Requirement of Fans for Pressurized Ventilation System in an Industrial Space, Summaries of Mechanical Engineering

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HEATING,

VENTILATION AND

AIR

CONDITIONING

TO CALCULATE THE

NUMBER OF SUPPLY AND

EXHAUST FANS FOR

PRESSURIZED VENTILATION

IN AN INDUSTRIAL SPACE

1. FIND OUT THE TOTAL QUANTITY OF AIR PASSES THROUGH THE SPACE DUE TO SPECIFIC NUMBER OF AIR CHANGES
2. FIND OUT THE TOTAL QUANTITY OF AIR REQUIRED TO REMOVE THE GENERATED HEAT WITHIN THE SPACE.
3. TAKE THE GREATER OF TWO DETERMINED VALUES
4. SELECT NUMBER OF FANS NEEDED TO BE INSTALLED.

NECESSARY STEPS :-

FIND OUT THE TOTAL NUMBER OF SUPPLY FANS

AND EXHAUST FANS WITH CAPACITY 4000 CMH

REQUIRED TO BE INSTALLED IN A CONTROL

ROOM 20m x 10m x 8m WITH 10 AIR CHANGES PER HOUR AND 20 KW HEAT LOAD TO MAINTAIN TEMPERATURE 5°C LESS THAN THE AMBIENT.

EXAMPLE

1. DIMENSION OF THE SPACE

a) LENGTH = 20 m

b) WIDTH = 10 m

c) HEIGHT = 8 m

2. No. OF AIR CHANGES PER HOUR = 10

3. HEAT GENERATED WITHIN THE SPACE

(HEAT LOAD) = 20 KW

4. FAN CAPACITY = 4000 Cu.m /Hour

GIVEN

a) Heat Load (Q) = 20 KW(KiloWatt) b) Temperature Difference (Δ T) = 5 c) We know Q = m.Cp. Δ T Cp (Specific Heat of Air)=0.24 Kcal /Kg°C So, Mass of the air (m) =(Q X 860)/ (Cp. Δ T) [ 1 KW = 860 Kcal per Hour] = (20 X 860 ) / (0.24 X 5) = 1433. Kg. d) Volume of the air = m / Density of air = 1433. / 1.225 Kg per Cu.m = 1170.06 Cu.m per Hour

STEP 2

a) Selected Air Quantities at intake

and exhaust are 16000 CMH (Cubic

Meter per Hour) and 12800 CMH.

b) No. of Supply Fan required =

16000 CMH / 4000 CMH = 4

c) No. of Exhaust Fan required =

12800 / 4000 = 3.2 ( 4 in round

figure)

d) Total no. of fan required =

STEP 3