Air Quality Engineering
Indoor Air Pollutant Dispersion
Goal
• Goal: To characterize air pollutant concentrations
in indoor environments, taking into account
various sources and sinks.
• Addresses Learning Objective #2
Perform calculations that characterize air pollutant
levels, including fundamental concentrations, those
that arise from the dispersion of pollutants, and those
that arise from the control of pollutants.
Indoor vs Outdoor Pollution
McGraw-Hill
McGraw-Hill
Waveland Press,
Result 1 of 1 in this book for epa-452/R-97-0032
Incorporated
McGraw-Hill
Education
Air Pollution Control
Cle
Engineering
Third Edition
Hardcover
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Hardcover
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586 pages
586 pages
586 pages
173 pages
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By Noel de Nevers
Engineers in multiple discipl
environmental, chemical, civ
mechanical—contribute to o
understanding of air pollutio
To that end, Noel de Nevers
incorporated these multiple
Fluid Mechanics
Common terms and phrases
By Noel De Nevers
adiabatic adiabatic lapse rate adsorbent air pollution air pollution control
air-fuel ratio Assume atm atmosphere auto average baghouse benzene burned
calculated carbon catalyst Chapter chemical coal coefficient collection efficiency
combustion compute concentration constant contains control device curve
cyclone cyclone separator difficult downwind emission rate
More terms and phrases
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Source: LETZ et al. US EPA Report No 600/9-84-001
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Modeling Indoor Pollutant Levels
Simple box model
– Assume perfectly mixed
– Infiltration/Exfiltration
– Pollution generated within/removed in structure
– Steady state conditions (no time dependence)
Infiltration/exfiltration: unintentional flow of air into and
out of the structure through leakage, cracks, etc.
Driving forces: wind, temperature differences, etc.
Modeling Indoor Pollutant Levels
Simple box model
Infiltrated Air
Q1Co
Q=volumetric
flowrate
of
C= conc.
polutant
Building Volume: V
Building Source: S
Building Sink: R
Building Concentration: Ci
Outdoor Concentration: Co
Q2Ci
What’s the material
balance?
Exfiltrated Air
pointant
polutant
Flow Flowe A generated
-
Within
structure
QcCi
(
·
=
=
0, C +S-R
Co + R
SinkS
Within
strict.
assume
M
=
G
Modeling Indoor Pollutant Levels
Estimate infiltration using (from ASHRAE):
Type of Room
per hour
changes
-air
# ACH
No windows or exterior doors
0.5
#ACH
Windows or exterior doors on one side
1
Q= FACH
Windows or exterior doors on two sides
1.5
Windows or exterior doors on three
sides
2
Entrance halls
2
9.
Intration
=
Trvolume
of struct
x
V
Notes:
(1) Assume that the windows are closed.
(2) For rooms with weather-stripped windows or with storm sashes, use 2/3 (two
thirds) of the values in the table.
Modeling Indoor Pollutant Levels
What does the simple box model tell us about how indoor
pollutants can be controlled?
the more air flow and space, the more dilute
the pollutants are
Think about this in terms of the COVID pandemic.
What do people say?
->
people felt more comfortable with less people
space and in places with air flow
or outdoors by it is more dilute.
in a given
·
Lower S
-
-
reduce #ppl
wear mask
·
Increase R
Modeling Indoor Pollutant Levels
What does the simple box model tell us about how indoor
pollutants can be controlled?
Consider:
1. Large Q1
C, = Co
2
&
dCi by MR
dCi by & Q,
2. Ci - Co and how this depends on S-R and Q1
3. Ci > Co, and the impacts of Q1 and S
Example Problem
S
A gas stove consumes 3000 kcal/hr of fuel. The
emission factor for NO2 for the gas stove is 61
µg/kcal. The air infiltration rate is 3000 ft3/hr, and
the outdoor concentration is 20 µg/m3. Assume that
Co
NO2 is not destroyed indoors. Estimate the steady
state concentration when the stove has run long
enough to ready steady state.
Ci
C
=
=
S-R
Co +
20+
Q
183,000
8
4.9 S
G= 2174.21M91me
Q= 3,000
ft384.9 m
S=3000Kca1 /hr (6/nglica))
=183,000 mglnr
Example Problem
A gas stove consumes 3000 kcal/hr of fuel. The
emission factor for NO2 for the gas stove is 61
µg/kcal. The air infiltration rate is 3000 ft3/hr, and
the outdoor concentration is 20 µg/m3. Assume NO2
is not destroyed indoors. Estimate the time required
to reach 90% of the steady state concentration that
was computed previously. How does this time
compare to the average time that you (or someone
in your household) might take to cook a meal?
Assume V= 1000 cubic ft
Example Problem
A gas stove consumes 3000 kcal/hr of fuel. The emission factor for NO2 for the gas stove is 61 µg/kcal. The air
infiltration rate is 3000 ft3/hr, and the outdoor concentration is 20 µg/m3. Assume NO2 is not destroyed indoors. Estimate
the time required to reach 90% of the steady state concentration that was computed previously. How does this time
compare to the average time that you (or someone in your household) might take to cook a meal? Assume V= 1000 cu ft
Solution:
V di = 0, Co
6 = +- += =
= 23,000
8
=
2154 M9ls
-
Q.Cit
ofen Ko-Ci+Safinitial
[Co-Ci+3/0]c+
1000 ft"
+ (n
3000ffYnr
-
(20-20 +21sn)
(20-10.9.21777 T2ISM
=0.77hv = 46mins
More Realistic Model
Makeup Air
Q3Co
Infiltrated Air
Q1Co
Filter
Intake Fan
Q3Co(1-F0)
Q4Ci
Filter
Q4Ci(1-F1)
Building Volume: V
Building Source: S
Building Sink: R
Building Concentration: Ci
Outdoor Concentration: Co
Q2Ci
Exhaust
Fan
Exfiltrated Air
Q5Ci
Accumulation = In flow –Out flow + Sources –Sinks
More Realistic Model
• Modern facilities: forced ventilation systems.
• Make up air is principle air flow in air conditioned
buildings. (No open windows.)
•
•
Selected – in the US- from the American Society of Heating
Refrigeration and Air Conditioning (ASHRAE) standards
Specify occupancy for the facility type and the required fresh air
supply.
Example:
Dining room occupancy = 70 people/1000 ft2
Minimum outdoor air flow required :
35 cfm/person for a smoking area
7 cfm/person for a non-smoking area
• Recirculation flowrate
•
•
Chosen to keep room occupants comfortable .
Typically 6-9 times the room volume per hour.