Liquid Pump Low Dif

[Krohnie84]

Hello,
I am having some small troubles with a liquid pump that will cut out on a low dif alarm. It will only occur when the vsl lvl gets above 40%. The pressure of the vsl and the pump are constaint but it will cut out at random only when above 40% on the vsl lvl.

Any ideas would be welcome. Thank you.

[NH3LVR]

Welcome to the forum Krohnie84!
We need a few more details. Refrigerant, type of pump, etc. Top or bottom feed coils?
Be aware that a differential pressure sensor can be tricky. I have seen cases where a compressor starting after a defrost can cause cavitation which could trip the differential sensor.

[Krohnie84]

Thank you for your response, the Refrigerant type is R-717 and the liquid pump is an oil less Teikoku pump. I only have the Teikoku on this one vsl all the others are Baldor motors/pumps. The normal running pressure for the Teikoku is 70-75 psi. The dif may depend on the suction pressure at the time but should be between 30-40psi. I will attach two pictures, one of the pump itself and the other of a trending graph showing the pump's pressure and the vessel's level. The yellow line is the level and the green is the pump pressure.

Trending.jpg

Liquid pump.jpg

[charlie n]

The spike in the liquid level is not normal & possibly not actually happening. The situation could be ocuring when make up liquid is introduced to the vessel. (Liquid solenoid opens). If the liquid injection is not entering the vessel properly it may be causing a lot of turbulence causing a false reading at the level transmitter and also causing the pump to loose it's prime & cavitate. Check to see where the liquid makeup comes in. It should not be below the liquid level in the receiver. The best place is into the wet suction return near the receiver inlet.

[Krohnie84]

Thanks Charlie, I checked the vessel and the liquid make up from the High pressure receiver to the med temp vessel feeds at/around the 50% mark.

Theses pumps are relatively new to the system (installed two yrs ago) but only since January of this year has this problem really become a nuisance. Before the pumps were installed the med temp only fed to four hanging evaps. All of them have TXVs on them with no liquid pumps. Two years ago we added another five units (pent houses) with hand expansions.

[RANGER1]

It could also be when liquid makeup closes causing sudden pressure drop & pump cavitation.
Check liquid reciever level has good working level & set liquid makeup to 60-70 % on at high load condition .
Compressors should not load to quickly

[Krohnie84]

@ ranger1-
When the receiver reaches 50% or so it starts to feed the med temp vessel. The liquid passes through a hand expansion that is set and we have checked to make sure that the flow rate has remained the same.

As for the compressors loading up too fast... the controls are set up to load very slowly; as in half hour or more.

[NH3LVR]

@ ranger1-
When the receiver reaches 50% or so it starts to feed the med temp vessel.

I am not quite following. When the receiver reaches 50%, it feeds what?
I think we need a better description of your system.

[Krohnie84]

I am not quite following. When the receiver reaches 50%, it feeds what?
I think we need a better description of your system.

This system has a charge of about 24,000 lbs give or take 500lbs.

I have six compressors.

Two are dedicated to med temp (Dock/cooler areas)

One dedicated to low temp

and three are able to swing between low and med temp.

The four that can run on the low side each have economizers.

I have four condensing units, one high pressure receiver, a vertical med temp vessel (where the issue is located) and a vertical low temp vessel.

As I understand it, the High pressure receiver will only feed into the med temp vessel when the liquid level in the receiver is at 50%. The feeding line has a hand expansion valve to regulate the flow of ammonia going to the med temp vessel. I have never had to mess with it besides a solenoid valve going to our purger.

[NH3LVR]

As I understand it, the High pressure receiver will only feed into the med temp vessel when the liquid level in the receiver is at 50%.

I am a bit more clear now. You have two Low Pressure Receivers, One at low temp and another at Medium Temp. Pumps going out to the coils and wet suctions returning to the LPR's. Standard setup.
What concerns me is what you said about the Med Temp Receiver only filling when the HPR is at 50%. This sounds like a control problem. Usually this is done with a float or electronic level control on the LPR. Check the control system carefully.
Cavitation is most likely the cause of your loss of differential pressure. Some posted a good bit of information on this recently. It may have been Ranger1. Pumps with sufficient head can be very prone to this. Another point to consider is the recirculation rate. If the pumps are allowed to overfeed the coils beyond the available NPSH (Net Positive Suction Head) they will cavitate.
But look at the control system for the LPR first.
That being said sometimes unconventional control systems are used. Sometimes they even work.

[Magoo]

I agree with NH3LVR,
cavitation is the major problem, with sudden pressure changes etc., do the vessels have anti-cavitation plates, and the pumps have the anti-cavitation infeed adaptor, and the nominal 2 + metres NPSH.

[RANGER1]

Krohnie84,
When pump cavitates what happens control wise ie stop after time delay etc .
Does the pump when it is restarted pump straight away?

Usually when level in pump vessel increases it should help pump except if pressure drops suddenly , causing boiling of liquid causing gas bubbles & cavitation .

Another cause of cavitation is if pump has low flow through it , but this is usually prevented with a minimum flow line tee'd off discharge of pump back into wet return line or upper part of vessel .
Basically pump should be able to continue running & pumping even if all room solonoids are closed with rooms down to temp .
The bypass line must be open enough to cope with this situation as well .

How is level guaranteed in med temp vessel , does it then supply low temp vessel?
System sounds critically charged type of set up!

[Krohnie84]

What concerns me is what you said about the Med Temp Receiver only filling when the HPR is at 50%. This sounds like a control problem.

Usually this is done with a float or electronic level control on the LPR. Check the control system carefully.

I will look into the controls further, but if I understood my co-worker.. there is a float control in the HPR and it won't allow flow until it gets to 50%. The more I think about this the more fishy it sounds to me as well.

I agree with NH3LVR,

cavitation is the major problem, with sudden pressure changes etc., do the vessels have anti-cavitation plates, and the pumps have the anti-cavitation infeed adaptor, and the nominal 2 + metres NPSH.

This system was built in 1995 and the med temp vessel was originally a pressure fed system. Not until two years ago is when pumps were finnaly added to the med temp side.

Krohnie84,

When pump cavitates what happens control wise ie stop after time delay etc .
Does the pump when it is restarted pump straight away?

Usually when level in pump vessel increases it should help pump except if pressure drops suddenly , causing boiling of liquid causing gas bubbles & cavitation .

Another cause of cavitation is if pump has low flow through it , but this is usually prevented with a minimum flow line tee'd off discharge of pump back into wet return line or upper part of vessel .
Basically pump should be able to continue running & pumping even if all room solonoids are closed with rooms down to temp .
The bypass line must be open enough to cope with this situation as well .

How is level guaranteed in med temp vessel , does it then supply low temp vessel?
System sounds critically charged type of set up!

When the pumps are restarted the pressures go right back to where they belong. There has only been a few instances where there was a stall before she took off. I could say that the computer controls are restarting the pump about 50-60% of the time and we aren’t seeing an alarm.

There is a bypass line and we have "tweaked" it a little, but I think our information might be backwards. I am going to look into it to see if we have been going the right direction with this.

The Med temp vessel feeds the low temp. This system is 25% med temp 75% low. At this time we believe we might be overcharged but we aren’t really worried about that at this time.

[Segei]

I looked at your graph. Why does this graph show pump pressure(medium pressure vessel) and level in HPR? Probably this is pressure and level in medium pressure vessel. This plant can't be critically charge, because it has liquid pumps. It means that medium pressure vessel should have level control system. In your case is should be control system+solenoid+hand expansion valve. Probably, the reason of mentioned event that expansion valve is open too much. When solenoid is open, liquid goes to medium pressure vessel and a lot of flash gas will be created. When level reach 50%, solenoid will close, but it takes time for compressors to unload. Pressure in medium vessel will go down, level up(see graph) and pump will loose prime. Operating time of this solenoid should be 50-70%. Level differential should be 5-10%.

[Krohnie84]

I looked at your graph. Why does this graph show pump pressure(medium pressure vessel) and level in HPR? Probably this is pressure and level in medium pressure vessel. This plant can't be critically charge, because it has liquid pumps. It means that medium pressure vessel should have level control system. In your case is should be control system+solenoid+hand expansion valve. Probably, the reason of mentioned event that expansion valve is open too much. When solenoid is open, liquid goes to medium pressure vessel and a lot of flash gas will be created. When level reach 50%, solenoid will close, but it takes time for compressors to unload. Pressure in medium vessel will go down, level up(see graph) and pump will loose prime. Operating time of this solenoid should be 50-70%. Level differential should be 5-10%.

The graph I attached shows three things: The yellow line is the Med Temp Vessel liquid level, the Green line is the Liquid pump differential pressure and the light blue line below them shows the suction pressure.

That is the case, there are solenoids, hand expansions and (not verified yet) mechanical floats. The main controller for both my liquid vessels (med and low temp) are Hanson controllers plus some redundant computer controls.

[Segei]

The graph I attached shows three things: The yellow line is the Med Temp Vessel liquid level, the Green line is the Liquid pump differential pressure and the light blue line below them shows the suction pressure.

That is the case, there are solenoids, hand expansions and (not verified yet) mechanical floats. The main controller for both my liquid vessels (med and low temp) are Hanson controllers plus some redundant computer controls.

Where is the level 50%(HPR or MPR)? For level control, you can have or solenoid+HEV or float, but not both of them.

[Krohnie84]

Alright, I would first like to apologize if this was getting confusing. I work with two refrig systems (In the same building). The one with the pump issue has a float control going from the High Pressure Receiver to the med temp vessel. The second system (smaller one) has a solenoid and hand expansion. I got them confused/mixed up.

Another thing I have been going over is the piping diagrams and I found that the vent for each pump is wide open. I also located the return/bleed/recirculation line. I turned it open another half a turn. < I was told that this valve was open all of the way but that was not correct.

[RANGER1]

Krohnie ,
It seems to me plant is critically charged & any excess refrigerant ends up in low temp vessel .
I'd assume liquid reciever is quite small or has thermosyphon oil coolers ?

As Sergei mentioned with unloading , compressors should unload a bit faster than they load with deadband of say 2 psi
Establish where all valves are set & see what happens .
Do you if pump does actually cavitate , or is something else just stopping it .
Is there a particular time it happens everyday ? defrost time or something?

[Krohnie84]

Krohnie ,
It seems to me plant is critically charged & any excess refrigerant ends up in low temp vessel .
I'd assume liquid reciever is quite small or has thermosyphon oil coolers ?

As Sergei mentioned with unloading , compressors should unload a bit faster than they load with deadband of say 2 psi
Establish where all valves are set & see what happens .
Do you if pump does actually cavitate , or is something else just stopping it .
Is there a particular time it happens everyday ? defrost time or something?

Your good, the receiver is quite small. Small enough that it is suspended from the ceiling and we also have thermosyphon cooling for each of the six compressors.

At this time there is only one Med temp compressor running, I will take a look at it's settings and compare them to the other med temp comps that we have.

See, what I keep hearing is that when a pump cavitates that it sounds like there are rocks going through it? I have been right next to the pump with it alarming and I can't tell the difference. I have discussed this with my fellow tech and he and I are thinking that the pump might be stalling? The pressure on the pump is still around 40-50 psi but the dif is too low and the computer alarms.

As for the time of day, I have been trying to figure out what the other causes might be but the way our program was set up is that the defrost times with vary depending on the amount of cooling. I could complain about it more but it would seem only sensible that we should be able to set the times for defrosts every day.

[Segei]

Alright, I would first like to apologize if this was getting confusing. I work with two refrig systems (In the same building). The one with the pump issue has a float control going from the High Pressure Receiver to the med temp vessel. The second system (smaller one) has a solenoid and hand expansion. I got them confused/mixed up.

Another thing I have been going over is the piping diagrams and I found that the vent for each pump is wide open. I also located the return/bleed/recirculation line. I turned it open another half a turn. < I was told that this valve was open all of the way but that was not correct.

I'm still confused about your system. It would be better if you give us simplified drawing of your plant.
Assume that you have float to control level in HPR and nothing to control level in MPR. This is very poor design. Every vessel with the pumps should have level control.
If you have critically charged system(float for HPR), level in MPR will be low when level in HPR is 50%. This means that your system is undercharged. When level in HPR is 40%, more liquid will be in MPR and pump will run fine. What is the level in MPR when this problem happen?

[RANGER1]

Sergei ,
I believe liquid reciever dumps liquid into med temp vessel when above 50%
Med temp vessel dumps into low temp vessel when level above 40%.
System is charged by low temp vessel level.
This style of system can be used with Witt or Hansen float valves.

[Segei]

Sergei ,
I believe liquid reciever dumps liquid into med temp vessel when above 50%
Med temp vessel dumps into low temp vessel when level above 40%.
System is charged by low temp vessel level.
This style of system can be used with Witt or Hansen float valves.

In this case LPR should be large vessel to accumulate liquid when load fluctuate. System should not be undercharged. I don't like this design.

[RANGER1]

Have seen it in abbatoirs with plate freezers .
Plant has approx 30 tonne charge , so not viable to have a liquid reciever for any pump down or storage , so low side accumulator is very large .
Seems to do the job ok .
Liquid reciever is only really purpose is for thermosypon oil coolers .

[Quality]

Sounds like there is some pump slip from your first posts not cavitation

Thats my theory

[Krohnie84]

I'm still confused about your system. It would be better if you give us simplified drawing of your plant.
Assume that you have float to control level in HPR and nothing to control level in MPR. This is very poor design. Every vessel with the pumps should have level control.
If you have critically charged system(float for HPR), level in MPR will be low when level in HPR is 50%. This means that your system is undercharged. When level in HPR is 40%, more liquid will be in MPR and pump will run fine. What is the level in MPR when this problem happen?

This system was first made to have the med temp vessel push the liquid out via med temp pressure. When we expanned the building and added five med temp units we added pumps. The first four units were dock units and now run a cooler. At this time there are no issues with getting liquid into the med temp vessel.

The reason behind having a liquid level of 50% or higher in the high temp receiver makes sure that the thermosyphon oil coolers for the compressors have enough liquid to cool the oil. Having enough liquid to cool compressors is more important than enough for med temp vessel.

I made a few adjustments to the pumps, and I had an alarm last night. A little more on a valve or two should work pretty well.

[RANGER1]

Sounds like there is some pump slip from your first posts not cavitation

Thats my theory

Quality can you explain what pump slip might be !

[RANGER1]

This system was first made to have the med temp vessel push the liquid out via med temp pressure. When we expanned the building and added five med temp units we added pumps. The first four units were dock units and now run a cooler. At this time there are no issues with getting liquid into the med temp vessel.

The reason behind having a liquid level of 50% or higher in the high temp receiver makes sure that the thermosyphon oil coolers for the compressors have enough liquid to cool the oil. Having enough liquid to cool compressors is more important than enough for med temp vessel.

I made a few adjustments to the pumps, and I had an alarm last night. A little more on a valve or two should work pretty well.

Please let us know what you did for interest when you get it sorted .

[Krohnie84]

I will do so, just so everyone will know at this time....
Each pump has an inlet, outlet and a vent. The pump is oil less and uses the ammonia to cool pump/bearings. Everything is submerged in the ammonia(take a look at my original attachment). My co-worker was told when this problem was first seen that the vent line needed to be opened more. The "vent" line has been slowly been opened all the way over the past 1yr. I have started to close these valves and have been working with another that is located off of the liquid trunk. If you would like a drawing I should be able to get something together to share, but I will still keep you guys updated with anything that may arise.
P.S. I have been reading the other threads and I have to say that this is a really good forum. All of you are very knowledgeable and helpful and I just want to thank you for helping me with this issue.

[RANGER1]

The vent line dosn't have to be open to much as its only for cooling & lubrication of bearings .
Still surprised that it would cause cavitation though if opened to much .

Liquid trunk , is that the main discharge line off liquid pumps back into wet return of vessel ?

[Krohnie84]

The vent line dosn't have to be open to much as its only for cooling & lubrication of bearings .
Still surprised that it would cause cavitation though if opened to much .

Liquid trunk , is that the main discharge line off liquid pumps back into wet return of vessel ?

My Co-worker was told that if he opened the vent more then it would stop any "cavitation".

It is the discharge off of the pumps going to the main liquid line, there is a T with an expansion valve that goes back to the vessel.

[Quality]

Quality can you explain what pump slip might be !

Pump slip is either when the differential pressure is to big for the pump to overcome or when the gears are worn liquid passes by the mating faces ,hence the liquid slips by the gears

[RANGER1]

Qualityfair enough , but in this case its a centrifugal pump .
Although if pump carbon bearings are worn the impellar can rub on housing causing possible excessive clearances .

Krohnie have you tried also to run stadby pump & notice any difference ?
Just a thought to eliminate pump itself .

[Quality]

Qualityfair enough , but in this case its a centrifugal pump .
Although if pump carbon bearings are worn the impellar can rub on housing causing possible excessive clearances .

Krohnie have you tried also to run stadby pump & notice any difference ?
Just a thought to eliminate pump itself .

Must of misread whoops

[Krohnie84]

Qualityfair enough , but in this case its a centrifugal pump .
Although if pump carbon bearings are worn the impellar can rub on housing causing possible excessive clearances .

Krohnie have you tried also to run stadby pump & notice any difference ?
Just a thought to eliminate pump itself .

We have switched the pumps after the alarm occurs, but it would still fault out hours/days after that.

[Segei]

It isn't easy to help you if we don't have correct information about your plant, but we'll try.
Right now you have 9 med temp. units. 4 for a dock and 5 in penthouses. How many penthouses do you have? This 5 units cool 1 or 2 separate rooms.
Look at the graph. This is good information that you gave us. You have spike of the level and spike is the reason of cavitation. Reason of the spike is sudden suction pressure drop. It can happen when load suddenly drop. For example. You run 1000 cfm compressor capacity. If temperature in your cooler is satisfied your load will drop to 500 cfm, but it takes time for compressors to unload. Compressor over capacity will pull pressure in the vessel down, level will spike and pump will cavitate. Give us more information about these 9 units. Do you supply liquid to the dock units from HPR or from MPR ? What is the medium suction pressure? What are the temperatures on the dock and in the coolers?

[Krohnie84]

It isn't easy to help you if we don't have correct information about your plant, but we'll try.
Right now you have 9 med temp. units. 4 for a dock and 5 in penthouses. How many penthouses do you have? This 5 units cool 1 or 2 separate rooms.
Look at the graph. This is good information that you gave us. You have spike of the level and spike is the reason of cavitation. Reason of the spike is sudden suction pressure drop. It can happen when load suddenly drop. For example. You run 1000 cfm compressor capacity. If temperature in your cooler is satisfied your load will drop to 500 cfm, but it takes time for compressors to unload. Compressor over capacity will pull pressure in the vessel down, level will spike and pump will cavitate. Give us more information about these 9 units. Do you supply liquid to the dock units from HPR or from MPR ? What is the medium suction pressure? What are the temperatures on the dock and in the coolers?

To make sure this comes out clearly, I have to explain this in two ways. This building was built in 1995, the med temp side at that time consisted of four hanging dock units (with txv's). Liquid was fed to them from the Med Temp Vessel via pressure (32psi) within the vessel.

Two years ago the building was expanded, that dock was "converted" into a cooler. Then five penthouse units (hand expansion valves) were installed for the new dock area. Since the length for the liquid line had now doubled if not tripled, liquid pumps were added to the vessel. The temperature of both areas maintains 33-35 degrees year round.

[Segei]

To make sure this comes out clearly, I have to explain this in two ways. This building was built in 1995, the med temp side at that time consisted of four hanging dock units (with txv's). Liquid was fed to them from the Med Temp Vessel via pressure (32psi) within the vessel.

Two years ago the building was expanded, that dock was "converted" into a cooler. Then five penthouse units (hand expansion valves) were installed for the new dock area. Since the length for the liquid line had now doubled if not tripled, liquid pumps were added to the vessel. The temperature of both areas maintains 33-35 degrees year round.

You can't supply liquid at 32 psig and return suction at the same pressure. Probably, liquid supplied to txv units from HPR and dry suction returns to MPR(4 old units). New 5 units are supplied from MPR by the pump.
As I mention above, sudden change in ref. load will lead to this event. When temperature on the dock is satisfied, 5 units will turn off and this will lead to spike of the level and pump cavitation.
Solutions.
1. Run fans nonstop and cycle liquid solenoids. This isn't energy efficient way, but it will help to avoid pump cavitation.
2. Start up and shut off units gradually(time delay). For example. When temperature on the dock is satisfied one unit off, in 30 sec second unit off and... The same at start up.
3. During cooler weather run less than 5 units(4,3). Increase suction pressure to 35 psig.

[Krohnie84]

You can't supply liquid at 32 psig and return suction at the same pressure. Probably, liquid supplied to txv units from HPR and dry suction returns to MPR(4 old units). New 5 units are supplied from MPR by the pump.
As I mention above, sudden change in ref. load will lead to this event. When temperature on the dock is satisfied, 5 units will turn off and this will lead to spike of the level and pump cavitation.
Solutions.
1. Run fans nonstop and cycle liquid solenoids. This isn't energy efficient way, but it will help to avoid pump cavitation.
2. Start up and shut off units gradually(time delay). For example. When temperature on the dock is satisfied one unit off, in 30 sec second unit off and... The same at start up.
3. During cooler weather run less than 5 units(4,3). Increase suction pressure to 35 psig.

You are correct, I was mistaken. When we added the pumps they attached the old liquid line with the new trunk that the installed for the penthouses. For some reason I was thinking it was that was to begin with (It sounded funny in my head when I wrote that).

Each unit has a seperate temperature probe. They will only run when the temperature in that area calls for it. The "old" dock area had about 23 or so overhead doors. The new area has over forty and some extra storage space. I think it might be 200 yards or so long.

The penthouse units have VFDs controlling them, when the units are not cooling they ramp the fans down and then speed up again when in cooling mode. The old hanging units have the option of turning off the fans when they aren't cooling but with the temperature sensitve product that is now stored there we would rather not turn them off.

[Segei]

You are correct, I was mistaken. When we added the pumps they attached the old liquid line with the new trunk that the installed for the penthouses. For some reason I was thinking it was that was to begin with (It sounded funny in my head when I wrote that).

Each unit has a seperate temperature probe. They will only run when the temperature in that area calls for it. The "old" dock area had about 23 or so overhead doors. The new area has over forty and some extra storage space. I think it might be 200 yards or so long.

The penthouse units have VFDs controlling them, when the units are not cooling they ramp the fans down and then speed up again when in cooling mode. The old hanging units have the option of turning off the fans when they aren't cooling but with the temperature sensitve product that is now stored there we would rather not turn them off.

Step by step you give us more and more information about your plant. Try to increase(gradually) suction pressure of MPR. This will be better for the plant operation and for the plant efficiency. I think that you can go up to 40 psig. Actually, during winter operation many docks require heating but not cooling.
For sensitive product you can install ceiling fans. They are cheap and use little energy.
Make sure that your probe measure temp. and control temp. Sometimes these are separate probes.

[Krohnie84]

Step by step you give us more and more information about your plant. Try to increase(gradually) suction pressure of MPR. This will be better for the plant operation and for the plant efficiency. I think that you can go up to 40 psig. Actually, during winter operation many docks require heating but not cooling.
For sensitive product you can install ceiling fans. They are cheap and use little energy.
Make sure that your probe measure temp. and control temp. Sometimes these are separate probes.

How would increasing the pressure to 40 make the system more efficient? That would bring the suction temperature within 7-8 degrees of my cooler temp?
Just wondering if I am missing something? The units almost run all day long as it is.

When I saw this I laughed a bit, not to insult you; I am going to take a picture of the cooler and the space above the product and the space around the cooling units. It is really kind of funny.

[Segei]

How would increasing the pressure to 40 make the system more efficient? That would bring the suction temperature within 7-8 degrees of my cooler temp?
Just wondering if I am missing something? The units almost run all day long as it is.

When I saw this I laughed a bit, not to insult you; I am going to take a picture of the cooler and the space above the product and the space around the cooling units. It is really kind of funny.

Yes temp. difference will be 7-8 degF but you don't need 15 degF when it is cool outside. At higher suction pressure compressor and usually plant efficiency is better. How many penthouses do you have. Usually, each penthouse has 2-4 units.
About fan ceiling. This may be looks laughable when you don't have enough information. I saw docks where people store some product and still use this room as a dock. If your dock(cooler) full of racks it is different story. Anyway you don't need to run the fans nonstop. Usually, units located under the ceiling or in penthouse. Temp. probe located at air inlet. When temp. is satisfied and unit shut off, due to gravity warm air will go up and cool air will go down. Within reasonable time and temp. difference warm air will turn the unit on and product won't suffer.

[Krohnie84]

Yes temp. difference will be 7-8 degF but you don't need 15 degF when it is cool outside. At higher suction pressure compressor and usually plant efficiency is better. How many penthouses do you have. Usually, each penthouse has 2-4 units.
About fan ceiling. This may be looks laughable when you don't have enough information. I saw docks where people store some product and still use this room as a dock. If your dock(cooler) full of racks it is different story. Anyway you don't need to run the fans nonstop. Usually, units located under the ceiling or in penthouse. Temp. probe located at air inlet. When temp. is satisfied and unit shut off, due to gravity warm air will go up and cool air will go down. Within reasonable time and temp. difference warm air will turn the unit on and product won't suffer.

How many units? Do you mean fans?

cold storage cooler.jpg
This is the "old" dock area. The space between the
bar joists and the product is only a foot and a half at best.

101.jpg
This is one of the units, it is seldom that there is empty space around the units themselves.

dock n.jpg
New dock North side.

dock s.jpg
New dock South side.

[Segei]

How many units? Do you mean fans?

cold storage cooler.jpg
This is the "old" dock area. The space between the
bar joists and the product is only a foot and a half at best.

101.jpg
This is one of the units, it is seldom that there is empty space around the units themselves.

dock n.jpg
New dock North side.

dock s.jpg
New dock South side.

Cooling units or evaporators or coils. How many penthouses do you have? 1,2...5

[Krohnie84]

In this system there are five med temp penthouses, four med temp hanging evaps, five hanging freezer evaps (two are blast freezers), five freezer penthouses and two convertible penthouses (med or low temp).

[Segei]

In this system there are five med temp penthouses, four med temp hanging evaps, five hanging freezer evaps (two are blast freezers), five freezer penthouses and two convertible penthouses (med or low temp).

As I mentioned, try to increase medium pressure. How do you heat your docks during winter time?

[Krohnie84]

We heat via hot gas, the penthouse units only run fans at 50% or so and the hot gas comes in at about 105psi.

[Segei]

We heat via hot gas, the penthouse units only run fans at 50% or so and the hot gas comes in at about 105psi.

It is good idea to use hot gas for the heating. Do you have pressure regulator for hot gas line? Do you use 105 psig to defrost your freezers?

[Krohnie84]

It is good idea to use hot gas for the heating. Do you have pressure regulator for hot gas line? Do you use 105 psig to defrost your freezers?

Yes, head pressure is regulated down the 105 for the penthouses on the docks and the new freezer units. The original units are regulated to 70-75 psi. There is no electric or air over coil defrosts.

[Segei]

Yes, head pressure is regulated down the 105 for the penthouses on the docks and the new freezer units. The original units are regulated to 70-75 psi. There is no electric or air over coil defrosts.

What do you mean by original units are regulated to 70-75 psi?

[Krohnie84]

The building was built in 1995, the original units were designed to defrost/heat with a regulated hot gas pressure of 70-75 psig. The expansion that took place in 2008 added units that are designed for 105 psig.