A Simulation-based Analysis of Heat Pump Oil Return Cycle Operation with regard to Buffer Tank Size

This paper investigates on the frequency of the oil return cycles in heat pumps operation, more specifically on the effect of varying buffer tank size. The analysis is carried out considering the cooling mode, with fan coil emitters, because this operating condition can lead to prolonged low-load operation and therefore create a more relevant scenario for oil migration from the compressor into the refrigerant circuit. The objective of this study is therefore to examine how different buffer tank volumes influence the oil return process and, more broadly, the operational performance of the heat pump. By focusing on this specific but critical aspect, the paper aims to contribute to a better understanding of compressor protection, system reliability, and the design implications of buffer tank integration in residential heat pump applications.