles Building Confidence
A Comparison of Solar Gain Factors
Control of solar gain is a central tenet of Part L. It will be necessary to pay greater attention to external solar shading.
Internal and external solar shading devices are sometimes provided to modify the daylight entering a building, and help reduce the glare potential of windows or to provide privacy. More normally they are required to control the admission of direct radiation.
Position of shading device
Internal shading devices can only intercept the solar radiation which has passed through the glass and can eliminate only that portion of the radiant energy which can be reflected through the glass again. Some of the radiation striking an internal device is absorbed, some convected and some re-radiated into the room.
If the interception occurs at the surface of the glass, part of the radiation will be reflected back at the entry layer, part of it transmitted and a part absorbed. The absorbed portion will be convected and re-radiated to the outside and into the room.
External shading devices dissipate the convected and re-radiated heat to the outside air and therefore external solar shading devices will more effectively minimise solar heat gain than internal solar shading devices. As an overall value, one could conclude that the effectiveness is increased by about 30% by using an external shading device instead of an internal one. To provide the most effective protection, moveable external shading devices should be designed as a special requirement to meet the solar geometry of the latitude of the building and the orientation of the windows.
Colour
Bright metallic, white or light coloured solar shading is the best reflector of solar radiation. Dark colours will absorb a higher proportion of the incident radiation. The absorbed radiation will heat the shading device and if it is inside the building it will re-radiate heat into the room and also warm the air by convection. For internal venetian blinds the use of light colours gives about 20% more protection than dark ones. With roller blinds the effect is even more pronounced and light colours give about 30% more protection than dark ones.
Conversely dark coloured external devices give slightly more protection than light ones. Less energy is reflected through the glass while the heat absorbed by the device is lost by convection and re-radiation to the outside air.
Use
Fixed or moveable external shading devices such as Levolux fins or other types of louvres will reduce the amount of daylight entering the building.
Internal and external shading devices can be used to exclude direct rays of sun from all or part of the room. Adjustable devices can be set to intercept the direct rays of the sun and reflect some of it onto the ceiling and walls reinforcing the daylight at the back of the room, when direct daylight has been reduced by the device itself.
Lightweight or open weave blinds and curtains can be used to reduce the intensity of the direct solar rays by diffusion. When the sun angle is high, louvres unlike densely woven blinds, can be set to intercept the direct sunlight without restricting the view out or impeding natural ventilation. Open weave blinds, particularly those of darker colour also allow good view out and maintain natural ventilation.
Operation and control
The operation of solar shading systems can be manual, generally by hand, or motorised using some form of electric motor.
The control of these devices can be hand operated, by switch, remote control or through a fully automated electronic control system using the latest hardware and specially written software to control the system to follow the path of the sun.
Levolux offers a full design service to provide the most suitable controls for their shading systems.
The need for effective solar shading is becoming more widely recognised as the way to reduce energy costs by providing natural ventilation and shading. Levolux’s shading solutions control solar heat gain, which can significantly reduce a building’s energy costs by limiting or even eliminating the need for air conditioning. The use of optimum daylight not only contributes to energy savings but also provides a better working environment.
It is imperative that the design process incorporating solar shading identifies the relationship between the building and the sun. The sun rises in the East and sets in the West, travelling in an arc throughout the day. Solar shading on a south facing façade will effectively only deflect the intense rays of the sun at its highest point of the day. Consideration must be given to shading on the East and West facades where the sun can still cause overheating.
Horizontal or vertical louvre systems can be used separately, or combined for maximum shading protection. Louvres can be fixed at a point in conjunction with design of the building, ensuring that optimum protection from the angles of the sun is achieved. Alternatively, a moveable louvre system can be designed ensuring that the louvres react the amount and direction of daylight that strikes them, producing the most effective system, shading when required yet making the best possible use of natural daylight when overcast.
Levolux thrives on providing solar shading solutions to technically demanding specifications and designs. Ongoing research and development programmes mean we shall continue to meet the most challenging specifications without compromising design or quality.