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Objectives. Finish with Duct Design Review the design procedure and explain the theoretical background Diffuser Selection. Frictional Losses. Dynamic losses. Losses associated with Changes in velocity Obstructions Bends Fittings and transitions. Air Distribution System Design.

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Presentation Transcript
Objectives
Objectives

  • Finish with Duct Design

    • Review the design procedure and explain the theoretical background

  • Diffuser Selection



Dynamic losses
Dynamic losses

  • Losses associated with

    • Changes in velocity

    • Obstructions

    • Bends

    • Fittings and transitions


Air distribution system design
Air Distribution System Design

  • Describe room distribution basics

  • Select diffusers

  • Supply and return duct sizing


Forced driven air flow diffusers
Forced driven air flowDiffusers

  • Grill (side wall)

  • diffusers

  • Linear diffusers

  • Vertical

  • Horizontal one side


Diffusers types
Diffusers types

  • Valve diffuser

  • swirl diffusers

  • ceiling diffuser

  • wall or ceiling

  • floor


Diffusers
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


Low mixing diffusers displacement ventilation
Low mixing Diffusers Displacement ventilation


Diffuser selection procedure

V = maximum volumetric flow rate (m3/s, ft3/min)

Qtot = total design load (W, BTU/hr)

Qsen = sensible design load (W,BTU/hr)

ρ = air density (kg/m3, lbm/ft3)

Δt = temperature difference between supply and return air (°C, °F)

Δh = enthalpy difference between supply and return air (J/kg, BTU/lbm)

Diffuser Selection Procedure

  • Select and locate diffusers, divide airflow amongst diffusers



Indicator of air distribution quality
Indicator of Air DistributionQuality

  • ADPI = air distribution performance index

  • Fraction of locations that meet criteria:

    • -3 °F < EDT < 2 °F or -1.5 °C < EDT < 1 °C

    • Where, EDT = effective draft temperature

      • Function of V and Δt (Eqn 18.1)

      • EDT=(tlocal-taverage)-M(Vlocal-Vaverage) , M=7 °C/(m/s)

        ADPI considers ONLY thermal comfort (not IAQ)





Select register
Select Register

  • Pick throw, volumetric flow from register catalog

  • Check noise, pressure drop

http://www.titus-hvac.com/ecatalog/subcategory.aspx?refid=186

http://www.nailor.com/

http://www.price-hvac.com/


Summary of diffuser design procedure
Summary of Diffuser Design Procedure

  • Find Q sensible total for the space

  • Select type and number of diffusers

  • Find V for each diffuser

  • Find characteristic length

  • Select the diffuser from the manufacturer data


Fans

  • Driving force to move air in buildings

  • Raise pressure and produce flow

  • Two main types:

    • Centrifugal

    • Axial


Relevant fan parameters
Relevant Fan Parameters

  • Total pressure rise

  • Static pressure rise

  • Power requirement

  • Efficiency

  • Note ηtot does not account for motor efficiency






Fan laws
Fan Laws

  • “Approximate relationships”

  • Given two aerodynamically similar fans, can extrapolate performance data

  • Be very careful


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