BN-97-07-3 -- Simulating Effects of Multispeed Compressors on Refrigerator/Freezer Performance PDF

Simulation analyses suggest that a multispeed compressor could increase steady-state operating efficiency by 4% to14%. An additional 0.5% to 4% energy savings might be obtained from the reduction in the cycling frequency of the refrigerator. Several aspects of the robustness of the capillary tube suction line heat exchanger design for the two-speed compressor system were also examined with the simulation model. It was shown that a system optimised for low-speed operation, when operating at the high speed, could have as much capacity as the original base case high-speed system. A relatively simple control strategy was proposed, one that requires measurement of on-cycle time and one or two compartment air temperatures. The effects of varying the speed of the evaporator or condenser fans at both compressor speeds were examined over a range of ambient temperatures. One energy-saving scenario was identified: decreasing the condenser fan speed for refrigerators operating at low ambient temperatures. By affecting the distribution of refrigerant charge throughout the system, the decrease in condenser fan speed reduces the superheat in the evaporator and increases the overall UA of the evaporator. The resulting increase in evaporator capacity more than offsets the decrease in condenser UA and the energy use of the refrigerator is decreased.

Units: Dual

KEYWORDS: year 1997, Refrigerators, freezers, performance, energy conservation, energy consumption, calculating, variable speed motors, compressors