Heat pumps are becoming an increasingly popular choice for hot water systems, but many people don’t fully understand how they work. They are often described as fridges that operate in reverse, but this doesn’t give a complete picture of the process.
A heat pump works by extracting heat from the air and concentrating it into a small volume of water. The key to this process is the large volume of air that the heat pump extracts heat from. It churns through over 150 litres per second of air, which is a little over 9,000 litres a minute, and over an hour is 550,000 litres of air that passes through.
For example, if the outside air is at 10°C, the heat pump can extract 8°C of heat from it. So the air enters the heat pump at 10°C and comes out the other side at 2°C. This process is made possible by the huge difference in volume between the air and the water. Low temperature heat is extracted from 550,000 litres of air in an hour, and high temperature heat is added to 300 litres of water. This is a 1833x difference in volume.
It is this harvesting and concentration of heat from the air that makes the heat pump so energy efficient. The process is also the secret to its high efficiency. When you consider an electric hot water unit, the energy from the electricity is simply converted into heat energy. However, with a heat pump, only 1/4 of the heat is gained from the conversion of electrical input into heat from the compressor. This results in an efficiency of 400%.
It’s important to note that the efficiency of a heat pump can change depending on the brand and the weather conditions. But understanding the process of extracting heat from the air is key to understanding the energy efficiency of a heat pump.