In many public buildings in northern China

direct expansion air conditioning systems are used for cooling

and the hot water from district heating networks is often used for heating

which requires two types of terminals. A multi-connected air conditioner with refrigerant and water using hot water from district heating system for direct heating is proposed in this study. Three-fluid heat exchangers are used in the indoor units of the system

which can use hot water from district heating system or heat pumps for room heating

achieving flexible switching between direct expansion air conditioning system and district heating system. Taking an office building in Beijing as an example

the air conditioning system is selected in the summer designed condition. The simulation model of the system is established

and the heating effect of the system during the heating season and transition season is analyzed. The results show that the user side water temperature required for the system during the heating season is less than 54 ℃; when using direct expansion system during the transition season for heating

the unit capacity is higher than the peak heating load during the transition season

and the energy efficiency exceeds 3.5 within 49% of the operating time. The system proposed in this article utilizes one terminal to ensure summer cooling and winter heating needs

and can use direct expansion system for heating after district heating system shutdown

simplifying the existing system form and improving heating comfort.