Air Conditioner to Heat?

Ok, let's get some things out of the way first. When most people think of Air Conditioning, the first thought is cooling. That's because we commonly use it in our cars, and originally, Air Conditioning was just for cooling. However, times have changed, and some people who are much more knowledgeable than I am have found ways to reverse the cooling process to create heating!

Now, when many hear the term HEAT PUMP, they have two reactions: they are either brilliant and save us a fortune, or they are seen as an absolute waste of time. We understand this perspective, but the truth is that a heat pump, when installed correctly in the right building with the appropriate solution, should provide you with the first part of that statement. They are indeed brilliant and can save you a fortune. The association we often have with heat pumps is their use in heating our homes through the traditional 'wet' system (radiators and pipes). Therefore, it is critical that the system is designed correctly to ensure optimal performance. Heat pumps operate at much lower temperatures than gas boilers and typically run much more efficiently at lower flow temperatures.

With an Air Conditioner, or what is formally known as an Air to Air heat pump, we can extract heat from the outside and transfer it indoors to provide heating in the winter, or in the opposite direction to remove heat from indoors and reject it outside, thus providing cooling. Because we are not trying to heat up water, we can run our A/C units in a far more economical way. For example, in a wet system, you may need to achieve a flow temperature of 40°C to distribute meaningful heat throughout a building. In contrast, with an Air to Air system, you might aim for a 21°C room temperature, but your unit doesn’t need to run this hot to achieve that temperature.

Most modern AC units can take an input power (say 1 kW, for example) and achieve over 300% efficiency (3 kW output in the space). How? It all comes down to how these systems work. When we run a refrigeration system, we use a special refrigerant that moves around a series of components to extract heat from one location and reject it to another. With a fridge, we remove heat from the insulated box and reject it into the room. That's why the back of a fridge is often hot. The heat cannot be destroyed; it can only be moved. The same principle applies to the heat pump. We supply the unit with power, which runs a compressor, fan motors, and control systems. You set the desired temperature, and the system begins to work. The outdoor unit turns on, and a fan runs, sucking air across the coils outside, absorbing heat—even in the middle of winter. (Yes, you read that right; technically, there is energy in the air down to -273°C (0 Kelvin), which means the units can extract this heat.) Of course, as the temperature drops to around -15°C, the units will be working very hard, and efficiency may be compromised, but hey, when did we last experience a winter that was -15°C?

The winter of 1963 - the coldest for more than 200 years - Met Office

Ok, fair point, 1963 did see a winter reach -20°C in the UK, and to be honest, your heat pump will struggle at this point.

However, in the last 10 years, I don't recall a winter that was colder than -8°C, and your heat pump will still operate with good efficiency at this level.

Panasonic Power Heat Outdoor Unit

So how do you get more output than what you put in? This is quite simple. When you put energy into the A/C unit, it powers the compressor, which consumes the most energy. As energy is consumed, heat is produced. This heat is transferred to the refrigerant and rejected into your home. This heat is not wasted, but it does not account for 100% of the input power. The compressor's main function is to compress the refrigerant into a high-pressure, high-temperature gas.

Heat pumps operate on the principle of moving heat rather than generating it. They extract heat from the outside air—even in cold temperatures—and transfer it indoors. This is why they can provide efficient heating even when temperatures drop significantly. The efficiency of a heat pump is often measured by its Coefficient of Performance (COP), which indicates how much heat is produced per unit of electricity consumed. For example, a COP of 3 means that for every unit of energy used, three units of heat are produced.

The refrigerant plays a crucial role in this process. It circulates through the system, absorbing heat from the outside air and releasing it indoors. The phase changes of the refrigerant—from liquid to gas and back—enable this heat transfer. The compressor increases the pressure and temperature of the refrigerant gas, facilitating the heat exchange process. This cycle continues, allowing the heat pump to maintain a comfortable temperature in your home efficiently.

In summary, heat pumps are a smart choice for energy-efficient heating, even in colder climates. By understanding how they work and the roles of the compressor and refrigerant, you can appreciate the technology that allows you to enjoy warmth during the winter months without excessive energy costs.

Panasonic Wall Mounted Etherea series with Nanoex

Thanks for reading my first blog! I would love to know what you thought, did you find this article interesting and useful?

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