In September 2018, the Greater London Assembly published; Low Carbon Heat: Heat Pumps in London. This report states that, to meet carbon reduction and air quality targets there needs to be a significant uptake in heat pumps in the next 10-15 years. Based on estimates of market share (Abesser, 2010), around 1,000 of the 1 million heat pumps sold in the EU in 2016 were Open Loop Ground Source Heat Pumps (GSHP). In 2017 heat pump sales grew 13%, the third consecutive year of growth (EPHA, 2017). Subsequent pressure on urban groundwater resources is expected to continue to rise with the proliferation of Open Loop GSHP systems.
In England the Environment Agency (EA) regulates Open Loop GSHP by Abstraction Licence and Environmental (discharge) Permits. Since the first Open Loop GSHP in 2000, London has 44 licensed systems. In this time, the EA have noted raised groundwater temperatures potentially reducing GSHP efficiency (EA, 2018). Stakeholder’s agreed that thermal impacts of GSHP systems should be increasingly considered by the EA, particularly thermal interference. The EA responded with a Legislation and Policy document (EA, 2008) and an Environmental Good Practice Guide (undated) advocating a risk-based approach. Based on experience, the author considers this to be broadly successful in managing groundwater levels in the Chalk Aquifer of the London Basin, corroborated by the Annual Groundwater Status Report (EA). However, regulatory focus on protecting groundwater levels do not guarantee abstraction volumes or temperatures. In that sense, it is the applicant’s responsibility to assess if the proposed GSHP will be sustainable or impact other systems (Fry, 2009). Local best practice for hydrogeological input into the design Open Loop GSHP systems is discussed in this context; undertaking Environmental Impact Assessment using numerical coupled groundwater flow and heat transport modelling.
In Christchurch, New Zealand the rapid uptake of Open Loop GSHP occurred in response to the 2011 earthquakes and with incentives including streamlined planning and funding grants (Seward et. al. 2017). Up to 20 systems are operational or planned in Central Christchurch, the majority being installed since 2012 (Rekker, 2017). The local regulator (Environment Canterbury) commissioned a groundwater model to investigate anecdotal reports of water table mounding in the city (Rekker, 2017). Groundwater modelling results and anecdotal evidence of groundwater flooding, reactivation of historical springs and problematic recharge pressures will be reviewed in the context of the local regulatory requirements. Christchurch’s layered confined aquifer system mitigates the potential for thermal interference, however, lessons learnt from the regulatory and design perspective will be discussed and presented in this context; demonstrating the absence of regulatory mechanisms to assess individual and cumulative hydraulic impacts of open loop GSHP systems may have led to undesirable outcomes for the City of Christchurch.