New Insights for Improving the Designs of Flexible Duct Junction Boxes (Fact Sheet)
IBACOS explored the relationships between pressure and physical configurations of flexible duct junction boxes by using computational fluid dynamics (CFD) simulations to predict individual box parameters and total system pressure, thereby ensuring improved HVAC performance. Current Air Conditioning Contractors of America (ACCA) guidance (Group 11, Appendix 3, ACCA Manual D, Rutkowski 2009) allows for unconstrained variation in the number of takeoffs, box sizes, and takeoff locations. The only variables currently used in selecting an equivalent length (EL) are velocity of air in the duct and friction rate, given the first takeoff is located at least twice its diameter away from the inlet. This condition does not account for other factors impacting pressure loss across these types of fittings. For each simulation, the IBACOS team converted pressure loss within a box to an EL to compare variation in ACCA Manual D guidance to the simulated variation. IBACOS chose cases to represent flows reasonably correlating to flows typically encountered in the field and analyzed differences in total pressure due to increases in number and location of takeoffs, box dimensions, and velocity of air, and whether an entrance fitting is included. The team also calculated additional balancing losses for all cases due to discrepancies between intended outlet flows and natural flow splits created by the fitting. In certain asymmetrical cases, the balancing losses were significantly higher than symmetrical cases where the natural splits were close to the targets. Thus, IBACOS has shown additional design constraints that can ensure better system performance.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Energy Efficiency Office. Building Technologies Office
- DOE Contract Number:
- AC36-08GO28308
- OSTI ID:
- 1118086
- Report Number(s):
- DOE/GO-102014-4298; KNDJ-0-40341-00
- Resource Relation:
- Related Information: Building America Case Study: Technology Solutions for New and Existing Homes, Building Technologies Office (BTO)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
RESIDENTIAL
RESIDENTIAL BUILDINGS
IBACOS
BUILDING AMERICA
CFD
COMPUTATIONAL FLUID DYNAMICS
DUCTED MINI SPLIT SYSTEMS
ACCA MANUAL D
ACCA MANUAL D GROUP 11 FITTINGS
DUCTS
DUCT FITTINGS
DUCT FITTING DESIGN
SMALL-DIAMETER DUCTS
WIRE-HELIX DUCT
JUNCTION BOXES
BOX PLENUMS
K-FACTORS IN DUCT FITTINGS
FITTING PRESSURE DROPS