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lana
02-05-2007, 05:30 PM
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.:confused:

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
02-05-2007, 07:08 PM
Does anybody know a good reference for Liquid overfeed system (http://www.refrigeration-engineer.com/forums/glossary.php?do=viewglossary&term=83) design?


Ha! Good luck with that one!:D

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.com/forums/showthread.php?t=4239&highlight=liquid+overfeed+system

http://www.refrigeration-engineer.com/forums/showthread.php?t=5989&highlight=liquid+overfeed+system

http://www.refrigeration-engineer.com/forums/showthread.php?t=7158&highlight=liquid+overfeed+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
03-05-2007, 04:02 AM
Thanks a lot US Iceman,
I was fearing that I would get this response.:eek:

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

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
03-05-2007, 04:25 AM
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
03-05-2007, 04:32 AM
I forgot to ask a question lana. Why was this thread started in the hydrocarbon forum? Just curious.:confused:

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
03-05-2007, 04:36 AM
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:D .

Thanks a lot.

lana
03-05-2007, 04:39 AM
I forgot to ask a question lana. Why was this thread started in the hydrocarbon forum? Just curious.:confused:

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:D .

Cheers

US Iceman
03-05-2007, 04:43 AM
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.:D 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.

US Iceman
03-05-2007, 04:52 AM
***** liquid overfeed systems do have some inherent drawbacks from a viewpoint of pump selections. Due to the *****s having a low latent heat (much lower than ammonia) you have to pump a lot more liquid for the given cooling load (than if the refrigerant were NH3).

One of things I'm working on now is to use a much lower circulation rate on NH3 systems. Instead of using 3 or 4 to 1 as a circulation rate I'm using 1.5:1. This reduces the total volume of liquid that has to be pumped.

Some of the old recommendations say a ***** system should use 6 to 8 to 1. Why? I don't know and cannot find a good reason.

If we used a rate of say 6:1 for ***** the volume flow would be horrendous! That affects the pump selection, piping, and other.

I think we can live with 1.5:1 rate for any refrigerant, if the system is properly designed.

lana
03-05-2007, 05:01 AM
Now this is a good start.

OK, I am not insistent about the refrigerant. We can discuss about ammonia and then mention the differences with '*****s".
Is there any overfeed system in operation in the US with "*****s"?

To be more clear I would like to draw a simple system and then go from there as an example.

Maybe this thread leads to a good design guide:D . Why not?

Thanks a lot.
Wait for my tons of questions (hopefully not very stupid:D ).

Cheers

US Iceman
03-05-2007, 05:06 AM
Is there any overfeed system in operation in the US with "*****s"?


Sure. Would you believe I have seen several installed in supermarkets using industrial refrigeration equipment?

Most of the industrial R-22 liquid overfeed systems were installed because of panic or resistance to the use of ammonia. Mostly in highly populated locations.

Another large R-22 liquid overfeed system I have seen was used as a heat pump with ice builders in a large government office building for HVAC in downtown Chicago.

I would hate to have to pay for the refrigerant charge in these systems though.:eek:

PS.



Wait for my tons of questions (hopefully not very stupid:D ).


You should know by now there is no such thing as a stupid question.;)

Unless...it is not asked and someone gets hurt. Then I might have a different opinion.:rolleyes:

lana
03-05-2007, 05:55 AM
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
04-05-2007, 12:40 AM
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
04-05-2007, 01:31 AM
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
04-05-2007, 03:37 AM
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
04-05-2007, 06:55 AM
Hi US Iceman,

Thanks for your reply and time.

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

lana
04-05-2007, 10:12 AM
I forgot to ask a question lana. Why was this thread started in the hydrocarbon forum? Just curious.:confused:

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.:o
I meant Halocarbon "*****".

If necessary please change the section.

Thanks

US Iceman
04-05-2007, 03:53 PM
If I understand you correctly, lets assume 4:1 circulation rate for the evaporators.


Why not give this a go on your own, and I'll watch what you do and comment when necessary.;)

This type of system was one of the hardest for me to figure out for the same reasons you were looking for a design guide.

The best way to learn, is to do...:cool: Answers fought for are remembered far longer than answers given.

lana
04-05-2007, 03:55 PM
Why not give this a go on your own, and I'll watch what you do and comment when necessary.;)

This type of system was one of the hardest for me to figure out for the same reasons you were looking for a design guide.

The best way to learn, is to do...:cool: Answers fought for are remembered far longer than answers given.

HI,
I lost you there. What do I do?

Josip
04-05-2007, 08:30 PM
Hi, Lana :)


This type of system was one of the hardest for me to figure out for the same reasons you were looking for a design guide.

The best way to learn, is to do... Answers fought for are remembered far longer than answers given.

-30C/+35C in one stage? It is possible but not too much economical;)

No subcooling of liquid entering into separator vessel!? What about economizer?

What about defrosting of evaporators?

You expect answers but here you have additional questions:eek: But...don't give up:)


Why not give this a go on your own, and I'll watch what you do and comment when necessary.

Best regards, Josip :)

lana
05-05-2007, 05:54 AM
Hi Josip,



-30C/+35C in one stage? It is possible but not too much economical


I know, I just want to start from a simple system then complete it as I go ahead.

My first question is this : Do we have to select the compressor with capacity (200kW in this example), te=-40C and tc=35C? Or other parameters must be taken into account?
If the capacity is high for one compressor, then can we use parallel arrangement?

Thanks for comments.
Cheers

Samarjit Sen
05-05-2007, 08:44 AM
We have just completed a project for an Ice Cream Hardening Room where the Room Temperature is being maintained at - 35 Deg. C. The refrigeration compressors being used are Dorin single stage semi hermetic compressor. We have installed DTC in both the compresssors. The refrigerant being used is R 22. We brought the Room Temperature down to - 40 Deg. C, but our client wanted to set the temperature at - 35 Deg. C. The capacity of each compressor is 12 kw at - 45 Deg C Te and 40 Deg C Tc.

The plants are running very well. The Evaporators are from Heatcraft Larkin.

The DTC system adopted is vapour injection to the compressor head.

This is just for information.

Josip
05-05-2007, 11:22 AM
Hi, Lana:)


Hi Josip,

I know, I just want to start from a simple system then complete it as I go ahead.

My first question is this : Do we have to select the compressor with capacity (200kW in this example), te=-40C and tc=35C? Or other parameters must be taken into account?
If the capacity is high for one compressor, then can we use parallel arrangement?

Thanks for comments.
Cheers

All new projects are connected to requirements/wishes and ability to fulfill them and you as design engineer are in between. You just start to dance with the wolfs;)

Generally the capacity of compressor/s must be little above the required one but more important is to install good condenser (maybe with one heat exchanger for sanitary water) to obtain lower and constant condensing pressure.

Regarding the number of compressors I prefer always to install more units (screws for full load and piston for reduced load in parallel work) because we need to have spare compressor to obtain reliable work. It depends on type of plant.

An example: for continuous freezing tunnel we can provide one/two screws for full capacity (one is/can be standby, depending how important is to have freezing tunnel to run in any time), but with cold store is much better to use mixed compressors with different capacities i.e. the same compressor you can use for tunnel or for cold store but with possibility to switch the system.

In your case maybe is not bad idea to think about two stage system -40C/-10C (-40F/14F) first stage and -10C/+35C (14F/95F) the second stage with 3 compressors. One for first stage , one for second stage and one connected to both system we use to call this one Jolly.

This way is of course more expensive, but this is only one idea.

Let's see some other suggestions;)

Best regards, Josip :)

Josip
05-05-2007, 11:30 AM
Hi, Samarjit Sen :)


.....

We have installed DTC ......

The DTC system adopted is vapour injection to the compressor head.

This is just for information.

Please can you explain this DTC vapour injection more?

Is that maybe liquid injection:confused:

Best regards, Josip :)

lana
05-05-2007, 12:30 PM
Hi Josip,

Thanks for your reply.

Actually this is an example and at this stage I want to know the compressor selection for liquid overfeed system.
As I mentioned before, Do we select the compressor for required capacity (in this case 200kW) and te = -40C tc=35C? or other parameters must be considered?
For DX system is so simple.

Thanks again.
Cheers

Samarjit Sen
05-05-2007, 01:56 PM
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,

Josip
05-05-2007, 02:00 PM
Hi, Lana :)


Hi Josip,

Thanks for your reply.

Actually this is an example and at this stage I want to know the compressor selection for liquid overfeed system.
As I mentioned before, Do we select the compressor for required capacity (in this case 200kW) and te = -40C tc=35C? or other parameters must be considered?
For DX system is so simple.

Thanks again.
Cheers

What makes you to think that DX system is more simple? In fact it is, but with some other problems too;)

If you have a constant load of 200kW and you need to remove it you must do it in this or another way, and you need compressor capable to do it.

Best regards, Josip :)

lana
05-05-2007, 03:42 PM
Hi josip,

DX system is simple. Liquid overfeed is more complicated and there is no design guide for it. People who know the design procedure are not willing to share therefore, it is a little bit "dark area".:mad:
When you know how to design, then it becomes easy:) .
I am trying to find the way, and sooner or later I will learn as much as I need.
Actually liquid overfeed system is not my area of work but for my curiosity I have to know more than I know now.

thanks a lot for your kind help.
Cheers

US Iceman
06-05-2007, 12:20 AM
The compressor selection for this is no different than any other refrigeration system

Since the proposed cooling load is 200 kW @ -40C evaporating temperature the compressor capacity is first based on:

Evaporating pressure - the total suction line pressure losses = compressor suction pressure. Do not use a constant such as 1 or 2 degrees K for the suction line losses as the equivalent pressure/temperature loss increases as the evaporating temperature is reduced.

Then you have to make the same kind of allowance for the condensing temperature and discharge pressure.

Condensing pressure + total discharge line pressure loss = actual discharge pressure.

The compressors are selected to provide the required capacity (200kW) at the suction pressure and discharge pressure. You can convert these pressures to equivalent temperatures and use that if you want to.

That's how you select compressor capacity. Selecting compressors is different. You need to know the load profiles that will be observed during operation. You need to know how much redundancy the owner wants to have, if a compressor fails. You need to know how much operating time is spent at partial capacity. You need to know the difference in part load performance between screws and recips.
If you use screws, will you use an economizer for liquid subcooling. Do you use two stage compression?

All of these go into the decision on the compressor selection process. it is a balancing act between first costs and operating costs.

lana
06-05-2007, 04:28 AM
Dear US Iceman,
Thanks a lot for your comment.
Spot on point as usual.;)

Really appreciate your time and kind reply.
These are the things I would like to know not the mathematical calculations. I do that all day;) .

Thanks again.
Cheers

US Iceman
06-05-2007, 05:40 AM
lana,

Please feel free to post some other questions if you want to. I will try to answer them as time permits.

I'm sure some of the other people will also be happy to provide some insight also.;)

Josip
06-05-2007, 02:42 PM
Hi, Lana :)


DX system is simple. Liquid overfeed is more complicated and there is no design guide for it. People who know the design procedure are not willing to share therefore, it is a little bit "dark area".:mad:

I cannot fully agree with you;) .

For everyone of us all unknown is some kind of "dark area", but reading some literature, getting some experience, asking other people and using common sense and hard work here we are...

I must admit I have the same feeling regarding DX ***** systems, because I do not have too much experience (working all my life with stinking refrigerant;) in industrial refrigeration), but at the end of the day approaching to design must be the same.

It is not possible to invent something new, maybe to improve something and trying to avoid mistakes from the past. There is always better design or better installation, but at what price and maybe with unknown consequences:confused: what is not easy to predict.


When you know how to design, then it becomes easy:) .
I am trying to find the way, and sooner or later I will learn as much as I need.

We all start as "Tabula rasa/raza" and we have to learn during all our life and you are on the right way...


Tabula rasa (Latin: scraped tablet or clean slate) refers to the epistemological thesis that individual human beings are born with no innate or built-in mental content, in a word, "blank", and that their entire resource of knowledge is built up gradually from their experiences and sensory perceptions of the outside world.http://en.wikipedia.org/wiki/Tabula_rasa

...to get more knowledge


"Whatever you cannot understand, you cannot possess."

and to understand


Actually liquid overfeed system is not my area of work but for my curiosity I have to know more than I know now.

Agree, but I think you must ask more direct questions (the area is too complex to explain all briefly;) ) and we can try to give the best possible answer or suggestion;) as stated below...


Please feel free to post some other questions if you want to. I will try to answer them as time permits.

Best regards, Josip :)

US Iceman
06-05-2007, 06:17 PM
We all start as "Tabula rasa/raza" and we have to learn during all our life and you are on the right way...

http://www.refrigeration-engineer.com/forums/images/misc/quotes/quot-top-left.gifQuote:http://www.refrigeration-engineer.com/forums/images/misc/quotes/quot-top-right.gifhttp://www.refrigeration-engineer.com/forums/images/misc/quotes/quot-by-left.gifOriginally Posted by: http://en.wikipedia.org/wiki/Tabula_rasa http://www.refrigeration-engineer.com/forums/images/misc/quotes/quot-by-right.gifhttp://www.refrigeration-engineer.com/forums/images/misc/quotes/quot-top-right-10.gifTabula rasa (Latin: scraped tablet or clean slate) refers to the epistemological thesis that individual human beings are born with no innate or built-in mental content, in a word, "blank", and that their entire resource of knowledge is built up gradually from their experiences and sensory perceptions of the outside world.http://en.wikipedia.org/wiki/Tabula_rasa http://www.refrigeration-engineer.com/forums/images/misc/quotes/quot-bot-left.gifhttp://www.refrigeration-engineer.com/forums/images/misc/quotes/quot-bot-right.gif


Now there are some interesting philosophical thoughts to consider. I think the above is true, but also present we are the sum of all of those who came before us.

Look at muscle memory. After your body repeats something for so many times your body adapts and this becomes reflex. Action without thought.

Before we know it we will be discussing the Tao of refrigeration...:D

lana
07-05-2007, 05:49 AM
Dear Josip,

Many thanks for your kind guidance.
Actually I am doing exactly as you mentioned : reading and getting some experience in the industrial field.

I am sure I will do my best about reading but not so sure about the experience.

I think I will know more about this with your and other experts help.
This is the beauty of this site, many people willing to help unconditionally.

I am reading and tiding up my confused brain:p , after that I will ask more.

God bless
Cheers

The MG Pony
08-05-2007, 08:32 PM
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
11-09-2007, 05:17 AM
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

Elliza
11-09-2007, 05:24 AM
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
11-09-2007, 07:14 PM
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.com/forums/member.php?u=6688

Best regards, Josip :)

Josip
11-09-2007, 09:37 PM
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:confused:

http://www.es-refrigerants.com/products/w/id/3/t/refrigerants/default.asp

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

Best regards, Josip :)

John Hunter
02-10-2007, 02:28 AM
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
02-10-2007, 02:41 AM
http://i68.photobucket.com/albums/i25/BigJon3475/copyofrefrigerationvi1.jpg

http://hvac-talk.com/vbb/showthread.php?t=121662&highlight=Liquid+overfeed+system

Maybe of some use may not.

John Hunter
02-10-2007, 02:54 AM
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
04-10-2007, 07:41 AM
Hi BigJon,

Nice schematic.
Thanks a lot.

Cheers

lana
04-10-2007, 08:06 AM
Hi everybody,

I have done my homework:D.

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
04-10-2007, 10:05 PM
Hi, lana :)


Hi everybody,

I have done my homework:D.

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
05-10-2007, 09:05 PM
Why you want to reduce ammonia? it smells but you know you have a leak r22 just kills you!!

Josip
05-10-2007, 09:16 PM
Hi, HallsEngineer :)


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

Why do you think I want to use R22:confused: (BTW I hate *****s) and I know all of them are silent killers:mad:

Best regards, Josip :)

lana
06-10-2007, 08:34 AM
Hi Josip,

Many thanks for your kind remarks.

As you know I am an apprentice in NH3;), and I would welcome any suggestion.
Liquid overfeed is a very interesting engineering work and as I thought before it is not very complicated as long as one understands the working principles of control valves (IMO).

Thanks again
Cheers

Josip
06-10-2007, 10:19 AM
Hi, lana :)


Hi Josip,

Many thanks for your kind remarks.

As you know I am an apprentice in NH3;), and I would welcome any suggestion.
Liquid overfeed is a very interesting engineering work and as I thought before it is not very complicated as long as one understands the working principles of control valves (IMO).

Thanks again
Cheers


I would not dare to call you "apprentice" (not even in NH3 field) because you did excellent "homework".

My remarks were only added just to underline something what can be forgotten (safety) due to lowering the price for complete plant (requested by owner;)) and usually that is related to safety.

An overall COP will be lower and installation price higher when using indirect cooling (to keep all NH3 within engine room), but it is more safe. Furthermore it is better for maintenance ...no ammonia leaks-no sensors, no oil in the system....etc.

My idea/suggestion to designers is to design NH3 plants very similar to nuclear plants (to keep dangerous matter in "core-engine room" and freezing tunnels i.e. low temp rooms next to "core-engine room" with easy access via technical corridor. For other facilities with higher temperatures it is quite acceptable to use indirect cooling systems..

Ammonia and water (glycols,brines) are "enemies" but working together in indirect cooling systems they can do a tremendous work and we have to utilize that;)

All our talks, here on RE forums, are to spread good things and ideas all around the world and engineers in any field are entitled to do that in the best possible way they can...

Hope agree with me;)

Best regards, Josip :)

lana
07-10-2007, 09:52 AM
Dear Josip,

I could not agree with you more.;)

Maybe you remember me saying "ammonia is dangerous", but when I studied the system and all the safety precautions then I realized it is safe like other refrigerants.

There you go, I joined the club!:D

Best regards,

LANA

US Iceman
07-10-2007, 08:56 PM
All our talks, here on RE forums, are to spread good things and ideas all around the world and engineers in any field are entitled to do that in the best possible way they can...


Safety first, then good operation, then cost...

Those are my priorities.;)

Refrigerants are as safe as the person working on the system. There are no SAFE refrigerants IMHO.

Lana, I suspect you have a new appreciation for industrial refrigeration after your research on liquid overfeed systems. I know this was one of the most interesting topics I have learned.:cool:

lana
10-10-2007, 06:43 PM
Lana, I suspect you have a new appreciation for industrial refrigeration after your research on liquid overfeed systems. I know this was one of the most interesting topics I have learned.:cool:

Hi US Iceman,

As always you are completely right. It is a nice piece of engineering work.;)

Cheers

amirjhanem
14-11-2007, 01:45 PM
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
20-12-2007, 10:26 PM
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

aansari
02-03-2008, 04:04 AM
Hallo to everybody:

There is an artical about the subject titled "Back to the Basics: What is the Right Liquid Feed Method for Your System? " puplished on IIAR, 2005, and written by Alan Simchick of Refrigeracion y Equipos, S.A. Mexico. I can emial it for you Lana if you send me your email. Of course US iceman got it.

Samarjit Sen
02-03-2008, 07:00 AM
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
03-03-2008, 11:54 AM
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
03-03-2008, 02:16 PM
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 (http://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.