1. Lecture Objectives
Ventilation Effectiveness
Thermal Comfort
Meshing

2. IAQ parameters Age-of-air air-change effectiveness (EV)
Specific Contaminant Concentration
contaminant removal effectiveness e

3. Single value IAQ indicators Ev 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

4. Air-change efficiency (Ev)
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

5. Air exchange efficiency for characteristic room ventilation flow types
Flow pattern
Air-change
efficiency
Comparison with average time of exchange
Unidirectional flow
1 - 2
tn < texc < 2tn
Perfect mixing 1
texc = tn
Short Circuiting
0 - 1
texc > tn

6. 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?

7. Differences and similarities of Ev and e
Depending on the
source position:
- similar or
- completely different
air quality
Ev = 0.41
e = 0.19
e = 2.20

8. Thermal comfort
Temperature and relative humidity

9. Thermal comfort Velocity Can create draft
Draft is related to air temperature,
air velocity, and turbulence intensity.

10. Thermal comfort Mean radiant temperature potential problems Asymmetry
Warm ceiling (----)
Cool wall (---)
Cool ceiling (--)
Warm wall (-)

11. Prediction of thermal comfort
Predicted Mean Vote (PMV)
+ 3 hot
+ 2 warm
+ 1 slightly warm
PMV = 0 neutral
-1 slightly cool
-2 cool
-3 cold
PMV = [0.303 exp ( M ) ] 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 = exp [ - ( PMV PMV2)]
Empirical correlations
Ole Fanger
Further Details: ANSI/ASHRAE standard 55, ISO standard 7730

12. 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.
outlet
inlet T1 T2
T1=30C
T2=20C
outlet
inlet

13. Grid type and resolution
Hexa
Uniform hexa
Nonuniform hexa
Unstructured hexa
Body-fitted coordinate hexa
- Structured
Unstructured
Tetra mesh
Structured
Polyhedral mesh

14. Grid type and resolution hexa
Unstructured hexa (2-D)
Uniform
boundary-fitted, structured grid
Nonuniform (2-D)

15. Grid type and resolution Tetra
Structured
Unstructured

16. Grid type and resolution Polyhedral mesh

17. Computational resource saving by mesh type