Objectives

1
Objectives

• Analyze Rotary Heat Exchangers
• Use Psychometric chart
• - Start Air Distribution Systems
• - Diffuser selection

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Sensible and Enthalpy Wheels
http//doas-radiant.psu.edu/4428.pdf
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Example of Dual Wheel System
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Psychrometrics of sensible and enthalpy wheel
Example NMS Building HVAC system
Fans
Enthalpy wheel
Exhaust air
Sensible wheel
D
A
C
1
B
2
Return air form building
Fresh air
Filters
Hot and fresh air to building
Preheater
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6
5
3
4
Heating coil
Cooling coil
Cool and fresh air to building
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Air Distribution System Design

• Describe room distribution basics
• Select diffusers
• Supply and return duct sizing

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Designing Room Airflow

• Very complex problem
• Pumped flow, buoyant flow (or mixed flow)
• What non-dimensional parameters govern each
  regime?
• Archimedes number Ar gßL?T/v2

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Computational Fluid Dynamics
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CFD in Air Distribution Design
Contaminant concentration in a kitchen
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Buoyancy driven flowExample of airflow in a
stairway
Heater (radiator)
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Forced driven air flowDiffusers
Grill (side wall) diffusers
Linear diffusers
Vertical
Horizontal one side
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Diffusers types
Valve diffuser
swirl diffusers
ceiling diffuser
wall or ceiling
floor
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Low mixing Diffusers Displacement ventilation
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18.7
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Diffuser Selection Procedure

• Select and locate diffusers, divide airflow
  amongst diffusers

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Find Characteristic Length (L)
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Indicator of Air DistributionQuality

• ADPI air distribution performance index
• Fraction of locations that meet criteria
• -3 F lt EDT lt 2 F or -1.5 C lt EDT lt 1 C
• Where, EDT effective draft temperature
• Function of V and ?t (Eqn 18.1)
• EDT(tlocal-taverage)-M(Vlocal-Vaverage) ,
  M7 C/(m/s)
• ADPI considers ONLY thermal comfort (not IAQ)

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Ideal and Reasonable Throws
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Select Register

• Pick throw, volumetric flow from register catalog
• Check noise, pressure drop

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Summary of Diffuser Design Procedure

1. Find Q sensible total for the space
2. Select type and number of diffusers
3. Find V for each diffuser
4. Find characteristic length
5. Select the diffuser from the manufacturer data

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Example 18.3

• Qtot 38.4 kBTU/hr
• ?h 9.5 BTU/lbma

Note omission in text
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Reading asignement

• Chapter 18
• 18.1-18.2 (including 18.2)