A Multi-connected Air Conditioner with Refrigerant and Water Using Hot Water from District Heating System for Direct Heating

In northern China, public buildings commonly use direct-expansion air-conditioning systems for cooling and district heating networks for heating, necessitating separate terminals for each function. This study proposes a multi-connected air conditioning system capable of utilizing refrigerants and water for direct heating with hot water from district heating systems. The system integrates three-fluid heat exchangers within indoor units, enabling seamless switching between direct-expansion air-conditioning and district heating systems. Using an office building in Beijing as a case study, the system was evaluated under summer cooling design conditions, and its heating performance during winter and transitional seasons was analyzed. Results reveal that during winter, the system requires user-side water temperatures below 54 ℃, while in transitional seasons, the direct-expansion mode delivers unit capacities exceeding peak heating demands with energy efficiency surpassing 3.5 over 49% of operating hours. This system simplifies existing configurations by providing a single terminal for year-round heating and cooling, enhancing efficiency and thermal comfort.