Objectives Finish with Duct Design Diffuser Selection 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 Describe room distribution basics Select diffusers Supply and return duct sizing

Forced driven air flow Diffusers Grill (side wall) diffusers Linear diffusers Vertical Horizontal one side

Diffusers types Valve diffuser swirl diffusers ceiling diffuser wall or ceiling floor

Diffusers http://www.titus-hvac.com/techzone/ 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

Diffuser Selection Procedure Select and locate diffusers, divide airflow amongst diffusers 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)

Find Characteristic Length (L)

Indicator of Air Distribution Quality 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

Diffuser testing

ADPI

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 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 Total pressure rise Static pressure rise Power requirement Efficiency Note ηtot does not account for motor efficiency

Balance Point

Fan Performance

Centrifugal fans

Axial Fans

Fan Laws “Approximate relationships” Given two aerodynamically similar fans, can extrapolate performance data Be very careful