How Heat Pumps work

Heat pumps are common.

Electric heat pumps are part of common household equipment because they are very efficient. While the heat pump uses energy for the fan and compressor, for every 1 unit of energy that the heat pump uses, it can move 6 times that energy as heat.

Heat pumps are used in:

  • Fridges: These heat pumps move heat from inside the fridge and into your kitchen. That’s why its good to have space around your fridge, so that warm air is not trapped around your fridge.
  • Reverse cycle air-conditioners: These heat pumps can cool a room by moving heat from inside the room to outside the house. When the cycle is reversed, they can heat the room by moving heat from outside your home to inside the room.

Heat pumps for hot water

You can use heat pumps to get your hot water.  You can run the heat pump during the day, powering the heat pump with electricity from photovoltaic solar panels.  After installing the panels and heat pump, you heat your water for free, generating no emissions. 

How a heat pump works to heat water

A good diagram here

A heat pump can heat your hot-water. It would move heat from the air outside your house into your hot water tank which is also on the outside of your house. It will have:

  • A refrigerant:  The heat pump contains a refrigerant, a liquid that boils at a low temperature like minus 26 C.
  • An electric fan: The fan blows air over a heat exchanger. As long as the air is above minus 26 C, it will tend to boil the liquid refrigerant in the evaporator.
  • An Evaporator:  The external air heats the refrigerant to above its low boiling point of minus 26 C. It will work even on a cold day like 5 C outside. So, the air heats the refrigerant which evaporates producing a gas. On a cold day, the fan has to work for longer to boil the refrigerant.
  • A Compressor:  A valve closes shutting the gas in the compressor where a pump compresses the air. As the pressure builds, the gas gets hotter, just as your bicycle pump gets hot as you pump up your tyres.  The gas is heated to 95 C.
  • A Condenser:  The hot, pressurised gas passes its heat, via another heat exchanger, to where you want it, to the water in your hot water tank.  In doing this, the gas cools and condenses into a moderate temperature liquid at high pressure.
  • An Expansion Valve:  The cooled gas moves from the high-pressure condenser, through an expansion valve,  returning to the current atmospheric pressure and to the place where it started, in the low-pressure evaporator. Then the cycle repeats.

Updated 28/11/2020

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