18
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 cham-
ber. When a sufficient amount of smoke is detected in the sens-
ing chamber, the sensor signals an alarm state and the control-
ler 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 photoelectric (light scattering principle) pro-
cess called differential sensing to prevent gradual environmen-
tal changes from triggering false alarms. A rapid change in en-
vironmental 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. 21.) Access is through
the fan access panel. There is no sampling tube used at this lo-
cation. The sampling tube inlet extends through the side plate
of the fan housing (into a high pressure area). The controller
module is mounted in the left side of the control box, accessed
by opening the Control Box access door.
Fig. 21 — 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. 22.) The holes in the sampling tube
face downward, into the return air stream. The sampling tube is
attached to the control module bushing that extends from the
control box through the partition into the return air section of
the unit. The sensing tube is shipped mounted to the indoor
blower housing and must be relocated to the return air section
of the unit. Installation requires that this sensing tube be at-
tached to the control module bushing. See installation steps.
Fig. 22 — Return Air Sampling Tube Location in Unit
Without Economizer
RETURN AIR WITH ECONOMIZER
The sampling tube is inserted through the side plates of the
economizer housing, placing it across the return air opening on
the unit basepan. (See Fig. 23.) The holes in the sampling tube
face downward, into the return air stream. 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 con-
troller location. (This sensor is shipped in a flat-mounting loca-
tion. Installation requires that this sensor be relocated to its op-
erating location and the tubing to the sampling tube be con-
nected. See installation steps).
Fig. 23 — Return Air Sampling Tube Location in Unit
with Economizer
S
UPPLY AIR
S
MOKE
DETECTOR
S
EN
S
OR
RETURN AIR DETECTOR
SAMPLING TUBE
RETURN AIR DETECTOR
SAMPLING TUBE
Summary of Contents for 50LC 14
Page 26: ...26 Fig 34 50LC 14 26 Control Wiring Diagram...
Page 27: ...27 Fig 35 50LC 14 26 RTU Open Control Wiring Diagram...
Page 28: ...28 Fig 36 50LC 14 20 208 230V 3 Phase Power Wiring Diagram...
Page 29: ...29 Fig 37 50LC 24 26 208 230V 3 Phase Power Wiring Diagram...
Page 30: ...30 Fig 38 50LC 14 26 460V 575V 3 Phase Power Wiring Diagram...