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The heat pump
Energy degradation
Finally, we wish to consider the application of the concept of entropy to the heat pump (see
figure 3). As has been shown above (page 64) a heat pump (HP) is a device with which it is
possible to harness the process of the degradation of high value energy (e.g. electrical energy)
to shift thermal energy (e.g. of the surroundings at temperature T2) to a higher temperature
T1. On condition that the overall devaluation is kept to a minimum, the quantity of electrical
energy W necessary to 'produce' a desired quantity of heat Q, (which is a measure of the efficiency
qHp) can be calculated as follows:
The entropy decrease of the surroundings at temperature T2
has to be compensated by the entropy increase
Q2
AS2 = -- ,(Q2 > 0)
T2
of the room heating, such that
Qi +
AS=ASl +AS2 7-- Qi+W >o
Tl T2
The efficiency is, therefore,
I
TI
1
w
I
T2 I
Figure 3. Diagrammatic representation of a heat pump.
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