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Why Ammonia?

 

First of all, why ammonia as a refrigerant? Don't we have other choices? Yes, many. The Handbook of Fundamentals, published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) lists over 100 different fluids that can be used in a vapor-compression refrigeration system (or unit). Because refrigeration is used in so many different fields, I am going to limit my discussion to food processing. In this arena, our refrigeration systems become very large. A typical (if this is possible!) food processing facility may have enough refrigeration capacity to provide air-conditioning to several thousand homes. When working with very large systems, refrigerant compressors also become large - 1,500 hp in a single compressor motor is not at all uncommon. Then we need to consider temperatures - at what temperature do we want a particular process to take place? In food processing, temperatures can run the gamut - from 50 F all the way down to -70 F! NH3 is the only refrigerant that can meet this wide range of temperatures. While ammonia has a strong pungent odor, this also works to its advantage - a leak is readily recognized, therefore something is done about it immediately. And finally, ammonia if released into the atmosphere, it is non-polluting - when mixed with water (which it does rapidly on its own) it is rapidly absorbed into the earth as a nitrogen-rich fertilizer. No other heat transfer fluid listed in Table 1, Chapter 18 of the ASHRAE Handbook of Fundamentals (2001) can boast this characteristic!

Several years ago, a colleague told me an interesting story. As he was flying in to Midway airport (Chicago), he noticed a large green area downwind from a frozen foods warehouse. He decided to rent a car and drive over into the area he spotted from the air. After parking his car, he walked the residential neighborhood and asked several people if they had ever smelled ammonia. "No, can't say that I have. Why do you ask", was the usual retort. Now as I relate this story to you, I do have to state that ammonia is indeed both a toxic and dangerous chemical in its 'concentrated' (liquid or vapor) form. I cannot stress enough the importance of following all IIAR safety guidelines and OSHA regulations because I strongly feel that these are all beneficial - they save lives. But the simple fact remains: once ammonia has bonded to water and has been further mixed with air (a minimum of 25 parts air to each part of ammonia), yes - the mixture is still 'smellable', but for cryin' out loud! - I've smelled stronger cat-boxes in my day. So there! - You have my take on using ammonia as a refrigerant. I think it is one of the 'safest' refrigerants around.

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