1 Application of for Predicting Indoor Airflow and Thermal Comfort.
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Transcript of 1 Application of for Predicting Indoor Airflow and Thermal Comfort.
1
Application of for Predicting Indoor Airflow and
Thermal Comfort
2
Preview
• Introduction
• CFD Theory
• Thermal Comfort
• Airpak
• Case Study
• Future Works
3
Introduction
• Indoor environment design and assessment
Airflow pattern, velocity, temperature, and contaminant
concentration
• Indoor energy analysis
Energy programs: uniform distribution of air temperature
Complication: forced ventilation and natural ventilation
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Introduction
• Experimental measurements and computational
simulations
Advantages: Low cost, high speed, complete information, ability to simulate realistic conditions and ideal conditions.
Disadvantages: fast computer with a large memory
• Computational Fluid Dynamics (CFD)
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Ventilation CFD Model
Sxx
uxt jj
jj
1
ju
T
C
Mass continuity
Momentum (u, v, w)
Temperature
Species
The Navier-Stokes equations
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Viscosity Models
• Laminar flow (Re < 2500)
• Turbulent flow (Re>= 2500)
k Model Standard
k Model RNG
Mixing-length model
Indoor zero-equation model
Com
putin
g tim
e
Low
High
Acc
urac
y
Low
High
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CFD Elements
Mathematical Description of the Problem of Interest
Flux Laws Conservation Principles Mathematical Models
Numerical Method
Computer Programs
Numerical Predictions
Post Processing Tools
Interpretation
Grid or Mesh Generation
Methods
Problem Parameters
Finite Volume Formulations
Finite Element Formulations
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Thermal Comfort
ASHRAE thermal sensation scale:
+ 3 Hot
+ 2 Warm
+ 1 Slightly Warm
0 Neutral
- 1 Slightly Cold
- 2 Cool
- 3 Cold
ASHRAE Summer and Winter Comfort Zone:
winter summer
Hu
mid
ity r
atio
, g/k
g
De
w p
oin
t te
mp
era
ture
0C
Operative temperature(ASHRAE standard 55)
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PMV (Predicted Mean Vote)
PPD (Predicted Percentage of Dissatisfied)
PMV
-0.5 0.5
10
20
PP
D
%
-0.8 0 0.8
5
-1.5-2.0 1.5 2.0
30
50
80
(ASHRAE Fundamental, 2001)
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1. Airflow patterns
2. Air turbulence
3. Contaminant transport
4. Temperature and humidity distribution
5. Thermal comfort
6. Room pressurization
7. Equipment effects
8. Process exhaust
Is a virtual prototyping CFD
software that lets you
evaluate and understand
your ventilation system
performance.
FLUENT
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1. Building Objects
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2.Physical Modeling and Boundary Conditions
Steady or Transient ?
Laminar or Turbulent ?
Solving variables?
Physical models?
Initial conditions?
Boundary Conditions?
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3. Meshing
Mesh quality is important!!!Generate first mesh
Examine the mesh
Re-examine the mesh
1. Flow objects
2. Local mesh control
3. Object-specific meshing control
Refine the mesh
Generate new mesh
Solve
OK
No
1. Aspect ratio
2. Face alignment
3. Volume
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4. Solving the Problem
1. Maximum number of iterations
2. Convergence criteria
3. Discretization scheme
4. Under-relaxation factors
Setup:
1. Accuracy of physical models
2. Accuracy of boundary conditions
3. Accuracy of the modeling assumptions
4. Numerical scheme
5. Resolution of mesh
Accuracy depends on:
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Case study
Ben
Edward
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Case study (a)Computer
108 w
People73 w
Induction Unit40 L/s, 21 0C
Light120 w
53 L/s, 15.8 0C
12 L/s
23 L/s
28 L/s
Outlet vent
Ben
04/06/2003
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Temperature 04/06/2003,Cooling
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Sensor 3
Sensor 4
Sensor 1
Sensor 2
x
z
Temperature Validation
Ben
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21
22
23
24
25
0 1 2 3 4 5Point
Te
mp
era
ture
Measured Data Predicted Data
5%
2% 4%
6%
Sensor04/06/2003
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Clothing Value (clo) Metabolic Rate (met) Relative Humidity Rad Temperature Air Velocity Air Temperature1 1.2 40% Compute Compute Compute
PMV
Y =
1.1
m
x
z
Ben
04/06/2003
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Airflow
Ben
04/06/2003
21
z
y
Airflow
BenEd
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x
y
Airflow
Ed
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Case study (b)
24Slot diffuser
Nozzle diffuser
Temperature Comparison
25Slot diffuser
Nozzle diffuser
Airflow Comparison
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PMV Comparison
Slot diffuser
Y =
1.1
mx
z
Nozzle diffuser
Ben
Ben
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Next!
Displacement ventilation
www.rehva.com
Mixing ventilation
www.haltoncompany.com
Underfloor ventilation
www.york.com
Occupied Zone
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Recommendations for future works
Energy Simulation Program
$ $$$$$$$
$ $$$$$$$
$ $$$$$$$
$ $$$$$$$
$ $$$$$$$
$ $$$$$$$
$ $$$$$$$
+
$ $$$$$$$
$ $$$$$$$
$ $$$$$$$
$ $$$$$$$
$$$$$$$ $$$$$$$
$$$$$$$$=
1. Cost Analysis
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Recommendations for future works2. Office Space Template
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Personal Inlet Diffuser
Personal Inlet DiffuserOutlet
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• Airflow • Temperature• Relative Humidity• Indoor Air Quality• Thermal Comfort
Energy Simulation Program
$ $ $
Cost Analysis
A tool to assist Real Property Operations
in improving the quality of indoor office environments and
reducing energy waste.
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Thanks!