As a designer or specifier you will set U value requirements for elements of your building in order to meet Building Regulations, ensure comfort and avoid condensation.
Suppliers will offer products to “comply” with your specifications and quote a U value. But is it the real U value?
There are too many people out there making claims based only on a “centre panel” U value, not a “whole product” U value, but without making this clear. Whether this is done through ignorance or guile is not always clear but the result certainly is – you’re not getting what you specified and paid for as the centre panel U value is inevitably better than the whole product U value.
Calculations of thermal losses are difficult and complex. For a natural ventilator for instance, all aspects of the ventilator construction – the lid, frame, base, etc – have to be taken into account and these are likely to have a complex construction. But that is no excuse for providing misleading data.
Generally if a U value looks too good to be true it probably is.
How do you avoid this? Well firstly a tight specification is helpful, detailing that U values must be whole product and based either on calculation as required in Building Regulations or upon test. Secondly question any suspicious U values. A couple of simple questions are usually enough.
Conor Logan is Associate Technical Director of Colt UK, Smoke and Climate Control Division. Conor designs innovative smoke control and HVAC systems and is also Chairman of the Smoke Control Association.