OIL INFLUENCE ON THE OPTIMAL CHARGE AND PERFORMANCE OF A PROPANE CHILLER

摘要

The paper presents the experimental results of a charge optimization study of a water-to-water chiller of approximately 14 kW cooling capacity which uses propane as refrigerant. The unit employs a Copeland scroll compressor and two BPHE exchangers. The unit does not incorporate any liquid receiver so that the refrigerant charge strongly affects the unit performance. A complete charge optimization study was performed for two different oils: mineral ISOVG68 and POE ISOVG22. The study covered a wide range of variation of condensation temperatures, all around the typical operating conditions of this kind of equipment for AC applications. The main conclusions are that the optimal charge is strongly different, depending on the solubility of the refrigerant into the oil, and that the POE oil seems to lead to better unit performance. The performance is also plotted vs. the subcooling as to show that this is the real parameter leading to the optimum COP. The obtained volumetric and compressor efficiencies are then presented and discuss to explain the observed difference in performance.