INDOORS AIR QUALITY CONTROL

There is some evidence that, in certain situations, mixed-gas indoor air quality sensors in buildings may pick up traffic-related pollutants.Current sensor technology indicates that, generally, the only cheap, practical option is a CO cell, although in certain circumstances CO2 or mixed-gas sensors may be feasible.

Locating a CO sensor in the air intake will cause the control to activate if outdoor air quality is poor and continues as long as the outdoor air exceeds the set points regardless of indoor levels.If the pollutant episode lasts for an extended period, at some point the indoor concentration will exceed that outdoors, but a sensor in the intake will not recognise this situation.

A number of ways had been identified as solutions, but the obvious way of overcoming the limitations of sensors in the air intake or return air alone is to use them both.(Fig. 26)

The use of one electrochemical CO sensor stretches the technology to its limits and two would need a dead band sufficiently large enough to account for the accuracy of both sensors.

The most appropriate control is a simple on/off type, the control objective being simply to minimise the effects of pollution.The pollutant set point is not a limit that can be controlled to, but an indication that action is required.

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