Objectives

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Objectives

• Finish with Duct Design
• Review the design procedure and explain the
  theoretical background
• Diffuser Selection

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Frictional Losses
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Dynamic losses

• Losses associated with
• Changes in velocity
• Obstructions
• Bends
• Fittings and transitions

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Air Distribution System Design

• Describe room distribution basics
• Select diffusers
• Supply and return duct sizing

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Forced driven air flowDiffusers

• Grill (side wall)
• diffusers

• Linear diffusers

• Vertical

• Horizontal one side

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Diffusers types

• Valve diffuser

• swirl diffusers

• ceiling diffuser

• wall or ceiling

• floor

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Diffusers

• Perforated ceiling diffuser

• Jet nozzle diffuser

• Round conical ceiling diffuser

• Square conical ceiling diffuser

• Wall diffuser unit

• Swirl diffuser

• Floor diffuser

• Auditorium diffuser

• Linear slot diffuser

• DV diffuser

• External louvre

• Smoke damper

• http//www.titus-hvac.com/techzone/

• http//www.halton.com/halton/cms.nsf/www/diffusers
  

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Low mixing Diffusers Displacement ventilation
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Diffuser Selection Procedure

• Select and locate diffusers, divide airflow
  amongst diffusers

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Find Characteristic Length (L)
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Indicator of Air DistributionQuality

• ADPI air distribution performance index
• Fraction of locations that meet criteria
• -3 F lt EDT lt 2 F or -1.5 C lt EDT lt 1 C
• Where, EDT effective draft temperature
• Function of V and ?t (Eqn 18.1)
• EDT(tlocal-taverage)-M(Vlocal-Vaverage) ,
  M7 C/(m/s)
• ADPI considers ONLY thermal comfort (not IAQ)

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Ideal and Reasonable Throws
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Diffuser testing
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ADPI
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Select Register

• Pick throw, volumetric flow from register catalog
• Check noise, pressure drop

http//www.titus-hvac.com/ecatalog/subcategory.asp
x?refid186 http//www.nailor.com/ http//www.pric
e-hvac.com/
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Summary of Diffuser Design Procedure

1. Find Q sensible total for the space
2. Select type and number of diffusers
3. Find V for each diffuser
4. Find characteristic length
5. Select the diffuser from the manufacturer data

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Fans

• Driving force to move air in buildings
• Raise pressure and produce flow
• Two main types
• Centrifugal
• Axial

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Relevant Fan Parameters

• Total pressure rise
• Static pressure rise
• Power requirement
• Efficiency
• Note ?tot does not account for motor efficiency

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Balance Point
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Fan Performance
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Centrifugal fans
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Axial Fans
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Fan Laws

• Approximate relationships
• Given two aerodynamically similar fans, can
  extrapolate performance data
• Be very careful