Objectives
• Finish with Duct Design
• Review the design procedure and explain the
theoretical background
• Diffuser Selection
• Answer question related to the exam
Frictional Losses
Dynamic losses
• Losses associated with
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Changes in velocity
Obstructions
Bends
Fittings and transitions
• Two methods
• Equivalent length and loss coefficients
System Characteristic
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
Diffuser Selection Procedure


Q
Q
V  tot  sen
Δh Δt
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)
• Select and locate diffusers, divide airflow
amongst diffusers
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
1)
2)
3)
4)
5)
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
Reading asignement
• Chapter 18
• 18.1-18.4 (including 18.4)
Review for the Exam
• Should be able to do all calculations associated
with lectures as well as HWs (except HW4b)
• Questions/problems may deal with context
• i.e. Explain how thermal conductivity influences fin
efficiency? Holding all other parameters equal, how
important is increasing the thermal conductivity?...
Psychrometrics and Processes (7 & 8)
• Know all parameters and their
location/orientation on a psychrometric chart
• Be able to look up conversions of parameters
on a psychrometric chart and with calculations
• Use protractor to calculate SHR and ΔW/Δh
• Plot processes on a chart for real buildings
• List what is held constant for different processes
• Everything we talked about AHU and
distribution: VAV, CAV , Dual Duct, Fan-coil,
Heat recovery, …
Direct Contact (10)
• Describe how a cooling tower works
• How evaporative cooler works
• Understand the Psychrometrics of chapter 10
…..
Cycles (3), Refrigerants (4)
• Describe Carnot cycle and components
• Understand constant variables for each component
• List, describe, and calculate (in)efficiencies
• Use figures, refrigerant tables and equations
for different substances
• List important parameters for refrigerant
selection/differentiation
Heat Exchangers (11)
• Differentiate types
• Calculate NTU, ε, cr, R, P, F, m, UA, etc.
• Broad analysis
• Which m is larger, which Δt is larger?
• Within and between heat exchangers
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Calculate and compare different thermal resistances
Describe influence of key factors
Integrate different parameters/resistances
Manipulate UA equation
Describe differences/parameters of relevance for wet
heat exchangers