Smoke Detector Locations, Supply Air

50HCQA

Duct smoke sensor

	controller
	Conduit nuts
	(supplied by installer)
	Conduit support plate
	Terminal block cover
Controller housing	Cover gasket
and electronics	(ordering option)
Conduit couplings	Controller cover
Conduit couplings
(supplied by installer)
	Fastener
	(2X)

	Trouble
Alarm	Power
	Test/reset
	switch

C08208

Fig. 58 - Controller Assembly

Air is introduced to the duct smoke detector sensor’s sensing chamber through a sampling tube that extends into the HVAC duct and is directed back into the ventilation system through a (shorter) exhaust tube. The difference in air pressure between the two tubes pulls the sampled air through the sensing chamber. When a sufficient amount of smoke is detected in the sensing chamber, the sensor signals an alarm state and the controller automatically takes the appropriate action to shut down fans and blowers, change over air handling systems, notify the fire alarm control panel, etc.

The sensor uses a process called differential sensing to prevent gradual environmental changes from triggering false alarms. A rapid change in environmental conditions, such as smoke from a fire, causes the sensor to signal an alarm state but dust and debris accumulated over time does not.

For installations using two sensors, the duct smoke detector does not differentiate which sensor signals an alarm or trouble condition.

Smoke Detector Locations

Supply Air —

The Supply Air smoke detector sensor is located to the left of the unit’s indoor (supply) fan. See Fig. 60. Access is through the fan access panel. There is no sampling tube used at this location. The sampling tube inlet extends through the side plate of the fan housing (into a high pressure area). The controller is located on a bracket to the right of the return filter, accessed through the lift-off filter panel.

Duct smoke sensor

Exhaust tube

Exhaust gasket

See

Detail A

Intake gasket

TSD-CO2 (ordering option)

Plug

Sampling tube

(ordered separately)

Coupling

Detail A

Magnetic test/reset switch

Sensor housing and electronics

Cover gasket

(ordering option)

Sensor cover

Smoke Detector Sensor

C08245

Fig. 60 - Typical Supply Air Smoke Detector Sensor

Location

Return Air without Economizer —

The sampling tube is located across the return air opening on the unit basepan. See Fig. 61. The holes in the sampling tube face downward, into the return air stream.

Alarm	Power
Trouble	Dirty

C08209

Fig. 59 - Smoke Detector Sensor

The sampling tube is connected via tubing to the return air sensor that is mounted on a bracket high on the partition between return filter and controller location. (This sensor is shipped in a flat-mounting location. Installation requires that this sensor be relocated to its operating

50HCQA specifications

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