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Heat Pump Water Heaters


What is a heat pump water heater?

Heat pump water heaters works like air conditioners. Heat is absorbed from the air by an evaporator and transferred into the water through a heat exchanger.


When the system starts, a fan draws air through the evaporator. A compressor pumps refrigerant through a thermal expansion valve, and the refrigerant expands and vaporises in the evaporator to extract heat from the surrounding air. This process creates cold air, which is discharged, and heated refrigerant gas. The heated gas is compressed to raise its temperature further, and enters the heat exchanger where its heat is transferred to the water. The gas then condenses back into a refrigerant liquid state. The liquid cools and depressurises as it passes back through the thermal expansion valve and the cycle repeats.


The system works with a circulating pump, water pipe and storage tank with a temperature probe immersed in a probe pocket in the middle of the tank. When the heat pump is switched on, the temperature probe senses the water is reaching the set temperature point. If the differential between the probe and water set point is more than 5 degrees Celsius, the circulating pump activates, drawing water from the bottom of the storage tank and pumping it up through the heat pump heat exchanger to boost the water temperature and return it to the storage tank. The heating process continues until the water in the storage tank reaches the required temperature, which can be up to 60 degrees Celsius.


Even on cold days, heat energy can be drawn from the surrounding air. The heat pump water heater will operate at air temperatures between -15 degrees Celsius and 45 degrees Celsius.


In some countries these systems are known as air-source heat pumps, air-to-water heat pumps, solar water heaters or hot water heat pumps. They can also be used for underfloor or radiator heating.


The main benefit of using these systems is that they do not heat your water directly like an electric resistant cylinder. Instead, the heat pump water heater extracts free thermal energy from the atmosphere and transfers it into your water cylinder. This reduces water heating costs by about 70% compared to a standard hot water cylinder, and also significantly reduces carbon emissions.