Impact of inter-building longwave radiative exchanges on building energy performance and indoor overheating

Despite inter-building longwave radiative exchanges playing an important role in determining building energy and environmental performance, simulation tools (e.g. EnergyPlus) simplify this by assuming the surface temperature of surrounding buildings to be equal to the air temperature, and therefore cause bias. Here we propose a ‘spin-up’ approach to update surrounding building external surface temperature using either air or the isolated building temperatures. Neighbourhoods with different plan area fractions of buildings (λ_P) are analysed to assess the impact on building external surface temperatures, cooling and heating energy demand as well as indoor overheating degree hours. Using the default EnergyPlus method causes a large bias in all metrics in a dense urban area (λ_P = 0.6) and climates assessed (cf. the new method): external wall temperature (3 °C less, midday median), annual energy demand for cooling (17.1% less) and heating (6.2% higher), annual overheating degree hours during the day (>28 °C, 24.5% less) and night (>26 °C, 60.1% less). These biases are larger at lower latitudes. Thus, neglecting the surroundings' influence on inter-building longwave radiation impacts critical design considerations of building energy and thermal performance in dense urban areas. An approach to account for proximal buildings should be used.