Specifications
M GD-100 M anual
6109-9000 Rev 3 15
2.3. Machinery Rooms
There is no absolute rule in det ermining t he num ber of sens ors and their
locations. However, a number of simple guidelines will help to make a
decision. Sens ors monitor a poi nt as opposed to an area. If the gas leak
does not reach the sensor then no alarm will be triggered. Therefore, it
is extremely important to carefully select the sensor location. Also
consider ease of access for maintenance.
The size and nature of the site will help to decide which met hod is the
most appropriate to use. Locations requiri ng the most protection in a
machinery or plant room would be around compressors, pressurized
storage vessels, refrigerant cylinders or storage rooms or pipelines. The
most common leak sources are valves, gauges, flanges, joints (brazed or
mechanic al), filling or draining connections, etc.
• When mechanical or natural ventilation is present, mount a
sensor in the airflow.
• In machinery rooms where there is no discernible or strong
airflow then options are:
Point Detection, where sensors are located as near as
possible to the most likely sources of leak age, such as
the compressor, expansion val ves, mechanical joints or
cable duct trenches.
Perimeter Detection, where sensors completely surround
the area or equi pment.
• For heavier-than-air gases such as halocarbon and
hydrocarbon refrigerants such as R404A, propane, and butane
sensors should be locat ed near ground level.
• For lighter-than-air gas (e.g., ammonia), the sensor needs to
be locat ed above the equipment to be monitored on a bracket or
high on a wall within 12 in (300 mm) of (or on) t he c eiling –
provided there is no possibility of a thermal layer trapped under
the ceiling preventing gas from reaching the sensor.
NOT E: At very low tem peratures (e.g., r
efrigerated
cold store), ammonia gas becomes heavi er than air.
• With similar density or miscible gases, such as CO or CO
2
,
sensors should be m ount ed about head high (about 5 feet
[1.5 m]).
• Sensors should be positioned just far enough back from any
high-pressure parts to all ow gas clouds to form and be detected.