Danfoss Gas detection in refrigeration systems Application guide

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Application Guide

Gas detection in refrigeration systems

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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	•	LFL	= Lower Flammability Level	•	GWP = Global Warming Potential
abbreviations	•	OEL	= Occupational Exposure Limits	•	TRK	= Technische Richtkonzentrationen
	•	ATEL = Acute-Toxicity Exposure Limit		•	MAK = Maximale Arbeitsplatzkonzentrationen
	•	ODL = Oxygen Deprivation Limit		•	TLV	= Threshold Limit Value
	•	OSH = Occupational Safety Limit		•	STEL = Short Term Exposure Limit
	•	ODP = Ozone Depletion Potential		•	PEL	= Permissible Exposure Limits

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Application Guide | Gas detection in refrigeration systems

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 hand-
	held 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.

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.

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

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	An oxidation / reduction reaction generates an
	gases and are suitable for ammonia.	electric current that is proportional to the gas
		concentration.

They consist of two electrodes immersed in an electrolyte medium.

max.

Tolerance range min.

	<![if ! IE]> <![endif]>Sensitivity	“High” gas concentration
	<![if ! IE]> <![endif]>Sensitivity	“Low” gas concentration
		“Low” gas concentration

Time

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).

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.

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%.

They are very selective and rarely subject to cross-interference. They may react to sudden large humidity changes but settle quickly.

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Application Guide | Gas detection in refrigeration systems

EC - Electrochemical sensor (continued)

<![if ! IE]>

<![endif]>Sensitivity

“Substantial” gas leak

Important!

Sensor must be calibrated or new sensor must be installed.

If the sensitivity of the sensor falls below 30%; install new sensor

Max. operating time before calibration

max.

Tolerance range min.

30% sensitivity

Time

Fig. 2: Large ammonia exposure shortens the lifetime of electrochemical sensors.

SC - Semiconductor sensor	The semi-conductor sensor functions by
(solid state)	measuring the resistance change (proportional to
	the concentration), as gas is absorbed on to the
	surface of a semi-conductor, which is normally
	made from metal oxides.
	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.
	These are low-cost, long life, sensitive and can be
	used to detect a large range of gases including
	all the HCFC, HFC refrigerants, ammonia and
	hydrocarbons.

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).

Interference from short term sources (e.g. 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 refrigerants.

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<![endif]>Sensitivity

<![if ! IE]>

<![endif]>Gas 1

<![if ! IE]>

<![endif]>Gas 2

<![if ! IE]>

<![endif]>Gas 3

<![if ! IE]>

<![endif]>Target Gas

<![if ! IE]>

<![endif]>Gas 4

<![if ! IE]>

<![endif]>Gas 5

“Broad” sensitivity spectrum

–Semiconductor

–Pellistor

“Narrow” sensitivity spectrum

–Electrochemical

–Infrared

Gas speciﬁcation

Fig. 3: Sensitivity spectrum of various sensor technologies

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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.

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.

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

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		Pellistor	Infrared
		Semi-conducter		Electro-chemical		(Catalytic)	Infrared
						(Catalytic)

Ammonia “low” concentration			–	4		–	–
(< 100 ppm)			–	4		–	–
(< 100 ppm)

Ammonia “medium” concentration		(4)		4		–	–
(< 1000 ppm) 1)		(4)		4		–	–
Ammonia “high” concentration		4		(4)2	(4)		–
(<10000 ppm)
Ammonia“very high” concentration			–	–	4		–
(> 10000 ppm)			–	–	4		–
(> 10000 ppm)
Carbon Dioxide			–	–		–	4
CO2			–	–		–	4
CO2
HC			–	–	4		–
Hydrocarbons			–	–	4		–
Hydrocarbons
HCFC - HFC		4		–		–	–
Halocarbons		4		–		–	–
Halocarbons
	Best solution		Suitable - but less attractive			Not suitable

1) Measuring range 0-1000 ppm. Can be adjusted in the whole range. 2) Up to 5000 ppm. For specific applications.

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Application Guide | Gas detection in refrigeration systems

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.

As shown in the graphic, the sensor reaction above 90% becomes slower and takes longer to read the 100%.

<![if ! IE]> <![endif]>Change	1
	0.9
	0.8

<![if ! IE]> <![endif]>Concentration	0.7
	0.6
	0.5
	0.4
<![if ! IE]> <![endif]>of	0.3
<![if ! IE]> <![endif]>Fraction	0.3
	0.2
	0.1
	0
	0	50	100	150	200	250

Time, s

Fig. 4: Sensor with a response time t90 of 90 seconds

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

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Application Guide | Gas detection in refrigeration systems

The need for gas detection	There are several reasons why gas detection	Hydrocarbons are classified as flammable. Thus,
	is required. Two obvious reasons are to protect	it’s critical to verify that the concentration around
	people, production and equipment from the	the refrigeration system does not exceed the
	impact of potential gas leakages and to comply	flammability limit.
	with regulations. Other good reasons include:	Fluorinated refrigerants all have a certain
	• Reduced service cost (cost of replacement gas	Fluorinated refrigerants all have a certain
	and the service call).	negative impact on the environment, for which
	• Reduced energy consumption cost due to lack	reason it’s very important to avoid any leaks.
	• Reduced energy consumption cost due to lack
	of refrigerant.	CO2 (Carbon Dioxide) is directly involved in
	• Risk for damaging stock products due to a	CO2 (Carbon Dioxide) is directly involved in
	• Risk for damaging stock products due to a	the respiration process and should be treated
	substantial leak.	the respiration process and should be treated
	substantial leak.	accordingly. Approximately 0.04% CO2 is
	• Possibility to reduce insurance costs.	accordingly. Approximately 0.04% CO2 is
	• Possibility to reduce insurance costs.	present in the air. With higher concentration,
	• Taxes or quota on non-environmentally	present in the air. With higher concentration,
	• Taxes or quota on non-environmentally	some adverse reactions are reported starting
	friendly refrigerants	some adverse reactions are reported starting
	friendly refrigerants	with increase in breath rate (~100% at 3%
		with increase in breath rate (~100% at 3%
	The various refrigeration applications require gas	CO2 concentration) and leading to loss of
	The various refrigeration applications require gas	consciousness and death at CO2 concentrations
	detection for different reasons.	consciousness and death at CO2 concentrations
	detection for different reasons.	above 10%.
		above 10%.

	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.

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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