Duct leakage impacts on VAV system performance in California large commercial buildings

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The purpose of this study is to evaluate the variability of duct leakage impacts on air distribution system performance for typical large commercial buildings in California. Specifically, a hybrid DOE-2/TRNSYS sequential simulation approach was used to model the energy use of a low-pressure terminal-reheat variable-air-volume (VAV) HVAC system with six duct leakage configurations (tight to leaky) in nine prototypical large office buildings (representing three construction eras in three California climates where these types of buildings are common). Combined fan power for the variable-speed-controlled supply and return fans at design conditions was assumed to be 0.8 W/cfm. Based on our analyses ... continued below

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56 pages

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Wray, Craig P. & Matson, Nance E. October 1, 2003.

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Description

The purpose of this study is to evaluate the variability of duct leakage impacts on air distribution system performance for typical large commercial buildings in California. Specifically, a hybrid DOE-2/TRNSYS sequential simulation approach was used to model the energy use of a low-pressure terminal-reheat variable-air-volume (VAV) HVAC system with six duct leakage configurations (tight to leaky) in nine prototypical large office buildings (representing three construction eras in three California climates where these types of buildings are common). Combined fan power for the variable-speed-controlled supply and return fans at design conditions was assumed to be 0.8 W/cfm. Based on our analyses of the 54 simulation cases, the increase in annual fan energy is estimated to be 40 to 50% for a system with a total leakage of 19% at design conditions compared to a tight system with 5% leakage. Annual cooling plant energy also increases by about 7 to 10%, but reheat energy decreases (about 3 to 10%). In combination, the increase in total annual HVAC site energy is 2 to 14%. The total HVAC site energy use includes supply and return fan electricity consumption, chiller and cooling tower electricity consumption, boiler electricity consumption, and boiler natural gas consumption. Using year 2000 average commercial sector energy prices for California ($0.0986/kWh and $7.71/Million Btu), the energy increases result in 9 to 18% ($7,400 to $9,500) increases in HVAC system annual operating costs. Normalized by duct surface area, the increases in annual operating costs are 0.14 to 0.18 $/ft{sup 2}. Using a suggested one-time duct sealing cost of $0.20 per square foot of duct surface area, these results indicate that sealing leaky ducts in VAV systems has a simple payback period of about 1.3 years. Even with total leakage rates as low as 10%, duct sealing is still cost effective. This suggests that duct sealing should be considered at least for VAV systems with 10% or more total duct leakage. The VAV system that we simulated had perfectly insulated ducts, and maintained constant static pressure in the ducts upstream of the VAV boxes and a constant supply air temperature at the airhandler. Further evaluations of duct leakage impacts should be carried out in the future after methodologies are developed to deal with duct surface heat transfer effects, to deal with airflows entering VAV boxes from ceiling return plenums (e.g., to model parallel fan-powered VAV boxes), and to deal with static pressure reset and supply air temperature reset strategies.

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56 pages

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OSTI as DE00819481

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  • Other Information: PBD: 1 Oct 2003

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  • Report No.: LBNL--53605
  • Grant Number: AC03-76SF00098
  • DOI: 10.2172/819481 | External Link
  • Office of Scientific & Technical Information Report Number: 819481
  • Grant Number: 400-99-012-1
  • Archival Resource Key: ark:/67531/metadc736878

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Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

Office of Scientific and Technical Information (OSTI) is the Department of Energy (DOE) office that collects, preserves, and disseminates DOE-sponsored research and development (R&D) results that are the outcomes of R&D projects or other funded activities at DOE labs and facilities nationwide and grantees at universities and other institutions.

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  • October 1, 2003

Added to The UNT Digital Library

  • Oct. 18, 2015, 6:40 p.m.

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  • Dec. 1, 2017, 9:44 p.m.

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Wray, Craig P. & Matson, Nance E. Duct leakage impacts on VAV system performance in California large commercial buildings, report, October 1, 2003; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc736878/: accessed December 15, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.