The world's first energy self-sufficient multi-family house – mission possible!

Umwelt Arena

It has become a fact! In the municipality of Brütten in Switzerland, the world's first multifamily house dwelling capable of operating year-round without any external sources of energy has been built. None of the nine apartments are connected to the grid as all of the electrical power comes from the sun and the heat comes from the earth. 

We are very proud to be a contributor in this amazing project! Hoval was selected as the preferred partner for the heat and hot water production thanks to its well-known product quality and reliability.

How has this project been possible?

The sun supplies around 5800 times more energy than required by the world - unfortunately, the sun doesn't provide energy exactly when it's needed. Nevertheless, to realise a 100% energy-autonomous building, the efficiency needs to be increased in every field: from the energy production, through the energy storage, to the consumption. The project: «energy-autonomous multi-family home» shows that the implementation of the “100% clean energy”-vision  is possible today already, if the available technology and the know-how will be consistently used intelligently.

Umwelt Arena - Gesamtansicht

How does it work?

Non-reflective photovoltaic modules are used as facade elements, visually breached by light wooden windows. The roof is covered with modern, high-performance photovoltaic modules. The solar energy is converted into an electric current by the solar cells and temporarily stored in daily and medium-term storage batteries (two to three days). For the long-term storage, there is a new conversion process from electric current to hydrogen. The hydrogen is temporarily stored and can be converted back into electric and thermal energy when required. Another part of the solar energy will be used to run the heat pump - to produce domestic hot water, to operate the underfloor heating system, as well as to charge the short- and long-term hot water storages. To achieve maximum efficiency of the heat pump, different sources of heatwill be used depending on requirements.


Which heat pump have we used?

As a heat source, awater/water heat pump with a geothermal probe is used. The engineering team decided to select a Hoval H19 heat pump – a standard Hoval product that is used in thousands of other multi-family homes and industrial buildings. Additionally, the heat, which is generated during the hydrogen production, is lifted on a high temperature level by the heat pump in the summer and is stored in thermal long-term storages or it is used to produce domestic hot water. The operating temperature around the heat source never drops below the freezing point, so there is no need to use antifreeze for the geothermal probes. The heat exchanger will be used only on such points, where they are technically absolutely necessary (i.e. heat generation from outside air and warm-up of the controlled residential ventilation). This decreases the pressure lost within the system and electrical energy can be saved for the operation of the heat pumps. 

The general principle is: generate maximum thermal energy with minimum electrical energy. During the development, the optimal use of the available environmental energy (geothermal heat, outside air) and the storage energy within the long-term storages is taken into consideration – always taking into account the situational most efficient usable energy source. If there is little electric current available, the control system always select the warmest energy source, to achieve a maximum degree of efficiency on the heating pump (COP). This reduces the electrical power absorbed by the heat pump, as well as the total electrical energy consumption. 


  • Heat pump Hoval Thermalia twin H19
  • System Water / Water
  • Heat output max. 28 kW
  • Flow temperature of the building heating 28° C
  • Flow temperature of the storage tank charging  up to 67° C
  • Heat sources geothermal probes, outside air, energy storage, waste heat of the electrolysis and inverters
  • Operating temperature of the source 6 – 25° C situational selectable
  • Geothermal heat probes 2 x 338 m


Heat pump – how does water/water work?

Heat pumps are using environmental heat as a source of heat, but the temperature level of the heat source is too low, to heat a building directly with it. Therefore the heat pump lifts the environmental heat within a electrically driven cyclic process to a usable level for the space heating but in order to directly heat a building. 

Heat sources of a heat pump 

Geothermal probes, groundwater, surface waters, air and waste heat can be used as a heat source. Which source is the best, has to be clarified individually. By right dimensioning of the heat source and the settings of the entire heating system to the calculated values, the demand for electrical energy of the building can be reduced to a minimum regarding to the heat energy. With the subsequent heat pump systems the following annual performance factors (APF*) can be achieved:

Heat pump

Construction (APF*)

Redevelopment (APF*)


2.8 – 3.5

2.5 – 3.0


3.5 – 4.5

3.2 – 4.0


3.8 – 5.0

3.5 – 4.5

*APF = the emitted thermal energy in relation to the supplied electrical energy over the entire year

Our tip: 

  • The lowest possible flow temperatures of the heating system and the optimal determination of the heat source are the keys for an efficient overall system.
  • Take account of possible blocking periods of the power plant and consider them in the design
  • Clarify precisely the installation location in case of air/water heat pumps (noise emissions)
  • Exactly verify the limitation of the maximal drilling depth and general conditions of geothermal probe system
  • Exactly analyse hot water energy demand for new buildings. It can make up a relatively big share in relation to the building energy demand (heating) or it could even be bigger.
  • Check, if there is an energy storage needed in order to ensure the minimum running times of the heat pump

Your benefit: 

  • Heat pumps are using environmental energy which is free of charge. The required electric current is transformed into a multiple of heat.
  • Due to the correct set up of the flow temperature, it is possible to save approx. 1,5 – 2 % of electrical energy with every reduction of one degree Celsius of the flow temperature.
  • There are no structural measures like a fireplace and a fuel storage

Now it’s your turn to be like investors of the first energy self-sufficient multifamily house and get more information about  H19 HeatPump– the same Heating Pump that is used in thousands of other homes. Ask for advice for your investment.


More information


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