ABSTRACT
All surfaces in the urban environment absorb solar radiation in the spectrum 0.3 micron (μm) to 3μm; we tend to refer to this as shortwave radiation exchange. These urban surfaces also transfer heat to other surfaces by radiation exchange in the spectrum 3–4μm to 100μm (i.e. the infrared part of the electromagnetic spectrum). This we tend to refer to as longwave radiation exchange. 1 These surface radiation exchange processes are an important determinant of the temperature of our urban surfaces, which correspondingly influences (and is influenced by) convective heat transfer to the air in contact with these surfaces as well as the transfer of heat by conduction into the material from which the surface is composed. The former transfer of heat by convection plays a key role in determining the urban climate, which may vary considerably in both space and time from that experienced in an adjacent rural context. We address this in detail in Chapter 4. For surfaces that represent a boundary between the outdoor and indoor environments of buildings, the transfer by conduction plays a key role in determining a building’s energy balance and thus the energy consumed within the urban environment due to buildings. In the case of transparent surfaces, transmitted shortwave energy may be converted into heat, or electricity in the case of thermal or photovoltaic solar collectors, or contribute directly to buildings’ energy balances.
