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Windows have a significant part to play in improving the energy performance of a building. Here, Martin Saunders, Sales Director of Eurocell, discusses whether future improvements will come from the frame or glazed units.

“The glazed unit receives its fair share of attention when it comes to thermal performance. The introduction of spacer bar technology, Low E glass and coatings have all had the effect of keeping attention focused on this area. However, improvements in glass performance are generally becoming incrementally smaller. What’s more, they can be expensive, forcing some specifiers to consider reducing the window size – often an unpopular move with homeowners. It is therefore no surprise that the industry is looking at other ways of achieving more cost effective ‘A’ rated windows.

Frame vs Glass

Over the last few years, glass and spacer bar manufacturers have been developing products to improve the performance of the sealed unit, which often turn out to be expensive – which is why we felt it was time a systems company did something to reduce the cost of an ‘A’ rated window. Thermal performance of the frame can be improved in several ways. For example, the benefit of multi chambered profiles on our Thermalogik profile system is already well understood and the challenge was therefore to use this principle as the basis to improve the performance of the frame even further.

The solution was found by developing a range of PVC-U Thermal Inserts. Subsequent performance modelling and extensive trials demonstrated that 4mm standard float glass can be used with thermal inserts, whilst still achieving an ‘A’ rating, because of the superior thermal efficiency of PVC-U over traditional steel or aluminium reinforcements.

The idea behind inserts is simple – they insulate the frame, reducing the amount of heat that escapes, just like insulation in the cavity wall. Our PVC-U Thermal Inserts, in addition to creating a better value ‘A’ rated window, are made of 100 per cent recycled material. That means the entire window frame is recyclable – making it quicker and easier to re-use post-consumer windows. It also means fabricators can highlight the recycled content to their customers.

A good example of the improvements in thermal performance offered by multi chamber profiles and PVC-U Thermal Inserts was highlighted in recent tests we carried out. Using PVC-U Thermal Inserts with our Eurologik profile system in conjunction with Thermalogik outer frames, the system achieved a BFRC ‘A’ rating without the use of Low Iron glass. Of course, some fabricators prefer to retain the higher glass specifications, allowing them to offer customers ‘A’ rated windows with an even better Energy Index.

Focus on achieving a higher Energy Index has resulted from the fact that ‘A’ rated windows are now widely available. Fabricators are therefore looking for other ways to retain their competitive edge – by achieving a higher Energy Index - and PVC-U Thermal Inserts are a cost effective way of doing this, as was demonstrated by our performance modelling.

A positive Energy Index means the window will allow more heat from the sun to pass through the glass and into the room than is going to be lost through the window. Using the PVC-U Thermal Inserts we developed, it is now possible to achieve an A 11 window, which is currently one of the best performing double glazed products on the market. This type of performance is usually only achieved by specifying expensive triple glazed units. In this example, the window will gain 11 kilowatt hours per square metre per year, which will contribute towards heating the home. Without PVC-U Thermal Inserts, the window would not have achieved A 11, as demonstrated when an identical window, without inserts achieved an ‘A’ rating of ‘0’ kWh/m²/year Energy Index – still a high performance window.

Working in partnership

Fabricators that use inserts in the frame find that it is a much more cost effective method of achieving an ‘A’ rating, with a higher Energy Index, than upgrading the glass specification. This is proving very effective in the current market as homeowners and housebuilders look for better value ‘A’ rated products.

In reality, achieving a better performing window will involve a combination of both frame and glass. As we move to zero-carbon homes by 2016 and non domestic buildings by 2018, any measures that improve the performance of the window are a good thing. Indeed, the best results are achieved when frame and glass manufacturers work together to create a solution that meets a market need. When we were developing our PVC-U Thermal Inserts, we worked closely with Solaglass to create the ideal combination of glass and frame specification that achieved a cost effective ‘A’ rated window.

Whether future innovation comes from the frame, glass or both, it is the built environment that will benefit. That is why fabricators should look at the technologies available to find the best solution when they are looking for cost effective and sustainable energy rated products. The solution often does not rest on the glass alone.”

For information on the PVC-u Thermal Inserts visit the Eurocell website: www.eurocell.co.uk or contact customer services on 0800 988 3049.