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Ammonia AC

07/30/2011 4:03 AM

i've worked on a few servel and trailer refrigerators that use ammonia rather than freon. why don't they use this system for running a natural gas heat pump or a auto ac by collecting heat from the engine to boil the ammonia?

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#1

Re: Ammonia AC

07/30/2011 7:52 AM

Because it's toxic. Highly concentrated it can be explosive.

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#2

Re: Ammonia AC

07/30/2011 9:40 AM

Freon is a Dupont trademarked name fits line of refrigerants. Freon isn't a "type" of refrigerant. Honeywell calls it's line of refrigerants Forane. They're chemically identical. It's like a Crescent wrench, which is a brand name for an adjustable wrench. Refrigerant 717 is ammonia.

And as stated, it can be quite deadly if released.

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#3

Re: Ammonia AC

07/30/2011 10:27 AM

To get the required capacity, the system would probably be too large and heavy.

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#4

Re: Ammonia AC

07/30/2011 6:13 PM

Ammonia was the coolant used in homes many years back and is still used today in many industrial conditions. While the Industrial Refrigeration Conference does correctly point out that the very strong smell (it does produce an involuntary gag response, too) of anhydrous ammonia makes any leak an immediate problem that will quickly be remedied. Also the PPM concentration that ammonia can be smelled are far below toxic levels, but ammonia does have true toxic levels. In contrast many modern coolants have both no toxicity and aroma levels. So a leaky ammonia refrigeration system will reek to high heaven long before it looses all cooling capability. In contrast a modern coolant system with a leak won't be noticed until nothing gets cold.

Despite the self alarming nature of an ammonia leak, in 2008 there were still 8 ammonia coolant fatalities in the USA.

Now getting back to your specific question, I thought that the boiling process was where heat entered the heat pump system. [ http://www.nhtres.com/differs.php ] So boiling the ammonia using the engine heat may help to cool the engine but it won't cool anything else then.

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#5
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Re: Ammonia AC

07/30/2011 9:54 PM

A lot of effort is made to keep ammonia systems safe, but even so, a few fatalities per year do still occur. I am curious as to the nature of the 8 incidents, if this information is readily available.

Depending on the individual, one can smell ammonia at around 10 ppm in air; the OSHA 8-hour exposure limit is 25 ppm. The IDLH level (immediately dangerous to life or health) is 300 ppm. The self-alarming feature is good, but the problem is large leaks that raise the concentration rapidly, before one can escape.

In the U.S., ammonia is not allowed as a direct refrigerant for comfort cooling, but I think it can be used indirectly to chill water or glycol as a secondary refrigerant. Ammonia has no ozone depletion or global warming potential, which is another advantage.

The largest ammonia refrigeration system I have heard of contains 750,000 pounds; I have done safety analysis and procedure writing for a 250,000 pound system; the plant where I work now has about 40,000 pounds.

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#11
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Re: Ammonia AC

07/31/2011 12:41 AM

I once worked on an Ammonia system that had 2 ea 1000hp compressors used in a textile treatment of cotton .NH3 makes cotton fibers swell, and when the ammonia is boiled out , there will be no shrinkage of the material after wards.

The woven material was dipped into a pan of raw ammonia, and the vapor was captured for re-use.The material entered through Teflon seals into a 100 meter long chamber with several sections inside.The sections were maintained at a slight vacuum,from-.2 inches H2O to -.6 inches H20.Some ammonia always escaped into the room however, and there were detectors to alarm and shutdown at certain levels.

25PPM is very near the explosive range for ammonia, and 5 ppm will put you on the run for fresh air.

The absorption cycle refrigeration systems also use Hydrogen and water in the cycle, not just ammonia, and the ratios are critical.

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#12
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Re: Ammonia AC

07/31/2011 12:51 AM

Wrong. The explosive range for ammonia is about 16-25%, not ppm. Although there might be exceptionally sensitive individuals (those with multiple chemical sensitivity, for instance), 5 ppm will not normally "put you on the run" for fresh air. For many people, 5 ppm is scarcely detectable, and considerably less than in a typical chicken house.

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#13
In reply to #12

Re: Ammonia AC

07/31/2011 1:07 AM

You are correct.Percent, NOT ppm.

My mistake.

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#14
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Re: Ammonia AC

07/31/2011 2:41 AM

No problem. Once in a while, I get my numbers crossed up, too. But the CR4 peer review soon enough straightens things out. This is one of the beauties of the forum.

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#7
In reply to #4

Re: Ammonia AC

07/30/2011 11:31 PM

Since ammonia is the most efficient low-boiling refrigerant, it is still used for mechanical refrigeration systems in some commercial installations. Its toxicity makes it an unwise choice for use in homes, and is in fact forbidden for residential use by present-day codes.

Gas-powered ammonia refrigerators like the old Servel units and present-day Electrolux boxes for RV's operate on the Absorption principle, which is much less efficient than mechanical refrigeration that uses a compressor. Although such machines are useful where electric service is not available, or to utilize otherwise wasted heat, part of the refrigeration cycle depends on the avidity of ammonia for water. The quantity of water that is required makes them much heavier than mechanical refrigerators of the same capacity, as anyone who has ever had to move one of the old Servel boxes can attest.

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#9
In reply to #4

Re: Ammonia AC

07/31/2011 12:14 AM

The heat source is used to compress the fluid and then the compressed fluid is cooled.

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#10
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Re: Ammonia AC

07/31/2011 12:31 AM

This process occurs in the "regenerator" of an absorption system. The high pressure ammonia is then condensed (more than just cooled), and then there is a second boiling process in the evaporator, which absorbs heat from the items to be refrigerated.

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#16
In reply to #4

Re: Ammonia AC

08/01/2011 1:17 AM

i thought scavaging heat from the exhast manifolds or a heat exchanger in an veichle would save a few mpg. now i understand why it would be too dangerous

a natural gas/ammonia heat punp still sounds reasonable though.

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#17
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Re: Ammonia AC

08/01/2011 6:41 AM

That's what they make turbos for

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#18
In reply to #17

Re: Ammonia AC

08/01/2011 7:55 AM

i have a new 6-72. interested?

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#6

Re: Ammonia AC

07/30/2011 11:06 PM

Ammonia is the first industrially successful refrigerant. Its qualities are excellent. And where it is needed, it is needed. The Space Station Rotary Base for the solar cell got a 5 pounds recharge this summer. So, it is not quite out of fashion.

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#8

Re: Ammonia AC

07/30/2011 11:43 PM

Ammonia has been used for industrial refrigeration applications since many years. Considering safety as main criteria it is less used for comfort refrigeration applications. However considering its excellent environmental properties( Global warming & Ozone depletion potential) it is emerging as one of potential future refrigerants.

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#15

Re: Ammonia AC

07/31/2011 2:14 PM

This piqued my interest so I reviewed some of the literature I have around. My answer is really "off topic" so I will mark it so.

I do not think I would e ever want ammonia in a closed compartment like a an automobile cabin, but is is a shame ammonia is not more widely utilized.

Ammonia is an excellent refrigerant, no doubt about it. It is the "greenest" of all, and it is cheap. However, it can kill you or make you very uncomfortable for a while.

The code-writers, probably with justification, prohibit so-called "high-probability" systems - those that were a leak to occur the refrigerant would enter an occupied area and become IDLH (Immediately Dangerous to Life and Health). "Low-probability" systems by their design usually through use of secondary coolants prevent ammonia entering the occupied space.

The biggest problem with ammonia is the tendency of the press to sensationalize any ammonia release that occurs, and there is always the occasional uninformed on-scene fire fighter commander who evacuates an entire town or portion of a city when there is a release. As previously noted, however, people do die or get very sick, even disabled, from ammonia. Persons with respiratory problems would be very much at risk if caught in the plume of dissipating ammonia.

When there is a large ammonia release the mist will settle to the ground before it evaporates - hence you should avoid white "clouds" of ammonia as life is unsustainable within such a cloud.

For a positive note, we plumb ammonia systems with schedule 80 or better iron pipe, the compressors and other components are - to say the least - robust, and there are always administrative rules requiring certifications workers assembling ammonia systems. However, too often the operators are insufficiently trained or managed, and this is probably because mechanical refrigeration is indeed a complicated science of physical principles and the technology of gas behaviors which not a lot of people ever become even reasonably competent.

All that being said, it is sad that designers are not coming up with more ammonia systems, especially those containing less than about 22 pounds of ammonia, which is the maximum allowable charge for commercial installations. With a little creativity the risk of potential exposure to ammonia in toxic concentrations could be significantly reduced.

For more of this kind of information Google the IIAR, buy ASHRAE Standard 15, or get a copy of Chapter 15 of the International Building Code.

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