Mine water as a resource: space heating and cooling via use of heat pumps

Abstract

Heat pumps (for example, refrigerators) are able to extract heat energy from a low temperature source and transfer it to a higher temperature sink, usually via a closed loop of volatile "refrigerant" fluid in a compression / expansion cycle. This pumping of heat "up" a temperature gradient requires an input of energy (to power the compressor), but the amount of energy delivered may be three to six times that of the input. Extraction of heat from geological strata and/or groundwater for space-heating of residences and public buildings is relatively seldom practised in the UK, although it is commonplace in nations such as Sweden, the USA and Norway (where groundwaters as cold as 5-6°C may be utilised). Abandoned mines, due to (i) the large volume of water they may contain, (ii) to the often high water throughflow and (iii) to the large rock-water interface across which heat transfer can occur, represent attractive heat energy reservoirs on which heat pump systems can be based. The fact that abandoned mines are often the sites of development of new industrial or retail parks, with large space heating requirements, render heat pump systems based on mine water particularly attractive: thus, a potential environmental liability can be converted into a resource. Of no lesser interest is the fact that the mine water can also be used for space-cooling in the summer, or removal of waste heat from computer facilities throughout the year. Case studies from Park Hills (Missouri, USA), Spring Hill (Nova Scotia, Canada), Kongsberg and Folldal (Norway) and Scotland, demonstrate the practicality of mine water-sourced heat pumps as a space-heating / cooling technology