1.5 Centralized Heat Pump for the Whole Building

Heat distribution and temperatures levels

Hybrid systems have several possibilities of separating space heating and DHW production. In most cases the heat pump delivers space heating during spring and autumn and will be assisted by the boiler during low outside temperatures in the winter. The better the insulation, the higher the contribution of the heat pump to the space heating demand.

Size of building, number of apartments

This solution is suitable for all sizes of buildings with the preference for larger buildings. Hybrid solutions may be useful if the installation of a heat pump with a large capacity is not possible. The limitation factors may be such as an insufficient heat source, particularly high supply temperature or a limitation of grid connection. In some cases, this solution allows for installation of a smaller heat pump as an add-on for existing boiler.

DHW and storage characteristic

DHW can be pre-heated by the heat pump and finally heated to the desired temperature by the fossil part of the unit. This solution allows for an easier solving of the legionella issue.

Energy standard, insulation level 

This concept can be used for buildings with a high, as well as a low level of insulation. More applicable for older, not refurbished buildings with a higher heating energy demand. This solution is generally not to be recommend for new buildings due to use of fossil energy sources.

Complexity of installation

In case of an add-on heat pump, the existing system (boiler) and the added heat pump must be connected and controlled together. The technical room must be large enough to install the heat pump and a storage tank close to the existing boiler.

Heat Sources

Hybrid heat pumps use commonly outside air as a heat source. Generally, all heat sources are possible.

Specific issues of the concept

The old heat generators may be replaced during retrofitting without changing the distribution system. The global performance of the system is aligned with the share of heat produced by the heat pump. Easy avoiding of legionella through achievement high DHW temperatures with the use of a fossil boiler. 

Positive aspects

• Smaller heat pump capacity
• Flexible: meets every grade of insulation
• Easy Legionella prevention

Negative aspects

• High distribution losses
• Partial use of fossil fuel