Abandoned coal mine cools homes in Jiangsu

This summer, 96 households in Xuzhou, Jiangsu province, have abandoned noisy air conditioners in favor of an innovative floor cooling system that provides comfortable temperatures, stable humidity and near-silent operation.

The system circulates naturally cool underground mine water through pipelines installed beneath the floor, creating radiant cooling throughout homes. Compared with conventional air conditioning, it consumes less energy and costs residents significantly less.

At the end of July, with outdoor temperatures in Xuzhou reaching about 36 C at noon, Wang Qingmei, 76, was observed at home cooking in comfort. A wall-mounted thermometer displayed an indoor temperature of 26 C.

"The floor is pleasantly cool, just the right temperature. It feels best to walk on it barefoot," she said.

Mine water is pumped to a heat exchange station, where a heat exchanger stabilizes the circulating water temperature in the pipeline network at between 20 C and 25 C before it is distributed to homes.

For Wang, the savings are substantial. In previous summers, running air conditioners to keep herself and her husband cool cost about 400 yuan ($59) a month for electricity. If the air conditioner stayed on for too long, her husband's neck would ache. If they turned it off, it became too hot to sleep.

Under the new system, residents pay 4 yuan per square meter for the entire cooling season. For Wang's home, a four-month cooling period costs about 410 yuan while maintaining a comfortable temperature around the clock.

"It's both quiet and comfortable," she said, adding that many neighbors have visited to experience the system and plan to use it next year.

What makes the project even more remarkable is that the cooling source comes from an abandoned coal mine that was once considered an environmental and financial burden.

After the Woniu Mountain coal mine was shut down, its mined-out voids gradually filled with groundwater, forming a vast underground cold-water reservoir. For years, the abandoned mine generated ongoing costs for safety monitoring and ecological restoration without creating economic value.

The turning point came when researchers from Xuzhou Coal Mining Group, which owns the mine, discovered that the mine water remains at a stable temperature of between 15 C and 20 C throughout the year and is available in abundant quantities.

The constant temperature makes the resource suitable for both winter heating and summer cooling. Heat can be extracted from the water during winter, while the naturally cool water provides cooling during summer.

The project also benefits from Xuzhou's existing infrastructure. The city operates Jiangsu's only large-scale centralized heating pipeline network, which can circulate hot water in winter and switch to cold water in summer, allowing dual-purpose use without installing an additional pipeline system.

"As a traditional industrial city, Xuzhou has many closed coal mines whose stored water is like a giant green charger, transforming abandoned resources into low-carbon energy carriers," said Zhang Tao, who oversees scientific research projects at Jiangsu Xukuang Thermal Power Co, a subsidiary of Xuzhou Coal Mining Group.

According to Zhang, surveys show strong public acceptance of centralized heating and cooling services, indicating solid market demand.

He added that the city's heating season lasts only about 110 days, from November to March. Extending infrastructure use with a 120-day cooling season from June to September can significantly improve utilization efficiency and asset returns.

The project's biggest technical challenge is Xuzhou's humid summer climate. Condensation can form on low-temperature pipelines and indoor surfaces, particularly in bathrooms and other high-humidity areas. Opening windows allows moist outdoor air inside, making condensation more likely on metal fixtures and tiled surfaces.

To solve the problem, the company partnered with Yunlong Lake Laboratory of Deep Underground Science and Engineering to develop a dedicated water-cooled dehumidifier that maintains indoor humidity at around 50 percent, a level considered comfortable for occupants.

The company is currently installing the dehumidifiers in residents' homes free of charge this year. The first group of users also received free cooling services from June 1 to July 31 and began paying for the service from Aug 1 to Sept 30.

The environmental benefits are equally significant, Zhang said.

According to the company's data, the system reduces energy consumption by about 50 percent compared with conventional air conditioners and cuts annual carbon dioxide emissions by approximately 50 metric tons.

Unlike air conditioners, which rely on air-to-air heat exchange and gradually lose efficiency because of heat waves, dust, willow catkins and restricted airflow through outdoor units, the floor cooling system uses liquid-to-liquid heat exchange, maintaining high efficiency with minimal performance degradation.

Conventional air conditioners also discharge heat into the atmosphere, contributing to the urban heat island effect. In contrast, the floor cooling system transfers heat back underground through mine water, achieving virtually zero atmospheric heat exchange, Zhang said.

The company plans to collect operational data after the cooling season ends before deciding on a broader rollout. It is also experimenting with using mine water for winter heating. Previously, the city's centralized heating relied on hot water supplied by power plants.

Zhang said a researcher from the United Kingdom visited to inspect the project and expressed strong interest in introducing the technology to a British town.

Although mine-water-based heating and cooling systems have been introduced elsewhere in China, they have all been installed in newly built residential communities. The Xuzhou project is the first to retrofit an existing residential community with the technology.

"It unlocks the energy potential of billions of existing buildings for the low-carbon transition, providing a replicable model for resource-exhausted cities across the country," Zhang said.

Guo Jun in Nanjing contributed to this story.