New Technologies
The U.S. Department of Energy (DOE), Washington, D.C., estimates the excessive energy used to compensate for leaky air ducts is costing Americans $5 billion annually. In its 40-plus years of experience in performing building retrofits, SWA has found every central exhaust ventilation system it has ever evaluated in an existing building performs sub-optimally from an indoor air quality and/or energy-usage standpoint.
Carlyle Towers’ ventilation system includes 25 main vertical shafts with 25 rooftop fans. The property owners observed energy usage for the apartment building was substantially higher than similar buildings in the neighborhood. Measurements taken by SWA prior to the retrofit indicated over-ventilation was occurring on the upper-floor apartments while lower-floor units were under- ventilated. This difference ranged from 135 CFM on the ninth floor to less than 10 CFM on the bottom floor. As a result, top-floor residents experienced loud, overly powerful exhaust while those living on the bottom floor found exhaust to be weak and inadequate.
SWA engineers recognized the complementary nature of two new technologies—constant airflow regulators (CARs) and aeroseal duct sealing. With funding from the New York State Energy Research and Development Authority, Albany, SWA was able to evaluate the effectiveness of using the technologies together to improve ventilation and energy efficiency at Carlyle Towers.
Traditional dampers consist of louvers that are manually adjusted and balanced at the time of construction. Then, each damper must be manually opened and closed on an ongoing basis to ensure an even flow of air is achieved on all floors of the building. Because the flow through any one grille interacts with the flow through all others, the process can be a long and arduous task; adjusting one grille requires re-measuring and readjusting all other grilles. Proper adjustments are difficult to attain and seldom accomplished. More importantly, because tall buildings are subject to ever-changing wind and stack-effect pressures, a system balanced in the summer may not be balanced in the winter.
CARs precisely regulate airflow across a wide range of pressures and automatically adjust to compensate for current conditions. Once installed, the CAR dampers open and close as needed to maintain a constant preset balance, no matter the changing environmental conditions.
Aeroseal is a duct-sealing technology that works from the inside of the shafts to locate and close any holes or gaps that may exist. Developed by LBNL with funding support from DOE, the Washington-based U.S. Environmental Protection Agency and others, the sealant consists of a nontoxic vinyl acetate polymer. Applied as an aerosol mist, the sealant is blown into the exhaust shafts where it remains suspended until it comes upon a leak. There, the sealant sticks to the edge of the hole and binds with other sealant particles until the hole is completely closed. Laboratory testing shows the sealant lasts at least 10 years, likely the lifetime of the duct system.