Arlan Burdick IBACOS, Inc. - NREL

[Pages:46]Advanced Strategy Guideline: Air Distribution Basics and Duct Design

Arlan Burdick

IBACOS, Inc.

December 2011

NOTICE

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Advanced Strategy Guideline: Air Distribution Basics and Duct Design

Prepared for: Building America Building Technologies Program Office of Energy Efficiency and Renewable Energy U.S. Department of Energy

Prepared by: Arlan Burdick IBACOS, Inc. 2214 Liberty Avenue Pittsburgh, Pennsylvania 15222

NREL Technical Monitor: Michael Gestwick Prepared under Subcontract Number KNDJ-0-40341-02

Deliverable 11.5.2 October 2011

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Contents

List of Figures ............................................................................................................................................ iv List of Tables ............................................................................................................................................... v Definitions................................................................................................................................................... vi Executive Summary ................................................................................................................................. viii 1 Overview ................................................................................................................................................ 1 2 Performance Criteria ............................................................................................................................ 4

2.1 Temperature Mixing and Uniformity...................................................................................4 2.1.1 Volume and Pressure of Air.....................................................................................4 2.1.2 Ductwork Materials and Configuration ...................................................................4

2.2 Supply Outlets......................................................................................................................5 2.2.1 Impact on Uniformity ..............................................................................................5 2.2.2 Throw .......................................................................................................................6

2.3 Noise ..................................................................................................................................7

3 Integrated Design ............................................................................................................................... 10 4 Design Principles ............................................................................................................................... 12

4.1 Pressure Drop.....................................................................................................................12 4.2 Room-by-Room Supply Requirements..............................................................................14 4.3 Return Air Design ..............................................................................................................16 4.4 Supply Air Outlets .............................................................................................................22 4.5 Duct Layout .......................................................................................................................26 4.6 Duct Size ............................................................................................................................29

5 Conclusion .......................................................................................................................................... 33 6 References .......................................................................................................................................... 34

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List of Figures

Figure 1. HVAC design flow ....................................................................................................................... 2 Figure 2. General steps for air distribution design ................................................................................. 3 Figure 3. Increased friction rate in compressed flexible duct................................................................ 5 Figure 4. High sidewall supply outlet example ........................................................................................ 6 Figure 5. Ceiling supply outlet example ................................................................................................... 6 Figure 6. Example throw and spread of air outlets ................................................................................. 7 Figure 7. Return placement introduces noise.......................................................................................... 8 Figure 8. Strategy to reduce return noise................................................................................................. 9 Figure 9. Framing duct integration strategy........................................................................................... 11 Figure 10. Pressure worksheet................................................................................................................ 13 Figure 11. Orlando House floor plan ....................................................................................................... 15 Figure 12. Locate the return first ............................................................................................................. 16 Figure 13. Orlando House return location .............................................................................................. 17 Figure 14. Chicago House return location.............................................................................................. 18 Figure 15. Over-the-door transfer............................................................................................................ 19 Figure 16. High/low through-the-wall transfer grille.............................................................................. 20 Figure 17. Attic transfer duct ................................................................................................................... 20 Figure 18. Poor return grille placement .................................................................................................. 21 Figure 19. Good design, high return ....................................................................................................... 22 Figure 20. Select and size air outlets ...................................................................................................... 22 Figure 21. Air supply outlet selection ..................................................................................................... 23 Figure 22. Example supply outlet performance data ............................................................................ 24 Figure 23. Orlando House family room and kitchen and nook area .................................................... 25 Figure 24. Chicago House family room and kitchen and nook area.................................................... 26 Figure 25. Duct layout............................................................................................................................... 26 Figure 26. Orlando House layout............................................................................................................. 27 Figure 27. Chicago House main floor ..................................................................................................... 28 Figure 28. Chicago House basement layout .......................................................................................... 29 Figure 29. Size ducts for airflow .............................................................................................................. 30

*Unless otherwise noted, all figures were created by IBACOS.

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List of Tables

Table 1. Comparative NC Values ............................................................................................................. 10 Table 2. Orlando House Room-by-Room Loads .................................................................................... 14 Table 3. Chicago House Supply Pressure Loss..................................................................................... 31 Table 4. Master Bedroom Duct Run ........................................................................................................ 32

*Unless otherwise noted, all tables were created by IBACOS.

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Definitions

ACCA ANSI ASHRAE Available Pressure

Btu Btu/h CF cfm Coanda Effect

Effective Length

Equivalent Length

Face Velocity Friction Rate

ft/min

Air Conditioning Contractors of America

American National Standards Institute

American Society of Heating, Refrigerating and AirConditioning Engineers

The difference between the static pressure and the pressure against which the selected equipment can deliver the cubic feet per minute of air. This value is what is available in the design for duct and supply outlet pressure losses.

British thermal unit

Btu per hour

Cooling factor

Cubic feet per minute

The tendency of moving air to attach itself to a surface and flow along it. As air from the supply outlet moves across the ceiling surface, a certain amount of friction occurs between the supply air and the ceiling surface. This resistance to the flow of the supply air pulls the supply air toward the ceiling surface, causing it stick to the surface.

The length of duct used for design purposes that includes the straight length of duct added to all the fitting equivalent lengths.

The amount of duct length added to a duct run by fittings. Often the equivalent length of a fitting can be equal to or longer than the straight duct lengths due to the additional friction of turning air.

The velocity of supply air as it leaves the supply outlet.

The pressure loss between two points in a duct system that are separated by a specific length. The units for friction rate are inches water column per 100 feet (iwc/100 ft).

Feet per minute

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