Cooling with Ammonia: The Facts.
Ammonia or Freon? It's a dilemma for many facility operators. They'll both cool your case of beer, admits one of Food Plant Engineering's team members. There has been much misconcept over the years on both halocarbon and ammonia systems - that is why we have written this paper, and the corresponding Freon Refrigation systems paper to help sort out the options.
Ammonia Refrigeration Basics
Ammonia (NH3 to science geeks like us) is naturally occurring and makes a great refrigerant. But how do you determine if it's right for your facility? Start with the facts and consider the following:
01Cost: To assess a facility's most cost-effective refrigeration option, first runs a load calculation. If it's less than 100 tons, you will most likely need a freon system. If it's over 200 tons, you can go with ammonia if certain provisions are met (see items below). This is a rule of thumb for costing purposes. Most likely in a system over 200 tons ammonia will be less expensive to install than the freon.
02Product, Capacity, and Temperature Requirements: What is the product and how much of it are you processing? Ammonia has traditionally been used in meat-processing plants, dairies, the brewery industry, petrochemical industry, and any place you need large tonnages of refrigeration. Bakeries generally don't have such large cooling needs, although bakeries that use spiral freezers should consider ammonia as a viable option.
Generally speaking, the lower the temperature requirements that your facility or process needs, the more cost-effective ammonia becomes. For example, using ammonia for your blast freezer (with a temp below minus 20 ̊F) may make more sense than using freon.
03Efficiency: Ammonia is a more efficient refrigerant than freon because ammonia has a higher latent capacity per pound compared with the same pound of freon. While freon can do the same amount of refrigeration work, you need to move more pounds of freon in a system to do the work. With ammonia you move less pounds of refrigerant to do the same amount of work. An ammonia system will cost less to operate because it will use less horsepower to move the refrigerant mass. This cost advantage is a compelling reason to use ammonia in a large system.
04Regulations: Ammonia is classified as a hazardous chemical so the federal government has mandated that it be subject to Occupational Safety and Health Administration's (OSHA) Process Safety Management Rules (PSM) as well as the Environmental Protection Agency's Risk Management Program Rules (RPM). Put simply: "You have to have the necessary programs and paperwork in hand when the good guys from the government come to look through your plant"
State and local regulations must also be considered. Some areas of the country are more stringent than others. And though you don't need a PSM program until you reach 10,000 lbs of ammonia (in your facility), you do have a duty to protect your employees (as stated under OSHA and EPA's "General Duty" clause), so have a program and call it something else if your facility falls under the range. The good thing about ammonia, however, is that it's self-alarming. If your system leaks, you'll know it quickly. Also, ammonia is lighter than air so it rises in a room. However relying on your nose to detect a leak isn't the best safeguard, so ammonia detectors are required by law.
05Flexibility: An advantage of the ammonia system is that you can do more things with it once it's installed. Unlike other refrigeration systems which are optimized for a certain operating condition, the individual components of an ammonia system can be adjusted if room temperatures or capacities change. You just adjust the controls. Think about your environment and the future of your business when you determine how much flexibility you'll need.
06Maintenance: Know your local expertise and keep up with mechanical integrity audits (every five years) of your own system. You must know what you're doing to care for an ammonia system. If you are an hour and a half away from a trained and certified technician, you may not want to go with ammonia. And if you have a leak, you must report it to the appropriate government agencies.
07Comfort Level: Brading admits that facility owners and operators must be comfortable using ammonia. Don't be afraid of it. Understand it. Respect it.
The Truth about Ammonia Systems
Many facility owners and engineers who are not familiar with ammonia may have an instinctive aversion to the chemical. However, often the benefits of the system outweigh the risks. While ammonia is a hazardous substance, keep in mind that all chemicals-- whether they are halocarbon class (i.e. freon) or ammonia--can be dangerous if used improperly. To avoid unnecessary risk, work with a professional with substantial experience and current knowledge of all codes.
Every system is unique and should be customized to your needs. If you've got a plant, get an engineer to design the system that is going to be the most efficient for you.
Now hopefully we've answered a few of those questions about ammonia refrigeration that you were afraid to ask!