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On top of climate change and its consequent temperature rises, urban areas have the added burden of the urban heat island (the urban area being warmer than the rural area especially at night under calm, cloud-free conditions). The urban heat island intensity (the difference between the rural air temperature and that in the city centre) can be as large as 10K for the major cities such as London. The urban heat island intensity, consequently, can have a significant effect on the sizing of heating, ventilating and air-conditioning plant and its energy consumption. At present, designers have access to empirical factors for design days only in June, July and August from the Chartered Institution of Building Services Engineers Guide. Or they can use the latest Design Summer Year which implicitly includes the urban heat island intensity. However, the empirical model discussed in this paper allows the designer to add on the hourly urban heat island intensity for central London to any recent year's hourly weather data set from London Heathrow or Bracknell, a more rural site. The model is similar to one for Manchester, suggesting that the model may well be of application to other UK cities.

Practical applications: Most buildings that building services engineers and other building designers are involved with are in urban or city centres. However, the weather data for their designs are based on near-rural weather data, which does not include the urban heat island effect. This paper describes the urban heat island effects that a designer needs to consider and the adjustments that can be made, related to London.