Do energy labels have the capacity to mislead?

摘要

A purchaser naturally expects the energy performance of an“A” labelled product to be better than a “B”, and so on downthe scale. The energy efficiency index that underlies the ratingscale has been carefully designed to ensure that, but onlyunder specific assumptions about installation conditions andmethod of use.For some products – notably heat generators – energy performancevaries substantially under differing load conditions.For example, model X may be better than model Y under fullload but Y is better than X under low load. The energy efficiencyindex might have been designed with this possibility inmind, calling for tests at two or more load conditions and combiningthe results in some way to produce the single-numberindex that determines the A to G rating. It is the combinationprocess that is the weak step here, because both X and Y mayachieve the same rating on the label but X would be better thanY if installed in a building with high loads and Y would be betterthan X with low loads.This presents a problem for an energy labelling scheme inwhich the installation conditions are not known at the timethe energy rating is calculated. Conditions can, of course, beassumed in the energy calculation but there is no prospect ofchanging the result to represent actual conditions without anothercalculation using real building data. It could turn out thatof two products X and Y, having energy ratings A and B respectively,X is not the better choice.Should we therefore abandon the energy labelling of productswhere the labelling method is too simplistic, inevitably sobecause building characteristics strongly affect performancebut are not known at the time of labelling? What other products,apart from heat generators, might be subject to similarmethodological weaknesses? Or are there other solutions thatcan overcome the difficulty and produce more reliable guidance?