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3Ventilation Effectiveness Rehva Guidebook no 2

Ventilation EffectivenessRehva Guidebook no 2

AUTHORS• Elisabeth Mundt, Professor,

KTH-Royal 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

FEDERATION OF EUROPEAN HEATING AND AIR-CONDITIONING ASSOCIATIONS "REHVA"


CONTENTS1 VENTILATION EFFECTIVENESS IN A NUTSHELL (3 p)

2 SYMBOLS AND TERMINOLOGY (4 p)

3 WHY VENTILATION EFFECTIVENESS (5 p)

4 TYPICAL CONTAMINANTS AND CONTAMINANTS DISTRIBUTION IN VENTILATED ROOMS (6 p)

5 THEORY AND DEFINITIONS (8 p)

6 MEASUREMENTS (12 p)

7 PREDICTION OF AIR QUALITY BY COMPUTATIONAL FLUID DYNAMICS (4 p)

8 CASE STUDIES (21 p)

9 DEFINITIONS OF VENTILATION EFFECTIVENESS IN DIFFERENT COUNTRIES (1 p)

10 APPENDIX 1 (1 p)

11 REFERENCES (4 p)


VENTILATION EFFECTIVENESSincludes

AIndices representing theability of a system toexchange the air in the room

air change efficiency,

local air change index,

BIndices representing theability of a system to removeair-borne contaminants

contaminant removaleffectiveness (CRE),local air quality index,

aεaPε c

Pε

cε


INTRODUCTORY CHAPTERS

1. VENTILATION EFFECTIVENESS IN A NUTSHELL2. SYMBOLS AND TERMINOLOGY3. WHY VENTILATION EFFECTIVENESS

aε

aPε

cε

cPε


-5 0 5 10 15 200

1

2

3

4

es θθ −

eP cc

4 TYPICAL CONTAMINANTS AND CONTAMINANTS DISTRIBUTION IN VENTILATED ROOMS

Return openingThe 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.


4 TYPICAL CONTAMINANTS AND CONTAMINANTS DISTRIBUTION IN VENTILATED ROOMS

Displacement ventilation and vertical concentration gradientThe 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

0,900,80

0,70

0,950,900,800,70

73,0exp =∗c 76,0exp =∗c


5 THEORY AND DEFINITIONS

Air Change Efficiency

What is the mean age of the air in the room?

Mean age of air in the exhaust 2 x Room mean age of airε a =

The mean age of air in the exhaustis always equal to the nominal time constant nτ

ε a

The room mean age of air can not be less than half the nominal time constant!

Thus the air change efficiency < 100 %

2nττ

=⋅


5 THEORY AND DEFINITIONS Air Change Efficiency

nτ

nττ =

%50=aε

nτ

nn τττ <<2

%100%50 ≤≤ aε

nτ

nττ >

%50≤aε

nτ2nττ =

%100=aε


Contaminant Removal effectiveness, CRE


Concentration in the exhaustMean concentration in the room

CRE =ecc

=


Contaminant Removal effectiveness, CRE

ec

ecc <

ec

ecc >

ec

ecc <

ec

ecc >



6 MEASUREMENTS

Injection of tracer gasFlowmeter(Rotameter)or mass flowcontroller

Injectionpoint

Closingvalve

Pressure control valve


6 MEASUREMENTS

Routines for how to measure and calculate the ventilation effectiveness

Alternative 2Tube from gas bottle

Alternative 1Tube from gas bottle

Exhaust airconcentration

Local room air concentrations

Switch

Analyser

5 10 15 20

Time (minutes)

Con

cent

ratio

n (p

pm)

This part of the curve could beused to calculate the decay λ

For calculation of the tail thecalculated decay is used

cn

ci-1

ci

titi-1

c0

2

4

6

8

10

12

14


6 MEASUREMENTSCommissioning

2. Incorporate commissioning specifications

Design

3. Review project design

4. Develop commissioning plan

5. Develop prefunctional checklist

6. Execute prefunctional checklist

8. Approve prefunctional checklist

9. Develop functional tests and diagnostic monitoring plan

10. Execute monitoring and functional plans

12. Accept equipment performance

13. Develop final commissioning report

1. Develop team

Installation

Acceptance

Post-acceptance

11. Is equipment in compliance?

7. Are expectedresults realised?

7A. Correct deficiencies

No

Yes


No

Planning

2. Incorporate commissioning specifications

Design

3. Review project design

4. Develop commissioning plan

5. Develop prefunctional checklist

6. Execute prefunctional checklist

8. Approve prefunctional checklist

9. Develop functional tests and diagnostic monitoring plan

10. Execute monitoring and functional plans

12. Accept equipment performance

13. Develop final commissioning report

1. Develop team

Installation

Acceptance

Post-acceptance

11. Is equipment in compliance?

7. Are expectedresults realised?


No

Yes


No

Planning


7 PREDICTION OF AIR QUALITY BY COMPUTATIONAL FLUID DYNAMICS

Contaminant distribution around a sedentary person, contaminant source at the floor


The exposure of a standing person from different surfaces with the same emission

7 PREDICTION OF AIR QUALITY BY COMPUTATIONAL FLUID DYNAMICS


8 CASE STUDIESDescription and Design Values, Measured Results, Discussion of Results

Auditorium

15,8 m

21,5

m6

m3,

6 m

3,8 kW ceiling light

320 seats

Measurement column


8 CASE STUDIESAuditorium

20 25Temperature, ºC

23,8 ºC

24,8 ºC

20,7 °C

22,4 °C

Room width: 21.5 m

19 m

890 ppm CO2

420 ppm CO2

0 1 2

Local air quality index

0,85- 0,97

0,56-0.82


8 CASE STUDIES

Office in town hall

Office in town hall Full scale experiments


8 CASE STUDIESOffice in town hall

Flow pattern before reconstruction of the ventilation system


8 CASE STUDIES

Office in town hall

Carpet as contaminant source Concentration profiles

0

1

2

3

0 1 2 3 4 5Dimensionless concentration (c/c e )

Hei

ght (

m)

New system

Old System


8 CASE STUDIESIndustrial building

Mixing ventilation

Displacement ventilation

10 14 18 22 26

4

3

2

1

(minPτ

Height (m)

Mixing ventilation

Displacement ventilation


8 CASE STUDIES

Homogeneous emission techniques

Laboratory hall Subdivision of the room


8 CASE STUDIESHomogeneous emission techniques

Local mean age of airLocal concentrations with point sources


Thank you for your attention

Grandchild 2003 Great-grandmother 1928Skansen 2004

Local mean age5 months

Local mean ageX years

Local mean age80 years

Life mean age 40 years?

The life

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