Systems for space heating are very similar to those for water heating, described in the previous chapter; and because the same considerations for combination with an auxiliary source, array design, over-temperature and freezing, controls, and the like apply to both, these will not be repeated. The most common heat transfer fluids are water, water and antifreeze mixtures, and air. The load is the building to be heated or cooled. Although it is technically possible to construct a solar heating or cooling system that can satisfy fully the design load, such a system would be non-viable, since it would be oversized most of the time. The size of the solar system may be determined by a life-cycle cost analysis described in Chapter 12.
Active solar space systems use collectors to heat a fluid, storage units to store solar energy until needed, and distribution equipment to provide the solar energy to the heated spaces in a controlled manner. Additionally, a complete system includes pumps or fans for transferring the energy to storage or to the load; these require a continuous availability of non-renewable energy, generally in the form of electricity.
The load can be space cooling, heating, or a combination of these two with hot water supply. When it is combined with conventional heating equipment, solar heating provides the same levels of comfort, temperature stability, and reliability as conventional systems.
During daytime, the solar energy system absorbs solar radiation with collectors and conveys it to storage using a suitable fluid. As the building requires heat, this is obtained from storage. Control of the solar energy system is exercised by differential temperature controllers, described in Chapter 5, Section 5.5. In locations where freezing conditions may occur, a low-temperature sensor is installed on the collector to control the solar pump when a preset temperature is reached. This process wastes some stored heat, but it prevents costly damage to the solar collectors. Alternatively, systems described in the previous chapter, such as the drain-down and drain-back, can be used, depending on whether the system is closed or open.
Solar cooling of buildings is an attractive idea because the cooling loads and availability of solar radiation are in phase. Additionally, the combination of solar cooling and heating greatly improves the use factors of collectors compared to heating alone. Solar air conditioning can be accomplished mainly by two types of systems: absorption cycles and adsorption (desiccant) cycles. Some of these cycles are also used in solar refrigeration systems. It should be noted that the same solar collectors are used for both space heating and cooling systems when both are present.
A review of the various solar heating and cooling systems is presented by Hahne (1996) and a review of solar and low-energy cooling technologies is presented by Florides et al. (2002a).
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Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.