Commercial thermal distribution systems, Final report for CIEE/CEC

Xu, Tengfang; Bechu, Olivier; Carrie, Rémi; Dickerhoff, Darryl; Fisk, William J.; Franconi, Ellen; Kristiansen, Oyvind; Levinson, Ronnen; McWilliams, Jennifer A.; Wang, Duo; Modera, Mark; Webster, Tom; Ring, Erik; Zhang, Qiang; Huizenga, Charlie; Bauman, Fred; Arens, Ed

doi:10.2172/753091

“…The EDS project goal is to bridge the gaps in duct system modeling capabilities, and to expand our understanding of duct thermal performance in California's large commercial buildings, by following through on the strategy outlined by Xu et al (1999). As steps toward this goal, the project involves three specific technical objectives:…”

Section: Project Objectivesmentioning

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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“…Xu et al (1999a) have reviewed these capabilities in detail; the following summarizes and expands upon their findings.…”

Section: Doe-21ementioning

confidence: 98%

“…The EDS project goal is to bridge the gaps in duct system modeling capabilities, and to expand our understanding of duct thermal performance in California's large commercial buildings, by following through on the strategy outlined by Xu et al (1999a). As steps toward this goal, the project involves three specific technical objectives:…”

Section: Project Objectivesmentioning

confidence: 99%

“…• Past efforts that assessed DOE-2 capabilities for modeling ducts in commercial buildings (Modera et al 1999, Xu et al 1999a), • A recent doctoral dissertation that used DOE-2 and TRNSYS to model duct thermal losses in large commercial buildings (Franconi 1999), • Recent DOE-2.2 modeling efforts that assessed duct system improvements for small commercial buildings (PG&E 2003a(PG&E , 2003b, and • Discussions of residential duct thermal models (Gu et al 1998a(Gu et al , 1998b, which are the basis for a recent proposal by the Florida Solar Energy Center to integrate duct thermal performance modeling into EnergyPlus for residential and small-commercial buildings.…”

Section: Report Organizationmentioning

confidence: 99%

“…According to Xu et al (1999a), later proprietary versions of DOE-2.1E were improved so that the user could specify a supply duct heat loss coefficient instead of simply a supply duct temperature change. The building space that "receives" the supply duct leakage air and that is linked to the surface heat transfer effects could also be specified using a new keyword: PIPE&DUCT-ZONE.…”

Section: Doe-21ementioning

confidence: 99%

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Duct thermal performance models for large commercial buildings

Wray¹

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; to Iain Walker (LBNL) for his assistance in defining the duct surface heat transfer models described in the body of this report; Nance Matson (LBNL) for her review and refinement of the DOE-2 data interchange with TRNSYS; 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 and EnergyPlus. The author wishes to thank Phil Haves, Fred Winklemann, Fred Buhl, Joe Huang, and Steve Selkowitz.The duct modeling discussions with Lixing Gu, Jim Cummings, Muthusamy Swami, and Don Shirey of the Florida Solar Energy Center and Pete Jacobs of the Architectural Energy Corporation helped define the approaches that we selected for duct thermal performance modeling in large commercial buildings, and the author is grateful for their input.Advice from Michaël Kummert of the Solar Energy Laboratory, University of WisconsinMadison regarding TRNSYS compiling issues was greatly appreciated; as was the explanation by Tim McDowell of Thermal Energy System Specialists about the details involved in coupling TRNSYS and EnergyPlus.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.

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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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Commercial thermal distribution systems, Final report for CIEE/CEC

Cited by 4 publications

References 12 publications

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

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

Duct thermal performance models for large commercial buildings

Performance of thermal distribution systems in large commercial buildings

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