Table 15-1.Advantages and Disadvantages of Air and Liquid Heating Systems
A I R
Can only be used to heat homes; can not presently be
economically adapted to cooling.
No freezing problems.
Large air ducts needed.
Minor leaks of little consequence.
Larger storage space needed for rocks.
As air is used to heat the house, no temperature losses due to
heat exchangers (devices which transfix heat from one fluid
Heat exchanger needed if system is to be used to heat water.
to another), when the system is used for space heat.
No boiling or pressure problems.
WATER OR LIQUID
Holds and transfers heat well.
Leaking, freezing, and corrosion can be problems.
Water can be used as storage.
Corrosion inhibitors needed with water when using steel or
aluminum. There are liquids which are noncorrosive and
Can be used to heat and cool homes.
nonelectrolytic; however, they are toxic and some of them
Compact storage and small conduits.
A separate collector loop using a nonfreezing fluid and a
heat exchanger or, alternatively, a draining water or
inhibited water system is required to prevent freezing. In
warm regions, where freezing is infrequent, electric warmers
or recirculation can be used.
The amount of solar energy collected by a
In addition to choosing the best collector tilt
solar collector depends on its efficiency. The
angle, take into consideration the direction that
construction, configuration, and the choice of
the collector faces. Normally, true south is the
material determines the efficiency of a solar
best and most frequent choice, However, 10
degrees west of south maybe preferable in some
locations if early morning haze or fog is a regular
SOLAR COLLECTOR ORIENTATION
Although solar collectors can collect heat
Equally important as collector location is
from the diffuse component of solar radiation,
keeping the collectors out of the shade, especially
solar systems are designed to use radiation. Direct
between 0900 and 1500 hours, when most of the
radiation is in the form of parallel rays coming
useful energy collection occurs. In summary
straight from the sun. To capture this energy, tilt
although many buildings do not have a perfect
the solar collector, as shown in figure 15-1, so it is
solar orientation, there are still many places with
nearly perpendicular to the solar rays.
good solar energy potential.