How do heat pumps work?
Heat pumps are a cleaner, cheaper alternative to traditional heating systems. They are four times more efficient than a gas or oil boiler and slash energy costs by up to 25%.
In this article, we'll delve into the anatomy of a heat pump, such as the heat exchanger and expansion valve. We'll also tackle the burning question: how do heat pumps actually work?
What is a heat pump?
Heat pumps efficiently transfer heat energy from one location to another, to provide properties with heating and hot water. Brought into residential use in the 1960s, heat pumps are a sustainable alternative to conventional gas boilers and heating systems.
Heat pumps use renewable sources (the air) to minimise energy consumption and carbon emissions. Countries like Sweden have embraced this technology, witnessing a significant reduction in CO₂ output from home heating compared to regions like the UK, which rely more heavily on traditional heating systems.
Not only are heat pumps built for maximum efficiency, even in cold weather, but they also contribute to lower energy bills.
How do heat pumps work?
Heat pumps work by transferring thermal energy from a cooler environment to a warmer one. Unlike traditional heating systems like fossil fuel boilers that generate warmth by combusting fuels or using electrical resistance, heat pumps move existing heat from one place to another.
Central to the workings of a heat pump is the refrigerant (our Aira Heat Pump uses R290) which circulates within the system, undergoing pressure changes that cause it to heat up or cool down.
A step-by-step guide to how a heat pump works
Step 1
The outdoor unit of the heat pump system draws in the surrounding air using a fan. This air passes over an evaporator, where the air's natural heat is absorbed by a refrigerant. The refrigerant, now in a gaseous state, is then compressed by a compressor, raising its temperature.
Step 2
The hot gas from the compressor travels into a condenser, where it transfers its heat to the water in the heating and hot water system. As it releases its heat, the refrigerant condenses back into a liquid.
Step 3
The now-liquid refrigerant passes through an expansion valve, where its pressure is reduced. This causes the refrigerant to cool down before it re-enters the evaporator to repeat the cycle. And that's it! Your home and hot water are heated using free, fresh air.
Types of heat pumps
There are three common types of heat pumps:
- Air source heat pumps
- Ground source heat pumps (otherwise known as geothermal heat pumps)
- Water source heat pumps
Each type extracts heat energy from different elements of the environment.
Air source heat pumps
An air source heat pump absorbs heat from the air via an outdoor unit and transfers it indoors to raise the temperature.
They come in two forms: air-to-water systems, which supply hot water and central heating via an indoor unit and buffer tank, and air-to-air systems, which directly warm the air in a room.
While the upfront installation cost can be higher than a traditional boiler, they are typically cheaper than ground or water source alternatives and the long-term savings they provide justify the investment. Additionally, there are a range of government grants in the UK to help offset the upfront costs.
See how an air to water heat pump works
Ground source heat pumps
Taking advantage of the relatively constant temperatures beneath the Earth's surface, ground source heat pumps extract heat from the ground via water or refrigerant circulating in loops of buried pipes.
The heat in the ground is captured by these pipes, before passing through a heat exchanger in the heat pump on the surface, which supplies the home with heating or hot water.
Ground source heat pumps require a large amount of outdoor space and are typically more expensive to install than an air source heat pump.
Water source heat pumps
Like their ground counterpart, water source heat pumps harness naturally occurring heat but, in this case, from bodies of water such as lakes, rivers or ponds. They operate by drawing heat from these water sources, compressing it to increase the temperature and then distributing it to heat living spaces or provide hot water.
Because water maintains a constant temperature, water source heat pumps are very energy efficient. However, a water source heat pump installation may be more complex and expensive than an air source heat pump unit.
Components of a heat pump system
Heat pumps might seem complicated, but they’re really just advanced central heating systems. Let’s break down the key components that make them work.
Evaporator coil
An evaporator coil is a network of tubes filled with cool refrigerant. It passes the cool refrigerant across the first heat exchanger, allowing it to evaporate from a liquid into a gas.Evaporator coil
An evaporator coil is a network of tubes filled with cool refrigerant. It passes the cool refrigerant across the first heat exchanger, allowing it to evaporate from a liquid into a gas.
First heat exchanger
The first heat exchanger is where heat from the external environment (air, ground or water) is efficiently transferred to the refrigerant inside the system.First heat exchanger
The first heat exchanger is where heat from the external environment (air, ground or water) is efficiently transferred to the refrigerant inside the system.
Compressor
The compressor's job is to compress the refrigerant gas, boosting its pressure and temperature. The efficiency of this process is crucial for the heat pump's overall efficiency, as it determines how much heat the pump can generate from each unit of electricity.Compressor
The compressor's job is to compress the refrigerant gas, boosting its pressure and temperature. The efficiency of this process is crucial for the heat pump's overall efficiency, as it determines how much heat the pump can generate from each unit of electricity.
Condenser coil
The compressed gas enters the condenser coil, before passing across a second heat exchanger to heat the home's heating system.Condenser coil
The compressed gas enters the condenser coil, before passing across a second heat exchanger to heat the home's heating system.
Second heat exchanger
The second heat exchanger is where the hot refrigerant heats cold water to warm your home and hot water. As it heats the cold water, its temperature reduces, condensing back into a liquid.Second heat exchanger
The second heat exchanger is where the hot refrigerant heats cold water to warm your home and hot water. As it heats the cold water, its temperature reduces, condensing back into a liquid.
Expansion valve
The expansion valve reduces the refrigerant's pressure, cooling it down further, and passes it into the evaporator coil for the process to begin again.Expansion valve
The expansion valve reduces the refrigerant's pressure, cooling it down further, and passes it into the evaporator coil for the process to begin again.
Does a heat pump work in winter?
Quality heat pump installation and additional measures like larger radiators and insulation are important to help mitigate heat loss during colder weather. But, overall, heat pumps are remarkably efficient in the cold, and even outperform fossil-fuel heating systems in terms of energy use.
For example, modern air source heat pumps, like the Aira Heat Pump, can maintain a cosy indoor environment even if the outdoor temperature reaches -25°C.
Learn more about heat pumps
Heat pumps vs boilers
Explore how heat pumps and boilers work, their differences, costs and long-term benefits, helping you decide which is right for your home.
How much is a heat pump?
Air source heat pumps have the power to slash your heating bills by 25%. And they cost less than you think.
What are air to water heat pumps?
Air to water heat pumps use thermal energy to heat your home and water. But how do they work and how are they installed?
