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Application of for Predicting Indoor Airflow and

Thermal Comfort

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Preview

• Introduction

• CFD Theory

• Thermal Comfort

• Airpak

• Case Study

• Future Works

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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!