Solar Engineering of Thermal Processes, 4th Edition

Chapter 12

Solar Water Heating: Active and Passive

This is the first of a set of chapters on thermal energy applications. In this chapter, we treat the use of solar heating for domestic or institutional hot-water supplies. Descriptions of systems, components, and important design considerations are outlined. Considerations important in designing water heating systems are also basic to solar heating and cooling systems, applications that are covered in succeeding chapters. Many of the principles noted here for service hot water for buildings also apply to industrial process heat, discussed in Chapter 16.

In recent years considerable knowledge has been developed about low-flow hot-water systems; these use collector flow rates a fifth or so of those that have been commonly used in forced-circulation systems. The of collectors operated this way is lower than that in conventional operation, but higher stratification in storage tanks can be obtained, resulting in lower collector inlet temperatures and improved performance. These developments are of sufficient importance that they are discussed in a separate section.

12.1 Water Heating Systems

The basic elements in solar water heaters can be arranged in several system configurations. The most common of these are shown in Figure 12.1.1. Auxiliary energy is shown added in three different ways; these are interchangeable among the four methods ...