In Numerical investigation of the convection heat transfer driven by airflows in underground tunnels (Sci-Hub mirror), a group of engineers from L'Ecole Polytechnique Fédérale de Lausanne and the Swiss Federal Institute of Technology propose that low-cost heat-exchangers placed in subway tunnels could be used to heat and cool homes essentially for free (the system would last 50-100 years, and the pumps would need replacing every 25 years).
The system would pump water or another heat-exchange medium through pipes in the subway tunnels, scavenging the underground cool in the summer and the trapped exhaust heat in the winter, then transfer the heat or cold to nearby residences, businesses and offices for efficient heating and cooling.
The research stems from the incredibly appropriately named co-author Margaux Peltier's Master's thesis; Peltier calculates that installing heat exchangers in just half of one of Lausanne's subway lines could provide heating and cooling for 800 apartments.
As Treehugger's Lloyd Alter points out, the work illustrates how important well-planned, high-density cities are mitigating climate change: high density systems allow for waste from one process to flow into another process as its input; to say nothing of the carbon benefits of building cities where the primary mode of transport is efficient subway trains rather than private automobiles.
Numerical investigation of the convection heat transfer driven by airflows in underground tunnels (Sci-Hub mirror) [Margaux Peltier, Alessandro F. Rotta Loria, Loïc Lepage, Etienne Garin and Lyesse Laloui/Applied Thermal Engineering]
Engineering heat out of metro tunnels [L'Ecole Polytechnique Fédérale de Lausanne (EPFL)]
Energy from subway tunnels could heat and cool thousands of homes [Lloyd Alter/Treehugger]
(via Naked Capitalism)
(Image: MS / EPFL 2019)
