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Technical manual
Page 12 of 72
ST0133 – A 02/09
SOLAR
()
G
tt
a
G
tt
a
amam
2
210
−
⋅−
−
⋅−=
ηη
[1]
Where:
η [-] thermal collector efficiency
η
0
[-] optical collector efficiency/zero loss coefficient
a
1
[W/m²/K] linear heat loss coefficient
a
2
[W/m²/K²] squared heat loss coefficient
G [W/m²] global incident radiation
t
m
[°C] collector middle temperature
t
a
[°C] collector ambient temperature
Figure 9 – SOLC220 heat loss modes
The collector heat loss front (7) and collector heat loss back (8) are dependant on the
operating conditions of the solar thermal collector, i.e. primarily on the temperature
difference between the collector module and the ambient air and wind speed. Applying
equation 1 to the Dimplex SOLC220 collector the graph shown in Figure 10 can be de-
rived.
1
8
2
3
4
6
7
9
5