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Lecture Objectives

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- Ventilation Effectiveness
- Thermal Comfort
- Meshing

- Age-of-air
air-change effectiveness (EV)

- Specific Contaminant Concentration
contaminant removal effectiveness e

- 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

- 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

Depending on the

source position:

- similar or

- completely different

air quality

Temperature and relative humidity

Velocity

Can create draft

Draft is related to air temperature,

air velocity, and turbulence intensity.

Mean radiant

temperature

potential problems

Asymmetry

Warm ceiling (----)

Cool wall (---)

Cool ceiling (--)

Warm wall (-)

- 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

Pat a) Numerical diffusion

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

the accuracy of result.

Hexa

- Uniform hexa
- Nonuniform hexa
- Unstructured hexa
Body-fitted coordinate hexa

- Structured

- Unstructured
Tetra mesh

- Structured
- Unstructured
Polyhedral mesh

Unstructured hexa (2-D)

Uniform

boundary-fitted, structured grid

Nonuniform (2-D)

Structured

Unstructured