A lecture hall hosts classes attended by anywhere from 5 to 200 students across a single day, with long unoccupied periods between sessions. The facilities team must choose between a passive-infrared (PIR) motion sensor and a carbon dioxide (CO2) sensor to drive ventilation for this space. For this particular use pattern, the stronger choice is:

Question

Accepted Answer

A CO2 sensor, because the ventilation rate needs to scale with the number of occupants and rising CO2 reflects that density level.

Answer

A PIR sensor, because an occupancy signal from a motion detector is sufficient for setting an appropriate fresh-air supply rate.

Answer

Either sensor performs equivalently, because both generate a binary occupied-or-not output on which the controller can act.

Answer

Neither sensor is appropriate, because lecture-hall ventilation should be run at the full design rate during all scheduled teaching hours.

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A lecture hall hosts classes attended by anywhere from 5 to 200 students across ...

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