Fraunhofer ISE has presented the results of retrofitted heat pump installations in detached houses in Germany. In one demonstration, solar electricity located on the roof and a multi-source heat pump developed in cooperation with Viessmann were presented. It uses air and ground heat as heat sources.
“In urban centers, there is often not enough space to drill wells for geothermal sensors, and the use of outdoor air as a heat source is relatively inefficient and the noise emission is higher,” Fraunhofer ISE said in a statement. “The multi-source heat pump system combines the advantages of two heat sources: the outside air and the ground. With this combination, a smaller drilling area is achieved, but the high efficiency of the heat recovery heat pump is still achievable.”
The researchers installed the solution in a 160-unit apartment building in Karlsruhe-Durlach, Germany. A peak load gas boiler and a 60 kW solar power system on the roof of the building were combined into the system.
“To achieve low CO emissions2 in terms of heat production in these buildings, the heat pumps were designed to be as comprehensive as possible, while the gas boiler is correspondingly rarely used,” said Fraunhofer.
During the first six months of operation in February-July 2022, the multi-source heat pump reached an average source temperature of 8 C according to Fraunhofer ISE. Its coefficient of performance (COP) was 3.2 during that time. The gas boiler accounted for 31% of the heat supplied to the building. This “is primarily due to the high temperature requirements of hygienic hot domestic water,” the research institute claimed. Overall, the retrofit system reduced carbon dioxide emissions by 42%.
“The demonstration apartment buildings of this project have shown that retrofitting apartment buildings is possible with heat pumps and low-energy technology,” says researcher Manuel Lämmle from the University of Freiburg.
– In order to achieve optimal operation, it is important to take into account the current situation, including heat distribution systems and the amount of space in the heating cellar, he said. “In connection with retrofitting, it is also important to hydraulically balance the heating system and check whether the temperatures of the supply water can be further lowered by, for example, changing individual radiators.”
The project included other technological developments such as hybrid heat pumps, propane heat pumps and high temperature heat pumps. Other technology partners were the German manufacturers Bosch, Beck+Heun and Kermi.