Lecture Objectives
• Answer your questions related to CFD
software
• Ventilation Effectiveness
• Thermal Comfort
IAQ parameters
Number of ACH
quantitative indicator
ACH - for total air
- for fresh air
Ventilation effectiveness
qualitative indicator
takes into account air distribution in the space
Exposure
qualitative indicator
takes into account air distribution and source position
and intensity
IAQ parameters
- Age-of-air
air-change effectiveness (EV)
- Specific Contaminant Concentration
contaminant removal effectiveness e
Single value IAQ indicators
Ev and ε
1. Contaminant removal effectiveness (e)
Ce
concentration at exhaust
ε
average contaminant concentration
 C
Contamination level
2. Air-change efficiency (Ev)
τn
Ev 
2 τ
shortest time for replacing the air
average of local values of age of air
Air freshness
τn  1 / ACS [sec]
Air-change efficiency (Ev)
• Depends only on airflow pattern in a room
• We need to calculate age of air (t)
τ
τ
t
t
 2t
 2t
 2t
   (Vx  Vy
 Vz )  (  t ) 2  (  t ) 2  (  t ) 2  
t
x
y
z
x
y
z
Average time of exchange
τexe  2 τ,
τn  1 / ACH [sec]
• 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 exchange efficiency for characteristic
room ventilation flow types
Flow pattern
Unidirectional flow
Perfect mixing
Short Circuiting
Air-change Comparison with average
efficiency
time of exchange
1-2
1
0-1
tn < texc < 2tn
texc = tn
texc > tn
τexe  2 τ
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 Ev and e
Depending on the
source position:
- similar or
- completely different
air quality
Ev = 0.41
e = 0.19
e = 2.20
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
Mean radiant
temperature
potential problems
Asymmetry
Warm ceiling (----)
Cool wall (---)
Cool ceiling (--)
Warm wall (-)
Prediction of thermal comfort

Predicted Mean Vote (PMV)
PMV
=
+3
+2
+1
0
-1
-2
-3
hot
warm
slightly warm
neutral
slightly cool
cool
cold
PMV = [0.303 exp ( -0.036 M ) + 0.028 ] L
L - Thermal load on the body
Empirical correlations
Ole Fanger
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)]
Further Details: ANSI/ASHRAE standard 55, ISO standard 7730