DHW heat pumps for high hot water comfort

The picture shows a DHW heat pump in combination with a condensing boiler
Vitocal 262-A DHW heat pump in combination with a condensing boiler

DHW heat pumps

DHW heat pumps, or domestic hot water heat pumps, use the thermal energy already present in the environment to generate domestic hot water. They are also suitable for optimal consumption of self-generated power from photovoltaic systems and can be coupled to an existing air distribution system.

Structure and operating principle of the DHW heat pump

A DHW heat pump consists of a unit containing all the important components for the heat recovery process. These include the evaporator, the compressor, the condenser and the DHW cylinder. Depending on the version, an additional solar heat exchanger will be integrated, which enables the connection of solar collectors.

During operation, the DHW heat pump absorbs the heat from the recirculation air or the extract air and conveys it to the evaporator. It contains a refrigerant that heats up at low temperature before turning to vapour. Since the temperature of the vaporised refrigerant is not yet high enough to heat the water, this is followed by a compression process. In this process, the steam is conveyed to a current-driven compressor, which compresses it until the required temperature is reached.

In the final step, the heated refrigerant vapour transfers its thermal energy to the built-in DHW cylinder, cools down and condenses. The refrigerant liquid is then expanded at high pressure by an expansion valve while it continues to cool down considerably. Once the refrigerant is back in its initial state, the compression process can begin again.

Domestic hot water heat pumps can extract heat from either recirculation air, outdoor air or extract air. Suitable rooms for a recirculation air DHW heat pump include basements that have a constant and relatively high temperature during the winter months. During operation, the temperature in the basement is cooled by about two to four degrees. At the same time, the basement air is dehumidified. If the temperature differential between the heat source and the heating system is small, the domestic hot water heat pump from Viessmann works extremely efficiently.

Another option is for heat pumps to heat the domestic hot water with extract air. In this case, the top cover of the extract air heat pump is replaced by an extract air cover and the heat pump is coupled to the existing air distribution system. The heat pump is supplied with the warm extract air from several rooms, which allow it to provide good ventilation for an average detached house. The extract air that is cooled down during DHW heating is routed outdoors as exhaust air. To avoid negative pressure, outdoor air must be supplied via separate supply air elements. Ventilation mode is also possible without DHW heating.

Viessmann DHW heat pumps are designed for both mono mode and dual mode operation with a solar thermal system. In the dual mode version, the solar circuit pump is switched on or off electronically, with the aid of a temperature differential control. If the solar circuit pump is active, DHW heating is not produced by the heat pump. This ensures optimal use of free solar energy. In addition, the heat pump can make optimum use of self-generated power from a photovoltaic system. Prepared for the use of solar energy

Viessmann DHW heat pumps are designed for both mono mode and dual mode operation with a solar thermal system. In the dual mode version, the solar circuit pump is switched on or off electronically, with the aid of a temperature differential control. If the solar circuit pump is active, DHW heating is not produced by the heat pump. This ensures optimal use of free solar energy. In addition, the heat pump can make optimum use of self-generated electricity from a photovoltaic system.

Benefits of a DHW heat pump

If the heat pump only produces domestic hot water, it has many benefits for system owners. One of them is the low investment and running costs. There is no need to develop a source of heat, as is the case with many systems, since the energy source is already available and is free of charge. And because a heat pump for water does not give off emissions, there is no need for a chimney. When combined with a solar system or an air distribution system, this heat pump works extremely efficiently.

Dehumidification of the installation site

Decoupling from the heating system has other benefits as well. The boiler can be switched off completely during the warmer months of the year, thus not requiring any electricity. It takes very little time to install a DHW heat pump. Ultimately, neither a gas connection nor an oil tank is necessary. And since no fossil fuels are burned for DHW heating, system owners save both the environment and their wallets in the long run. Last but not least, a DHW heat pump, if installed in a basement room, can dehumidify the room as well. This reduces the risk of mould growth and protects the masonry. For the other benefits of heat pumps, see the section on the benefits of a heat pump.

DHW heat pumps

Independently of any other heating system, the DHW heat pump heats domestic hot water, inexpensively and efficiently, by utilising heat from the room

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