Danfoss Gas detection in refrigeration systems Application guide
Application Guide
Gas detection in
refrigeration systems
GDIR.danfoss.com
Application Guide | Gas detection in refrigeration systems
Contents Page
Commonly used abbreviations......................................................................3
Introduction........................................................................................4
Sensor technology..................................................................................4
EC - Electrochemical sensor .....................................................................4
SC - Semiconductor sensor (solid state)..........................................................5
P- Pellistor sensor...............................................................................6
IR - Infrared.....................................................................................6
Which sensor is suitable to a given refrigerant? ..................................................6
Sensor response time ...............................................................................7
The need for gas detection..........................................................................8
Legislation and standards...........................................................................8
Requirements for gas detection according to EN 378:2016 and ISO 5149:2014 ....................9
F-Gas legislation.............................................................................. 10
Requirements for gas detection according to ASHRAE 15-2016 (USA)........................... 10
Requirements for gas detection according to ANSI/IIAR-2 (USA) ................................ 10
Installation guideline ............................................................................. 11
Location of gas detectors ......................................................................... 12
Number of gas detectors in a facility............................................................... 13
Calibration / test.................................................................................. 13
Calibration methods ..............................................................................14
Method I Calibration by means of replacing sensor heads...................................... 14
Method II Calibration of gas detectors by means of calibration gas .............................14
Bump test ....................................................................................15
Alarm / sensitivity range gas detectors ........................................................ 16
Danfoss recommendations for alarm levels.................................................... 16
Actions triggered by gas detection ...............................................................18
References .......................................................................................19
Annex I - Common refrigerant data................................................................ 20
Annex II - EN 378:2016 and ISO 5149:2014 ......................................................... 20
Annex III - ASHRAE 15-2016 ....................................................................... 21
Commonly used
abbreviations
© Danfoss | DCS (mwa) | 2018.08
• LFL = Lower Flammability Level
• OEL = Occupational Exposure Limits
• ATEL = Acute-Toxicity Exposure Limit
• ODL = Oxygen Deprivation Limit
• OSH = Occupational Safety Limit
• ODP = Ozone Depletion Potential
• GWP = Global Warming Potential
• TRK = Technische Richtkonzentrationen
• MAK = Maximale Arbeitsplatzkonzentrationen
• TLV = Threshold Limit Value
• STEL = Short Term Exposure Limit
• PEL = Permissible Exposure Limits
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Application Guide | Gas detection in refrigeration systems
e
Sensitivity
Introduction Gas detection and leak detection are two distinct
activities that covers the same topic, but the
methods are very different.
Gas detection covers the analysis of air samples
to determine whether they contain refrigerant
gas. Leak detection is a systematic inspection
of a refrigeration system to determine whether
it is leaking. The terms gas detection and leak
detection are not interchangeable, and must not
be mixed.
Leak detection equipment is normally handheld equipment carried by people, and used for
detection of leaks in refrigeration systems. There
are several types of leak detectors available,
ranging from simple techniques like soapy water
to sophisticated electrical instruments.
Gas detection equipment is usually used in
a fixed installation with a number of sensors
located in areas where refrigerant might be
expected to accumulate in the event of a plant
leak.
Sensor technology The choice of sensor technology for refrigerant
gas detection will depend on the specific target
refrigerant gas and ppm range required. Danfoss
offers a range of different sensor technologies
These locations depend upon the layout of
the machinery room and adjacent spaces, on
the configuration of the plant and also on the
refrigerant in question.
Before selecting the appropriate gas detection
equipment, a number of questions have to be
answered:
• Which gases have to be measured and in what
quantities?
– Which sensor principle is the most suitable?
– How many sensors are needed?
– Where and how should they be positioned
and calibrated?
• Which alarm limits are appropriate?
– How many are required?
– How is the alarm information processed?
This application guide will address these
questions.
to match most commonly used refrigerants,
appropriate ppm ranges, and safety requirements
for refrigeration systems.
EC - Electrochemical sensor Electrochemical sensors are mainly used for toxic
gases and are suitable for ammonia.
They consist of two electrodes immersed in an
electrolyte medium.
“High” gas concentration
“Low” gas concentration
Max. operating time
before calibration
Fig. 1: Sensitivity of electrochemical sensors
They are very accurate (+/- 2%) and tend to be
used mainly for toxic gases, which cannot be
detected otherwise, or where high levels of
accuracy are needed (fig. 1).
An oxidation / reduction reaction generates an
electric current that is proportional to the gas
concentration.
max.
Tolerance rang
min.
Time
Exposure to large ammonia leaks or constant
background ammonia will shorten the sensor life
(fig. 2). EC sensors can be re-calibrated as long as
the sensitivity of the sensor is above 30%.
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Danfoss offers specific EC sensors for ammonia
in ranges up to 0-5.000 ppm with an expected
lifetime of 2 years, depending on exposure to
target gas.
They are very selective and rarely subject to
cross-interference. They may react to sudden
large humidity changes but settle quickly.
© Danfoss | DCS (mwa) | 2018.08
Application Guide | Gas detection in refrigeration systems
e
Sensitivity
Gas specification
Sensitivity
EC - Electrochemical sensor
(continued)
“Substantial”
gas leak
Important!
Sensor must be calibrated or new
sensor must be installed.
max.
Tolerance rang
min.
SC - Semiconductor sensor
(solid state)
If the sensitivity of the sensor falls
below 30%; install new sensor
Max. operating time
before calibration
Fig. 2: Large ammonia exposure shortens the lifetime of electrochemical sensors.
The semi-conductor sensor functions by
measuring the resistance change (proportional to
the concentration), as gas is absorbed on to the
surface of a semi-conductor, which is normally
However, they are not selective, and are not
suitable for detecting a single gas in a mixture, or
for use where high concentrations of interfering
gases are likely to be present (fig. 3).
made from metal oxides.
Interference from short term sources (e.g.
These can be used for a wide range of gases
including combustible, toxic and refrigerant
gases.
It is claimed that they perform better than the
catalytic type in the detection of combustible
gases at low concentrations, up to 1.000 ppm.
exhaust gas from a truck), creating false alarms,
can be overcome by enabling a delay of the
alarm.
Semi-conductors for halocarbons can be used
to detect more than one gas or a mixture
simultaneously. This is particularly useful in
monitoring a plant room with several different
These are low-cost, long life, sensitive and can be
refrigerants.
used to detect a large range of gases including
all the HCFC, HFC refrigerants, ammonia and
hydrocarbons.
30% sensitivity
Time
“Broad” sensitivity
spectrum
– Semiconductor
– Pellistor
“Narrow” sensitivity
Gas 1
Fig. 3: Sensitivity spectrum of various sensor technologies
Gas 2
Gas 3
Gas 4
Gas 5
Target Gas
© Danfoss | DCS (mwa) | 2018.08
spectrum
– Electrochemical
– Infrared
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Application Guide | Gas detection in refrigeration systems
P- Pellistor sensor Pellistors (sometimes called a bead or catalytic)
are mainly used for combustible gases including
ammonia, and are the most popular sensors for
this application at high detection levels.
The sensor functions by burning the gas at
the surface of the bead and measuring the
resultant resistance change in the bead (which is
proportional to concentration).
These are relatively low-cost, well established
and understood, and they have a good life span
(expected life time 3 to 5 years). The response
time is usually below 10 seconds.
They can be subject to poisoning in certain
applications.
IR - Infrared Infrared technology utilises the fact that most
gases have a characteristic absorption band in
the infrared region of the spectrum, and this
can be used to detect them. Comparison with a
reference beam allows the concentration to be
determined.
Even though they are relatively expensive in
comparison to other sensor, they have long life
time of up to 15 years, high accuracy, and low
cross sensitivity
Poisoning is the reduction of the reaction of the
sensor to the target gas due to the presence
(contamination) of another substance on the
surface of the catalyst, that either reacts with it or
forms a layer on top of it reducing its capacity to
react to the target gas. Most common poisoning
substances are silicon compounds.
Pellistors are used mainly with combustible gases
and are therefore suited for ammonia and the
hydrocarbon refrigerants at high concentrations.
They do sense all combustible gases, but they
respond at different rates to each, and so they
can be calibrated for particular gases.
There are ammonia specific versions.
Due to its measuring principle infrared sensors
can be subject to issues in dusty environments,
where the presence of too many particles in the
air may disturb the reading.
They are recommended and commonly used for
Carbon dioxide detection. Although technology
exists for other gases also, it is not common to
find it in commercial solutions.
Which sensor is suitable to a
given refrigerant?
Based on the target refrigerant gas and the
actual ppm range the below table provides an
overview of the suitability of the various sensor
technologies offered by Danfoss.
Suitability of different sensor technologies:
Semi-conducter Electro-chemical
Ammonia “low” concentration
(< 100 ppm)
Ammonia “medium” concentration
(< 1000 ppm) 1)
Ammonia “high” concentration
(<10000 ppm)
Ammonia “very high” concentration
(> 10000 ppm)
Carbon Dioxide
CO₂
HC
Hydrocarbons
HCFC - HFC
Halocarbons
Best solution
1
) Measuring range 0-1000 ppm. Can be adjusted in the whole range.
2
) Up to 5000 ppm. For specific applications.
–
(4) 4
4 (4)
– –
– – –
– –
4
Suitable - but less attractive Not suitable
Pellistor
(Catalytic)
4
2
– – –
– –
– –
(4)
4
4
Infrared
–
–
4
–
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© Danfoss | DCS (mwa) | 2018.08
Application Guide | Gas detection in refrigeration systems
1
Time, s
Fraction of Concentration Change
250
Sensor response time
The response time is the elapsed time for a sensor
to read a given percentage of the actual value for
a step change in the target gas concentrations.
Response time for most sensors is given as t90,
meaning the time that it takes the sensor to read
90% of the actual concentration. Fig. 4 shows an
example of a sensor with a reponse time t90 of 90
seconds.
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
050 100 150 200
Fig. 4: Sensor with a response time t90 of 90 seconds
As shown in the graphic, the sensor reaction
above 90% becomes slower and takes longer to
read the 100%.
GAS Sensor technology Response time t90, seconds
Electrochemical 0-100/ 0-300 ppm <40s
Electrochemical 0-1000ppm <40s
Ammonia
Electrochemical 0-5000ppm <40s
Semiconductor >120s
Pellistor <20s
Infrared Infrared <90s
Halocarbons Semiconductor >120s
Hydrocarbons Pellistor <15s
© Danfoss | DCS (mwa) | 2018.08
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Application Guide | Gas detection in refrigeration systems
The need for gas detection
There are several reasons why gas detection
is required. Two obvious reasons are to protect
people, production and equipment from the
impact of potential gas leakages and to comply
with regulations. Other good reasons include:
• Reduced service cost (cost of replacement gas
and the service call).
• Reduced energy consumption cost due to lack
of refrigerant.
• Risk for damaging stock products due to a
substantial leak.
• Possibility to reduce insurance costs.
• Taxes or quota on non-environmentally
friendly refrigerants
The various refrigeration applications require gas
detection for different reasons.
Ammonia is classified as a toxic substance with
a very unique smell, as such it is “self alarming”.
However, gas detectors are required to guarantee
early warnings, and to monitor areas where
people are not always present, such as machinery
rooms. It is important to be aware that ammonia
is the only common refrigerant lighter than air.
In many cases, this will lead to ammonia rising
above the breathing zone making it impossible
for people to early detect ammonia leakages. The
use of gas detectors in the right zones ensures
early warnings in case of ammonia leakages.
Hydrocarbons are classified as flammable. Thus,
it’s critical to verify that the concentration around
the refrigeration system does not exceed the
flammability limit.
Fluorinated refrigerants all have a certain
negative impact on the environment, for which
reason it’s very important to avoid any leaks.
CO2 (Carbon Dioxide) is directly involved in
the respiration process and should be treated
accordingly. Approximately 0.04% CO2 is
present in the air. With higher concentration,
some adverse reactions are reported starting
with increase in breath rate (~100% at 3%
CO2 concentration) and leading to loss of
consciousness and death at CO2 concentrations
above 10%.
Legislation and standards The requirements for gas detection are different
across countries worldwide. An overview of the
most common rules and regulation can be found
on the following pages.
Europe:
The present safety standard for refrigeration
systems in Europe is EN 378:2016.
The specified alarm levels in EN 378:2016 are set
at levels to allow evacuation of an area. The levels
do not reflect the effects of long term exposure
to leaked refrigerants. In other words, in EN 378
a gas detector is to warn when a sudden large
release occurs, while machine room ventilation
and system quality measures are to ensure that
small leaks are too small to cause adverse health
effects.
Note!
Requirements for gas detection
equipment in Europe are covered by
national legislation in the different
countries, and consequently may differ
from the requirements specified in EN
378.
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© Danfoss | DCS (mwa) | 2018.08
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