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BERKELEY LAB RESEARCHERS INVENT AN AEROSOL DUCT SEALING SYSTEM TO REDUCE ENERGY LOSS IN LARGE COMMERCIAL BUILDINGS
A new atomizer prevents nozzle clogging by using high-velocity heated gas (through outer orifice), which will mix and dry the liquid sealant (center orifice), to cool an insulating layer of ambient-temperature air (middle orifice). MASIS, which stands for "mobile aerosol-sealant injection system," is based on the aerosol duct-sealing device developed by Berkeley Lab researchers for sealing ducts and reducing energy loss in residential and small commercial systems. However, it incorporates two new patented technologies that permit effective sealing in the larger, more complicated duct systems of commercial buildings. Duo Wang, a scientist in Berkeley Lab's Environmental Energy Technologies Division, developed the technology, with assistance from Mark Modera, the scientist who developed the original sealing system for residences. Carrier Aeroseal has licensed the system for exclusive use in sealing ducts in commercial buildings. Modera and colleagues developed the aerosol-based technology for sealing the ducts of heating, ventilating, and air-conditioning systems in residential and small commercial buildings in the 1990s. Their research showed that homes with ducts in contact with outside air in the United States wasted on average 20 percent of all heating and cooling energy because of leaky ducts. They pioneered a system that could seal these ducts remotely and inexpensively, using an aerosol that is injected into the ducts through the heating register in a home. The aerosol flows through the system, gradually building up a flexible seal at holes, tears, and other duct leaks. The team successfully tested the technology in the field and licensed it to a start-up company called Aeroseal, which was eventually acquired by Carrier Corporation. Residential duct sealing that uses the Berkeley Lab technology is available through contractors trained by Carrier. The research by Modera and his colleagues also suggested that energy losses in the ducts of large commercial buildings are probably as large in scale as those in homes. Although research continues at Berkeley Lab to quantify the losses in commercial buildings, scientists here estimate that sealing ducts in these buildings could potentially save billions of BTUs of natural gas and billions of kilowatt-hours of electricity. (A BTU, or British thermal unit, is the heat required to raise the temperature of a pound of water by one degree Fahrenheit.) Large commercial buildings present special problems that the residential sealing technology cannot address. "The HVAC duct system in large buildings typically has a large trunk duct system, and a number of smaller sub-duct systems connected to it," says Wang. "Trunk duct systems are longer and have a larger cross-section than residential systems, and they are connected to many branched duct systems. One problem is that large aerosol particles from a residential-scale duct sealer would fall out of the air stream too quickly to seal leaks effectively in these larger commercial ducts. Another problem is that the branch systems often contain heating or cooling coils that cannot be exposed to aerosol sealants. "To increase the flow of aerosol sealant in larger ducts, we designed a sealing system that uses a number of compact aerosol injectors," Wang continues. "Several of these are installed along the trunk line of a commercial building duct, injecting aerosol simultaneously. This substantially increases the sealing rate of leaks in the duct system." The prototype induced-cooling pneumatic atomizer is made with standard tube fittings. The researchers developed new technology to adapt the aerosol-based sealer to commercial buildings. The induced-cooling pneumatic atomizer is a spray nozzle that converts the sealant into an aerosol and sends it flowing into the duct system. The commercial system needed a nozzle that could inject sealant at a smaller spray angle and a higher flow rate. Not finding an appropriate commercially available nozzle, the research team developed their own design, which provided the right particle size and flow rate at the correct spray angle, without clogging. MASIS consists of a sealing-process monitoring system and portable injectors. In one design, each unit contains an air compressor and a cart that carries an aerosol sealant injector wand, a liquid sealant tank, a peristaltic pump, a control box, and a dedicated toolbox. In another design, the injectors are all fed by a central station and are daisy-chained via umbilical cords. To seal the trunk system, injectors are installed along the duct and are run simultaneously. To seal the branch duct systems, injectors are installed downstream of the heating and cooling coils, which are usually located in variable air volume boxes. Each branch seals independently, and all of the injectors can operate simultaneously.
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