One refrigerant that is commonly overlooked in the HVAC industry is ammonia, which does not appear to affect global warming or cause ozone depletion. ASHRAE does recognize ammonia in three of its four handbooks (Refrigeration, Fundamentals, and HVAC Applications), but its application is more in the process cooling and freezing industries. Ammonia is toxic and flammable but, when engineered correctly in refrigeration systems, it is safe.
Today, design engineers, as well as equipment manufacturers, must take a renewed account for their projects and the equipment being engineered. Performance, safety, reliability, environmental acceptability, and economics can each influence an engineer’s HVAC application. All too often, the selection of the optimum refrigerant for the HVAC application bypasses the aforementioned points of discussion. Seldom do HVAC designers rely on equipment manufacturers to provide information regarding their projects' refrigeration systems, so the decision for which refrigerant to use is determined by the equipment manufacturer representative who calls on the consulting engineer(s).
Refrigeration for process cooling can be considered a boutique engineering initiative. In cooler-freezer applications (e.g., frozen food plant), the design engineer more often than not will be the decision-maker for the five points of a refrigerant: performance, safety, reliability, environmental acceptability, and economics. Here, the equipment manufacturer will have less influence, and the application result may often be the use of ammonia.
I believe consulting engineers for commercial HVAC applications need to follow the lead of industry consulting engineers if we are to achieve the goal of stopping global warming and truly begin to protect the environment.