User guide

Application Guide | Gas detection in refrigeration systems
16 DKRCI.PA.S00.A1.02 | 520H12772 © Danfoss | DCS (MWA) | 2018.05
Alarm / sensitivity range
of gas detectors
All commonly used gas detectors have a
proportional output signal (4-20 mA, 0-10 V, or
0-5 V), and some pre-set alarm settings.
When selecting the actual measuring range and
sensor type, several factors should be considered:
In general, alarm levels should be as low as
practically possible, depending on the actual
refrigerant and the purpose of the alarm.
There are often requests for more alarm levels,
but experience shows that two alarm limits are
sufficient for gas detection.
The pre-alarm provokes a reaction, either
automatically and/or in the form of alarm
instructions; if not, the main alarm may
be triggered. This entails a whole series of
consequences, including switching off machines.
A main alarm should rarely (and preferably never)
be necessary!
Alarms can be chosen to warn against gas
concentrations less than levels acceptable for
personal safety on short term or long term. Alarm
levels can also be chosen to specific levels due to
flammability/explosion risk.
The following recommendations are based on
the present experience with suitable limits,
taking into account the above mentioned
conditions, but also requirements in EN 378:2016,
ISO 5149:2014, IIAR 2-2017 and ASHRAE 15:2016.
The Danfoss gas detection units offer two pre-
set alarms and a proportional output signal,
both analog 4-20 mA and digital Modbus.
With this configuration, is it possible to fulfil all
requirements for alarm levels needed within the
specific operation range of the sensor.
DANFOSS recommendations for alarm levels:
EN 378:2016
National
requirements
Comply with: EN 378
Sensor type
LEVEL
I
Personal safety
(occupational)
( TWA-values)
Sensor type
LEVEL
II
(pre-alarm)
Sensor type
LEVEL
III
(main-alarm)
[ppm] [ppm] [ppm]
Ammonia R717
Machinery rooms EC 500 P 30000
Machinery rooms EC 25 EC 150
Safety valves -
vent line
– SC 9000
Carbon Dioxide R744 (CO
2
) IR 5000 IR 9000
Halocarbon
HFC
R134a, R404A,
R407C, R410A, R507
SC 500
1
) SC 900
Hydrocarbon
HC
R290, R600, R600a,
R1270
Concentration
≤ 20% of LFL
CT 800 CT 2500
1
) 50% of TWA-value
Note: All proposed levels are ≤ the max. values in EN 378:2016
Danfoss recommendations
for alarm levels
DANFOSS recommendations for alarm levels:
ASHRAE 15:2016
Comply with: ASHRAE 15:2016
Sensor type
LEVEL
I
Personal safety
(occupational)
( T WA-values)
Sensor type
LEVEL
II
(pre-alarm)
[ppm] [ppm]
Carbon Dioxide R744 (CO
2
) IR 5000 IR 9000
Halocarbon
HFC
R134a, R404A,
R407C,R410A, R507
SC 500
1
) SC 900
Hydrocarbon
HC
R290, R600, R600a,
R1270
Concentration
≤ 25% of LFL
CT 500 CT 2500
1
) 50% of TWA-value
Note: All proposed levels are ≤ the max. values in ASHRAE 15:2016