Environmental Engineering Reference
In-Depth Information
6.4.1 Solar Thermal Heating of Domestic Hot Water
6.4.1.1 Outline Design
In Germany, Britain and other temperate regions, solar thermal domestic hot water
systems are normally designed so that on a yearly average the sun covers 50 to 60%
of the hot water requirement. As the amount of sunshine in these regions fl uctuates
considerably during the year, a solar system can usually only cover the total hot
water demand during the summer months. In the winter, the sun's share can fall
below 10% (Figure 6.19). A conventional heating system then has to cover the rest.
In sunny regions like California and Southern Europe the solar share can easily
reach more than 80%.
100
%
90
%
80
%
70
%
60
%
50
%
40
%
30
%
20
%
10
%
0
%
Jan.
Feb. March
April
May
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
Figure 6.19
Typical solar share of solar thermal domestic hot water systems in Berlin,
London and Los Angeles (5 m
2
fl at-plate collector in Berlin and London, 4 m
2
in Los Angeles,
300
l
storage cylinder, 2700 kWh hot water demand).
A simple rule of thumb for designing solar thermal systems to provide domestic hot
water, based on the number of people in a household, is:
■
Collector size:
1 - 1.5 m
2
fl at-plate collectors per person
80 - 100 litres per person
If vacuum-tube collectors are used, the collector size can be around 30% smaller.
The collectors should not be less than three to four square metres in area because
below this size the losses in the tubes increase to above average.
■
Storage size:
6.4.1.2 Detailed Design
Hot water requirements have to be determined before a detailed design can be drawn
up. Ideally, the system should include a hot water meter that provides a direct
reading of actual consumption or a record listing hot water use over a long period