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Averting the risk of asphyxiation, acute toxicity

VRF/VRV systems have many advantages over traditional DX splits and water-based systems, but the risk of refrigerant leakage in the occupied spaces should be fully assessed and provisions made, writes Dr Jason Shilliday

| | Oct 11, 2018 | 10:51 am
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The first synthetic refrigerants, CFCs (with R-12 being one of them) were invented in the 1930s. They rode on the virtues of safety, in terms of being non-toxic and non-flammable gases, and on having the correct pressure-temperature relationship, which made them suitable to be used as refrigerants.

A lot has changed since that first batch of gases were produced. The Montreal Protocol, which came to be established in 1987, placed restrictions, then a ban, on the use of CFCs, owing to their high ozone-depleting potential (ODP). Their replacements, the HCFCs (with R-22 being one of them) were less damaging but still were restricted under the same international protocol and eventually phased out. The next batch of replacements, HFCs (R-410A, etc.) are currently being phased out due to their high global warming potential (GWP), as restricted by the Kyoto Protocol (2005). HFOs (R1234yf) and HFCs with lower GWP (R-32) are the latest advancements in the area of synthetic refrigerants and have mostly been accepted due to their low GWP; however, issues have been raised due to their mildly flammable nature.

Different countries have applied different legislative measures to ensure the safe use of refrigerants in HVACR systems, and some – case-in-point the European F-Gas regulations – have gone a step further and regulated their use.

Leaks of synthetic refrigerants from refrigeration and air conditioning systems are harmful to the environment due to their GWP, but they are also harmful to people. There are risks due to some of the gases being toxic and flammable, but there is also a high risk of asphyxiation in a confined space due to a leak. There would be significantly less health and safety risks in buildings, less environmental damage, and also more economical advantages if the refrigerant leakages from these systems were controlled more effectively. Early refrigerant leak detection is one way in which to prevent heavy leakages from occurring. It would alert operators to any refrigerant leak, giving them ample time to carry out repairs. That way, the quantity of refrigerant lost to the atmosphere would be limited.

In this article, I wish to explain some of the international standards related to refrigerant safety and use, which hopefully will help at the time of designing buildings or cooling facilities to international standards. The advancement in the operational efficiency of direct expansion and VRF/VRV systems has brought refrigerants in large volumes much closer to the public. VRF/VRV systems have many advantages over traditional DX splits and water-based systems, but the risk of refrigerant leakage in the occupied spaces should be fully assessed and provisions made in the design to reduce the risks of acute toxicity, asphyxiation and flammability-related hazards.

Enter EN378
EN378 is a European standard that was updated in 2016 to include further design information to be considered for the planning stages, when using refrigerants with a low-flammability classification (A2L). The standard was also updated to include a design methodology on how to calculate the maximum refrigerant charge that should be applied to a refrigeration or air conditioning system. If an indoor unit or pipework passes through an occupied space, the whole gas charge could potentially escape into this space. The EN378 standard sets RCL (refrigerant concentration limits) to reduce the risks of acute toxicity, asphyxiation and flammability-related hazards. The following terms are required:
QLMV: Quantity Limit with Minimum Ventilation in kg/m3
QLAV: Quantity Limit with Additional Ventilation in kg/m3
RCL: Refrigeration Concentration Limit in kg/m3

Table 1

Table 1, shows some of the common refrigerants listed in the standard, along with their allowable refrigerant charge. The total refrigerant charge divided by the room volume should not exceed these values. If the charge limit is exceeded, appropriate measures, such as ventilation (natural or mechanical), safety shut-off valves, safety alarms or gas-detection devices should be designed into the system or building.
Further details on when each appropriate measure should be applied is given in the standard.

To elaborate by way of an example, let’s consider a VRF/VRV system charged with R-410a (an A1 refrigerant). The system is deployed in a hotel with bedroom sizes of 6m x 3m x 2.4m. The total room volume is 43.2 m3. For a hotel room above ground with a VRF system, the QLMV/QLAV values in Table 1 apply. If the total refrigerant charge exceeds these limits, then a leak-detection system should be used in the hotel room. The maximum VRF/VRV system charge equals 43.2 x 0.42, which equals 18.14 kg.
To comply with the standard, the VRF/VRV system should have a charge less than this, or a refrigerant leak-detection system with safety alarms should be installed.
At this juncture, I must highlight the much lower RCL/QLMV/QLAV values for R-32 and HFO R-1234ze. In other words, split or future VRF systems using these refrigerants would result in a much lower maximum charge limit.

ASHRAE 15
Typically, purpose-built machine rooms for compressor systems or water-cooled chillers contain the largest volumes of refrigerant, either in the liquid receivers, condensers or evaporators. For example, a large centrifugal water chiller used for District Cooling could contain up to 1500 kg of refrigerant gas. Refrigerants are generally denser than air, except ammonia, so if a leak were to occur the gas would concentrate on the floor rather than move upwards. Synthetic refrigerants have no smell, so the user would only know that there has been a leak if the chiller starts to lose its performance. As the refrigerant displaces the air, anyone working at the chiller would be at risk of asphyxiation. To lower this risk, ASHRAE 15, the EPA and many local building codes state the following: Each machinery room should contain a detector located at a point, where a refrigerant leak would concentrate. The detector should also trigger an audible and visual alarm both inside and outside the mechanical room and activate mechanical ventilation by way of remedying the situation and ensuring the safety of personnel.

Dr Jason Shilliday is Business Development Manager (HVAC), MSA Middle East. He can be contacted at
Jason.Shilliday@msasafety.com.


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