This document discusses fundamentals of air distribution systems including duct materials, shapes, sizing methods, and design considerations. It covers topics such as duct pressure classifications, sealing requirements, outlet selection factors, and fan sizing calculations. The key points are that ducts distribute air through a building, duct materials include galvanized iron and aluminum, and fan selection involves calculating pressure drops through ducts, dampers, and terminals to determine required static pressure.

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AIR DISTRIBUTION
SYSTEM

2. AIR DITRIBUTION
SYSTEM ..
AIR FLOW PATTERN

3. AIR DITRIBUTION
SYSTEM ..
AIR FLOW PATTERN

4. AIR DITRIBUTION
SYSTEM ..
AIR FLOW PATTERN

5. AIR DITRIBUTION
SYSTEM ..

6. HEAT LOAD ESTIMATION
CONTD ..

7. AIR DISTRIBUTION
CONTD..
SOME FUNDAMENTALS
1. DUCT IS SIMPLY A PATH TO DISTRIBUTE & MANAGE
THE AIR FLOW TO THE REQUIRED /DESINED
ZONES/AREAS
2. DUCT SHAPE MAY BE CIRULAR,SQUARE,RECTANGULAR
OR SPIRAL
3. GALVANIZED IRON,ALUMINIUM,STAINLESS STEEL,
BLACK IRON ETC ARE SOME OF THE COMMONLY USED
DUCT MATERIALS

8. AIR DISTRIBUTION
CONTD..
SOME FUNDAMENTALS
1. THE THICKNESS OF THE DUCT SHEET IS MENTIOINED BY ITS
GAUGE
2. ASPECT RATIO IS THE RATIO OF DUCT WIDTH TO HIGHT
3. ASPECT RATIO 1 TO 4 IS GENAERALLY ADVISED FOR DUCT
SIZING.
4. THE SIZE & SHAPE OF THE DUCT WILL DEPEND UP ON THE
CFM ,AVAILABLE SPACE FOR DUCTING, APPLICATION ETC

9. AIR DISTRIBUTION
CONTD..
SOME FUNDAMENTALS
1. THE DUCT IS CONNECTED TO THE EQUIPMENT THROUGH
FLEXIBLE CONNECTOR
2. ALL THE BRANCEHS ARE FITTED WITH VCD
3. FIRE DAMPER IS PROVIDED AT THE EQUIPMENT OUTLET &
OTHER DUCT PENITRATING FIRE WALL AREAS
4. THERMAL INSULATION IS DONE FOR SUPPLY AIR DUCT
5. ACCAUSTIC INSULATION IS DONE FOR SUPPLY DUCT

10. AIR DISTRIBUTION
CONTD..
SOME FUNDAMENTALS
1. AIR OUTLETS ARE SELECTED BASED ON THE MANUFACTURES
DESIGN DATA
2. TYPE & LOCATION OF THE AIR TERMINALS WILL DEPEND UP
ON THE ROOM DESIGN AND AESTHATICS
3. LOUVERS ARE FITTED AT THE FRESH AIR DUCT ENTRY
4. FITTINGS AND TRANSITIONS ARE DESIGNED ACCORDING TO
SMACNA & ASHRAE

11. AIR DISTRIBUTION
CONTD..
SOME FUNDAMENTALS
1. FLEXIBLE CANVAS CONNECTION SHOULD BE USED TO
CONNECT THE EQUIPMENT & DUCTING SYSTEM
2. ACCESS SHUOLD BE PROVIDED FOR DAMPERS
3. AHU SHOULDE BE PROVIDED WITH DRAIN PAN & U TRAP
4. GASKETS TO BE USED BETWEEN DUCT JOINTS TO PREVENT
LEAKAGE
5. NEVER RUN THE AHU UNLESS THE AHU ROOM IS CLEANED
AND FILTERS ARE MOUNTED

12. AIR DISTRIBUTION
CONTD..
TYPE OF DUCTS
1. SUPPLY AIR DUCT
2. RETURN AIR DUCT
3. FRESH AIR DUCT
4. EXHAUST AIR DUCT

13. AIR DISTRIBUTION
CONTD..
DUCT DESIGNING METHODS
1. VELOCITY REDUCTION METHOD
2. EQUAL FRICTION METHOD
3. STATIC REGAIN METHOD

14. AIR DISTRIBUTION
CONTD..
VELOCITY REDUCTION METHOD
1. VELOCITY(FPM) = VOLUME(CFM)/AREA (SQFT)
2. MAIN DUCT VELCOITY -1200 TO 1500 FPM
3. BRANCH DUCT VELOCITY - 750 TO 900 FPM
4. COLLAR/DROPPER VELOCITY - 300 TO 500 FPM
5. PLENUM BOXES – 500 FPM
6. RETURN AIR DUCT VELOCITY SHALL BE LEES THAN
SUPPLY AIR DUCT VELOCITY

15. AIR DISTRIBUTION
CONTD..
EQUAL FRICTION METHOD
1. CONSIDERS THE TOTAL DUCTING WILL BEAR THE
SAME FRICTIONAL LOSS
2. 0.08”WATER/100 FT TO 1” WATER/100 FEET
3. THE RANGE WILL DIFFER DEPENDING UP ON THE
APPLICATION AND USE OF SPACE

16. AIR DISTRIBUTION
CONTD..
DUCT CLASSIFICATION DW-
144
DUCT
PRESSURE
CLASS
STATIC
PRESSURE LIMIT
+ve -ve
pa pa
MAXIMUM AIR
VELOCITY
PERMISSIBLE AIR
LEAKAGE
M/sec
Litters per sec per
square meter
Low Pressure
Class-A
500 500 10 0.027 X p^0.65
Medium Pressure
Class-B 1000 750 20 0.009 X p^0.65
High Pressure
Class-C 2000 750 40 0.003 X p^0.65
Where p is in Pascal

17. AIR DISTRIBUTION
CONTD..
● Duct Classification as per SMACNA
1
7
DUCT PRESSURE
CLASS OPERATING PRESSURE
IN WG Pa
1/2 125 Not exceeding 1/2” wg
1 250 Exceeding 1/2” wg but not exceeding 1” wg
2 500 Exceeding 1” wg but not exceeding 2” wg
3 750 Exceeding 2” wg but not exceeding 3” wg
4 1000 Exceeding 3” wg but not exceeding 4” wg
6 1500 Exceeding 4” wg but not exceeding 6” wg
10 2000 Exceeding 6” wg but not exceeding 10” wg

18. AIR FLOW MANAGEMENT
● Duct seal class.
SEAL
CLASS
APPLICABLE STATIC
PRESSURE CLASS SEALING REQUIREMENTS
A
More than 3” wg
(750 Pa)
All transverse joints, longitudinal seams
and duct wall penetrations.
B
More than 2” & upto 3”
wg (750 Pa)
All transverse joints & longitudinal seams
C Upto 2”wg (500Pa) Transverse joints only
PRASHANT
DESAI
10

19. AIR FLOW MANAGEMENT
PRASHANT DESAI 19

20. AIR DISTRIBUTION
CONTD..
DUCT DESIGN & CONSTRUCTION CONSIDERATIONS
1. THE DUCT SHOULD CONSIDER THE AVILABLE SPACE FOR
DUCTING
2. DUCTS SHOULD BE TESTED FOR LEAKAGE
3. TRANSITIONS & FITTINGS PRESSURE LOSE SHOULD BE
CONSIDERED FOR BLOWER DESIGNING
4. 20 % MAX AREA REDUCTION IS ALLOWED IN DUCTING IN
CASE OF OBSTRUCTION

21. AIR TERMINAL DESIGN..
FACTORS TO BE CONSIDERED
1. AIR FLOW
2. THROW
3. NOISE LEVEL
4. APPERANCE
5. SPACE RESTRICTIONS

22. DISTRIBUTION SYSTEM
PLANS & SYMBOLS
Positive Pressure (supply)
Negative Pressure (return or exhaust)

23. Arrow indicates
air flow direction

24. FLOW PATTERNS
1-way
4-way
2-way
3-way

25. Thermostat
Smoke/Fire
Damper
T

26. AIR DISTRIBUTION
CONTD..
AHU FAN DESIGNING
1. THE CFM TO BE DELIVERED IS OBTAINED FROM HEAT LOAD
CALCULATION
2. THE FAN STATIC WILL DEPENED UP ON:
1. THE PRESSURE LOSS THROGH DUCT AND DUCT FITTINGS
2. THE PRESSURE LOSS AT DAMPERS
3. THE PRESSURE LOSS AT FLEXIBLE DUCT
4. THE PRESSURE LOSS AT TERMINAL
5. INTERNAL FAN LOSSES

27. FAN SELECTION..
CALCULATING THE PRESSURE DROP
1. IDENTIFY THE PATH HAVING THE MAXIMUM PRESSURE
2. CALCULATE THE PRESSURE DROP IN THE SELECTED PATH
DUCTING & DUCT FITTINGS
3. CALCULATE THE PRESSURE DROP IN THE PATH DAMPERS &
OTHER ACCESSORIES
4. CALCULATE THE PRESSURE DROP @ THE TERMINAL
5. ADD INTERNAL LOSS & SUM UP THE CALCULATION