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Lecture Objectives. Addres your questions related to Project 1 Define parameters for Thermal Comfort and Air Quality analyses in CFD. Thermal comfort. Temperature Relative humidity Air velocity Mean radiant temperature. Thermal comfort. Temperature and relative humidity. - PowerPoint PPT Presentation
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Addres your questions related to Project 1
Define parameters for • Thermal Comfort and • Air Quality analyses in CFD
Lecture Objectives
Thermal comfort
• Temperature
• Relative humidity
• Air velocity
• Mean radiant temperature
Thermal comfort
Temperature and relative humidity
Thermal comfort
VelocityCan create draft
Draft is related to air temperature, air velocity, and turbulence intensity.
Thermal comfort
Mean radianttemperature
potential problems
AsymmetryWarm ceiling (----)Cool wall (---)Cool ceiling (--)Warm wall (-)
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 ( -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
IAQ parametersNumber 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
Single value IAQ indicators Ev and ε
1.Contaminant removal effectiveness ()
concentration at exhaust average contaminant concentration
Contamination level
2. Air-change efficiency (v)
shortest time for replacing the air average of local values of age of air
Air freshness
C
Cε e
τ2
τEv n
[sec] ACS/1τn
Air-change efficiency (v)
• Depends only on airflow pattern in a room• We need to calculate age of air ()
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
2
2
2
2
2
2
z)(
y)(
x)()(
τtttzyx z
Vy
Vx
τV
[sec] ACH/1 τ,τ2τ nexe
Air exchange efficiency for characteristic room ventilation flow types
Flow patternAir-changeefficiency
Comparison with average time of exchange
Unidirectional flow 1 - 2 n < exc < 2n
Perfect mixing 1 exc = n
Short Circuiting 0 - 1 exc > n
τ2τexe
Contaminant removal effectiveness ()
• 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 Depending on the source position:
- similar or - completely different
air quality
v = 0.41
= 0.19 = 2.20