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Simple
and Cheap Air Change Rate Measurement Using CO2 Concentration
Decays
Claude-Alain
Roulet 1 and Flavio Foradini.2
1 LESO-PB, EPFL, Lausanne, Switzerland.
2 E4Tech, Rue Louis Ruchonnet 57, CH 1003 Lausanne.
Abstract
Buildings are aired to
evacuate indoor pollutants, in particular those produced by the occupants.
CO2 is a good indicator of occupancy, as long as there is no
other significant source. This is the case in most buildings. Cheap,
portable analysers and loggers that allow easy recording of the CO2
concentration in a room or in the exhaust duct of a ventilation system are
available on the market. The peak value of CO2 concentration
during occupancy is an indicator of the minimum air flow rate per person.
Analysis of the decays observed when the occupants leave the building
provides the nominal time constant of the ventilated space, which is
directly dependent on the outdoor air flow rate from the ventilation
system and infiltration. Depending on the state of the ventilation system
during the decay, this method provides either the total outdoor air flow
rate provided by the system, or the infiltration rate. When combined with
a simple pressure differential measurement, this method can also be used
to check the air tightness of building envelopes. A user-friendly computer
program helps with the interpretation of the records. This paper describes
the method, its application to several rooms and buildings, and its
validation by comparison with SF6 tracer gas measurements.
Key words:
carbon dioxide concentration, occupancy, air infiltration, air flow
rate, tracer gas measurements air tightness.
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