The impacts of duct design on life cycle costs of central residential heating and air-conditioning systems

Abstract

Many central residential HVAC systems in the U.S. operate at high external static pressures due to a combination of system restrictions. Undersized and constricted ductwork are thought to be key culprits that lead to excess external static pressures in many systems, although the magnitude of energy impacts associated with restrictive ductwork and the costs or benefits associated with addressing the problem are not well known. Therefore, this work uses annual energy simulations of two typical new single-family homes in two separate climates in the United States (Austin, TX and Chicago, IL) to predict the impacts of various external static pressure ductwork designs from independent HVAC contractors (using both flexible and rigid sheet metal ductwork materials) on annual space conditioning energy use. Results from the simulations are combined with estimates of the initial installation costs of each duct design made by each contractor to evaluate the total life cycle costs or savings of using lower pressure duct designs in the two homes over a 15-year life cycle. Lower pressure ductwork systems generally yielded life cycle cost savings, particularly in homes with PSC blowers and particularly when making comparisons with constant ductwork materials (i.e., comparing flex only or rigid only).