R-717
Also known as: R717, NH3, Ammonia, Anhydrous Ammonia
Natural refrigerant with zero GWP and zero ODP. The dominant industrial refrigerant for cold storage, food processing, and large-scale cooling. B2L safety class requires specialized handling.
Regulatory Timeline
Ferdinand Carre demonstrates first practical ammonia compression refrigeration system
Clean Air Act — ammonia exempt from HFC/HCFC restrictions as a natural substance
OSHA Process Safety Management (PSM) standard establishes requirements for ammonia systems above 10,000 lbs
Kigali Amendment drives interest in low-GWP industrial refrigerants including ammonia
What R-717 (Ammonia) Is
Ammonia (R-717, NH3) is the oldest industrial refrigerant and remains the most energy-efficient refrigerant available for large-scale applications. Its thermodynamic properties are exceptional: high latent heat of vaporization, excellent heat transfer characteristics, and zero ODP and zero GWP. Ammonia is a natural substance — any emissions return to the natural nitrogen cycle without climate or ozone impact.
Ammonia has been used in industrial refrigeration since the 1860s. Modern large-scale cold storage facilities, food processing plants, ice rinks, breweries, and chemical plants continue to rely on ammonia systems for primary refrigeration. The installed base spans every major HVAC and refrigeration market sector where energy efficiency and long system life are priorities.
The distinguishing constraint on ammonia is its B2L safety classification — it is toxic (threshold limit value is 25 ppm TWA) and mildly flammable. Ammonia leaks above approximately 300 ppm cause severe respiratory distress. Systems above 10,000 pounds of ammonia are subject to OSHA PSM and EPA RMP program requirements, which mandate detailed hazard analysis, operating procedures, and emergency response planning.
Ammonia in Modern Low-Charge Systems
The industry response to ammonia safety constraints has been the development of low-charge systems that reduce the ammonia inventory to levels below PSM/RMP thresholds while retaining the thermodynamic efficiency advantages. Indirect systems using ammonia as the primary refrigerant in a closed machine room loop, with secondary refrigerants (propylene glycol, CO2) distributed to equipment, limit the total ammonia charge to a few thousand pounds.
CO2/ammonia cascade systems are gaining adoption in supermarket and food processing applications. CO2 handles the low-temperature load in the display cases and processing areas; ammonia provides the efficient primary refrigeration in a dedicated machine room. This approach combines the safety advantages of distributed CO2 with the efficiency of ammonia primary refrigeration.
For contractors primarily servicing commercial HVAC, ammonia systems are typically outside the scope of regular work. They require specialized training, different tooling, and safety protocols that are distinct from HFC service work. Technicians should not attempt ammonia system service without appropriate training and personal protective equipment.