Editing Heat pump (section)

===Improvement of coefficient of performance by subcooling===
{{main|Subcooling}}
Heat input can be improved if the [[refrigerant]] enters the evaporator with a lower vapor content. This can be achieved by cooling the liquid refrigerant after condensation. The gaseous refrigerant condenses on the heat exchange surface of the condenser. To achieve a heat flow from the gaseous flow center to the wall of the condenser, the temperature of the liquid refrigerant must be lower than the condensation temperature.

Additional [[subcooling]] can be achieved by heat exchange between relatively warm liquid refrigerant leaving the condenser and the cooler refrigerant vapor emerging from the evaporator. The [[enthalpy]] difference required for the subcooling leads to the superheating of the vapor drawn into the compressor. When the increase in cooling achieved by subcooling is greater that the compressor drive input required to overcome the additional pressure losses, such a heat exchange improves the coefficient of performance.<ref>{{Cite book |title=Heat Pump Technology |last=Ludwig von Cube |first=Hans |publisher=Butterworths |year=1981 |isbn=0-408-00497-5 |pages=22–23 |url=https://books.google.com/books?id=YNH8BAAAQBAJ&dq=heat+pump+principle&pg=PP1 |access-date=2023-01-02 |archive-date=2023-04-03 |archive-url=https://web.archive.org/web/20230403214400/https://books.google.com/books?id=YNH8BAAAQBAJ&dq=heat+pump+principle&pg=PP1 |url-status=live }}</ref>

One disadvantage of the subcooling of liquids is that the difference between the condensing temperature and the heat-sink temperature must be larger. This leads to a moderately high pressure difference between condensing and evaporating pressure, whereby the compressor energy increases.{{Cn|date=January 2025}}