ABSTRACT
Solar heating has many other applications than the heating of water; this chapter reviews some of the most important, using the theory of heat transfer and storage already considered in Chapters 4 and 5. We introduce main concepts only and give guidance to specialist literature for detailed knowledge. Keeping buildings warm in winter, and cool in summer, accounts for up
to half of the energy requirements of many countries (see Figure 16.2). Even a partial contribution to this load, by designing or redesigning buildings to make use of solar energy, abates nationally significant amounts of fuel per year. Section 6.3 considers the design and construction of energy-efficient, solar-friendlybuildings that hasbecomean important aspect ofmodernarchitecture (yet sadly somevery energy-inefficient buildings are still constructed!). For best results, the design requires an integrated approach, taking account of not only the solar inputs and their interaction with the building envelope, but also the internal heat transfers in the building, not least those gains arising from the activities, equipment, plant andmachines of the occupants. Solar heat can also be used to heat air for drying crops (Section 6.4).
Much of the present world grain harvest is lost to fungal attack, which could be prevented by proper drying. Crop drying requires the transfer not only of heat but also of water vapour. This is even more so in the solar desalination systems discussed in Section 6.6, including the use of solar heat to distil fresh (potable) water from saline or brackish impure water. Heat engines convert heat into work (which may in turn be converted
to electricity), and can be powered by solar radiation. Indeed, since the potential efficiency of heat engines increases with their working temperature, there are theoretical advantages in using solar radiation, which arrives at a thermodynamic temperature of 6000K, as discussed in Section 6.8. High temperatures are obtained by concentrating clear sky insolation on a surface of area much less than that of the concentrating mirror. Indeed, if the concentrators are large and the area is shielded in a cavity, temperatures approaching but not equalling 6000K can be obtained. Such devices
