Introduction Heat pumps facilitate the transfer of heat from a low temperature to a higher temperature, against the natural flow. In terms of renewable energy technologies, heat pumps can be applied to transfer heat from the air, water or the ground to provide space and water heating in buildings or for industrial processes. Many systems are reversible, therefore can be used to remove excess heat from buildings to the surrounding environment. Scotland has a target to produce 11% of heat demand from renewable sources by 2020. The current contribution is 3% (2012), most of which comes from woody biomass. There is great potential for heat pumps to make a much greater contribution to the installed capacity of renewable heat in Scotland.
A new application of heat pump technology is to use them to extract the heat from the water accumulated in abandoned mine workings. The main benefit of targeting water from workings is the greater accessibility via mine shafts, where the supporting structures from when mining was in operation are likely to be in tact creating huge voids of warm water. There are a number of examples of this technology in action across Europe and in Scotland at varying scales but with high success levels. Glasgow, and Scotland's central belt, has a rich mining history, particularly in what can be deemed shallow - mine workings right up to hundreds of meters depth. There are a number of factors that will influence areas suitability for this type of installation including, depth and location of mine workings, water temperature, geological condition, pollution and environmental conditions , current research at Glasgow Caledonian University, with the support of Scottish Power and British Geological Survey, aims to address some of these issues.
Materials/ Methods Computer software, namely ArcGIS can be used to map the location of mine workings from historical mine abandonment records, as well as allowing other spatially referenced physical and social data to be displayed and analysed.
Mine water samples obtained from various locations across the city have been subject to chemical analysis using Atomic Absorption Spectroscopy (AAS), Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Palintest methods. In addition, at one location boreholes allowing access to mine water have been used to monitor the temperature of mine water over a period of time where the surface temperature is subject to change, with the aim of providing empirical data on mine water temperatures in the area as well as demonstrating that mine water at depth is unaffected by changes in ambient air temperature.
Results/ Discussion As expected, mine water temperatures were found to be constant over a number of winter months, regardless of changes in ambient air temperatures above ground, and of a suitable temperature able to provide low grade heat to buildings. This type of heating system would therefore lend itself well to buildings with a low heat demand, for example well insulated domestic properties, or office buildings with a high proportion of electrical equipment contributing to casual heat gains.
Additionally there was little in the chemical analysis of mine water to cause any alarm, especially since heat pumps using water systems are closed loop systems where the mine water is not exposed to the atmosphere or used for domestic hot water, where there may be potential for contamination or oxidation of water impurities.
The use of ArcGIS is effective in displaying and disseminating data related to the location and interaction of abandoned mine workings. This information is vital in locating areas where this technology is best deployed and allows other physical as well as social factors to be considered when considering site suitability.
Conclusions The existence of heat pump installations that utilise the heat in water found in abandoned mine workings in Europe and particularly in Scotland demonstrate that this is a viable renewable heat solution. Glasgow's industrial past, a wealth of historical mining data and new site specific data relating to the conditions of mine water, all contribute to Glasgow being a potential world leader in renewable heat generation using water in abandoned mine workings.