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Ventilation Effectiveness REHVA Guidebook no 2
AUTHORS •
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Elisabeth Mundt, Professor, KTHRoyal Institute of Technology, Stockholm, Sweden (editor) Hans Martin Mathisen, Ph.D., Sintef, Trondheim, Norway Peter V. Nielsen, Professor, Aalborg University, Denmark Alfred Moser, Ph.D., ETH, Zürich, Switzerland
CONTENTS 1.
VENT VENTIL ILA ATION TION EFFE EFFECT CTIV IVEN ENES ESS S IN IN A NUTS NUTSHE HELL LL (3 p)
2.
SYMBOLS AND TE TERMINOLOGY (4 (4 p)
3.
WHY WHY VE VENTILATION ION EFF EFFECTIVENESS (5 (5 p) p)
4.
TYPI TYPICA CAL L CO CONTA NTAMINA MINANT NTS S AND AND CONT CONTA AMINA MINANT NTS S DISTRIBUTION IN VENTILATED VENTILATED ROOMS (6 p)
5.
THEORY AND DE DEFINITIONS (8 p)
6.
MEASUREMENTS (12 p)
7.
PRED PREDIC ICTI TION ON OF AIR QUA QUALITY LITY BY COMP COMPUT UTA ATION TIONAL AL FLUI FLUID D DYNAMICS (4 p)
8.
CASE STUDIES (21 p)
9.
DEFI DEFINI NITI TION ONS S OF VENT VENTIL ILA ATION TION EFFE EFFECT CTIV IVEN ENES ESS S IN DIFFERENT COUNTRIES (1 p)
10.
APPENDIX 1 (1 p)
11.
REFERENCES (4 p) p)
VENTILATION EFFECTIVENESS includes
A Indices representing the ability of a system to exchange the air in the room
B Indices representing the ability of a system to remove air-borne contaminants
a
air change efficiency,
local air change index, P
a
contaminant removal c effectiveness (CRE), (CRE), c
local air quality index, P
INTRODUCTORY CHAPTERS 1. VENTI VENTILATI LATION ON EFFECTI EFFECTIVENES VENESS S IN IN A NUTS NUTSHELL HELL 2. SYM SYMBOL BOLS S AND AND TER TERMIN MINOLO OLOGY GY 3. WHY VENT VENTILA ILATIO TION N EFFECT EFFECTIVE IVENES NESS S Distributed source Q, mean concentration
Concentration field resulting from point source Q
ce
ce
a
c
c s
Distributed source Q
Point source Q
Keep concentration low
ce
a P
c s
ce
c P
Point sensor P P
Point sensor P
c s
Point source Q
c s
4 TYPICAL CONTAMINANTS AND CONTAMINANTS DISTRIBUTION IN VENTILATED ROOMS c P ce
Return opening
4
The location of a return opening may have a very large influence on the concentration distribution, although it only has a small influence on the velocity distribution.
3
2
1
0 -5
0
5
10
15
20
s e
4 TYPICAL CONTAMINANTS AND CONTAMINANTS DISTRIBUTION IN VENTILATED ROOMS Displacement ventilation and vertical concentration gradient The idea behind displacement ventilation is to accept a variation in the concentration distribution with a high value below the ceiling and a low value in the occupied zone.
0,95
0,90
0,95 0,90
0,80 0,70
0,80 0,70
exp
c
0,73
exp
c
0,76
5 THEORY AND DEFINITIONS Air Change Air Change Efficiency
a
qv
Mean age of air in the exhaust = 2 x Room mean age of air a
P
n
2
qv The mean age of air in the exhaust is always equal to the nominal time constant n
Age 0
=V/qv
n
What is the mean age of the air in the room? The room mean age of air can not be less than half the nominal time constant! Thus the air change efficiency < 100 %
5 THEORY AND DEFINITIONS Air Change Air Change Efficiency Piston flow
Fully mixed flow n
n
n
2
n
a
100 %
a
50 %
Displacement flow
Short-circuit Short-circuit flow
n
n
2
50 % a
n
n
100 %
a
n
50 %
5
THEORY AND DEFINITIONS Contaminant Removal effectiveness, CRE
Concentration in the exhaust CRE = Mean concentration in the room
ce c
5 THEOR THEORY Y AND DEFINITIONS Contaminant Removal effectiveness, CRE
Contamination source close to exhaust
Contamination source in a stagnant zone
ce
ce
c
ce
c
Contamination Contamination source close to exhaust
ce
Contamination source in a stagnant zone
ce
ce c
ce
c
ce
6 MEASUREMENTS
Pressure control valve Closing valve Injection of tracer gas
Injection point point Flowmeter (Rotameter) or mass flow controller
6 MEASUREMENTS Exhaust air concentration
Analyser Switch
Alternative 1 Tube from gas bottle
Local room air concentrations
Alternative 2 Tube from gas bottle
Routines for how to measure and calculate the ventilation effectiveness c0 14 ) 12 m p 10 p ( n 8 o i t a r 6 t n e 4 c n o C 2
ci-1 ci
This part of the curve could be used to calculate the decay
For calculation of the tail the calculated decay is used
t i-1 t i
5
10
Time (minutes)
15
20
cn
6 MEASUREMENTS Planning
1. Develop team 2. Incorporate commissioning specifications
Design 3. Review project design
4. Develop commissioning plan
Installation
5. Develop Develop prefunctional checklist checklist
6. Execute prefunctional checklist 7A. Correct deficiencies 7. Are expected results realised? No Yes 8. Approve p refunctional refunctional checklist 9. Develop functional tests and diagnostic monitoring plan
Acceptance
10. Execute monitoring and functional plans
11A. Correct deficiencies 11. Is equipment equipment in compliance?
No
Post-acceptance
12. Accept equipment performance
13. Develop final commissioning report
Commissioning
7 PREDICTION OF AIR QUALITY BY COMPUTATIONAL FLUID DYNAMICS
Contaminant distribution around a sedentary person, contaminant source at the floor
7 PREDICTION OF AIR QUALITY BY COMPUTATIONAL FLUID DYNAMICS
The exposure of a standing person from different surfaces with the same emission
8 CASE STUDIES Description and Design Values, Measured Results, Discussion of Results Auditorium 3,8 kW ceiling light
m 6 m 6 , 3
320 seats
m 5 , 1 2
Measurement column
15,8 m
8 CASE STUDIES Auditorium Temperature, ºC 22,4 °C
20
25
24,8 ºC 23,8 ºC
20,7 °C
Local air quality index 890 ppm CO2
0
1
2
0,56-0.82 0,85- 0,97
19 m Room width: 21.5 m
420 ppm CO2
8 CASE STUDIES Office in town hall
Office in town hall
Full scale experiments
8 CASE STUDIES Office in town hall
Winter case
Summer case
Warm supply air jet
Cold down-draught from windows
Draught from the subcooled supply air jet
Flow pattern before reconstruction of the ventilation system
8 CASE STUDIES Office in town hall 3
New sy stem st em Old Old Sys tem
2
) m ( t h g i e H
1
0 0
Carpet as contaminant source
1 2 3 4 Dim Dimensionless concentration (c/c e )
Concentration profiles
5
8 CASE STUDIES Industrial building Section A-A m 8 m 5
25 m
A
Height (m) 4
Mixing ventilation
A Measuring position
38 m
24 m
75 m Section A-A
m 8 m 5
25 m
3 2 1
A
10
14
18
22
26
Displacement ventilation Mixing ventilation A Measuring position
Displacement ventilation
38 m
24 m 75 m
P
(min)
8 CASE STUDIES Homogeneous Homogeneou s emission techniques 7m
4m
13,2 m
Laboratory hall
Subdivision of the room
8 CASE STUDIES Homogeneous Homogeneou s emission techniques
c/c e
1
1
0
0
0,35 0,28 0,27 0,33
0,42 0,35 0,28 0,33
0,50 0,45 0,43 0,48
c/c e
1,33 m above the floor
Computed local mean age of air in the subvolumes between the two layers
0,54 0,60 0,63 0,57
1
1
0
0
1,33 m above the floor
c/c e
1
1
0
0
c/c e
1
0
1
0
Floor level The shadowed ellipses show the positions of the two 750 W air convectors at the floor level
Local mean age of air
Floor level The shadowed ellipses show the positions of the two 750 W air convectors at the floor level
Local concentrations with point sources
Thank you for your attention The life Grandchild 2003
Skansen 2004
Great-grandmother 1928
Local mean age 5 months
Local mean age X years
Local mean age 80 years
Life mean age 40 years?
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