The Thermo Road – Harnessing the water-energy nexus for combined sustainable urban drainage and geothermal district heating and cooling
VIA University Collage
Due to restrictive building energy regulations and climate change, new buildings in Denmark require both heating and cooling. Moreover, the ability to manage rainwater and storm water runoff locally is becoming increasingly more important, as water utilities are challenged by the increased levels of precipitation and extreme rainfall events. The Thermo Road concept seeks to tackle both challenges at once by 1) creating a subsurface rainwater basin in the roadbed to store and delay extreme precipitation, and 2) by supplying fossil-free geothermal district heating and cooling.
Challenge
The building sector consumes 50% of all energy produced in Europe and roughly 80% of that energy is produced with fossil fuels. Considering that, the building sector is falling behind all other sectors, when it comes to climate gas emissions. In addition to heating the cooling demand worldwide has an impact on global warming and will triple by 2050. Climate change is accelerating, and increased precipitation and flooding are already destroying human lives and material value on an unprecedented scale. Sector integration is key to tackling the long-term reduction of climate gas emissions and to mitigate climate change symptoms here and now, by creating tangible synergies when combining multiple utilities in single, climate change adaption systems.
In a world with increased global warming fueled by climate gas emissions, large-scale reductions in the use of fossil fuel energy sources are critical. Nevertheless, this is not adequate, as climate change is already causing havoc with frequent flooding events across the globe. Efficient management of the increased levels of precipitation and efficient, combustion-free sources of domestic heating and cooling are key to mitigating and preventing further climate change.
Solution
The Thermo Road solves both challenges at once, by draining rainwater to the porous roadbed, which can retain, while it delays a 100-year precipitation event. The roadbed has embedded geothermal piping, and in addition to geothermal boreholes and a wastewater heat exchanger, these clean sources of geothermal energy provide consumers with emission-free district heating and cooling throughout the seasons by distributed heat pumps. These ground-source heat pumps operate at unparalleled efficiency including minimal strain on the electricity grid and without the noisy and aesthetically displeasing outdoor air-source heat pump units.
Implementation
The Thermo Road has been built in full scale near Horsens in Denmark, to serve as a multiutility system for 12 rental, single family houses. The roadbed is 100 m. long and 1.3 m. deep and can contain roughly two consecutive 100-year precipitation events (150 mm. of rain). Water is drained to the rainwater sewer through a water brake that restricts maximum flow to 0.78 l/s which implies that the sewer can never be overloaded by flow from the roadbed. Instead, water is retained in the roadbed and drained safely later. 1200 meters of geothermal piping have been embedded in the roadbed, combined with three geothermal boreholes and a wastewater heat exchanger supplies the 12 buildings with district heating and cooling throughout the year. The consumers are connected by a thermonet, which is a shared grid of uninsulated pipes, similar to traditional district heating. As grid temperatures levels are close to those of the undisturbed ground, no insulation is required. Unlike traditional district heating, grids that loose heat, the thermonet grid produces energy for heating and cooling as it exchanges energy with the ground during both winter and summer.
Further studies have shown that the run-off water quality is improved dramatically and to the levels like that of surface rainwater basins which currently is considered the best available technology for water quality management. The implications are rather staggering as subsurface rainwater basins free up costly areas for further urban development, generating significant revenue streams and reduced costs for the private developer and the municipality. Thus, instead of having zero utility, the roadbed provides three utility services: rainwater management, rainwater quality and finally geothermal emission-free district heating and cooling in addition to reuse of excess heat from the central wastewater pipe and increased revenue streams for private and public stakeholders.
Results
The case demonstrates that multi-utility systems can be built in full scale and for real consumers and that the technical and financial risks are manageable. It also emphasizes that using existing infrastructure (the roadbed) for several purposes rather than just for structural integrity is a credible path for lowering the overall life cycle climate impact of roads and future utilities while potentially improving the financial business case.
Partners
VIA University Collage, Hedensted Municipality, GeoDrilling, HTN Entreprenør, Land & Plan, Hedensted Spildevand, Læsning Fjernvarme, NCC, Energy Machine, Kamstrup, Bravida, Kemic Vandrens, Frese, Salling Plast, NID, and PlanEnergy.
Contact
Søren Erbs Poulsen
Head of Research Programme, VIA University College
soeb@via.dk.
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