Environmental Engineering Reference
In-Depth Information
Figure 6.8
Comparison of fl at-plate and vacuum-tube collectors.
Illustration: Viessmann
Werke.
6.3 Solar Thermal Systems
6.3.1 Hot Water from the Sun
6.3.1.1 Gravity Systems
The sun can be used to heat water to a high temperature. This is something we
learned from Archimedes, who used a convex mirror to bring water to the boil as
far back as 214 BC. That's not surprising, some will say, because Archimedes was
not from Hamburg, London or Vancouver. In Southern Italy it is simply easier to
use the sun's energy. This is quite correct, but only up to a point.
The temperatures in the Mediterranean region are much higher than in Germany,
Great Britain or Canada and there is no worry there about frost damage to hot water
systems. Systems that use solar energy to produce hot water can be constructed
more simply and thus more cheaply in frost-free regions than in colder climates.
However, even at high latitudes solar energy is an excellent option for producing
desired heat.
Unfortunately, not all the people in sunny countries have received the message that
they should be making use of solar energy. Thermal solar systems are common in
Cyprus and Israel but not in Spain or the southern USA, although these areas also
have a sunny climate. Gravity systems are mainly used in countries that do not
get frost (Figures 6.9 and 6.10). A fl at-plate or vacuum-tube collector collects the
solar radiation and heats water that fl ows through the collector. A hot water storage
