By Dave Pest
Any observant building manager or owner can't help but notice the proliferation of exposed spiral sheet metal HVAC ductwork as a key architectural design element in both the new construction and renovation of commercial buildings.
From high-end cafés to hip home-furnishings stores, the use of spiral duct creates a contemporary look in any space, which raises a question: Is the move to spiral duct simply a trend or is it supported by practical considerations such as higher energy savings and better indoor environmental quality?
Perhaps we can borrow from a popular late-night talk show host and create our own Top 10 list of reasons why spiral duct is gaining in popularity ...
10. Air leakage at duct joints can lead to energy loss and impaired system efficiency. Quality self-sealing spiral duct systems can guarantee a system that meets or exceeds the highest industry air-leakage standard.
9. When leakage is virtually eliminated, the cost of filtering, heating, cooling, and distributing conditioned air is kept to a minimum. One study shows that a national shift to more airtight systems would lead to an annual energy savings comparable to the annual energy product of three nuclear power plants.
8. The pressure drop of air leaving an air-handler is usually lower in a typical spiral system. The spiral design provides equal pressure internally and allows the air to flow evenly and efficiently, also leading to lower energy use.
7. Air leakage can be detrimental to indoor air quality. Because of concern regarding "sick buildings," there is a demand for more fresh-air intake. With airtight ducts, it is easier and more economical to meet these stricter demands.
6. The problem of noise breakout can be avoided with spiral duct because the reverberation created by the pressure differential existing in rectangular duct does not occur with spiral duct.
5. The inherent design of rectangular duct involves air moving around sharp edges, dampers, and turning vanes. Obstruction to airflow can contribute to noisy turbulence. With spiral duct, less sharp edges equal less noise.
4. Many facilities now require regular inspection and internal cleaning of ductwork. The approved cleaning methods for spiral duct are readily available, economical, and effective.
3. With rectangular duct, extra space - up to 3 inches extra - must be factored in for the connections and reinforcements needed at each joint. This is not a consideration when installing spiral ductwork.
2. Air-flow measurement, a periodic responsibility of a mechanical engineer, can be simplified. Many accurate and inexpensive flow-measurement devices specifically designed for spiral duct enable regular check-ups or continuous monitoring.
1. The installed cost of spiral duct - which includes product, parts, labor, warehousing, transportation, packaging, and waste disposal - can be considerably less than rectangular duct (in some cases, up to 50-percent less).
Dave Pest is vice president of operations at Portsmouth, VA-based Lindab Inc. (www.lindabusa.com) and president at the Irmo, SC-based Spiral Duct Manufacturers Association (www.spida.org).
