An energy and life-cycle cost comparison of residential PSC and ECM blower systems operating at excess pressures due to restrictive ducts

Abstract

This study is to comprehensively evaluate energy impacts and life cycle costs of duct designs for residential central HVAC systems. Building energy simulations were performed under two different climates (Chicago, IL and Austin, TX) to predict the heating and cooling energy use in systems with blowers of different types of motors, namely electronically commutated motors (ECMs) and permanent split capacitor (PSC) motors, paired with ductworks of varying flow resistance and duct materials. In addition to the energy use, the life cycle cost of each duct design was determined over a 15-year lifetime. Depending on the specific duct design, the annual energy cost in the Chicago home decreased by 11–17% for systems with ECM blowers and 3–8% for systems with PSC blowers as the flow resistance decreased from 0.8 to 0.3 in. w.g. (200–75 Pa). In the Austin home for the same flow resistance decreases, the annual energy costs decreased by 16–18% for systems with ECM blowers and 7–8% for systems with PSC blowers. Although the cost-effectiveness of a specific duct design is shown to be heavily dependent on initial duct fabrication and installation costs, the use of lower flow resistance ductworks generally leads to lifetime savings in the presence of 10% supply and return leakage. Specifically, the lifetime saving is achieved in 6 out of 8 simulated cases for the Chicago home and all simulated cases for the Austin home.