Objectives Discuss Rotary Heat Exchangers In Psychometric Chart Learn about Specifics of VAV and DOAS Systems Start with Duct Design

Sensible and Enthalpy wheels

VAV Example One system Multiple Spaces/Zones - VAV box for each space/zone http://www.trane.com/commercial/library/vol242/v24b6.asp

VAV System Terms & Equations (you can find them in ASHRAE Standard 62) Fraction of minimum outdoor air in space/zone supply air Xi = VOAi / VSAi Critical space Space with maximum Xi , Z=max(Xi) Fraction of outdoor air in system supply air X = sum(VOA ) / sum(VSA) Required Fraction of outdoor air: Y=X/(1+X-Z)

Other Issues Related to VAV Reheaters (sizing and control) Fan control Minimum supply air Occupancy sensors

DOAS System www.doas.psu.edu

DOAS with multi-split systems Fresh air?

DOAS fresh air configurations

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 Two methods Changes in velocity Obstructions Bends Fittings and transitions Two methods Equivalent length and loss coefficients

Loss Coefficients ΔPt = CoPv,0

Example 18.7 Determine total pressure drop from 0 to 4

Conversion Between Methods

Reading asignement Chapter 18 18.1-18.4 (including 18.4)