Extension of a virtual refrigerant charge sensor

• Three virtual refrigerant charge sensor models studied for variable-speed compressor systems.
• Original model works well except at extreme conditions and low compressor speed.
• Adding evaporator inlet quality as input improves accuracy at low compressor speeds.
• Adding compressor discharge improves accuracy with saturated conditions entering compressor.

The primary goal of the work described in this paper was to evaluate and extend a virtual refrigerant charge sensor (VRC) for determining refrigerant charge for equipment having variable-speed compressors and fans. Based on the evaluations, the original VRC sensor (termed model I) was found to work well in estimating the refrigerant charge level for systems with a variable-speed compressor. However, for extreme test conditions such as low compressor speed, the model I needed to be improved. To overcome the limitations, the model was modified to include a term involving the inlet quality to the evaporator (termed model II). The model II gave better performance for systems with a variable-speed compressor. When the superheat of the compressor was zero, neither model II could accurately predict charge level. Therefore, a third approach (Model III) was developed that includes the discharge superheat of the compressor.