Technical Bulletin
2
SuperDuct Four-Wire Duct Smoke Detector
Related documents
In addition to this document, important information regarding
the proper installation and maintenance of duct smoke
detectors is provided in the following standards:
• NFPA
70
National Electrical Code
• NFPA
72
National Fire Alarm Code
• NFPA
90A
Installation of Air Conditioning and
Ventilating Systems
• UL
268A
Smoke Detectors for Duct Applications
• ULC
529
Smoke Detectors for Fire Alarm Systems
• NEMA
Guide for Proper Use of Smoke Detectors in Duct
Applications
Duct smoke detector limitations
SuperDuct duct smoke detectors will not operate without
electrical power.
SuperDuct duct smoke detectors will not operate as designed
outside of the listed electrical and environmental
specifications.
SuperDuct duct smoke detectors will not sense smoke unless
the ventilation system is operating and the sensor’s cover is
properly installed.
SuperDuct duct smoke detectors may not operate as designed
unless the duct detector is installed in accordance with these
instructions and all applicable national and local codes as
determined by the local authority having jurisdiction.
Product description
Overview
The SuperDuct Four-Wire Duct Smoke Detector is used to
detect smoke under extended temperature ranges in self-
contained commercial HVAC units, such as those typically
found on building rooftops. In self-contained commercial
HVAC units, the HVAC equipment is enclosed in a single
package to protect the internal components (compressor,
condensing unit, heating coils, etc.) from adverse
environmental conditions. Hinged or removable service panels
provide access to the equipment.
WARNING:
The SuperDuct duct smoke detector is not
intended as a substitute for open area protection.
The SuperDuct duct smoke detector (see Figure 1) comprises a
controller and one or two sensors. Its primary function is to
provide early warning of an impending fire and shut down the
HVAC unit in order to prevent smoke from circulating
throughout the building. It is typically used to detect smoke in
the supply side of the HVAC system but can provide
supervision of the return side as well.
Note:
Install supply-side sensors at a point downstream from
the supply fan and air filters and return-side sensors at a point
before the return air is diluted by outside air.
Fan
Fan
FACP
Outside
air
Smoke
sensor
CO
sensor
2
Return
air
Exhaust
Smoke
sensor
Supply
air
Filter
Coil
HVAC
controls
Test/reset
station
Next controller
CO sensor output
2
Sensor
controller
Damper
Power
distribution
panel
Rooftop HVAC unit
Figure 1: Duct smoke detector application diagram
The controller is designed for multiple operating voltages and
provides relay contacts for connection to fire alarm systems,
HVAC controls, and other auxiliary functions. It can be
attached to a sensor and installed as a single unit or it can be
installed separate from the sensor. In installations where the
duct smoke detector’s controls and indicators are hidden from
view, a remote test/reset station can be connected to the
controller to provide these functions.
Note:
In installations using two sensors, the duct smoke
detector does not differentiate which sensor signals an alarm
or trouble condition.
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. When the sensor’s
ability to compensate for environmental changes has reached
its limit (100% dirty), the sensor signals a trouble condition.
Air is introduced to the duct smoke detector’s sensing
chamber through a sampling tube that extends into the HVAC
duct and is directed back into the ventilation system through
an exhaust tube. The difference in air pressure between the
