Performance degradation of an air source heat pump in a dormer room enclosure
In densely populated urban areas, installing the outdoor unit of an air-source heat pump can be challenging due to space and noise constraints. One available solution is integrating the unit into an inverted dormer roof, placing it within the attic space. While this approach offers aesthetic and practical benefits, it may restrict airflow and increase air recirculation, potentially reducing performance. To quantify these effects, a commercial air-to-water heat pump was tested in a climate-controlled chamber under two configurations: with and without the dormer enclosure. Key parameters measured included evaporator inlet air temperature, heating capacity, coefficient of performance (COP), and defrost cycle frequency. Results indicate a full-load capacity reduction of 6–10% when the enclosure is present and requiring approximately 6% higher compressor speed to maintain output in half-load conditions. Frost formation occurred at higher ambient temperatures with the dormer roof in place, so over a heating season the heat pump will have defrost more often. The measurements suggest recirculation as a contributing factor to the performance degradation. These findings highlight the need for careful airflow design in roof-integrated heat pump installations to avoid efficiency losses and increased defrosting.