Nr 2 Ventilation Effectiveness

8/11/2019 Nr 2 Ventilation Effectiveness

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Federation of European Heating, Ventilation and Air-conditioning Associations

Address:

Rue Washington 401050 Brussels

Belgium

www.rehva.eu

[email protected] Tel: +32 2 514 11 71

Fax: +32 2 512 90 62

Federation of European Heating, Ventilationand Air-conditioning Associations


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Guidebook.

Please refer the original author always when makingthe presentation.

Inform REHVA secretariat each time the presentationis used: [email protected]


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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, Zrich,Switzerland


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CONTENTS1. VENTILATION EFFECTIVENESS IN A NUTSHELL (3 p)2. SYMBOLS AND TERMINOLOGY (4 p)

3. WHY VENTILATION EFFECTIVENESS (5 p)

4. TYPICAL CONTAMINANTS AND CONTAMINANTSDISTRIBUTION IN VENTILATED ROOMS (6 p)

5. THEORY AND DEFINITIONS (8 p)

6. MEASUREMENTS (12 p)

7. PREDICTION OF AIR QUALITY BY COMPUTATIONAL FLUIDDYNAMICS (4 p)

8. CASE STUDIES (21 p)

9. DEFINITIONS OF VENTILATION EFFECTIVENESS INDIFFERENT COUNTRIES (1 p)

10. APPENDIX 1 (1 p)

11. REFERENCES (4 p)


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VENTILATION EFFECTIVENESS

includes

A

Indices representing the

ability of a system toexchange the air in the room

air change efficiency,

local air change index,

B

Indices representing the

ability of a system to removeair-borne contaminants

contaminant removal

effectiveness (CRE), local air quality index,

a

a

P cP

c


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INTRODUCTORY CHAPTERS

1. VENTILATION EFFECTIVENESS IN A NUTSHELL

2. SYMBOLS AND TERMINOLOGY

3. WHY VENTILATION EFFECTIVENESS

Keep concentration low

Point source Q cs

ce

Point sensorP

cs

ce

Point source Q

Concentration field resulting from point source Q

Distributed source Q

cs

ce

Point sensor P

Distributed source Q, mean concentration

cs

ce

a

a

P

c

c

P


7/26Federation of European Heating, Ventilation and Air-conditioning Associations

-5 0 5 10 15 20

0

1

2

3

4

es

eP cc

4 TYPICAL CONTAMINANTS AND CONTAMINANTS

DISTRIBUTION IN VENTILATED ROOMS

Return opening

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.



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.

0,950,90

0,800,70

0,950,90

0,800,70

73,0exp

c 76,0exp

c



5 THEORY AND DEFINITIONS

AirChangeEfficiency

qv

qv

Age

0 n=V/qv

P

What is the mean age of the air in theroom?

Mean age of air in the exhaust2 x Room mean age of air

a

=

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

n

a

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

Thus the air change efficiency < 100 %

2

n




AirChangeEfficiency

Fully mixed flow

n

n

%50a

Displacement flow

n

nn 2

%100%50 a

Short-circuit flow

n

n

%50a

Piston flow

n2n

%100a



Contaminant Removal effectiveness, CRE


Concentration in the exhaust

Mean concentration in the roomCRE =

ec

c


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6 MEASUREMENTS

Injection of tracer gas

Flowmeter

(Rotameter)or mass flow

controller

Injection

point

Closing

valve

Pressure control valve



6 MEASUREMENTS

Routines for how to measure and calculate the ventilation effectiveness

Alternative 2

Tube from gas bottle

Alternative 1

Tube from gas bottle

Exhaust air

concentration

Local room air concentrations

Switch

Analyser

5 10 15 20

Time (minutes)

Concentration(ppm)

This part of the curve could be

used to calculate the decay

For calculation of the tail the

calculated decay is used

cn

ci-1

ci

ti

ti-1

c0

2

4

6

8

10

12

14



6 MEASUREMENTS

Commissioning

2. Incorporate commissioning

specificationsDesign

3. Review project design

4. Develop commissioning plan

5. Develop prefunctional checklist

6. Execute prefunctional checklist

8. Approve p refunctional 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 expected

results realised?

7A. Correct deficiencies

No

Yes


No

Planning

2. Incorporate commissioning

specificationsDesign

3. Review project design

4. Develop commissioning plan

5. Develop prefunctional checklist

6. Execute prefunctional checklist

8. Approve p refunctional 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 expected

results 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

21,5m

6m

3,6m

3,8 kW ceiling light

320 seats

Measurement column



8 CASE STUDIESAuditorium

20 25Temperature, C

23,8 C

24,8 C

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


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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)

Height(m)

New system

Old Sys tem


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8 CASE STUDIESIndustrial building

Mixing ventilation

Displacement ventilation

Section A-A

Measuring position

A

A

75 m38 m 24 m

25 m

5m8

m

A

A

75 m38 m 24 m

Section A-A

25 m

5m8

m

Measuring position

10 14 18 22 26

4

3

2

1

(min)P

Height (m)

Mixing ventilation

Displacement ventilation


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8 CASE STUDIES

Homogeneous emission techniques

Laboratory hall Subdivision of the room

7 m

4 m

13,2 m


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8 CASE STUDIESHomogeneous emission techniques

Local mean age of airLocal concentrations with point sources

Computed local meanage of air in the sub-

volumes between the

two layers

0,35 0,42 0,50 0,54

0,28 0,35 0,45 0,60

0,27 0,28 0,43 0,63

0,33 0,33 0,48 0,57

1

0

1

0

c/ce

1

0

1

0

c/ce

1,33 m above the floor

Floor level

The shadowed ellipses

show the positions of

the two 750 W air

convectors at the floor

level

1

0

1

0

c/ce

1,33 m above the floor

Floor level

The shadowed ellipses

show the positions ofthe two 750 W air

convectors at the floor

level

1

0

1

0

c/ce


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Nr 2 Ventilation Effectiveness