TUM Examines 13 Residential Heating Sources & Finds A Winner – Heat Pumps – CleanTechnica

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Last Updated on: 10th February 2025, 01:13 pm

Recently, researchers at the Technical University of Munich (TUM) conducted a study recently that found heat pumps are often the best choice for homeowners when finances and ecology are taken into account. The study asked three questions:

• What are the environmental impacts of various heating systems?
• What are the costs associated with operating these heating systems?
• Which heating system has the highest eco-efficiency?

The findings were published in the December 2024 edition of the Journal of Building Engineering. Here are their findings as stated in the abstract of the study:

Transitioning from fossil fuels to renewable heating is essential for rapidly reducing greenhouse gas emissions. Besides greenhouse gas emissions, other environmental and economic impacts are crucial for successfully implementing renewable heating systems. This study evaluates 13 residential heating systems’ environmental, economic, and eco-efficiency performance for a typical German two-story dwelling. The life cycle assessment method is employed to quantify the environmental impacts.

Assuming a sustainable supply of biomass-based fuels, biomass heating systems exhibit the lowest environmental impacts, whereas gas heating systems are associated with high environmental impacts. Among heat pump systems, the water-source heat pump demonstrates the lowest environmental impact. Additionally, integrating a PV system into heat pump systems reduces the environmental impacts across all heat pumps. The evaluation indicates that the air-source heat pump is the most economical system, while the pellet boiler with solar thermal support and the heat pump with ice storage incur the highest costs.

However, the cost differences among the heating systems are relatively small, making it challenging to establish a clear ranking based solely on economic evaluation. An eco-efficiency assessment, which combines environmental and economic aspects into a single indicator, reveals that the most eco-efficient systems are the air-source heat pump, both with and without a PV system, and the wood gasifier heating system. In contrast, the ice-storage heat pump and the pellet heating with solar thermal support show the lowest eco-efficiency.

While the electricity sector has significantly transitioned to renewable energy sources, the researchers explain, the heating sector has lagged behind. In Germany, the share of electricity generated from renewable sources has nearly doubled over the past decade and now accounts for more than 50% of gross electricity consumption. Yet the share of renewables in the heating sector has grown slowly and currently stands at about 20%. Due to the heavy reliance on fossil fuels, emissions from heating systems are a significant contributor to anthropogenic pollution. In Germany today, about 20% of the total greenhouse gas emissions originate from residential heating,

To achieve Germany’s goal of greenhouse gas neutrality by 2045, the heat supply from renewable sources must increase significantly. Although the number of heat pumps installed in Germany has grown substantially over the past 20 years, CO2-intensive gas heating systems remain the most common. However, when comparing different heating systems, it is essential to consider other environmental impacts in addition to greenhouse gas emissions.

The scientists said something that should be obvious to all. Economics often play a more important role in deciding whether to buy and install a more efficient heating system than technical specifications. Many homeowners are motivated by the environmental performance of a heating system but even more so by its cost effectiveness. Since the economically optimal option often differs from the ecologically optimal one, an eco-efficiency analysis incorporating both perspectives can provide a more balanced evaluation of heating systems.

The research involved and investigation into 13 different heating systems suitable for a typical two story building that focused on both environmental and economic perspectives. First, dynamic building and system simulations were conducted to determine each system’s fuel and electricity requirements. This was followed by an economic evaluation through a dynamic investment calculation. Next, the environmental impact was assessed using the life cycle assessment method. Finally, an eco-efficiency analysis was performed to compare the heating systems in terms of both economic and environmental impacts. Here is a list of the heating sources studied and compared.

Heating system		Abbreviation	Components considered
Fossil systems	Natural gas condensing boiler	GCB	Heat generator, natural gas connection system, chimney, thermal storage tank
	Natural gas condensing boiler with solar thermal system	GCB_ST	Heat generator, solar thermal system, natural gas connection system, chimney, thermal storage tank
Biomass systems	Pellet boiler	PB	Heat generator, fuel storage, chimney, thermal storage tank
	Pellet boiler with solar thermal system	PB_ST	Heat generator, solar thermal system, fuel storage, chimney, thermal storage tank
	Wood gasification boiler	WB	Heat generator, chimney, thermal storage tank
	Wood gasification boiler with solar thermal system	WB_ST	Heat generator, solar thermal system, chimney, thermal storage tank
Heat pump systems	Air-source heat pump	ASHP	Heat generator, thermal storage tank
	Air-source heat pump with photovoltaic (PV) system	ASHP_PV	Heat generator, PV system, thermal storage tank
	Ground-source heat pump with geothermal probe	GSHP	Heat generator, geothermal probe, thermal storage tank
	Ground-source heat pump with geothermal probe and PV system	GSHP_PV	Heat generator, geothermal probe, PV system, thermal storage tank
	Water-source heat pump	WSHP	Heat generator, well system, thermal storage tank
	Water-source heat pump with PV system	WSHP_PV	Heat generator, well system, PV system, thermal storage tank
	Ground-source heat pump with ice storage and solar collectors	HP_ICE	Heat generator, solar thermal system, ice storage, thermal storage tank

Heat Pumps Are Best In Most Cases

Evaluating both ecological impacts and economic costs allowed the researchers to combine real world financial considerations because while the most eco-friendly system may be desirable from a societal perspective, cost is often the determining factor in  selecting heating equipment. Of the 13 systems considered, the researchers found that using the economic evaluation, the results vary significantly depending on the assumptions made, making it difficult to determine which heating systems are associated with the lowest costs. However, the air-water heat pump, with and without a PV system, and the gas heating system, perform better even in the worst-case scenario than four systems in the best-case scenario, suggesting that these three systems are highly likely to be the most cost-effective.

The lifecycle assessment, which assumes a 20-year useful life, shows the gas heating system has the lowest environmental impact in 11 out of 16 impact categories. However, this system also has the highest impacts in three categories, including the critically important greenhouse gas emissions. Besides the gas heating system, the wood log boiler performs best in four categories when disregarding biogenic CO2-eq emissions, but also has the highest environmental impacts in four categories. The normalization and weighting of the midpoint LCA results indicate that, despite its good performance in most impact categories, the gas heating system has the second-highest single score, indicating high overall environmental impacts. Conversely, the lowest environmental impacts are observed for the wood log boiler, pellet heating system, and the water-water heat pump with a PV system.

In  the eco-efficiency analysis conducted to relate the costs of the heating systems to their environmental impacts, the air source heat pump with PV system and the log wood gasification boiler perform best in this analysis and thus have the highest eco-efficiency. Three other heating systems — water and ground source heat pumps with PV and air-source heat pump — also exhibit higher eco-efficiency than the gas heating system.

In Conclusion

The findings suggest that a gas-fired heating system is cost competitive with various heat pump systems, which is not surprising since air to water heat pumps are fairly expensive compared to a standard gas boiler. Over their useful lives, however, the costs even out, but the heat pump has significantly less carbon dioxide emissions during its useful life. If there is a takeaway here, it is that incentives and policy support will remain essential in order for more homeowners to opt for heat pumps over standard gas heating equipment. That, of course, assumes that any national government puts enough of a premium on maintaining the Earth as a place where humans can continue to thrive.