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CASE STUDY
Two Dogs and Two Cats – Insufficient Air Exchange with High CO2
A Black Box IAQ™ was placed in the main living area of a pre-1900 home. The house had been refurbished with
a high efficiency gas furnace (external combustion air) and had vinyl siding installed within the past five years.
Two occupants live in the house with two mid-size dogs and two cats. The occupants work during the day.
Page 1-2 of the report shows reasonable comfort exists in the house, with the average temperature and
humidity in a range where short sleeves and shorts would be comfortable for most people. The data was
collected during early summer.
Air flow was found to be low in the main living area of the house, resulting in higher than desirable carbon
dioxide concentrations. The air flow rate dial below the comfort chart on page 1-2 of the report shows an air
exchange rate that is less than the 15 to 25 cubic feet per minute per person air exchange rate needed to keep
pollutant concentrations acceptable.
Page 1-3 confirms that carbon dioxide levels are high due to insufficient air exchange rate. VOCs (Volatile
Organic Compounds) are less than 1,000ppm, indicating that other sources of pollution such as fumes from
off-gassing of home furnishings, cleansers, cosmetics, and cooking odors are not significantly adding to VOC
generation beyond that of the occupants’ (human and pets). When VOCs are from human and animal
metabolism, VOC concentration will be less than that of carbon dioxide because VOCs more readily react and
breakdown, and because VOCs are absorbed into building and furnishing surfaces.
Page 2-1 contains a table with summary information and suggestions for improving air quality. Because carbon
dioxide concentration is greater than desired, the table suggests increasing the air exchange rate to a level
that will reduce carbon dioxide concentration from the measured average level of 1,599 ppm to 1,000 ppm.
Assuming that VOCs are generated at a similar rate as measured during the test, VOC concentration will also
be reduced from 601 ppm to 501 ppm.
The table on page 2-1 recommends doubling the flow of air through the space from 19 to 38 cfm (cubic feet
minute). The best method for improving air quality is with fresh air ventilation. Fresh air ventilation systems,
such as our CERV™ fresh air conditioning system, efficiently exchanges energy between fresh air and exhaust
air streams while managing air quality.
Page 2-2 includes two plots that graphically display the test measurements and changes in pollutant levels due
to the suggested ventilation modifications. The top figure shows the measured carbon dioxide and VOC
concentration levels and the air exchange flow rate as solid markers. The hollow markers show the change in
carbon dioxide and VOC concentrations after the air exchange flow rate is adjusted. Increased ventilation
decreases carbon dioxide to 1,000ppm and with an associated decrease of VOC pollutants.
Black Box
Indoor Air Quality Report
Test Number:
Name:
Email address:
Test Location:
Box Location:
Report Date:
Black Box Case Study 6
Two Dogs Two Cats
[email protected]
Central Illinois
living room
6/1/2012
Overview: This Black Box IAQ™ report provides an assessment of indoor air quality (IAQ) over the tested
time period for the designated space. Black Box IAQ™ measures temperature, humidity, carbon dioxide
(CO2), and volatile organic compound (VOC) levels. Based on these measurements, the air exchange rate
and pollutant generation rates are determined. The report is divided into two sections as follows:
Section 1: Test Summary Information Reports the measured and calculated values of temperature,
humidity, CO2, VOCs , and air flow rate for the measurement space. A determination is made as to whether
the levels are acceptable or not. Unacceptable levels suggest corrective action.
Section 2: Recommendations Test results for the measured CO2 and VOC levels are plotted against the
calculated air flow rate through the space. Suggested changes to the air exchange rate are given and the
impact of changes to the air exchange rate on pollutant levels are provided. Trends in radon gas levels due
to changes in air exchange rate are also discussed.
Use our building energy modeling software to design a healthy, comfortable, efficient home.
A free version is available at www.buildequinox.com/zeros
CERV: Monitor pollutant levels, get fresh air, and recover energy.
Learn more at www.buildequinox.com/products/cerv
* Disclaimer: This test is provided for informational purposes only. Results are dependent on a number of
testing conditions. It is vital to appreciate that a test result only gives a “snap-shot” estimate for a single
time period and a single location under conditions at the time of testing – how well it represents other
locations and times is uncertain since the amounts and types of pollutants and air flow rates in the
environment is always changing.
pg. 1-1
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©Build Equinox 2013
Rev 1.9.2, Report # Black Box Case Study 6
1: Test Summary Information
Measured Temperature and Humidity Levels:
Comfort Chart
% Relative Humidity
100
80
Slacks & Long Sleeves Comfort
Region
60
Shorts & Short Sleeves Comfort
Region
40
Room Condition Data Points
20
Average Room Condition
0
60
65
70
75
80
85
90
Temperature (F)
Temperature and relative humidity measured during the test period are shown in the above figure. The
two regions represent different comfort levels of clothing for sedentary (eg, office work activity)
persons. Room conditions falling mostly within the comfort regions provide confidence that building
conditioning systems are operating appropriately. Extended periods of high indoor humidity can be an
indirect indicator of mold, a known component of poor indoor air quality.
Infiltration or Controlled Ventilation Air Flow Rates:
Optimal
Air
Flow
High
Air
Flow
Low
Air
Flow
Less than 15
15 to 25
Greater than 25
Air Exchange rate per occupant
(cfm/person)
Air Exchange
10.7
cfm/person
Air flow to the measured space results from either controlled ventilation or uncontrolled infiltration
through cracks and inadequate sealing around doors and windows. The Black Box IAQ™ analysis
calculates the space air flow rate and is reported in two ways: 1) as cubic feet per minute (cfm) and 2)
as cfm per equivalent person (cfm/equiv. person) as shown above. It is important to point out that the
calculated equivalent person is not the same as the number of occupants. The equivalent person
number is based on typical pollution generation rates per person but can be different from the number
of occupants due to occupant activity such as cooking using gas cooktops or actual occupancy time in
the tested space. Air flow rates less than 15 cfm/equiv. person contribute to “stale air” and higher
levels of indoor pollutants. Air flow rates greater than 25 cfm/equiv. person are higher than needed to
maintain adequate indoor air quality and thus increase the heating and cooling energy required to
condition the space.
pg. 1-2
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©Build Equinox 2013
Rev 1.9.2, Report # Black Box Case Study 6
Measured CO2 and VOCs Levels:
Optimum
Air
Optimum
Air
Poor
Air
Quality
Excess
Dilution
Air
VOC Level
CO2 Level
1598.
Poor
Air
Quality
Excess
Dilution
Air
601.3
ppm average
Less than 800ppm
800 - 1000 ppm
ppm average
Greater than 1000
Air pollutant ranges
The dial graphs above show the level of measured pollutants during the test period. The table below
categorizes the measured levels ranging from “very good” or low pollutant levels to “very poor” or high
pollutant levels based on ASHRAE (American Society of Heating, Refrigeration and Air Conditioning
Engineers) recommended ranges.
CO2 and VOC Levels:
The most common source of indoor CO2 generation is human and correlates with human respiratory activity.
Indoor combustion of natural gas, such as from stoves and fireplaces or improper flue venting of gas water
heaters and furnaces, is a large contributor of CO2. Indoor CO2 levels that are unusually high may cause
occupants to grow drowsy, get headaches, or function at lower activity levels. The ASHRAE recommended CO2
upper limit is 1,000 parts per million (ppm).
VOCs are also emitted from human respiration, but additionally as gases from certain solids or liquids. VOCs
include a variety of chemicals, some of which may have short- and long-term adverse health effects. VOCs can
be emitted by a wide array of products including carpet, furnishings, paint, cleaning solutions, cosmetics, and
building materials among many others. Natural gas combustion and cooking/food preparation are also sources
of VOCs. VOCs should also be kept below 1,000 ppm.*
*VOC measurements are correlated to a CO2 reference as the amount of VOCs produced in proportion to
human CO2 production.
pg. 1-3
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©Build Equinox 2013
Rev 1.9.2, Report # Black Box Case Study 6
2: Recommendations
The interaction between pollutant level and air flow rate to the space is described in more detail in this section.
The first table below summarizes the average measured values of CO2 and VOCs during the test period and
estimated levels after adjustments are made. The second table summarizes the calculated values of air flow rate
to the space during the test period; recommended adjusted level of air flow rate to keep CO2/VOC levels below
1,000 ppm. Controlled ventilation adjustments are based on cfm values.
As air flow rate to the space increases, pollutants are diluted. Conversely, decreases to the air flow rate
concentrates pollutants.
Summary Information from Your Test
CO2
VOC
Space Air
Flow Rate
Average level
during test period
Estimated level
after adjustment
1598.8 (ppm)
601.3 (ppm)
1000.0 (ppm)
500.8 (ppm)
Calculated level
during test period
Recommended
adjusted level
18.9 (cfm)
10.7 (cfm/equiv. person)
37.8 (cfm)
21.4 (cfm/equiv. person)
Recommended action to achieve adjusted level
Add or increase controlled ventilation
The following plot provides additional details showing how air exchange flow rate, pollutant generation, and
pollutant levels are related. Current pollutant levels and air exchange flow rates are shown with solid symbols
for CO2 and VOCs. Also plotted on the figures are lines showing the relative pollution generation rates
(equivalent people generation rates for CO2 and VOCs). Hollow symbols show how the suggested air exchange
flow rate will impact pollution levels in the space.
The suggested change in ventilation is based on CO2 and VOC levels. Whichever is greater is used to determine
the suggested ventilation change. If the concentration level is greater than 1,000 ppm, an increase in room
ventilation is suggested. If the concentration level is less than 1,000 ppm, a decrease in room ventilation and/or
infiltration is suggested.
A second plot provides guidance related to trends in radon levels due to adjustments in ventilation and/or
infiltration levels. Radon testing must be conducted by either certified radon technicians or by individual
homeowners using state approved testing methods. The red, horizontal line in the plot marks the maximum
recommended level of radon per EPA guidelines. If you have conducted a certified, state approved (where
applicable) radon test concurrent with the Black Box IAQ™ test, your radon level should be plotted on the solid
vertical line marked "Current Air Exchange Rate". For example, a reading of 4 pCi per liter would be a point
located at the intersection of the solid vertical line and the horizontal red line. Increasing fresh air ventilation
air flow may reduce radon levels, while decreasing air infiltration air flow may increase radon concentration.
The second vertical (dashed) line represents an adjusted air flow rate recommended for maintaining
reasonable levels of CO2 and VOCs. The curved lines represent different rates of radon flow into the tested
space. Drawing a line that follows the nearest curved line from the current radon level plotted on the solid
vertical line to the dashed vertical line shows the expected trend in radon due to air flow adjustments. See our
case studies and informational reports for additional guidance. Conducting a second radon test after any
changes to the ventilation and infiltration characteristics is recommended.
pg. 2-1
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©Build Equinox 2013
Rev 1.9.2, Report # Black Box Case Study 6
Carbon Dioxide (CO2) and Volatile Organic Compounds (VOCs)
CO2 & VOC Characteristics
2000
1 equiv. person
2 equiv. person
4 equiv. person
1800
max CO2 & VOC levels
preferred lower range limit
1600
Carbon Dioxide & VOC (ppm)
0.5 equiv. person
your space VOC
1400
your space CO2
adjusted VOC
1200
adjusted CO2
1000
Preferred Range
800
600
400
0
20
40
60
80
100
Controlled Ventilation or Infiltrated Air Flow Rate (cfm)
120
Radon Level Trends versus Air Flow Rate
20
10 pCi/sec radioactivity flow
18
20 pCi/sec radioactivity flow
Radon (pCurie/liter)
16
50 pCi/sec radioactivity flow
14
100 pCi/sec radioactivity flow
12
maximum radon level
Current Air Exchange Rate
10
Adjusted Air Exchange Rate
8
6
Acceptable Levels
4
2
0
0
20
40
60
80
100
Controlled Ventilation or Infiltrated Air Flow Rate (cfm)
120
pg. 2-2
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©Build Equinox 2013
Rev 1.9.2, Report # Black Box Case Study 6