New Style of HVAC Ducting Saves Money, Reduces CO2, and Improves Thermal Efficiency

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No one sees their air conditioning ductwork, so it doesn't get a lot of attention. But ductwork one of the biggest energy wasters in a building's energy system. Properly constructed, however, ductwork can be one of a building's biggest energy savers, making the air handling system positively green. Lifecycle-cost payback of this new system design is immediate—up-front costs are less than those for traditional metal duct systems. The system is easier to install because the material is lightweight, easy to manipulate, and could be completely installed without need for a separate, hazardous insulation step using fiberglass. In a study, annual HVAC operating costs were shown to be less than an equivalent traditional system.

Internal air handling in residential structures is traditionally made of galvanized sheet metal. When the ducting is in an attic or other unconditioned space, it is traditionally wrapped in fiberglass after installation to improve thermal efficiency. This approach has two problems.

  • The ductwork leaks. It turns out that leaks waste more energy than poor insulation.
  • Installation is a chore. Sheet metal ductwork is hard to handle, and fiberglass is irritating and messy.

Kingspan Insulation Ltd invented a method of constructing ductwork from rigid insulation board that is almost entirely leak free, and is easy to install because it is lightweight and does not need separate insulation. The brand name of the product is KoolDuct. The product is seeing increasing application in the US, particularly where energy specifications are high. KoolDuct meets or exceeds insulating and leakage requirements, providing a cost-effective, energy saving, and carbon-reducing solution for air distribution systems.

A recent real-world study took advantage of an organization (Luther Home of Mercy in Williston, Ohio) that built two identical residential cottages, using insulated sheet metal ductwork in one building and KoolDuct in the other.

The study compared the energy use, associated CO2 emissions, and the installed, operational, and whole-life costs of the two HVAC ductwork installations.

The structures house 12 residents, four in each wing of the T-shaped buildings. Where the wings meet, residents use a common dining room, activity area, and kitchen. They were particularly interested in comparing the air-leakage rates of the systems.

An independent firm, MDA Engineering Inc. performed the study. MDA had designed the HVAC systems for the buildings. The HVAC systems consisted of high-efficiency furnaces, cooling system condensing units, and ductwork in the attic.

The Installation and Test
The KoolDuct system was constructed according to Kingspan standards of fabrication. Transverse joints between sections used connectors designed to work with the product and sealed with RTV adhesive. All joints were also sealed with aluminum foil vapor barrier tape.

The metal ductwork was competitively bid to ensure fairness. Constructed to SMACNA Class B standards, sections were assembled in the shop to ensure good seals on the longitudinal joints. The longitudinal Pittsburgh seams were sealed with RTV silicone adhesive before the lap was folded. Transverse joints were assembled and sealed in the field with Hardcast 321 Duct-Seal. The metal duct system was insulated with fiberglass to match the KoolDuct insulation R-value.

Both systems were designed to meet ASHRAE 90.1-2004 and 2006 IECC duct insulation requirements.

An independent testing, adjusting, and balancing (TAB) contractor performed the leakage tests on both systems, from furnace to registers, using new, certified testing equipment. The KoolDuct system outperformed the conventional duct system. For numbers and other details from the study, refer to the white paper described at the end of this press release.

The Analysis
To conduct the analysis, the consultants created three building models with the same physical characteristics in Trane's Trace 700 energy analysis program. The first was a building with perfect ducts and zero leakage. Models 2 and 3 represented the actual KoolDuct and metal duct buildings. They used local utility rates and the Toledo weather file. Simulations were run for 8,760 hours (equivalent to one year).

The life-cycle cost analyses included material and labor, finance costs, a 5% interest rate, a 3% inflation rate, and a 10% discount rate. Financing and project life were set at 30 years.

Summary and Conclusions
The results showed that the KoolDuct system leaked less and cost less, despite the fact that the metal duct system had been constructed with great attention to sealing and installed at the lowest price from the competitive bids.

  • The lifecycle-cost payback of the KoolDuct system was immediate. All costs were less than costs for the metal system.
  • The capital cost was nearly 17 percent less for KoolDuct.
  • The KoolDuct was faster and easier to install.
  • Operating leakage cost for the KoolDuct system was nearly 80% less than the metal system.
  • First-year operating costs were 70% less than the metal duct system.
  • Overall HVAC operating costs were 7% less.
  • The KoolDuct system saved a yearly estimated gasoline consumption equivalent of 639 gallons.

Final word

KoolDuct was introduced to the United States in 2002 and has been used increasingly on many high-specification projects requiring ductwork that delivers design performance in practice.

To download a copy of the white paper this press release refers to, visit http://www.insulation.kingspan.com/internationalkoolduct/pdf/koolduct_flyer_luther_home_of_mercy_us.pdf

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