近年来，随着人们对普通氟碳制冷剂的全球变暖潜能（GWP）的担忧不断增加，许多低GWP制冷剂越来越受到关注。因此，工业界正在寻找具有低可燃性和低GWP以及良好热力学效率的替代制冷剂。主要替代品包括HFC-32、HFO-1234yf和HFO-1234ze；目前正在考虑将其用于住宅空调和小型商用制冷等应用。根据ASHRAE标准34-2010，HFC-32、HFO-1234yf和HFO-1234ze被视为可燃性等级为2L的制冷剂，这意味着由于其火焰速度较低，属于轻度易燃。因此，如果处理得当，它们可能会带来可控的风险。随着这种新的2L分类在全球范围内得到认可，在住宅和商用直接膨胀（DX）空调中使用HFC-32或HFO-1234yf等制冷剂变得更加可行。 为了帮助暖通空调行业评估在固定暖通空调和制冷系统中使用2L级制冷剂的可行性，需要进行全面的风险评估。这些风险评估的输入值必须通过严格的科学评估获得，包括测试和模拟，以及从行业来源收集数据。该风险评估的结果，以及有关系统成本和性能的信息，将构成有关使用2L制冷剂的系统的市场引入决策的基础。本报告中描述的工作可以为该风险评估提供一些必要的数据。

As concerns about the global warming potential (GWP) of common fluorocarbon refrigerants have mounted in recent years, many low-GWP refrigerants have garnered increasing attention. Consequently, industry is seeking alternative refrigerants which have low flammability as well as low GWP, combined with good thermodynamic efficiency. Prime alternatives include HFC-32, HFO-1234yf, and HFO-1234ze; these are being considered for applications such as residential air conditioning and small commercial refrigeration.According to ASHRAE standard 34-2010, HFC-32, HFO-1234yf, and HFO-1234ze are considered flammability class 2L refrigerants, meaning that they are mildly flammable due to their low flame velocities. They may therefore present manageable risk if handled properly. With this new 2L classification becoming accepted globally, the use of refrigerants like HFC-32 or HFO-1234yf in residential and commercial direct expansion (DX) air conditioners is becoming more viable.In order to help the HVAC industry evaluate the viability of using class 2L refrigerants in stationary HVAC and refrigeration systems, a comprehensive risk assessment is necessary. The input values to these risk assessments must be obtained through a rigorous scientific evaluation, consisting of testing and simulations, as well as data gathering from industry sources. The results of this risk assessment, combined with information about costs and performance of the systems, will form the basis for decisions regarding the market introduction of systems which use 2L refrigerants. The work described in this report can provide some of the data necessary for this risk assessment.