Advances in solar heating and cooling systems
The Physics Teacher
At the advent of a worldwide crisis in energy consumption and supply, interest in the sun as an alternative source of energy has increased dramatically. The impressive attributes of solar energy: the unlimited supply at zero fuel cost, the fact that it is nonpolluting, and its wide distribution over the earth, make this undeveloped energy source enormously attractive. An energy resource that cannot be exhausted or subject to price increases, that is environmentally ideal, and totally immune to
... totally immune to political embargo must be considered a prime alternative to the conventional energy fuels. Solar energy does have some disadvantages; most notably an intermittent and diffuse nature. But engineering technology is quite capable of overcoming the difficulties of a low energy density as well as the day-to-day and weather-induced fluctuations of the solar radiation. The prime obstacle, however, to the widespread utilization of solar energy is economics. Solar energy can provide virtually any form or amount of useful energy needs, if we are willing to pay the cost. Because of the complex economics of solar energy, we are only now arriving at a point where it can hope to compete in the market place with conventional fuels. Solar heating and cooling of buildings represent the best near term possibility for economical competitiveness. And because of this, a large and varied research and development effort on economical solar heating and cooling systems is now being conducted. This has provided for some impressive advances in solar energy technology; this paper will discuss several of the most noteworthy advances. A basic criterion for the choice of these ideas is that of a potential near term commercial feasibility . Solar collectors A solar collector is nothing more than a means of accepting incident solar radiation with the capability of delivering useful energy, usually in the form of heat. Figures 1 and 2 show simple, baseline, flat-plate collectors capable of using solar heating and cooling systems. Essentially each collector consists of an absorber plate (commonly a black metal surface) which absorbs the incident solar radiation and converts the solar energy to heat, which can be transferred to another part of the system by utilizing some appropriate heat transfer fluid. In the process of collecting energy, the absorber plate will, of course, tend to come to thermal equilibrium with its surroundings by giving up heat. The solar collector other than the absorber plate is designed for the single purpose of reducing these heat losses from the absorber plate . Heat may be lost from the absorber plate by the three methods of heat transfer: radiation, conduction, or convection . Insulation beneath the absorber redu ces all three methods of loss as does the transparent APRIL 1976 Dan S.