liquid overfeed system design guide

[lana]

Hi everybody,

Does anybody know a good reference for liquid overfeed system design? Including all the necessary calculations and ...
The theory is simple and I think every refrigeration engineer knows about it, but what about the calculations and design?

Please don't say ASHRAE because I read it and there is still long way to go.

I have looked a lot for this information but no luck.
I would appreciate any help.

I am very very thirsty for info. SOMEONE help.

Thanks in advance.

[US Iceman]

Does anybody know a good reference for Liquid overfeed system design?

Ha! Good luck with that one!

The ASHRAE material is woefully lacking, but that is all there is. Here are several links to threads on the RE site if you have not seen them lana.

http://www.refrigeration-engineer.co...verfeed+system

http://www.refrigeration-engineer.co...verfeed+system

http://www.refrigeration-engineer.co...verfeed+system

Unfortunately, this is another of those topics that does not receive very much attention in articles, much less design guides.

If you have some specific questions, go ahead and post them in a new thread. We'll see what we can do.

[lana]

Thanks a lot US Iceman,
I was fearing that I would get this response.

Believe me or not I read all the links you mentioned but still I have tons of questions.

Let me categorized the questioners then I will post it one by one here. I hope I can satisfy my curiosity.

Thanks a lot for your kind help.

Cheers

[US Iceman]

I was fearing that I would get this response.

Well, it's not because I don't want to help. I have never seen one either.

Most of what I have learned was due to working on systems that had problems. These systems are one of the things I hinted at in my signature. There are so many functions occurring at the same time it is hard for a novice to separate the independent variables. In other words, you have to de-couple them and look at them as independent concepts.

For instance, hand expansion valves... They do not really expand any liquid as they only act as hydraulic balancing valves to ensure sufficient liquid pressure to each coil.

To have that pressure you have to properly calculate the head and friction losses in the liquid line piping.

Then you have the refrigerant pumps, which operate under the same principles as a steam condensate return system. The liquid is saturated.

Because of this operation at the saturation point, any pressure loss causes flash gas and bubbles in the pump suction line.

The only way to overcome this is to provide sufficient NPSHA (Net Positive Suction Head Available). Which is a long winded way of saying you have to provide some subcooling of the liquid in some form.

This comes from static head above the pump suction.

[US Iceman]

I forgot to ask a question lana. Why was this thread started in the hydrocarbon forum? Just curious.

Are you thinking of using a liquid overfeed system on a hydrocarbon system? That would be interesting, but no reason it could not be done.

[lana]

I forgot to ask a question lana. Why was this thread started in the hydrocarbon forum? Just curious.

Are you thinking of using a liquid overfeed system on a hydrocarbon system? That would be interesting, but no reason it could not be done.

Actually yes. I would like to know about liquid overfeed system with "*****".
As I mentioned, I maybe never ever use this system in real life but I must know how to design it .

Cheers

[lana]

I forgot to ask a question lana. Why was this thread started in the hydrocarbon forum? Just curious.

Are you thinking of using a liquid overfeed system on a hydrocarbon system? That would be interesting, but no reason it could not be done.

My mistake, sorry.
I meant Halocarbon "*****".

If necessary please change the section.

Thanks

[lana]

Well, it's not because I don't want to help. I have never seen one either.
.

Nothing meant by my statement. meant that I feared that there would be no good references.
Actually, I was sure that only you can answer my questions.
The system theory I know and it is very obvious (I have the background you know). As you said, one has to experience the system in real life. I don't work with ammonia and therefore, I haven't had the chance to visit and work in a system. In here, liquid overfeed system with "*****" are very very rare.
So yo can see the picture. BUT my curiosity kills me and am sure with your help I will be fine .

Thanks a lot.

[US Iceman]

Nothing meant by my statement. meant that I feared that there would be no good references.

I knew what you meant and you are correct. The only thing I have seen were several articles that were probably 40 years old.

Some of the better articles were written by Prof. Gustav Lorentzen but these are extremely hard to find. And I have tried...

Feel free to ask away. Some of the other ammonia guys can lend a hand also. ***** liquid overfeed systems are no different from ammonia systems other than the oil return problems.

[lana]

Hi,
Here I go.

I attached a simple system schematic with two evaporators each 100kW.
Assuming the refrigerant is ammonia.
First, any comments on the system arrangement?
RV is regulating valve, I mean the flow regulating valve.
Cheers

[US Iceman]

That's a good start for a basic system with one temperature.

Now, let me ask a question. Where does the mass flow change in this system?

[NH3LVR]

Now, let me ask a question. Where does the mass flow change in this system?

Must have breathed too much Ammonia yesterday Iceman. I do not understand your question .

[US Iceman]

HI there,

I was referring to lana's drawing.

Basically what I was asking is that there are two distinct mass flows in a liquid overfeed system. One of them is much lower from the pump receiver to the compressor, condenser, and high pressure receiver. In this area you can say the circulation rate is 1.

The other is from the pump receiver to the pumps, evaporators, and back to the pump receiver. In this area the circulation rate could be 3-4 times higher than what the compressor, condenser, receiver will see.

Part of the idea of understanding how a liquid overfeed system works is to know where the mass flow is different in different parts of the system.

One of the inherent problems with discussing these systems is the often confusing terminology. We call these systems both liquid overfeed and liquid recirculation to mean the same thing.

However, as I have alluded to we have circulation rates and liquid overfeed. This too is another area where the terms have to have proper definitions.

The pumps are based on circulation, while the evaporators are concerned with the degree of overfeed.

You may have heard people use the term recirculation rate. I prefer the term circulation rate. This is just the multiplier used to find the total pump GPM (or cubic meters per minute).

The overfeed rate if you have heard this term is something completely different. This is what happens in the evaporators.

Does this make sense so far?

[lana]

Hi US Iceman,

Thanks for your reply and time.

If I understand you correctly, lets assume 4:1 circulation rate for the evaporators.
Cheers

[Samarjit Sen]

Hellp Josip,

You are absolutely correct it is liquid injection to the compressor head.

Regarding the capacity of the compessor being slightly oversized and a very good condensation system as stated by you, I feel the same thing applies to reciprocating compressors as well.

We are at present installing another plant with Copeland semihermetic compressors, wherein we have to maintain a temperature of - 40 Deg. C in one room and - 35 Deg. C in another room. The compressors are seperate.

I am proposing to install another plant for - 40 Deg C with CO2 refrigerant, wherein I shall be needing your valued advice.

With best wishes,

[The MG Pony]

Hey why not some guy made up the Tao of programming!

As for blank slate yup, all ya got when your born is a basic programing that tells you how to learn and thats it.No such thing as innate knowledge, one must learn it throughly through life.

[Elliza]

Hi everybody
i'm back but i have some problem about the theory of Hc-12 blossom, coz i need it for my project and until know i never hear it about this *****, does everyone know about this *****s? oh i'm so desparate right now to founded that information. if does have the literature about that *****s would you tell me please...
sorry my english is bad
thanks

[Josip]

Hi, Elliza

Hi everybody
i'm back but i have some problem about the theory of Hc-12 blossom, coz i need it for my project and until know i never hear it about this *****, does everyone know about this *****s? oh i'm so desparate right now to founded that information. if does have the literature about that *****s would you tell me please...
sorry my english is bad
thanks

I'm not sure, but refrigerant "HC-12 blossom" does not exist, maybe I am not right..could be Halon 12B1 (CBrClF2-halon 1211), but for sure one gave you some project to do must obtain some more info to you...

Let's see if someone on this forum can put some more light on this matter...

Here you can find some Industrial 12a refrigerant...

Enviro-Safe™ Industrial Refrigerant is highly refined! Enviro-Safe does not contain the “rotten egg, sulfur, propane” odor. We add a fresh “Pine Scent” to our refrigerant to assist consumers in leak detection.

.....pine scent....blossom

http://www.es-refrigerants.com/produ...ts/default.asp

personally I think there is a lot of questionable statements, but...

Best regards, Josip

[Elliza]

ow.. does anyone could help me to find out all my post in this forum coz i need it to know all the posting for my literature. sorry i forgot in what topick i'm posting my question hee..hee.. because i'm very long time not active in this forum.
thank you so much

[Josip]

Hi, Elliza

ow.. does anyone could help me to find out all my post in this forum coz i need it to know all the posting for my literature. sorry i forgot in what topick i'm posting my question hee..hee.. because i'm very long time not active in this forum.
thank you so much

Click on your avatar, sign in, if you are not yet and then you can see: View profile: Elliza on the same page you can find all about yourself and your posts..

or follow this link:
http://www.refrigeration-engineer.co...ber.php?u=6688

Best regards, Josip

[John Hunter]

I just picked up this thread , don't always look in the Hydrocarbons but it is an interesting subject.
The over feed in NH3 systems, always around 4 or 5 to 1., I think stems from the type of evaporators that were predominantly used with ammonia in industry. Some of the old evaporators, some still in use had an attached accumulator, with float level control, which fed directly to the primary circuits of the unit at every alternative bend there was a stub pipe to vent off the evaporated has back to the top of the accumulator and from thence to the "Dry" suction pipe. Some systems even had "Dry" and Wet returns. in all of these systems the quantity of refrigerant in circulation had to be large as the draw was never constant.
In recent years we have moved away from this design to a more compact unit. The design of the new units is quite involved but the intention it try to ensure the individual coil is "Wet" for the most of its length but still allow for gas space. These units are controlled by Flow balance valves, often incorrectly referred to as expansion valves, a term corrected by US Iceman before. These valves are quite different in purpose to a TEV etc. . With the newer evaporators there is still the need to supply more liquid than the critical design may call for as the duty conditions can vary greatly and so a single valve setting cannot be set to handle all conditions.
In brand new NH3 installations where the system is known to be clean we re now using sub cooled HP ammonia in DX systems with some success. The only complaints I have received relate to conditions where the duty demands are greater that the design limits, and this is what clients have to get used to . In the older systems there was always extra refrigeration capacity on demand, within limits, but with the new DX TEV, critical charge plants once designed and installed you get what you paid for no more.
Years and year ago I was witness to a R22 pumped circulation system with accumulator pots with "Scum" systems for oil etc. It was a passage to the home for the insane.

[BigJon3475]

http://hvac-talk.com/vbb/showthread....verfeed+system

Maybe of some use may not.

[John Hunter]

Hi Big John
I wish all the systems were installed as your Henry design. Its amazing the systems arround now where pencil sharpening has eliminated many of the real operating valves and stsyten aux's required. Some ammonia systems have no or minium pump out facilities and installed pump out compressors are considered not necessary. One plant had a spare liquid pump in "The Box" , I was told if and when you need it. There was no pump out unit and next to no connections where you could connect to. When you come up against this you feel like walking away, but in the end because we are service people in the end we do what we have to do.

[lana]

Hi BigJon,

Nice schematic.
Thanks a lot.

Cheers

[lana]

Hi everybody,

I have done my homework.

With help of a dear friend who is a system designer (ammonia overfeed system), I have learned a lot about this system and satisfied my curiosity.

For everyone who wants to learn about the design of liquid overfeed system, I would suggest the following steps which will get you there easily.

1- Learn the overall system arrangement (briefly).
2- Learn about PM valve with its Pilot valves. Use Danfoss site for very good information and drawings.
3- Learn every valve station on the system : before evaporators, before separators, before receivers, before condenser.
4- Learn about hot gas defrost.
5- Learn about oil draining procedures.
6- Learn how to design the separators.
7- Learn about liquid pumps and every issue about it.
8- Learn about pipe sizing.
9- Learn about compressor capacity control.
10- Control algorithm.
11- Safety.


I must admit that designing an overfeed system needs more engineering knowledge than a DX system.

It is fascinating.

Hope these steps help those who wants to learn more about this system.

Cheers

[Josip]

Hi, lana

Hi everybody,

I have done my homework.

With help of a dear friend who is a system designer (ammonia overfeed system), I have learned a lot about this system and satisfied my curiosity.

For everyone who wants to learn about the design of liquid overfeed system, I would suggest the following steps which will get you there easily.

1- Learn the overall system arrangement (briefly).
2- Learn about PM valve with its Pilot valves. Use Danfoss site for very good information and drawings.
3- Learn every valve station on the system : before evaporators, before separators, before receivers, before condenser.
4- Learn about hot gas defrost.
5- Learn about oil draining procedures.
6- Learn how to design the separators.
7- Learn about liquid pumps and every issue about it.
8- Learn about pipe sizing.
9- Learn about compressor capacity control.
10- Control algorithm.
11- Safety.


I must admit that designing an overfeed system needs more engineering knowledge than a DX system.

It is fascinating.

Hope these steps help those who wants to learn more about this system.

Cheers

Agree with you, but I will put no. 11 to no. 01 NHF, please.

On the scheme is all except charging valve....

Maybe couple of words more...use overfeed NH3 system only for low temp i.e direct cooling, otherwise use indirect cooling (PHE) to reduce total amount of NH3 in the plant...

Best regards, Josip

[HallsEngineer]

Why you want to reduce ammonia? it smells but you know you have a leak r22 just kills you!!

[amirjhanem]

Dear Friend,
ASHREA Refrigeration hand book can help you about it .
if didnot have contact me
amirjhanem@gmail.com
or
amir.ghanem@ salemyork.com

[Chris Burton]

Hiya Lana, i work in a large Refrigerated depot with 3 seperate R22 overfeed systems doing +7c, +3c and -20c running on stal open drive recips. I've got some technical specs for design and sizing for surge drums from the 1970's which are really indepth. All run on a saturated design temp of +35c with single stage compression. Each compressor has an individual oil seperator plus an oil seperator in common discharge. If you need an info send me a post

[Samarjit Sen]

Hello aansari,

Maybe some members like me are also interested on the Liquid Overfeed System. Would not it be better if you provide a link to the same in this forum, so that others may also view it.

[aansari]

Dear Samarjit:
The artical is more than 1.2 MG and I can not attach it, please send your emial to sant it to you.

[Samarjit Sen]

Hello aansari,

Thanks for your offer. I tried to send you a PM stating my e mail, but could not do so as I was made to understand that either you have chosen not to recieve any PM or are not as yet authorised to recieve the same. Could I please request you to upload the same in www.yousendit.com and post the link in the forum in this thread.

Stating our e mail id on the post is not permitted. You may check my profile in the forum and send the mail.