Metrics for energy performance in operation: The fallacy of single indicators

Many countries and organisations have now endorsed the climate emergency. New and existing buildings must play a big part in tackling this, though past history has been disappointing, e.g. with major gaps between predicted and actual energy performance. What metrics should be used to understand a building’s energy and carbon performance in operation? Here there is uncertainty. For example, the United States is introducing carbon metrics, the UK has used them for many years, while the European Union recently made primary energy the common standard. Even though the reduction of greenhouse gas emissions may be the prime objective, UK experience suggests that undue concentration on any single headline metric can lead to severe unintended outcomes. The paper outlines the history and some results of various energy and carbon metrics used in UK policies and publications for non-domestic buildings since the 1973 oil crisis, with a few examples from other countries. It suggests how multiple indicators may help resolve future problems, what metrics might be used and how to make the underlying detail more accessible, e.g. with component and system benchmarks. Policy relevance Recent UK policy on the climate impact of buildings has been largely framed in terms of CO2. This seemingly sensible paradigm has had unintended consequences. (1) Contributions from low-energy 'passive' design; efficient equipment; good construction, commissioning and handover; effective energy management; and renewable and low-carbon energy supplies are conflated. There is no target for energy consumption itself. (2) This has divorced building professionals from the realities of in-use performance and deprived many of the necessary agency to improve it. (3) The limited amount of feedback means that policies can favour measures that look good in theory, but which do not work well in practice. This can make buildings too complicated, with high operational and management costs. To stimulate sustainable investment in truly low-carbon buildings, a suite of metrics and benchmarks needs to focus on performance in practice and motivate all the players involved. Elements of a viable approach are presented. Once in-use energy performance becomes reliably visible, action can become more effective.