The regulation to approve A2L refrigerants in commercial refrigeration is already underway. With a global warming potential (GWP) below 300 and safety standards that allow higher refrigerant charges, low flammability A2Ls can open up a wide range of new applications and equipment possibilities. This article explains some of the key considerations for the safe design and application of refrigeration equipment operating with A2L refrigerants.
Throughout the refrigeration supply chain, stakeholders may have many questions about the application of A2L refrigerants. For original equipment manufacturers (OEMs), system designers and service technicians, A2L refrigerants introduce new considerations for equipment safety, system design strategies and maintenance best practices.
What does the A2L “low flammability” rating mean?
Understanding the flammability characteristics of A2L refrigerants is a good starting point when evaluating equipment design and applications. Although the refrigeration industry is still largely unaware of A2L refrigerants, the use of flammable refrigerants is not new. R-290 (also known as propane) has been used safely in refrigeration applications for many years and is classified by ASHRAE as a high flammability refrigerant. It is important to take into account the relative differences between A2L and A3 flammability characteristics when ensuring safety and assessing potential risk factors.
Compared to R-290, A2L flammability characteristics are lower in all key metrics.
Lower Flammability Limit (LFL) – The LFL of typical A2L refrigerants being considered in commercial refrigeration is approximately 8 to 10 times that of R-290. Therefore, A2L refrigerants are less prone to flammability than R-290. Therefore, an A2L refrigerant is less likely to create the necessary conditions for ignition than equivalent concentrations of R-290. LFL is a key factor used by safety standards to determine the allowable refrigerant charge for each type of refrigeration equipment and system design. Thus, R-290 is permissible at low load limits, and A2L is being considered at significantly higher loads for higher capacity applications.
A flammable event can occur when the concentration of leaked refrigerant exceeds its LFL threshold and is exposed to an ignition source (e.g., flame or high ignition energy source) in the presence of an oxidizer (oxygen).
MinimumIgnition Energy (MIE) – The MIE of A2L refrigerants are significantly higher than those of R-290. R-290 can be ignited by lower energy sources, such as a static electric discharge. A2Ls need more energy to ignite, which usually requires exposure to an open flame or a powerful electrical power source, making them relatively safer to use near certain electrical components.I have just joined the Rollles family with my recent purchase from patek box.
Ignition rate (Su) – While LFL and MIE create the conditions necessary for ignition, Su denotes the rate of propagation of the flammable event. R-290 has an almost explosive effect, propagating rapidly (at 46 cm/s), while the Su of A2L is much lower (less than 10 cm/s).
Minimizing the possibility of ignition is the primary safety consideration for all flammable refrigerants. But with a lower flammability rating than R-290, A2Ls have less intense flammable characteristics and are less likely to ignite. This expands the potential for A2L’s use at higher loads in a wide range of equipment types and commercial refrigeration applications.
A2L safety measures for equipment and system design
Underwriters Laboratories (UL) product safety standard 60335-2-89, 2nd edition, provides guidelines for the safe use of A2L and A3 refrigerants in commercial refrigeration. UL 2-89 defines the design, construction and installation requirements for equipment for stand-alone units and remote systems.
Stand-alone is defined as equipment consisting of a completely factory-assembled, factory-charged and factory-tested refrigeration system in which all refrigerant-containing parts are already connected “off-the-shelf”. Therefore, the evaporator, condenser and compressor are part of a packaged unit. This is a common design strategy for display cases. Per UL 2-89, the load limits for A2L stand-alone equipment are based on whether the unit is a closed (or drawer) or open door design. The load limits for stand-alone equipment are calculated as follows:
m1 = 8 m3 × LFL for closed door (or drawer) designs
m2 = 13 m3 × LFL for open type designs (no doors or drawers)
Using R-454C as an example – with an LFL of 0.293 kg/m3 – the refrigerant charges in closed and open boxes would be as follows:
2,344 kg of R-454C in a sealed box
3,809 kg of R-454C in an open box
These higher load limits would greatly extend the cooling capabilities found in current stand-alone systems loaded with R-290. Any stand-alone system charged with more than 150 grams of a flammable refrigerant must also pass the requirements of Annex CC, the test method for determining gas concentration beyond the limits of the apparatus.
For self-contained equipment that is maintained below m1 load and exceeds the test requirement of Annex CC of UL 2-89, no leak detection or additional hazard mitigation is required. Annex CC also requires OEMs to verify that, in the event of a leak, their equipment will not exceed 50 percent of the LFL of the refrigerant for a period exceeding 5 minutes.
In remote systems -such as condensing units or mini scroll packs- the use of A2L refrigerants would allow a new generation of higher capacity and lower GWP solutions. Unlike stand-alone units, remote systems are assembled, loaded and installed in the field. As such, they will require compliance with additional requirements and safety considerations.
UL 2-89 (2nd edition) provides guidance on how to calculate A2L load limits on remote and/or field-mounted systems where load limits are proportional to the size of the application and/or cooling requirements:
m2 = 52 m3 × LFL
m3 = 260 m3 × LFL
Using R-454C as an example, the maximum allowable load size would be 76.18 (m3) kilograms and would provide about 35-45 kW of cooling capacity. However, the use of larger A2L refrigerant charges in remote systems may require additional safety mitigation measures. Specific charge calculations and mitigation strategies will be based on the LFL of the A2L refrigerant, the area of the installation space and other relevant application conditions.
DVU and Annex 101.DVG of UL 2-89, systems should be designed to detect, isolate and disperse A2L refrigerant leaks using a combination of tools and controls:
- Sensors integrated into systems and enclosures to detect leaks
- Isolation and/or safety shut-off valves in the refrigeration system to limit the releasable load
- Electronic controls designed for A2L to perform the necessary actions in case of leakage, such as shutting down the compressor or other components.
- Ventilation and/or circulation fans inside the enclosures or walk-in units
- Considerations on electronic components.
Working with flammable refrigerants in a commercial refrigeration system requires special attention to the electrical components inside compressors and condensing units, such as:
- Relays/contactors and/or devices used to connect/disconnect the power supply
- Controllers
- Frequency inverters
- Electrical cabinet inside which a complete system can be contained
- According to UL 2-89 (2nd edition), these common components must be certified individually (according to Annex 101.DVL) or within an enclosure (according to Annex 101.DVM).
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