Research on innovative applications of water-cooled multi-split system technology in Beijing Subway

During the 14th Five-Year Plan period, Beijing Metro Operation Co., Ltd. has deeply cultivated technological innovation in rail transit, fully promoting smart metro construction, and has implemented a total of 191 scientific research projects. Over five years of dedicated efforts, a total of 182 scientific and technological innovation achievements have been formed, 39 provincial, ministerial, and industry awards have been won, 140 authorized patents and 109 software copyrights obtained, 29 industry standards have been co-authored, and 1,372 professional technical papers have been published, using technological innovation to solidify the foundation for rail transit operation support.

To highlight the outstanding technological innovation achievements of Beijing Subway during the 14th Five-Year Plan period and provide a panoramic view of intelligent operation and maintenance innovation practices, the "Beijing Subway Window" WeChat public account has specially launched the column "Technology Empowerment, Intelligent Exhibition," unlocking various cutting-edge technological achievements one by one. This issue introduces the application research of adjustable cooling water air conditioning systems in subway station rooms based on water-cooled multi-split technology.

System principle layout schematic diagram

Targeted problem-solving — addressing multiple pain points in traditional station air conditioning systems

Beijing subway station rooms traditionally use air-cooled multi-split air conditioners, which face difficulties in outdoor unit installation, low operational efficiency, and inconvenient pipeline anti-freeze operation and maintenance in winter, lacking efficient energy-saving air conditioning solutions suited to the local subway climate. This project focuses on urban rail transit ventilation and air conditioning, focusing on intelligent operation and maintenance of station air conditioning systems and energy conservation and carbon reduction through technical breakthroughs. Using the Beijing Subway Line 5 Huixin West Street North Entrance Station as a demonstration station, it developed a water-cooled multi-split adjustable cooling water air conditioning system, aiming to address the operational and maintenance shortcomings of traditional air conditioning systems.

Technical breakthrough—building a complete system for air conditioning energy saving and intelligent operation and maintenance

The project focuses on five core research points in subway station air conditioning systems, researches water-cooled multi-split system adaptation technology for underground station conditions, and optimizes system configuration and operation strategies based on existing cooling towers and pump facilities; Overcoming precise regulation technology for adjustable distributed cooling water, innovating pump-valve replacement and pump-valve mutual assistance models to solve problems of hydraulic imbalance in pipelines and uneven distribution of low-load water; Developed low-energy circulation insulation technology for subway air conditioning water systems in winter, using air source heat pumps combined with microcirculation in pipelines to achieve anti-freeze and low-energy pipeline operation; Simultaneously conducting research on efficient heat exchange, water quality treatment, and uniform water distribution technology for cooling towers to alleviate equipment scaling and heat transfer decay; By integrating IoT and big data, an intelligent air conditioning operation and maintenance management platform has been built, enabling real-time monitoring of operating parameters, intelligent fault warnings, and digital inspection management, replacing traditional manual inspection models.

Key breakthrough—multiple core technologies have set new levels for subway air conditioning energy efficiency

Cooling tower selection design drawing

Air source heat pump equipment

The project has achieved multiple key technological innovations, adopting plate heat exchangers for indirect heat exchange, isolating the adverse effects of cooling tower water quality on multi-split main units; Optimize water-cooled multi-split systems and matching solutions for pump and heat pump capacity to form operation and maintenance strategies suited to metro stations; Establish supply-return water balance and flow monitoring algorithms, using dual temperature and flow indicators for variable frequency regulation to keep cooling water flow deviations within 10%; Fully activate the station's existing cooling water system resources, optimize the cooling tower's variable frequency operation and uniform water distribution capacity; Innovative winter air source heat pumps combined with low-maintenance maintenance technology for station return air waste heat, using low-frequency pipeline circulation and temperature-linked start-stop to significantly reduce winter anti-freeze energy consumption.

Outstanding Results—Significant Energy Saving and Carbon Reduction Benefits from Applying Results

During project R&D, innovative achievements were consolidated, with a total of 2 patents, 1 software copyright, and 1 professional technical paper published.

Currently, the system has completed a demonstration renovation at the North Entrance Station of Huixin West Street on Line 5. According to third-party tests, the system achieves an energy-saving rate of 37%, saving equipment space of 40-50㎡, and in winter, the pipeline anti-freeze energy consumption is only 40% of that of conventional solutions; Compared to air-cooled multi-split systems, a single station saves over 160,000 kWh of electricity and 90% of water annually, extending equipment lifespan by 3-5 years. At the same time, it effectively reduces equipment operating noise and saves valuable station space, enabling refined intelligent operation and maintenance of air conditioning equipment, providing mature conditions for replication and promotion across metro lines across the entire network.

Looking Ahead—Empowering Green and Low-Carbon Smart Operation of Subways Next, Beijing Subway will continue to promote the expansion of water-cooled multi-split adjustable cooling water air conditioning systems across all lines, constantly optimize system regulation algorithms and intelligent operation and maintenance platform functions, improve supporting technical standards and operation and maintenance specifications, continuously tap into the energy-saving potential of ventilation and air conditioning systems, and use technological innovation to help subways save energy, reduce carbon emissions, reduce costs, and increase efficiency, comprehensively enhancing the intelligent and green operation of station equipment.

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