Specifications

Halogen Gas Monitor – MultiZone Remote Display
Instruction 3015-5157
7
Functional Overview
General Description
Refrigerant monitors are specified to support compliance to federal, state and local safety codes governing
refrigerant emissions. Avoiding significant refrigerant loss reduces equipment replacement costs, maintains
equipment efficiency, promotes safety, and protects the environment.
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 HGM-RD 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 user to identify the cause of the fault.
Communication Options
The HGM-RD features full two-way communications via an RS-485 interface. MODBUS RTU is the
communication protocol standard. The instrument can be connected to a Building Management System or it
may be operated as a stand-alone system with Bacharach’s HGM-MZ (P/N 3015-5074).
Please refer to the Appendix for a more complete discussion of communication protocols.
Understanding Monitoring Levels
Effective use of this instrument requires an understanding of what constitutes reasonable alarm set points for
the types of gasses being monitored. Refrigerant manufacturers define allowable exposure levels and
threshold limit values in units of parts per million (ppm). Bacharach has developed recommended monitoring
levels based on compliance to ANSI/BSR ASHRAE 15-1994 and ASHRAE Safety Code 34-1992. These
reference levels are listed in the Appendix.
Setting the unit 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 set points may need to be adjusted either up or down to achieve effective monitoring.
Suggested Location of Sampling Points
At the point of a refrigerant leak the gas is nearly pure. As the refrigerant is dispersed into the air, the gas
molecules diffuse causing a dilution of the original concentration. The HGM-MZ measures the refrigerant
concentration at the precise point the sample is collected. Therefore, if the termination of the collection line is
not at the exact point of the refrigerant leak, then the unit will read a diluted mixture of the refrigerant gas
and air.
It should also be noted that refrigerant gas is heavier than air and tends to collect below the point of a leak.
Therefore samples taken near the floor will have a greater concentration of gas than those collected above
the source of a leak will. Consequently, sampling points should ideally be located as close as possible to the
source of potential leaks. Line-end filters should be mounted 12" to18" above the floor. If this is impractical,
then the alarm set points should be adjusted for that zone to compensate for the dilution of the refrigerant gas.
DO NOT plug any of the zones. Plugging a zone will give the monitor a false indication during start up.
The HGM-MZ should be centrally located in the mechanical room and be readily accessible for easy visual
monitoring and servicing. Air sample tubing may be run in lengths up to 500 feet. The fresh air purge line
should draw from an area that does not contain any refrigerant gas and cannot exceed 300 feet in length. The
exhaust line should run to an out side location if possible. The length of the exhaust line cannot exceed
300 feet.
Ideally, two to three pick up points spaced around each chiller will provide sufficient coverage. It may be
necessary to perform a “smoke” test of the mechanical room to determine the best locations. The smoke test
would provide the pattern of air currents present in the mechanical room.