Renewable energy combined with sustainable drainage: Ground source heat and pervious paving

Taken individually, Ground Source Heat (GSH) pervious paving systems (PPS) and rainwater harvesting are not new, but in combination, this energy-water blend is relatively recent. Sealed with impermeable geomembrane, PPS becomes a water harvesting tank and by installing GSH collectors in the base, there is the potential to sustainably heat and cool buildings, provide flood resilience and improve water quality. A review of the literature found that Coefficients of Performance suggest that such systems could be considered viable, reaching the value of 2.875 required by the EU Renewable Energy Directive, 2009. Small-scale laboratory-based test rigs of the combined system were able to reduce pollutants by up to 99% for biological oxygen demand and 95% for ammonia-nitrogen, with rare occurrences of potentially pathogenic bacteria e.g. Legionella, and low survival rates of E.coli. Whilst test rigs provide valuable information, field monitoring at the building scale is the only way to validate the technology. Thus, this paper presents previously unpublished results of monitoring a combined system at the building scale which found that there is clear potential 2 to use a clean, renewable and sustainable source of heat at the same time as providing flood resilience, water quality improvements and some amenity in a domestic setting. However, it was also found that seasonal changes and building use affected levels of comfort achievable. Lessons were learnt, such as construction strategies to optimise design, including depth of the heat collectors and the optimal surface area of the PPS available to infiltrate water.