INCORPORATING COLD CHAIN
FEATURE
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refrigerated storage sample kits has all but eliminated the possibility of frozen sample holes by removing the sample point from the cold area — instead , placing it outside the freezer .
The sampling kit shown in Figure 1 branches off the main pipe , and with its unique design the sampling hole is transposed to an upstream location ( that is , at ambient temperature ) while maintaining an open-ended pipe inside the refrigerated area . This arrangement also allows pipe network maintenance to be carried out entirely above the refrigerated area at ambient conditions rather than inside the refrigerated area .
The ASD should be able to provide the staged alarms from a single detection device to keep costs down .
In freezer applications where sampling pipes are installed outside the chilled area , the pipes should be lagged or insulated to avoid condensation and possible freezing on the exterior walls of the pipe . Normally a single layer of 9mm thick insulation is adequate . Sampling pipe penetrations , through ceiling or wall insulation panels , must be properly sealed with urethane foam and / or flexible mastic .
Locating ASD sampling holes at specified intervals at the ceiling level is in many cases all that is needed to be code compliant . However , sampling pipes can often easily be extended to provide detection at lower elevation , for example within storage racks . That not only provides a higher density of sampling locations at a relatively low cost , but also helps to ensure that cold , diluted smoke from a small fire can quickly be detected .
The ASD units need to be installed in locations where they are unlikely to experience sub-zero temperatures . For sub-zero freezers it stands to reason that the units will always be installed outside the protected area , typically in a service corridor or ceiling void . Highend ASD systems will tolerate sampled air temperatures as low as -20 ° C , but do check specifications to assess operating limits . If sampled air is likely to arrive at the ASD unit at a temperature lower than product specification allows , it is relatively easy to warm the sampled air before it enters the detector , either through ambient temperature transfer or in some cases by installing dedicated trace heating on the sample pipes . Manufacturers of ASD systems should be able to provide advice , taking into
The product has been tested to ensure it ’ s suitable for use in harsh environments , such as cold stores and freezers .
consideration temperature and pipe material characteristics .
Exhaust air from the ASD unit must be piped back into the protected area . That creates a closed loop system , which prevents pressure differences from affecting airflow monitoring and avoids warm air migrating into the freezer if the unit is shut down .
ASD systems are often used to activate pre-action sprinklers . Early warning alarms from the ASD may be used for early , manual intervention , while the later , confirmed fire alarm can be used for activation . Alternatively , if more than two
ASD units are installed , then ‘ coincidence detection ’ can be deployed where both detectors need to reach pre-determined alarm thresholds before extinguishing is activated .
A properly engineered ASD design using a product that does not alter its calibration and performance over time , accompanied by a pipe network design using established methodologies , should result in a system that provides cost effective , reliable detection at all times , with significantly reduced probability of false alarms . CLA
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