Why does the COP increase when the temperature decreases?

Performances RT MyDATEC VMC double flux thermodynamique economie d'énergie

This is one of the unique features of heat pumps that operate solely on exhaust air, like MyDATEC RT, where the heat source is at a constant temperature of about 20°C (Indoor temperature). Air travels through the heat pump’s cold coil, which extracts its heat. In terms of fresh air intake, with an example of an outside air temperature of around +7°C, the air is heated by travelling through the heat pump’s hot coil, which contains fluid at around 60°C. If the fresh air’s temperature decreases, for instance to -7°C, the heat transfer between the colder fresh air and the heat pump’s hot coil is more efficient than in the scenario where the fresh air is at +7°C. This is because the difference in temperature is greater and as the transfer is more efficient, the heat produced is more effective with similar energy consumption, which thus explains the increase in performance and COP when there is a decrease in the outdoor temperature.

In comparison, other well-known heat pumps, which operate using outdoor air, draw their heat solely from this air. When the outdoor temperature decreases, calories are more difficult to recover. This is why COP drops as the outdoor temperature drops. Saying this, the volume of air dealt with by these machines is significant and heat pumps relying on outdoor air can offer higher heating power than exhaust air heat pumps, which, despite the available ventilation, are limited in the volume of air flow, which is dependent on the size of the home.

F. Lavogiez (Étude 2012) – MyDATEC Technical Director