ABSTRACT
This chapter mainly introduces the application of the variable volume ratio two-stage compression heat pump technology on the split-type room air conditioner of air source heat pump type, variable refrigerant flow (VRF) multi-split heat pump and modular VRF multi-split heat pump. The cooling and heating performances of the variable volume ratio two-stage compression heat pump system are compared with those of the conventional two-stage compression heat pump system and the single-stage compression heat pump system under various operating conditions. For the VRF multi-split heat pump using two two-stage compressors with variable volume ratio connected in parallel, the capacity control, oil balancing control, oil return control, subcooling control, and vapor injection control strategies are introduced.
