Environmental Engineering Reference
In-Depth Information
100
%
optical losses
90
%
80
%
70
%
thermal losses
60
%
50
%
40
%
30
%
20
%
10
%
0
%
0 0 0 0 0 0 0 0 0 0 0 0 0 0
temperature difference collector - ambient air in °C
Figure 6.3
Collector effi ciency curve.
heat loss than small ones. The storage volume increases considerably faster than the
size of the storage surface. However, storage losses depend only on the size of the
surface of the storage.
6.2 Solar Collectors - Collecting the Sun
6.2.1 Swimming Pool Absorbers
Different types of collectors are available for different purposes. The simplest type
of collector consists of only one absorber. Placing a dark garden hose fi lled with
water in the sun for a time produces enough heated water for a short but warm
shower. A garden hose thus already has the characteristics of an absorber. In prin-
ciple, a professional swimming pool absorber is also nothing more than a simple
black plastic pipe that absorbs the sunlight almost optimally due to its dark colour.
Weather-resistant plastics that cope well with UV light and chlorinated pool water
are used for this purpose. The materials that are suitable are polyethylene (PE),
polypropylene ( PP ) and ethylene - propylene - dien - monomere ( EPDM ). PVC should
be avoided for ecological reasons. In winter it is futile trying to use a garden hose
to extract warm shower water. The same applies to swimming pool absorbers.
Although an absorber continues to absorb the sun's radiation, the heat loss in the
absorber pipe itself is so great that hardly any heat can be drawn from the end of a
pipe. Technically more sophisticated collectors are required to use the sun's heat
during winter and the transitional periods of the year or when water temperatures
should be warmer than the water in a swimming pool.
