5The performance of a typical air source heat pump could be increased dramatically by a relatively stable air 6 temperature with a high humidity, even during the peak heating months. In this short communication we show such 7 conditions exist in the underground transport tunnels of the Glasgow Subway system, where we had conducted an 8 annual survey of air flow, air temperature and relative humidity at thirty different points within the subway network. 9We found relatively stable temperatures and sufficient air movement inside the twin tunnels (average temperature 10 during winter = 15 o C, annual variation = 2.6 o C; average air flow = 16.47 m 3 /h) indicating higher system efficiency 11 compared to a conventional air source heat pump installation. Potential energy and carbon savings are discussed. 12

An installation of a Water Source Heat Hump (WSHP) at Glasgow’s Underground Station, has been using the subsurface wastewater ingress to heat the office at St. George’s Cross station. The performance of the Glasgow Subway’s new heating system was observed for a few months. The energy output readings are being presented. An average coefficient of performance (CoP) of 2.5 and a 60% energy input reduction for the heating system based on the old heating system’s energy demand indicates the actual system’s performance. The purpose of this research is to detect the likelihood of implementing the same setup in similar underground environments where the excess wastewater may support a viable and eco-friendly heating system. Fifteen cities across Europe have been identified and presented, with the adequate water quantities, where similar heating systems may be applied. The output of this study indicates not only the financial benefit but also the energy and carbon reduction of this trial. It highlights main subjects which were encountered in such a challenging subway system. Future steps to commercialize the excess heat energy output are explored together with opportunities to promote the same setup in similar cases.

Minimising the maintenance costs of water ingress in transportation tunnels is a significant challenge. Decreasing the overall cost of a ground source heat pump system is equally challenging. An effort to address both issues at once has been made in relation to groundwater ingress in the Glasgow Subway system. Inflowing water is a valuable resource which could be channelled through a water source heat pump (WSHP) to produce heat energy for domestic or public use (heating and domestic hot water). Water flow and water temperature have been recorded for a year at 21 different points within the network of the underground tunnels and platforms. The points of highest water influx were identified, and the heat energy content of each has been calculated. Working from these data, several options were identified for capturing the water and diverting it to a WSHP to recover heat. A final design for a pilot system within the tunnels was developed. The findings of this study are expected to contribute a renewable heat solution through a cost-effective heat pump system design. Notation COP H coefficient of performance E required energy: kW G heat energy flux: kW H total heating effect S VC specific heat capacity of water: J/(l K) Z flow rate: l/s Dq temperature drop:°C r density of water: kg/m 3 300 Cite this article

Glasgow is one of many locations within the United Kingdom once dotted with a number thriving coal mines. Before the suitability of the water stored in mines can be determined for use in GSHP heating applications, it is essential to rule out any risk of contamination caused by exposure to this water. This study examines water samples obtained from boreholes drilled directly above abandoned and flooded mine workings. It indicates that the chemistry of the water flooding the mines beneath Glasgow is suitable for use in ground source heat pump (GSHP) heating applications. The development of such systems in the future could help bring Glasgow forward in its ambition to become one of Europe's top ten sustainable cities by the year 2020, as well as helping to transform previously neglected and impoverished areas of the city, to areas full of potential by creating a number of jobs, homes and opportunities for the people living in this area.

In this short communication, we demonstrate that the performance of a typical air source heat pump (ASHP), exploiting a relatively stable air temperature within a subway environment, is high, even during the peak heating months. After a nine-month operational run, the coefficient of performance is demonstrated to be 3.5. The design and installation difficulties are stated together with the lessons learnt following this trial. The actual energy and carbon savings are discussed.