How a heat pump works

How A Heat Pump Works

NIBE Heat Pump Range

The Refrigeration Cycle

All heat pumps operate using a principle called the refrigeration cycle. The heat pump uses low grade energy to change the state of a refrigeration fluid from a liquid to a gas. During this change of state high grade heat energy is produced.

The important point to note is that refrigerant gas has a very low boiling point, around minus 40 degrees C. This allows heat pumps to extract heat from what would other wise be considered as cold sources of energy.

Stage one - Evaporation:

This is a heat exchanger which takes low temperature heat out of the source (ground or air) and transfers it to the circulating refrigerant. The refrigerant is forced on by the expansion valve and the suction effect of the compressor to change from a liquid to a gas within the evaporator.

Stage two - Compression

This compresses the low temperature, low pressure gas into a high pressure gas, which causes it to increase in temperature to a high temperature gas.

Stage three - Condenser:

This is where the high pressure hot gas gives up its heat into the water or air circulating around the heating system and turns to liquid as it condenses. This is the reverse action of stage one – evaporation.

Stage four – Expansion:

The high pressure refrigerant liquid from the condenser travels through the expansion valve, which acts as a pressure differential valve (high pressure one side low pressure the other), turning it into a low pressure, and hence low temperature liquid. The cycle then begins again.

Refrigeration Cycle

Different NIBE Heat Pump Types:

Air Source Heat Pump Principles

Air Source Heat Pumps Principles

How an air source heat pump works

Air source heat pumps draw in heat energy from the surrounding air, hence the name air source heat pump. The air source heat pump comes in the form of a small-medium size unit that sits outside the building. Air source heat pumps are the most common type of heat pump. 

Like any heat pump, it works using the refrigeration cycle, illustrated on the diagram through labels A-E, to provide heating and hot water.

Ground Source Heat Pump Principles

Ground Source Heat Pump Principles

How a ground source heat pump works

Ground source heat pumps harness their energy from the ground, hence the name ground source heat pumps. 

Once the heat energy has been collected, it follows the same principle as an air source heat pump by going through the refrigeration cycle to provide heating and hot water to the building. There are a number of collector type for ground source heat pumps.

Exhaust Air Heat Pump Principles

Exhaust Air Heat Pump Principles

How an exhaust air heat pump works

Exhaust Air Heat Pumps combine mechanical extract ventilation (MEV) or mechanical ventilation with heat recovery (MVHR) with the refrigeration cycle principles to create a system that provides heating, hot water and ventilation. The process works by bringing fresh air into the property through air vents fitted in the walls, then naturally warming up as it passes through the house.

The warm room air is then collected by the air vents in particular rooms and drawn through the ducting to the heat pump. It then passed through an evaporator inside the unit, which takes out the energy from the air.

The heated refrigerant gas is then passed down to a condenser coil sited in the cylinder’s outer jacket, which then heats the primary water in the outer cylinder jacket and in turn heats the hot water inner jacket.

The waste cold air is then discharged outside. Mechanical ventilation eliminates the risk of moisture damage in building, removing stale air and providing a supply of fresh air.

Types of Ground Source Collector:

Horizontal Surface Collector

Horizonal Surface Collector

Horizonal Surface Collector

Trenches are dug anywhere between 1m-2m deep for the installation of a surface collector system.

This is where collector pipework is laid approximately 1-2m underground, extracting energy from the soil which has been absorbed from the sun.  A horizontal collector will require adequate land and is therefore not suitable for every property.  Trenches for surface collector pipework are traditionally dug at 1m intervals to avoid the over extraction of energy and long term performance reduction of the system.

Borehole Collector

Borehole Rock Collector

Borehole Rock Collector

Borehole rock collectors can be anywhere between 50m deep to 250m deep, depending on the required energy extraction.  It is not uncommon to drill several shallower boreholes depending on the geology and site specific conditions. 

A borehole rock collector is drilled vertical into the ground, anywhere from 50m+ to 100’sm depending on the size of the property and heat demand.  Due to the small diameter of the borehole this solution required significantly less land than the surface collector.  

Closed Loop Lake Collector

Closed Loop Lake Collector

Closed Loop Lake Collector

Where possible, a closed loop lake collector can be installed to provide the energy for a ground source heat pump.  This involves a series of pipework, similar to a surface collector, being buried at the bottom of a lake or water source.  Careful sizing must be carried out to ensure the transfer of energy does not impact the temperature or aquatic environment of the lake. 

Open Loop / Ground Water Collector

Open Loop / Ground Water Collector

Open Loop / Ground Water Collector

An Open loop ground water collector relies on their being a sufficient supply of running water either at ground level, such as a river source, or below ground level, such as an aquifer. 

Water is pumped from upstream of the source, which passes across a plate heat exchanger to extract energy before being returned to the source down stream.  Design considerations are also required for a open loop collection, such as a requirement to obtain an abstraction licence from the environmental agency.  

Photovoltaic-Thermal Panels

Photovoltaic-Thermal Panels

Photovoltaic-Thermal Panels

The PV-T system collects solar energy to produce electricity while extracting aerothermal heat energy from the air to power a Ground/Multi Source heat pump.

PV-T systems provide an alternative energy source for use with a Ground or, better named, ‘multi-source’ heat pump product.  PV-T can act as a standalone collector system, or can be used to supplement a borehole or surface collector system. 

PV-T is not to be confused with solar thermal. The NIBE PV-T system has been specifically designed for heat pump systems.

How efficient are heat pumps?

Heat pumps are much more efficient than other heating systems. This is because the amount of heat they produce is higher than the amount of electricity they use. The Coefficient of Performance (CoP) is used to measure the amount of heat produced for every unit of electricity.

Will installing a heat pump help save money on my heating bills?

If you buy a good-quality heat pump and get it properly installed, then it’s likely to save you money in the long run. This is because a heat pump is three to four times more efficient than a gas boiler, which means you should be able to reduce your heating bills. This is especially relevant if you’re replacing an old, inefficient system.

Advantages vs disadvantages of a heat pump

While the benefits of heat pumps outweigh the negatives, there are some arguments that can be made for both sides. In order to help you decide whether a heat pump is the right solution for you, we have listed some of the key pros and cons below.

The advantages of a heat pump system

A heat pump system is one of the most efficient and popular ways to heat and cool a home. They can also be used to provide hot water.

Lower running costs

Heat pumps have a much better average efficiency rating than gas boilers, maximising the output for the energy consumed. Not only is this good for performance, but also in terms of saving you money each month.

Less maintenance

In comparison to gas boilers, heat pumps require less maintenance and tend to not need servicing as often. This is partly because there are fewer safety concerns. You’ll just need to factor in the annual servicing.


Good quality heat pumps tend to be straightforward to use, with easy-to-follow controls and little maintenance required. In the main, they can also be used and adjusted using an app from your chosen device.

Reduces carbon emissions

Heat pumps burn no fossil fuels and rely solely on electricity. This means you’re able to heat your home more sustainably and also reduce the expensive costs associated with gas bills.

Provides cooling and heating

Not only is a heat pump great for heating your home, but it can also be used to keep your home cool during warmer months. Therefore, with a heat pump, it’s likely you won’t need an air conditioning unit.

Eligible for Boiler Upgrade Scheme

If you are a homeowner and your boiler is more than five years old, you may be eligible for the Boiler Upgrade Scheme. The scheme offers a free boiler replacement for homeowners who meet the eligibility criteria.

The disadvantages of a heat pump system

A heat pump system is a great way to heat and cool your home, but it does have some disadvantages.

Higher upfront cost

Unfortunately, the cost of installing a heat pump can be quite expensive. However, there are a number of grants available to help if you have financial concerns. Plus, once it’s installed, it should save you money in the long run.

Uses more electricity

As heat pumps rely on electricity, you’ll inevitably see a rise in your electricity bill. However, if you’re on the right tariff, then heat pumps are still considerably more efficient to run. We recommend you get in touch with your supplier to ensure you’re on the appropriate tariff.

Proper planning is needed before installation

It’s very important that your heat pump is installed correctly in order to enjoy its true benefits. Your property will need to be well insulated and the location of your heat pump to be properly assessed before installation. Use our search tool to find a reputable installer near you.

What to consider before buying a heat pump

There are a few things you should consider before you buy a heat pump. Some of those considerations include:

  • Climate
  • Size
  • Budget
  • Efficiency rating
  • Features
  • Design
  • Brand
  • Sustainability
  • Maintenance

Advanced features to look for in heat pump systems

When shopping for a heat pump system, be sure to look for advanced features. These features can help improve the efficiency and performance of your system, and can save you money on your energy bills. Features we recommend you look for include:

  • Variable speed compressor
  • Inverter technology
  • Built-in thermostat
  • Programmable settings
  • Humidity control

What are the costs of a heat pump system?

A heat pump system can be an affordable way to heat your home and can save you money on your energy bills. However, the cost of a heat pump system will vary depending on the size of your home, the type of system you choose, and the installation and running costs. For sustainable, cost-effective heat pumps, take a look at our range of market-leading products.

Why heat pumps are worth the investment

Heat pumps are one of the most efficient and environmentally-friendly ways to heat your home. This means they can save you money on your energy bill and are a great way of reducing your carbon footprint.

Check if a heat pump could be suitable for your home

The latest reports show that heat pumps are suitable for any house type. The total heat a property requires to be heated to 21 doesn’t change with a heat pump in comparison to a gas boiler or equivalent.

The emphasis should be back to the design of the system, where older houses will need a thorough heat loss survey and existing system inspection to determine if any pipework or radiators will need replacing.

It’s also worth considering improving your property’s thermal efficiency. For example, increasing insulation levels, in addition to installing a heat pump, will help deliver savings and reduce energy usage and your carbon footprint.

In the UK, air source heat pumps are the most common type of domestic heat pump, as they tend to be more suitable for most homes and, generally, less disruptive to install.

For more information about which heat pump is right for you, take a look at the ‘help me choose’ section of our website. Alternatively, you can speak to a NIBE expert who will review your project and put you in touch with a NIBE Pro Installer.

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