Combining cooling of underground railways with heat recovery and reuse

The paper concerns the recovery and use of secondary/waste heat and identifies secondary heat sources in London of 71TWh i.e. c10% more than demand. London Underground (LU) railway tunnels generate significant quantities of low grade heat. There is also a requirement for active cooling to reverse the long term trend of rising tunnel temperatures. A novel combined cooling and heat recovery scheme for LU tunnels, utilising existing ventilation shafts, was proposed. Recovered heat was upgraded using a heat pump, for reuse in a local district heating network (DHN). A new model was developed to investigate the thermodynamic performance, economic feasibility and potential carbon savings available. It was concluded that the system could simultaneously provide 900 kW of cooling to the tunnel, and after upgrading to 70°C, approximately 1.1 MW of heat, which could be used as a source for a DHN. The model predicted that this could be carried out economically and could deliver massive carbon and cost savings. With 200 ventilation shafts in London, >360,000 tonnes of carbon could be saved annually, while generating revenues of £40,000,000. Applying this technology to 50% of 150 metro systems worldwide would enable more than 27 million tonnes of carbon savings.