title: Groundwater heating and cooling - an evaluation of resilience in the context of recharge and temperature
Creators: name: Birks, David C.
Publisher: name: University of Glasgow
Year: 2019
Subjects: subject: Groundwater, heating, cooling, resilience, recharge, temperature, low, carbon, climate change, decarbonisation, heat, injectivity, specific capacity.

description: The Climate Change Act (2008) committed the UK to reducing greenhouse gas emissions by 80% by 2050 compared to 1990 levels. Heating accounts for 47% of total UK final energy consumption and more than three quarters (77%) of energy use across all non – transport sectors. The displacement of heating and cooling technologies, which are reliant on the combustion of fossil fuels and which may be contributing to CO2 poisoning, is thus the primary driver for increased utilisation of heat pump technologies in the UK and globally. Deployment of open loop groundwater heating and cooling systems and other genres of geothermal systems which utilise heat pumps has been much higher in Europe and North America than in the UK. For example, in Sweden the total installed capacity for heating and cooling was reported to be 6.8GW, approximately 70 times the installed capacity in the UK. The Netherlands, Sweden, Canada, France, Switzerland, Germany and the USA are at the forefront of technical development globally. In the UK the use of fossil fuel heating and cooling technologies remains prevalent. Uptake of alternative, low carbon technologies in the UK is slow because it must compete with proven technologies and users are reluctant to take risks. Furthermore, there is scepticism amongst potential users of the ground source heat pump technology and their advisors, possibly due to reports of poorly performing systems, and this may be having a negative impact on confidence. It is possible that proponents of some types of geothermal systems, in the UK, are over estimating outputs of useable heat and underestimating system operating costs. Additionally, the use of numerical modelling techniques that are either not explained or validated against analytical calculations, may be contributing to unreliable economic forecasts. The research presented in this thesis evaluates two risk factors associated with the operation of groundwater heating and cooling systems which have arisen due to the requirement to return the groundwater to the originating aquifers. These risk factors may be contributing to the slow rate of uptake of the technology in the UK and comprise i.) recharge of groundwater via injection wells; and ii.) potential recycling of waste heat leading to a progressive decline in performance. Three sites were evaluated over a number of years to enable a meaningful analysis of recharge performance and changes in abstracted groundwater temperature, giving an indication of how these may impact costs over a full system working life. Data presented are rare, as it is unusual for industry or operators of such schemes to allow publication which may either be commercially or reputationally sensitive. This evaluation has only been economically viable as an academic study, where consent was granted by the system operators. The data were collated over a period of ten years under multiple commercial consultancy commissions. This, and the fact that analysis is so labour intensive, may account for the paucity of published studies of this nature. A description of the technology and its place in UK planning and legislation, is presented in Chapter 1. The author’s motivation for and contribution to the research is also defined. Appendix A and Chapters 2 to 5 inclusive comprise published journal articles. The series of papers, as presented, outlines an improved understanding of system performance in respect of abstracted groundwater temperature and recharge over a progressively longer timescale. Chapter 6 presents new (unpublished) material describing the performance of systems installed in the Chalk aquifer at the Royal Festival Hall and Green Park Underground Station over a sustained period of six years. Following a progressive decrease in recharge performance of approximately 50% during testing at the Tate Modern in 2010, there is evidence to show that recharge (cited as specific capacity) stabilised in the Thames River Terrace Gravels aquifer at approximately, 1.65 ls-1 m-1, deemed to be a satisfactory level. There is also evidence to show heat rejection of up to 1.37 GWh per annum is sustainable because the cumulative effect of naturally occurring heat loss mechanisms exceeds this level of heat rejection. There is evidence to show that recharge stabilised in the Chalk aquifer at the Royal Festival Hall at approximately 0.25 ls-1m-1 during a sustained period of recharge of 6 years, which was deemed to be a satisfactory level. In contrast, monitoring of recharge at Green Park Underground Station confirmed a slow but progressive decline over the same interval, which did not stabilise. Monitoring of abstracted groundwater temperature in the Chalk aquifer at the Royal Festival has demonstrated that heat rejection of 1 – 2 GWh per annum caused abstracted groundwater temperature to increase by an amount that was detrimental to operations where the distance between abstraction and recharge wells is 144 m. Operations at the Royal Festival Hall were modified to avoid overheating. Monitoring in the Chalk aquifer at Green Park Underground Station has shown that abstracted groundwater temperature remained unchanged over a 6 year period between 2012 and 2017, supporting the hypothesis that thermal breakthrough was unlikely to occur over this timescale due to the distance (approximately 300m) between abstraction and recharge locations. Detailed interrogation of operational datasets from the Tate Modern Art Gallery, the Royal Festival Hall and Green Park Underground Station resulted in an improved understanding of how recharge performance and abstracted groundwater temperature can impact over the longer term. This should help make the technology more investable.