AKO Leak Detection and Management System

Introduction

Current Situation and New Needs
Refrigerant gas leaks currently represent one of the most significant problems in industrial and commercial refrigeration, driven in large part by the current instability of the refrigerant gas market, its prices, and availability. Thus, the analysis and detection of refrigerant gas in the broader context of industrial and commercial refrigeration must be developed to serve as an effective tool to minimize and even eliminate refrigerant gas leaks, the primary objective of this manual.

 Social Context and Cultural Change
Over the past decades, growing social and political awareness regarding the environment in general and global warming in particular has led nations to advance protocols such as the Montreal Protocol (1988) and the Kyoto Protocol (1992), along with subsequent agreements and amendments. As a result, high-ozone-depleting CFC and HCFC refrigerants (e.g., R22) in developed countries are being phased out. Similarly, thanks to the Kigali Agreement of December 2016, all countries (197) have agreed on the gradual reduction (phase-down, not elimination) of HFC refrigerants. Through various regulations described in this manual, the gradual reduction of environmentally impactful refrigerants is driving a radical shift in their use, cost, and impact in the refrigeration environment. This rapidly changing context is causing a progressive increase in the cost of refrigerant gases, especially HFCs, which in a significant number of existing commercial refrigeration installations remain one of the most technically and economically viable options, provided that the currently common refrigerant gas leaks can be minimized or eradicated.

Consequently, the ability to prevent leaks of these HFC gases into the atmosphere is of extreme importance for all refrigeration agents, since these leaks have a major environmental, economic and operational impact. Even beyond HFC gases and their current increase in price, the present situation is also highlighting the strong relationship between the energy efficiency of refrigeration installations and refrigerant gas leaks, with a significant decrease in system efficiency due to refrigerant losses in the installation.
For all these reasons, the current and future short, medium and long term must incorporate new tools, techniques, procedures, components and detection and management systems to achieve a minimization of refrigerant gas leaks in all applications, with special mention to commercial refrigeration applications, where the leak problem is especially serious. There are multiple sources that describe in detail the serious problem related to leak rates in refrigeration. As can be seen in Table I prepared by ADEME in February 2017 [2], commercial refrigeration presents leak rates of between 15% and up to 33% annually on average.

Sector	Subsector	Leakage emission rate 2015	Detected in	Trend
Domestic refrigeration	Fridges, combis and freezers	0.01%	New equipment	Constant
Commercial refrigeration	Supermarkets	28%	Previously installed	Constant 30% until2013
	Hypermarkets	33%	Previously installed	Constant 35% until2013
	Condensing unit with hermetic units for small shops and vending machines	1%	New equipment	Constant
	Small commercial condensing unit	15%	New equipment	Constant

Table 1: Leakage in domestic and commercial refrigeration according to [2] in 2015

 Structure and Objectives of the Manual
This manual provides a comprehensive review of the state-of-the-art in refrigerant gas detection within the industrial and commercial refrigeration context, covering causes, consequences, nature, objectives, and detection techniques for leaks. It also analyzes various technological alternatives for resolving and minimizing these leaks, including extensive normative aspects that help understand the current situation and regulatory requirements. Moreover, the manual aims to enrich and expand traditional refrigerant leak detection into proactive and early detection (or “leak management”). Ultimately, the manual’s primary goal is to offer all the necessary information to reduce the environmental, economic, and operational costs associated with refrigerant gas losses in refrigeration installations, making early refrigerant gas detection an essential part of resolving current issues in industrial and commercial refrigeration.

The AKO Leak Detection and Management System
Faced with the significant challenge in industrial and commercial refrigeration, AKO has developed a unique refrigerant leak monitoring, detection, and management system composed of highly sensitive and precise gas transmitters and a set of communication, monitoring, and management tools, as described in section 13. This system is presented as an essential part of the necessary technological and cultural change to address refrigerant gas leak issues.

Causes of Leaks in a Refrigeration System

Refrigeration systems operating on the vapor compression cycle require a refrigerant fluid circulating within them. This fluid changes state within the refrigeration machine, transitioning from vapor to liquid in the condenser and from liquid to vapor in the evaporator.

Due to the necessary characteristics of a refrigerant, the following circumstances arise:

•  Refrigerants exist in a gaseous (vapor) state at typical ambient pressure and temperature conditions.
• Refrigerants confined within a refrigeration system (or refrigerant container) are usually at a pressure higher than atmospheric pressure.

These two circumstances lead to the unavoidable conclusion that, in the event of a failure-no matter how minor in the sealing of the refrigeration system, refrigerant will escape into the atmosphere—commonly referred to as a “leak.” Total sealing of a refrigeration system throughout its useful life is very difficult due to pressure and temperature variations, vibrations, and maintenance activities that may affect the system’s initial sealing.

Recent studies indicate that leaks in refrigeration systems are mainly due to nine distinct causes, including:

• Flawed welds
• Loose or over-tightened nuts and bolts
• Uninstalled valve caps
• Incompatibility between mechanical components and lubricating oils (retrofit issues)
• Vibrations near compressors
• Thermal expansion (defrost)
• Corrosion caused by food products (e.g., refrigerated cabinets, islands, displays)
• Metal contact (copperiron), leading to abrasion or galvanic corrosion
• Poor pipe support or mechanical stress

These causes will be specifically addressed, along with recommendations to avoid or minimize them, in subsequent sections 4, 5 and 6.

Consequences of Refrigerant Leaks in Refrigeration Systems

Refrigerant leaks affect four interconnected aspects:

• Refrigeration system performance
• Environmental impact
• Economic impact
• Safety

Refrigeration System Performance Consequences
Smallsized refrigeration systems with capillary, without a liquid receiver, are “critical load” refrigeration systems, since any loss of refrigerant immediately results in a lack of refrigerant supply to the evaporator, immediately decreasing the refrigeration capacity, increasing the consumption of the compressor, and quickly reaching a situation in which the refrigeration system cannot keep the temperature of the refrigerated space. In systems with a liquid receiver and expansion valve, symptoms of refrigerant loss do not appear until a minimum refrigerant level is reached. Below this level, vortex effects introduce gas bubbles into the liquid line, detected through a liquid sight glass.

When this happens, the efficiency of the system begins to deteriorate, as gas bubbles in the liquid line (the socalled flash gas) reduce the capacity of the expansion valves, increase the superheat of the evaporators and increase the time that compressors need to reach the temperature setpoint. Therefore, the energy consumption of the system increases (See Figure 1).

From that moment on, if the leak continues to increase, there will come a time when the system pressures decrease, and the desired setpoint temperature will not be reached in the refrigeration services (lack of refrigeration). In the case of refrigeration plants, typically, the furthest service is the first to show the symptoms of a lack of refrigerant, with an obvious difficulty in reaching its setpoint temperature.

 

Economic Consequences
Refrigerant leaks increase the energy consumption of refrigeration systems, raising their operational costs. For instance, a commercial refrigeration system operating with 20% less of the required refrigerant charge, will consume an average of 15% more energy. Figure 2 shows the evolution of the increase in operating costs of the refrigeration installation with the percentage of leakage according to [8].

Other associated costs include:

• Refrigerant replacement costs, which may include taxes (e.g., in Spain, the Fluorinated Gas Tax adds € 78/kg for R404A).
• Leak repair costs
• Potential product losses due to a break in the cold chain
• Temporary business shutdowns caused by refrigeration failure

Environmental Consequences
Hydrogen, fluorine and carbon molecules that compose HFC refrigerants, act in the atmosphere in a similar way to CO2 molecules, absorbing and radiating thermal radiation from the planet’s surface back towards the Earth, which is known as the greenhouse effect and plays a major role in global warming.

The great stability of these HFC molecules implies that they stay in the atmosphere for long periods of time -several decades or even centuries-, resulting in a long-term problem for the environment. This is why the GWP indicates the equivalent in kgs of CO2, in terms of global warming, when 1 kg of the refrigerant in question is released. For example, 1 kg of R404A released into the atmosphere equals 3800 kgs of CO2 released. This data considers its thermal absorption and irradiation activity, as well as the stability time in the atmosphere during which this “greenhouse effect” activity is present.

There is also an indirect environmental effect, due to the increase in electricity consumption, already analyzed, when a leak occurs: electricity generation also releases greenhouse CO2. The magnitude called TEWI (Total Equivalent Warming Impact) includes the direct and indirect effects on global warming produced by the operation of a refrigeration system. Therefore, a leak in a 0% refrigeration installation increases its TEWI.

Type	Name	GWP*	Class
CFC	R12	10900	A1
	R-502	4657	A1
HCFH	R-22	1810	A1
	R-408A	3152	A1
	R-409A	1909	A1
HFC	R-32	675	A2L
	R-134a	1430	A1
	R-404A	3922	A1
	R-507A	3985	A1
	R-407A	2107	A1
	R-407C	1774	A1
	R-407F	1825	A1
	R-410A	2088	A1
	R-442A	1888	A1
	R-23	14800	A1
	R-152a	124	A2
HFO	R-1234yf	4	A2L
	R-1234ze (E)	6	A2L
Mixtures HFC / HFO	R-448A	1387	A1
	R-449A	1397	A1
	R-513A	631	A1
	R-450A	604	A1
	R-452A	2140	A1
Naturals	R-170	6	A3
	R-290	3	A3
	R-600a	3	A3
	R-717	0	B2L
	R-744	1	A1
	R-1270	2	A1

Table 2: GWP values for various refrigerants and their corresponding safety classification.

Safety Consequences

• A refrigerant leak in an enclosed space represents a potential danger to people: it can cause drowsiness, loss of consciousness and even asphyxiation (due to oxygen displacement) in high concentrations.
• Currently, the increased use of low GWP refrigerants (thanks to their low stability in the atmosphere) entails, precisely because of their low stability, certain degrees of flammability, corresponding to groups A2L, A2 and A3 (See Table 2).
• These gases represent a challenge for the safety of these installations in the event of leaks. The risk of flammability, if not treated properly, can endanger the safety of people and property.
• The safety aspect is contemplated by the Spanish Safety Regulations for refrigeration installations and the European standard EN 378:2016 and previous ones, as discussed in section 9.

Nature of Refrigerant Emissions

Refrigerant emissions from a refrigeration installation, often called refrigerant “losses”, can be classified into 6 different types. Although the emission modes are very different, it is important to identify them to limit and contextualize them. In this sense, we must consider leaks as a particular case among emissions.

Diffuse emissions: they constitute what is commonly called “leaks”

They are emissions whose precise emission location cannot be established. For example, when an ambient detector/transmitter indicates an abnormal concentration of refrigerant in a room, these emissions are diffuse for this detector. When the control scale is modified and a search for the leak is carried out with a portable detector, a diffuse emission can become a point emission. A combination of strategically placed ambient transmitters can also speed up the detection of the specific leak point, as will be seen later. Diffuse emissions may come from small leaks, resulting from degradation of tightness, or because of breakages, accidents, etc. as described in the following sections.

Degradation of tightness
Tightness is not only static, as briefly discussed in section 2, but also depends on, among others:

• Temperature variations
• Pressure variations
• Vibrations

These circumstances induce a degradation of static tightness and can, in an unpredictable way, cause a significant increase in leakage flows. This is why a refrigeration unit that has passed a static tightness test with satisfactory results may subsequently present leaks after a certain period of operation.

Therefore, we could speak of the concept of dynamic tightness, checked after a period of operation of the installation. Leaks that are consequence of the deterioration of the tightness represent one of the most difficult challenges to treat because they are difficult to detect. Emissions due to the tightness deterioration can be limited in practice by using very sensitive ambient transmitters or dynamic tightness checks every certain period of operation, as we will see later.

The sensitivity of the refrigeration system operation to the deterioration of the tightness depends on the initial load of the system: for a ministation containing 15-20 kg of gas, the deterioration of the tightness of the gland of a valve can, in one year, cause the entire load to be lost. While the same gland in a large refrigeration plant could go unnoticed.

Breakage
Refrigerant losses, i.e. emissions due to breakages, are exceptional. Breaks may be caused by:

• Poor installation design
• Compatibility problem of materials with the refrigerant-oil partner (seals, for example)
• Noncompliance with good professional practices or the equipment manufacturer’s instructions.
• Lack of preventive maintenance.
• Set pressure of safety valve too high.
• Using the installation’s pipes as a “step” to step on.
• Water corrosion of the tube bundle of a multi-tube exchanger, due to the presence of unwanted contamination in the water.
• Tool marks on the tubes (e.g. bending machines, flaring tools, etc.)
• Over-tightening of the nuts on the flare causing its breakage.

One of the main causes of breakage is poor installation performance and, therefore, it is possible to avoid these breakages by applying appropriate corrective measures. In any case, if these occur, the presence of ambient detectors/transmitters represents the only possible early warning. Depending on the type of failure, the amount of leakage can be avoided to a greater or lesser extent.

Handling of the refrigerant
Emissions due to handling of the refrigerant are common.
During gas charge: purging of air from the flexible hoses with refrigerant, absence of shut-off valves at the ends of the flexible hoses, poor connection of the flexible hoses.

• Due to the purging of residual quantities from the loading cylinders
• During the refilling of smaller cylinders
• During the loading of components without previously creating a vacuum in the installation or the corresponding section
• Due to the absence of recovery
• Due to poor recovery efficiency
• During maintenance operations: degassing of the oil extracted from the installation, and the purging of non-condensable.

In the current context of phasing out high-GWP HFCs, refrigerant changes in facilities are an important opportunity to recover the “old” refrigerant in a systematic manner, rather than waiting to change the refrigerant after an incident and breaking the cold chain.

 Accidents
Accidents, caused by causes external to the circuit and involving refrigerant emissions, are of various types:

Fires Explosions Vandalism Theft 

End of the installation’s life
When a refrigeration installation reaches the end of its useful life, the refrigerant must be recovered. If this is not done, the refrigerant will eventually be released into the atmosphere when the installation is dismantled. In fact, emissions at the end of the installation’s life are included in the formula that calculates the TEWI (Total Equivalent Warming Potential) as one of the components that cause atmospheric warming by a refrigeration installation. As the reader can see, the use of refrigerant gas detection systems helps to de-tect and, consequently, reduce the different types of refrigerant gas emissions; they are essential above all to detect small leaks which, as has been said, are the most difficult to treat. In such a case, very high sensitivity transmitters are essential, as will be discussed in section 10.

 Distribution of emissions by type of installation

The different refrigeration applications can be classified according to the characteristics of their construction. These lead to a different distribution among the 6 types of emissions defined in the previous point.

Fully welded systems (hermetically sealed systems)
Domestic refrigerators, air conditioning split units and numerous refrigeration furniture for sale with a builtin unit are fully welded systems, charged at the factory. The refrigerant charge is indicated on the equipment, and it is critical for the correct performance of the equipment in question.

The main characteristics of these systems are:

• No access to the refrigerant
• No maintenance, except for the electrical part and the cleaning of the condenser for correct heat exchange.

According to the Safety Regulations for Refrigeration Installations, (RSIF, Spain) these units must leave the factory with a test certifying a leak rate of less than 3 grams per year under a pressure equivalent to at least 25% of the maximum pressure allowed by the unit.
For this reason, the average refrigerant losses are very low, 1 to 2% of the initial charge. Generally, this percentage comes from the eventual lack of tightness of some welding that is noted during the month following startup, and that did not manifest itself in the factory test, due to some dynamic effect (temperatures, pressures or vibration in real operation). Breakages are also possible due to improper use of the unit, typically, “piercing” the evaporator by trying to remove ice from it with a sharp element.

“Chiller” type systems
Water chillers are found both in air conditioning and in many industrial processes, condensed by water or air. The essential characteristics of this equipment are:

• A low ratio of refrigerant mass/refrigerating capacity (from 200 to 350 g/kW of refrigerant)
• An intrinsic tightness that can be of a very good level. The annual losses due to diffuse emissions can be of the order of 1 to 3% of the initial load, provided that the tightness has been considered from the design of the system and that it is controlled during operation.
• Significant emissions during maintenance operations, if effective recovery materials are not used

There are no precise figures for emissions from this type of equipment, but practice indicates that the level of emissions due to breakage (safety valves, pipes, exchangers) is not negligible and that the presence of an ambient transmitter (preferably inside the bodywork of this equipment) allows a rapid and early warning in these cases.

 Individual direct expansion systems (with condensing units)
These systems are made up of 2 parts connected by pipes:

• On the one hand, a cold room or refrigeration cabinet containing the evaporator(s).
• On the other, a motor-compressor group associated with a condenser (the unit is called a condensing unit), located at a distance from the installation (from a few meters to tens).

This type of system may have fittings, filters, service valves depending on the complexity of the installation. The fittings are a source of diffuse emissions. The fittings and service valves may suffer deterioration of tightness.

The leak rate of this type of system is very variable, depending on the design of the system (avoiding flared joints, using welded filters and valves, etc.) can significantly reduce emissions. They can range from 3% in well-designed systems to 20% in those with a more obsolete design. See Table 1. In this type of installation, although it is not mandatory by regulation (it will depend on the refrigerant charge and dimensions of the cold room), it is very interesting to install an ambient transmitter in the cold room and another in the condensing unit (mandatory if there is a machine room). This action strongly reduces the leak rate, since leaks will appear prematurely.

Centralised direct expansion systems
LCentralized direct expansion systems are the fixed systems with the highest refrigerant consumption. Indeed, the refrigerant distribution networks are long, and the number of mechanical fittings or welded elements is high. The usual layout consists of a machine room where the compressor unit(s) are concentrated. This machine room can be quite far from the cold rooms and/or cabinets, with distances that can vary between 20 and 200 meters. The total refrigerant charge of this type of installation can typically vary between 200 and 1500 kg.
Studies on emissions in this type of system indicate that the predominant factors are deterioration of the tightness and breakages. The diagnosis of leaks is quick if there are strategically placed ambient transmitters, with detection cells of the appropriate technology (NDIR technology would be recommended, as will be seen in section 10) and in good working order (see section 13).On the other hand, certain air condensers have structural weaknesses, particularly the joints between the copper tubes and the metal structure (heads), which can lead to shear breakage of the copper tubes, causing a total loss of the installation load.

In this type of installation, the average leak rates have historically been high, between 20 and up to 35% of the annual load (see Table 1). Currently, and due to the existing problems with HFC refrigerants, a global leak reduction strategy, including a greater and better presence of fixed transmitters and fast and demanding action protocols, could allow this rate to be reduced to levels of 10-15% and even to values below 5%. It is important to note, as will be explained later, that the sensitivity (detection limit) of detection techniques is essential to ensure that their use has a positi-ve impact on the detection and subsequent repair and elimination of leaks or leaked gas, so detection technology is essential (see section 10).

The sensitivity of the operation of a centralized installation to degradation of tightness depends on the load of the installation. Indeed, in an installation with 10-15 kg of load, the deterioration of the gland tightness can cause the entire load to be lost. While the deterioration of tightness of the same gland in a large central installation may go unnoticed, as discussed above. The sum of the surfaces of component joints in the machine room on the one hand, and in the sales area on the other, determines the ratio of diffuse emis-sions between the two large portions of the installation.

Approximately 75% of the joint surfaces are in the machine room. The other four areas of the installation are the sales area, the cold storage rooms, the processing rooms and the roof where the condenser is located. As regards leaks detected in the sales room, the percentage has been decrea-sing in recent years as refrigerated units have been incorporating expansion val-ves to be welded at both ends. However, this problem still exists for older units, since a classic leak point is the threaded connection of the expansion valves, as well as the poor fastening of the inlet pipes to the refrigerated units, which vibrate every time the solenoid valve is activated. The use of electronic expan-sion valves, without a previous solenoid, can also help to reduce this problem.

Therefore, monitoring using appropriate refrigerant leak transmitters in the ma-chine room is adequate and allows to follow-up, in a reliable manner, most leakage degradations, as well as breakages and accidents. The same applies in general to all areas of the refrigeration circuit, especially those with connecting pipes, condensation areas (even open ones) and storage and sales areas (in commercial refrigeration applications) where evaporators are located.

For this monitoring to be globally effective and to limit emissions, it is necessary:
That the initial leak control over the entire circuit is carried out with highly sensitive detectors (1 g/year), preferably at the maximum operating pres-sure and with a tracer gas (N2/H2 mixture) That a thorough and regular inspection of corrosion is carried out both on the evaporators of the refrigeration units and on the condensers. It is interesting to note that if the refrigerators and condensers are conti-nuously monitored by a sensitive detection system, this inspection can be reduced in frequency, since the transmitting equipment will indicate the leak, if there is one.

Probable leak points in a refrigeration installation

 General considerations
Experience and various studies allow us to identify the most likely leak points in a refrigeration installation. Leakage degradation due to manipulation of valves or plugs is easy to analyze. On the contrary, the study of leak degradation due to vibrations requires relati-vely complex technical means.

The analysis of the causes of the lack of tightness cannot be based solely on the static emission characteristics of the components; the role of the most common actions during routine maintenance must also be integrated into the analysis. The usual manipulations in a refrigeration installation are the opening and clo-sing of service valves, the screwing of various fittings or plugs, the assembly and disassembly of flanges.

It is recommended that, for each refrigeration installation, a list of the most probable leak points be drawn up and identified. This list will simplify and speed up the leak search process during periodic leak checks, prioritizing the search for elements on this list, noting in each inspection those that present leaks. This methodology allows having a database on the leaks in the installation, the frequent leak points, and their evolution. This data will allow future decisions to be made on modifications or replacements of elements of the installation aimed at improving its operation and tightness.

Is the compressor an important leak point?

• It depends on the type of compressor in relation to the encapsulation of the motor.
• Hermetic compressors consist of a fully closed and welded casing, so their ti-ghtness is total. In smaller compressors, the suction and discharge pipes are welded and therefore also offer a high level of tightness.
• The only possible leak point is when a valve (Schrader valve) is welded to the pressure tapping tube.
• On larger hermetic compressors the compressor outlets may be fitted with Ro-talock valves, which may eventually leak through their stems.
• The exploded view of a semi-hermetic compressor (see Figure 4) shows a high number of seals and fittings.

The following are located on the compressor:

• Suction and discharge valves
• Schrader pressure taps (valves)
• The oil differential pressure switch and its conical SAE threaded connec-tion (only in the case of mechanical PDA, electronic pressure switches, e. g. Delta PII, are non-invasive)
• The safety valve (in some cases)
• The suction filter and the oil filter, which can be removed for cleaning.
• The motor cover and cylinder heads, which are disassembled during major mechanical inspections.

Fig. 4: Exploded view of a semihermetic compressor

• Therefore, the semi-hermetic compressor contains a large number of potential sites for diffuse emissions or leaks, taking into account the lengths of the seals and the number of maneuverable or threadable components.
• Factory tightness checks, using 1 g/year sensitivity detectors, generally indicate a very good level of tightness. Tightness has in fact been integrated from the design and is carefully verified at the end of the production line.
• Maximum levels of around 5 g/year are set and verified in specialized test chambers.
• Operational checks ensure that the initial tightness is not impaired by vibrations, pressure pulsations and temperature variations during on-off cycles.
• Semi-hermetic compressors are a good example of a component whose tight-ness may be critical, but which has a very good initial tightness level.
• On the other hand, valve stems or Schrader plugs mounted on these compres-sors can be major sources of emissions.
• Finally, open compressors, driven by external motors, have a shaft for their drive. Said shaft is equipped with a gland seal to prevent leaks, but it is an element that wears out over time and can also leak in the event of very long downtimes. This is a very likely leak point.
• The maintenance of the gland seal and its periodic replacement are of paramount importance for proper long-term sealing. The amount of oil lost by the gland seal is a good measure of its tightness. The improvement in efficiency and reliability of semihermetic compressors is increasingly relegating them to ammonia-only applications.

Most probable leak points
The most probable leak locations in a refrigeration installation, based on the causes of leaks and emissions previously discussed, have been studied by multiple sources [3, 4 and 5].

We present a summary of them. See Figures 5 and 6:

• Operable components:
  • Service valves
  • Plugs
• Screw-on components:
  • Valve plugs
  • Flare connections
  • SAE connections
• Removable components:
  • Filters
  • Flanges
• Other components:
  • Condensers
  • Evaporators

Manoeuvrable Components Service Valves
A service valve with a manoeuvrable stem, like the one shown in Figure 7, is widely used.

Position 1: Stem in its lowest position. The refrigerant outlet to the system is closed. The service port detects the pressure inside the compressor or liquid receiver.

Position 2: Stem in its highest position. The service port is closed. This position allows connection of the hoses.

Position 3: Stem in its intermediate position. All three valve paths are connected. The valve must be in this position to measure the system pressures during operation.

Fig. 8: Operation of a service valve

• The sealing integrity of the service valve’s gland when closed and properly tightened is significantly different once it has been used. Components that are regularly manipulated should be distinguished from those that are not.
• Initial sealing measurement protocols for valves, established by manufacturers, should evaluate the evolution of sealing integrity based on the number of openings and closings. There is a trade-off between sealing integrity and the manoeuvrability of low-cost glands.
• Proper use requires that the nut securing the gland in its housing be loosened when it is necessary to manoeuvre the valve stem and then retightened once the manoeuvring is complete. This best practice rule is not always followed, and as a result, the sealing integrity of this component can change significantly.
• It is crucial to emphasize to operators performing interventions on refrigeration installations to carry out this process of loosening and retightening the gland EACH TIME they manipulate a service valve.

Caps

• LCaps, whether metallic or plastic, provided with service valves (see Figure 9) or available for Schrader valves and SAE-threaded service ports, are crucial for ensuring better sealing of the mentioned components.
• It is important to replace the caps on these components after use, as they serve as the final Fig. 9: Cap barrier against potential leaks. Caps with elas- tomeric seals are preferable; however, in any case, using a cap is better than leaving the component uncapped.
• The use of thread sealants is also an advisable practice, particularly for caps that are not frequently manipulated.

Threaded Components Schrader Valves
One of the most frequent actions is connecting a flexible hose to a Schrader valve to measure pressure. A Schrader valve (or connection, see Figure 10), once used, exhibits a very different level of emission compared to one that has ne-ver been manipulated.
In fact, the sealing cap, as mentioned earlier, is essential for maintaining the sealing integrity.

• Additionally, it is necessary to retighten the inner mechanism of the Schrader valve to ensure it is not “loose.”
• Attention should be given to these details so that operators adjust their habitual practices accordingly.
• The initial design should incorporate the best possible sealing and, therefore, avoid the proliferation of Schrader valves, preferring manoeuvrable valves instead.
• It should be noted that the use of Schrader valves in installations operating with CO2 as a refrigerant is not authorized in most cases.

Flared Connections
Flared connections are, according to multiple studies, one of the most likely points for leaks (see Figures 5, 6, and 11). Indeed, the flaring procedure for the pipe is critical, as a deformed, cracked, or scratched flare due to debris will result in leaks.
For this reason, flared connections should be avoided and replaced whenever possible by other types of connections, preferably welded ones.

A common case of leakage in flared connections involves the connection of thermostatic expansion valves. This issue is further exacerbated by the temperature variations that occur at this connection.
The RSIF Safety Regulations for Refrigeration Installations, which must be complied with, in its Technical Instruction IF-06 ‘Components of the installations’, indicates the following regarding this type of connection:

Flared joints

• Flare connections shall not be used for the connection of expansion valves. Flare joints shall be avoided where reasonably practicable.
• The use of flared joints shall be limited to annealed pipes with an outside diameter less than or equal to 19 mm and shall not be used with copper and aluminium pipes with an outside diameter less than 9 mm.
• Where flared joints are made, precautions shall be taken to ensure that the flare is of the correct size and that the torque used to tighten the nut is not excessive. It is important that the threaded and sliding surfaces are lubricated before joining with oil compatible with the coolant. Pipes whose material has been hardened by cold handling shall not be flared.
• Threaded compression joints are a preferable alternative to flared joints.
• The torque applied to a flared connection is critical because, on one hand, it must ensure the sealing integrity of the connection, and on the other hand, it must not be excessive, as this could crack the pipe, leading to a loss of sealing.
• For this reason, it is highly recommended to use torque wrenches when tightening this type of connection.

Tables 3 and 4 provide the recommended torque values for flared connections as well as for caps:

Pipe	Tightening torque (N*m)	Corresponding stress (With a 20 cm spanner)
6.35 mm (1/4”)	14-18	Wrist strength
9.52 mm (3/8”)	32-41	Arm strength
12.70 mm (1/2”)	49-61	Arm strength
15.88mm (5/8”)	62-75	Arm strength

Table 3: Recommended tightening torques for flare connections.

Type	Tightening torque (N*m)
Service connections (Schrader)	7-9
Valve protection caps	25-29

Table 4: Recommended tightening torques for protection caps
As stated in the RSIF (Regulation on Safety in Refrigeration Installations), it is preferable to replace flared joints with compressiontype threaded joints (like seen in Figure 12)

 

SAE Connections

SAE connections are very common conical connections in refrigeration. Flared connections are joined to a component with an SAE male thread. This section addresses connections where both elements are premachined SAE components, one male and one female.
This type of joint is used, for example, to connect pressure gauges, pressure switches, etc., as well as to connect flexible charging hoses. The issues they present are similar to those of flared connections, although they have a lower probability of leaks since the components are factory machined. The sealing integrity of SAE connections should be checked periodically, as vibrations, pressure changes, and/or temperature variations can loosen the joint and cause leaks.

When an SAE connection is made between components of different materials (e.g., a brass Schrader valve and a ferrous or stainless-steel nut), the differing properties of the materials (coefficient of expansion, ductility, etc.) demand the use of a conical copper washer (Figure 13). This washer deforms to adapt as a sealing joint, reducing the likelihood of leaks in the SAE connection. The use of thread sealants can be beneficial to enhance the sealing integrity of this type of connection. The Regulation on Safety in Refrigeration Installations (RSIF), which is mandatory in Spain, specifies the following about this type of connection in its Technical Instruction IF-06 “Components of the Installations”:

 

Threaded Conical Joints
Threaded conical joints should only be used to connect measurement and control devices. These joints must be of solid construction and sufficiently tested. Fillers and seals that are not properly tested should not be used on the threads.

Removable Components Filters
During the replacement of filters/dehydrator cartridges, refrigerant leaks from the system are common. Removable filters with replaceable cartridges typically do not have a connection that allows the refrigerant contained within to be evacuated. Therefore, it is necessary to install one. This provision reduces the leaks caused during filter replacement, as it allows the refrigerant to be evacuated and the system to be vacuumed. Filters should always be installed with 2 valves, upstream and downstream of the filter respectively.

The procedure should include evacuating the liquid line through the system’s compressor until atmospheric pressure is reached. Another common leak point is the O-ring, which should ensure the sealing integrity of the cartridge filters. This O-ring must be replaced whenever the car-tridges are replaced. This replacement should be anticipated, and the necessary Oring should be available during the cartridge replacement process.

Flanges

• Flanges are present in refrigeration systems, particularly in valves (on compressors, liquid receivers), as well as on some line components such as filters, solenoids, or pilot-operated valves.
• Between the flange and its counterpart, there is always a gasket, which can be flat or an O-ring. This gasket is responsible for ensuring the sealing integrity of the joint. Therefore, its condition is of utmost importance to prevent leaks.
• The gasket must be made of a material compatible with the refrigerant-oil pair in the system and must be replaced whenever the flange is disassembled.
• The bolts on the flanges must always be tightened using a cross-pattern technique.
• The sealing of this type of joint must be systematically inspected after every disassembly and reassembly.
• If possible, self-locking nuts or washers should be used to prevent loosening due to vibrations or pressure/temperature cycles.

Other Components

Condensers
A potential leak point is where the tubes pass through the header, especially when the header is made of steel sheets and the tubes are copper. There are other more recommended options, such as aluminium headers or “floating battery” systems, which eliminate this possibility.
This issue can worsen if vibrations are transmitted to the condenser. These should be avoided by installing vibration absorption systems and properly supporting the pipes that connect to the condenser.

Evaporators
The same issue observed in condensers is also present in evaporators (see Figure 14, liquid distributors in an evaporator).

Another potential leak point occurs in the capillary tubes that exit the liquid dis-tributor, due to friction between them. Isolating the distributor from vibrations and implementing methods to prevent friction (such as plastic coating of the capillaries or using silicone) eliminates this risk. Regarding evaporators, minimizing defrost cycles can also reduce the risk of leaks in these components. The pulsating thermal stress caused by frequent daily defrost cycles poses a risk of thermal fatigue to the multiple welds in these components over the years.

 Techniques for leak detection

The techniques for leak detection are differentiated depending on whether they are:

• Prior to the start-up of the installation (and, therefore, prior to its char-ging with refrigerant gas)
• With the installation in service (already charged with refrigerant)

Leak Detection Prior to Commissioning
Leak detection, which is carried out prior to the start-up of refrigeration installa-tions, is not only required by law, but also aims to limit the leaks that will occur during the service life of the installation. This point is of great importance, since experience shows that a well-executed leak control during start-up drastically limits the leaks that will occur during the operation of the installation.

It is therefore imperative to dedicate the necessary time and the appropriate techniques to this process. The techniques available to professionals are:

• Nitrogen tightness test
• Tracer gas test (N2/H2 mixtures)
• Vacuum test

Leak Detection During Operation
Leak detection once the installation is in service and, therefore, charged with refrigerant gas can be of the following types, as summarized in Figure 15:

• Discontinuous detection: with portable detectors/transmitters and/or other techniques
• Continuous detection, which can be:
• Direct continuous: with gas detectors/transmitters in the environ-ment
  • Passive (gas enters the detector by diffusion)
  • Active (gas is pumped to the detector, away from the analysis environment)
• Indirect continuous: e.g. weighing the gas load in the container, analyzing the operating parameters of the installation (pressures, temperatures, etc.).

Next, we will analyze each of the techniques.7.2.1.- Intermittent Detection

This refers to the leak detection method involving periodic checks using manual (portable) detectors. The minimum frequency (every 3, 6, 12, or 24 months) is determined by the applicable regulations. In Spain, as explained in Section 9, this is governed by the RSIF (R.D. 138/2011) and the European F-Gas Regula-tion 517/2014.

As this technique is applied periodically, it does not ensure 100% leak detection for the entire installation. Therefore, it is a method generally limited to systems with small refrigerant charges and serves as a complementary technique to con-tinuous detection in medium and large installations. It is especially important to note that performing exhaustive and detailed intermittent detection in large installations with hundreds of meters of piping and numerous high-risk compo-nents is highly time-consuming and, therefore, not cost-effective.
Most Common Types of Portable Detectors are:

Electronic Detectors

 

These use electronic gas detection sensors and let out a beeping sound when a leak is detected. According to the RSIF, their sensitivity must be below 5 g/year. However, a drawback of lower-quality detectors is that, in atmospheres saturated with refrigerant, they become overwhelmed and continuously beep, making them less effective in such conditions. There are various electronic sensor technologies, and it is essential to choose one that is suitable for detecting the specific refrigerant in question. It is important to note that the sensitivity of portable electronic detectors de-creases as the battery charge level drops. Additionally, some electronic sensors have a specified lifespan, determined by the manufacturer, after which they must be replaced.

Ultraviolet Detectors
These detectors consist of ultraviolet (UV) flashlights that reveal leak points through fluorescence of a substance previously in-troduced into the system in an appropriate dose. The dose is usually proportional to the refrigerant/oil charge of the system. Some compressor manufacturers do not authorize the use of these substances, as it may void the warranty. The minimum sensitivity of these systems is approxima-tely 7 g/year.

Bubble Detection
This method involves using soapy solutions or similar products that produce bubbles in the presence of a gas leak. It is not a highly precise method, as it depends on the skill/training of the observer and the visual access to the leak point. It is often used as a low-cost or com-plementary method alongside other detectors. The sensitivity of this method is around 20 g/year, de-pending on the internal pressure of the system.

 

Ultrasonic Detectors

These detectors “listen” to the ultrasonic sounds emitted by refrigerant leaks. Their sensitivity is lower than that of electronic detectors

Continuous Detection
Continuous detection involves a leak detection system that is always present alongside the refrigeration system, monitoring it continuously or at regular in-tervals (several times a day) without requiring operator intervention.

As shown in Figure 15, continuous detection can be divided into two subtypes:

Direct Continuous Detection
This system relies on the presence of refrigerant detectors/transmitters in the environment, which continuously analyse whether the refrigerant concentration in the air exceeds a specified threshold (detectors) and/or measure the refrige-rant concentration in the environment (transmitters, see Figure 20). Direct continuous detection allows determining whether the refrigerant charge is escaping from the refrigeration system, pinpointing the leak by zones. As will be analysed later, the percentage of leaks monitored by this detection system will depend on the sensor technology, the number of detectors/transmi-tters, and their placement.

This detection technique is non-invasive to the refrigeration system since the detectors/transmitters are placed outside and around it. Therefore, it is a univer-sal technique that can be adapted to any refrigeration installation. This method enables rapid leak detection, provided the sensitivity (minimum detectable concentration) is low—less than 20 ppm in the air, even in contro-lled atmospheres with compositions different from atmospheric air (e.g., low-O2 atmospheres for fruit ripening). This requirement influences the choice of sensor technology, as will be extensively covered in Section 10.

Refrigerant transmitters in the environment allow for quicker leak detection and repair since the leak will be located near the transmitter that triggered the alarm. This enables a more efficient and cost-effective localization and repair of the leak. Environmental detectors/transmitters also serve a safety function for people by alerting them to the presence of a gas that can displace oxygen. Furthermore, according to the RSIF, the alarm from a refrigerant detector/transmitter located inside a cold room must shut off the refrigerant supply to the evaporator(s) installed within the cold room to prevent the refrigerant concentration from continuing to rise in this enclosed space. This is achieved by cutting power to the liquid solenoid or electronic expansion valve. However, in systems serving multiple cold rooms, it is also advisable to install a check valve at the outlet of the evaporators. Without this, gas from other evaporators may continue leaking into the room. As detailed in Section 10, the most suitable, specific, reliable, and precise technology for fixed refrigerant gas detectors/transmitters is NDIR (Non-Dispersive Infrared)

Indirect Continuous Detection

Indirect continuous detection systems identify a malfunction in the refrigeration system that indicates the presence of a leak. This method is based on abnormal behaviour in one or more parameters, such as pressure, temperature, compres-sor consumption, or liquid levels.
A traditional method used by refrigeration technicians, which could be conside-red an “indirect method” (although not continuous), is the “low-level method,” where a leak is identified by observing an abnormally low refrigerant level in the liquid receiver. However, this method only detects leaks once they are significant and after a substantial amount of refrigerant has already escaped.

Indirect continuous methods are based on thermodynamic principles and in-volve monitoring numerous parameters of the system (primarily temperature, pressure, and receiver level). The system’s instantaneous operation is compared to a reference operation. If a prolonged deviation occurs, the system alerts to the presence of a potential leak. The reference operation is established during an initial learning period when the system is first started. This comparison can be performed continuously or a few times per day, de-pending on the method used. Some systems rely on weighing a volume of re-frigerant linked to the liquid receiver, requiring the refrigerant charge to be collected in the receiver to compare with the initial state. Naturally, this type of system can only perform checks a few times daily, as this practice disrupts the refrigeration process.

A drawback of indirect continuous systems is that after the system is recharged following a leak, a new “learning” period must be initiated. During this time, which can last several days, the system is left unsupervised. This learning period activation can be exploited by less professional operators to delay leak detec-tion and avoid immediate troubleshooting. Although indirect continuous systems monitor 100% of the installation and should detect any leak, breakage, or accident, they require a minimum deficit (between 1% and 10% of the total charge, depending on the speed of the leak in g/h, as well as the measurement system and its precision [2]). Consequently, some systems may require the loss of several dozen kilograms of refrigerant before alarms are triggered, making their response slower than that of direct systems.
Additionally, indirect systems are not immune to false alarms and require highly precise setup to ensure proper functionality. Another limitation of these systems is that when an alarm is triggered, they provide no indication or clue about the leak’s location. This necessitates a comprehensive and exhaustive inspection of the entire installation to locate the leak(s) responsible for the detected refrige-rant gas deficit.

Need for Continuous Gas Detection

There are several reasons why continuous refrigerant detection in the environ-ment is necessary, including:

The first and, until now, the primary reason is compliance with current regulations: RSIF (in Spain) and the F-Gas Regulation in Europe.

However, this purely administrative approach is now complemented by the awareness that continuous gas transmitters are a powerful maintenance tool, enabling significant cost savings for the user/owner of refrigeration installa-tions. The reasons include:

• Reduction of fluorinated gas tax payments
• Reduction of energy consumption, as energy usage increases, as pre-viously mentioned, when the refrigeration system operates with insuffi-cient refrigerant
• Reduction of maintenance costs
• Reduction of product losses associated with the malfunction of the sys-tem due to a lack of refrigerant
• Possible reduction in insurance premiums
• Minimization of business disruption caused by the unavailability of refri- geration services

Other Reasons Supporting the Need for Continuous Detection:

• Safety of personnel: Refrigerants can displace oxygen, causing asphyxia-tion (e.g., HFC, HFO, CO2), or they may be toxic (e.g., NH3) or flammable (e.g., hydrocarbons, NH3).
• Environmental protection: HFC refrigerants contribute to global warming (greenhouse effect)

Legislation and Regulatory Aspects of Leak Detection

As mentioned in the introduction, legislation and regulatory aspects in rela-tion to refrigeration systems have changed dramatically over the last few years in most developed countries, especially at European (EU) and North American (USA) levels. It is important to highlight its original role in the cultural and operational change regarding the treatment of refrigerant gases in general, and especially, although not only, in those applications that use or have historically used HFC gases.
Environmental awareness and the high impact of refrigerants due to their re-lationship first with the ozone layer (CFC, HCFC) and then due to their effect on global warming (HFC) have gradually promoted different legislations that largely explain the current transitional context.
As also mentioned in the introduction, the primary objective of this leak detec-tion manual is to reduce the economic and operational costs associated with refrigerant gas losses in refrigeration installations, beyond the regulatory and mandatory aspects that are still mainly limited to aspects of personal safety, as will be seen in the following sections.

However, legislative and regulatory aspects are also of great interest to refri-geration agents and, as such, this manual provides a summary analysis of two different vectors:

• Short, medium and long-term practices and prohibitions on the use of refrigerant gases
• Mandatory requirements on leak detection in refrigeration installations

These vectors are specifically analyzed for two different geographical areas: the European Union in general (EU) and Spain in particular. The regulatory and legislative section in the USA is outside the scope of this manual, although the corresponding documents of interest are briefly cited in the following section.

 Overview of Legislation in Spain, the EU, and the USA
Regulatory and legislative aspects are fed and complemented by different docu-mentary sources. It is necessary to differentiate these texts to structure the mes-sage and to clarify which aspects and practices are recommended or references (regulations) and which aspects are mandatory (legislation and regulations). This aspect is complex in relation to refrigeration and refrigerant gases due to the overlapping of regulations and legislation at state and European level, and the parallel effect of expert technical committees which, through modifications in the reference standards (EN 378 in Europe and AHSRAE 34, 15 and 147 in the USA), encourage successive adaptations and changes to the same regula-tions and legislation.

Table 5 presents an overview of the regulatory and normative status in these three geographical areas:

Zone	Legislation (mandatory) in 2018	Basic European legislation	Related standards
Spain	RD 138/2011 (Industry, Refrigeration systems)RD 115/2017 (Environment)	N/A517/2014	EN 378 2008-2009N/A
EU	Regulation 517/2014 (Prev. 842/2006) Legislation finally applicable at national level Ej. France: Arreté 29 Février 2016Ej. Spain: RD 138/2011 + RD 115/2017	517/20141516/2007	EN 378 2016 1-4(Safety & Environment)EN 14624(For gas detectors)
USA	Clean Air Section 608 Clean Air Section 612 (SNAP)	N/A	ANSI ASHRAE 34(Ref. Classification) ANSI ASHRAE 15(Safety)ANSI ASHRAE 147(Environment)

Table 5: Regulations and standards relevant to refrigeration systems in Spain, the European Union (EU) and the USA.
A general reflection is that safety and environmental aspects are mixed in both standards and regulations. The most significant aspects are detailed in the following sections.

 Legislation in the European Union
In the European Union, the regulation with the greatest impact on refrigerant ga-ses is the one popularly known as F-Gas: Regulation 517/2014 (European Parlia-ment regulation on fluorinated gases) which repeals (modifies and complements) the purpose of the previous regulation 842/2006, also known as F-Gas.

This extensive regulation affects multiple aspects in relation to the use and treatment of refrigerant gases, which we summarize later in section 9.2.1. The still valid Commission Regulation 1516/2007 of 19 December 2007 laying down, pursuant to Regulation (EC) No 842/2006, standard leakage monitoring requirements for fixed refrigeration equipment, air conditioners and heat pumps containing certain fluorinated greenhouse gases (OJ L 335 of 20.12.2007, p. 10) is discussed in section 9.2.2. Finally, section 9.2.3 briefly discusses the Eu-ropean reference standard EN 378, in its most updated version of 2016, only as regards the refrigerant gas detection requirements.

 F-Gas Regulation (517/2014) • The regulations of the European Union are binding on all member states.
However, the power to impose sanctions lies with the states and, usually, although not always, the states themselves legislate additionally, complementing and/or extending the EU regulations. An example is the Spanish case, with RD 138/2011 (complemented by various resolutions and by RD 117/2017) which includes and extends what was imposed by the FGas (Regulation 842/2006 and amendments according to Regulation EU 517/2014), as we will see later.
Regulation (EC) No. 517/2014 (F-Gas) has as its primary objective the protecion of the environment by reducing emissions of fluorinated greenhouse gases, through the establishment of:

• Standards on the containment, use, recovery and destruction of fluorinated greenhouse gases, as well as on the related accompanying measures
• Conditions for the marketing of specific products and equipment that contain fluorinated greenhouse gases or whose operation depends on them
• Conditions for specific uses of fluorinated greenhouse gases, quantitatively limiting the marketing of hydrofluorocarbons.
• Standards on the use of detection systems and minimum frequencies of leak inspections. to complement and/or extend EU regulations.

In an extraordinarily summarized way, the four basic pillars on which F-Gas is based are:

A-PROHIBITIONS on new equipment (Commercialisation)
Domestic refrigerators and freezers containing HFCs con GWP ³ 150	From 1/1/2015
Refrigerators and freezers for commercial use (hermetically sealed):-Containing HFCs with GWP ³ 2500 (p. ej. R404A, R507)-Containing HFCs with GWP ³ 150	From 1/1/2020 From 1/1/2022
Stationary refrigeration containing GWP ³ 2500(except for applications with product temperature below -50°C.)	From 1/1/2020
Multipack centralised refrigeration systems for common use with capacity > 40kW containing mixture with GWP ³ 150EXCEPTION: Primary cooling circuit of a CCD system with GWP ³ 1500	From 1/1/2022
Single split A/C with <3kg of HFCs containing blends with GWP ³ 750	From 1/1/2025

Table 6: Prohibitions on placing new equipment on the market according to F-Gas 517/2014

B-PROHIBITIONS on equipment in service and maintenance
Equipment with load higher than 40 Tn. of CO2 eq. of HFCs and with GWP ³ 2,500 (e.g. system with 10 kg of R-404A) Affects supermarkets, industrial refrigeration, food shops, etc.EXCEPTION:-Applications with product temperature <-50°C-Military equipment-HFCs recycled/recovered with GWP ³ 2500	Until 31/12/2019 Until 31/12/2029

Table 7: Prohibitions on maintenance of equipment according to F-Gas 517/2014
As seen in Table 7, typical refrigeration systems currently in operation in commercial and industrial refrigeration that use gases like R-404A will no longer be serviceable (i.e., they cannot be recharged if they have leaked or lost refrigerant) starting January 1, 2020. However, and most importantly when discussing leak reduction, these systems can still be maintained if the recharge gas comes from dismantled installations (i.e., regenerated/recycled gas).

As the reader will imagine, keeping leaks to a few kilograms per year could in fact extend the life of these facilities until 2030, making it a technological option environmentally, economically and legally viable, especially when the technological alternatives in 2020 are still presumed to be immature and expensive, especially in southern climates such as Spain [6, 7].

As illustrated in Figure 21, the HFC Phase-down under 2024 amendment aims for a sharp and significant reduction in the introduction of new HFCs into the market. The phase-down entails that by 2030, the impact (in CO2 equivalent tons) of the introduction (production and importation) of HFCs in Europe will represent only 21% of the baseline consumption in Europe between 2009 and 2012.

This aspect explains, on one hand, the strong price and availability pressures for the most polluting gases (e.g., R-404A), since 1 kg of R-404A in terms of quota is equivalent to approximately 3 kg of R-134A. On the other hand, it underscores the critical importance of keeping refrigerant gas contained within refrigeration systems. As seen, doing so enables the operation of refrigeration systems to be decoupled from the shrinking refrigerant market, making them environmentally, economically, and legally viable. It is important to note that this Phase-down, in the interests of the Kigali agree-ment of December 2016, will be carried out worldwide at different speeds, with 2034 being the final date (21% of baseline) for developed countries and before 2047 for developing countries.

D-MANDATORY AND FREQUENCY of leakage checksLeakage checks continue to be based on the same frequency as specified in Regulation 842/2006.
	Frequency of leakage check
	No detection system	With detection system
5 tonnes of CO2 equivalent	12 months	24 months
50 tonnes of CO2 equivalent	6 months	12 months
500 tonnes of CO2 equivalent	N/A	6 months

Table 8: Mandatory and frequency of refrigerant leakage inspections according to F-Gas 517/2014.

For illustrative purposes, the kilograms of the most common refrigerants are indicated in their regulatory equivalents (in tons of CO2) in Table 9. As seen, the obligation (according to European F-Gas regulations) of detection systems depends on the refrigerant used by the refrigeration system, ranging between charges of 127 kg (for R-404A) and 828 kg (for R-450A):

	5 T CO2 equiv. (kg)	50 T CO2 equiv. (kg)	500 T CO2 equiv. (kg)
R-134	3.5	35.	349.7
R-404a	1.3	12.7	127.5
R-407a	2.4	23.7	237.3
R-407c	2.8	28.2	281.8
R-407f	2.7	27.4	274.0
R-410a	2.4	23.9	239.5
R-448a	3.6	36.0	360.5
R-449a	3.6	35.8	357.9
R-450a	8.3	i82.8	827.8
R-452a	2.3	23.4	233.6
R-507	1.3	12.5	125.5
R-513a	7.9	79.2	792.4

Table 9: Relationship between mass of refrigerant and tonnes of CO2 equivalent.
The mandatory installation of leak detection systems, as well as the establishment of minimum inspection frequencies are a final point that characterizes the F-Gas. These controls and detection systems are mandatory for refrigeration systems with more than 500 tons of CO2 equivalent (e.g. 127 kg of R404A, see Table 8), while for smaller systems, the use of detection systems allows to reduce by half the mandatory frequency of exhaustive control (inspection) of leaks.
We can deduce that the control leak regulation is frankly unambitious compared to the strong limitations on the sale of refrigerants regulated by the same norm. We conclude that, in terms of regulations, the Commission’s strategy is to:

• Force an abrupt technological change (of doubtful economic viability in such a short period, [6, 7]) and/or
• Improve the techniques and practices for detecting and minimizing refrigerant leaks implicitly, as a response to market shortages and prices, and not explicitly, by imposing procedures and reviews that are difficult to follow, effective and sanction by the Member States.

A definitive reflection in this context is that if the refrigerant is kept within the facilities, no rule or regulation prevents the normal operation of the installation until at least 2030, even using the most polluting gases, that is, the gases with the greatest greenhouse effect such as R-404A and R-507.

9.2.2. – Final Considerations on Legislation and Regulation
Regulation 1516/2007 on leak control in refrigeration installations adds or complements (understood as the F-Gas regulation) good practices and is state of the art regarding leak inspection and repair. Within the framework of this manual, we highlight the following articles in Table 10:

Article 2	Responsibility of the system maintainer for condition and leakage recording
Article 4	Mandatory systematic checks on the components most susceptible to leakage (where applicable according to 517/2014)
Article 5	Mandatory use of a direct or indirect measurement system to locate leaks; the direct detection system is suitable for all cases (where applicable according to 517/2014)
Article 6	Definition of direct detection systems (mandatory annual system check in case of stationary detection systems)
Article 7	Definition of indirect detection systems (to be complemented by direct detection systems according to section 2, when a leak is detected)

Table 10: Relevant articles of regulation 1516/2007 (in force) in relation to refrigerant gas leaks.

 EN 378 2016. Refrigeration systems and heat pumps.

Safety and environmental requirements.
The European standard EN 378 plays a fundamental role in the development and implementation of both European and national regulations and legislation. This is an extremely extensive text with a high technical content that refers to the design, construction, use, safety, maintenance and dismantling of refrigera-tion systems and heat pumps. It consists of 4 parts:

• Part 1: Basic requirements, definitions, classification and selection criteria
• Part 2: Design, manufacture, testing, marking and documentation
• Part 3: On-site installation and protection of people
• Part 4: Operation, maintenance, repair and recovery

The title of the standard itself indicates that the technical considerations des-cribed therein refer to both the safety of people and environmental aspects (closely related to the treatment of refrigerants), so we particularly highlight the aspects related to the use of leak detection and repair systems, in parts of the standard:

Part 1
The title of the standard itself indicates that the technical considerations des-cribed therein refer to both the safety of people and environmental aspects (closely related to the treatment of refrigerants), so we particularly highlight the aspects related to the use of leak detection and repair systems, in parts of the standard:

Part 2
The title of the standard itself indicates that the technical considerations des-cribed therein refer to both the safety of people and environmental aspects (closely related to the treatment of refrigerants), so we particularly highlight the aspects related to the use of leak detection and repair systems, in parts of the standard:

Part 3

• Forced ventilation in machine rooms must be activated by refrigerant gas detectors/transmitters, always at levels that are safe for people.
• The maximum permissible alarm levels (for the safety of people) for the detectors/transmitters are defined.
• At least one detector/transmitter must be installed in the machinery rooms (compressor rack).
• Detectors/transmitters must be continuously monitored.
• Detectors/transmitters for halogenated refrigerants must comply with EN 14624 (standard that defines technical requirements, marking, precision, response time, etc. for refrigerant gas detectors/transmitters)
• Detectors, alarms and related actions (activation of forced ventilation, for example) must be checked at least once a year.

The focus of refrigerant gas detection in the EN 378 standard is fundamentally the safety of people and not the detection and/or reduction of leaks.

Legislation and Regulation in Spain
As mentioned in section 9.2.1, although European regulations are mandatory in all member states, the control and sanctioning tasks fall on the states themsel-ves. This means that member states usually legislate based on European regu-lations. This step often involves very extensive legislation, which combines the political spirit of the European regulation with technical aspects of reference standards, producing texts that are much more complete and even more restric-tive than the European regulation itself.

The Spanish case is a good example of this:
RD 138/2011 is the Royal Decree that approves the Safety Regulations for Re-frigeration Installations (RSIF) and its complementary instructions. It is a very extensive text with 19 technical instructions. The Regulation approved in RD 138/2011, amended by 7 technical resolutions (published between 2012 and 2017) and by an additional Royal Decree (115/2017, which includes the most significant changes to European Regulation 117/2014 with respect to the pre-vious 842/2006) today represents the mandatory legislative text in Spain and, therefore, includes a priori at least everything required by European regulations.

In general terms, its foundations coincide with European regulations 517/2014 and 1516/2007, although many instructions and technical details are added based mainly on the EN 378 standard. Regarding the inspection, detection and correction of refrigerant gas leaks in refrigeration installations, we highlight the following RSIF particularities that can be considered as additional requirements to F-Gas itself:

• Instruction IF-04 (USE OF DIFFERENT REFRIGERANTS) indicates the obligation to install R-744 (CO2) in machine rooms and in premises of more than 30 m3 where it is used, provided that the practical limit can be exceeded (maximum allowable refrigerant density 2). Such detection systems must activate forced ventilation of the room(s) at levels below 5000 ppm and force evacuation of people at levels below 10000 ppm.
• In IF-16 (PREVENTION AND PERSONAL PROTECTION MEASURES) it is mandatory to install leak detection systems inside cold rooms when the practical limit as set by EN 378 and the RSIF itself may be exceeded. For example, for R404-A (practical limit of 0.48 kg/m3) a room of even 200 m3 (extraordinarily large in the commercial refrigeration environment) would require a detection system if the refrigeration plant has at least 96 kg of refrigerant (or more). For smaller rooms, load quantities in the plant even less than 50 kg would require the installation of the detection system.
• Instruction IF-16 (PREVENTION AND PERSONAL PROTECTION MEASU-RES) also stipulates that at least one coolant detector/transmitter is man-datory in machine rooms. This system must be capable of triggering an alarm in a space occupied by people and must be able to isolate parts of the cooling system in the event of a leak.

Final considerations on legislation and regulation
If the reader has been able to reach the final point on legislation and regulation, he/she will have noticed that, despite the large amount of information and technical details in the mandatory texts (in the Spanish case we can speak of more than 500 pages of regulations, European and national regulations), the detection of refrigerant gas leaks is fundamentally based on the safety of peo-ple and, in the vast majority of cases (and especially for gases such as HFCs) its obligation falls only on machine rooms and small and medium-sized cold rooms, even for the restrictive Spanish legislation.

More significantly, the importance of the European regulations (and global re-gulations after the Kigali agreement) lies in the bans and quotas on the pro-duction/introduction of refrigerant gases that are effectively drastically transfor-ming the market and implying serious operational and economic difficulties for refrigeration system users.

In this context, it is crucial to reiterate the prohibition dates for maintaining existing systems:

• 2020: for refrigerants such as R404A or R507 (if they are to be maintai-ned with new, non-regenerated refrigerants)
• 2022: for virtually any HFC refrigerant not used in a cascade system with CO2. The commission must clarify whether it will be possible to maintain installations prior to 2022 with refrigerants with GWP<2500 using new, non-recycled refrigerants, although their price is expected to be prohibi-tive from 2021.
• 2030 for any refrigeration systems that are maintained with recycled HFC gases (which will only be viable if the system has very low leak rates)

With this scenario, and to avoid the complete renewal of all refrigeration systems still in service today with technologies that may not be sufficiently mature in an extraordinarily short period of time [6,7], it is essential to reduce leak rates.
Therefore, this leak detection manual emphasizes that the current regulatory framework on leak detection is merely a minimum baseline reference. The cu-rrent economic and operational challenges demand much more powerful, ex-tensive, robust, and reliable leak detection practices and systems than those legally required today, as discussed extensively throughout this manual.

Technologies and Principles of Gas Detection / Measurements

In section 7, leak detection techniques were discussed in a general sense, de-fining direct continuous, indirect continuous and discontinuous detection. This section focuses on a technical and scientific analysis regarding the sensing te-chnologies (refrigerant gas detection and/or measurement) that are used in direct continuous (stationary) detection systems. This information may be useful to the reader interested in understanding the performance and limitations of the different technological alternatives and the viability of these technologies to meet their detection needs.

Definitions
Before starting, it is convenient to define a series of terms that are generally used in the gas detection environment, which will increase the clarity of the text and facilitate its understanding.

TECHNICAL EQUIPMENT	Sensor	Electronic component which returns an electronic output when gas is present (usually without display, without relays, without protection, not installable, etc.)
	Detector	Installable electronic equipment that only indicates if there is a gas concentration (also defined as indicator according to EN 14624) Can be stand-alone or linked to an alarm centre
	Transmitter	Installable electronic equipment measu- ring gas concentration (also defined as a meter according to EN 14624) Can be stand-alone or linked to an alarm centre
	Alarm centre	Installable electronic equipment that centralises 1 or several detectors / trans- mitters and summarises their equipment status and alarms
BACKGROUND	Concentration	Volume occupied by the gas relative to the total volume. Measured in ppm (parts per million) by volume
	Sensitivity	Minimum amount (in concentration, ppm) of a device fordetection / measurement
	Precision (See fig.22)	Ability of 1 or N detectors/transmitters to consistently repeat a given output for a given exposure (in N tests for 1 device or for N devices in 1 test).
	Accuracy (See fig.22)	Ability of a device to reliably (truthfully) measure actual concentration values
	Selectivity	Ability of the equipment to react only to the gas of interest and not to cause false alarms to other substances or gases.

Table 11: Definitions and fundamentals of refrigerant gas detection and measurement technologies.

 

 Relationship between mass and concentration
As can be seen from the definitions, the general technique for detecting and measuring gas is based on the concentration of the target gas (not another gas or substance) in volume (parts per million -ppm- of the analyzed volume where the target gas is located).
This means, for example, that the gas concentration in a refrigerant cylinder (in the gaseous part that may remain inside it) is 106 ppm (1 million ppm), which is equivalent to saying that 100% of the analyzed volume is occupied by the gas in question, without any dilution in another gas, such as air.

In general, and especially in the world of leak detection, the concentration value is rather insignificant; the interest relies on the mass of gas that can be detected and/or measured. This is because the mass (kg) is the business and operational unit of interest for the agent or user of refrigeration. To show this relationship, and for illustrative purposes, the theoretical connec-tion between refrigerant mass for R134A and different detection volumes is presented in Table 12. The values indicated in the table are approximately simi-lar for most HFC gases, however they do not apply to CO2 or NH3 (ammonia):

Mass – volume ratio for R-134A(1 atm, 21 ºC)		Volume (m3)
		5	50	250
Mass (Kg)	0.1	3.5	35.	349.7
	1	1.3	12.7	127.5
	10	~ 400000 ppm	~ 40000 ppm	~ 8000 ppm

Table 12: Theoretical mass to concentration ratio for different R-134A volumetries.
As observed, for small analysis volumes (a small 5000-liter cold room) an accu-mulated gas quantity of 100 grams of refrigerant produces very high concen-tration values. On the other hand, for a compressor room (250 m3) the same accumulated quantity can generate very low concentrations (80 ppm). It is important to highlight the term “accumulated”, since this mass of gas must remain in volume to achieve this concentration. This is not obvious since the refrigerant gas has a significant diffusion coefficient and tends to expand and, consequently, leave the analysis volume after a certain time, given that the rooms are not airtight, in addition to having doors and traffic of people and goods in many cases.

The diffusion capacity of the refrigerant gas on the one hand and the speed of the leak (g/h) on the other indicate that small leaks (orders of grams in orders of hours) in enclosures of more than 1000 liters require detection values always below a few hundred ppm and even below 100 ppm in many cases.

Gas Sensor Technologies
In our field, we are mainly focused on refrigerants of the HFC, HFO, CO2 and NH3, there are several valid technologies for detection and measurement:

• EC (Electro Chemical) technology
• SC (Semi-Conductor) technology
• NDIR (Non Dispersive InfraRed) technology.

Electrochemical (EC) technology is suitable for toxic gases (such as CO2 and NO2) and for ammonia (NH3), although the latter can also be detected with semi-conductor (SC) technology. That is why in the field of refrigeration we highlight and analyze two of the technologies mentioned: SC (Semi Conductor) technology and NDIR (Non Dispersive Infra Red) technology.
As already mentioned in section 7, the qualities and limitations of these techno-logies will allow us to understand their use and suitability for the leak detection environment and, consequently, to discern what performance can be expected and what applications are suitable for them.

SC, Semi-Conductor Technology
Semiconductor technology is based on affecting the electrical conductivity of a semiconductor surface (made of metal oxides) that adsorbs the gas to be detected and/or measured. The higher the gas concentration, the greater the absorption by the semiconductor surface and the greater the effect on its con-ductivity (See Figure 23).

The major advantages of semiconductor technology are its low cost, stability and resistance to poisoning (i.e. they do not degrade every time they detect gas). These attributes have made semiconductor technology the most popular technology for detecting HFCs and even NH3, (ammonia) in the refrigeration environment, despite not being suitable for detecting CO2.

On the other hand, SC technology has several important limitations, from lesser to greater severity:

• Sensitivity: Its sensitivity is moderate. The minimum detection level is always higher than a few hundred ppm, which represents a problem for detecting small quantities of refrigerant, as indicated in the previous section.
• Precision: Its construction makes semiconductors equipment with low precision, so its readings are related to significant dispersions, making its reading a quantitative value generally not very consistent. This is why, among other reasons, semiconductor sensors are mainly used in detec-tion equipment and not in gas transmitters or meters.
• Selectivity: Possibly its most severe limitation. This technology is not ca-pable of differentiating the target refrigerant gases from other gases that are adsorbed in a similar way on the semiconductor, so they can also react to ethylenes, alcohols, cleaning products, yeasts, etc.

From an application and operational point of view, the limitations of the techno-logy explain why SC sensors are used only in gas detectors calibrated to react at 500, 1000 ppm or even higher concentrations. In fact, using lower reaction ed-ges would imply an even higher number of false alarms than are already usual. With these detection levels, it is not generally possible to detect small leaks and, therefore, they are not recommended for this application if a reliable system and a generation of leak alarms useful for the user or maintainer are desired.
On the contrary, for purposes of personal safety (as regulated, as set out in section 9), this technology is perfectly valid since it ensures its reaction at con-centrations much lower (between 5 and 30 times) than the maximum permitted by regulations, always under the criterion of personal safety.

Non Dispersive Infrared Technology (NDIR), Semi-Conductor Technology
NDIR sensors consist of an infrared energy emitter, a receiver, and a chamber (small volume) for analysis between the two. Gases in general and refrigerants in particular have molecular characteristics that make them vibrate (and thus absorb energy) more or less easily at different wavelengths in the infrared spec-trum. The concentration (ppm in volume) of the target gas is obtained from the energy difference between the emission and reception, since this energy deficit is caused by the presence of the gas that vibrates at this wavelength (See Figure 24).

From the sensor’s operating principle, one of the great qualities of this tech-nology can be deduced: its selectivity. Indeed, it is relatively easy to study the refrigerant gas and determine at which wavelength its molecular bonds are most absorbent (what is called the gas fingerprint). The use of filters to focus the infrared emission of the transmitter at this wavelength greatly reduces false alarms produced by other substances. Additionally, NDIR sensors (and their associated transmitters) have other advan-tages that are relevant in the detection of refrigerant gas leaks:

• They are very precise.
• They are very accurate and also allow calibration and zeroing processes.
• They are very sensitive, with detection limits below 20 ppm.
• They are stable and durable (life-span > 7-10 years) Their main disadvan-tage is their sensitivity to small geometric changes during installation (an orientation different from the original calibration or a small deformation of the optical channel can generate an appreciable offset).

It is therefore highly recommended to reset the sensor zero to its final ins-tallation position and temperature, especially for the detection of refrigerant gas leaks, when the zero ppm value is very significant, as an indication of the existence of a leak. See section 13 for more details.

Comparative Summary of SC vs. NDIR Technologies
For the detection of refrigerant gas leaks there are fundamentally four essential qualities: sensitivity, precision, accuracy and selectivity. Sensitivity allows the detection of small quantities of refrigerants in large spaces and even outdoors, depending on forced air flows. High sensitivity is therefore essential to detect small leaks at the precise moment they occur, prematurely.

Precision and accuracy are essential to measure the severity of the leak. If the user or maintenance of the installation correlates the volume of the transmitter (approximate volume of the space where the transmitter is located) with the concentration value read, it is easy to estimate whether the leak is slight, severe or very severe. Finally, selectivity makes it possible to provide robustness and reliability to the detection system, since in a very high percentage, the readings detected will correspond to real leaks that must be repaired, avoiding false alarms that would mean, first, loss of resources and time in the search for the leak and, finally, loss of confidence in the system.
To summarize these aspects and in a comparative view of the different sensor technologies in the field of refrigeration, Table 13 is presented as a synopsis:

	Semiconductor	NDIR
Precision	Low	High
Accuracy	Medium	High
Selectivity	Very low	Vary high
Performance / Features	Detection	Measurement
Recommended use	Personal safety	Leak detection

Table 13: Comparison of technologies for the detection and measurement of refrigerant gases

Direct Continuous Detection – Installation of Gas Transmitters in the Environment

After what has been seen in section 10, the reader will have noticed that the technology necessary for the detection of small leaks, a consequence of the loss of tightness of the system, and which constitute the most difficult challenge for the maintenance of refrigeration installations due to their difficult detection, must be treated with gas transmitters capable of measuring the gas concen-tration using NDIR technology. That is why in this section we will speak only of transmitters, leaving the concept of detector for applications of personal safety, as described in previous sections.

 Approaches to the Installation of Environmental Transmitters
There are three possible approaches to installing continuous gas transmitters in the environment:

• Perimeter Installation Approach: Transmitters are placed around the perimeter of the space to be monitored. This setup aims to supervise the en-tire area using the minimum number of transmitters. Often, solely to meet regulatory requirements, only one detector or transmitter is installed.
• Point Installation Approach: Transmitters are installed at specific hi-gh-risk points for leaks to monitor them efficiently.
• Mixed Installation Approach: This combines the two previous approa-ches, placing perimeter transmitters alongside others at specific high-risk points for leaks.

The mixed approach achieves the best results in terms of the percentage of leaks detected and response speed. For this method to be successful, the most likely leak points must be identified, and the positioning of the perimeter trans-mitters must be chosen carefully. Examples and specific recommendations are provided later in this section.

General Rules for Transmitter Installation
Most refrigerant gas transmitters are installed inside closed enclosures with specific volumes, whether in machine rooms, cold rooms, furniture, display cabi-nets, false ceilings, etc. The guidelines indicated below are aimed at this type of installation. If the transmitters are installed outside, there are some differences that will be discussed specifically later. The general rule for the installation of ambient transmitters assumes that the enclosure is ideally “tight to the entry of outside air” and without sources that generate air movement. In this type of enclosure, the exchange of air with the outside (through natural gaps) does not exceed 10% of the volume of the room per hour (0.1 outside air/h) and the air speed does not exceed 20 cm/s. In this way, air movement inside the room is caused by density differences, convection or movement of people/goods. Some large machine rooms fit well into this classification. Under these conditions, the height above the floor at which the gas transmitters must be installed in the ambient is related to the gas to be detected and its relative density with respect to air (See Figure 25).
Other general rules regarding installation are:

• Do not install them on structures that are subject to vibrations or impacts, such as pipes or pipe supports.
• Do not place them near sources of heat, water or excessive humidity.
• Do not install them in areas where condensation may form.
• Do not mount them where they may be exposed to direct sunlight.

Perimeter transmitters
A gas denser than air will tend to fall towards the ground, and therefore the transmitter must be placed close to the ground, at a height of less than 1 m above it. This group includes CFCs, HCFCs, HFCs, HFOs, CO2 and some hydro-carbons such as propane (R-290), propylene (R-1270), isobutane (R-600a) and butane (R-600).

Gases that are less dense than air rise, and therefore the transmitter must be placed high up, either on the walls or on the ceiling, considering that they are accessible for maintenance later. This group includes NH3 and methane (CH4). When it comes to gases with a density like air, the transmitter is mounted at the height of the head of a person of average height. This group includes, for example, ethane (R-170). See information on relative densities of various gases in Annex 1 (Table 1).

In addition, the transmitter will be located close to the machinery that can generate leaks. Transmitters intended for refrigerants of safety groups L2 (gases A2, B1, B2) and L3 (gases A3, B3) must be explosion-proof or have some form of protection suitable for the atmosphere generated. In some countries, it is mandatory to connect a UPS (uninterruptible power supply) to gas transmitters to keep them running in the event of a power failure. Point transmitters (installed near a specific leak point) In this case, the same guidelines as in the previous case will be followed, but placing the transmitter below, above or at the same height respectively as the leak point to be monitored.

 

 

 Improvements in the positioning of fixed gas transmitters

Perimeter transmitters.
The general rule is a first approximation to the problem of the placement of ambient transmitters, since many enclosures cannot be considered ideally “watertight”. In order to position transmitters in an improved way, it is imperative to know the characteristics of the air movement within the room where they are installed.

The first step to achieve this is to identify all possible sources that generate air movement, such as ventilation systems, hot surfaces, movement of people or products, sources of thermal radiation, etc. The second step is to simulate the air movement using smoke tubes/canisters/ generators (which produce smoke), without forgetting to also analyze dead spaces, such as corners, gaps in ceilings and drains. The improvement will come from installing transmitters in the detected air stream.

Case: room with ventilation
For example, if there is permanent ventilation equipment in the room, the trans-mitter must be placed in the ventilation outlet duct/grille, or in the path of the air flow caused by said ventilation. See Figure 26.

Care must be taken to ensure that ventilation is permanent; if it is only activa-ted sporadically, any leak will only be detected when ventilation is on. In these cases, one transmitter can be placed as per the general rule and another in the ventilation outlet duct/grid.
A particular case of a ventilated room is cold rooms with ventilated evaporators. In this case, the ventilated evaporator creates a circular flow, since the cold room is “sealed” and the air is constantly recirculated. The best position for the perimeter gas transmitter in these cases is in the air flow drawn in by the evaporator, since its speed is more moderate than on the wall opposite the evaporator, where the flow of air driven is more forced, although this is also a valid position (See Figure 27).

Case: room with heat sources
Another common case is one in which there are sources in the room that dissipate heat, such as machines with very hot surfaces, boilers, heat exchangers, etc. The energy dissipated by these sources heats the air around them and makes the air rise towards the ceiling. The hot air is distributed from the ceiling to the walls, where it cools and falls back towards the floor, creating a downward air movement.

This movement drags the gases regardless of their density. The turbulence of these circular currents facilitates the mixing of the leaked gas with the air, dilu-ting the concentration, which will increase over time. The strength of the air currents will depend on the surface temperature of the heat sources and their difference with the ambient temperature prevailing in the control room. It also depends greatly on the size of the dissipation surfaces. The use of smoke will reveal the influence of these factors. In these cases, transmitters should be installed above the heat source, or where the air flow can be detected (See Figure 28).

Case: false ceilings
False ceilings through which pipes pass or valves are located must also be monitored with continuous ambient transmitters, especially if they are practical for maintenance work. The probability of leaks in these spaces, which contain several dozen meters of pipe, welds and several valves, is relatively high, so it is interesting to have control points in these areas. Additionally, let us not forget that refrigerants displace oxygen and that an accumulation of gas in a false ceiling can be dangerous for the safety of the operators. Case of refrigerated furniture and/or: corridors with refrigerated furniture

Corridors with refrigerated furniture, on one or both sides, can also be monitored with continuous ambient transmitters, optionally, if a high percentage of leak detection is desired. In these cases, the refrigerants used are heavier than air, so the transmitters will be placed at the bottom, towards the end of the aisle in the preferred direction of public circulation, if there is one. In the case of clearly bidirectional aisles, the transmitters will be installed in the center of the aisle path.

In relation to refrigerated furniture, a more effective installation option consists of locating the transmitter inside the refrigerated furniture (i.e. punctually), provided that the transmitter can work at the temperatures of the furniture. This alternative confers a very high degree of probability of leak detection, since the volume of the refrigerated furniture is reduced and the transmitter, even with open furniture, can detect leaks of fractions of a gram per hour very quickly. This discretion, although it requires a greater investment, is also essential in locating the leak, since the different transmitters clearly indicate which piece of furniture is leaking, and the leak must be inspected in detail, the leak isolated and only the piece of furniture identified by its transmitters repaired.

Point transmitters
The same reasoning given for perimeter transmitters can be used to improve the placement of point transmitters. An example has been outlined in the previous case on refrigerated furniture:

• If there is ventilation, the point transmitter will be placed after the air flow passes through the probable leak point that must be controlled.
• If there are hot spots under a point to be controlled, the transmitter will be located above said element
• Etc.

Transmitters installed outdoors

Perimeter transmitters
The high sensitivity of ambient transmitters with a detection cell with NDIR technology allows them to be installed outdoors, although it will always be a more complex detection than in interior enclosures with finite volumes. The mounting position must be made taking into account the same factor already indicated for interiors, that is, the relative density with respect to the air and also, the direction of the prevailing wind at the site. The use of smoke remains the best system to determine the movement of the air. To increase the effecti-veness of the transmitters, screens or cones can be installed that “collect” the gas to concentrate it towards the transmitter. It should also be studied if there are partitions, structures or machinery that serve as a barrier in the path of the leaked refrigerant. In this case, a transmitter located in front of these structures also improves the effectiveness of the detection. In any case, the transmitters will be installed close to the machinery that may generate the leak.

Point transmitters
For point transmitters outdoors, the guidelines already indicated for indoors will be considered, adding the variable of the prevailing wind.

Recommendations for the Number of Fixed Detectors/Transmitters

The number of transmitters to be installed is related to the objective to be achieved by installing them.

Objective: Compliance with Regulations
This is the traditional approach, where detectors/transmitters are installed solely to meet legal requirements. These systems are not intended to be used as tools for maintenance or to reduce costs associated with refrigerant leaks. Detectors/transmitters used for this purpose are usually low-cost and often lack adequate sensitivity or specificity. For example, they may trigger false alarms in the presence of solvents or gases emitted by fruits or other food products.
According to the RSIF, detectors/transmitters are required only in installations exceeding the following thresholds:

• 10 kg of refrigerants from Group L1
• 2.5 kg of refrigerants from Group L2
• 1 kg of refrigerants from Group L3

(Refer to Table 1 in Annex 1 for refrigerant group classifications.)
For regulatory compliance, the number of detectors/transmitters required is:

• 1 detector/transmitter in the machine room
• 1 detector/transmitter per cold room (or other refrigerated spaces used for processing), provided that a leak could exceed the practical limit of the refrigerant. Refrigerated display cases are not considered cold rooms.

This approach results in a low percentage of detected leaks. If SC technology-based detectors are used, it is likely that small or slow leaks caused by system wear will not be detected, as such leaks rarely reach a concentration of 500 ppm or more. In these cases, the detectors ensure that dangerous concentrations, which could harm people, are avoided.

Objective: Reducing Costs Associated with Refrigerant Leaks
This is a more modern and professional approach, which benefits from the improvements made in gas detection technology represented by NDIR sensors. To achieve the cost reduction objective, a mixed transmitter strategy (perimeter + point) must be implemented, using highly sensitive transmitters with NDIR technology. Section 13 provides an overview of the system, methods and procedures for this objective.

Regarding the number of transmitters, this strategy allows:

• Reducing the annual cost of refrigerant and associated taxes
• Reducing the annual maintenance cost associated with the repair of leaks
• Reducing the cost associated with the loss of merchandise and process downtime.
• Avoiding the disruption of economic activity linked to the potential loss of refrigeration capacity of the establishment.
• Properly implemented, this strategy can detect 90% to 98% of leaks, according to prior experience.
• Next, we make a recommendation of transmitters to install. This represents the ideal optimal recommendation. The closer the actual configuration is to the optimal, the higher the percentage of leaks found.

The optimal recommendation of transmitters to install will be:

In machinery rooms: 

• Perimeter transmitters: One transmitter for every 300 m3 of volume.
  • If there is a compressor / central / chiller in the room, place the transmitter on the perimeter of the unit.
  • In the case of two, place the transmitter between them.
  • With three or more, place the transmitters between them and on each side.
• Point transmitters: One point transmitter in each condensing unit / central / chiller, located near the most probable point or with a history of leaks (in most cases, the pressure gauge/switch panel).

In cold rooms / refrigerated premises: 

• Perimeter transmitters: One transmitter per cold room (in large cold rooms, 1 transmitter for every 500 m3), preferably located in the air stream drawn in by the evaporator(s).
• Point transmitters: One transmitter located next to the expansion valve of each evaporator, for evaporators with a cooling capacity greater than 30 kW at high temperature and 20 kW at low temperature. Also recom-mended for smaller evaporators with a history of leaks.

In remotely located condenser (optional): 

• Point transmitter: located next to the condenser inlet and outlet collectors. Especially in condensers with a history of leaks.

In the sales area of supermarkets and hypermarkets (optional): 

• Perimeter transmitters: One transmitter for each aisle with refrigerated cabinets. Preferably installed towards the end of the aisle in the preferred direction of public circulation, if any. If it is clearly bidirectional, it will be installed in the centre of the corridor.
• Perimeter transmitters: One transmitter every 200 m2 in false ceilings.
• Point transmitters: One transmitter located next to the expansion valve of each refrigerated cabinet, especially if the cabinet has a history of leaks.

 Leak Detection System Monitoring, Detection, and Associated Procedures

• Throughout the manual, the different perspectives related to the detection of refrigerant gas leaks have been dissected in detail: from causes, consequences, potential leak elements, related regulations and detection techniques.
• More specifically, in sections 10, 11 and 12, the techniques that can allow the detection of refrigerant gas leaks have been explained, with explanations on the necessary technology and recommendations on the location and number of transmitters.
• This section aims to provide an overview of the detection system, and how to interact with it to achieve the primary objective of the manual, which is to reduce leak rates to values below 5% per year in any refrigeration installation.

Detection System: Components
The detection system consists of the following basic components:

• A network of NDIR technology transmitters that are networked and centralized.
• A monitoring and recording console.
• The transmitter network extends throughout the refrigeration installation, as described in Sections 11 and 12. The likelihood of detecting leaks is proportional to the number of control points, i.e., the installed transmitters.
  The transmitters communicate via a network and are centralized in a monitoring and recording center. The monitoring center (PC-based) provides an over-view of the status of all transmitters: ppm readings (concentration) and alarm status. Each transmitter is identified by its location and can be related to its associated volumetry.
• With this data, the user or system maintainer can clearly identify which alarm levels are considered necessary for each transmitter. For example, a transmitter located in a 3000 liter linear can have a prealarm level of 100 ppm and an alarm level of 500 ppm (in a small volumetry, leaks due to loss of tightness are more easily concentrated); while a transmitter located in a 300 m3 compressor room may have a pre-alarm level of 10 ppm and an alarm level of 100 ppm, since its “tightness” is much lower and therefore high concentration levels are practically unattainable with small leaks.
• Alternatively, the pre-alarm and alarm values can generally be set at 500 and 1000 ppm (safety of people) and possible leaks (values between 10 and 500 ppm) can be analysed in each transmitter with daily monitoring, as described in the following section.
  In general, and whenever working with HFC refrigerants, the expected level of the transmitter should be equal to zero. Any reading above zero should alert and be considered as a probability of refrigerant leakage around the transmitter. This is why, as discussed in section 14.3, it is of great importance to ensure that the transmitter is zeroed in its final position and temperature during start-up, so that it can be ensured that values greater than zero are significant and indicative of a high probability of a leak in the vicinity of the transmitter.
  For applications with CO2, the analysis must be statistical and therefore the recording component of the monitoring center is important. From the comparison with the usual levels for a specific transmitter, an abnormality in the CO2 levels and, consequently, the probability of a leak in the area can be noted.

Procedures: Leak Detection, Localization, and Repair

• The success of the system will ultimately depend on the capacity and speed of repairing the leak, which in practice will consist of reducing to a few grams of refrigerant loss those leaks that, if not detected, would leak several kilograms or tens of kilograms throughout the year.
  Although the operation of the detection system is essential, the interaction with the detection system, the final location and the repair are no less important. We define the necessary procedures in the following points:
• Monitoring: The person or persons responsible for the detection system (owner, user or maintainer) must review the detection system monitoring console once every 24h or 48h to verify that all transmitters indicate zero ppm (in the case of HFC, HFO, NH3, etc.) or statistically normal values in the case of CO2. In this process, not only the current values will be read, but also 2 values corresponding to the last 24 or 48 hours, depending on the last verification of the system status. This process can last a few minutes for systems with up to 30 or 40 control points. If the person in charge has set alarm values adjusted to the volume of each transmitter (as described in the previous section), this monitoring will not be so necessary, although it is always recommended, since the alarm system will act according to the set values.
• Premature detection/discrimination: If a transmitter indicates concentrations above zero ppm (or statistically normal values for CO2), although less than a few tens of ppm (typically up to 100 ppm), the maintainer must perform an offset test. This test will simply consist of applying nitrogen to the transmitter and observing that its value drops to zero ppm. In this case, the reading will effectively confirm a leak of refrigerant gas. Otherwise, the equipment has acquired an offset and it will be necessary to perform a zeroing with the same nitrogen (a 30-second process). Rarely will an piece of equipment require more than one zeroing throughout its life as long as the installation conditions and temperature of the equipment do not change.
• Communication: Once the detection has been confirmed, it is necessary for the person in charge to immediately communicate to the system maintainer the observed situation: transmitter(s) involved and the moment of the start of the leak.
• Leak location: The system maintainer should use any of the techniques described in section 7.2.1 in the most likely area near the transmitter or transmitters that have detected a leak. For example, in a cold room, the expansion valve and evaporator (all welds) should be carefully inspected for the leak. In a compressor room, if there is more than one transmitter, the transmitter readings (recorded on the monitoring console) should be analyzed and the leak should be searched for near the transmitter that first indicated the change in concentration or, if all transmitters indicated a change at the same time, near the transmitter that indicates the highest concentration. The elements most likely to leak are listed in section 6 and should therefore be the first elements inspected to reduce detection time as much as possible.
• Leak repair: Once the leak has been located, its repair is the most basic step in the entire procedure, since it will consist of modifying the tightening of a nut/plug, performing a weld and/or deciding whether the component in question should be replaced, among other actions that are well known to professionals in the sector.

Final considerations on the detection system
As the reader will notice, the success of the system lies in the fact that the frequent procedures associated with the detection system are relatively fast (in the order of minutes) when there are no leaks. On the other hand, when the leaks are detected and their location approximately confirmed, there are two aspects to highlight:

• Because the leak is approximately localized, the efficiency and exhaustiveness in the final location of the leak can be much greater than in the procedures that have been usual up to now, when the entire installation is in question and an exhaustive inspection of the entire system takes an excessive amount of time.
• Because the leak is approximately localized, the efficiency and exhaustiveness in the final location of the leak can be much greater than in the procedures that have been usual up to now, when the entire installation is in question and an exhaustive inspection of the entire system takes an excessive amount of time.
• However, it is essential to associate the procedures and the zeal in their application with the use of the detection system, since without these procedures, the system will be unable to provide benefits to the user or maintainer of the system.

Maintenance and Inspection of Detectors/Transmitters

• The degree of success of a continuous direct detection system, as explained, depends on the quantity, quality, location and condition of the detectors/transmitters. Obviously, a detection system that uses detectors/transmitters in a nonperational or malfunctioning state will not be able to generate quality information for leak detection.
• This section is responsible for defining the procedures and practices necessary to maintain the state of the detectors/transmitters in optimal conditions. It is worth reiterating, once again, that at this point there are normative and regulatory conditions (such as minimum criteria) and, additionally, other aspects and practices are described that can help maintain the equipment at its maximum performance.

Definitions

Bump test	Minimum functional test of the detector/transmitter. This consists of demonstrating that the detector/transmitter reacts to the presence of the target gas and is capable of activating relays, lights, alarms, etc. if that is its purpose
Verification	For transmitters (meters) only. It consists of checking how close the value indicated by the transmitter is to the value of a calibrated gas standard (technically also defined as calibration (*))
Calibration (*)	For transmitters (meters) only Process in which the transmitter output is corrected to the calibrated gas value. It has two necessary steps: zeroing and full scale adjustment
	Reset to zero	The transmitter output ‘0’ is reset under conditions where the target gas is at0 concentration. Clean air (**) or N2 (100% nitrogen) are useful to force such a scenario
	Full scale setting	The ‘full scale’ utput of the transmitter is reset under conditions where the target gas (calibrated gas) is at a concentration equal to full scale

Table 14: Basic definitions on maintenance of refrigerant gas detectors/transmitters

• In scientific language, calibration consists of measuring the accuracy of a meter against a calibrated and known standard (with a known error tolerance). For the sake of clarity in the refrigeration sector, this step is defined here as verification, thus redefining the calibration process as the process in which the output of the transmitter is effectively adjusted to the value of the calibrated and known standard gas.
• Clean air (not contaminated by the target gas) is not useful for resetting the zero value when the transmitter measures CO2, since it is normally present in the air. In this case, it is essential to use N2 (100% nitrogen) to reset the zero.

Regulatory aspects on the maintenance of detectors and transmitters 
European regulation 517/2014 (F-Gas) indicates that leak detection systems in refrigeration systems must be checked at least once every 12 months. The RSIF (Technical Instruction IF-17) indicates that leak detection systems should be checked at least every twelve months to ensure their proper operation. Finally, the EN 378 standard also indicates that detectors should be checked regularly, at least once a year, to ensure that they are working correctly. As the reader will notice, the three sources agree on a minimum check frequency of 12 months. At the same time, it is noted that the regulations require checks or controls, without further details. The common practice in the sector is to perform a simple “bump-test” to comply with this requirement.

It is interesting to note that the “bumptest”, which as defined in the previous section consists of exposing the detector/transmitter to the target gas, is clearly improvable. While exposure to the target gas validates basic operation, it does not provide any measure of the concentration at which the detector/transmitter is activated (which may be excessive) and it also does not shed any light on aspects such as sensitivity, precision and accuracy; characteristics relevant in early leak detection, as discussed in the previous section. For all these reasons, additional practices are recommended in the following section.

Advanced maintenance of detectors and transmitters
To obtain maximum performance from detectors and transmitters, it is recommended to perform advanced maintenance adapted to the performance of the leak detection system (when using NDIR transmitters) and even to systems for the safety of people only (when using SC detectors). Firstly, for SC detectors it is advisable to perform the “bump test” with gases calibrated at the maximum permitted concentration or lower. This practice avoids, on the one hand, venting refrigerants into the atmosphere and, on the other, guarantees that the detector reacts within the range required by the regulations. Regarding NDIR transmitters, the maximum performance of the equipment will be achieved when sensitivity, precision and accuracy are at their factory levels or very close. This will be achieved by the following steps:

• Immediately after installation: When the equipment has reached its normal working temperature (between 15 and 30 minutes after start-up) the zero must be reset, preferably with N2 (100% nitrogen), which is a com-mon gas for refrigeration installers and maintainers. This point will ensure the correct sensitivity of the equipment in the final installation conditions.
• Once a year (in accordance with regulations):
  • Check the precision and accuracy of the equipment with calibrated gas (at a concentration equal to the full scale). This test allows you to check the functionality of alarms, etc. (as a “bump test”) and, additionally, to check whether the precision and accuracy of the equipment are adequate.
  • If the result is not the desired one, the verification operation itself (provided that a zero reset has been performed previously) allows calibration (adjustment of the full scale) so that full accuracy is recovered.

Regarding the calibration or recalibration of the equipment, it is interesting to note that the great stability and linearity of the NDIR sensors for refrigerant gases do not generally make recalibration processes necessary throughout the life of the equipment (up to 7 years), so the factory full scale is valid during that entire time. However, it is highly recommended to reset the zero of the equipment at least once, just after installation, when the final geometric and thermal conditions have been set.

Finally, it should be noted that advanced maintenance operations for both detectors and transmitters ideally require “injection” systems (of calibrated gases or N2) into the detector/transmitter in order to minimize the amount of gas used during the process, minimize the time needed for the process and maximize the quality of the gas introduced into the sensor. Figure 29 shows a component designed for advanced maintenance tasks on NDIR transmitters with which nitrogen or calibrated gas is introduced into the transmitter. This tool is also valid for bumptest type tests on SC detectors.

Illustrative Examples of Leaks Detected in Commercial Installations

To complete the manual, some illustrative examples of refrigerant gas leaks detected, located and resolved using the AKOGAS early detection system are presented. These examples allow us to observe several of the concepts analysed and explained throughout the manual and, therefore, are a good example of the reality of commercial and industrial refrigeration systems, on the one hand; and very significant for highlighting the fundamental concepts of early detection of refrigerant leaks, on the other.

Supermarket (Valencia)
The first example of leaks detected by the AKOGAS system involves a supermarket in Valencia. This location experienced frequent refrigerant refills throughout the year. The first example of leaks located by the AKOGAS system is that of a supermarket in Valencia, a site that had many refrigerant gas refills throughout the year. Table 15 presents a summary of the most significant data of the refrigeration system in question on the one hand and of the AKOGAS system installed on the other hand. Of the 6 leaks located in the first 30 days, 2 are present (located in the first 2)

Refrigerant	R-448A
Nominal load	272 kg
Annual leakage	45% of nominal load
No of transmitters	21
Areas analysed by the system	Compressor rack, sales room, cold storage rooms
Commissioning	July 14th, 2018
Leaks detected	6 within 30 days

Leak 1: oven room (25 m³)
In the prebaked products room, of 25m³, an average reading of 123 ppm of refrigerant is observed, without dropping to 0 ppm at any time. The refrigerant gas concentration is shown in Fig. 30 for the period 18 July – 31 July. The behavior of the concentration shows the variations generated by the controlled entry of refrigerant (via solenoid control), the effects of defrosts and the transit in the room.

Based on the correlations generated by the AKO research department, this leak has an annual leak potential (IPF: Leak Potential Index) of approximately 65 kg of refrigerant per year (7.3 g/h).

Leak 2: dairy line (10 linear meters)
Another of the transmitters installed in the AKOGAS system in the Valencia supermarket is responsible for analyzing the evaporators of a 10 m long dairy line in the sales room (See figure 31). For the dairy line, the average reading is 117 ppm, as can be seen in Figure 32.
From the shape of the concentration signal the perforation of the circuit occurs in the evaporator since presumably the frost itself, which is generated on the evaporator, partially prevents the leakage of refrigerant gas by partially blocking the pore itself. Indeed, if the concentration signal is observed, a periodic valley/jump is noted (every 6 hours) that coincides with the defrosts. At the time of the defrost, the circulation of refrigerant is shut off and the concentration plummets to 110 ppm. At the moment that the defrost ends (15-20 minutes later) the entry of refrigerant occurs in a frost- free evaporator and for a longer period (since the linear must recover the temperature gained during the defrost) and it is at that moment that the refrigerant begins to leak through the completely open pore, which explains the peak concentration observed immediately after (125-130 ppm).

From that moment on, the frost begins to deposit on the pore, which limits the quantity of gas leaked by the evaporator and therefore the concentration of refrigerant gas accumulated in the evaporator tank, which stabilizes around 117 ppm. Based on the correlations generated by AKO’s research department, this leak has an annual leak potential (IPF: Leak Potential Index) of approximately 25 kg of refrigerant per year (2.8 g/h). Note that for a concentration similar to that observed in the cold room of the same establishment (120 ppm) the estimate of leaked refrigerant is significantly lower, because the volume of the leak is also significantly lower.

Logistics Center (Tarragona)
In industrial refrigeration applications, the large refrigerant load, generally exceeding 1500 kg, underlines the importance of refrigerant gas leak detection, since moderate and even small leaks can involve large quantities of refrigerant throughout the year. Table 16 presents the summary of the refrigeration system and the AKOGAS system designed to monitor and detect the areas of greatest risk of leakage, according to AKO’s property perception and knowledge of refrigerant diffusion in large volumes.
The concentration reading for a transmitter located near one of the two evaporators in a cold room (-22 ºC) is presented in Figure 33, for the period 3 August – 15 August:

Refrigerant	R-448A
Nominal load	1950 kg
Annual leakage	95% of nominal load
No of transmitters	23
Areas analysed by the system	Compressor racks, cold rooms, unloading docks, valve pianos (over cold rooms), evaporative condensers
Commissioning	August 1st, 2018
Leaks detected	4 within 30 days

As can be seen, since the system was started up (1 August) significant concentration peaks (approximately 350 ppm) have been observed every 4 hours, coinciding with defrosts. Taking into account the large volume of the system and despite the fact that the transmitter is located close to the evaporator, therefore taking non-stabilized and non-homogenized information on the concentration in the cold room, the high concentration indicates a large amount of gas expelled and, at the same time, that the leak is in the hot gas operation itself, which is the defrost method used in this installation.

After 5 days, the hot gas valve is changed and the concentration level drops noticeably, to concentrations close to 60 ppm. This indicates that the main problem is resolved, although the evaporator is still presumably perforated at some point. AKO estimates that the first leak, related to the hot gas valve, could represent a leak of more than 500 kg per year, while the perforation of the evaporator could represent a leak of approximately 100 kg/year.

Supermarket (Madrid)
A final installation that shows the capabilities of highly sensitive and precise detection systems is that of a supermarket in Madrid. The characteristics of the system, as well as the AKOGAS system installed, are described in Table 17.
This refrigeration installation has the added feature that, at the time of the AKOGAS system start-up, it had just been completely reviewed and adjusted, due to a “retrofit” carried out 1 month earlier (April 2018), going from a high GWP refrigerant (R404A) to one with a lower environmental impact and, consequently, with lower rates (R450A). This aspect is especially significant, since it shows how an installation adjusted and reviewed by highly qualified maintenance teams can still hide refrigerant gas leaks, if the appropriate tools for their detection are not available.

Refrigerant	R-450A
Nominal load	175 kg
Annual leakage	70% of nominal load
No of transmitters	13
Areas analysed by the system	Compressor rack, cold rooms, sales room, condensers
Commissioning	May 1st, 2018
Leaks detected	10 within 30 days

Table 17: Supermarket (Madrid) refrigeration system and AKOGAS system sheet

Among the leaks detected in the first 30 days, one stands out in an evaporator in the fruit and vegetable cold room. This leak was detected immediately (1 day after the system was started up) and highlights the need for highly sensitive transmitters to achieve early detection of refrigerant gas. The concentration signal read by the transmitter installed inside the cold room is shown in Figure 34 (for May 13) and shows an average concentraion level (for that day) of only 53 ppm. The correlation of the concentration with the defrost and cycling (control) processes of the solenoid valve clearly indicates the perforation of the evaporator, with the concentration rising when the refrigerant enters and falling (due to diffusion of the refrigerant inside the cold room) when the refrigerant is closed.
Based on the correlations generated by AKO’s research department, this leak has an annual leakage potential (IPF: Leak Potential Index) of approximately 55 kg of refrigerant per year (6.3 g/h). Based on this estimate, the owner decided to close the service and change the evaporator. This process, which lasted approximately 2 weeks, was recorded in the AKOGAS system, which shows how, once the evaporator was changed, the refrigerant concentration levels inside the cold room dropped to 0, indicating that the leak was effectively resolved. This evolution is shown in Figure 35.

In Figure 35, a common phenomenon in this phenomenology is also observed (evaporator leak), since despite closing the service (May 15) the concentration does not fall to 0 ppm immediately, with the evaporator still open and in contact with the low pressure collector of the compressor rack, which sends refrigerant to it depending on the pressure gradients and pressure loss in the evaporator. These quantities of refrigerant gas are noticeably lower than the original ones, although not zero, which is achieved by eliminating the perforation of the circuit with a new evaporator (June 4). It is noteworthy how in a fruit and vegetable cold room, which generally generates various gases related to the ripening and respiration of fruit (ethylene, CO2, etc.) the absence of refrigerant is read as 0 ppm by the transmitter, thus showing the high selectivity of the NDIR transmitter to the refrigerant gas, without receiving interference from other gases.

References

1. Zero Fuite. Limitation of refrigerant fluid emissions. Denis Clodic. PYC Edition Books 1997.
2. Füite detection. Study on the methods of detection of the leakage of refrigeration and air conditioning installations. ADEME. February 2017.
3. Tightness of Commercial Refrigeration Systems. Ralf Birndt, Rolf Riedel, Dr. Jürgen Schenk. ILK Dresden. September 2001.
4. REAL Zero – Reducing refrigerant emissions & leakage feedback from the IOR Project. David Cowan, Jane Gartshore, Issa Chaer, Christina Francis and Graeme Maidment. The Institute of Refrigeration. April 2010.
5. Refrigerant Containment Study. Eric Devin et al. Conducted for ADEME by Cemafroid and IRSTEA. September 2015.
6. COMMISSION REPORT of 4.8.2017 on the evaluation of the requirement for 2022 to avoid high global warming potential hydrofluorocarbons in certain commercial refrigeration systems
7. ANNEXES to the REPORT FROM THE COMMISSION on the evaluation of the requirement for 2022 to avoid high global warming potential hydrofluorocarbons in certain commercial refrigeration systems
8. Refrigerant Loss, System Efficiency and Reliability– A Global Perspective; GEA Refrigeration UK Ltd for Institute Of Refrigeration (IOR) ). ©Institute of Refrigeration Annual Conference 2013

 Nomenclature

Refrigerant Gas	Compressible fluid used in heat transmission that, in a refrigeration system, absorbs heat at low temperatures and pressures, releasing it at higher tempRatures and pressures. In a gaseous state at atmospheric pressure
Leak	Discrete quantity of gas (refrigerant) that escapes from the refrigeration circuit and is diluted in the environment at atmospheric pressure
Emission	Discrete quantity of refrigerant gas that is emitted into the atmosphere, due to a leak in the refrigeration circuit or other causes (recharging processes, destruction of refrigeration equipment, etc.)
HFC	Refrigerant based on molecules that combine Hydrogen, Fluorine and Carbon (Hydro Fluorocarbon Refrigerant)
HCFC	Refrigerant based on molecules that combine Hydrogen, Chlorine, Fluorine and Carbon (Hydro Chloro Fluorocarbon Refrigerant)
HFO	Refrigerant based on molecules that combine Hydrogen, Fluorine and Carbon (Hydro Fluoro Olefin Refrigerant), the bonds between the carbon atoms being double, unsaturated, and not very stable in the atmosphere
CFC	Refrigerant based on molecules that combine Chlorine, Fluorine and Carbon. (Chlorofluorocarbon refrigerant)
CO2	Carbon Dioxide (natural refrigerant)
NH3	Ammonia (natural refrigerant)
PCA	Atmospheric Warming Potential of a refrigerant gas measured as kilogram CO2 equivalents in the atmosphere in greenhouse terms.
GWP	Global Warming Potential Equivalent to GWP in English
TEWI	Total Equivalent Warming Impact: Indicator that measures the impact of a refrigeration installation on atmospheric warming. It contains a direct part (due to emissions related to the refrigerant of the installation) and an indirect part (related to the CO2 produced to generate the energy consumed by the refrigeration system)
A1	Safety group for low toxicity (A) non-flammable refrigerants (1)
A2	Safety group for low toxicity (A) slightly flammable refrigerants (2L)
A2L	Safety group for low toxicity (A) flammable refrigerants (2)
A3	Safety group for low toxicity (A) highly flammable refrigerants (2)
B1	High toxicity (B) non-flammable refrigerant group (1)
B2L	Safety group for high toxicity (B) slightly flammable refrigerants (2)
B2	Safety group for high toxicity (B) flammable refrigerants (2)
B3	Safety group for high toxicity (B) highly flammable refrigerants (3)
L1	High safety refrigerant group (A1)
L2	Medium safety refrigerant group (A2, A2L, B1, B2, B2L)
L3	Low safety refrigerant group (A3, B3)
RD 138/2011	Royal Decree 138 of February 4, 2011 approving the Safety Regulation for refrigeration installations and its complementary technical instructions in the Kingdom of Spain (RSIF)
517/2014	Latest version of the European F-Gas regulation 842/2006 Previous version of the European F-Gas regulation
842/2006	Previous version of the European F-Gas regulation
RSIF	Safety regulation for refrigeration installations and its complementary technical instructions. Mandatory in Spain
EN 378:2016	European standard for refrigeration systems and heat pumps. Safety and environmental requirements
Refrigerant detector	Electronic device that detects the presence of refrigerant in the environment. It does not indicate its concentration and usually detects from high concen- trations (>500 ppm)
Refrigerant transmitter	Electronic equipment that detects the presence of refrigerant gas and measures its concentration in ppm (parts per million)
SC	Gas detection and measurement technology based on the electrical conductivity of Semi-Conductive surfaces in the presence of gas. It is moderately sensitive and very unselective
NDIR	Gas detection and measurement technology based on the absorption of energy in the infrared spectrum by the gas. It is sensitive, selective, precise and accurate
EC	Gas detection and measurement technology based on an oxidation/reduction reaction that modifies the electric current between electrodes in the presen- ce of gas. It is very sensitive, precise and accurate although its life depends on exposure to the gas
N2/H2	Technical hydrogenated nitrogen. Useful for pressurizing refrigeration circuits to detect possible leaks

AKO ELECTROMECÁNICA , S.A. Avda. Roquetes, 30-38 08812 • Sant Pere de Ribes. Barcelona • Spain www.ako.com

We reserve the right to supply materials slightly different to those described in our data sheets. Updated information on our website.

FAQ

• Q: How often should the gas transmitters be calibrated?
  A: It is recommended to calibrate the gas transmitters annually or as per the manufacturer’s specifications to ensure accurate detection of refrigerant gas leaks.
• Q: Can the system be integrated with existing refrigeration equipment?
  A: Yes, the AKO Leak Detection and Management System can be integrated with various types of existing industrial and commercial refrigeration installations.

Documents / Resources

AKO Leak Detection and Management System [pdf] Instruction Manual 0000H024 Ed. 01 en, Leak Detection and Management System, Detection and Management System, Management System

References

• User Manual