How Do Heat Pumps Work?

There is so much heavy-handed science that normal people are expected to understand when it comes to heat pump explanations. We’ll do our best to keep the science and jargon to a minimum while giving you the information you need. Setting aside energy saving and cost of heating bills concerns, heat pumps work as follows: They do what your fridge/freezer does, just with a different goal You think of your fridge as a unit used for cooling its contents down.

Instead, think of it as a unit that removes heat energy from the inside and transfers it elsewhere. That heat energy has to go somewhere, so it plonks it into your room. It uses energy from the grid (electricity) to do this. Your Freezer does this as well, except it manages to draw heat energy from a much colder environment and put it in the room, which requires more energy from the grid to do so. The slight variance between a fridge and a heat pump is, the heat pump takes a smaller amount of energy from the grid and it uses that to draw a larger amount of heat energy from the environment. It can draw this larger amount because the environment it draws energy from (the outside world) has an abundance of potential heat energy compared to your fridge.

This is what is called the COP (Coefficient of performance), you and I call this efficiency. If a COP for a heat pump is 3, it means that for every 1 KWh drawn from the grid, 3 KWh of heat energy makes it into the hot water that circulates the radiators. We would call this 300% efficient. Anyway, the science is there and it has been for some time. Ignore all the technical stuff you see online, all we need to understand to prove to ourselves that the technology can work is just that heat pumps are basically a very advanced fridge.

What are the different types of heat pump?

You’ll see online that there are different types: Air to air, ground-to-air, and even water-to-water. We aren’t in the USA where central air is popular and we aren’t likely to be close to a running body of water to draw energy from there. Let’s just focus on the two that matter to us as normal people, in the UK: Air source heat pump/air to water heat pump

1. Takes energy from the grid.
2. Uses this grid energy to take energy from the air outside.
3. Efficiency (COP) is more unpredictable, as the lower the temperature is outside, the more energy is required from the grid to harvest, therefore the more expensive it is to run at those times.
4. Max internal operating temperature (water temperature in radiators) is 55°C.
5. The higher the internal temperature in radiators, the less efficient it is and the more it costs to run.
6. A big box has to be installed on the side of the property.

Ground Source heat pump

1. Works the same as above, but you need to dig up your garden to run ducting because it takes energy from the ground not air.
2. Can have a higher internal operating temperature (water temperature in radiators).
3. Has less flaky COP due to ground temperatures not shifting as much as air and generally being higher.
4. Costs a lot more to install + whatever is needed to make your garden nice again.
5. The further north you go, the more likely you need this rather than Air to water.

How can lukewarm radiators heat my home?

Whatever politician said this, there was some kind of agenda (I mean, come on!). Political theories aside, the second law of thermodynamics when applied to something like a radiator tell us:

1. The temperature of the radiator vs the temperature of the room determines how much energy can transfer from the radiator to the room.
2. The hotter the water inside the radiator, the quicker the rate of transfer.
3. To heat a constant (the room) and lower the temperature of the water, we must provide it with a higher surface area to facilitate the same level of heat transfer.

Bigger radiators and heat-emitting surfaces are required. As long as the temperature of the radiator is greater than the room temperature, energy will flow from the radiator to the room. Unlike some, I’m not going to challenge the last 200 years of science. Don’t worry there is plenty I have issue with, just not this! So yes, provided you size the Radiators for the new operating condition of the heat pump, they will heat your home. If you want savings on energy costs as well, then you have to consider the sizing in relation to the COP requirement of the heat pump.

Does this new technology work?

As I said, it is not new technology.

1. How long ago was the first commercial ice-making machine invented (which works in the same way as a heat pump)?
2. 169 years, dude! (I don’t care if it’s a stretch, I’ll quote Bill and Ted any time it's remotely possible, 1854-2023 at the time of writing, fated in the stars)
3. How?
4. Don’t know, but probably no coincidence that the second law of thermodynamics was established a few years prior by Rudolf Clausius and William Thomson aka Lord Kelvin (Kelvin comes from this person, but Celsius while close is from a Swedish person called Anders Celsius).
5. So what is the issue? Why the horror stories of increasing bills with heat pumps?
6. The science is sound and has been for a very long time, the underlying technology has existed in our home (refrigerator) since 1913. The problem isn’t science, it isn’t technology, it is the same issue we have every time there is a change in the heating industry - the way it is rolled out to our homes.

  So the questions about whether this technology works are besides the point, the questions we need to ask are around “Does this technology work for me”, now that is a very different kettle of fish as the answer needs to consider:

• My geographical location
• My property type and age
• Impacts on my ongoing energy costs
• The size of radiators I need vs the space I have available

All of this determines whether this technology can work for you. To learn more about this, you can start with our “Myth-Busting Heat Pumps” blog or “Can Heat Pumps Work with Radiators”, both of which will take you down a path of discovery and help you make an educated choice.