A heat energy recovery system from tunnel waste water

Abstract

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

Heat energy from a shallow geothermal system in Glasgow, UK: performance evaluation design

“…We have previously reported that the total heat load at St George's Cross Station was 5.2 kW (Hytiris et al, 2016). Thus, a 9kW WSHP was required to meet this station's heating and domestic hot water demand.…”

“…Once water enters the tunnel network, the flows are eventually directed to the pumping station sumps either via a drainage channel set within the concrete trackbed between the running rails or via drainage pipes, dependant on the location of sumps and discharged through a pumping system. In a previous publication (Hytiris et al, 2016) we detailed water flow and water temperature measurements carried out over a 15-month period 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 was calculated.…”

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This study reports on the actual energy and economic performance of a water source heat pump recently installed and operated at a Glasgow Subway Station using subsurface water ingress to provide heating and domestic hot water. This follows from a previous publication (Hytiris et al, 2016) that detailed the empirical measurements and design of a heating system designed on the basis of a fifteen-month monitoring period of the water flow and temperature. The perennial water flow at a relatively high temperature enabled the system to operate more efficiently than a typical heat pump system with boreholes or trenches.

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Recovery and Valorisation of Energy from Wastewater Using a Water Source Heat Pump at the Glasgow Subway: Potential for Similar Underground Environments

“…This was planned, designed and carried out on location during the last quarter of 2015. St George's Cross station's heat demand was calculated to be 5.2 kW [8]. Therefore, a 9 kW water source heat pump was necessary to cover the heating and the domestic hot water demand.…”

Energy Performance of a Heating System via Wastewater Management

“…This was designed and delivered on site in late 2015 and commenced operation in the last quarter of 2015. 112-3 The total heat load at the St George's Cross Station was calculated in 5.2 kW [2]. Thus, a 9kW WSHP was required to meet this station's heating and domestic hot water demand.…”