The Effect of Compressor Speed Variation and Vapor Injection on the Performance of Modified Refrigeration System

Abstract

This work presents an experimental and numerical investigation of vapor compression refrigeration system performance with variable speed compressor and vapor injection. A test rig of 5 ton capacity split air conditioner equipped, with frequency inverter to control the speed of scroll type compressor, and a secondary capillary tube to expand the refrigerant in the vapor injection circuit are used to conduct the experimental work. Three different vapor injection mass ratios (2, 3, and 4%) are investigated with variable compression speed for frequency range from 35 to 60 Hz. TRNSYS-16 is the software is used to simulate a single zone building conditioned with the modified split air conditioner. The results showed that, the reduction of the compressor speed to the frequency of 35Hz leads to an improvement of the COP by 36% and reduces the power consumption by 18%, compared to the conventional refrigeration system. The usage of the vapour injection with variable speed compressor has improved the COP of the modified system by 47% at 35 Hz and 2% vapour injection ratio. The average improvement in cycle capacity at different compressor speeds is about 24.6%, 28.77% and 34.28% respectively for the vapor injection ratios of 2%, 3& and 4%. It was observed that the reduction of compression speed can extend the compressor lifetime by reducing the ON/OFF cycle of the system at a speed of 35Hz and 2% vapor injection by 17.3%, compared to the conventional system. While at a speed of 60Hz, the ON/OFF cycle has increased by 9.3 and 12% for 2% and 4% injection ratios, respectively. The comparison between the numerical and experimental results of the modified system with vapor injection ratio 2% and 35 Hz compressor speed has displayed an increase in the numerical results around 2.57% for COP, 5.8% for cooling capacity and 5.68% for compressor power consumption.