Page 322 - Handbook of Energy Engineering Calculations

media. And air systems are generally not suitable for comfort cooling or
liquid heating, such as domestic hot water.
Eutectic salts can be used to increase the storage capacity of air systems
while reducing the volume required for storage space. But these salts are
expensive, corrosive, and toxic, and they become less effective with repeated

use. Where it is desired to store thermal energy at temperatures above 200°F
(93.3°C), pressurized storage tanks are attractive.
Solar “heat wheels” can be used in the basic solar heating and cooling

system in the intake and return passages of the solar system. The wheels
permit the transfer of thermal energy from the return to the intake side of the
system and offer a means of controlling humidity.
For solar cooling, high-performance flat-plate collectors or concentrators
are needed to generate the 200 to 240°F (93.3 to 115.6°C) temperatures

necessary for an absorption-chiller input. These chillers use either lithium
bromide or ammonia with hot water for an absorbent/refrigerant solution.
Chiller operation is conventional.

Solar collectors can be used as a heat source for heat-pump systems in
which the pump transfers heat to a storage tank. The hot water in the tank can
then be used for heating, while the heat pump supplies cooling.
In summary, solar energy is a particularly valuable source of heat to
augment conventional space-heating and cooling systems and for heating

liquids. The practical aspects of system operation can be troublesome—
corrosion, deterioration, freezing, condensation, leaks—but these problems
can be surmounted. Solar energy is not “free” because a relatively high initial

investment for equipment must be paid off over a long period. And the
equipment requires some fossil-fuel energy to fabricate.
But even with these slight disadvantages, the more solar energy that can be
put to work, the longer the supply of fossil fuels will last. And recent studies
show that solar energy will become more cost-competitive as the price of

fossil fuels continues to rise.

6. Give design guides for typical solar systems
To ensure the best performance from any solar system, keep these pointers in
mind:

a. For space heating, size the solar collector to have an area or, 25 to 50