You may have heard of "self-heating hot pots" and "self-warming hot pots," but have you ever heard of a "heat-collecting tunnel" that can absorb and release heat? In the near future, China's first "heat-collecting tunnel"—a tunnel capable of autonomously harvesting geothermal energy to supplement the energy consumption of stations or administrative buildings—will soon be implemented in Shanghai.

At the recently held Shanghai International Carbon Neutrality Technology, Products and Achievements Expo, the application prospects of geothermal tunnels were showcased at the booth of Tunnel Engineering Co., Ltd. Urban Construction Design Group. The project has been officially approved by the Shanghai Municipal Commission of Housing and Urban-Rural Development and the Shanghai Municipal Science and Technology Commission, and is expected to be piloted in a new cross-river tunnel project in Shanghai.

Geothermal energy is a clean and renewable energy source. As long as one goes deep enough underground, the temperature of the strata remains essentially constant, which is precisely why basements are warm in winter and cool in summer. In Shanghai, the strata temperature below 10 meters is basically maintained at around 18°C, and most underground infrastructure such as subways, regional railway tunnels, underground utility tunnels, and drainage pipe networks are located within this "18°C constant-temperature layer." Leveraging this natural advantage, tunnels can continuously draw energy from underground and deliver it to tunnel stations, administrative buildings, and surrounding structures.

"Simply put, an energy tunnel is a large heat exchanger that, through ground-source heat pump technology, delivers harvested geothermal energy to energy-consuming buildings," said Jiang Hong, Chief Engineer of Tunnel Engineering Co., Ltd. Urban Construction Design Group. If the ground-source heat pump is compared to a "heart," then the tunnel is the "lungs," and the buildings or stations that use the energy are the "organs." The ground-source heat pump continuously transfers unwanted energy from buildings into the strata, while simultaneously transferring energy drawn from the strata back into the buildings, achieving heating in winter and cooling in summer.

The air-conditioning systems of tunnel stations or administrative buildings are the most direct application scenario for geothermal tunnels. The geothermal energy harvested by the tunnel can replace part or all of the air-conditioning system. In the future, under large-scale development, surplus energy could also be used in office buildings, commercial centers, or residences along the tunnel route.

"At present, Shanghai's planned regional railway network covers nearly 1,000 kilometers. If 30% of the underground sections were developed for geothermal energy, the energy harvested annually could reach 1.2 billion kWh, equivalent to the total annual heating and cooling energy of 30,000 ordinary households," Jiang Hong said. Compared with conventional air-conditioning systems, geothermal energy can save more than 40% of electricity consumption and carbon dioxide emissions.