Reclaimed water refers to non-potable water that can be reused within a certain range after sewage or wastewater has been treated to meet specific water quality standards. It is called the "second water source" of the city. In common public knowledge, recycled water reuse is an important way to alleviate water shortages, but few people may know that recycled water has now unlocked a new use - providing thermal energy for urban heating. As winter gets stronger, Beijing is about to usher in a new heating season. This year, recycled water will join the ranks of thermal energy. How to extract heat energy from 15℃ recycled water to protect people’s livelihood temperature?
When you walk into Dongsheng Science and Technology Park (Phase II) in Haidian District, Beijing, you will not see towering chimneys or roaring boilers. The warmth here comes from the modern "energy heart" hidden in the underground space - the centrifugal water source heat pump unit. They are powered not by coal or natural gas, but by the city's recycled water, which flows day and night. During the heating season, at least 100,000 m³ of reclaimed water every day will start from the Qinghe reclaimed water plant, which is only 1.8 kilometers away from here. It will be injected into the "energy heart" of the heat pump unit like flowing blood, and then transported back to the water plant drop by drop. This time, what changes is the temperature of the recycled water.
Wang Minghua, project manager of the Operations Safety Department of Beijing Beipai Clean Energy Investment Co., Ltd., introduced that through the refrigerator in the unit, the low-grade heat energy in the pool is exchanged and turned into high-grade heat energy at the end. The incoming water is about 15°C, and the return water is about 10°C. The temperature difference of 5°C is extracted. In the process, only the water temperature is used and no water consumption is needed. After being heated by the unit, the water output from the energy supply terminal is about 45°C.
The 5°C heat energy transported through the "air-to-air heat exchange" of the centrifugal water source heat pump unit is enough to meet the heating needs of the entire Dongsheng Science and Technology Park. Wang Minghua used this analogy: the heat pump unit itself does not produce energy, but is a "porter" of energy. How does such an efficient "porter" operate?
Wang Minghua: The centrifugal water source heat pump unit includes an evaporator, compressor, condenser, and economizer. There is refrigerant in the evaporator, and the regenerated water goes around in the pipe, and the temperature is sucked away by the low-temperature refrigerant. When it enters the compressor to do work, it becomes a high-temperature and high-pressure gas; it then enters the condenser and is converted into a high-temperature liquid, and the economizer adjusts the temperature of the outlet water.
The transfer of heat is like a pair of friends hugging each other, with the cold body getting warm from the hot body. The inlet and return water of the recycled water are not connected to the heating pipes. It will not enter the heating pipes, and the water quality will not be affected. The recycled water after extracting the heat will not be consumed at all. It will be returned to the water plant immediately, and the temperature will also meet the standards for continued recycling.
Dong Haifeng, deputy general manager of Beijing Beipai Clean Energy Investment Co., Ltd., told reporters that compared with traditional energy heating, the water source heat pump project can save more than 30% of fossil energy consumption, is a veritable zero-carbon emission, and has certain economic benefits; at the same time, it has also opened up an innovative path of "sewage resource + clean energy" for the urban heating field, "extracting" the value of renewable water resources to the maximum extent, turning water resources into energy, and realizing the "twice" in the resource reuse process.
Dong Haifeng: We currently provide services to users inside and outside the group such as Dongsheng Technology Park and Huaneng Thermal Power Plant. According to statistics, the heating area reaches 2.86 million square meters, which can save more than 30,000 tons of standard coal a year and reduce carbon emissions by more than 70,000 tons, which is equivalent to planting 4.4 million trees. Our next plan is to actively explore the heating and cooling needs of industries and residents around the water plant, including the formulation of project plans; and then rely on points with recycled water and sewage conditions around Beijing’s heating network to supplement the heating network in Beijing.
It is understood that in the process of relying on recycled water waste heat resources and promoting wastewater waste heat to "turn waste into treasure", Beipai Energy Company, a subsidiary of Beijing Drainage Group, on the one hand, connects water source heat pumps to the urban heat grid to implement grid-connected heat supplements, and continues to increase the proportion of green heat sources in the municipal heating network. It has also launched China's first high-efficiency coupling project between recycled water waste heat recovery and urban centralized heating pipe network - Huaneng Beijing Thermal Power Plant's recycled water waste heat recovery grid-connected centralized heating project.
Wang Zhe, deputy section chief of the Recycled Water Section of the Beijing Drainage Management Affairs Center, said that recycled water, as the capital's stable and reliable second water source, will be utilized in excess of 1.3 billion cubic meters in 2025, accounting for more than 30% of the city's total water supply. It is mainly used for ecological water replenishment of rivers and lakes, industrial production, landscaping and urban sanitation. In terms of the use of clean energy, the temperature of recycled water is stable all year round, making it a good hot and cold source for water source heat pumps.
Wang Zhe: Now Beijing is also actively promoting the use of water source heat pumps. There are 11 reclaimed water plants in the central city that use reclaimed water source heat pumps to provide cooling and heating to the factory areas. Water source heat pump projects such as Dongsheng Science and Technology Park, Beijing South Railway Station, and Gaobeidian Huaneng Phase I have been completed and are running stably. The South Central Axis and Gaoantun heat network greening projects are also actively advancing preliminary work.
At present, my country has introduced relevant policies at the national and local levels to support the application of heat pumps, and has proposed clear implementation scenarios. In March 2025, the "Action Plan to Promote the High-Quality Development of the Heat Pump Industry" issued by six departments including the National Development and Reform Commission, the Ministry of Industry and Information Technology, and the Ministry of Ecology and Environment proposed to support the use of water source and other types of heat pumps to replace coal-fired boilers and bulk coal combustion.
As a very large city, Beijing has a huge demand for central heating in winter and has obvious rigid demand attributes. The supplement and structural optimization of heat sources may have become an important issue to ensure the safety of urban heating. Wang Zhe further stated that the Beijing Municipal Water Affairs Department will match the heating demand in the preliminary study of water affairs projects, and promote the implementation of the project through planning, so as to make the technical path of "green thermal flow" smoother.
Wang Zhe: Since the source of the water source heat pump is recycled water, we must first expand its source. The first step will be to fully promote the construction of key recycled water plants such as Jiuxianqiao Second, Hebei, and Taihu, and reserve implementation space for thermal energy utilization in the design stage of new, reconstruction and expansion of recycled water plants. At the same time, the recycled water itself requires transmission and distribution conditions, so the next step is to upgrade the recycled water pipelines and sewage pipe networks to provide a transmission and distribution network for thermal energy utilization. It is also necessary to actively coordinate and coordinate the layout of sewage and recycled water utilization facilities and cooling and heating facilities in the site selection, land use planning, and engineering construction of these projects.
Reporter: Han Xueying
