Duct systems in large commercial buildings: physical characterization, air leakage, and heat conduction gains

Fisk, William J.; Delp, William W.; Diamond, Rick; Dickerhoff, Darryl; Levinson, Ronnen; Modera, Mark; Nematollahi, Matty; Wang, Duo

doi:10.1016/s0378-7788(99)00046-8

Cited by 30 publications

(18 citation statements)

References 2 publications

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“…This is similar to the findings by Fisk et al 1998, which report that the estimated air-leakage ratios in the two large systems ranged from zero to approximately 30%.…”

Section: Lbnl-44331supporting

confidence: 90%

Performance of thermal distribution systems in large commercial buildings

Xu¹,

Carrié²,

Dickerhoff³

et al. 2002

Energy and Buildings

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This paper presents major findings of a field study on the performance of five thermal distribution systems in four large commercial buildings. The five systems studied are typical single-duct or dual-duct constant air volume (CAV) systems and variable air volume (VAV) systems, each of which serves an office building or a retail building with floor area over 2,000 m 2 . The air leakage from ducts are reported in terms of effective leakage area (ELA) at 25 Pa reference pressure, the ASHRAE-defined duct leakage class, and air leakage ratios.The specific ELAs ranged from 0.7 to 12.9 cm 2 per m 2 of duct surface area, and from 0.1 to 7.7 cm 2 per square meter of floor area served. The leakage classes ranged from 34 to 757 for the five systems and systems sections tested. The air leakage ratios are estimated to be up to one-third of the fan-supplied airflow in the constant-air-volume systems. The specific ELAs and leakage classes indicate that air leakage in large commercial duct systems varies significantly from system to system, and from system section to system section even within the same thermal distribution system. The duct systems measured are much leakier than the ductwork specified as "unsealed ducts" by ASHRAE. Energy losses from supply ducts by conduction (including convection and radiation) are found to be significant, on the scale Page lof29LBNL-44331 similar to the losses induced by air leakage in the duct systems. The energy losses induced by leakage and conduction suggest that there are significant energy-savings potentials from duct-sealing and insulation practice in large commercial buildings.

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“…This is similar to the findings by Fisk et al 1998, which report that the estimated air-leakage ratios in the two large systems ranged from zero to approximately 30%.…”

Section: Lbnl-44331supporting

confidence: 90%

Performance of thermal distribution systems in large commercial buildings

Xu¹,

Carrié²,

Dickerhoff³

et al. 2002

Energy and Buildings

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“…The values shown in Figure 18 assume that each floor's HVAC system, which serves 15,000 ft 2 of conditioned floor area, has a duct surface area of 5,250 ft 2 . This surface area is based on commercial duct characterization data (Fisk et al 2000). For large commercial HVAC systems, duct surface area ranges from 27 to 43% of the building floor area, and the area downstream of the VAV boxes ranges from 50 to 75% of the total duct surface area.…”

Section: Hvac System Operating Costsmentioning

confidence: 99%

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

Wray¹,

Matson²

2003

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ACKNOWLEDGEMENTSThe largest debt of gratitude goes to former and current Energy Performance of Buildings staff members: Ellen Franconi (Nexant Corporation) for her development of the DOE-2/TRNSYS modeling approach and for implementing the duct models in a form that could readily be used in this project; and Brian Smith (LBNL) for computer applications support throughout the project.LBNL staff members in the Building Technologies Department were also helpful and supportive of this work, particularly regarding the intricacies of DOE-2.1E. The authors wish to thank Joe Huang, Fred Winkelmann, and Fred Buhl.Advice of Michaël Kummert at the Solar Energy Laboratory, University of Wisconsin-Madison regarding TRNSYS compiling issues was greatly appreciated.This project evolved from the ideas and work of Mark Modera (LBNL), who was the original project lead. Even after he left the project, Mark continued to provide contributions and was a valuable resource for the project team. ii ABSTRACT 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 lowpressure 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 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 ...

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“…Air leakage rates from ducts in light-commercial buildings are of the same order as residential buildings (~24%) (Delp, et al, 1998). Much less is known about large buildings, but the limited data available suggests that leakage areas are similar to those in light-commercial buildings (Fisk, et al, 1999). Actual leakage rates vary widely between buildings of a similar type.…”

Section: Air Leakage In Ductsmentioning

confidence: 99%

“…Anecdotally, a typical floor to ceiling height is 4 m (14 ft). Flow rate data from studies in small numbers of buildings are available in research reports (e.g., Fisk et al, 1999); however, the largest and most useful data set is from the EPA-BASE study (USEPA, 1994). For air handlers serving the study spaces in 100 office buildings, the BASE study recorded the design supply air flow rate, a measured supply air flow rate, and the floor area served by the air handler.…”

Section: Rates and Times Of Air Flow Through Filtersmentioning

confidence: 99%

Factors affecting the concentration of outdoor particles indoors (COPI): Identification of data needs and existing data

Thatcher¹,

McKone²,

Fisk³

et al. 2001

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The process of characterizing human exposure to particulate matter requires information on both particle concentrations in microenvironments and the timespecific activity budgets of individuals among these microenvironments. Because the average amount of time spent indoors by individuals in the US is estimated to be greater than 75%, accurate characterization of particle concentrations indoors is critical to exposure assessments for the US population. In addition, it is estimated that indoor particle concentrations depend strongly on outdoor concentrations. The spatial and temporal variations of indoor particle concentrations as well as the factors that affect these variations are important to health scientists. For them, knowledge of the factors that control the relationship of indoor particle concentrations to outdoor levels is particularly important. In this report, we identify and evaluate sources of data for those factors that affect the transport to and concentration of outdoor particles in the indoor environment. Concentrations of particles indoors depend upon the fraction of outdoor particles that penetrate through the building shell or are transported via the air handling (HVAC) system, the generation of particles by indoor sources, and the loss mechanisms that occur indoors, such as deposition. To address these issues, we (i) identify and assemble relevant information including the behavior of particles during air leakage, HVAC operations, and particle filtration; (ii) review and evaluate the assembled information to distinguish data that are directly relevant to specific estimates of particle transport from those that are only indirectly useful and (iii) provide a synthesis of the currently available information on building air-leakage parameters and their effect on indoor particle matter concentrations.

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Duct systems in large commercial buildings: physical characterization, air leakage, and heat conduction gains

Cited by 30 publications

References 2 publications

Performance of thermal distribution systems in large commercial buildings

Performance of thermal distribution systems in large commercial buildings

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

Factors affecting the concentration of outdoor particles indoors (COPI): Identification of data needs and existing data

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