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

AbstractEarlier 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.

Air conditioning ductsThe 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

WORKING PRINCIPLES OF DUCTS

Ductwork ConsiderationsShapeSizeAspect ratioVelocityStatic Pressure

MaterialsSheet metal (by gauge) Galvanized Iron AluminumFlexible Insulated Tube (socks)

01

01

01

02

02

03

04

04

05

05

05

06

Shape and Size

Round

Oval

Rectangular

RectangularLower 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

Air Distribution Systems

Three Types Above Ceiling Displacement Under floor

Services Supply air Return air Ventilation air Relief air Exhaust air

Above Ceiling Distribution System

horizontalhorizontalheat pumpheat pump

supplysupplyductduct

returnreturnductduct

diffuserdiffuser

return airreturn airgrillegrille

Other Design Considerations

Thermal massNatural lightSolar shadingControl strategiesLife safety issuesInfiltration

Mixed Air conditionsEnergy in the airComfort level of the airThe amount of water in the air

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.

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

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 increase the pressure loss.