Abstract
Air-to-water heat pumps (AWHPs) with propane (R290) as working fluid have gained attention as efficient and environmentally friendly space heating solutions. This study conducts field tests and analyzes the performance of an R290 AWHP heating system during winter operation in Oslo, Norway. Field observations demonstrate effective defrost operations, resulting in reliable heating performance and high energy efficiency under cold and humid outdoor conditions. A field-measurement-based model is developed to evaluate seasonal performance of R290 AWHP systems under Nordic climate conditions, providing valuable reference data for their application in one of the most challenging environments for heat pump operation.