low GWP refrigerants, 2L refrigerants, ISO 817, ASHRAE 34, hot surface ignition test
Transitioning to low global warming potential (GWP) refrigerants will be critical as the world rises to solve the issues of climate change. Finding low GWP alternatives for HVAC equipment which can be safely used and serviced in varying applications is the new challenge. An interesting class of low GWP alternatives are the “mildly flammable” or class 2L refrigerants. ISO 817 and ANSI/ASHRAE Standard 34 both employ the “mildly flammable” or “2L” refrigerant classification. Class 2L refrigerants are not easily ignited due to their relatively high minimum ignition energy (MIE) and high lower flammability level (LFL) compared to class 3 refrigerants. Therefore, the traditional autoignition test (AIT), which has been used for standards and equipment design may be not be the appropriate parameter to define mildly flammability refrigerants. A more relevant test may be the hot surface ignition test (HSIT), where the 2L refrigerant is released onto a hot surface and monitored for subsequent ignition or non-ignition under dynamic conditions. HSIT data was presented in an earlier paper using Annex KK of the IEC 60335-2-40 standard as framework. This current study builds on previous information and further expands that work. Specifically, the HSIT test was updated by adding a cylindrical tube to confine refrigerant after releasing onto the hot surface. The cylindrical tube was added to simulate the confinement found in HVAC ductwork. Data is presented for ten different A2L refrigerants in this updated HSIT design. The updated HSIT method shows more differentiation between refrigerants particularly as temperatures are observed between 800C and 850C.