1. NARSIMHA REDDY ENGINEERING COLLEGE
Design of air conditioning ducts
Submitted in partial fulfillment of
requirements for the award of the degree of
BACHELOR OF TECHNOLOGY
MECHANICAL ENGINNEERING
Under the esteemed guide
SURESH.P
Assistant professor (M.TECH)
Department of Mechanical Engineering
Submitted by
MD ZEESHAN 13X01A0366
SANDEEP SINGH 13X01A0392
ZAFARYAB HAIDER 13X01A03C2
MD RIZWAN 13X01A0367
2. Abstract
Earlier the use of air-conditioning for
comfort purpose was considered a luxurious
but now-a-day, it has been a necessity in
extreme climatic conditions, such as
extreme cold and hot in western countries.
Window air conditioners are preferred for
office rooms while large centralized units
are installed for conditioning the
auditorium, hospitals etc.
3. Air conditioning ducts
The purpose of air conditioning
ductwork is to deliver air from
the fan to the diffusers which
distribute the air to the room.
Air Moves Through the
Ductwork in Response to a
Pressure Difference Created by
the Fan
8. Rectangular
Lower aspect ratios
More energy efficient
Use less ductwork
Velocity and Area have
an inverse relationship
to the CFM (CFM = V x
A)
Velocity and Pressure
Drop have a direct
relationship
W
D
Aspect ratio = W / D
1 to 1
9. Air Distribution Systems
Three Types
Above Ceiling
Displacement
Under floor
Services
Supply air
Return air
Ventilation air
Relief air
Exhaust air
11. Other Design
Considerations
Thermal mass
Natural light
Solar shading
Control strategies
Life safety issues
Infiltration
Mixed Air
conditions
Energy in the air
Comfort level of
the air
The amount of
water in the air
12. DISPLACEMENT
PRINCIPLES
•Conditioned air moves upward past the
persons breathing zone.
•This invisible plume continues an upward
movement toward the ceiling.
•A person will breathe lower contaminant
levels vs. a mixing design.
13. Displacement
Advantages/Disadvantages
Advantages
Moderate supply
air temperature
Low velocity
Air delivered to
the comfort zone
without mixing
Accommodate
more outside air
for same energy
cost
Very quiet
Disadvantages
Higher initial
cost
Less well
understood
Too quiet
14. CONCLUSION
1)The cooling load calculation of an auditorium is done,
applying CLTD method and duct design is carried out by
equal friction method.
2)The calculated value of frictional pressure drop
is less as compared to existing plant or value used in
industry. Due to less value, duct diameter is increased
but loss in static pressure, velocity pressure can be
avoided. Smaller diameter of duct would increase noise
level. So requirement of sound attenuating devices may
need. Also probability of dampers is decreased with
increasing diameter. But first cost is increased with
increasing duct diameter
2) Due to proper branching of ducts, loss is
minimized in this design. But in existing plant, there is
straight branching in so many locations, which may
Editor's Notes
Rectangular Ductwork
A. Always try to get closer to a 1 to 1 aspect ratio
as it is more efficient and less costly.
B. A 12 x 12 duct has approximately 4 sq. ft per lineal foot
A 18 x 8 duct has approximately 4.33 sq. ft. per lineal foot
Using a weight of 1.4 pounds of galvanized steel per foot of
ductwork, the 12 x 12 duct generates 5.6 pounds per foot
while the 18 x 8 duct generates 6.06 pounds per foot
An increase of 8%!
Air Distribution System
Water-source heat pump systems that use horizontal, vertical, rooftop, and sometimes vertical-stack configurations, typically include a supply-duct system to transport the air from the heat pump, through the diffusers, and into the space. A successful supply duct design achieves the following:
Minimizes the static pressure and associated power requirements of the fan
Limits the installed cost without sacrificing system efficiency
Supplies the proper quantity of air to the space without excessive noise
Accommodates space limitations without excessive pressure drop
Minimizes design time
Figure 33 is an example of a horizontal water-source heat pump installed in the ceiling plenum above a space. These particular supply and return duct systems are designed to minimize the noise transmitted to the space. Acoustics is a primary consideration in the design and layout of any air distribution system. This issue will be discussed further in Period Six.