How Heat Pumps work

Heat pumps are common.

Electric heat pumps are part of common household equipment.  Heat pumps are used in:

  • Fridges: these heat pumps move heat from inside the fridge to your kitchen.
  • Reverse cycle air-conditioners: these heat pumps: (1) cool by moving heat from inside your home to outside, and (2) heat, when the cycle is reversed, by moving heat from outside your home to the inside.

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
http://en.wikipedia.org/wiki/Heat_pump

A heat pump that heats your hot-water will move heat from the air outside your house into your hot water tank.  They have:

  • A refrigerant:  The heat pump contains a refrigerant, a liquid that boils at a low temperature like minus 26 C.
  • An electric fan on the outside of your house: It blows air over a heat exchanger and so that the air warms 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 air heats the refrigerant which evaporates producing a gas. On a cold day, the fan has to work for longer to warm the refrigerant.
  • A Compressor:  This gas is removed from the evaporator and compressed.  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 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.
  • An Expansion Valve:  The cooled gas moves from the high-pressure condenser, through an expansion valve,  returning to the where it started, in the low-pressure evaporator,  and the cycle repeats.

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