How a heat pump works

How a heat pump works

How does a heat pump work?


A heat pump works like a fridge in reverse. A fridge produces cold from external heat, while a heat pump draws energy from its surroundings (air, ground or water) and returns it to the building in the form of heat via a heat exchanger.

The design and operating principles of heat pumps

The following illustration shows the design of a heat pump and how it works in individual steps:


  1. Heat source
  2. Heat pump
     a) Evaporator
     b) Compressor
     c) Condenser
     d) Expansion valve
  3. Heat distribution

Types of heat pump

The type of heat pump varies depending on the medium the energy is being drawn from (ground, water or air):


  1. Brine-water heat pump (geothermal probe)
  2. Water-to-water heat pump
  3. Air-water heat pump

Below, we will explain how these three different types of heat pump work:


Brine-water heat pump (geothermal probe)

Brine-water heat pumps – often called geothermal probes – provide heating using heat from the earth. There are various ways of using heat from the earth. In addition to geothermal probes, vertical posts, spiral probes or horizontal probes can also be fitted into the ground. However, the geothermal probe is the most commonly used technology by some margin.


How geothermal probes work

Due to the constant temperature underground, geothermal probes are highly efficient, although they have a higher upfront investment cost. Boreholes for geothermal probes cannot be drilled everywhere. Each individual case must be reviewed, especially in areas with groundwater reserves. Municipal approval is required.


Water-to-water heat pump (groundwater)

In water-to-water heat pumps, there are two possible energy sources:

  • groundwater (the most common)
  • surface water (lakes, rivers, streams)
How water-to-water heat pumps work

In the case of groundwater heat pumps, groundwater is supplied via an extraction and absorption well and absorbed by a heat exchanger (the heat is then extracted). Groundwater stays at almost the same temperature all year round, making this type of heat pump highly efficient.

If the groundwater is of a good quality, existing wells can also be used. The groundwater level and its potency are crucial here. As in the case of geothermal probes, municipal approval is also required.


Air-water heat pump

An air-water heat pump uses energy from the surrounding air to heat the building. The air is constantly being heated by the sun’s radiation. The heat pump absorbs this energy at a low temperature level and increases it to a higher level. Air-water heat pumps are relatively easy to install and are also excellent value for money.


Should air-water heat pumps be installed indoors or outdoors?

Air-water heat pumps can be installed indoors or outdoors. Both options are equally beneficial from an economic perspective.

  • If installed indoors, the air-water heat pump will be installed in a cellar. All parts of the circuit will be located inside the building, with only the intake and outlet of air occurring on the outside.
  • Installation outdoors is the most common installation type. This involves the use of compact heat pumps which produce heat in the device installed outdoors and then transfer it to the space to be heated via the storage tank.
  • In the case of split heat pumps, the circuit is divided so that the evaporator is outdoors while the condenser is indoors.

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Advantages and disadvantages of indoor and outdoor installations

Indoor installation

Heat pump installed indoors

  • no outdoor installation
  • no noise disturbance


  • takes up space
  • air ducts through the walls of the house
Outdoor installation

Heat pump installed outdoors

  • easy to retrofit
  • minimal penetration of the building envelope
  • ideal installation if it is compact and can be fitted directly next to the building


  • can be an eyesore when installed outside
  • slight noise emissions
  • heating and water pipes on the outside of the house
Split devices

Split heat pump

  • takes up little space inside


  • coolant pipes on the outside (if not directly attached to the house)

Air source, ground source or water source - what type of heat pump do I need?

An air-water heat pump is easy to install and relatively good value, making it the most widespread type of heat pump in Switzerland.

In 2016, roughly 67 % of all heat pumps purchased in Switzerland were air-water heat pumps.

Geothermal probes (brine-water heat pumps) are highly energy efficient – although are more expensive to install than air-water heat pumps.
Water-water heat pumps (groundwater) are extremely efficient, but they are seldom approved or installed for water protection reasons.
The ideal heat pump for your house depends on your specific circumstances.

Heat pump versus oil heating

Brine-Water (geothermal probe)

Oil heating
Installation cost medium high medium
Efficiency medium high low
Purchase cost   high low
Operating and energy costs medium low high

Heat pumps - products and manufacturers

Stiebel Eltron

Air-water heat pumpt (outdoor installation)

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Stiebel Eltron

Air-water heat pump (indoor installation)

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Stiebel Eltron

Brine-water heat pump (Geothermal probe)

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Stiebel Eltron

Integral storage tank for heating and hot water

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Air-water heat pump (outdoor installation)
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Air-water heat pump (split devices)
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Brine-water heat pump (geothermal probe)
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Air-water heat pump (outdoor installation)

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Air-water heat pump (split devices)

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Additional benefits of heat pumps

  • An oil heating system is cheaper to buy upfront, but a heat pump works out better in the long term due to its lower operating costs.
  • In the long term, an average detached house or block of flats can be heated more cost-effectively by a heat pump.
  • A heat pump consumes three times less energy than oil heating.

  • At least 70 to 80 % of the energy generated by a heat pump comes from the environment.

  • A heat pump is more environmentally friendly than oil heating.

  • Heat pumps barely require any maintenance and have an average service life of 20 years.


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