LAUSR

Abstract This study presents a potential approach for reducing the propane (R290) charge required in air conditioners (ACs) by introducing micro bare-tube heat exchangers as the condenser and evaporator. A theoretical model is developed to predict the performance of a split AC unit, and the unit is tested in an experiment. The split AC unit is tested under the ISO 5151:2017 standard capacity rating test condition in a psychrometric room (outdoor conditions: 35 °C dry bulb/24 °C wet bulb; indoor conditions: 27 °C dry bulb/19 °C wet bulb). The compressor input electricity power is 928 W with 62-W condenser fan power and 82-W evaporator fan power. The test cooling capacity is 3645 W with a system coefficient of performance of 3.40. The stainless steel micro-tube heat exchanger has a 0.58-mm outer diameter and 0.38-mm inner diameter. Owing to the use of micro bare tubes, the optimal propane charge is 248±5 g, which follows the EN378-1:2016 regulation. The use of micro bare-tube heat exchangers in a split AC unit could be a potential approach to reducing the R290 charge required in ACs and heat pumps.