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The provided document is an application note for Xtralis' VESDA-E air sampling smoke detection system, specifically designed for use in ventilation ducts. It offers comprehensive guidance for designing, installing, commissioning, and maintaining VESDA-E systems in this particular application.
The core function of the VESDA-E system in this context is to provide early warning smoke detection within ventilation ducts, which are critical pathways for air circulation in various environments. By continuously sampling air from within the ducts, the system can detect the presence of smoke particles at very early stages of a fire, often before visible flames or significant heat are present. This early detection capability allows for timely intervention, potentially preventing the spread of fire and minimizing damage. The system is designed to be highly sensitive and reliable, ensuring that even minute traces of smoke are identified.
For small ducts, defined as those with a width of less than 1 meter (3.28 ft), the VESDA-E VEP-1P detector utilizes an inlet pipe installed in the middle of the duct at half its height (H/2). An exhaust pipe is positioned approximately 0.5 meters (1.64 ft) downstream of the inlet pipe, at a quarter of the duct's height (H/4). Both sampling and exhaust pipe holes are oriented to face the duct airflow, a design choice intended to optimize air sampling efficiency and minimize flow faults. The number and size of sampling holes on the inlet pipe vary depending on the duct width, as detailed in Table 1 of the document. The exhaust pipe, however, consistently features four 10 mm (13/32 inch) holes, positioned in the middle of the duct width, at least 50 mm (2 inches) from the side walls. For the VESDA-E VEA system in small ducts, return air sampling is achieved using microbore tubes inserted into the return air duct, behind the exhaust grill. These tubes are recommended to be installed perpendicular to the duct airflow. A specific sampling point, VSP-980-ST, is used for VEA's duct sampling and can be mounted with a VEA Sampling Point Duct Bracket (VSP-1008). The inlet tube for the VEA detector is also installed in the middle of the duct at half its height.
In larger ducts, with widths ranging from 1 to 2 meters (3.28 to 6.56 ft), the VESDA-E VEP-1P system employs a more elaborate setup. The inlet pipe is branched into two sections, both located at a quarter of the duct's height (H/4). The exhaust pipe is inserted mid-height, approximately 0.5 meters (1.64 ft) downstream of the inlet pipes. This configuration ensures comprehensive air sampling across the wider duct. Similar to small ducts, the number and size of sampling holes on the inlet pipes are adjusted based on the duct width, as outlined in Table 2. The exhaust pipe in large ducts also maintains four 10 mm (13/32 inch) sampling holes, centrally located and at least 50 mm (2 inches) from the side walls. A crucial design consideration for both small and large ducts is that all inlet and exhaust pipes must be sealed at their far end with an end-cap. The pipes should be securely held in position at the duct walls using fittings like rubber grommets, with silicon recommended for an airtight seal. It is explicitly stated that the system is not suitable for use in flexible ducts. Furthermore, the document emphasizes that the detector should never simultaneously sample from multiple ducts or ambient environments.
Environmental conditions play a significant role in the system's performance. For the VESDA-E VEP-1P, installers need to measure temperature, humidity, static pressure, and air pressure within the duct. In air-return ducts, the smoke detector must be installed where static pressure is above -500 Pa and air velocity is below 20 m/s. The exhaust pipe should always be vented back into the ventilation duct, even if duct pressure is sometimes low, to account for future system changes. Condensation is a potential issue, especially when the dew point temperature of the air in the duct is at or above the ambient temperature where the detector is installed. To combat this, mounting the detector on its side is a recommended solution, positioning the laser chamber higher than the aspirator to prevent water from reaching the detection chamber. Regular inspection of sampling pipes for condensation, particularly during winter, is advised. For the VESDA-E VEA, sampling points must be installed in duct pressures within -30Pa to +30Pa, with a maximum differential pressure of 30Pa between sampling points on the same VEA unit. The exhaust of the VEA unit must also be within a pressure range of -30Pa to +30Pa.
Key installation considerations include ensuring that for air-return (negative pressure) ducts, smoke sampling occurs upstream and away from fans, humidifiers, heating coils, filters, and fresh air intakes. If the smoke detector is mounted on a vibrating duct, visco-elastic foam should be inserted between the mounting bracket and the duct surface. The inlet pipe/tube should be inserted at a distance of six to ten duct widths or diameters from any flow disturbance caused by sharp bends, plenums, nozzles, or branch connections. Sampling holes/points must be at least 50 mm (2 inches) away from the duct walls.
Commissioning the VESDA-E system involves a critical step: hole orientation adjustment. The differential pressure across the inlet and exhaust pipes must be maintained within ±20 Pa for normal smoke detector operation. Three methods are provided for this adjustment. Method 1 involves drilling holes, connecting pipes to the detector, normalizing airflow, inserting pipes with holes facing airflow, and then slightly rotating them until the %Flow is within 5% of the original reading. Method 2 requires a manometer to measure pressure, with pipes rotated until the pressure reading is within ±20 Pa. Method 3 is similar to Method 2 but uses a clear, flexible U-tube containing water, with pipes rotated until the water level on both sides of the tube is the same. After adjustment, the pipe positions are marked for future maintenance, and the detector is connected.
System performance verification is crucial and involves several steps. This includes connecting to the detector using the VESDA System Configurator (VSC) software or a hand-held programmer, recording initial background readings, conducting smoke tests inside the duct with a smoke cartridge, and recording peak smoke readings and time to reach the peak. Air leakage into the detector is also tested by removing the front cover, covering the electronics, and introducing smoke into the interior housing. If peak smoke readings exceed the initial background reading by more than 0.05%, it indicates possible leakage that needs correction. All pipe connections are checked, and tests are repeated if necessary. Finally, any additional tests required for compliance with local codes and standards are completed.
Maintenance features are outlined to ensure the system's long-term reliability. Local codes and standards for maintenance must always be adhered to. For the first year, the performance verification procedure should be repeated at least every six months, with any discrepancies investigated. The smoke detector will indicate when its on-board filter needs replacement, after which the performance verification procedure must be repeated. During each site visit, at a frequency specified by local codes and standards, several checks are performed. These include checking flow readings at the smoke detector(s) for any differences from previous visits, which could indicate issues like pipe fatigue, creep, or hole blockage. Condensation in the pipes/sampling tubes is also checked and addressed. For VEP-1P, the original hole orientation marks are checked to ensure they haven't moved, and readjustment is performed if necessary. Additionally, pipe maintenance involves disconnecting inlet and exhaust pipes from the detector, removing end caps, back-flushing with compressed air, ensuring all pipes are returned to their original configuration, and checking overall system performance.
General| Laser Class | Class 1 |
|---|---|
| Number of Sampling Pipes | 1 |
| Air Sampling Type | Continuous |
| IP Rating | IP30 |
| Type | Aspirating Smoke Detector |
| Operating Temperature | 0°C to 39°C (32°F to 102°F) |
| Operating Humidity | 10% to 95% RH (non-condensing) |
| Power Supply | 24 VDC nominal (18 VDC to 30 VDC) |
| Dimensions (H x W x D) | 200 x 200 x 100 mm |
| Sensitivity Range | 0.005 to 20% obscuration/m |
| Communication Interface | RS-485, Ethernet |
| Alarm Levels | Alert, Action, Fire 1, Fire 2 |
| Fault Relays | 1 |
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