The UK climate can be very variable. A typical August temperature might reach 35 degrees in some parts, whereas January can be as low as minus five and beyond. It is a dramatic contrast, challenging homeowners and commercial property managers everywhere to keep their buildings cool in summer but warm in winter.
A modern answer to that particular problem might be to blast the air conditioning throughout the hottest parts of the year and crank up the heating when the mercury drops, but there is an important, natural concept that should be explored if we are to get the balance of comfortable temperature just right: solar gain. In this guide, we hope to answer the question ‘what is solar gain’ and provide some helpful insights along the way.
Let’s start by defining exactly what we mean by the term.
What is solar gain?
Solar gain is the concept whereby short-wave infrared rays from the sun penetrate a building through its windows and other transparent parts to be absorbed by surfaces and objects within. Those rooms and objects then emit heat in the form of long-wave infrared radiation which can’t escape, making areas significantly warmer than they might be without solar gain.
How does the G-value of glazing impact solar gain?
Every piece of glazing – from windows to walls and roofs to doors – has a G-value, which is also known as total solar energy transmittance. The G-value asigns a numerical rating (between 0 and 1, also 0% and 100%) based on how much heat energy is allowed to pass from one side of the glazing to the other. For example, a window with a G-value of 0 will allow no heat to pass into a space, whereas a window with a G-value of 1 will allow all of the sun’s heat through.
If you were to step into a greenhouse at the height of summer, it would probably be uncomfortably hot, suggesting that its G-rating is almost 1 because it is letting all of the heat in. The sweet spot for any home or office space will be between 0.4 and 0.6, indicating that some solar gain is allowed to take place to make a space feel warm in winter without overheating in summer.
Is solar gain good or bad?
Solar gain isn’t exclusively a good thing and it isn’t exclusively a bad thing. Instead, its positive and negative effects depend on the environment in which it occurs, the season, and how the solar gain is managed. For example, in winter, some heat gain is necessary to raise the internal temperature without relying on central heating, but too much solar gain in those rooms at the height of summer can make them feel very uncomfortable without the aid of air conditioning. As we have already mentioned, the sweet spot for a G-value is approximately 0.4-0.6, allowing the glazing to harvest some heat in winter, whilst keeping the majority out in summer.
The biggest question you should be asking is whether the solar gain outweighs any heat loss through the same glazing. For example, single glazing allows the most amount of solar gain to take place, but because it lacks sufficient insulation it also lets a huge amount of warm air to escape, likely leaving you deceptively warm with the winter sun in the sky but quite cold when it disappears. Double and triple glazing offer the best solutions because despite their typically low solar gain, they lock heat in a room far better than single glazing.
How to increase solar gain
The best way to increase solar gain is to increase the surface area of your glazing on the south, east and west sides of your house whilst also allowing the warm air to flow through your space. As you leave summer behind and begin to navigate autumn, it is also a good idea to clean the windows and prune any surrounding trees/shrubs, preventing any obstacles (big or small) from limiting the amount of sunlight hitting your glazing. It is also worth noting that increasing solar gain in winter is good, but it should also be a consideration for summer too (high solar gain in summer can prove to be quite uncomfortable).
How to reduce solar gain
Experts suggest that the installation of double glazing instead of single can reduce solar gain by as much as 10%, but there are other initiatives you can implement to reduce your property’s solar gain. For example, a low-emissivity coating limits the amount of heat-causing infrared radiation passing through the glass by reflecting it outside without impacting the visible light. In the summer this coating limits the amount of heat entering the building; in the winter it prevents the heat from leaving so easily.
On the otherhand, a more technical approach would be to install smart glazing, whereby glass can be electromagnetically activated via a remote control to limit the solar gain whenever you like. A variation of this smart glazing is thermochromic glass which changes its tint in direct response to temperature changes.
Our approach to solar gain
As you may have gathered from this blog post, the concept of solar gain is a complicated one. You, as a homeowner, project manager, architect or contractor should not simply eliminate solar gain or increase it to the max. Instead, our advice is to manage the solar gain using premium glazing and modern technologies like low-emissivity coatings, smart glazing and thermochromic glass. You can also install physical barriers like retractable awnings, pergolas, blinds and shutters.
The perfect solution is out there, but it can sometimes be difficult to know exactly what that looks like for you and your project. For over three decades, we have been helping clients to balance solar gain within their homes and commercial buildings; if you would like us to help you, speak to our team of glazing specialists today.
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