4207 -- System Performance Characteristics of a Helical Rotary Screw Air-Cooled Chiller Operating Over a Range of Refrigerant Charge Conditions PDF

This paper presents a study involving the operation of a 70-ton helical rotary, dual-circuit, air-cooled chiller while three independent variables are experimentally altered. The independent variables included in the study are refrigerant charge level within the chiller plant, outdoor air temperature, and percentage nominal chiller load. This paper examines the effects of the three independent variables on superheat and subcooling temperatures, chiller kW per ton, chilled water set-point temperature control, and compressor suction and discharge pressures. After analyzing the significance of refrigerant charge, outdoor air temperature, and percentage nominal chiller load on the operation of a chiller plant in an actual building, the consequences of refrigerant undercharge or overcharge are fully investigated and documented.

All experimental testing was conducted in a full-scale heating, ventilation, and air-conditioning (HVAC) laboratory using a realistic load profile and actual outdoor air temperature conditions. Experimental testing began with an evacuation, recycle, and recharge of R-22 from both circuits of the chiller. The charge tests included holding the refrigerant charge in circuit #2 constant at the manufacturer's recommended level. The notation adopted for the manufacturer's recommended charge or nominal charge level was 0% charge. Circuit #1's refrigerant charge was varied from -60% to +15% of nominal charge in 5% increments.

Units: Dual