Fluke 975 AirMeter Installation and operating instructions

Application Note
Fluke 975 Air Meter:
Environmental carbon
dioxide analysis
From the Fluke Digital Library @ www.fluke.com/library
Carbon dioxide (CO2) is a naturally
occurring, colorless, odorless, non-
combustible gas that is ever present
in the atmosphere, usually ranging in
concentrations from 300-600 ppm
(parts per million).
In nature, CO2is used in plants for
photosynthesis (CO2in, O2out), released
through the respiration of aerobic
organisms (O2in, CO2out), released
by decaying life forms and outgassing
volcanoes, and is a product of the
complete oxidation (combustion) of
carbon based compounds. CO2is also
commercially produced and has many
commercial and industrial uses from
beverage carbonation to “dry ice” to
fire extinguishers. How, then, is CO2a
significant factor in environmental Indoor
air quality?
Processes that produce CO2in a
typical occupied space include
human and animal respiration,
decaying plant and animal life,
such as garbage in a kitchen,
and combustion processes of
fossil fuel burning equipment.
Most fossil fuel burning equip-
ment, such as furnaces, boilers,
water heaters and fireplaces, has
provisions to vent the combus-
tion products directly to the out-
doors—but venting systems can
become inhibited or even fail.
Stoves, ovens and space heat-
ers may not utilize a vent sys-
tem, relying instead on exhaust
hoods, building ventilation, or
in the case of many residential
applications, natural ventilation
through stack effect and struc-
tural leakage.
CO2standards
ANSI/ASHRAE Standard 62.1-
2004 Ventilation for Acceptable
Indoor Air Quality addresses
minimum requirements for ven-
tilation and indoor air quality for
typical indoor breathing spaces
that will be acceptable to occu-
pants. The requirements are
“intended to minimize the poten-
tial for adverse health effects.”
The standard is applicable to
indoor occupied spaces except
when other usages or standards
require greater amounts of ven-
tilation. Generally speaking,
ventilation rates are selected for
contaminant and odor control
based on the maximum expected
occupant density and activity
level.
•When these ventilation rates
are maintained, CO2levels
created by human respiration
should always be at accept-
able, healthy levels.
•When the occupied space is at
maximum expected occupancy
with the recommended venti-
lation rate, CO2levels will gen-
erally be, depending on space
usage, about 350-1,000 ppm
above outside air CO2levels.
This is well below the OSHA
workplace threshold of 5,000
ppm CO2. NIOSH and ACGIH fur-
ther stipulate a maximum expo-
sure rate of 30,000 ppm CO2for
15 minutes. CO2is an asphyxi-
ant, and at 50,000 ppm CO2is
considered to be an immediate
threat to life.
Measuring air flow at a supply register.

2 Fluke Corporation Fluke 975 Air Meter: Environmental carbon dioxide analysis
Proper ventilation must be
maintained in occupied spaces,
but ventilation is not free. HVAC
equipment must be sized, not
only for the building load, but
the ventilation load as well.
Outside air used for ventila-
tion must be heated, humidified
and cleaned in the winter, and
cooled, dehumidified and cleaned
in the summer. A building may
not have maximum occupancy in
all spaces at all times. Since ven-
tilation rates are based on maxi-
mum occupancy, over-ventilation
will occur when spaces are not
at maximum occupancy. When
ventilation is more than required,
energy is wasted.
CO2monitoring and
demand controlled
ventilation
CO2can be used as a gauge for
determining the effective ven-
tilation rate of occupied spaces
and as a warning signal for
some processes that may have
gone wrong. It’s a predictable
indicator of occupancy. When
CO2monitoring is used to con-
trol building ventilation rate, it’s
called demand controlled venti-
lation (DCV).
The primary purpose of DCV
is to avoid over-ventilation and
thereby reduce energy costs
when spaces are not at full occu-
pancy. One or more CO2sensors
are used to control the position
of the ventilation air dampers
based on the CO2level within
the occupied space.
The maximum open position of
the outdoor air dampers is based
on the ventilation rate, as though
DCV were not being used. The
minimum open position during
the occupied period is normally
set at 20 % of the maximum rate
regardless of the CO2content of
the occupied space, however,
depending on the age and usage
of the building, this base ventila-
tion rate could be anywhere from
15 to 50 %. This minimum posi-
tion is required for basic build-
ing function ventilation, such as
materials off-gassing.
To qualify for DCV, a time
lag requirement must be met.
To meet it, proper CO2levels
must be achieved within a time
period, and that time period
depends on the total cfm/person
ventilation rate and the volume
of the space to be ventilated.
The data logging function of the
Fluke 975 AirMeter™test tool can
be used to ensure the time lag
conditions are being met.
The three most common DCV
control schemes are proportional
control, PI or PID control, or set-
point control. With proportional
control, the ventilation rate is
directly proportional to the rising
and falling indoor CO2level. PI
or PID (Proportional+Integral+De
rivative) control compensates or
compensates and anticipates for
rising and falling CO2levels by
accelerating the ventilation rate
according to the indoor CO2rate
of change.
For spaces that are typically
either empty or fill rapidly, like a
classroom, setpoint control goes
to maximum ventilation as soon
as an increase in CO2is sensed.
Since CO2can vary widely
depending on environment (300-
600 ppm), DCV target ventilation
rates are based on the differ-
ential between outdoors and
indoors. The outdoor air damper
“start open” setpoint should be
set at the minimum outdoor CO2
level unless CO2differential is
used. CO2differential uses an
outdoor CO2 sensor to compare
actual outdoor verses indoor CO2
levels for more accurate control.
Mysterious CO2
Fossil fuel burning appliances
such as stoves, ovens, furnaces,
boilers and water heaters pro-
duce high concentrations of
CO2during complete combus-
tion and are not always directly
coupled to a vent system. While
a properly ventilated occupied
space may have CO2levels of
1,500 ppm, the combustion
products of a fossil fuel burning
appliance has CO2levels ranging
from 70,000-120,000 ppm, with
30-70 ppm CO as well if the
appliance is clean and properly
set up.
Stoves and ovens may be
unvented in residential applica-
tions, or rely on exhaust hoods
in commercial applications to
vent the combustion products to
the outdoors. Improperly applied
kitchen exhaust systems can
ventilate the kitchen, but not the
appliance. This can be checked
by monitoring CO2levels in the
kitchen and adjoining spaces.
Until recent years, gas fur-
naces, boilers and water heaters
were decoupled from the vent
system (chimney) by a draft
hood. Vents that produced exces-
sive draft would ventilate the
equipment room, but not neces-
sarily the gas appliance because
of the “cold curtain” that was
created at the draft hood. The
result of this was flue products
spilling into the equipment room.
DCV differential target levels are based on the ventilation cfm requirement
per person. Combined with those figures, the 975 AirMeter™can be used
to determine whether the space is properly ventilated, over-ventilated, or
under-ventilated. And with that kind of information, technicians can venti-
late the space at the lowest possible heating and cooling cost.
10 cfm/person= 1,000 ppm CO2differential between indoors and outdoors
15 cfm/person= 700 ppm CO2differential between indoors and outdoors
20 cfm/person= 500 ppm CO2differential between indoors and outdoors
25 cfm/person= 420 ppm CO2differential between indoors and outdoors
30 cfm/person= 350 ppm CO2differential between indoors and outdoors

3 Fluke Corporation Fluke 975 Air Meter: Environmental carbon dioxide analysis
Since CO2is heavier than air,
the CO2would settle at the floor
where the water heater burner
is typically located, depriv-
ing it of oxygen, and resulting
in incomplete combustion and
elevated CO. As this process con-
tinued, the concentration of CO
increased creating a more dan-
gerous situation.
Monitoring CO2levels in the
equipment room is likely to alert
occupants to potentially haz-
ardous situations more quickly,
before the process gone wrong
can accelerate the production of
CO. (CO2is heavier than air and
tends to settle, CO is lighter than
air and tends to rise.) Since the
combustion process of fossil fuels
produces 1.3 to 2 times as much
water as CO2, an unexplained
increase in humidity levels, or
condensation on cold surfaces,
can also alert one to a venting
problem.
When an occupied space
is adjacent to a warehouse or
parking garage, simultaneous
increases in both CO2and CO
can indicate ventilation system
problems. Garages and ware-
houses should be independently
exhausted and the absolute
pressure of the occupied space
should be maintained above the
absolute pressure of the adjoin-
ing garage or warehouse.
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©2006 Fluke Corporation. All rights reserved.
Printed in U.S.A. 10/2006 2786485 A-EN-N Rev A
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Conclusion
Whether one wishes to:
•spot check areas of concern
•use the MIN MAX feature on
the Fluke 975 AirMeter™to
narrow in on problem sources
•use the “technical detective”
data logging feature to analyze
a space over an extended time
period to solve elusive prob-
lems
the Fluke 975 AirMeter™is a
tool that can save time, money,
and even lives.
Reading CO2levels in an office space.