Insights into Thermal and Energy Efficiency of a Residential Heating System: A Case Study on Asphalt Collector Integration with Heat Pumps

This study investigates the integration of three distinct thermal energy sources—Borehole Heat Exchangers (BHE), Solar Collectors (SC), and Asphalt Collectors (AC)—with heat pumps, supplemented by wastewater heat pump, for space heating, domestic hot water supply, and free cooling (FC) in residential build-ings in Vienna, Austria. The system includes 64 boreholes for the BHEs, each 142 meters deep, providing a capacity of 410 kW. The SC, an unglazed collector with a surface area of 290 m², has a capacity of 87 kW, while the AC offers a capacity of 40.5 kW with an exposure area of 135 m². These sources are integrated to support three heat pumps with capacities of 138 kW, 175 kW, and 155 kW, respectively, while the BHEs are also used directly for FC, handling a load of 266 kW. Addition-ally, the system leverages the heat absorbed by the AC and SC to regenerate subsur-face soil, contributing to the reduction of the urban heat island effect.
While the integrated system shows significant potential for harnessing renewable energy sources, and mitigating climate change impacts, challenges arose due to inef-ficient design, planning, and operational practices. In this paper, we investigate these issues, based on a comprehensive analytical analysis of year-long in-situ measure-ments. These measurements include temperatures, flow rates, weather conditions and energy consumption. We also provide recommendations for optimizing system operation and control, aiming to promote the adoption of such systems to achieve sustainability goals on a city-wide scale.