Evaluating past and future building operational emissions: Improved method

A simple method is presented to improve the evaluation of past and/or future CO2 emissions of heating and/or cooling a building. The degree-day energy emission coefficient (DD-EEC) method relies on two established techniques. It starts with a building’s known annual heating and/or cooling energy consumption. Degree-days are employed to estimate the consumption in other years, unveiling how climate warming influences the annual energy need for heating and/or cooling. The resulting emissions are then quantified by associating the energy need in each year with the emission factor for energy production that year. A case study demonstrates an application of the method: a 1950s' school building in Finland. Its past heating-related operational CO2 emissions are reconstructed from its erection until today, and the future heating and cooling emissions are forecasted until 2100. The case demonstrates the impact of climate warming and projected energy decarbonisation on emissions, showcasing that the past may not be the best future predictor. In the 2010s, the emissions were estimated to be 57% of the 1960s' level. In the 2090s, they could be as little as 5% of the 2010s' level, even though the building’s technical properties remain unchanged. PRACTICE RELEVANCE This new method is a straightforward technique that can be replicated and easily used by researchers and, most importantly, practitioners. The method is based on degree-days, which are widely used in building energy practice. The technique refines existing methodology, which does not yet consider the impact of a warmer climate and energy decarbonisation on a building’s emission generation, at least not together. The availability of robust research-based data determines whether the method can be applied only retrospectively or also prospectively; such data are available in the European Union and other places. The practice relevance of this method is it can improve decision-making based on whole-life life cycle analysis (LCA), where the ratio between a building’s embodied and operational emissions is a focal consideration in many kinds of decision-making situations. Too simple modelling of operational emissions risks getting this ratio wrong, potentially leading to decision-makers drawing incorrect conclusions with real-life adverse effects.