Sensitivity of refrigeration system performance to charge levels and parameters for on-line leak detection

The environmental impact of refrigeration systems can be reduced by improving their efficiency and reducing refrigerant leakage. This paper presents results of experimental investigations on the effect of refrigerant charge on steady-state system performance and identifies parameters sensitive to charge level for on-line leak detection in vapour compression refrigeration systems. The investigations were performed on a small 4 kW nominal cooling capacity vapour compression water-to-water chiller equipped with plate type heat exchangers. The results indicate that the chiller could operate over a wide range of charge levels, 25% below to 25% above the design value without significant impact on its performance. Outside this range, the performance of the chiller was found to be strongly dependent upon the charge level. The degree of superheat at the evaporator outlet and sub-cooling at the condenser outlet were shown to be significantly dependent on the level of refrigerant charge. Overcharging was found to lead to excessive discharge pressures, but suction pressure was found to be relatively insensitive to charge level. It can be concluded that the parameters of superheating and sub-cooling together with discharge pressure can form the basis of a reasonably inexpensive on-line leak detection system.