Development of Optimized Supply Concepts and Sustainable Quality Assurance Measures for Heat Pumps in Existing Single-Family Homes

Looking at current energy system studies, heat pumps play a key role in achieving climate protection targets in the building sector and should be established as a central heating supply technology in existing buildings. To support this rollout, the demonstration and analysis of the efficiency and operating behavior of heat pumps under typical conditions in older buildings, as well as the development of suitable measures for efficiency assurance, are required. This is where the BMWE-funded research project "HP-QA in Existing Stock," focusing on single-family homes, comes into play.

Initial Situation

Just over half of the single-family and two-family houses in Germany were built before 1977, before the first thermal insulation regulations came into force. About 15% of the buildings were constructed up to the third thermal insulation regulation in 1995 and nearly 10% until the first Energy Saving Regulation in 2002. Some of these buildings have been energetically renovated in various forms since their construction. Additionally, there is a status quo regarding heating systems, storage, and heat distribution and transfer systems that has developed over several generations of heating technology. In terms of the practical use of heat pumps in this area, the involved parties face a significantly more complex starting situation than in new construction. Therefore, measures must be developed to ensure efficient heat pump operation. At the same time, there are further questions regarding bivalent systems, combinations with photovoltaic systems and batteries, or noise exposure from air-source heat pumps.

Objective

The project objectives can be summarized as follows:

• demonstration and analysis of heat pump efficiency in existing single-family homes
• analysis of the operating conditions of heat pumps in relation to the condition of buildings and heat transfer systems
• detailed analysis of efficiency and operating behavior of monoenergetic and monovalent systems
• detailed analysis of efficiency and operating behavior of bivalent (hybrid) systems
• development and application of a measurement methodology for the actual noise exposure of air-source heat pumps in the field
• investigation of heat pumps in combination with PV and battery storage regarding self-consumption and autonomy as well as interactions with the electricity distribution network
• assessment of greenhouse gas emissions from the operation of heat pumps considering time-variable factors
• derivation of measures to ensure efficient heat pump operation

Approach

At the center of the project was the measurement investigation of 77 commercially available heat pumps, 61 of which used air as a heat source, conducted as part of a field test. All systems are used for both space heating and domestic hot water heating. The buildings' construction dates back to 1826, with the degree of energy renovation ranging from unrenovated original states to fully renovated buildings. The measurement concept included at least minute-accurate recording of measurement data. On the side of electrical consumers, in addition to compressors, controls, and heating rods, the drives in the heat source were also recorded. In the hydraulic circuits of the heat source and the heat utilization system, energies, performances, flow rates, and temperatures were recorded. The efficiency evaluation of the measurement data was automated using the software mondas®. This investigation was complemented by the results of an extensive research and analysis of the master data for the individual measurement objects.

Results

The main evaluation period with the largest sample size was the year 2024. During this period, 49 air-source heat pumps achieved seasonal performance factors (SPF) between 2.6 and 4.9, with an average of 3.4. The 13 ground-source heat pumps with geothermal probes achieved SPF values of 3.6 to 5.4. No correlation between the building age and the SPF of the heat pumps was found. This is related to the main influencing factor on the efficiency of the heat pumps: similar required temperatures for space heating were measured across all construction age periods. Based on these efficiency values, greenhouse gas emission savings of 37% to 70% compared to a gas boiler can be calculated for the observation period and 61% to 90% by the year 2030. Considering time-variable factors, the greenhouse gas savings in 2024 are 6% lower. At the same time, the detailed investigation revealed further optimization potentials: many heat pumps are oversized based on consumption, and some systems show excessively high switching frequencies. Furthermore, the interaction between heat pump, heat storage, and heat utilization can be optimized further. These and other findings are summarized in detail in the final report.

• Bosch Thermotechnik GmbH
• Glen Dimplex Deutschland GmbH
• Lechwerke AG
• Max Weishaupt GmbH
• NIBE Systemtechnik GmbH
• Panasonic Heating & Ventilation Air-Conditioning Europe
• DAIKIN Airconditioning Germany
• Viessmann Werke GmbH & Co. KG
• Stadtwerke Stuttgart GmbH
• Stiebel Eltron GmbH & Co. KG
• Vaillant GmbH

The project "HP-QA in Existing Buildings" (WP-QS im Bestand) project was funded by the Federal Ministry for Economic Affairs and Energy (BMWE) (FKZ: 03EN2029A).