Retrofitting heat pumps
Energy expert Prof. Dr.-Ing. Michael Bauer, a partner at Drees & Sommer, discusses the challenges of the heating transition and the obstacles to the increased use of heat pump technology. He recommends a standardized approach – especially for established residential buildings.
Professor Bauer, the German government wants six million heat pumps to be installed in German residential buildings by 2030 as part of the heating transition. How realistic is that?
Professor Bauer: Up to now the market has not had the necessary know-how. In other words, planners, consulting centers, contractors and customers need to know how existing fossil fuel heating systems can be economically converted to use heat pumps.
So even though we know how to do it in theory, putting it into practice is not that simple?
Exactly. Let me give an example: Each single-family home would first have to be examined in detail to develop an economical solution for it. Generally, small businesses cannot afford to provide this service. It is even beyond the scope of many energy consultants because heat pump technology requires lower operating temperatures than most legacy heating systems, and the questions that need to be answered quickly become quite complex. For example: How does the current heating system operate? How far can operating temperatures be lowered to allow the heat pump to run economically while still providing sufficient heat? What conversions are required? Are storage tanks needed? How cost-efficient are they? What will the whole setup cost? Could photovoltaics be used to improve cost-efficiency? What heat sources are available? Are there any practical alternatives to heat pumps? At the same time, consultants need to familiarize themselves with possible subsidies for heat pumps: Who is entitled to a subsidy? How much is it and for what exactly does it apply? And finally, how economically viable would a heat pump solution be overall?
What do you have to consider when it comes to heat pumps?
- The key problem with heat pumps in established buildings is the large temperature difference between the heat source and the operating temperature of the heating system.
- Possible solutions include lowering the operating temperature of heating systems and selecting a suitable heat source.
- The most commonly used heat sources for heat pumps in residential buildings are outside air, groundwater, geothermal energy, wastewater, and ground loops.
- The cost and benefits must be weighed up when choosing a heat pump and the appropriate heat source.
- Different heating strategies can be adopted depending on the building. For example, a heat pump can be supplemented by a local or district heating network.
That’s enough to make your head spin! Are there no aspects of this technology that are already certain?
Yes, there are. All the necessary technical components are available. And they are also mature. What is missing is sufficient design and operational experience, particularly when it comes to finding the right combination of components in established buildings.
That was my next question: In new buildings, heat pumps are virtually taken for granted. But what is holding back the technology in established buildings?
First, I have to explain a basic physical principle of heat pumps: The technology is most effective when the temperature difference between the heat source, such as the outside air or geothermal energy, and the so-called heat sink – that is, the operating temperature of the heating system – is as small as possible.
The problem is that heating systems in established buildings generally have higher operating temperatures than in new buildings – usually around 70 degrees Celsius or higher – which means that the difference between the heat sources and the operating temperature is generally quite high. As a result, the operation of heat pumps in established buildings is usually less economical than in new buildings.