The energy-saving potential of domestic zonal space heating controls: a socio-technical assessment of semi-detached and owner-occupied UK homes

Abstract

Over the past thirty years, heating in at least 79% of UK homes has involved warming the entire indoor space through the use of a central heating system (Office of National Statistics, 2019), resulting in heating rooms that are used rarely or periodically (e.g. bedrooms) as well as rooms that are used commonly (e.g. living rooms). Zonal heating controls are among the new smart heating technologies on offer and allow occupants to choose which rooms they heat, for how long they are heated and the temperature to which they are heated. This interdisciplinary research aims to evaluate the energy-saving potential of domestic zonal heating controls. A socio-technical research design was used to investigate how the occupants of a set of semi-detached, owner-occupied homes across the Midlands region of the UK (n = 24) interacted with zonal heating controls provided as part of their involvement with a previous research study and how their gas use and indoor air temperature changed following installation.A comparison of weather-normalised gas use for twelve months before and twelve months after installation of zonal heating controls showed a change in gas use between a 25% reduction and a 37% increase in the second year. A further twelve months of gas use was analysed to assess the consistency of change, highlighting an equally broad variation (range of 37% reduction to 18% increase against the baseline). However, 61% of homes consistently reduced, consistently increased or did not appreciably change their gas use over the 24 months following installation of zonal heating controls. Household interviews were used to identify extraneous variables and revealed that, while zonal heating controls could not be definitively attributed to observed gas use change, they may have been influential. Whilst there were small changes in average indoor air temperature after the installation of zonal controls (range of 1.2°C decrease to 1.4°C increase against the baseline), no relationship was found between change in gas use and change in living room or main bedroom air temperature. The assessment of heating times showed that the majority of homes observed to have reduced their gas use were at least 0.2°C cooler over mornings, afternoons, evenings and nights, while homes that had increased their gas use tended to have warmer mornings and cooler evenings. Insights from the household interviews led to the identification of three heating strategies enabled by the zonal heating controls: 1) A basic strategy where zones were heated to the same setpoint for equal durations, 2) An intermediate strategy where zones were heated to different setpoints for equal durations, and 3) An advanced strategy where zones were heated to different setpoints for different durations. No commonality was found between reported strategies or heating motivations and observed change in gas use.Data relating to the operation of the zonal controls were also examined, to determine whether the change in gas use or air temperature could be predicted by the frequency of heating setpoint temperature changes, the frequency of manual overrides or the frequency of changes made using the smartphone app. Operation of zonal heating controls was found not to correlate with change in gas use or air temperature. Household interviews revealed that the eight out of ten households found the zonal controls to be less complicated and have improved functionality compared to their conventional heating controls. For the majority of homes, one occupant continued to ‘take charge’ of making changes to the heating schedule. Almost half (48%) of the homes interviewed did not make use of the smartphone app to alter their heating schedule. No relationship was observed between the perceived difference in usability, who operated the zonal heating controls and preference for means of control and observed change in gas use.This research has built on studies that rely on modelling and laboratory experiments by investigating the energy-saving potential of zonal heating controls through a multi-year field study. The mixed-method approach has enabled a holistic consideration of the role that zonal heating controls could play in the future of domestic space heating in the wider market. This meets a critical need to complement the analysis of gas use and air temperature change after installation of zonal heating controls, to evaluate their potential as an energy-saving measure, with an assessment of how and why energy use may have increased or decreased. This research contributes to the evidence base for new policies aimed at reducing domestic space heating demand, bolsters understanding of heating strategies for use in modelling applications and supports the future design of heating controls.