Note: Heat Pumps are only available for the Dutch matket. In winter, a heat pump automatically defrosts itself. When the outside temperature drops around freezing point, ice can form on the fins and the evaporator. This defrosting process is called defrosting or the defrost cycle of the heat pump. In this article, we explain how this defrosting or defrost cycle works and how the heat pump operates in winter.
Why does a heat pump need to defrost?
An air-to-water heat pump is often a monoblock unit, in which the entire heat production process takes place. In most cases, this unit is installed outdoors on the roof of the building. The heat pump extracts heat from the outside air using fans. This warms the refrigerant, which evaporates into hot gas. During this process, the evaporator becomes colder than the outside air, which can cause frost or ice to form on the fins and evaporator at low outdoor temperatures and high humidity. Ice formation can occur even at temperatures above freezing. The fan then struggles to blow or draw air over the fins and evaporator, which significantly reduces the heat pump’s efficiency. The defrost cycle ensures that the ice melts and the heat pump can operate properly again. Read more about heat pump performance in winter in our blog.
How does defrosting work?
To melt the ice that has frozen onto the fins and the evaporator, this part needs to be heated. This is done by reversing the heating process, causing the refrigerant to change its flow direction. The heated refrigerant then flows through the evaporator and the outdoor coil in the outdoor unit, melting the ice. The defrosting process stops as soon as the sensors indicate that the ice has disappeared.
What do you notice during this defrosting process?
During defrosting, the heat pump temporarily does not supply heat to the building. Without a buffer tank, cold or cooled water then flows through the radiators in the building. Usually, this process only lasts about 5 to 10 minutes. Most air-to-water heat pumps have a buffer tank to ensure optimal performance. In this case, the indoor temperature remains stable. The buffer tank makes sure that the stored heat can still be used in the building’s heating system.
There are also heat pumps in which pipes carrying hot water run along the fins and the evaporator. This water is electrically heated, independently of the heat pump’s operation. In this case, the heating process does not need to be reversed by the heat pump.
The sound of the heat pump may temporarily change because the compressor and fan switch their speeds. The meltwater flows away through the condensate drain. For this reason, a proper drainage system is recommended.
Frequency of defrosting
How often the defrost cycle occurs depends on the outside temperature and humidity. It also depends on the design of the fins and the evaporator, which varies by brand. In general, ice and frost most frequently form when the outside temperature is around freezing and humidity is high, resulting in more defrost cycles. This can even happen as often as once per hour. In dry frost conditions, for example at -5°C with low humidity, fewer defrost cycles are needed. The heat pumps from Eco Heating Systems intelligently regulate this process using temperature and pressure sensors.
Heat pump efficiency in winter
The efficiency (COP) decreases in winter due to the defrost cycle and the slower heating of the refrigerant. However, this is normal and is accounted for in the annual performance of the heat pump (SCOP). You can read more about this in our blog on heat pump efficiency. A proper installation is crucial for optimal performance. Ensure there is free airflow, enough space around the outdoor unit, and a reliable condensate drain. If a heat pump needs to defrost too often or for too long, this may indicate installation or maintenance issues. This could be caused, for example, by incorrect placement, blocked airflow, or a faulty sensor.
Do you want to learn more about defrosting a heat pump in winter?
The defrost cycle is an essential part of the operation of an air-to-water heat pump. It is important that a heat pump defrosts itself automatically so it can continue to operate efficiently at maximum performance. Do you want to learn more about this process? Or do you have questions about the defrost cycle of your heat pump? Feel free to contact us—we are happy to assist you.
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