Fundamentals Basic Selection and Application

8/16/2019 Fundamentals Basic Selection and Application

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Basic Selection & Proper Application

of Overhead Air Distribution Devices


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GRD Selection & Application

• Terms

• Selection

– Throw – Sound

• Installation Variations affect Performance

• Inlet Effects


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Basics

Coanda

Total

Air

Primary Air

Induced

Room Air

Entrained

Room Air

Return Air


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Basics

• ASHRAE Standard 70-2006

– Standard Defines Testing Procedures,

Spaces, and Equipment

– Isothermal Testing

– Non-Turbulent, Smooth Inlet Conditions

– Obtain Catalog Data


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Selection – Throw

1) Throw – Distance to a specified Vt

2) Terminal Velocity (Vt) – Maximum

airstream velocity at the end of a throw.

50 fpm TV

100 fpm TV150 fpm TV


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Selection – Throw

• Outlet Patterns – 150 cfm – 6” Inlet

Plaque- 6’

Slot - 19’ Slot - 29’

Perf - 10’Louver

Face - 16’


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Selection – Throw

• 380 cfm, 10” Neck, 700 fpm, T50

10‟ Square Cone

9‟ Round Cone

14‟ 4 Way - Perf Curved Vane

33‟ 1 Way - Perf Curved Vane

24‟ 4 Way - Louver Face


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Selection – Throw

• Deflection and Spread


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Selection – Throw

• Throw Boundaries – Mapping

Vt Maximum of 75 fpm


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Selection – Throw

• Occupied Zone


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Selection – Throw

• Generally:Throw (Vt at 50 fpm) = Distance to Boundary


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Selection – Throw

• Non-Isothermal Effects

Adjust Throw at V t = 50 fpm

1% Per° F of Differential

Cooling Heating

Horizontal – +

Vertical + –


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Selection – Throw

• Obstructions

– Air jet will typically remain on surface, if angle

created by the ceiling, diffuser, and bottom of

obstruction is


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Selection – Sound

• Catalog Data

– NC Rating

• Average Room Size

• Distance from Source

– Assumes 10 dB Room Absorption

– Single Diffuser or Standard Length


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Selection – Sound


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Selection – Sound


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Selection – Sound


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24” x 24” Diffuser, 380cfm, 700 fpm Neck Velocity

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Selection – Sound


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NC 45

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Selection – Sound

NC 37

NC 36NC 31

1 - 1”Slot, 4‟, 270cfm, 800 fpm Neck Velocity


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Installation – Sound


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Damper Location

Pressure Ratio = 2

(normal pressure

drop X 2)

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Installation – Sound

0 dB

+ 3 dB

+ 9 dB


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Inlet Effects


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ASHRAE Standard 70 – Throw Room

• Measurements taken in a „Standard Test Room‟

– Height => 9‟

– Minimum Length = 24‟

– Minimum Width = 18‟

– All lights and windows shall be flush to the surface they

are attached.

– Air exhausted away from supply path.


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• 2 Different Types of Test Ducts

– Large Pressurized plenum

– 3 Diameters Straight duct• Air outlet device is to receive uniformly

distributed air from the supply duct.

ASHRAE Standard 70 – Inlet Conditions


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Effect of Inlet Conditions on Throw

• Test Standard Installation

– Repeatable, uniform throw distances

– Repeatable, drop

– Repeatable, discharge pattern

• Hard 90 Degree Elbow

• Flex Duct 90 Degree Elbow

• Radial Opposed Blade Damper • Butterfly Damper

• Bowtie Damper


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A “Special” Field Installation


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More Poor Workmanship Examples


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Louver Face Ceiling Diffuser


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Louver Face Ceiling Diffuser - Hard 90 Degree Elbow

350 CFM


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Louver Face Ceiling Diffuser - Flex Duct 90 Degree Elbow

350 CFM


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AHHHH!! FLEX MONSTER!!



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Louver Face Ceiling Diffuser - Radial Opposed Blade Damper

350 CFM – Damper set for 0.25 inches of water



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Louver Face Ceiling Diffuser -Butterfly Damper


L F C ili Diff


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Louver Face Ceiling Diffuser -Bowtie Damper



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More Poor Workmanship Examples


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Plaque Ceiling Diffuser

C ff


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Pl C ili Diff


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Plaque Ceiling Diffuser - Test Standard Installation

350 CFM



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Plaque Ceiling Diffuser - Hard 90 Degree Elbow

350 CFM


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Plaque Ceiling Diffuser - Radial Opposed Blade Damper




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Plaque Ceiling Diffuser - Butterfly Damper




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Plaque Ceiling Diffuser - Bowtie Damper



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Ceiling Slot Diffuser

Square Plenum

Sloped Plenum


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- Test Standard Installation

350 CFM with straight plenum

350 CFM with sloped plenum


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g- Flex Duct 90 Degree Elbow

350 CFM with straight plenum




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Ceiling Slot Diffuser- Radial Opposed Blade Damper

350 CFM with straight plenum (dpr set to .25inWC)


(dpr set to .25inWC)


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C ili Sl t Diff


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Ceiling Slot Diffuser- Bowtie Damper

350 CFM with straight plenum (dpr set to .25inWC)

350 CFM with sloped plenum(dpr set to .25inWC)

W k hi C t !


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Workmanship Counts!


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Sidewall Grille Video (12X6)


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Sidewall Grille Video (12X6)

0 Dia 1 Dia

2 Dia 3 Dia


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GRD Selection & Application

• Terms

• Selection

– Throw

– Sound

• Installation Variations affect Performance

• Inlet Effects

Fundamentals Basic Selection and Application

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