Installation and Operation Guide | DGS Modbus
© Danfoss | ADAP-KOOL® | 2016.12
4 | RS8HJ102 |
NOTE
: The DGS Modbus should be installed plumb and level and
securely fastened to a rigid mounting surface.
Sensors must be located within the appropriate wire lengths from
the central control unit (if used).
In all cases the sensor supplied is designed for maximum sensitiv-
ity to a particular gas. However, in certain circumstances false
alarms may be caused by the occasional presence of sufficiently
high concentrations of other gaseous impurities. Examples of situ-
ations where such abnormalities may arise include the following:
• Plant room maintenance activity involving solvent or paint fumes
or refrigerant leaks.
• Accidental gas migration in fruit ripening/storage facilities (ba-
nanas - ethylene, apples - carbon dioxide).
• Heavy localised exhaust fumes (carbon monoxide, dioxide,
propane) from engine-driven forklifts in confined spaces or close
to sensors.
It is recommended setting the alarm delay to minimise false
alarms.
2.1 Machinery Rooms
There is no absolute rule in determining the number of sensors
and their locations. However, a number of simple guidelines will
help to make a decision. Sensors monitor a point 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 care-
fully select the sensor location. Also consider ease of access for
maintenance.
The size and nature of the site will help to decide which method is
the most appropriate to use. Locations requiring the most protec-
tion in a machinery or plant room would be around compressors,
pressurised storage vessels, refrigerant cylinders or storage rooms
or pipelines. The most common leak sources are valves, gauges,
flanges, joints (brazed or mechanical), filling or draining connec-
tions, etc.
• When mechanical or natural ventilation is present, mount a sen-
sor 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 leakage, such as the compressor, expan-
sion valves, mechanical joints or cable duct trenches.
Perimeter Detection, where sensors completely surround the area
or equipment.
• For
heavier-than-air
gases
such as halocarbon and hydrocarbon
refrigerants such as R404A, propane, and butane sensors should
be located near ground level.
• For
lighter-than-air gas
(e.g., ammonia), the sensor needs to be
located above the equipment to be monitored on a bracket or
high on a wall within 300 mm (12 in) of (or on) the ceiling – pro-
vided there is no possibility of a thermal layer trapped under the
ceiling preventing gas from reaching the sensor.
NOTE: At very low temperatures (e.g., refrigerated cold store), am-
monia gas becomes heavier than air.
• With similar density or miscible gases (e.g., CO2), sensors should
be mounted about head high (about 1.5 m [5 ft]).
However, with CO2 in a machinery room it is recommended to
mount it 0.3 m (1 ft) above the floor as the air flow is low and
CO2 slightly heavier than air.
• Sensors should be positioned just far enough back from any
high-pressure parts to allow gas clouds to form and be detected.
Otherwise, a gas leak might pass by in a high-speed jet and not
be detected by the sensor.
• Make sure that pits, stairwells and trenches are monitored since
they may fill with stagnant pockets of gas.
• For racks or chillers pre-fitted with refrigerant sensors, these
should be mounted so as to monitor the compressors. If extract
ducts are fitted the airflow in the duct may be monitored.
2.2 Refrigerated Spaces
In refrigerated spaces, sensors should be located in the return
airflow to the evaporators on a sidewall (below head-high is
preferred), or on the ceiling, not directly in front of an evapora-
tor. In large rooms with multiple evaporators, sensors should be
mounted on the central line between 2 adjacent evaporators, as
turbulence will result in airflows mixing.
2.3 Chillers
In the case of small water- or air-cooled enclosed chiller units
mount the sensor so as to monitor airflow to the extract fans. With
larger models also place a sensor inside the enclosure under or
adjacent to the compressors.
In the case of outdoor units:
• For enclosed air-cooled chillers or the outdoor unit for vari-
able refrigerant volume and variable refrigerant flow (VRV/VRF)
systems, mount the sensor so as to monitor airflow to the extract
fan. With large units also place a sensor inside the enclosure
under or adjacent to the compressors.
In the case of non-enclosed outdoor units:
• If there is an enclosed machinery section locate a sensor there.
• In the case of units with enclosed compressors, mount sensors in
the enclosures.
• Where you have protective or acoustic panels mount the sensor
low down under the compressors where it is protected by the
panels.
• With air-cooled chillers or air-cooled condensers with non-
enclosed condenser sections it is difficult to effectively monitor
leaks in the coil sections. With some designs it will be possible
using an airflow sensor to monitor airflow to the start–up fans in
the front or rear sections.
• If there is a possibility of refrigerant leaks into a duct or air-han-
dling unit install a sensor to monitor the airflow.
Weatherproof sensors should be used for unprotected outdoor
applications.
2. General Placement Guidelines
