Detailed Performance Assessment of Variable Capacity Inverter-Driven Cold Climate Air Source Heat Pumps
Enabled by the advancement and incorporation of inverter-driven compressors and controls, cold climate air source heat pumps (CC-ASHP) are being introduced in the Canadian marketplace. Such systems are capable of efficiently meeting space heating loads at much colder ambient temperatures in comparison to single speed compressor air source heat pump (ASHP) technologies and are additionally capable of efficiently modulating to meet heating loads at warmer ambient temperatures without cycling on/off. Coupled with their lower capital costs than ground source heat pump systems, significant interest in these systems has been generated; however their widespread adoption is hindered by the unknown performance and lack of tools to evaluate their energy saving potential. This paper presents the results of detailed performance tests measuring the heating output and power input of two types of CC-ASHPs popular in the Canadian residential marketplace; a centrally ducted 3 ton split ASHP designed for whole house heating and cooling and a 1 ton ductless split ASHP designed for displacing zone heating and cooling requirements. The tests are completed by varying the outdoor temperature and indoor load (or compressor speed/capacity depending on the test approach) in climate controlled test facilities. The test results validate the systems’ capability of efficiently heating at low ambient temperatures as well as modulating to meet more moderate part load conditions. However, several factors including the operating mode of the system as well as built-in protection controls for discharge temperature and pressure can serve to limit the maximum available heating capacity. Defrost settings can have a substantial impact on total system performance at cold temperatures. At mild ambient temperatures, relatively small heating load requirements can result in short cycling. The results highlight the importance of properly sizing and commissioning these heat pump systems for their application and indicate the type of data required to better simulate the performance and properly evaluate their energy saving potential.
KeywordsAir source heat pumps Air to air heat pumps Cold climate air source heat pumps Variable capacity Inverter-driven Cold climate
Funding for this work was provided by NRCan through the Energy Innovation Program and Office of Energy Efficiency Equipment Division and SUMARAN Inc.
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