A New and Better Tool for Measuring
Indoor Air Quality
For most of us a
glass thermometer is the device we first think of when asked how
to measure temperature. The glass thermometer is an excellent
tool for some temperature measurements, such as your child's fever.
It is certainly not the only way to measure temperature and in
many applications it is not the best. To measure the high temperatures
of molten metals it is better to use a thermocouple. To measure
a few l/ l00ths of a degree temperature change in a chemical reaction
a thermistor is a better choice. These devices are all useful
tools. All have applications in which they are the best choice
and all of them work poorly or not at all in other applications.
When we set out to measure other parameters such as air quality
we again use tools. The particular tool is not important. It is
only important that it is readily available, affordable and provides
reproducible results.
Why is CO2 monitoring often specified?
When building tenants and owners first decided to monitor indoor
air quality a suitable tool was required. One approach was to
assume that the deterioration of indoor air quality was directly
attributable to human occupancy. One measure of human occupancy
is carbon dioxide, because we all exhale carbon dioxide. Since
CO2 detectors originally developed for greenhouses were available,
almost affordable and reproducible at the time, standards were
developed based on parts per million of carbon dioxide. CO2 served
as a convenient tool for predicting human comfort. However like
the expansion of mercury in a glass thermometer CO2 has little
direct effect on human comfort. CO2 is not harmful to people in
the concentrations normally encountered in buildings. It tracks
the occupancy level of a space but fails completely to respond
to other contaminants that can be much more serious. These other
contaminants include, formaldehyde from new carpets and construction
materials, CO from incomplete combustion and solvents from paint
and art supplies.
The new tool
Full spectrum sensors, sometimes called VOC sensors because they
measure “Volatile Organic Compounds” sense ketones in human respiration.
They also sense chemicals which have been associated with health
problems such as formaldehyde given off by chip board and carpets..
Potentially, they offer the promise of improved air quality monitoring
since they measure both human occupancy and environmental chemicals.
Until now instruments using these sensors could lack the sensitivity
to accurately measure the very low levels of VOC’s associated
with human occupancy. They also were affected by changes in temperature
and humidity. The new electronics in our AQT-2000 have overcome
these limitations. Our 15 bit A/D convertor technology is 32 to
128 times more precise than older instruments. The on-board temperature
and humidity sensors eliminate errors. Our smart micro-processor
algorithm has been developed through four years of field experience.
The AQT-2000 is comparable to CO2 monitors in accuracy of monitoring
human occupancy. It has the significant advantage that it also
detects harmful and dangerous chemicals in the occupied space.
It is also lower in cost than CO2 monitors.
Because the AQT-2000 is much newer than CO2 monitors there will
be a time delay before standards groups write it into there specifications.
Until that time the hand held module incorporates a convenient
and inexpensive data logger which can be left attached to the
monitor to log air quality for periods from a day to 2 weeks.
The data can be easily transferred to a desktop computer and graphed
to demonstrate to potential clients that it is working well.
Which choice?
Why choose the AQT-2000 over CO2 monitors?
1. It does more. It senses and can exhaust harmful chemicals that
may be present in buildings. As well, it can provide fresh air
in proportion to demand from occupancy.
2. It costs less. Typically the air quality monitor will cost
less than half as much as a CO2 monitor.
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