This paper reports on an investigation of the effectiveness of automated continuous adjustment of refrigerant charge level on DX packaged air-conditioner cooling capacity and energy efficiency. In the laboratory, baseline performance parameters were established by analyzing energy efficiency as refrigerant charge level was manually adjusted above and below the manufacturer nameplate charge amount at a range of operating conditions. Then, automated charge tuning controls along with a performance monitoring system were installed on a package unit at a field site. In a field installation, a small loss of cooling capacity is not likely to be noticed by occupants or service technicians, especially where units are commonly oversized, but the concomitant loss of energy efficiency can significantly increase energy cost. The charge control utilizes a relational strategy to maximize energy efficiency by increasing or decreasing the mass of liquid refrigerant held in the receiver as operating conditions change.

Results show the potential exists for significant efficiency enhancement. It is concluded that continuous refrigerant charge adjustment can improve energy efficiency, especially at operating conditions distant from the factory IEER rating conditions. The charge controller successfully detected and compensated for inadequate or excessive refrigerant charge and maximized energy efficiency. Continuous tuning resulted in EER gains of up to 40% compared with the EER with a constant nominal charge.