Comfort Impacts of Partial Coverage ASHPs

A limiting factor to rapid adoption of air-source heat pumps (ASHPs) for residential retrofit applications is the first costs associated with installing a heat pump system that provides the home’s full heating and cooling loads with direct distribution into all conditioned rooms of the home. This is true with both ducted and ductless technologies and impacts low-to-moderate income customers disproportionally. Anecdotal evidence (from previous utility programs) suggests that systems are often oversized to 140% of peak design load.   Homeowners who installed heat pump systems to meet 70-90% of the heating loads engaged through TRC’s various heat pump program implementation efforts, have indicated that they do not use their backup/supplemental heating systems and that their homes maintained personal comfort ranges even with outdoor air temperatures below design conditions.   Using market assessment and thermal comfort modeling this project will quantify the comfort impacts of various part-load scenarios, and quantify first-cost and operating cost savings of part-load scenarios in CA. Heat pumps intended to satisfy the full design load are sized to provide heating and cooling at the 1% and 99% temperatures seen annually. However, smaller capacity heat pumps may operate in their efficient modulating zone for more time annually. The net result is more annual hours of efficient operation and less annual hours of inefficient low-load cycling.