Popular Across the PondOne thing that several of his predecessors used in ventilating workspace was woven fabric ducts in their air distribution systems. This approach yields a quiet, low-velocity air supply without any condensation by the air displacement principle.
Simply stated, air-handling units with 85% -1 micron pre-filtration supply clean air into the cloth ducts. The air seeps through the weave in the cloth at a very low velocity. Natural air displacement occurs as the cool, dry air falls to floor level and lifts the warm, moist air upward to the exhaust fan. Cloth duct systems incorporating the air displacement principle have been in wide use in the European food processing industry for more than fifteen years, and they provide quiet, draft-free, and energy efficient heating, cooling, and refrigeration for both new and remodeled structures.
Beyond baking, the technology has begun to catch on in other applications (including offices, factories, hospitals, churches, and gymnasiums) that need aesthetically appealing design, short-term payback, and long-term energy savings.
Less Turbulence is KeyWhen Steve Schmidt, Yale Mechanical’s (Bloomington, MN) hvac project engineer, discussed air displacement and the cloth duct system with Kelsey, both owner and engineer quickly agreed on the Q-Sox® woven polyester cloth duct by Air Displacement, Inc. (Minneapolis).
The two-story production facility has a total of 24,000 sq ft, with 18,000 devoted to baking operations. In the cooling and packaging rooms, the need is to quickly reduce baked products from 350˚F oven temperature to 80˚ without reducing product moisture. Historically, this has been accomplished with an arrangement of high-speed floor fans aimed at the baked goods to remove product heat. Dough and baked goods, in general, are very sensitive to air movement that affects product shape, texture, and taste. Unfortunately, the fan turbulence also reduces product moisture as well as dispersing residual flour particles into the production environment.
Two Lennox (Richardson, TX) LGA Heat/Cool rooftops units (15-ton and 10-ton) and a 4,500-cfm Rupp (West Union, IA) RAM15 makeup air unit introduce fresh, dry air into the baking process by gently distributing supply air through the cloth ducts. Two duct sections 18 in. in diameter and totaling 32 ft in length provide 6,000 cfm of cool, low-velocity air that seeps through the woven cloth and descends to the cooling room floor. Heat from both the baking ovens as well as heat from product cooling is displaced upward to the Greenheck (Schofield, WI) 3,200-cfm exhaust fan. Similarly, two 15-in. diameter, 85-ft long Q-Sox ducts bring 4,000 cfm into the packaging room.
Pièce de RésistanceSeven months after installing the new system, bakery owner Kelsey has noticed how many of his 56 employees prefer to work in the two air displacement areas when they have a choice to do so. Secondly, he is really impressed with the air cleanliness evident by the absence of flour dust typically layered on the many flat surfaces in bakery operations. Lastly, Kelsey likes the ability to maintain cleanliness by laundering the cloth ducts with little production downtime as compared to cleaning a metal duct installation.
Project manager Schmidt noted that the installation costs for the woven cloth duct system were about one-fourth the costs to install a typical metal duct system. This fact was further reinforced by the comment from a local code inspector who stated to Schmidt that, “Anybody could install this stuff!”