Temperature adjustments for design data for urban air conditioning design

The urban heat island, where the urban area air temperature is higher than the nearby rural or semi-rural air temperature reference site, is now hopefully well known. The urban heat island intensity is the actual urban air temperature minus the rural air temperature. However, the “air conditioned urban heat island intensity” is measured by the air temperature sensor in an air conditioning condenser unit minus the rural air temperature. This is often different to the standard urban heat island intensity. Designers need to appreciate this difference, as it determines how the air conditioning system performs. It is most likely affected by the radiant temperature. This can also vary significantly from the rural, semi-rural radiant temperature due to the variation in solar absorptance of the urban buildings and the shading effects. Measurements have shown significant variations in the infrared temperatures over the urban areas. Calculations of the radiant absorption and long wave radiation loss also show significant differences to the rural counterparts in frequency and magnitude. This “surface urban heat island” is important for air conditioning plant situated often in areas exposed to solar irradiation. The exhaust air from the air conditioning units itself is also briefly considered. This paper examines these effects and proposes how the engineer can include for them in design. Practical application:The results of this paper will be useful for designers of buildings with air conditioning and air conditioning plant itself to assess the effect of the micro urban heat island. This micro urban heat island surrounds the air conditioning plant. The example is for London.