Steady-State Simulation Approach of Heat Pump Type Multi-Unit Air Conditioning Systems with Vapor Injection

Abstract

Vapor injection technology can effectively enhance the heating performance of heat pump-type multi-unit air conditioning systems （heat pump VRF） under low-temperature conditions. However， complex system configuration and component coupling necessitate a more general steady-state simulation approach for VRF heat pumps. This study proposes an improved graph-theory-based steady-state simulation method for a multiunit air-conditioning system with vapor injection. By abstracting the components into computational units， a graph-theory-based description method guided by the refrigerant flow paths was established. A directed graph of computation units was employed to characterize the adjacency relationships in cooling/heating modes， with mode switching achieved using a four-way valve model. A dual-layer path generation method for system pressure and flow paths is proposed， along with a decoupled iterative algorithm for flow pressure calculation. Validation based on experimental data from a heat pump VRF system with vapor injection （four indoor units） shows that the model prediction error is within ±5% under rated cooling/heating conditions. A steady-state simulation platform with customizable system configurations was developed based on the proposed method， providing a convenient digital tool for the VRF system design.