The detector provides early detection of smoke in the air moving through heating and ventilation (HVAC) ducts in commercial and industrial premises. Its purpose is to prevent the re-circulation of smoke from an area on fire to areas unaffected by the fire when used with a Series 65 or Orbis detector. It provides a volt-free changeover relay rated at 30V, 1A.
The duct smoke detector is supplied as a housing with a base fitted for either a conventional detector or an analogue addressable detector. The housing has provision for electrical connections depending on the type of detector fitted. For technical data on the detector head, please refer to the relevant product guide or PIN sheet.
The duct smoke detector is fitted to the side, the top or the bottom of the ventilation duct and has two tubes which extend into the air duct through holes in the duct wall. The perforated sampling tube which spans the duct is placed in the airflow upstream of the exhaust tube which causes a pressure differential in the duct detector. Air is sucked up the sampling tube, across the detector and exhausted back into the air duct.
The duct smoke detector is designed to operate in ducts with a width of between 300mm and 3000mm. A sampling tube of 360mm, suitable for duct widths up to 540mm, is supplied as standard. Longer sampling tubes for wider ducts may be ordered separately:
- 150—750mm: Part no 53541-170
Part no 53541-171
Part no 53541-172
The tubes should be long enough to reach from one side of the duct to the other and it may be necessary to use a tube that is too long and cut it to slightly more than the duct width. Since the tube needs to be supported on both sides a hole should be cut in the opposite wall of the air duct to allow the tube to protrude slightly. The tube must be closed with the small red bung provided.
The exhaust tube does not need to extend across the duct and is therefore supplied at a fixed length.
To minimise the impact of air turbulence and stratification on performance a duct smoke detector should be located as far as possible downstream
from any obstruction (ie, deflector plates, elbows, dampers, etc). In all situations confirmation of velocity and pressure differential within specifications is required.
A uniform non-turbulent (laminar) airflow between
0.5 and 20m/s must be present in the air duct. The pressure differential between sampling (high pressure) and exhaust (low pressure) tubes should be
between 0.025 and 3mbar.
If installing the detector in the return air side of the air duct, locate it at a point where it will not be diluted with outside air.
If possible, install duct smoke detectors upstream of air humidifiers and downstream of dehumidifiers.
To minimise false alarms avoid mounting the detector in areas of extreme high or low temperatures, in areas of high humidity or in areas containing gases or high amounts of dust.
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