U-values or WERs?
Jason McCabe, commercial and site director of Clayton Glass, discusses the relationship between product innovation and customer demand.
There are many variables affecting the market for energy efficient products, not just in our industry, but across many global industrial and consumer sectors; while customer demand can often drive product design and specification, it’s sometimes a bigger influence such as government policy, legislation or social stimuli that can have a far deeper impact and this push seems to have been lost in recent years.
Interestingly, over the last couple of years, we have seen the increased adoption of U-values as a means of measurement for energy efficiency in windows and doors, particularly in the timber and aluminium segments, where architects are more often involved. That is not to say the death of the Window Energy Ratings (WERs) is nigh, but that U-values are becoming increasingly adopted.
I think this is a good thing because I believe the assessment of U-values is a more useful means of evaluating the performance of glazing than the WER scheme in its current guise.
One way of seeing this is by comparing two insulated glass units, one at 1.2W/m2/K, and the other at 1.0W/m2/K.
On one hand, we have a WER-optimised 1.2 unit, which, while having a good U-value, could be better, but instead has the potential of additional insulation traded off for some theoretical free solar gain. Depending on a number factors (elevation, season, sun direction, shading etc) the amount of positive solar gain is debatable – let alone being able to standardise it in a typical dwelling.
Conversely, however, designing your windows by optimised U-value would mean the selection of a 1.0W/m2/K unit as opposed to 1.2, and the effect is much more direct, calculable and simple. The dwelling – regardless of location – will lose 17% less heat through the glass, all year, every season, all day, every day. Here, the overriding factor is easy to see, and I’m left wondering why around 80% of the energy efficient units we sell lose more heat than they otherwise could.
Additionally, here at Clayton, because of our very high level of activity within the conservatory sector, we also do a lot of work on thermal efficiency but at the other end of the scale. With our Smartglass brand, we offer market leading levels of solar control, and we do this not just in the roofing plane, but also in the side frames with our Smartglass-W product.
Careful design and planning can dramatically reduce solar gain in a conservatory or garden room – fitting standard WER side frames and a mid-specification blue roof for example will get you to a decent average of around 55% whole room G-value, blocking 45% of solar gain.
Yet, with more consideration and by using (for example) our top-end Ultra 86 product partnered with a 1.0/50% wall panel, the aggregate G-value for the room will be more like 32% – that’s over 40% less solar gain, together with improvements in comfort and a reduction in cooling costs, etc.
Service is also key, and this is certainly driving customer demand. Over the course of this year we have had a number of enquiries from companies looking for a more consistent supply chain for IGUs. Historically we’ve quoted otif levels of 98% as an overall expectation of what we could deliver, yet recently we’ve seen much better.
With a ‘zero fail’ attitude, we’ve averaged over 99.99% otif on more than one account. That’s total consistency over a 10-month period with single figure shortages from over 40,000 units transacted.
The drive for energy efficiency in glazing should be considered in replacement markets and the conservatory and glazed extension markets. Lower U-values and a better ability to limit solar heat gain must remain high on the agenda for the industry as consumers look to us for expert advice and better solutions for a modern way of living with glass.