Refrigerant Gas Detection Systems for Commercial Applications Using HFCs, HFOs, & A2L Refrigerants
Commercial refrigeration systems are vital components of various industries, relying heavily on a diverse array of gases and gas blends that include both HFC and HFO refrigerants. This reliance persists even in regions where there has been notable progress in the adoption of CO2 refrigeration systems. Across sectors such as supermarkets, food retail establishments, the food service sector, cold rooms, walk-in freezers, cold storage facilities, and food processing plants, these refrigerants play a crucial role in preserving perishable goods and maintaining optimal storage conditions.
Why are HFO and HFO refrigerant gas detectors needed?
The necessity for HFC and HFO detectors arises due to several factors. In response to the imperative to mitigate the impact of refrigerant leaks on climate change, there has been a growing adoption of gases aimed at lowering the global warming potential (GWP) of refrigerants. This has led to a rise in the utilization of A2L classified refrigerants, often termed as “mildly flammable,” the flammability of which adds another layer of risk than that posed by the A1 classified refrigerants formerly more prevalent in their use.
While most of these refrigerants exhibit low acute toxicity, leaking HFC and HFO gases can displace oxygen, leading to discomfort, danger, and the potential for fatalities.
Below are examples of what happens in a non-ventilated room of approximately 1750ft3/ / 50m3 with leakage of R134a.
R134a leakage (lbs / kg) | R134a concentration (ppm) | Oxygen level (%) | Effect on humans |
0 | 0 | ~21 | Normal, fresh air |
46 / 21 | 100,645 | ~19 | Reduced oxygen delivery to cells, adverse effect on ability to function |
139 / 63 | 301,395 | ~15 | Increased pulse rate, rapid breathing, impaired coordination, compromised thought processes |
185 / 84 | 402,581 | ~13 | Nausea, vomiting, risk of permanent heart damage |
255 / 116 | 553,547 | ~10 | Convulsions, inability to move, loss of consciousness, loss of life |
The above figures are based on even dispersion throughout the room. This, however, is a highly unlikely scenario because refrigerant gases have a much higher molecular weight than air and will sink to the lowest part of the room. It is therefore possible that 0.5m above the ground, a 21kg leak could actually have the same oxygen displacement effect as 84kg dispersed evenly in the room. This presents a clear and real danger to life and health.
In many countries, regulatory frameworks and industry standards mandate the monitoring of HFC and HFO gas leakage, exemplified by regulations such as F-Gas and EN378 in Europe, and ASHRAE 15 in the United States.
It’s also crucial to recognize that in refrigeration systems, the occurrence of refrigerant leakage not only compromises operational efficiency but also poses the risk of system failure over time.
Moreover, the repercussions extend beyond concerns over operational efficiency, as the leakage of refrigerants can lead to even more significant and acute economic impacts. The diminished efficiency and potential failure of refrigeration systems can result in substantial losses, particularly in terms of perishable or frozen goods where temperatures fall outside of the limits of food safety standards. This highlights that effective refrigerant monitoring and prevention of refrigerant leakage are imperative not only for operational integrity but also to mitigate economic losses associated with spoiled produce.
Guidelines for Implementing HFC & HFO Gas Detection
HFCs and HFOs, being denser than air, tend to settle rapidly towards lower areas within a room, such as stairwells or sumps. To optimize detection efficacy, gas detectors should be strategically positioned at low levels, approximately 8” / 20cm above the ground or the lowest part of the room.
It is common practice to install gas detectors in close proximity to the areas identified at the most likely potential leak sources, such as valves, flanges, joints, and pressure reducers. Additionally, detectors can be situated near areas with a high concentration of refrigerant, including compressors, storage tanks/cylinders, pipes, and conduits.
Accounting for airflow and ventilation—both natural and mechanical—is crucial. As leaked gas disperses gradually into the environment, it can be influenced by ventilation currents. Therefore, placing gas detectors within these airflow paths is recommended for enhanced detection efficacy.
NOTE: There is no general rule or standard for establishing the appropriate number of sensors and their location for each application. Therefore, the guidance given is intended as support for installers, and not as rules in their own right. All local, state, and national regulations should be adhered to.
HFC, HFO, and A2L Refrigerant Sensor Selection
HFC, HFO, and A2L refrigerant detection is most typically using semiconductor sensors or infrared sensors, though other technologies are emerging and becoming available for refrigerant detection, albeit often at a higher relative to what they can chieve. Semiconductor sensors, also known as metal oxide sensors, are a long-proven method used in refrigerant gas detection for HFC and HFO refrigerants and blends. They have a number of benefits. They are very cost effective, have a relatively long lifetime, and generally have fairly low maintenance costs.
Semiconductor sensors can be cross-sensitive to other reducing gases, and to significant shifts in temperature or humidity. Consideration should be given to this when selecting an installation location. As an example, locations close to where forklifts are either refuelled or recharged can be an issue – respectively, hydrocarbons fumes from fuel and the hydrogen off-gas from electric charging are both reducing gases which will react with a semiconductor sensor, giving the potential for false alarms. Such issues can, in most cases, be mitigated through thoughtful installation of a system done with the knowledge of how a particular refrigerant gas sensor works. This allows both the strengths and drawbacks of a sensor to be considered, so it can be placed in the most effective location for a specific site.
Infrared sensors are field proven as a highly stable technology for implementation in refrigerant gas detectors and are impervious to cross-interference from other gases typically found in commercial refrigeration applications. Temperature compensation effectively eliminates drift due to environmental factors.
Infrared sensors are available for detecting refrigerants leaks in a parts per million range (ppm). There are options for detecting very low levels under 10-15ppm, generally coming at a higher cost and with a form-factor that lends itself to centralised aspirated systems. For a more distributed system using refrigerant detectors where the gas diffuses into the sensor, more affordable options exist, detecting accurately from 150ppm – still significantly lower than the levels designated for safety-based refrigerant gas detection systems by standards such as ASHRAE 15 and EN 378. In both cases, the benefits of higher stability, longer life, and a lack of cross-interference are gained.
For A2L detection (and R290 / propane detection, though that isn’t the subject of this article), very small-format refrigerant detectors are available using extremely cost-effective infrared sensors. These detect in a higher range, reading in percentage Lower Flammability Limit (% LFL), which is the concentration at which the target refrigerant has the potential to propagate a flame and cause an explosion. These are only used for flammable refrigerant detection. This type of detector is ideally suited for integrated installation in appliances such as heat pumps, refrigerated display cases, portable chillers, and other self-contained refrigeration systems. Certification to standards such as IEC 60335-2-40 and UL 60335-2-89 is advantageous for refrigerant leak detectors of this type.
Gas Detectors Suitable for Refrigerant Detection
Masny gas detectors are available on the market. They are, however, not all suitable for every application. The environments in which refrigerant gas detectors are installed can have some challenges not present in other sectors.
A suitable HFC and HFO refrigerant leak detector should have the following characteristics:
- A fast response time: this is required by standards, but more critically is essential to the application of detecting a leak quickly rather than identifying gradual shifts in atmospheric conditions over time.
- Appropriate temperature range (e.g. -40°F – +122°F / -40°C – +50°C): refrigerant monitoring can be needed in temperatures as diverse as typical a machinery room, a supermarket store floor, a cold room, and a freezer. A refrigerant detector with a temperature range to cover all these use-cases is important in enabling a system using the same detectors to be installed in sites where these multiple requirements are present. This facilitates simpler processes for connectivity and integration to control systems, and a more efficient service program.
- Suitable IP rating for the installation environment (e.g. IP66, IP67): the nature of the application is that refrigerant leak detectors are in areas that get washed down, often with high-pressure jets. They need to be able to withstand this without suffering from water ingress.
- Outputs for system integration, control & safety alerts: refrigerant gas detection systems generally must be integrated with other safety system elements (such as audio-visual alarms, ventilation fans) and often with refrigeration control systems. The required integration should be identified early to allow for the right gas detectors to be selected, with the needed combination of relays, analogue outputs, and digital communication protocols such as Modbus.
- For any areas zoned as being potentially explosive, a detector with the appropriate ATEX certification for that zone should be selected.
The Right Tool for the Job
Refrigeration applications are wide ranging in their requirements. The array of refrigerant gas detectors available is just as diverse as the applications they serve. The first question anyone looking into refrigerant leak detection systems should ask themselves is, what do they need to achieve? The answer here should go a little deeper than the obvious response “to detect refrigerant leaks”, looking at why that is a requirement for them and what the mitigatory actions will be in the event of a refrigerant leak being detected.
Good results for HFC, HFO, and A2L refrigerant detection are achieved when thoughtful consideration of these drivers is combined with a knowledge of how and where to effectively install a gas detection system, the advantages and drawbacks of different sensor types, and the environmental and systems integration characteristics needed from a refrigerant leak detection system.