OVERHEATING | TESTING MODELS MODEL HOUSING To minimise overheating in homes it is important to produce accurate models to understand where risks might lie. To test the accuracy of modellers predictions, researchers led by Ben Roberts compared four models with real-life temperatures in two homes The 1930s test houses in the East Midlands R educing the risk of summertime overheating in UK homes is important because of the health implications of high indoor temperatures, and the increase in electricity demand if more air conditioning is used. The Committee on Climate Change has identified dynamic thermal modelling (DTM) programs and CIBSE Technical Memoranda TM52 and TM59 as potential enablers of new standards or regulation to reduce overheating risk. To be viable, DTM programs must steer designers towards low-risk designs by predicting correctly the relative overheating experienced by alternative design proposals. The 2020 Carter Bronze medal-winning research paper Predictions of summertime overheating: comparison of dynamic thermal models and measurements in synthetically occupied test houses1 compared DTM program predictions of summertime temperatures with those measured in the matched pair test houses at Loughborough University. It was a collaborative empirical validation and inter-model comparison between four modellers and a monitoring and validation team. The four modellers were all employed in professional organisations and none was involved in the experimental work, or had prior knowledge or experience of the test houses. Each chose a CIBSE AM11compliant DTM program that they use regularly in their work and which is widely used in industry. Two modellers selected versions of one program, while the other two selected versions of a different one. The test houses are two nominally identical, semi-detached homes, built in the 1930s in the East Midlands, UK. They are south facing, with windows on the east and west faades covered and insulated so that solar gains are consistent. The houses have the same uninsulated cavity-wall construction, a suspended timber ground floor with a ventilated void below, and ventilated roof space. Both were retrofitted with 300mm of insulation above the first-floor ceiling and double glazing to all doors and windows, with identical operable elements. The facility is fully instrumented, with calibrated sensors inside and out. Synthetic occupants systems for the automation and control of internal heat gains (electrical heaters), internal doors, windows, blinds and curtains allow accurate and repeatable side-by-side experiments to be carried out. The houses have been used in numerous research projects on topics including mitigation of summertime overheating, model validation, thermal performance evaluation, thermal comfort, ventilation, energy-saving performance, and energy flexibility. A side-by-side overheating experiment was carried out in the houses from 16 June to 6 July 2017. There was a spell of hot weather during this period, which caused overheating and tested the models reliability for making accurate predictions. Heat-gain profiles in each house were set to mimic those recommended in TM59. Blinds and curtains were opened in accordance with the TM59 sleeping schedule. Windows stayed closed in the East house but were opened in the West house if the room air temperature exceeded 22C and it was occupied (according to TM59 occupancy profiles) and closed if the air temperature fell below 22C or the room was unoccupied. Peak temperatures of the East house reached 28.9C in the living room and 31.9C in the front double bedroom. With operable windows, peak temperatures in the West house were only slighter cooler, at 28.5C (living room) and 30.9C (front bedroom). Predictions were made in two phases: blind and open. In the blind phase, modellers were given only information on the house construction, geometry, synthetic occupancy, heat-gain profiles and weather, and asked to make predictions of indoor temperature without knowing the measured indoor temperatures. In the open phase, the modellers were given indoor temperature data, revised their models, and made new 36 September 2020 www.cibsejournal.com CIBSE September 2020 p36-37 Measuring overheating.indd 36 21/08/2020 14:56