Objectives

1
Objectives

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

2
Sensible and Enthalpy wheels
3
VAV Example

• One system
• Multiple Spaces/Zones
• - VAV box for each space/zone

• http//www.trane.com/commercial/library/vol242/v24
  b6.asp

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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 , Zmax(Xi)
• Fraction of outdoor air in system supply air
• X sum(VOA ) / sum(VSA)
• Required Fraction of outdoor air
• YX/(1X-Z)

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Other Issues Related to VAV

• Reheaters (sizing and control)
• Fan control
• Minimum supply air
• Occupancy sensors

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DOAS System

• www.doas.psu.edu

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DOAS with multi-split systems

• Fresh air?

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DOAS fresh air configurations
9
DOAS fresh air configurations
10
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)

11
Pressures

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

12
Relationship Between Static and Total Pressure
13
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

14
System Characteristic
15
Electrical Resistance Analogy
16
Frictional Losses
17
Non-circular Ducts

• Parallel concept to wetted perimeter

18
Dynamic losses

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

19
Loss Coefficients

• ?Pt CoPv,0

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Example 18.7

• Determine total pressure drop from 0 to 4

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Conversion Between Methods
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Reading asignement

• Chapter 18
• 18.1-18.4 (including 18.4)