Objectives Duct Design AND Diffuser Selection DOAS System

Objectives • Duct Design AND Diffuser Selection

DOAS System • www. doas. psu. edu

DOAS with multi-split systems » Fresh air?

DOAS fresh air configurations

Issues Related to DOAS • Split of sensible and latent load • Selection of hydronic system • Winter vs. summer operation • Winter operation with DX systems (heat pump)

Pressures • Static pressure • Velocity pressure • Total pressure – sum of the two above

Relationship Between Static and Total Pressure

Duct Design • Total and static pressure drops are proportional to square of velocity • Plot of pressure drop vs. volumetric flow rate (or velocity) is called system characteristic

System Characteristic

Electrical Resistance Analogy

Frictional Losses

Non-circular Ducts • Parallel concept to wetted perimeter

Dynamic losses • Losses associated with • • Changes in velocity Obstructions Bends Fittings and transitions • Two methods • Equivalent length and loss coefficients

» ΔPt = Co. Pv, 0 Loss Coefficients

Example 18. 7 • Determine total pressure drop from 0 to 4

Conversion Between Methods

Air Distribution System Design • Describe room distribution basics • Select diffusers • Supply and return duct sizing

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

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

Diffusers » Perforated ceiling diffuser » Wall diffuser unit » Linear slot diffuser » Jet nozzle diffuser » Swirl diffuser » DV diffuser » Round conical ceiling diffuser » Floor diffuser » External louvre » http: //www. titus-hvac. com/techzone/ » http: //www. halton. com/halton/cms. nsf/www/diffusers » Square conical ceiling diffuser » Auditorium diffuser » Smoke damper

Low mixing Diffusers Displacement ventilation

Reading asignement • Chapter 18 • 18. 1 -18. 4 (including 18. 4)