Environmental Engineering Reference
In-Depth Information
Figure 6.16
Principle of solar cooling with absorption-refrigerating machines.
water itself under low pressure can be used as a cooling agent. Lithium-bromide is
then suitable as the solvent.
The cooling agent boils in a vaporizer at low temperatures. In the process it extracts
the heat from the cooling system. The cooling agent then has to be liquefi ed again
so that it can provide continuous cooling through renewed evaporation. With the
help of a few tricks and an indirect way through sorption, the liquidation also suc-
ceeds through the use of solar heat.
The cooling machine absorber fi rst mixes the cooling agent vapour with the solvent.
This produces sorption that releases the heat. This heat is either used to heat the
water or is transferred to a cooling tower.
A solvent pump transports the liquid solution, which has been enriched with a
cooling agent, to the generator. The generator separates the cooling agent and the
solvent on the basis of their different boiling points. Heat from effi cient solar col-
lectors is used for the boiling process. Temperatures of 100 °C to 150 °C are optimal.
The separated vapour-formed cooling agent then enters a condenser, which liquefi es
the cooling agent. The condensation heat is also dissipated either as useful heat or
over a cooling tower. The liquid cooling agent enters the vaporizer over an expan-
sion valve and the solvent returns again to the refrigerating machine absorber. The
cooling agent cools down considerably through the expansion in the expansion valve
and can again deliver cooling to the cooling system over the vaporizer.
6.3.5 Swimming with the Sun
During the outdoor swimming season in Central Europe water temperatures normally
reach 10 to 19 °C. The water is only warmer than this for a few days during the height
of summer, although this period is becoming longer because of global warming.
These water temperatures are a result of swimming pool water being heated by the
sun. The following example shows how enormous the energy content of the sun is.
The example uses Lake Constance, a popular lake for swimming that is visited by
