General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General...
Transcript of General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General...
![Page 1: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/1.jpg)
General and Dilution Ventilation
![Page 2: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/2.jpg)
Dilution Ventilation q The solution to pollution is dilution? q Do you want to move a lot of air? q What happens in the winter? q How do you get a sweeping effect? q Why bother with local exhaust if there are too
many sources to vent them all? q To have effective DV we need to:
q Mix contaminated air with large volume of fresh air q Have sufficient air changes/hour to prevent build-up q Create air movement and mixing at all required locations
![Page 3: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/3.jpg)
General Ventilation - Purpose
q General ventilation q Provide heating or cooling q Provide make-up air q Provide dilution and reduction of contaminants
such as CO2 and body odor q Dilution ventilation
q Provide dilution of contaminants to safe levels (<TLV or LEL)
q Constrained by comfort and other factors q Usually initial cost: DV cost << LEV cost q Usually for operation: DV cost >> LEV cost
![Page 4: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/4.jpg)
Dilution Ventilation - applications
q Toxicity of contaminant is low to moderate (High TLV)
q Velocity and generation rate of contaminant low to moderate – must consider periodic generation too
q Sources are not well localized or identifiable q Mobile sources or variable work process q Energy costs are not a significant concern
![Page 5: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/5.jpg)
“Laminar” Flow Dilution System
Exhaust Plenum
Supply Plenum
![Page 6: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/6.jpg)
WITH ARROWS
POISON
![Page 7: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/7.jpg)
WITHOUT ARROWS
POISON
![Page 8: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/8.jpg)
Distance from the source and concentration gradients When No Cross-Drafts Exists
500 200
5010
See Nicas: Am Ind Hyg Assoc J. 1996 Jun;57(6):542-50
![Page 9: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/9.jpg)
Mixing by entrainment
High velocity air entrains as much as 20 times!its original volume.!
Velocity falls to 10% at 30 diameters.!
22°Vo 0.10 Vo
30 Outlet diameter
![Page 10: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/10.jpg)
Interactive Effects of Cross-Drafts and Proximity to Exposure
20
20050 350
10 40
![Page 11: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/11.jpg)
Effects of Cross-Drafts and Worker’s Proximity to the Source
20
20050 350
10 40
Wake zone downstream of body draws contaminant from source within handʼs reach (“campfire” phenomenon)
![Page 12: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/12.jpg)
POISON POISON
![Page 13: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/13.jpg)
Reverse the flow?
POISON POISON
![Page 14: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/14.jpg)
Blowing with entrainment produces large scale eddies & mixing
Elevation
ExhaustSupply
General
Zones of Ventilation
![Page 15: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/15.jpg)
G =d Volvapor( )
dtG =
Amount Evaporatedt2 ! t1
q We are concerned about dynamic conditions q Assume constant generation rate
Computing Generation Rate
![Page 16: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/16.jpg)
Calculating dilution volumes
VolumeCont = MassOfTheLiquidMassForOneMole
!VolumeForOneMole
VaporVol =MassOfTheLiquid
MW! 24.04L ! 273.15C + T
293.15" #
$ % 760mmHgOPatm
" #
$ %
VaporVol =sp.grav.! "H 2O !Volliquid( )
MW!24.04L ! 273.15C + T
293.15# $
% & 760mmHgOPatm
# $
% &
![Page 17: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/17.jpg)
Target Concentration
Toxicity
TLV ppm Ct as a % TLV
highly toxic, radioactive < 20 local exhaust onlyor carcinogenic
moderately toxic 20œ100 25somewhat toxic 100-200 50slightly toxic > 200 75
![Page 18: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/18.jpg)
Concentration if perfect mixing
C =GQ
Concentration if not perfect mixing
C =G
Q / m
![Page 19: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/19.jpg)
Values of mi for each work station
mi =Ci
Cexhaust
m due to non-uniformity Supply air mixing Contaminant release Distance from worker
Plan View
3 .3
2 .23 .0 2 .5
3 .0 3 .0
4 .0 2 .0
2 .0
3 .0
0 .5
![Page 20: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/20.jpg)
Mixing factors
Cavg =1
8hoursCiti
i
n
!
mi =Ci
Cexhaust
Cavg =Cexhaust8hours
mitii
n
!
Mpeak =C15min
CexhaustMavg =
18hrs
mitii
n
!
![Page 21: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/21.jpg)
Accumulation = Generation – Removal
Q & CsQ & CG
RCt =Gdt +Qms
!
"# $
%&Cs dt –
Qms
!
"# $
%&Ct dt
C2 = C1e-Qt/mR +mGQ
+ Cs!
"# $
%1- e-Qt /mR( ) ⎟
⎠
⎞⎜⎝
⎛ −+= ts CmQC
mQG
dtdCV
( )mVQts
mVQt eCQmGeCC //
12 1 −− −⎟⎟⎠
⎞⎜⎜⎝
⎛++=
![Page 22: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/22.jpg)
Room Dilution equations
Above eqn applies to transient conditions... but it is not used for steady state.
With clean inlet air at steady state we get:
Ct =mGQ
( )mVQts
mVQt eCQmGeCC //
12 1 −− −⎟⎟⎠
⎞⎜⎜⎝
⎛++=
![Page 23: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/23.jpg)
t2
C2
"Steady"-StateGeneration
Application of Equations
Ct =mGQ
( )mVQts
mVQt eCQmGeCC //
12 1 −− −⎟⎟⎠
⎞⎜⎜⎝
⎛++=
![Page 24: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/24.jpg)
Application of Equations
t2
Cmax
Build up
C1
C2
t2
C1
PurgeC2Cs
( )mVQts
mVQt eCQmGeCC //
12 1 −− −⎟⎟⎠
⎞⎜⎜⎝
⎛++=
![Page 25: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/25.jpg)
Cyclic operations
q Short emission cycles, effects “average out”
CyclicGeneration
t2
C2
![Page 26: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/26.jpg)
When conditions change with time • Solve for time interval during which all conditions are
constant • If conditions change continuously, make interval one
minute • Use result as initial conditions for next interval
• OR… use a time-dependent numerical solution [advanced topic]
( )mVQts
mVQt eCQmGeCC //
12 1 −− −⎟⎟⎠
⎞⎜⎜⎝
⎛++=
![Page 27: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/27.jpg)
DESIGNING NEW SYSTEM
Locate sources near exhaust fans • Locate supply air outlets to direct air away from face and towards exhaust fans
• Separate sources from traffic using barriers
• Block undesirable cross drafts and competing sources of motion using barriers.
![Page 28: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/28.jpg)
EXISTING SYSTEM IMPROVEMENTS
• Substitute less volatile or toxic chemicals • Install or improve local exhaust hoods • Reduce incidence of spills and leaks • Relocate supply and exhaust points • Relocate workers or the sources — or both • Increase airflow
![Page 29: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/29.jpg)
Confined Space Ventilation
Purging fans
![Page 30: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/30.jpg)
Confined Space Ventilation
G
• Drain before purging
• Lock out
• Purge before entering
• Blow air in; don’t suck it out
• Move nozzle around
• Measure before entering
• Purge during work
![Page 31: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/31.jpg)
Confined Space Ventilation-Purge Time
G
• Should be computed
• Then test against measurements
• Wait minimum time even if measurement says okay
• Time less with bigger blower
• Bigger blower more costly, harder to manuever
If supply air clean, then:
⎟⎟⎠
⎞⎜⎜⎝
⎛⎟⎠
⎞⎜⎝
⎛=
⎟⎟⎠
⎞⎜⎜⎝
⎛⎟⎟⎠
⎞⎜⎜⎝
⎛=
2
1
2
1
ln
ln
CC
tVmQ
CC
QVmt
![Page 32: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/32.jpg)
Example Problem
Initial measurements indicate 10,000 ppm of xylene in aconfined space. Assuming that Ct!=!0.25!*!TLV, howmuch should Q be to allow entry in 30 minutes if:a.
R=1000 ft3, M=3, Cs = 0
Q =Rm!t
"#
$% ln
G +QCs /m –QCo /mG +QCs / m – QC2 /m&
'()
*+=
1000 ft 3 * 330min
"
#, $
%ln
010-2
025 *10-6
&
'()
*+= 599 ft3/min
b. R=2000 ft3, M=3, Cs = 0 : Solution: Q = 1198 ft3/minc. R=1000 ft3, M=6, Cs = 0 : Solution: Q = 1198 ft3/mind. R=1000 ft3, M=6, Cs = 15 ppm: Solution: Q = 1381 ft3/min
![Page 33: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/33.jpg)
Summary • Estimating G and m can be difficult
• Reduce G as much as possible
• Reduce greatest contributors to exposure and perceived exposure first
• Use sweeping, but be realistic about it
• Complement local exhaust systems
• Provide winter and summer
• Purge before and during confined space entry
![Page 34: General and Dilution Ventilationcourses.washington.edu/envh557/Class Documents/6...General Ventilation - Purpose ! General ventilation !Provide heating or cooling !Provide make-up](https://reader033.fdocuments.net/reader033/viewer/2022052101/603aad9b2b0e04481d3f1ff7/html5/thumbnails/34.jpg)
STOP HERE