• Energy Research

This paper proposes and demonstrates, in full scale, a novel type of energy geostructure (“the Climate Road”) that combines a ground-source heat pump (GSHP) with a sustainable urban drainage system (SUDS) by utilizing the gravel roadbed simultaneously as an energy source and a rainwater retarding basin. The Climate Road measures 50 m × 8 m × 1 m (length, width, depth, respectively) and has 800 m of geothermal piping embedded in the roadbed, serving as the heat collector for a GSHP that supplies a nearby kindergarten with domestic hot water and space heating. Model analysis of operational data from 2018–2021 indicates sustainable annual heat production levels of around 0.6 MWh per meter road, with a COP of 2.9–3.1. The continued infiltration of rainwater into the roadbed increases the amount of extractable heat by an estimated 17% compared to the case of zero infiltration. Using the developed model for scenario analysis, we find that draining rainwater from three single-family houses and storing 30% of the annual heating consumption in the roadbed increases the predicted extractable energy by 56% compared to zero infiltration with no seasonal energy storage. The Climate Road is capable of supplying three new single-family houses with heating, cooling, and rainwater management year-round.

Heating and Cooling constitute a major part of society's final energy use and a significant contributor to greenhouse gas emissions. The world society ought to mitigate climate change through decarbonisation, which must include the transition to low-temperature, sustainable and renewable heating and cooling technologies. Shallow Geothermal Energy is one of the most energy efficient and least greenhouse gas emitting available alternatives to provide space heating and cooling. The decarbonisation of the heating and cooling sector may have to comprise both individual systems and shared electrified heating and cooling systems from renewable sources of energy, where economies of scale and synergies between different types of consumers can be exploited. To this end, the focus of this paper is on the integration of shallow geothermal energy technologies into district heating and cooling systems. A key contribution of this work is the illustration of a number of practical case studies, highlighting the potential of existing shallow geothermal systems for DHC networks, which, as front runners in adopting such technologies, serve as paradigms for future development. Follows a discussion providing an outlook over the next 25 years. All in all, the future of utilizing shallow geothermal energy for district heating and cooling seems to be promising to play a pivotal role in sustainable urban development and decarbonizing the heating and cooling sector.

This paper presents a multifunctional full-scale demonstration road, the Climate Road, which combines climate adaptation and mitigation in a single system. The Climate Road is located at Hedensted, Denmark and is 50 m long and 8 m wide, and the depth of the roadbed is 1 m. Half of the Climate Road, i.e., 25 m, is paved with permeable asphalt and the remaining 25 m with traditional asphalt. All surface water drains into the roadbed, which stores up to 120 m3 of water, either directly through the permeable asphalt or by drain grates. In addition, 800 m of geothermal pipes are embedded in the roadbed, distributed over four 200 m w-loops, two buried 1 m below the asphalt and two similar loops at 0.5 m depth. The Climate Road was tested from May 2019 to May 2021. In the project period, a total precipitation value of 1654 mm was recorded, the mean temperature was 9.3 °C and the most intense rainfall was 40.3 mm/30 min. The long-term infiltration performance of the permeable asphalt shows that the overall infiltration capacity slowly reduces. The reduction can be hindered, but not completely prevented, with annual restorative cleaning. After two years of operation, the Climate Road still, by a large margin, fulfils the recommendations of the infiltration capacity of 97.2 mm/h for the vast majority of the road section. The total volume reduction capacity is estimated to be between 15 and 30%. Based on an analysis of 61 single rain events, the event detention time is found to range between 10 and 130 min, with an average of 35 min. During the project period, the Climate Road produced a total of 98 MWh for a nearby kindergarten, with an average coefficient of performance (COP) of 3.1.