Utilizing the road bed for combined ground source heating and sustainable rainwater drainage in Hedensted, Denmark

We present a novel climate adaption technology – the Climate Road - that combines collective, ground source heat pump (GSHP) based heating with sustainable urban drainage of rain water (SUDS). The system utilizes the road bed simultaneously as a retarding basin for excess rain water and as the energy source for a GSHP. Surface water percolates through the permeable road paving and is retained in the gravel road bed during extreme precipitation events where the sewage system is often overloaded. Water is subsequently released once capacity is available again on the sewage network. In addition, geothermal piping is embedded in the roadbed, serving as the collector for individual GSHPs that supply connected households with heating. The primary benefit of the combined system is the saved digging costs and lost property value from establishing a separate rainwater basin and trench for the geothermal piping as the road bed is to be established under any circumstances. However, there is also a subtle yet positive effect on the performance of the GSHP, from constantly watering the geothermal piping.

We have constructed 50 m of Climate Road in Hedensted, Denmark. The road bed is 1 m deep and 8 m wide and can retain a maximum of 150 mm of precipitation, given that the catchment area is twice that of the road surface. Moreover, the road bed is hydraulically disconnected from the surrounding soil by means of bentonite mats, to prevent seepage of groundwater into the road bed. Water is discharged by drainage pipes to a nearby rainwater basin for experimental and practical purposes only. 800 m of geothermal piping is embedded in the road bed, supplying a nearby kindergarten with domestic hot water and room heating by means of a GSHP. The Climate Road is fully instrumented with temperature sensors in the road bed, flow meters to measure water discharge and energy metering on the GSHP. We present the performance of the Climate Road in terms of supplied heating and the coefficient of performance (COP) for the heat pump in addition to drained water volumes for the first year of operation.