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# Lecture Objectives PowerPoint PPT Presentation

Lecture Objectives. Ventilation Effectiveness Thermal Comfort Meshing . IAQ parameters. Age-of-air air-change effectiveness (E V ) Specific Contaminant Concentration contaminant removal effectiveness e. Single value IAQ indicators E v and ε. Contaminant removal effectiveness ( e )

Lecture Objectives

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### Lecture Objectives

• Ventilation Effectiveness

• Thermal Comfort

• Meshing

### IAQ parameters

• Age-of-air

air-change effectiveness (EV)

• Specific Contaminant Concentration

contaminant removal effectiveness e

### Single valueIAQ indicatorsEv and ε

• Contaminant removal effectiveness (e)

• concentration at exhaust

• average contaminant concentration

Contamination level

• 2. Air-change efficiency (Ev)

• shortest time for replacing the air

• average of local values of age of air

Air freshness

Depends only on airflow pattern in a room

We need to calculate age of air (t)

Average time of exchange

What is the age of air at the exhaust?

Type of flow

Perfect mixing

Piston (unidirectional) flow

Flow with stagnation and short-circuiting flow

### Contaminant removal effectiveness (e)

• Depends on:

• position of a contaminant source

• Airflow in the room

• Questions

1) Is the concentration of pollutant in the room with stratified flow larger or smaller that the concentration with perfect mixing?

2) How to find the concentration at exhaust of the room?

Ev= 0.41

e= 0.19

e= 2.20

### Differences and similarities of Evande

Depending on the

source position:

- similar or

- completely different

air quality

### Thermal comfort

Temperature and relative humidity

### Thermal comfort

Velocity

Can create draft

Draft is related to air temperature,

air velocity, and turbulence intensity.

### Thermal comfort

temperature

potential problems

Asymmetry

Warm ceiling (----)

Cool wall (---)

Cool ceiling (--)

Warm wall (-)

### Prediction of thermal comfort

• Predicted Mean Vote (PMV)

• + 3hot

• + 2warm

• + 1slightly warm

• PMV =0neutral

• -1 slightly cool

• -2cool

• -3cold

• PMV = [0.303 exp ( -0.036 M ) + 0.028 ] L

• L - Thermal load on the body

• L = Internal heat production – heat loss to the actual environment

• L = M - W - [( Csk + Rsk + Esk ) + ( Cres + Eres )]

• Predicted Percentage Dissatisfied (PPD)

• PPD = 100 - 95 exp [ - (0.03353 PMV4 + 0.2179 PMV2)]

Empirical correlations

Ole Fanger

Further Details: ANSI/ASHRAE standard 55, ISO standard 7730

outlet

inlet

outlet

T1=30C

T1

inlet

outlet

inlet

T2

T2=20C

### Meshing (Project 1)

Pat a) Numerical diffusion

The purpose of this project part is to analyze how mesh size and orientation affects

the accuracy of result.

### Grid type and resolution

Hexa

• Uniform hexa

• Nonuniform hexa

• Unstructured hexa

Body-fitted coordinate hexa

- Structured

• Unstructured

Tetra mesh

• Structured

• Unstructured

Polyhedral mesh

### Grid type and resolutionhexa

Unstructured hexa (2-D)

Uniform

boundary-fitted, structured grid

Nonuniform (2-D)

Structured

Unstructured