Citation: Crawley, J.; Manouseli, D.; Mallaburn, P.; Elwell, C. An Empirical Energy Demand Flexibility Metric for Residential Properties. Energies 2022, 15, 5304. https:// doi.org/10.3390/en15145304 Academic Editor: Fabrizio Ascione Received: 22 June 2022 Accepted: 18 July 2022 Published: 21 July 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). energies Article An Empirical Energy Demand Flexibility Metric for Residential Properties Jenny Crawley, Despina Manouseli *, Peter Mallaburn and Cliff Elwell UCL Energy Institute, University College London, London WC1H 0NN, UK; jenny.crawley@ucl.ac.uk (J.C.); peter.mallaburn@ucl.ac.uk (P.M.); clifford.elwell@ucl.ac.uk (C.E.) * Correspondence: d.manouseli@ucl.ac.uk Abstract: Shifting from heating using fossil fuel combustion to electrified heating, dominated by heat pumps, is central to many countries’ decarbonisation strategy. The consequent increase in electricity demand, combined with that from electric vehicles, and the shift from non-renewable to renewable generation requires increased demand flexibility to support system operation. Demand side response through interrupting heating during peak demands has been widely proposed and simulation modelling has been used to determine the technical potential. This paper proposes an empirical approach to quantifying a building’s potential to operate flexibly, presenting a metric based on measured temperature drop in a dwelling under standard conditions after heating is switched off, using smart meter and internal temperature data. A result was derived for 96% of 193 homes within a test dataset, mean temperature drop of 1.5 ◦ C in 3 h at 15 ◦ C inside-outside temperature differential. An empirical flexibility metric may support decision making and decarbonisation. For households it may support the transition to heat pumps, enabling time of use costs and tariffs to be better understood and system to be specified by installers. Electricity system stakeholders, such as aggregators and DNOs may use it to identify the potential for demand response, managing local networks, infrastructure and aggregation. Keywords: flexibility metric; domestic buildings; temperature decay; electrified heating; smart meter data; demand side response; heat pumps; energy performance certificate 1. Introduction Reaching net zero CO 2 emissions requires rapid decarbonisation of the built envi- ronment [1]. Globally, over half of buildings are heated using direct combustion of fossil fuels [2], but decarbonisation of heating is widely expected to require switching to heat pumps powered by renewable or other low carbon electricity [3]. The electrification of heat will create new challenges for local and national electricity systems, such as local grid congestion [4] and large seasonal variation in electricity demand [5] alongside increased electricity demands from the electrification of the transport sector [6]. These challenges have led to much work on how demand-side flexibility may be used to decrease and diversify the peak electricity demand [7]. The UK has a stock of 28 million dwellings, with approximately 24 million gas boilers and 2 million oil boilers [8] to replace with low carbon alternatives. The energy perfor- mance of UK homes, with their respective energy conversion technologies, is indicated through Energy Performance Certificate (EPC) ratings, which are also used to provide recommendations to householders and landlords on cost-effective energy related upgrades. EPC ratings in the UK are derived from closely related methods to those used in many territories: physical survey of properties, followed by modelling which estimates the annual energy costs from a standard usage pattern [9]. As the energy system decarbonises and the requirements placed upon it change through the electrification of heat and transport, the information provided by EPCs may need to change to better reflect the costs to consumers Energies 2022, 15, 5304. https://doi.org/10.3390/en15145304 https://www.mdpi.com/journal/energies