ASHRAE Journal - October 2010 - 35

on prototype vending machines using carbon dioxide,2 which should provide a path for eventual SNAP approval. Safety standards requiring high mechanical safety factors represent another barrier, because trans-critical systems using CO2 operate at higher pressures than other refrigerants. For example, Underwriters Laboratories (UL) Standard 984 requires pressure safety factors as high as five times the design pressure, which may make designs expensive or infeasible because it necessitates much thicker walls for components. Changes to UL 471 and ASHRAE Standard 15-2007 have begun to address this issue by lowering the safety factor required for carbon dioxide used in secondary loops.

based on its relatively lower flammability compared to other Class 2 refrigerants. Ammonia is used primarily in industrial plants with stringent safety measures. Ammonia has achieved EPA SNAP approval in many refrigeration and stationary air conditioning applications, but several restrictions apply. In Standard 15-2007, ammonia is subject to additional specific safety requirements, while exempted from others. National standards often prescribe specific requirements for ammonia systems. Generally, these additional requirements do not impose insurmountable barriers to the use of ammonia systems; however, they can create a large burden on manufacturers and facilities. For users of large amounts of ammonia, the additional oversight required to satisfy EPA and Occupational Safety and Health AdEurope ministration (OSHA) requirements can create a significant burden. In Europe, equipment using carbon dioxide may fall within Most requirements are aimed at mitigating major catastrophes the scope of the Pressure Equipment in the case of major leaks. Satisfying Safety Group Directive (PED). The PED categorizthese regulations requires special safety es equipment based on pressure and Higher Flammability equipment and procedures. Keeping A3 B3 volume. Due to the high pressures, ammonia on premises also requires A2 B2 carbon dioxide systems are subject Lower Flammability developing a risk management proB2L* A2L* to additional reporting and safety gram and a project safety management A1 B1 assessments. While this is not an in- No Flame Propogation program. surmountable hurdle, it has deterred Lower Toxicity Higher Toxicity some component manufacturers from * A2L and B2L are lower flammability refrigerants with a maximum burning Europe investing in these products. There velocity of ≤10 cm/s. Ammonia is considered a toxic does not appear to be any other major Table 1: ASHRAE Standard 34-2007 Addendum ak, substance in the EU. For equipment EU-wide barriers to implementing refrigerant safety group classifications. using flammable and/or toxic refrigCO2 as a refrigerant. erants, the PED limits the pressure and volume levels more than for non-flammable refrigerants. Japan IEC 60335-2-40, which applies to much of the EU, places A regulatory gap may exist for safety standards pertaining charge limits on air-conditioning equipment containing flamto refrigerants in transportation-related applications. The High mable refrigerants such as ammonia. These restrictions depend Pressure Gas Safety Act (HPGSA) does not cover mobile ap- on the lower flammability limit of the refrigerant, the size of the plications. This is particularly relevant to carbon dioxide, due room in which the equipment is installed, and the ventilation to its high operating pressure. provided. These restrictions may not be problematic for small, self-contained products, but can present a barrier for larger Ammonia residential or commercial equipment. United States European standard EN 378 contains requirements for maAmmonia is a flammable and toxic refrigerant. ASHRAE chine rooms using ammonia, which include installation of a 34-2007 classifies ammonia as class B2, whereas the recent catchment system and emergency washing facilities. Other ISO 817 draft classifies ammonia as flammability subclass 2L, requirements state that ammonia must not come into contact
ASHRAE 34 Designation Carbon Dioxide Ammonia Hydrocarbons A2L Fluids
1 By

ASHRAE 34 Safety Global Warming Group Classification Potential (100 Year) A1 B2 A3 A2 (Future A2L) 11 02 <53 4,4 6,5 6756

Current Applications MVAC, Small Stand-Alone Refrigeration, Supermarket Systems Large Industrial Systems, Supermarket Systems, Chillers, Indirect Air Conditioning Small Commercial Refrigeration, Small Residential and Commercial Air Conditioning, Supermarket Systems, Chillers MVAC, Residential and Commercial Air Conditioning (Possible Future Applications)

R-744 R-717 R-290, R-600, R-600a, etc. R-1234yf, R-1234ze, R-32

definition; 2 International Institute of Ammonia Refrigeration; 3 IPCC Fourth Assessment Report, Working Group 1 Report, Table 2.15; 4 Dupont. “Development and Evaluation of High Performance, Low GWP Refrigerants for Stationary AC and Refrigeration, Feb. 17, 2010; 5 Honeywell HFO-1234ze Data Sheet; 6 IPCC Fourth Assessment Report, Working Group 1 Report, Table 2.14.

Table 2: Summary of low-GWP refrigerant characteristics and current applications.
October 2010 ASHRAE Journal 35

ASHRAE Journal - October 2010

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