occupancy sensors

[badwolf]

Call out today to price some work, general stuff no problem, chap also asked if I could look into a problem with his bathroom lights. Main switch turns downlights and fan on. Ceiling mounted occupancy sensor turns on recessed tile lights, apparently when the wind blows, it activates the sensor, and subsequently the tile lights. so the wind gusts through the outside vent, to the fan and into the bathroom and its this that activates the sensor , my question is why? Is it a change in pressure or temp causing this, and any ideas how it could be rectified.

 

[davesparks]

Fit a gravity flap grille or back draught shutter in the duct

 

[badwolf]

I can't change the grill because it's mounted in the soffit, I can fit a fan with shutters, want to know really why it's doing it!, can you buy inline flappy bits, not seen them before! (Edit just seen them online that's probably the solution, still want to be able to give a reasonable explanation to the chap!)

 

[davesparks]

PIRs detect changes in heat which they 'see' as infra-red emissions (Passive Infra Red detector)
So the movement of hot air versus cold can set them off.
Or the draught is blowing something around in the room causing the operation

 

[NDG Elecs]

Fit an inline back draught and an external gravity flap. That should stop most of it quite well. The fan may have built in shuttering also. But check the fan is pushing the air through ok. Although that's not why you were called there I suppose.

Other than that I think Dave's answer above is logical.

Plastic Ducting Back Draught Shutter - Fantronix Limited

Huge choice of gravilty vent flap shutter wall ventilation grille colours - White, Brown, Black, Grey, Stone and Terracotta - Fantronix Limited

 

[Spoon]

PIRs detect changes in heat which they 'see' as infra-red emissions (Passive Infra Red detector)
So the movement of hot air versus cold can set them off.

And this is why you shouldn't fit PIR's for alarms above radiators. (general info)

 

[Richard Burns]

Occasionally some PIR sensors for indoor use also have a sound activation function as well as the motion detection, so if your sensor has this then it could be the sound of the wind activating the sensor.