Risk assessment of HFC-32 and HFC-32/134a (30/70 wt.%) in split system residential heat pumps. Final report

摘要

Flammable refrigerants such as HFC-32 and blends of HFC-32/134a have been proposed as HCFC-22 alternatives. Hydrocarbons such as propane have also been proposed and used as alternatives in a few cases, but to date their use has been limited as they are much more flammable than HFC-32. Therefore, in order to better understand the risks of the range of flammable refrigerants, a risk assessment focusing on marginally flammable refrigerants such as HFC-32 was performed. Although substances like HFC-32 are flammable by currently accepted laboratory testing standards, their actual safety risks in real-world applications may be tolerably low. The environmental benefits of these refrigerants should be balanced with their potential safety risks, which have been estimated through a risk assessment of the use and service of residential unitary heat pumps which use HFC-32 and HFC-32/134a (30/70% by weight). In the first phase of the project, small scale testing of various ignition sources was conducted at Underwriters Laboratories (UL) to determine whether these common sources could ignite pure HFC-32 and the blend under optimum conditions for ignition. This small scale testing was performed in a 1 ft (sup 3) (28.3 liter) plastic box containing the ignition source in the presence of a flammable mixture of the refrigerant and air. Full scale room testing of HFC-32, as well as HFC-32/134a (30/70 wt. %) in its worst case fractionated blend composition, was conducted to provide additional data for the risk assessment. Two sets of tests were performed: concentration mapping tests and ignition tests. A fault tree analysis was then conducted to estimate the frequency of fires and explosions that could result from substituting HFC-32 or HFC-32/134a (30/70 wt %) for HCFC-22 in a residential unitary heat pump. Overall the risk of a fire resulting from use of HFC-32 is estimated to be about 1 per million units/year for operation and 3 per million units/year for service.