User Guide

Single Zone Gas Monitor
P/N: 3015-4256 Rev 10 3
The Bacharach SZ is designed to continuously test for the presence of gas in an area that is located up to
500 ft (152.4 m) away from the monitor. The SZ monitor displays the type of gas being monitored, along
with displaying both the current gas level and the peak gas level detected in that area on its front panel
LCD. The monitor retains a log of previous readings that can be easily accessed for analysis.
An audible alarm and front panel indicators are provided to signal alarm and fault conditions, and relay
contacts are provided that can be used to trigger external alarm devices in the event of a system fault, or
if a leak (small), spill (medium), or evacuation (large) level of gas is detected. The system also includes a
4−20 mA current loop interface that can be connected to remote monitoring equipment.
The SZ requires only minor periodic maintenance such as the occasional replacement of filters. The
monitor incorporates active diagnostics that continuously check the system for proper operation. A front
panel indicator is provided to alert an operator of system malfunctions, and fault codes are generated that
enable the operator to identify the cause of the fault.
1.6.2. Understanding Monitoring Levels
Effective use of this monitor requires an understanding of what constitutes reasonable alarm set points for
the type of gas being monitored. Most systems leak some gas. In a good “tight” installation these
background levels will be acceptably low and often do not require corrective action. You can reduce
nuisance alarms and needless service calls if the alarm levels are set at practical limits. Bacharach has
developed recommended monitoring levels based on compliance to ANSI/BSR ASHRAE 15-2007 and
ASHRAE Safety Code 34-2007. These reference levels are listed in the Appendix.
The SZ monitor is shipped with its leak, spill, and evacuate alarm levels set at 100, 300 and 500 ppm
respectively. Setting the monitor at these recommended alarm levels will satisfy the needs of most users.
However, the ppm levels generated by system leaks into the environment are greatly influenced by the
volume of air in the sampling area, air circulation, size of the leak, distance to the monitoring point, and a
host of other variables. In some cases the alarm set points may need to be adjusted either up or down to
achieve effective monitoring.
1.6.3. Suggested Location of Sampling Point
At the point of a gas leak, the gas is nearly pure. As gas is dispersed into the air, the gas molecules
diffuse, causing a dilution of the original concentration. The SZ monitor measures the gas concentration
at the point the sample is collected. Therefore, if the termination of the collection line is not at the exact
point of the gas leak, then the monitor will read a diluted mixture of gas and air.
It should be noted that when refrigerant and ammonia gases are cold, they are heaver than air and settle
below the leak point. When the gas warms to room temperature, it becomes lighter than air and tends to
collect above the leak point. Consequently, the sampling point should be located as close as possible to
the source of a potential leak. If this is impractical, then the alarm set points should be adjusted to
compensate for the dilution of the gas.
The SZ monitor should be mounted outside of the mechanical room or just inside a doorway to the room.
This is the “split architecture design” for safety of the operator. The monitor should be readily accessible
for easy visual monitoring and servicing. The total length of the sample line + exhaust line can be up to
500 ft (152.4 m). If the area around the monitor is not well ventilated, then an optional exhaust line and
purge line can be run to an outside location. The total length of the exhaust line + the purge line cannot
exceed 200 ft (61.0 m).
It may be necessary to perform a “smoke” test of the mechanical room to determine the best monitoring
point. The smoke test would provide the pattern of air currents present in the room.
The SZ monitor should be kept dry. When used in a wet or humid area, it is highly recommended to use
the optional water stop accessory to avoid internal damage.