Lecture objectives
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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 )

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Lecture Objectives

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Lecture objectives

Lecture Objectives

  • Ventilation Effectiveness

  • Thermal Comfort

  • Meshing


Iaq parameters

IAQ parameters

  • Age-of-air

    air-change effectiveness (EV)

  • Specific Contaminant Concentration

    contaminant removal effectiveness e


Single value iaq indicators e v and

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


Air change efficiency e v

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

Air-change efficiency (Ev)


Air exchange efficiency for characteristic room ventilation flow types

Air exchange efficiency for characteristic room ventilation flow types


Contaminant removal effectiveness e

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?


Differences and similarities of e v and e

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

Thermal comfort

Temperature and relative humidity


Thermal comfort1

Thermal comfort

Velocity

Can create draft

Draft is related to air temperature,

air velocity, and turbulence intensity.


Thermal comfort2

Thermal comfort

Mean radiant

temperature

potential problems

Asymmetry

Warm ceiling (----)

Cool wall (---)

Cool ceiling (--)

Warm wall (-)


Prediction of thermal comfort

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


Meshing project 1

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

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 resolution hexa

Grid type and resolutionhexa

Unstructured hexa (2-D)

Uniform

boundary-fitted, structured grid

Nonuniform (2-D)


Grid type and resolution tetra

Grid type and resolutionTetra

Structured

Unstructured


Grid type and resolution polyhedral mesh

Grid type and resolutionPolyhedral mesh


Computational resource saving by mesh type

Computational resource saving by mesh type


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