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16-10-2005, 06:08 AM #1
Thermostaic expansion valve for NH3 refrigeration system.
Hi all,
Could anybody help me?
Can I install refrigeration system for cold storage 1000MT(room temp. -25oC), refrigerant NH3, liquid suplly thermostaic expansion valve.
Thanks and best regard,
Hphien
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16-10-2005, 09:29 AM #2
Re: Thermostaic expansion valve for NH3 refrigeration system.
Sure, I know that Danfoss has these valves in their program and certainly other manufactures
It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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16-10-2005, 10:38 PM #3
Re: Thermostaic expansion valve for NH3 refrigeration system.
Evaporator manufacturers usually mention a lower limit on the use of TXV's for ammonia. The -12C temperature is approaching the lower limit we use here in the US.
At low temperatures (with ammonia) the usual feed method is flooded or liquid overfeed.
This can be especially helpful if the system experiences capacity changes.
You should also be aware that the ammonia TXV's will have to be rebuilt or replaced on a regular basis. The pins and seats wear out in about 2-5 years. They are also dependent on liquid subcooling to last this long.
For big systems, liquid overfeed would be the preferred method.Last edited by US Iceman; 12-11-2005 at 02:36 AM. Reason: lower limit changed to -12C (temp. conversion error)
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18-10-2005, 04:31 AM #4
Re: Thermostaic expansion valve for NH3 refrigeration system.
Thanks you very much
In this application, i will use liquid overfeed system for big store.
Can i use DX for small store?
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18-10-2005, 03:41 PM #5
Re: Thermostaic expansion valve for NH3 refrigeration system.
The short answer is yes.
However,....
I have found that if the number of evaporators used in the cold storage space increases, a liquid overfeed system can become cost effective.
When using TXV's for ammonia service you still need a suction accumulator. You also need some liquid subcooling to maintain the liquid quality entering the TXV.
You might also include a liquid transfer system to pump liquid from the suction accumulator to the high pressure receiver, when the accumulator liquid level increases.
BY the time you add up the equipment costs for all of this and the installation costs, liquid overfeed system start to become cost effective on small systems.
I've worked on too many ammonia TXV systems to say I would install one. Just my opinion...
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08-11-2005, 12:25 PM #6
Re: Thermostaic expansion valve for NH3 refrigeration system.
Generally ammonia TXV's are not applied beow about 0 dF. Based on my experience, I try to limit their aplication to now lower than +10 dF.
Ken
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11-11-2005, 02:48 PM #7
Re: Thermostaic expansion valve for NH3 refrigeration system.
If ammonia is used in a DX system wouldn't there be an oil return problem?
Even Einstein Asked Questions
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11-11-2005, 09:09 PM #8
Re: Thermostaic expansion valve for NH3 refrigeration system.
Not really, unless the evaporator piping is trapped. For the most part, DX with NH3 works OK as long as the evaporating temperature is not below about 0F.
I prefer not to use DX on ammonia for other reasons.
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11-11-2005, 10:43 PM #9
Re: Thermostaic expansion valve for NH3 refrigeration system.
Hi. This is proberly not the right place to ask but i try anyway.
I just commisioned a Vilter 1501 in Africa i just want to ask US Iceman.Do you think ther is any way to get the Vission control to show the pressure and temp in BAR/Celcius.as my client dont understand F/psig
I just ask as i know you worked for Vilter before.
When i ask Vilter they dont seem to understand the ;Problem:
Best Regards
Claus
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12-11-2005, 08:47 PM #10
Re: Thermostaic expansion valve for NH3 refrigeration system.
Hi Us Iceman.
I thank you for the reply.I have solved the problem by asking John Lancaster at Vilter.(You just have to know whom to ask)
You can switch o BAR/C But only in the main picture.All the setup settings is displayed in PSIG/F..??
I hope we can convince Vilter that it has to be an option as we are going to be the Vilter dealer in Africa/Middel East and Europe.I mean that its difficult to get a engnieer in Angola to start to learn PSIG/F if he is used to deal with BAR/C .Anyway nowh i am in Malawi to commision a 16 cyl Vilter.They seems to like this compressores after Sabroe give the news that they stop making the SAB Screws.
Thanks for the help.
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13-11-2005, 04:53 AM #11
Re: Thermostaic expansion valve for NH3 refrigeration system.
Hi Iceman,
Many thanks for your very good explanation.
Cheers.Even Einstein Asked Questions
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13-11-2005, 08:58 PM #12
Re: Thermostaic expansion valve for NH3 refrigeration system.
The problems I have seen using ammonia DX is the circuiting and circuit loading or velocity. Since ammonia is generally about 1/3 of the mass flow of the "*****" refrigerants, cooler or coil circiting can be come critical.
With the circuiting we also get the oil return problem. Due to the higer refrigerant mass flows of the "*****s" you will naturally have more opportunity to move the oil which mixes with the refrigerant to varing degres. With ammonia, the oil and refrigerant do not mix and the oil wants to drop out as soon as you get some velocity reduction. The oil pools readily and you get oil not coming back to the compressor or in larger volumes.
The lower temperatures only aggriavate the oil return as the oil gets viscous where an oil that mixes with the refrigerant will be thinner and more likely to be returned.
Oil return in flooded ammonia sytsems is handled with oil pots or oil stills to allow the ol to settle out where it can be heated and returned to the compressor.
Last DX ammonia chiller I was involved with, the heat exchanger vendor finally gave up and converted the DX chiller vessel to a thermsiphon. We were running a 10 dF ET. We monted a thermosiphon drum over the exchanger and changed out the heads for a one pass design. Worked like a champ after the conversion.
Ken
Ken
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13-11-2005, 09:03 PM #13
Re: Thermostaic expansion valve for NH3 refrigeration system.
Originally Posted by TXiceman
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23-11-2005, 06:59 PM #14
Re: Thermostaic expansion valve for NH3 refrigeration system.
US,
Sounds like you and I have hoed the same row of cotton more than once.
Ken
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23-11-2005, 07:13 PM #15
Re: Thermostaic expansion valve for NH3 refrigeration system.
Ken,
I'm pretty sure both of us have plowed over the same fields.
Since we both have been in the business for about the same amount of time, I would not be surprised if we both had the same stories to tell.
The names and places may change, but the same problems always seem to occur.
Thanks for the laugh. I had not heard that expression for a long time.Last edited by US Iceman; 23-11-2005 at 09:37 PM. Reason: text editing
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04-12-2005, 09:06 PM #16
Re: Thermostaic expansion valve for NH3 refrigeration system.
Originally Posted by TXiceman
To simplify... Superheat is the bane of an ammonia refrigeration system. DX systems demand superheat to function, for which ammonia systems take a large penalty.
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