Field Performance of Multi-Head Ductless Heat Pumps in Cold Climates

Ductless heat pump applications have continued to grow in cold climates as the performance of inverter driven heat pumps have continued to improve and installation costs have decreased. With increased interest in these products, new applications and installations have developed. Recent trends show an increased interest in homes opting for multizone applications using two, three, and even more indoor heads paired to a single outdoor unit. All major manufacturers now offer multi-head ductless systems. Recent research projects have installed and monitored the performance of these multi-head systems in single-family and multifamily buildings. Detailed data collection of over 20 measurements per site at one second intervals has shown performance considerations unique to these systems that impact capacity and efficiency. Ductless heat pumps are a key opportunity to improve space heating efficiency and reach decarbonization and electrification goals. This research highlights the unique challenges of designing multi-head systems. Careful design and implementation of multi-head systems is needed; systems installed without these designs and approach may reduce annual heating efficiencies as much as 30%. Important operational details around defrost control, operating multi-head simultaneously, operating indoor heads intermittently, and integrating heat pumps with backup systems especially across different heating zones have been characterized and compared to standard single-head and single outdoor unit systems. Key takeaways and best practices will be shared to improve multi-head system designs and increase installed performance.