IIAR

Although ammonia has been the refrigerant of choice in industrial refrigeration systems for more than a century, it has faced competition from numerous synthetic refrigerants, most recently 1234yf and R32. Although the use of ammonia brings with it a greater regulatory burden, it remains the more logical choice of refrigerant in larger refrigeration systems, especially from a safety, efficiency and environmental standpoint.

From a safety perspective, ammonia possesses numerous advantages over 1234yf. For example, while both refrigerants have reasonably comparable heat of combustion and flame-spread characteristics, ammonia has a much higher required vapor density at standard air temperature and a higher auto-ignition temperature, critically important features in the case of a release. Exhausting ammonia, especially from an equipment room, is relatively easy and does not present a global warming issue.

“Ammonia has a low molecular weight, and its vapor is inherently light,” says Jerry von Dohlen, president of Newark Refrigerated Warehouse. “So, if ammonia leaks in an engine room, the vapor will rise to the ceiling. That makes it easy to get rid of the vapor by placing fans on the ceiling. When you sense a leak, you increase the fan rate, the ammonia is shot into the air at a high velocity and it rises and dissipates.”

Conversely, 1234yf vapor is almost seven times heavier than ammonia and in the event of a leak it will drop to the floor, displacing breathable oxygen. When 1234yf falls to the floor, people can suffocate before even realizing they are in danger and that means there is a great reliance on refrigerant detectors.

That leads to another advantage with ammonia, which is that it can be detected at less than five parts-per-million. People can tolerate ammonia at an exposure of up to 300 ppm for short periods of time without ill effects. And ammonia’s odor provides a self-alarming system, causing people to evacuate the area, while 1234yf is odorless, making it a potentially silent killer.

Furthermore, the lower liquid density of ammonia allows for easier low-side oil separation. Oil adds to the flammability of any refrigerant. In the case of a fire, extinguishing the flame is easier with ammonia because an ammonia-air mixture with 10 percent or more water vapor will not support combustion.

Plus, if a fire occurs with 1234yf, it will emit poisonous gasses. “If you breath ammonia when it burns it may make you sick,” von Dohlen said. “But if you breathe burned 1234yf, you could easily die.” Ammonia is also a better choice when it comes to efficiency.

Ammonia’s heat of vaporization is 589 BTU/lb., versus 77 BTU/lb. for 1234yf. Therefore, to achieve 589 BTU of cooling with ammonia you would pump one pound, as compared to almost eight pounds with 1234yf. “Any time you are pumping through a pipe you have frictional losses, but those losses are much lower with ammonia than with any other refrigerant at common temperatures,” von Dohlen said.

There are other advantages to using ammonia. The compression of 1234yf is less efficient because it requires nearly twice as much compressor displacement. Ammonia’s boiling point is lower, which means it will be in a vacuum less often for medium- to low-temperature applications. Ammonia is also less expensive, around 88 cents per pound, compared with a 1234yf and R32 price of $40 to $50 per pound. Ammonia is a common commodity and is available nearly world-wide.

Finally, ammonia is a wiser environmental alternative. “No matter how much ammonia is released it will not affect the ozone layer or the global warming potential,” von Dohlen said. “It’s a natural refrigerant, so there is zero impact on the environment.”

The principal drawback to ammonia is the current regulatory burden. The EPA requires a facility to report within 15 minutes an ammonia leak of 100 pounds or more over the preceding 24 hours. “Ammonia weighs a little less than six pounds per gallon, so 100 pounds is equal to about five-gallons a can spilled on the roof over 24 hours,” von Dohlen said. “There are people adopting 1234yf because they don’t want to deal with the excessive regulatory burden of ammonia. But if the government would consider the physical properties of ammonia vs. other synthetics it would realize that ammonia offers many benefits to our food chain and, due to improved efficiencies, could significantly reduce refrigeration industry demands on our electrical grid.

“In the end, the benefits of ammonia are safety, efficiency, the cost and the fact that it’s good for the environment. If the regulatory burden can be reduced, the choice of ammonia is a no-brainer,” von Dohlen said.