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Tr inin
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Natural VentilationDriven by
uoyancy ec
Wind
na ys s oo s
Airflow Network models Fi ure Source: J Good et al, SimBuild 2008
Computational Fluid Dynamic (CFD)
n unne stu y measurement
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Airflow Network Model Developed by NIST (Walton 1989)
oup e o
Bulk airflow movement, avera e tem eratures
Nodes connected by air flow elements
n ressure oe c ent p va ues nee to
be defined Input/Auto
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Airflow Network Model..contdCp determination
epen s on u s ape, w n rec on, near y
buildings, vegetation, terrain etc.
Can be only obtained from Wind tunnel test
ASHREA handbook of fundamentals Restricted to low rise rectangular buildings
=2
w . . . p. z
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Airflow Network Model..contd
CP Values : Source: ASHRAE handbook of
fundamentals, 2005 pp 16.5
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AIRNET Model.. contd
Plan view of a simple airflow network showing a possible airflow pattern
Source: Lixing Gu , roceedings: Building Simulation 2007
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2 Modes
DesignBuilder offers 2 Nat vent modes: Scheduled
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Scheduled Nat Vent
Infiltration is constant.
Interior airflow through mixing
Avoidance of heating
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Basic Scheduled natural ventilation model
Controlled Natural ventilation
Infiltration
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Same as first but with Internal Airflow
Check change in results
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Calculated Natural ventilation:
Set window opening % + schedule
Infiltration
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Tutorial 4As previous but with variations:
,
Wind effects
Internal vent airflow
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analytical procedure to predict the flow of
u s a r, wa er e c.
Develo ed for the aerod namics industr as a
faster alternative to wind tunnel testing
temperature, velocity, direction of flow,pressure an energy momentum o a u
particle in the solution domain
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Focus: Incompressible fluids
Continuity and Momentum Equations
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Methods based on the vorticity equation
Methods that use pressure iterations or
pressure correct on. Fract ona - StepMethods SIMPLE SIMPLERSIMPLEST, PISO etc.)
Semi Implicit Method for Pressure Linked Equation Revised
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What can we use CFD for?Architectural Applications
Airflow in and around buildings
onvect ve an ra at on eat trans er amongbuilding components effectiveness of radiant
eat ng an coo ng systems.
Natural Ventilation Design Displacement Ventilation design
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DesignBuilder CFD
Distribution of air temperature, velocity etc Internal and External Analyses
Calculations
Boundary conditions
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reate a ra ator component
Convert the component to an assembly Assign CFD boundary conditions to the assembly
Add assembly to the assembly library.
Place radiator assembly x 2 E i FD ri
Add cell monitor points
.
Comfort calculations.
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Create model for external analysis.
Perform the CFD calculation
Review the results