While large windows can flood households with natural light, they can also cause draughts, making the colder months extremely expensive. Research by Greenspec found that, without proper insulation, windows can cause around 10% of a home’s heat to escape. However, by replacing old, single-glazed windows and doors with thermally efficient double-glazed frames, homeowners can reduce their energy bills by an average of 12%.
Joe Halsall, Digital Marketing Manager at doors and windows specialist Origin Global, says: “Having large windows can be very aesthetically pleasing and the size doesn’t need to be compromised in order to retain heat.
“With the use of solar gain, large windows and doors can be environmentally friendly, create a more comfortable living space and save the homeowner money.”
What is solar gain?
Solar gain is when short-wave radiation from the sun increases the temperature inside a property. A home can take advantage of this by:
• gathering heat when the sun shines through a window
• keeping it surrounded by materials that store heat, such as concrete, brick and stone—also known as ‘thermal mass’
According to some reports, up to 75% of solar energy hitting a window is converted into thermal energy. Using solid materials in a building’s structure means solar gains can be stored through the day then released as the temperature drops. The same materials also absorb heat from warm air in the house during the colder months.
Solar heat is transferred and stored in different areas of the house by radiation and convection, with some households using fans to distribute the heat around the home.
Duncan McCombie, CEO of YES Energy Solutions, said: “Theoretically, passive solar gain is good as it provides free heat across the year.
“The solid elements of the construction of a house (the thermal mass) warm up in the sun’s heat, slowly releasing it like a radiator when the sun goes down.
“[The number of hours of heating that might be saved] is house-specific and relates directly to its construction and insulation, as well as the thermal gain from the sun, so is also weather related.”
How to make your home as efficient as possible
When fitting more efficient windows, always consider:
• the U-factor—a measure of how much heat the window will let escape
• the Solar Heat Gain Coefficient (SHGC)—the fraction of heat radiated from the sun that travels through a window to the inside of a property
To keep your home as warm as possible during cooler months, you want a low U-factor and a high SHGC, but this will vary depending on the climate in which you live.
Low emissivity (Low-E) glass, which often has an invisible coating of metal oxide, is the most energy-efficient type of double glazing. This glass absorbs light and heat and lowers the volume of heat that can seep out.
Colin Rees, Consulting Manager of IES, a world leader in 3D performance analysis software used to design energy efficient buildings, said: “Solar gain is an important element when considering a building’s energy and comfort performance.
“Assessing the building façade and passive design strategies is significant due to the interaction of solar gain and how this is either captured through glazing and thermal mass, or rejected through local shading, and avoided due to surrounding buildings/topography.
“Correctly assessing solar capture has a great impact on the building’s peak space loads and how to reduce plant need and then accurately size plant capacities.”
Best face forward
The orientation of a building has a dramatic effect on solar gain, so taking advantage means carefully choosing where you buy or build a property.
For maximum efficiency, it’s important to place new windows or bi-fold doors where they will receive the most sunlight. North-facing windows admit an even amount of light that does not produce a glare, while south-facing windows adapt well to seasonal changes by absorbing plenty of heat through winter and less during summer.
Duncan said: “The additional benefit of having suitable doors, bifold or trifold, is beyond the obvious savings.
“Reducing drafts and leaking heat from gaps brings great energy savings. However, there is an equally important comfort and aesthetic benefit that is achieved by having a ‘usable space’.
“This is very particular to the house, but the best room will be where there is the greatest use of the room, be that living room, kitchen or family room.”
Reducing solar gain in hotter climates
Solar gain can be extremely beneficial during winter but threatens overheating through the hotter months. To avoid this, shade windows from direct sunlight. Blinds, curtains and even deciduous trees planted in front of windows can limit solar gain through summer, without it affecting the rise of solar heat needed in winter.
Colin added: “Air Conditioning systems are commonly placed to manage the cooling requirements due to captured solar gains, particularly in buildings with highly glazed façades.
“However, the AC will not solve potential high mean radiant temperatures on space surfaces so operative temperatures may still be high. Analysis and interrogation will unlock these findings.
“Where buildings experience high occupancy then correctly managing solar gains is imperative to avoid overheating for naturally ventilated spaces.”
Homeowners can minimise the need for air-conditioning by using heat-reflective glass. The glass enables visible light to pass through, while the reflective coating (which has a mirror-like appearance) reduces heat gain and glare.
Colin said: “Exposure to solar gains and managing how they work with a building can often be the deciding factor to a high-performance building or one that occupants experience significant discomfort.”
Increasingly, people are looking for ways to help the environment and reduce their carbon footprint, be it through cutting down on plastic packaging or reducing air miles. Harnessing the sun to reduce lighting and heating bills is another great way to make changes.
While many homeowners consider adding bi-fold doors to their property for reasons of style and functionality, such an addition also helps you let the sun into your home and benefit from the heat and warmth it supplies.