Oil type influence on the optimal charge and performance of a propane chiller

The paper presents the experimental results of a charge optimization study of a water-to-water chiller with two different oils: Mineral and POE. The employed chiller is a prototype which works with propane as refrigerant and provides for a cooling capacity of approximately 16 kW. A complete charge optimization study was performed for two different oils: mineral ISO-VG 68 and POE ISO-VG 22. The study covered a wide range of variation of condensation temperatures, all around the typical operating conditions for AC applications. The obtained performance and compressor efficiencies are studied and discussed to explain the observed differences due to the oil type. 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.