Page 262 - Alternative Energy Systems in Building Design

238 PASSIVE SOLAR HEATING TECHNOLOGIES

WASTE HEAT FROM
LOW PRESSURE STEAM

HIGH PRESSURE
GENERATOR
REFRIGERATED VAPOR
TO CONDENSER

LOW PRESSURE
ABSORBER
REFRIGERATED VAPOR
FROM CONDENSER

REJECTED HEAT
Figure 6.11 Evaporation and condensation cycle in refrigeration.

Steam will condense back to a liquid state if heat energy is removed from it. The
liquid, in turn, will change into its solid state (ice) when sufficient heat energy is
removed from it. The processes can be reversed when heat energy is introduced into
the medium.
The state of change is related to the fact that in various substances, depending on
the presence or absence of heat energy, a phenomenon referred to as atomic thermal
agitation causes expansion and contraction of molecules. A close contraction of mol-
ecules forms solids, and a larger separation transforms matter into liquid and gaseous
states. In border-state energy conditions, an excess lack (beyond the solid state) or
excess surplus (beyond the gaseous state) of energy creates the states referred to as
supercooled and superheated, respectively.

PRINCIPLES OF REFRIGERATION

Refrigeration is accomplished by two distinct processes (see Fig. 6.11). In one
process, referred to as the compression cycle, a medium, such as Freon gas, is first
given heat energy by compression, which turns the gas into a liquid. Then, in a