Environmental Engineering Reference
In-Depth Information
Reflection at
glass cover
8%
100%
Absorption of glass cover
Glass cover
2%
Reflection at
absorber 8%
Heat emission
of absorber 6%
Convection
13%
Absorber
60%
Heat conduction
3%
Source:
Wagner and Co, 1995
Figure 3.7
Energy Conversion in the Solar Collector and Possible Losses
The use of special materials for the front cover can increase the collector
efficiency. These materials should let incoming radiation through, but reflect
the outgoing infrared emissions coming from the absorber plate back inside.
Infrared reflecting glass such as In
2
O
3
or ZnO
2
with high transmittance for
visible light but high reflectance for infrared meets these requirements. Table
3.5 shows the parameters of these materials; however, higher costs and poorer
transmittance of visible light compared to standard glass have prevented the
widespread use of these materials.
The
collector housing
can be made of plastic, metal or wood. The housing
must seal the front glass cover so that no heat can escape and no dirt, animals
or humidity can get into the collector. Many collectors have controlled
ventilation to avoid humidity inside the collectors condensing on the inside of
the cover glass.
Figure 3.8
Processes at the Collector Front Glass Cover
