Task 05-11. Duct Leakage Assessment in Residential/Commercial Duct Construction and its Effect on Overall Thermal Performance of the HVAC System

Objective

The homebuilding industry has gravitated towards flexible duct systems because of the ease of installation as well as the relatively low cost. Forced-air heating and cooling can be made to perform extremely well, delivering high levels of comfort and efficiency. However, research over the past decade has shown that duct systems, as actually installed, often perform far below expectations in both of these areas. Ducts may be the single worst performer in the energy performance of a house (Jump et al. 1996 [223] and Siegel et al. 2001). Duct leakage, duct insulation compression, and other poor installation practices can reduce duct efficiency by 30% from even a moderate level of design performance. It has been shown that even a 15% leakage of the duct system can reduce the air-conditioner capacity to half and system capacity by about 30% (Walker et al. (1998a)). Sherman and Dickerhoff (1994) have compiled data from a large number of pressurization tests in the United States, and have found the average normalized leakage to be 1.72 for single family dwellings.

It has been shown that ducts will lose significant amounts of energy through leakage and conduction to their surroundings (Cummings et al. 1990, Davis 1993, Modera et al., 1991, Modera 1993, Modera and Jump 1995, Parker 1989, Parker 1993, Proctor et al. 1992, Treidler and Modera 1994). For example, Modera et al. (1991) found that conduction losses averaged 23% of furnace output in California’s mild climate. It was also found that the leakage of ducts was approximately 1 cm2 of effective leakage area per m2 of floor area.

The main objectives of this project are to

• To investigate the component sources of typical residential air duct leakages through the development of potentially new technologies to achieve that in situ.
• To assess cost effective ways to seal air duct leaks depending on the percentage of total leak and where the leak is located in the residential duct system.
• To estimate potential savings and payback period applying these duct sealing approaches.

Major Sub-awardees

This project is being executed by the University of Nevada, Las Vegas. The Principal Investigator is Samir Moujaes, Ph.D., Professor.
This project was initiated October 1, 2005 and will be completed in 12 months.