CO2 Monitoring
The monitoring of spaces for optimum ventilation formerly
involved excessively expensive instrumentation. Invariably, such
measurements required the use of special tracer gas, injection devices,
trailing tubes and complex data recorders. As a consequence, even to this
day, little is really known about the ventilation rate in the majority of
buildings.
Measuring the concentration of metabolic carbon dioxide,
as a means of determining the ventilation
rate, has, for sometime, held an
attraction. However, again, factors such as equipment cost, the need for
regular calibration and the lack of a real understanding about the role of
CO2 as
an indicator of occupancy generated pollution, have prevented widespread
uptake.
These problems are now largely overcome following the availability
of a new generation of stable CO2
sensors combined with inexpensive data loggers.
There is therefore little excuse for accepting poor ventilation in
occupied spaces.
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Case Study
The CO2 trace,
illustrated in Figure 1 demonstrates the potential
and power of this approach. This Figure
illustrates measurements made in a cellular office of approximately
10m2
floor area. The office is naturally ventilated, with openable windows, and
is probably typical of many working environments within the UK.
The trace, itself, is largely self explanatory but demonstrates
that, on the particular day of monitoring, the room was inadequately ventilated. As indicated in the Figure, various parts of the
trace can be selected to evaluate the per person ventilation rate and the
whole room ventilation air change rate - tasks that once required almost
prohibitive cost and effort.
A quick check that the sensor is giving
sensible results is possible by measuring the outdoor CO2
concentration. In this instance, the measured value was between 380-400ppm
and, hence, well within the expected range.
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