Super‐heating degree responsive control strategy of variable refrigerant flow air conditioning system for energy saving and stable operation

Abstract

AbstractThe control strategy is important for variable refrigerant flow (VRF) air conditioning system to realize energy saving and stable operation. In this work, the super‐heating degree (SHD) responsive control strategy was developed to dynamically adjust the respective SHD target value (ΔTe,tar) of indoor units so as to adapt to the variable cooling load. The capacity code (Ecode) is introduced into the control model to quantify the reference target value of SHD. To responsively adapt to variable cooling load, the correction target values of SHD based on discharge temperature and deviation of the outlet air temperature are introduced in the SHD model for operation protection of the compressor and the consistency of refrigerant distribution. The enthalpy difference analogy method is developed to estimate the performance of the VRF system including cooling capacity, electric power, and energy efficiency ratio (EER). The performance was tested under the conditions of different ΔTe,tar. Experimental results demonstrate that the ΔTe,tar is an important factor to determine the operation frequency, which affects cooling capacity, power, EER, and operation status of the system. The cooling capacity and electric power at the ΔTe,tar of 9°C was about 55.2% and 63.5% lower than those at the ΔTe,tar of 1°C, and the corresponding EER was improved by 22.6%. To further verify the SHD control strategy, the VRF system was tested by the responsive control model under the condition that Ecode and ΔTe,tar were constantly automatically adjusted and changed with the actual indoor ambient temperature. Experimental results demonstrate that the VRF system can achieve a good and uniform cooling effect and realize energy saving and stable operation according to the responsive super‐heating degree control.