Controlling energy efficiency

Tony Pell, product manager at JELD-WEN, considers how windows play a much greater part in controlling both energy efficiency and heat loss in a property.

WITH THE latest innovations in product design and technology, it has never been easier to control the internal environment within a building through the right choice of window.

In the past, choosing windows meant a trade-off between letting sufficient light into a property to create an acceptable standard of living (the larger the window the better), whilstensuring the building was thermally efficient (smaller windows traditionally meant less heat loss).

Recent improvements in both glass and frame design mean timber windows now offer some of the best thermal performances on the market. The glazed area can therefore be increased, whilst still controlling the temperature in the home.

Whereas previously, blinds and shutters were needed to control solar gain, the advent of microscopically thin metal coatings to glass, gas filling technology and warm edge spacer bars means the new generation of high performance timber windows provide a key element of a sustainable build.

With around 20% of heat typically lost through windows, choosing the right frame and glass combination is vitally important. Research carried out by the timber industry shows that wood windows are capable of achieving equally as good insulating properties as any other material and, indeed the thermal performance of timber is equal to that of most of the other common frame materials. As the only completely renewable material, there has been a significant increase in demand in the market for Chain of Custody certified timber windows because of their sustainable benefits.

Developers are increasingly demanding greater functionality from their windows. Instead of just having aesthetic appeal, they are required to provide; lower U-values, controlled solar heat gain, better light transmittance from outside to inside, reduced air leakage and low maintenance. This helped lead to our development of high performance windows with U-values as low as 1.1Wm2K and the A-E energy rated Ultra range. Ultra range windows are available in our Sovereign Stormsure and our vertical sliding sash styles.

They provide enhanced energy performance and we have made ‘A’ rated timber windows a commercial reality. These windows are proving popular with developers and self builders as they are helping them to meet the requirements of current building regulations and the Code for Sustainable Homes.

Achieving better temperature control throughout both summer and winter is a vital function of these windows. Temperature is controlled because of advances in glazing efficiency due to innovation in the development of Low-E glass. Its thin metallic coating to the internal surface of Low-E glass, within the airspace, keeps heat from radiators during winter in the room, whilst reflecting solar radiation back to the outside during hot summer days, which keeps the room cooler.

Soft-coated Low-E is even more effective than conventional Low-E glass and is being specified by those within the industry looking for the greatest thermal performance from their windows. We are already seeing many developers choosing timber windows with high specification glass units because of the ideal combination between sustainability and energy efficiency.

Glass units make up the major part of any window, covering over 75% of the overall area. When making windows more energy efficient, the insulated glass unit (IGU) has to be carefully considered. Inert gases such as Argon and Krypton are being widely used between insulated glass units to provide even greater efficiency and the resulting windows are making a significant difference to the lives of many homeowners.

As most heat loss from windows occurs around the edges i.e, the junction between the IGU and window frame material, there are major advantages in using warm edge spacer bar technology. This improves heat retention along the junction of IGU and window material in line with the basic requirements of Approved Document L.

With the rising costs of fuel bills and improvements in manufacturing efficiencies, triple glazing is another fast growing area of the window market at the moment.

As the mainstream market for triple glazing grows, developers and contractors are increasingly purchasing factory glazed windows to ensure maximum performance. However, it is not just the window design that matters, but also the installation that is equally important. This is the reason why supply and fit services are becoming more prominent in the window industry, where correct installation techniques and therefore thermal performance is guaranteed.

Fitting energy efficient windows goes a long way towards helping building owners and occupiers to reduce their energy usage, save on fuel bills and do their bit for the environment. The ever tightening building regulations and the requirements of the Code for Sustainable Homes have further enforced the need for careful consideration of the type of windows specified. Never before has specifying the right windows been so important in reducing whole building running costs.