The inclusion of the urban heat island effect in design weather for net-zero buildings

Dry bulb air temperatures are increasing especially in the UK. On top of this there is the urban heat island intensity (UHII), the temperature difference between rural and hotter urban temperatures. This is important as most new and existing buildings are in urban areas subject to the urban heat island (UHI)., In this paper is an analysis of weather data in Manchester city centre is compared to the CIBSE Design Summer Year type 3 (DSY 3) weather data. The latter, based on weather data from the Meteorological Office at a non-urban contains little if any UHII data. The DSY3 is based on a very warm year but the lack of the UHII data severely underestimates city centre night time temperatures and overestimates the winter minima temperatures. This underestimates the heating effect for net-zero design for urban buildings. A simple algorithm, which has been derived from Manchester and London data, is shown to give a useful method of adding in the UHII. Practical application Some standard weather files underestimate night-time urban temperatures and this has potential for inaccurate heating and cooling predictions for new net-zero building designs. By comparing Manchester city-centre data with CIBSE DSY3 and applying a simple urban heat island intensity algorithm, designers can more accurately model real urban conditions, improving the reliability of thermal performance assessments and supporting better-informed building design decisions.