Environmental Engineering Reference
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eventually accumulate in wells for groundwater, which further increases the amount
of pumping energy needed. As ambient air temperatures in winter are lower than
ground or groundwater temperatures, hot-air heat pumps work most effi ciently at
that time of the year.
11.2 Working Principle of Heat Pumps
All heat pumps need a refrigerant that is located in a closed loop. The refrigerant
absorbs the low-temperature heat. The heat pump then heats up the refrigerant to a
higher temperature, the heat of which is then used. Based on the working principles,
a distinction is made between
Compression heat pumps
Absorption heat pumps
Adsorption heat pumps
11.2.1 Compression Heat Pumps
Compression heat pumps are by far the most common type (Figure 11.3). The
principle of these heat pumps is based on a refrigerant with a low boiling point that
vaporizes when temperatures are very low and reaches high temperatures when it
is compressed (Table 11.2). The heat supplied from the low-temperature source in
the vaporizer is suffi cient for vaporization.
Figure 11.3 Principle of a compression heat pump.
A compressor (usually electrically driven) brings the vapour-forming refrigerant to
a high operating pressure. During this process it heats up considerably. This process
is similar to what happens with a bicycle pump when one uses one's thumb to stop
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