Hot Surface Ignition Testing for 2L Class Refrigerants (ST-16-C067)

Faced with more stringent regulatory pressures, the demand for environmentally friendly substances is high. The number of low global warming (GWP) refrigerants entering the market is rapidly increasing to meet market needs.  Many of the new low GWP refrigerants are “mildly flammable” or “2L” as classified by ISO 817 and ANSI/ASHRAE Std 34. The new refrigerant flammability class provides the heating/air-conditioning/refrigeration industry potential options to meet environmental regulations with equipment designed to meet reduced flammability concerns.  Mildly flammable refrigerants are defined as refrigerants which have burning velocity less than 10 cm/sec and heat of combustion (HOC) less than 19,000 kJ/kg.  Although not part of classification requirements, mildly flammable refrigerants have higher lower flammability level (LFL) and exhibit higher minimum ignition energy (MIE).  Current MIE testing of 2L refrigerants has employed ASTM E582, which use an electrical spark ignition source.  Results from that testing has shown that typically, class 2L refrigerants have MIE values which are two to four orders of magnitude greater than highly flammable or ISO 817/ANSI 34 class 3 refrigerants. The high MIE values determined for mildly flammable refrigerants denotes that they are typically very difficult to ignite. A relatively unexplored potential ignition source is a hot surface which can be found in air conditioning auxiliary heaters and other refrigeration systems.  Maximum hot surface temperatures are also specified in several equipment standards.   Recently, work was conducted to review potential ignition/non-ignition for several 2L refrigerants which were released onto a hot surface. A new test was designed to simulate a 2L refrigerant leak onto a hot surface within a piece of equipment.    In particular, individual refrigerants were released onto a heated metal surface and potential ignition was observed for a set time period after the refrigerant was released.  Interestingly, ignition values noted were several hundred degrees higher than literature auto-ignition temperature (AIT) values. This work summarizes the test apparatus used, the hot surface ignition testing conducted with various 2L refrigerants, and ignition testing results.