Liquid Overfeed Systems

[US Iceman]

Hi Nico,

Thanks for posting the drawing on the sump details.

Do you work for a contractor, manufacturer, ???

What type of liquid feed control valve are you using to maintain a constant liquid level in the vessel?

[Tycho]

This detail will be more clear I guess.

Ah, thanks Nico, that was the part I was unsure about

In the previous drawings it seemed like you fed the pumps from the bottom of the dropleg

as you see in my drawing, we take it out on the side, and the bottom of the vortexbreaker has a triangular opening cut into it, allowing oil to drain to the bottom of the dropleg if it happens to enter into the vortexbreaker...


The votexbreaker you use, is it just a "cross" of flatsteel welded across the top of the suction line?

cant say other that different solutions same result

tho I cant say other than your solution looks as good as any, I'm stuck in my ways and I'm gonna do it [Sings]Myyyyy waaaaaaaaaaaay[/sings] :d

[Tycho]

Hi Nico,

Thanks for posting the drawing on the sump details.

Do you work for a contractor, manufacturer, ???

What type of liquid feed control valve are you using to maintain a constant liquid level in the vessel?

wouldnt a system be in a somewhat equilibrium, depending on how many "consumers" are in use, in regards to the liquid level in the LP vessel? less consumers = higher level and all.

When I calculate the ***** charge I go by rule of thumb 1 vertical freezer = 5 x 57 Kg (5 x 125 pounds) or 5 bottles of *****.
a normal cargohold on a ship is approx 2-5 bottles


Usually we charge from 800 Kg (17681 pound) tanks on a new system, and as it goes, I'll just open the consumers one by one till I loose pump pressure.

when I loose pump pressure I'll wait to open the next consumer till I have pump pressure again, then rinse and repeat till you have pump pressure with all consumers running.

Of course you gotta keep an eye out so you dont charge more than the capacity of the LP reciever/tank... I never charge more that 80% of the LP reciever volume, it's the law, and no way no how anm I going to be struck down by some insurance company for either destroying a ship, or wrecking a compressor

[US Iceman]

Hi Tycho,

wouldn't a system be in a somewhat equilibrium, depending on how many "consumers" are in use, in regards to the liquid level in the LP vessel? less consumers = higher level and all.

Yep, if the system is something similar to a critically charged system, which may be what you are describing.

On some systems there might be a need to control how much liquid enters the vessel, which is how I see most of the liquid overfeed systems (except those designed for a critical charge).

I have seen some level controls using a simple float switch controlling a solenoid. Others might use a capacitance probe and a modulating liquid feed valve.

I was wanting to see what type Nico used.

I never charge more that 80% of the LP receiver volume...

Is this when the system is being commissioned? Hopefully, not 80% full when operating at full load.

[Nico]

As a one man company I work for several big contractors and manufacturers,as well asfor larger users. I (try to) help with design / commisioning / training and trouble shooting. Always traveling. Lots of fun!

The level control of the separator depends on the country (regulations), the system and the budget.

When there are lots of small clients, than you can work with a simple level switch, solenoid valve and regulator valve from a liquid receiver.
If you have an analog level sensor, you can use the same valves and program a proportional pulse pause regulator or -if you have the monney- a regulator valve. I know that the Danfoss SV float regulator with PMFL valve works perfect for decades.
A high pressure float valve gives you the lowest NH3 charge (I like that), but most clients want to see a good level in a large Ammonia vessel (Middle East and Africa). Your separator will be exspensive (large) with a HP float valve, but you don't need a liquid receiver.

[US Iceman]

Your separator will be expensive (large) with a HP float valve, but you don't need a liquid receiver.

I have done this on several projects and really like it. If the float valve is sized properly you can allow the compressor discharge pressure to decrease to really low pressures (if everything else is sized correctly).

Works great!

[Tycho]

Hi Tycho,

Is this when the system is being commissioned? Hopefully, not 80% full when operating at full load.

Yes, on commisioning, and 80% with all the consumers defrosted

-I know that the Danfoss SV float regulator with PMFL valve works perfect for decades.

on all our plants older than 5 years we used the danfoss SV-1 HP float with a pilotreciever with about 40 liter capacity, worked like a charm

we still use the sam pilotreciever, but are now using danfoss AKS level transmitters... lots of trouble with them in the beginning, with them failing after a short time and so such... but with feedback from all the users danfoss has weeded out most of the problems and we now use this solution up against either AKV valves or PM valves.

[Nico]

Have not seen the AKS 41(?) yet.
Do you use the EKC 347 as an controller, or direct to the PLC?
What do you use as control valve?

I have used the RTK NI1321 a lot. Problem with this sensor is that they are density sensitive. If the evaporating temperature changes, than you get an offset.
We always controll through the PLC. With one click you program a controller, so why install others?
For regulator valves we are often directed by the client's standard; Samson, Worchester etc. We use RTK Kornwestheimer as our "standard".

[US Iceman]

Hi Tycho,

Yes, on commissioning, and 80% with all the consumers defrosted

OK, I'm assuming that when the vessel is 80% full the load is is very small. If the vessel is 80% full, I would think this would limit how much compressor capacity you could have ON during this time.

The separation space in the vessel would be very small. I'm also assuming you have really good controls to limit how fast the users can be activated and how fast the compressor(s) load up to prevent liquid slugging.

I suppose the reason I raised the question in the first place is... Someone who is not familiar with the particular requirements you normally see may assume this is standard practice for any overfeed system.

[Josip]

Hi,

on attached drawing you can see the old fashioned way of level control, pump protection and compressor protection if customer does not like to spend to much money

AMMONIA SEPARATOR.pdf

All is working Ok.

Yes, one pump is stand-by.

Best regards,

Josip

[US Iceman]

Hi Josip,

Are those strainers/filters in the suction line to the pumps?

[Josip]

Hi, US Iceman

Hi Josip,

Are those strainers/filters in the suction line to the pumps?

Yes, and mostly on new plants during start up, we have to clean them often. Also they are bigger then the pump inlet connection. Pumps are Hermetic CAM 2/3 with Qmax and Qmin orifice.

That filter we install as the lowest part of the pump inlet pipe.

See you are , but we have to protect pumps (on ammonia plants with dirty black steel separators and pipes) on some way, but that is another long story .

Best regards,

Josip

[US Iceman]

Hi Josip,

What you say makes a lot of sense. The carbon steel pipe can be dirty with the scale that comes in the pipe.

Do you normally find a lot of weld slag in these strainers?

Do you use weld rings (not sure what you might call them)? They fit inside the end of the pipe to help with alignment and help to prevent weld slag from blowing into the pipe.

Have you tried pickled pipe before? This is very clean, but must be protected until the insulation and paint are applied to the pipe.

Here in the US we normally allow the strainers before the solenoid valves to catch this junk.

The strainers in the pump suction line add pressure drop which decreases the net positive suction head on the pumps. This can cause cavitation.

You are correct. This could be a long story.

[Andy]

Hi Josip,

What you say makes a lot of sense. The carbon steel pipe can be dirty with the scale that comes in the pipe.

Do you normally find a lot of weld slag in these strainers?

Do you use weld rings (not sure what you might call them)? They fit inside the end of the pipe to help with alignment and help to prevent weld slag from blowing into the pipe.

Have you tried pickled pipe before? This is very clean, but must be protected until the insulation and paint are applied to the pipe.

Here in the US we normally allow the strainers before the solenoid valves to catch this junk.

The strainers in the pump suction line add pressure drop which decreases the net positive suction head on the pumps. This can cause cavitation.

You are correct. This could be a long story.

I have always seen a strainer in the pump suction line, pumps can be quite expensive and systems can be dirty
Probably a good idea to remove the strainer after a year or so use or fit a large mesh nut and bolt catcher at this point.
Small mesh strainers can become oil traps on LT systems, best to avoid smaller mesh strainers on these types of applications.

Backing rings were fitted in the past, but now we are more advanced
TIG welded roots are the norm with the filler and cap in stick

Kind Regards Andy

[US Iceman]

Hi Andy,

I have always seen a strainer in the pump suction line, pumps can be quite expensive and systems can be dirty
Probably a good idea to remove the strainer after a year or so use or fit a large mesh nut and bolt catcher at this point.
Small mesh strainers can become oil traps on LT systems, best to avoid smaller mesh strainers on these types of applications.

Absolutely no doubt the systems can be quite dirty.

What size mesh screens do you use for low temp and higher temp. applications?

I'm not disagreeing with the use of strainer, just saying the pressure drop should be accounted for in the pump NPSH calculations. The pressure drop of this device could add a meter or more of head required for the pump suction. (just a guess, but it's probably something like this)

Backing rings were fitted in the past, but now we are more advanced
TIG welded roots are the norm with the filler and cap in stick

Are you saying I'm old fashioned?

I would prefer exactly what you are doing Andy. This makes a much better weld. I always suspected the backing rings could collect junk under the collar and create a potential corrosion site from inside. I also think the weld rings are harder to read in an x-ray.

Do you use consumable inserts for the first pass TIG weld? Or, just simply fit them up by hand? Or, use a pipe alignment fixture.

[Andy]

Hi Andy,



Absolutely no doubt the systems can be quite dirty.

What size mesh screens do you use for low temp and higher temp. applications?

I'm not disagreeing with the use of strainer, just saying the pressure drop should be accounted for in the pump NPSH calculations. The pressure drop of this device could add a meter or more of head required for the pump suction. (just a guess, but it's probably something like this)



Are you saying I'm old fashioned?

I would prefer exactly what you are doing Andy. This makes a much better weld. I always suspected the backing rings could collect junk under the collar and create a potential corrosion site from inside. I also think the weld rings are harder to read in an x-ray.

Do you use consumable inserts for the first pass TIG weld? Or, just simply fit them up by hand? Or, use a pipe alignment fixture.

We use filters in the range 40 to 100 micons range, quite fine really I favour big bore long drop legs, put the surge drum on one floor and the pumps on the floor below with a straight line down into the pump (vortex breaker at the top of the pipe, ball valve at the pump, all say 6" on a 2 1/2" or 3" inlet pump.

TIG root is not used with a ring. The pipe is champhered, with the slope creating a vee for the weld to be built up in. The pipe or fitting is gapped by 2 to 3mm all the way round, to allow a weld bead to form evenly on the inside of the weld, much like a mini cap on the inside.

Kind Regards Andy

[Josip]

Hi, US Iceman

Not to much of weld slag (nowdays mostly use TIG for root weld) but lot of particles remain after grinding to make a cone for weld. this you have even with sand or CO2 blasted pipes.

I have to admit about weld rings and backing rings I do not know, because, never used them (please, post a link or some picture ). We used sometimes alignment tool for pipes (in case of X-ray) but mostly doing that by hands of experienced pipe fitters , faster and cheaper.

Yes, installing filter in front of the pump will reduce NPSP but filters are of very big size and pressure loss is very small.

I think Andy, did explain almost all but in much better english than me , thanks Andy

We use filters in the range 40 to 100 micons range, quite fine really I favour big bore long drop legs, put the surge drum on one floor and the pumps on the floor below with a straight line down into the pump (vortex breaker at the top of the pipe, ball valve at the pump, all say 6" on a 2 1/2" or 3" inlet pump.

TIG root is not used with a ring. The pipe is champhered, with the slope creating a vee for the weld to be built up in. The pipe or fitting is gapped by 2 to 3mm all the way round, to allow a weld bead to form evenly on the inside of the weld, much like a mini cap on the inside.

best regards,

Josip

[US Iceman]

Andy,

TIG root is not used with a ring

Depnding on the customers pipe welding specification it may be called for. Here are some links to suppliers of these. We used these when the specifications were very stringent in chemical plants.

They are ordered in the same material as the pipe, with the inserts being consumed during the fusing process. They make a really nice joint, which sometimes is hard to tell the joint from the main pipe.

http://www.robvon.com/html/proc_consum.html

http://www.robvon.com/html/consumables.html

Main page:
http://www.robvon.com/
Also see their link for backing rings. This is listed on the left hand side of the webpage.

http://www.imperialweldring.com/new/consumable.html

Josip,

...you have even with sand or CO2 blasted pipes.

I have used sand blasted pipe before but never CO2. Does this work well? I'm assuming they use dry ice for the blasting right?

[Josip]

Hi, US Iceman

thanks for links, very good things (kind of VFD for pipe fitters and welders

http://www.cryogenesis.co.uk/

Yes they use dry ice and complete work is very clean. I did not use it but got some info about from my friends.

Best regards,

Josip

[Tycho]

Have not seen the AKS 41(?) yet.
Do you use the EKC 347 as an controller, or direct to the PLC?
What do you use as control valve?

I have used the RTK NI1321 a lot. Problem with this sensor is that they are density sensitive. If the evaporating temperature changes, than you get an offset.
We always controll through the PLC. With one click you program a controller, so why install others?
For regulator valves we are often directed by the client's standard; Samson, Worchester etc. We use RTK Kornwestheimer as our "standard".

We make our own control system with PLC and the AKS is wired directly to the PLC, with readouts and calibration made possible from the plc display.

we have also retrofitted older systems with an AKS working with a EKC 347... Works fine with either...

Had some problems with the EKC tho, not sure what was done, but the electrician doing the wiring also powered up the system before I got there, and managed to burn out the contacts on the EKC, so I had to use the alarm contact for either hi or lo level, cant remember... the customer is non the wiser and the system works

We use mainly Danfoss valves, ranging from ERV to PM (depending on system size)

[Tycho]

Hi Tycho,



OK, I'm assuming that when the vessel is 80% full the load is is very small. If the vessel is 80% full, I would think this would limit how much compressor capacity you could have ON during this time.

The separation space in the vessel would be very small. I'm also assuming you have really good controls to limit how fast the users can be activated and how fast the compressor(s) load up to prevent liquid slugging.

I suppose the reason I raised the question in the first place is... Someone who is not familiar with the particular requirements you normally see may assume this is standard practice for any overfeed system.

To put it in other words, we design our plants so that we can fit all the liquid in the LP tank, incase the consumers need major service.

Mostly, getting all the liquid back to the tank is done by service personel from us or whatever other company is available at the time.

it is also safe for the onboard engineer to do this, close the pump inlets, shut of the pumps, have one compressor running in auto and our load controll system takes care of the rest.

The 80% Charge I said is also more like a rule of thumb

Lets say I have a system with 20 plate freezers, but the tank can only hold a charge for 18 of those (18 if the tank is topped off), I will then fill enough to run 15 freezers at one time, inform the ship owner and chief engineer that "your tank can only hold enough charge to run 15 freezers at a time yadda yadda yadda, live with it"

ofcourse there are some ships running with a 120% charge, cause the chief engineers are ordered by the ship owner to charge more *****, to get more consumers running...

But when we charge, we charge just so that we can fill the tank to the brim without getting liquid back to the compressors.

if that made any sense

[Tycho]

We use filters in the range 40 to 100 micons range, quite fine really I favour big bore long drop legs, put the surge drum on one floor and the pumps on the floor below with a straight line down into the pump (vortex breaker at the top of the pipe, ball valve at the pump, all say 6" on a 2 1/2" or 3" inlet pump.


Kind Regards Andy

I always put ladies nylon stockings inside the pump outlet/ice filter (our pumps can handle the dirt, so we only have outlet filters brag brag brag ), on new plants, and re built plants.

I supply the onboard engineer with some spares so he can change them if there is to much dirt, or if there isnt, I'll change them the next time they are in, I run the plant with the stockings for a minimum of a month, usually two months.

The reason for this is that you can run the plant with a bigger mesh filter afterwards.

but it's always embarrasing when you go to the store and stock up on nylon stockings like another perv

This one time I accidently bought ancle high when I needed thigh high stockings, and I had to go back to get the ones I needed... same very very handsome looking girl operating the register when I got there with my second armful of stockings.

Her: "Oh... I see you really like those"
(I turned lobster red in less than a second.. it was like *POOOF* I'm red)
Me: "oh.. hehe no, ummm filter... mesh and yeah, they... I use them... they are fine meshed... umm as a filter"

We use condoms to cover up the safety valve outlet when checking for small leaks in the safety valve, and one time we had a poor guy have to go to the store to get nylon stockings, condoms and dishwasher soap...

I'm just glad I wasnt that guy

oh, this should have been in the chit chat section, buy hey

[US Iceman]

if that made any sense

Perfectly...

BTW, do you have a preference on the color of the stockings you buy?....for filters that is.

I have used and recommend the condoms over the relief valve vent lines also. It sure does get a lot of comments when one valve is leaking.

[corineramer]

guys do you know where i can buy equipments for liquid overfeed system online that has a brochure... nid help pls...

[abdulazman]

Hi guys,

Anybody got any ideas or prices or website for Ebara Direct Fire CHILLERS-RAD-G028.

Could use any help.

[slsammoniaman]

One location to find information on recirculation packages is to check out the Evapco website at evapco.com

[US Iceman]

Hi corineramer,

What type of equipment are you looking for?

Pumps, evaporators, valves, pressure vessels, ???

If you can provide some more details, we can provide more information to help you.

[corineramer]

well US Iceman im just a student... we have a plate that we need to finish.. we're to design one utility of an ice cream plant and we picked the refrigeration system and we used the liquid overfeed system our proffesor told us to use that system... we dont have any idea where we could find all the equips that we need the eveporator, condenser,separator, ammonia pumps, etc.. we have a minimum capacity of 50 TOR... can u help me?? is there a site where they offer all of the equips?? we only need the brochure or specs.. thnx for replying we badly need help.. also 1 of our problems is we havnt been to an ice cream manufacturing plant we dont hav any idea what the machines look like inside the plant how they are arranged, that sort of thing... we need it for our plant lay-out...

[Josip]

Hi, corineramer

follow this link and enjoy

http://www.refrigeration-engineer.co...7621#post47621

Best regards, Josip

[US Iceman]

Here is a link for evaporative condensers:
http://www.evapco.com/media/pdf/173B...Con-EngMan.pdf

Here is a link for liquid overfeed packages (vessel & pumps)
http://www.evapco.com/media/pdf/asme-recircular.pdf

Here is a link for the celing hung evaporators for the holding freezers:
http://www.evapco.com/media/pdf/nt-series.pdf


Here is a link to some ice cream production machines:
http://www.tetra-pak.com/ Look under the links for "Production".

Here is a link to some compressor information:
http://docnav.grasso-global.com/DocN...e/Screws_e.htm

Here is a link for control valves + other good information:
http://www.danfoss.com/North_America...+Selection.htm

That should keep you busy for awhile.

[Josip]

Hi,

That should keep you busy for awhile.

Maybe for whole life like us

Best regards, Josip

[US Iceman]

Hi Josip,

I've been doing this for a long time and I still learn something new everyday. I bet you do too.

The next big project to figure out is process AC systems, something like your project you are working on now. I'm still going to school after all this time.

[corineramer]

hi josip and us iceman,

thnx

[corineramer]

hi josip and us iceman,

thnx for the help... i hav seen the topics for the ice cream plant and im im currently

[corineramer]

hi josip and us iceman,

thnx for the help... i hav seen the topics for the ice cream plant and im currently checking it out now... we hav a problem in finding the exit temperature of our refrigerant which is ammonia.. the temperature entering the evaporator is -30C and our only data is the temp of the ice cream which is the temp entering is 4degC and exits at -5degC... by the way this is the freezing of the ice cream which is a closed system... correct me if im wrong but we're doing the mass balance and energy balance.. is this correct? are we in the right track hope u reply because we're running out of time... thank you so much sir or sirs...

[US Iceman]

Hi corineramer,

the temperature entering the evaporator is -30C and our only data is the temp of the ice cream which is the temp entering is 4degC and exits at -5degC... by the way this is the freezing of the ice cream which is a closed system...

If the liquid ammonia is being pumped into the evaporator at -30C, it also exits the evaporator at -30C on an overfed system.

Therefore, if your ice cream is entering at 4C and leaving at -5C, that is your heat load for the mass flow you have.

To do the energy balance, the heat load divided by the latent heat of ammonia at -30C will provide the vapor mass flow out of the evaporator. You have to be careful, as the ammonia liquid mass flow will be even higher.

The whole purpose of an overfeed system is to pump in more liquid than will boil off.

[corineramer]

hi us iceman,

i thought that there would be a temp change in the ammonia because of the heat transfer through the evaporator... so, there would be not temp change in the ammonia... thnx for the help.. just post here for my progress and questions.. tnx again

[US Iceman]

The refrigerant is boiling at -30C. As long as the refrigerant pump is supplying sufficient liquid into the evaporator, the refrigerant exits the evaporator at -30C.

If the pump is not selected properly, or the hand expansion valve is too far closed, you can get some superheating of the gas leaving the coil. With superheat, you would have a temperature change.

The boiling process is all latent heat, so the temperature does not change.

Good luck on the school project.

[corineramer]

hi us iceman,

now its getting clear... our prof told us that there would be no temp change but the pressure will be higher so we need a back pressure valve before the vessel i think to minimize the pressure until it equals the temp of our vessel, right? then for the compressor, the suction pressure will be the pressure at the vessel and the discharge will be depending on the ambient condition in the condenser... pls correct me if im wrong... wow! it feels good now because im beginning to understand this system... the next will be the computations... im having fun in this design... hehehe

[US Iceman]

...but the pressure will be higher so we need a back pressure valve before the vessel i think to minimize the pressure until it equals the temp of our vessel,

I'm not sure why he thinks you need a back-pressure regulating valve. These are used to keep the pressure higher in the evaporator. BY increasing the evaporator pressure with this valve, you increase the saturated evaporating temperature. This would reduce the evaporator capacity.

Unless, there is something I don't know about in your system design.

Without this valve, the evaporating pressure would be equal to the compressor suction pressure plus the suction line pressure drop. If your ice cream freezer is the only evaporator on the system, the -30C evaporating temperature will require a slightly lower compressor suction temperature.

The suction line pressure loss is equal to a specific value for the equivalent temperature loss.

Adding a back-pressure valve at -30C increases the suction line pressure loss and also decreases the compressor capacity.

[corineramer]

hi us iceman,

now im getting confused... this is his explanation, when the ammonia leaves the evaporator there will be a slight or big increase in the ammonia pressure I think...then he said that the pressure of the refrigerant should be equal to the vessel thats why we nid this valve... he said that the compressor suction pressure should be equal to the saturation pressure at -30C... By the way he said that this valve decreases the pressure of the ammonia so that it will be equal to the pressuer of the vessel... what does a back-pressure valve do? is this correct? i have another question he added that we can use 1 condenser in our freezing, hardening and storage... he said that when the ammonia has been compressed by the 3 compressors we can join them in 1 line to the condenser... is this possible? then im thinking on how to distribute the ammonia that exits from the condenser... im really confused... can I send u the details of our design to your email? if its ok with you.. and have your comment on it.. thank you for the time..

[US Iceman]

Hi corineramer,

Let's see if we can clear this up.

when the ammonia leaves the evaporator there will be a slight or big increase in the ammonia pressure I think

No. When the liquid is pumped into the hand expansion valve, the pressure is reduced to the evaporating pressure (the saturation pressure of the ammonia at -30C). The pressure does not rise. In fact, the pressure decreases some due to the pressure loss of the refrigerant flowing through the evaporator circuits.

then he said that the pressure of the refrigerant should be equal to the vessel thats why we need this valve... he said that the compressor suction pressure should be equal to the saturation pressure at -30C

If we neglect all pressure losses, the evaporator pressure is the same as the vessel pressure is the same as the compressor suction pressure.

By the way he said that this valve decreases the pressure of the ammonia so that it will be equal to the pressure of the vessel...

My guess is, he is making a common mistake on liquid overfeed systems. The refrigerant pump provides the pressure to move the liquid out to the evaporators. When the liquid flows through the hand expansion valves, the liquid pressure is reduced down to the evaporating pressure on the outlet of the hand expansion valve.

Once the liquid is in the evaporator, it is also at the evaporating pressure equal to -30C. The pump pressure is all gone. All of the gas and liquid exist at the evaporating/suction pressure (Again, I'm assuming we have neglected the pressure losses due to flow.).

The refrigerant flashes in the evaporator, not after the back-pressure valve.

[/quote]
what does a back-pressure valve do?
[/quote]

A back-pressure regulating (BPR) valve controls the pressure of the refrigerant upstream of the valve. If the BPR valve is set for a pressure higher than the evaporator pressure, the liquid will not boil at -30C. Adding BPR's to a liquid overfeed system creates a lot of additional problems that must be solved.

If you only have one evaporating temperature on your system (-30C) you do not need a BPR to make the system work.

he said that when the ammonia has been compressed by the 3 compressors we can join them in 1 line to the condenser

That's OK. This is done all of the time. You must make sure the piping on the condenser is absolutely correct to allow gravity drainage. Condenser piping is probably one of the most mis-understood areas of indutrial refrigeration systems.

The outlets of each condenser coil (most larger condensers have at least two outlet connections) must be trapped at the bottom. The equalizing line from the receiver to the condenser inlets must also be large enough to allow the liquid to drain properly.

[Josip]

Hi,

seems to me that the teacher is more confused then students

Best regards, Josip

[US Iceman]

HI Josip,

That teacher would not be the first either.

[NH3LVR]

I have not been on in a while. Seems Summer breakdowns have had us running. North Star Icemakers (My favorite). Compressor seals, etc.
So lets open a can of worms on Hand Expansion Valves used with Liquid Recirculation.
Just once I have installed a AFR3 Flow Control from Refrigeration Specialties. In all other cases we have used H.E. Valves.
I believe you can calculate the orifice size of any H.E. Valve from the Manufacturer's literature and from then calculate the approximate opening turns to start with, although I have never done it.
The proper method of adjusting after startup is to open the H.E. Valves until Evap performance starts ti fall off. (Using Air Temp measurements across a coil for instance). Once the coil is overfed ("Brining") the performance starts to fall off.
Of course if the Liquid pump loses pressure as the valves are opened you need to start over.
Last Summer I started up a Medium Temp warehouse with a dozen or so NH3 Evaps. It would have taken several days to go through the procedure, especially as product was being moved in as we were starting up.
So we make an educated guess as to the settings. That is made easier by the fact that this customer does not insulate the control valves, and that they are installed on the roof. You can see the effects of the liquid return and adjust accordingly.
Liquid recirculation is certainly more tolerant of underfeed and overfeed than other methods but I suspect many of the systems I work on are underfeeding.
Does anyone have a better adjustment system, or is this way most of you do it?

[Andy]

I have not been on in a while. Seems Summer breakdowns have had us running. North Star Icemakers (My favorite). Compressor seals, etc.
So lets open a can of worms on Hand Expansion Valves used with Liquid Recirculation.
Just once I have installed a AFR3 Flow Control from Refrigeration Specialties. In all other cases we have used H.E. Valves.
I believe you can calculate the orifice size of any H.E. Valve from the Manufacturer's literature and from then calculate the approximate opening turns to start with, although I have never done it.
The proper method of adjusting after startup is to open the H.E. Valves until Evap performance starts ti fall off. (Using Air Temp measurements across a coil for instance). Once the coil is overfed ("Brining") the performance starts to fall off.
Of course if the Liquid pump loses pressure as the valves are opened you need to start over.
Last Summer I started up a Medium Temp warehouse with a dozen or so NH3 Evaps. It would have taken several days to go through the procedure, especially as product was being moved in as we were starting up.
So we make an educated guess as to the settings. That is made easier by the fact that this customer does not insulate the control valves, and that they are installed on the roof. You can see the effects of the liquid return and adjust accordingly.
Liquid recirculation is certainly more tolerant of underfeed and overfeed than other methods but I suspect many of the systems I work on are underfeeding.
Does anyone have a better adjustment system, or is this way most of you do it?

I suppose the way I go about it would be. Check my selection on the Dircal software, it gives valve openings.
Setthe valves up something less than that. Observe the frosting on the evaporator, should be less than fully fed. Keep opening the valves until the evaps are all frosted, all just fully flooded and all the same. Then give the valves another 1/2 turn or so open. I would then check the air on and offs on the central monitoring system, they should be all similar, the poor ones I would then look at more closely and adjust to get the best performance. To my mind you should have no big drop off when overfeeding, if you do you are just wasting pump power at the expense of evaporator and system performance.

Kind Regards Andy

[US Iceman]

HI NH3LVR,

Welcome back.

I believe you can calculate the orifice size of any H.E. Valve from the Manufacturer's literature and from then calculate the approximate opening turns to start with,...

Yes, that is correct. A little number crunching will get you there.

Does anyone have a better adjustment system,...

I'm not saying this is better, it's just the way I would go about it.

The first thing to do is to check the refrigerant pump pressures and operation to make sure it is dialed in properly. If a small compressor has been started to pull down the suction pressure in the vessel, the pump will start to cool off. As the suction pressure approaches the normal operating condition, the pump should be very close to it's operating temperature.

It is a lot easier to do a cold start-up on a liquid overfeed system than a hot start-up.

The evaporators that are the farthest away from the pumps, or the ones that are at the highest elevation are the coils that need the most liquid pressure to HE valves.

I would start at one of these coils with the adjustment of the HE valves. Shut off the fans on the coil and begin to crack open the HE valve. As the frost pattern begins to approach the suction outlet header, you are getting fairly close. Turn the fans on and move to the next coil.

Continue to work your way back to the pumps.

Once you get this far, you can go back and check the air temperature drops across the coil. You can determine the exact number (TD) you should be trying to get. By the time you get ready to start measuring air TD's, the system is starting to stabilize.

I certainly don't think this question is, or will be a can of worms, but it is a very good question. I think the biggest problem is the HE valves are normally adjusted too far open, causing the coils to overfeed and nuisance problems with the pumps.

BTW, we have another thread going under English Language... . You should post this saying " a can or worms" in there.

[corineramer]

hi us iceman,

our equips are not complete do you know a site where i can have brochures of liquid receivers?? tnx.. BTW, the hand expansion valve is located after the pump before the evaporator, right?

[US Iceman]

If you go back to the Evapco web site, they will have a complete brochure for various pressure vessels. You should be able to find something in there.

The liquid feed valve train for the coil usually consists of these items:

1. Service valve
2. solenoid valve with close-coupled strainer
3. Hand expansion valve
4. Check valve (required only if hot gas defrost is being used)
5. Service valve

Having a service valve on the beginning and the end of the valve train allows you to service any of the valves in that valve group, without pumping down the evaporator coil.

Here is a link for some information about one type of refrigerant pump. It shows some of the typical installation details. These details vary somewhat if you use a hermetic pump.

[corineramer]

hi us iceman,

wat link are you referring to? the evapco site or other sites? we're really confused.. we're not that familiar with this system because the cycle that we have studied is the vapor compression cycle... im sorry if our progress is slow... i thought we understand this cycle but not there's a lot of things we need to learn.. also we have 3 evaporators that has 3 different temp we're trying to figure out if we will use one condenser in this 3 evaps or provide them with their own condensers... tnx