Working Principle - Bosch DOMESTIC HOT WATER HEAT PUMP Technical Manual

1.3 Working principle

The heat pump working principle is based on the transfer of the heat, and not on conversion of electrical energy
into heat. It removes energy from a low temperature source (ambient air) and transfers it into a high temperature
source (hot water tank).
Electricity is used to upgrade the comfort (temperature) of heat energy and not to generate heat energy. That is the
reason why COP (Coefficient Of Performance) of the heat pump is higher than 3 (which corresponds to an
efficiency of 300 %).
1. Liquid refrigerant R 134a boils at a low temperature in the evaporator. The output is a low temperature and low
pressure vapour.
2. Vapour pressure and temperature increase in the compressor. The electric motor is used to drive vapour
through the compressor and increase vapour temperature and pressure.
3. Heat exchange is done in the condenser. The refrigerant transfers heat to the water and cools up, condensing
and leaving energy there.
4. The liquid returns to the evaporator after passing through an expansion valve.
decreases and the liquid evaporate again.
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Pict.4 – Energy and electrical input
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Pict. 5 – Generic overview of the 4 stages of gas
6720649497 SM HP270-1 2012/09 en
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4
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The refrigerant pressure