Standards for Duct Sizing and Duct Details 022506

Prepared by: JSB Prepared On: 03/11/02 Revised By: JSB Revised On: 02/26/06

STANDARD FOR DUCT SIZING Page 1 2/25/06 C:\Documents and Settings\jamesb\My Documents\FORMS\STANDARDS FOR DUCT SIZING AND DUCT DETAILS 022506.doc

STANDARDS FOR DUCT SIZING AND DUCT DETAILS

YOU MUST USE THE WRITTEN CRITERIA AS OUTLINED BY THE PRODUCT MANAGER ON ANY GIVEN PROJECT REGARDLESS OF THE STANDARD, OTHERWISE USE THE FOLLOWING:

1. USE ONLY EVEN DUCT SIZES FOR DESIGN UNLESS APPROVED IN WRITING BY THE PROJECT MANAGER. ALL DUCTWORK SHALL BE SIZED USING A TRANE DUCTULATOR, ONLY UNLESS OTHERWISE APPROVED IN WRITING BY THE PROJECT MANAGER.

2. CONSTANT OR VARIABLE VOLUME SUPPLY AIR SYSTEMS: (MULTIZONE, DOUBLE DUCT, SHUTOFF

VAV)

A. TRUNK DUCTS FROM AHU TO EXTERIOR ZONES: MAX. S.P. = 0.10” W.G., MAX VELOCITY = 1500 FPM. DUCTWORK SIZED AT THIS VELOCITY SHOULD HAVE NO BRANCH DUCTS TO DIFFUSERS. REDUCE DUCT VELOCITY BEFORE CONNECTING ANY DIFFUSERS.

B. TRUNK DUCTS TO INTERIOR ZONES AND EXTERIOR ZONE DUCT WHERE TAKEOFFS TO

DIFFUSERS ARE CONNECTED: MAX. S.P. = 0.08, MAX VELOCITY – 1200 FPM.

3. VARIABLE VOLUME PRIMARY AIR SYSTEMS/CONSTANT VOLUME SECONDARY AIR SYSTEMS:

A. PRIMARY AIR DUCTS, AHU TO TAP FOR VAV DEVICES: MAX S.P. = 0.12” WG, MAX VELOCITY – 1800 FPM.

B. TAP TO VAV TERMINALS: MAX S.P. 0.10” WG, MAX VELOCITY – 1500 FPM.

C. CONSTANT VOLUME SECONDARY DUCTWORK: MAX S.P. = 0.08” WG, MAX VELOCITY = 1200 FPM.

4. SIZE BRANCH DUCTS: MAX S.P. = 0.08, MAX VELOCITY - 1200 FPM.

A. 90º RECTANGULAR BRANCH DUCT CONNECTION TO TRUNK DUCT IS USED FOR ONE OUTLET

ONLY AND FOR A VERY SHORT DISTANCE TO CONNECT, SIDEWALL REGISTERS, ETC., AN AIR EXTRACTOR MUST BE INSTALLED AT THE STRAIGHT TRUNK DUCT CONNECTION. IT IS PREFERRED TO USE AN “EXPANDED TAP” IN LIEU OF STRAIGHT TAP.

90º Straight Branch 90º Expanded Tap* *The scoop damper may be replaced with a balancing damper in the branch.


B. ROUND DUCT CONNECTIONS TO TRUNK DUCT AT 90º ARE USED FOR A SHORT DISTANCE AND TO

ONE DIFFUSER ONLY.

C. 45º CONNECTIONS TO TRUNK DUCTS ARE USED FOR AIR QUANTITIES OF 500 TO 1,000 CFM AND FOR ONE DIFFUSER ONLY AND 500 TO 1,000 CFM FOR SLOTS.

D. SPLIT TRUNK DUCTS AND INSTALL SPLITTER DAMPER (CONSTANT VOLUME SYSTEM) WHERE BRANCH DUCT SERVES MORE THAN ONE DIFFUSER OR BRANCH DUCT HAS A LARGE AIR QUANTITY. SEE DUCT SPLIT DETAILS, IEMS 29 AND 30.

5. CONNECTIONS TO DIFFUSERS SHOULD BE APPROXIMATELY 600 FPM. USE DIFFUSER NECK SIZE

FROM BRANCH DUCT TO DIFFUSER IF POSSIBLE. CHECK DIFFUSER STATIC PRESSURE DROP FOR CFM AND BRANCH DUCT OR FLEX SIZE.

6. SIZE PLENUMS ABOVE LINEAR DIFFUSERS AT 600 FPM WITH SUPPLY TAPS TO PLENUM

APPROXIMATELY 12’-0” O.C. DIVIDE THE TOTAL AIR VOLUME FOR THE PLENUM BY THE QUANTITY OF TAPS INTO THE PLENUM. DIVIDE THE RESULT IN HALF (ASSUMING EQUAL SPACING ON TAPS) IN HALF AND BY 600 FPM. DIVIDE THE AREA (SF) BY THE TAP DIAMETER OR HEIGHT TO DETERMINE THE WIDTH OF THE PLENUM. REFER TO FOLLOWING EXAMPLE.

EXPANDED TAP WITH SCOOP DAMPER

PREFERRED


EXAMPLE: 2400 CFM OF SUPPLY AIR

1. DIVIDE THE AIR QUANTITY BY THE NUMBER OF TAPS. TAP AIR QUANTITY = 2400 CFM ÷ 2 = 1200 CFM 2. DIVIDE THE TAP AIR QUANTITY IN HALF (ASSUMING THE TAPS ARE EQUALLY

SPACED). 1200 ÷ 2 = 600 CFM 3. DIVIDE THE AIR QUANTITY ABOVE (600 CFM) BY 600 FPM TO DETERMINE THE

PLENUM CROSS SECTIONAL AREA. CROSS SECTIONAL AREA = 600 CFM ÷ 600 FPM = 1.0 SQ.FT. (144 SQ.IN.) 4. DIVIDE THE CROSS SECTIONAL AREA BY THE TAP DIAMETER OR HEIGHT ON

RECTANGULAR DUCTS PLUS INSULATION THICKNESS: PLENUM WIDTH = 144 SQ.IN. ÷ 14 IN. (12 IN. DIAMETER TAP WITH 1 IN. THICK

INSULATION) = 10.3 IN. USE 11 IN.

5. PLENUM WILL BE 14 IN. HIGH X 11 IN. WIDE INSIDE CLEAR. A DETAIL SHOULD BE PROVIDED INDICATING HOW THE LINEAR DIFFUSER IS CONNECTED TO THE PLENUM. ALSO, THE PLENUM WOULD NORMALLY BE INSULATED SO ONE MUST VERIFY THAT THE SELECTED DIMENSIONS INCLUDING THE INSULATION WILL FIT THE SPACE AVAILABLE. IT MAYBE NECESSARY TO REDUCE THE SIZE OF THE PLENUM BY REDUCING THE SIZE OF THE TAPS WHICH WOULD INCREASE THE QUANTITY OF TAPS.

7. SIZE RISERS AS FOLLOWS:

TREATED O.A. SUPPLY: MAX S.P. = 0.10” MAX VEL = 1500 FPM RAW O.A. SUPPLY: MAX S.P. = 0.10” MAX VEL = 1500 FPM TOILET EXHAUST: MAX S.P. = 0.10” MAX VEL = 1500 FPM RELIEF AIR: MAX S.P. = 0.15” MAX VEL = 2000 FPM SMOKE EXHAUST: MAX S.P. = 0.15” MAX VEL = 2000 FPM SIZE BRANCH CONNECTION ON EACH FLOOR AT 0.10” WG FOR OUTSIDE AIR SUPPLY AND EXHAUST

DUCT TO RISER.

8. ANYTIME YOU DRAW A DUCT ON ANY JOB, KNOW THAT IT WILL FIT IN THE SPACE YOU ARE SHOWING IT, INCLUDING BRACING, INSULATION AND COORDINATE IT WITH OTHER TRADES.

9. ALL KITCHEN EXHAUST DUCTWORK SHALL HAVE RADIUS ELBOW (90˚ AND 45˚) WITH NO TURNING

VANES. SIZE BASED ON VELOCITY (FPM) AS INDICATED IN CODE BUT NOT LESS THAN 2000 FPM.

10. SPECIAL EXHAUST SYSTEMS (LABORATORY EXHAUST, CAR EXHAUST PIPE SYSTEM, ETC.) SHOULD BE SIZED ON VELOCITY ALL THE WAY FROM THE INLET THROUGH THE FAN TO OUTLET. REFER TO CODES, INDUSTRIAL VENTILATION HANDBOOK, OR MANUFACTURER’S DATA FOR VELOCITY LIMITS.


11. ALL 90º ELBOWS 13” AND LARGER SHALL HAVE SQUARE CORNERS WITH TURNING VANES. ALL 90º 12”

AND SMALLER MAY BE LONG RADIUS AT THE CONTRACTOR’S OPTION. THIS INCLUDES ALL SYSTEMS (SUPPLY, RETURN AND EXHAUST EXCEPT KITCHEN EXHAUST).

*DRAW SQUARE ELBOWS WITH TURNING VALVES ON DRAWINGS SO THAT IF DUCTWORK IS RESIZED WE WILL NOT HAVE TO REDRAW.

12. ALL 45º ELBOWS SHALL BE RADIUS TYPE FOR ALL DUCT SYSTEMS. NO TURNING VANES ARE

REQUIRED, UNLESS NOTED IN A PARTICULAR ELBOW FOR A GIVEN LOCATION. A TRANSITIONING 45˚ ELBOW CAN HAVE A 25% MAX. CHANGE IN WIDTH AND/OR DEPTH. ANY DEVIATIONS FROM THESE RULES MUST BE AUTHORIZED BY THE PROJECT MANAGER, SUCH AS SOUND ATTENUATING ELBOWS WITHOUT TURNING VANES, ETC.

13. NEVER CONNECT A BRANCH DUCT TO AN ELBOW OR INTO A TRANSITION.

14. DO NOT CONNECT A BRANCH DUCT, DOWNSTREAM OF A RADIUS ELBOW (90˚ AND 45˚) CLOSER THAN

1-1/2 TIMES WIDTH OF ELBOW, UNLESS FULL LENGTH TURNING VANES ARE INSTALLED IN ELBOW. ALSO, DO NOT CONNECT A BRANCH DUCT WITHIN 3’-0” MIN. OF A VAV TERMINAL OUTLET.

15. ALL WATER COILS, FAN COIL UNITS, AND AIR HANDLING UNITS ABOVE CEILING MUST HAVE AN

AUXILIARY DRAIN PAN WITH DRAIN LINE RUNNING TO NEAREST FLOOR DRAIN. 16. ANY QUESTIONS CONCERNING FABRICATION OR INSTALLATION OF DUCTWORK SHALL MAKE

REFERENCE TO SMACNA LOW VELOCITY DUCT STANDARDS MANUAL, 4TH EDITION.

17. ALL SUPPLY DUCTS FROM MULTI-ZONE AIR HANDLING UNITS SHALL HAVE MANUAL DAMPER LOCATED IN MECHANICAL ROOM, AND AN ACCESS PANEL IN EACH ZONE DUCT AT ZONE CONTROL DAMPER.

18. ALL DUCT MOUNTED HOT WATER HEATING COILS SHALL BE SIZED FOR MAXIMUM FACE VELOCITY OF

700 FPM WITH DUCT TRANSITIONS PER THE REQUIREMENTS HEREINAFTER IN ITEM NO. 32. REFER TO COIL MANUFACTURER FOR AVAILABLE SIZES. ALLOW PIPING CLEARANCE FOR EACH COIL AND A DRAIN PAN WITH DRAIN LINE TO FLOOR DRAIN IN MECHANICAL ROOM UNDER COIL AND PIPING WHEN HEATING COIL IS LOCATED OVER OCCUPIES SPACK.


19. ALL ELECTRIC HEATING COILS SHOULD BE POSITIONED IN DUCT WITH A MINIMUM OF 4 FEET FROM

ANY UPSTREAM OBSTRUCTION (ELBOWS, DAMPERS, TAPS, TRANSITIONS, ETC.) AND MINIMUM OF 3’-0” FROM ANY DOWNSTREAM OBSTRUCTION (ELBOWS, DAMPERS, TAPS, TRANSITIONS, ETC.).

20. FLEXIBLE DUCT CONNECTIONS SHOULD BE DRAWN WITH CONNECTIONS PERPENDICULAR TO BOTH SUPPLY DUCT AND DIFFUSER. MAXIMUM DUCT LENGTH TO BE 6’-0”.

21. TYPICAL CEILING DIFFUSER AT END OF DUCT SHALL BE CONSTRUCTED WITH ELBOW, AND TURNING VANES WHERE CEILING SPACE PERMITS. TAP DIFFUSER INTO BOTTOM OF DUCT AND INSTALL EXTRACTOR WHEN YOU DO NOT HAVE ROOM FOR AN ELBOW, IS AN ALTERNATE CONNECTION.

VOLUME DAMPERS ON EXHAUST GRILLES ONLY

AIR FLOW

AIR FLOW

OFFSET IF NECESSARY PREFERRED


22. DOG LEG OFFSET’S MAY BE INSTALLED WHERE CHANGE IN DUCT POSITION IS 20º OR LESS.

*OFFSETTING TRANSITIONS SHALL HAVE A MAXIMUM ANGLE OF 10º ON ANY SIDE. VERIFY ALL SIDES IN LAYING OUT TRANSITION ELBOWS. TRY TO OFFSET BEFORE TRANSITION OR VICE VERSA.

23. USE 45º RADIUS OFFSETS WITH LONG RADIUS ELBOWS OR “S” FITTINGS WHERE CHANGE IN DUCT

POSITION IS GREATER THAN 20º.

24. WHERE SPACE LIMITATIONS WILL NOT PERMIT A DOG LEG, OR 45º RADIUS OFFSET, SQUARE ELBOWS WITH TURNING VANES MAY BE USED AS A LAST RESORT.

25. CHANGE WIDTH IN ELBOW WHEN CHANGE IS 25% OR LESS.

PIPING OBSTRUCTION (TYP.)


26. WHEN WIDTH CHANGE IS GREATER THAN 25% TRANSITION MUST BE MADE WITH TRANSITION FITTING (NOT IN ELBOW).

27. TRANSITION RQUIRED FOR DEPTH CHANGE OF DUCT. (DEPTH CHANGE CANNOT BE MADE IN

ELBOW). 28. TRANSITION REQUIRED FOR DEPTH AND WIDTH CHANGE OF DUCT. IN THIS CASE, TRANSITION

REQUIRED DUE TO DEPTH CHANGE AND WIDTH CHANGE GREATER THAN 25%, SO BOTH CHANGES ARE MADE IN ONE TRANSITION FITTING.

29. CHANGE WIDTH IN ELBOW IF CHANGE IS 25% OR LESS AND DUCT DEPTHS ARE THE SAME.

* THE DESIGNER MUST ALLOW SUFFICIENT LENGTH BEFORE THE SPLIT FOR SPLITTER DAMPER AND ITS MOVEMENT. THE SPLITTER DAMPER LENGTH IS 1.25 TIMES THE SMALLEST PART OF THE SPLIT PLUS 3” FOR MOVEMENT. FOR THE ABOVE EXAMPLE: (15” X 1.25) + 3” = 18.75”, USE 19”. THE SPLITTER DAMPER CAN BE OMITTED IF A MANUAL DAMPER IS INSTALLED EACH BRANCH OR THE SPLIT IS IN THE PRIMARY TRUNK DUCT ON A VAV SYSTEM.


30. DO NOT CHANGE WIDTH IN ELBOW AND DEPTH IN TRANSITION TO CHANGE WIDTH AND DEPTH OF DUCT. SEE DETAIL #29 BELOW.


31. KEEP BOTH HEELS OF ELBOW THE SAME WIDTH AND INSTALL TRANSITION ONLY WHEN CHANGE IN

DUCT WIDTH IS OVER 25% OR WHEN DEPTH OF DUCT CHANGES.


32. DUCT TRANSITIONS SHALL BE AS FOLLOWS: TAPER ON CONTRACTING AIR FLOW SHALL BE A TOTAL

ANGLE OF 20º OR 13” FOR 36” LONG TRANSITION, AND TAPER ON DIVERGING AIRFLOW SHALL BE A TOTAL ANGLE OF 30º OR 20” FOR A 36” LONG TRANSITION. NO TRANSITION SHALL BE LESS THAN 12” IN LENGTH.

TRANSITION LENGTH (CONTRACTING) “L” = DUCT CHANGE X (36/20) OR DUCT CHANGE/TAN 30º TRANSITION LENGTH (DIVERGING) “L” = DUCT CHANGE X (36/13) OR DUCT CHANGE/TAN 20º


33. TRANSITIONS SHOULD BE SINGLE SIDED WITH A CHANGE IN ONLY ONE DIMENSION (“H” OR “W”). TRANSITIONS SHOULD BE LIMITED TO A MINIMUM OF 6”.

34. LOUVER SIZING SHOULD BE BASED ON THE FREE AREA AS FOLLOWS:

NOTE: WHEN DESCRIBING LOUVERS THE DRAWINGS SHOULD INDICATE THE GROSS LENGTH AND HEIGHT WITH THE MINIMUM FREE AREA. IT SHOULD NOTE THE LOUVERS ARE BY THE GENERAL CONTRACTOR. COORDINATE LOCATION AND REQUIREMENTS WITH ARCHITECT.

35. PLENUM BEHIND LOUVERS SHALL BE SIZED ON 600 FPM.

EXAMPLE: 400 CFM OF INTAKE AIR.

1. DIVIDE THE AIR QUANITY BY THE NUMBER OF TAPS.

TAP AIR QUANTITY = 4000/1 = 4000

2. DIVIDE THE TAP AIR QUANTITY BY HALF.

4000/2 = 2000 CFM

3. DIVIDE THE AIR QUANTITY BY 600 FPM TO DETERMINE THE PLENUM CROSS SECTIONAL AREA.

AREA = 2000/6000 = 333 USE 3.5

4. DIVIDE THE AREA BY THE HEIGHT OF THE LOUVER TO DETERMINE THE DEPTH.

DEPTH – 3.5 – 1.16 USE 1.2” OR 14.5” (NO LESS THAN 12”)


36. FAN CONNECTIONS SHOULD BE MADE WITH SMOOTH CONNECTION USING THE NATURAL AIR FLOW PATTERNS. PROVIDE FLEXIBLE CONNECTIONS ON THE INLET AND OUTLET OF ALL FANS. MOUNT FANS ON ISOLATION.

37. AIR HANDLING CONNECTIONS SHOULD FOLLOW THE RULES SHOWN IN ITEM NO. 36. THE CONNECTION SHOULD USE THE NATURAL FLOW CHARACTERISTICS OF THE AIR. THE FLEX CONNECTION CAN BE DELETED FOR INTERNALLY ISOLATED AIR HANDLING UNITS.

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