Environmental Engineering Reference
millions of tourists annually. In winter the lake cools off quite considerably and in
1880 and 1963 it was even completely frozen over. In summer, in contrast, it reaches
a temperature high enough to attract hordes of swimmers. If the entire supply of coal
consumed in Germany each year were used to heat the water, it would only be enough
to heat up the 50 cubic kilometres of water of Lake Constance just once to a tem-
perature of 9 °C. Looking at the USA, the whole US American primary energy supply
of one year would only suffi ce to heat up Lake Michigan by less than 5 °C on one
occasion. The sun, on the other hand, can provide pleasant water temperatures
without a problem and do it over many weeks.
Despite the heat of the sun, many bathers still fi nd swimming pool temperatures too
low in summer, so that pools are artifi cially heated. And because we only have to
heat up a small swimming pool and not all of Lake Constance or Lake Michigan,
many places pull out all the stops. In Germany there are about 8000 public outdoor
and indoor swimming pools. In addition, there are around 500 000 private pools. In
the USA there are about 8.6 million pools in total and 270 000 commercial pools.
Several hundred million euros are spent each year alone on heating public pools.
Yet alternatives are available that would defi nitely enable us to use the sun to save
fuel costs and considerably reduce the emission of carbon dioxide.
Outdoor swimming pools are particularly suitable targets for the use of solar energy.
Simple swimming pool absorbers heat up pool water directly. A pump conveys the
water through an absorber and a simple control ensures that water is only pumped
when the sun actually can heat it up (Figure 6.17). If the water were pumped through
the absorber tube at night as well, this would result in the pool water being cooled
again. A good half-square metre of solar absorber surface is needed per square metre
of pool area. The surface space that is needed is often found on buildings near the
swimming pool. Covering a pool at night can save further energy.
Figure 6.17 System for swimming pool heating using solar energy.