compressor pwm control, evaporator flooded, linear compressor
This paper presents some experimental results of two alternative solutions to improve household refrigerators energy consumption, the flooded evaporator architecture and the pulse width modulation (PWM) control logic for a variable capacity compressor. The experiments were carried out in a 360-liters bottom-mounted refrigerator-freezer, with natural draft evaporators, at two different ambient temperatures: 16°C and 32°C. The flooded evaporator solution can imply the same performance of the parallel circuit but with the simplicity of the serial-hybrid circuit, demanding no check valve nor need for pump out. The flooded evaporator circuit has a liquid accumulator connecting the evaporator’s outlet, which allows working with high evaporating temperatures during refrigerator compartment cooling. The liquid accumulator construction jeopardizes the compressor oil to return therefore it can be trapped in the circuit; hence the solution requires an oiless compressor oil to operate. The PWM control solution may lead to compressor performance improvement at low cooling capacity, so it is especially applicable to compressors which have lower COP at smaller capacities. The PWM solution works through short on-off cycles – on period has high input power and high capacity, and along the off period the compressor has zero capacity at lowest power input – which overall results in higher COP with low cooling capacity. The experiments were set to modulate compressor cooling capacity according to the compressor power input, small cycle period and duty cycle. The experimental results indicate the flooded evaporator solution lead to a reduction in energy consumption of 4.7% at 32°C and the PWM solution implied a reduction in energy consumption of 2.7% at 32°C and 7% at 16°C.