351_Air Distribution System

7/27/2019 351_Air Distribution System

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Air Distribution System

PM Muhammad Abd Razak

FKM UiTMPP



AIR CONDITIONING

• Achieving desirable temperature.• Achieving desirable humidity.

• Supply the right amount of conditioned air

• Provides air movement.• to properly distribute conditioned air within the

space.

WHAT IS ACCEPTABLE AIR DISTRIBUTION ?• “pulling” of room air by the supply air due to the

temperature difference in the region outside the

occupied zone.• No excessive draft (air motion) to users.

• No excessive room air temperature distribution.

• No excessive fluctuation room temperature, air motion and noise.



Ts=55.4 F / 13 C

SA

Mixing Zone

Occupied Zone

62.6 F

73.4 F

TR=77F / 25C







TERMINOLOGIES

Diffusion: Rapid mixing of supply air with the roomair.

Diffusion temperature: Supply air to space air

temperature differenceEg. SA= 13°C / 55.45°F

RA= 25°C / 75°F

TD= 12°C / 21.6°FInduction / “Entrainment”: “pulling” of room air to

cause mixing, due to temperature difference

Throw / blow: The horizontal distance to SA travels

before reaching its “terminal” velocity. Maximum

throw distance is 10ft. Also known as Radius of

Diffusion.



Diffuser:The supply outlet of SA. Symbol

- square (2’x2’, rooms / halls)- round (nice looking, difficult to install)

- slot/linear (hotel ball rooms)

- grilles(rectangular, provide double deflections)

Grille: The return air inlet(rectangular, square).

Normally situated in the

stagment zones (roomcorner or end)



square round swiral

linear / slot

(ceiling mounted)volume control

damper

double grille

(wall mounted)



What types to use, where to place depends how

many to use on:• Architectural requirement / aesthetic - depending on

type of usage and taste of user- (hotel ?,

rooms/halls ?, supermarkets ?)• Structural requirement: building structure behind;

walls, ceiling or floors will resist ductworks.

• Locations; obstructions from:beams, fire fighting

pipes, electrical points etc

• Diffusion temperature difference : higher location

needs bigger ∆TD and CFM

• Quantity: it is good to have many but acceptable if noise is not a factor.

• Size of diffuser / grilles



Determining the required air quantity (CFM) for each room.

V (CFM) = ________ RSH__________

1.09 x ∆T diffusion (°F)

Or

= _______ RSH__________

1.2 x ∆T diffusion (°C)

Or by Rules of Thumb, (ROT)

= _RSH_ x 50012 x 103



Good air distribution:

• Should be able to counteract all convection,radiation and conduction effects related to the

room.

• Low noise level at supply (diffuser). eg: for residence 400 - 700 CFM.

• Return grille not located where by-passing of

supply air can occur. (Short circuiting)

• Adequate return grilles to avoid hissing noise. (due

to suction force)

• Avoid excessive throw near walls to prevent

bouncing and creating draft.• Diffusers with adjusting features (for balancing of

flow)

• Row of diffusers may be located closer to theoutside wall to compensate extra heat load.

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351_Air Distribution System