Environmental Engineering Reference
In-Depth Information
Figure 13. Daily instantaneous efficiency at mid-day during January and June 1985.
7.1.2. Daily Heat Collection Efficiency
The daily heat collection efficiency is defined as the ratio of the amount of heat produced
by the collector bank divided by the amount of solar radiation falling on the absorber plates.
The daily amount of heat produced and the daily amount of incident solar radiation are
estimated from the summation of their hourly values during a day which are measured and
recorded by the data acquisition system. Figure 14 shows the daily heat collection efficiency
for the months of January and June 1985. It can be seen that the daily efficiency for sunny
days is normally above 50% except for days with prolonged overcast periods, such as in
January, during which the daily efficiency can drop below 40%.
Figure 14. Daily heat collection efficiency for January and June 1985.
7.2. Heat Accumulator System
7.2.1. Heat Loss from the Heat Accumulator
Table 10 gives the monthly heat loss from the heat accumulator as a percentage of the
incident solar radiation on the collector field for several months during 1985. As can be seen,
the heat loss varies from 4.6% (for June) to 6.6% (for December). The percentage heat loss is
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