How Heat Pumps work

Andrew on January 25, 2022

Heat pumps are common & efficient

Electric heat pumps are an essential part of standard household equipment:

  • Refrigerators: a heat pump cools a refrigerator’s interior by moving heat from the interior and into the kitchen.
  • Reverse cycle air-conditioners: a heat pump cools a room by moving heat from the room to outside the house. When you reverse the cycle, the heat pump heats the room by transferring heat from outside your home to inside the room.

Heat pumps use electricity to run a fan and compressor – and can be amazingly efficient. A high-performance residential heat pump can use one unit of electrical energy to move six times as much heat energy into your house, an efficiency of 600%.

By comparison:

  • Electrical heaters have an efficiency of 100% as they can convert all the electrical energy into heat, and
  • Gas heaters have an efficiency of between 50% and 95%, as some of the heat generated can escape up the heater’s flue and heat the house exterior.

A Heat pump hot water service

One use of a heat pump is to heat your hot water. You can run the heat pump when the sun is up and use electricity from photovoltaic solar panels to power the heat pump. After installing the panels and heat pump, you heat your water for free, generating no emissions. 

The heat pump heats your hot water by moving heat from the air outside your house into your hot water tank. It uses a refrigerant, a liquid that boils at a low temperature, like minus 26 C, and works in a cycle as follows.

The Heat pump cycle

Consider the heat pump’s cyclic operation with its changes to the refrigerant and heat flows. (The diagram below uses the numbers of the numbered points in the following text.)

  1. The Refrigerant is initially a liquid at room pressure in the heat pump’s evaporator.
  2. The Evaporator: An electric fan heats the refrigerant by drawing air from outside the house and passing it over a heat exchanger. The air warms the heat exchanger’s metal, which boils some refrigerant, turning it into a gas. (When the outside air temperature exceeds the refrigerant’s boiling point, minus 26°C, the air can heat and vaporise liquid refrigerant—but the colder the day, the harder the fan must work.)
  3. The Refrigerant is now a cold gas at room pressure.
  4. The Compressor: A valve closes, shutting the refrigerant gas in the compressor where an electric pump compresses the gas. As the pressure builds, the gas gets hotter, just as a bicycle pump gets hot as you pump up the tyres. The gas can heat to 95 C.
  5. The Refrigerant is now a gas at high temperature and high pressure.
  6. The Condenser: The hot, pressurised refrigerant gas enters a second heat exchanger, heating the heat exchanger’s metal, which then heats the water in the water tank. As the refrigerant gas releases its heat, it condenses, returning to a liquid state. Due to the refrigerant being under pressure, it condenses at a higher temperature than its minus 26°C boiling point at room pressure in the evaporator.
  7. The refrigerant is now a warm liquid, still under high pressure.
  8. The expansion valve opens, releasing the refrigerant into the evaporator. The pressure around the liquid refrigerant drops, causing the refrigerant to vaporise and cool.
  9. The refrigerant is now a cold liquid at room pressure: It is back where it started in the evaporator, ready to repeat the heat harvesting cycle.

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Refrigerant: a liquid at room pressure.
(1) & (9)		 Evaporator: Fan blown air boils the refrigerant (2)
Expansion valve: Release the pressure (8)Refrigerant: a cool gas at low pressure (3)
Refrigerant: a warm liquid at high pressure (7)Compressor: Pump pressurises the refrigerant gas (4)
Condenser: Produces hot water & cools the refrigerant (6)Refrigerant: a gas at high temperature & high pressure (5)
The heat pump cycle diagram

Further information

Updated: 24 July 2024

Australia’s strong sun

Andrew on April 30, 2018

Australia could become a renewable energy superpower.  One factor behind this is that Australia gets stronger sun than most developed countries.

Two world maps superimposed

Here is a fascinating map that demonstrates this.
http://www.dailymail.co.uk/sciencetech/article-4707544/Antipodes-Map-lets-dig-virtual-tunnel-Earth.html

It is two maps superimposed on one another. The first is a normal map of the world.  The second map shows, for each point on the first map, where you would be if you drilled straight down through the centre of the Earth to the other side.

The closer a place is to the equator: (1) the more the sun is directly overhead, (2) the more sunshine it gets, (3) the more electricity is generated from each solar panel, and (4) the cheaper it is for that place to generate electricity from the sun.  This is ignoring other factors like how cloudy a place is.

From this map you can see that:

  • Australia is closer to the equator than the developed countries in northern Europe, northern Asia and northern America.
  • Northern Greenland, Canada, Alaska and Russia are as far from the equator as northern Antarctica
  • Melbourne is as far from the equator as southern Spain, so most of Australia gets stronger sun than Spain and most of Europe.
  • Northern Australia is as far from the equator as the border between the Sudan and Egypt.
  • The southern border of the USA is about the same distance from the equator as Port Macquarie (halfway between Sydney and Brisbane). So northern Australia gets more sun than the south of the USA.

Manchester in England is as far north as Macquarie Island is south

Look at this yet another way. Australia gets far stronger sun than most of Europe because we are closer to the equator.

People often think of Macquarie Island as being in the Antarctic as it lies far south of New Zealand at latitude 55 degrees south. Well, Manchester in England lies at latitude 54 degrees north, so Manchester is as far north as Macquarie Island is south – and both experience a similar level of sun exposure.

Northern America and northern Europe get very weak sun compared to most of Australia. Europe would be very cold without the Gulf Stream.

Australia has quality solar resources

So, considering only the factor of sun strength (closeness to the equator), Australia has better solar resources than most developed countries – and we have other advantages too, which mean that Australia could become a renewable energy superpower.

Updated: 21 June 2024