Refrigerants are chemicals that are used in HVAC systems and refrigerators to cool the building or items inside the refrigerator. Common refrigerants include chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). However, these refrigerants have been found to deplete the ozone layer and expedite global warming. Therefore, in the late 1980s, the United Nations developed the Montreal Protocol, which is an international treaty that mandates the phase-out of CFCs (the most harmful) by 2010 and the phase-out of HCFCs (the second most harmful) by 2030.

Ozone Depleting Potential, or ODP, and Global Warming Potential, or GWP, are both ways to measure the impact of refrigerants on the atmosphere. It is important to note that ODP is more harmful to the environment than GWP, so refrigerants with higher ODP are considered worse than those with high GWP.For the exam, you will need to memorize the following refrigerants and their corresponding levels of ODP and GWP (listed in order from most harmful to least harmful:1) CFCs: High ODP, Medium-High GWP2) HFCs: Low ODP, Medium GWP3) Hydrofluorocarbons (HFCs): Zero ODP, Highest GWP4) Natural Refrigerants/Hydrocarbons (HCs): Zero ODP, Low-Zero GWPExamples of natural refrigerants: Water, CO2, Ammonia, Propane, Butane, Isopentane, etc.5) Natural Ventilation: Zero ODP, Zero GWPIt is important to remember the order from worst (CFCs) to best (natural ventilation) for the environment. Keep in mind that although HFCs have the highest GWP, they are not the most harmful, because ODP is worse than GWP (and CFCs and HCFCs have higher ODP).