Objectives
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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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Objectives

Objectives

  • Finish with Duct Design

    • Review the design procedure and explain the theoretical background

  • Diffuser Selection


Frictional losses

Frictional Losses


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


Find characteristic length l

Find Characteristic Length (L)


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)


Ideal and reasonable throws

Ideal and Reasonable Throws


Diffuser testing

Diffuser testing


Objectives

ADPI


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


Objectives

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


Balance point

Balance Point


Fan performance

Fan Performance


Centrifugal fans

Centrifugal fans


Axial fans

Axial Fans


Fan laws

Fan Laws

  • “Approximate relationships”

  • Given two aerodynamically similar fans, can extrapolate performance data

  • Be very careful


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