Heat Pump Knowledge

Analysis of Low Outlet Water Temperature of Heat Pump Water Heaters


The outlet water temperature of heat pump water heater are 50℃~60℃ in general . Sometimes it may reach 60℃~65℃ that will affect the working life of the units.

Problem Description

The water temperature isn’t able to reach the setting temperature and go up slowly, or the units run overtime but the water temperature is still very low. The heating water, the measured temperature of which is around 40 or less, can hardly be used. The systems kept operating while the temperature remains low.

Problem Analysis

As heat pump water heaters should absorb the external heat to heat the water in the tank, there are two possibilities can explain why the low water temperature happens in the tanks.

The water temperature will be invariant when the heat run off is equal to the heat flow in.

Firstly, the incomplete insulation layer and big temperature difference will cause the heat lost, especially, when the water inlet isn’t sealed well or convert part isn’t insulated well. In addition, the discontinuous insulation between the outside pipes and tanks will increase the heat lose as well.

Secondly, the hot water flow out and the cold water compensate that cause the heat lost in the heat pump water heaters, which often happen in the water tank design solution. For the places which have hot water demand all the 24 hours, like hotels and hair salons of quite a lot people, the cold water fills the tank and the hot water serves all the time. When the machine works well, the heat that the units absorb from the outdoor will reduce significantly as long as the weather becomes cold.  Meanwhile, as users’ increase the demand for heat, the heat in water tanks is not enough. As a result, the water temperature goes up difficultly, or even remains cold.

Poor capacity of refrigerant for carrying heat decrease the heat exchange efficiency in every single cycle

One possibility may be the unsuitable refrigerant type. The refrigerant used for heat pump water heaters, which should have specific physical and chemical stability is different from the traditional one, and this is the core technology of the units. Some heat pump water heaters apply the refrigerant lack of the features above.

The other possibility is less amount of refrigerant or leakage. Heat pump water heaters produced from the regular manufacturers will be added enough refrigerant and tested strictly before package to ensure stable working capacity. If not follow the shipping sign to transport the units during the shipment, which will cause refrigerant leakage, the units can’t reach the rated efficiency.