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georgedvf
22-07-2010, 06:15 PM
Hello everyone!

When using a Parallel Compressors Rack System for several rooms at different temperatures I have seen EPR's (1 for each room) installed just before the rack's suction manifold to mantain the different room's pressures, and I have seen that Solenoid Valves are installed just after the liquid manifold (1 for each room) to cut refrigerant flow when set temperature is reached or when defrost is required.

Doesn't the EPR's should be enough to control temperature? Is it necessary to use Solenoid Valves?

Thanks in advanced!

chemi-cool
22-07-2010, 06:27 PM
EPR is used to maintain a certain pressure\ temp in the evaporator.

SV will close when the room have reached the desired temp.

georgedvf
22-07-2010, 06:40 PM
Thanks chemi-cool.

Do you use to put SV at the Rack or at the Evaporator??

One thing I noticed is that when big diameter pipes are used it "hits" really strong when SV opens and liquid start to flow.

Peter_1
22-07-2010, 09:04 PM
If you install a SV far from the TEV, you can brake the TEV due to liquid hammer.
You have to install the SV as close as possible to the TEV.
Installing all the SV's in the machineroom is a very bad practice.

georgedvf
22-07-2010, 09:09 PM
Thanks Peter_1, that's what I though.

Regarding to the use of EPR's, somebody told me there was no need to cut flow off with the SV because the EPR would manage to keep the room at required temperature, Is that possible?

Peter_1
22-07-2010, 09:21 PM
Georgedvf, you need and an EPR and a SV in a 'normal application'
The EPR will prevent too cold draft blowing from the evaporator where the SV maintains the room temperature.
You can regulate room temperature with the EPR but you then need and EPR which adapts its evaporating temperature according to the room temperature.Danfoss has a special valve for this http://www.ra.danfoss.com/TechnicalInfo/Literature/Manuals/01/USCOPC320A122.pdf That's in fact a little bit what a VRV/VRF airco is doing. Adapting mean coil temperature to the room temperature.

Paul J
22-07-2010, 10:58 PM
We had a problem with large liquid lines hammering when the solenoid valve opened, moving the solenoid to the evap can be a huge job, what we did was install a small 1/4 inch solenoid which opened first around the larger solenoid, this filled the larger liquid line then opened the large solenoid after a preset time

Sandro Baptista
23-07-2010, 08:17 AM
We had a problem with large liquid lines hammering when the solenoid valve opened, moving the solenoid to the evap can be a huge job, what we did was install a small 1/4 inch solenoid which opened first around the larger solenoid, this filled the larger liquid line then opened the large solenoid after a preset time

Yes, that's right

Sandro Baptista
23-07-2010, 08:23 AM
Thanks Peter_1, that's what I though.

Regarding to the use of EPR's, somebody told me there was no need to cut flow off with the SV because the EPR would manage to keep the room at required temperature, Is that possible?


Georgedvf, you need and an EPR and a SV in a 'normal application'
The EPR will prevent too cold draft blowing from the evaporator where the SV maintains the room temperature.
You can regulate room temperature with the EPR but you then need and EPR which adapts its evaporating temperature according to the room temperature.Danfoss has a special valve for this http://www.ra.danfoss.com/TechnicalInfo/Literature/Manuals/01/USCOPC320A122.pdf That's in fact a little bit what a VRV/VRF airco is doing. Adapting mean coil temperature to the room temperature.


George, if you don't use SV you could control the room temperature by switching on/off the aircoolers fans...however there is a big big risk/probability that you flood the suction line manifold and the compressor with liquid :rolleyes:.

chemi-cool
23-07-2010, 08:52 AM
George, if you don't use SV you could control the room temperature by switching on/off the aircoolers fans...however there is a big big risk/probability that you flood the suction line manifold and the compressor with liquid :rolleyes:.

Bad advice my friend, very bad. :eek:

NoNickName
23-07-2010, 09:24 AM
This is a typically wrong application, with legacy components and inherited operation from jurassic experience.
If one wants to control a room temperature, for what good dam reason does one control the suction pressure? Wouldn't it be more logic to control the room temperature and cycle on that?
EPRs would be useless (superheating regulated per room) and SV would only be needed to stop liquid feeding TEVs for the rooms already at set. And to prevent hammering, just stop pumping down.

Sandro Baptista
23-07-2010, 09:56 AM
Bad advice my friend, very bad. :eek:

Chemi,

I didn't said that's a good solution, by contrary is very risky


This is a typically wrong application, with legacy components and inherited operation from jurassic experience.
If one wants to control a room temperature, for what good dam reason does one control the suction pressure? Wouldn't it be more logic to control the room temperature and cycle on that?
EPRs would be useless (superheating regulated per room) and SV would only be needed to stop liquid feeding TEVs for the rooms already at set. And to prevent hammering, just stop pumping down.

The room temperature it would not be controled by suction pressure. A thermostat it would be used but instead acting on the solenoid valve on/off it would act on the fans.

NoNickName
23-07-2010, 09:59 AM
Which is also wrong. When ventilation stops, air stratifies.

Sandro Baptista
23-07-2010, 10:28 AM
Which is also wrong. When ventilation stops, air stratifies.

And what's the problem of that?

NoNickName
23-07-2010, 10:41 AM
And what's the problem of that?

The temperature probe does not fully reflect the room temperature, which changes along the vertical profile.
If you've got food along vertical racks, it may not be properly refrigerated when stacked at high level, or may be too cold at low levels for fresh produce like lettuce or fruits.

Sandro Baptista
23-07-2010, 10:56 AM
The temperature probe does not fully reflect the room temperature, which changes along the vertical profile.
If you've got food along vertical racks, it may not be properly refrigerated when stacked at high level, or may be too cold at low levels for fresh produce like lettuce or fruits.

1st » When the aircooler is working (because the temperature is higher than the set-point) every thing is okay, right? the ventilation ensure the air circulation.

2nd » When the fans stops I understand that the a "cooled" air flow will down. But this will be a very little refrigeration effect when compared with "static aircooler" (natural convection / no fans).

NoNickName
23-07-2010, 11:06 AM
I'm only saying that if air settles and statifies, the warm air will rise, and the cold air will sink. This is also known as convection.
It has nothing to do with refrigeration.

Sandro Baptista
23-07-2010, 11:41 AM
Which is also wrong. When ventilation stops, air stratifies.


I'm only saying that if air settles and statifies, the warm air will rise, and the cold air will sink. This is also known as convection.
It has nothing to do with refrigeration.

okay man...I just still can see what's the problem of that.
That's a good debate;)

NoNickName
23-07-2010, 01:05 PM
Ok, if warm air rises, the goods stocked at high level will be warmer than the goods at low levels.
The quality of some goods require strict temperature control, for example lettuce and fresh produce, flowers, bananas....
Imagine a mushroom growing chamber. You would expect different growing rates from warmer to colder shelves.

Sandro Baptista
23-07-2010, 01:24 PM
Ok, if warm air rises, the goods stocked at high level will be warmer than the goods at low levels.
The quality of some goods require strict temperature control, for example lettuce and fresh produce, flowers, bananas....
Imagine a mushroom growing chamber. You would expect different growing rates from warmer to colder shelves.


Okay...put the probe on the higher part (higher temperature as it should be)...but like I have told you we are talking about an aircooler that is not for natural convection so the aircooler capacity with the fans off will be very smaller and this effect would not be notice.
Maybe we are running away a little of this thread, don't you think?

NoNickName
23-07-2010, 02:08 PM
I think you don't understand. If I put the probe at higher level, the temperature on the floor would be even colder.
I know it is an aircooler, BUT WHEN THE FANS ARE OFF, NATURAL CONVECTION HAPPENS, BELIEVE IT OR NOT, YOU WANT IT OR NOT.

georgedvf
23-07-2010, 02:21 PM
This is a typically wrong application, with legacy components and inherited operation from jurassic experience.
If one wants to control a room temperature, for what good dam reason does one control the suction pressure? Wouldn't it be more logic to control the room temperature and cycle on that?
EPRs would be useless (superheating regulated per room) and SV would only be needed to stop liquid feeding TEVs for the rooms already at set. And to prevent hammering, just stop pumping down.

NoNickName, I didn't understand the last part about prevent hammering stopping pump down. Since I'm talking about a Parallel Compressors Rack for several rooms.

Can you tell me more about what would be a "New age" control solution for this kind of systems? Where can I find info?

Sandro Baptista
23-07-2010, 02:27 PM
Hey chill out man. I understand it will be cooler on floor...but I just say that effect will be smaller for this air forced cooler...and besides that the cold air will heat exchange with the products and air at the neighbourdhood so when it reaches the floor the temperature will not be so different to create a big deal.

This is my opinion, that's all.

NoNickName
23-07-2010, 02:35 PM
NoNickName, I didn't understand the last part about prevent hammering stopping pump down. Since I'm talking about a Parallel Compressors Rack for several rooms.

Yes, this is typical compressor pack / multiplex system. When the last of compressors stop, it is a common practice to stop it on a low pressure switch. This is referred as pump down procedure. At restart, when the SV opens, refrigerant fills up the vacuum created by the pump down, and the result is liquid hammering.



Can you tell me more about what would be a "New age" control solution for this kind of systems? Where can I find info?

Register yourself and download the programmable controllers brochure form www.dixell.it . You can have a slight glance of the new ideas for the refrigeration sector

georgedvf
23-07-2010, 02:44 PM
Yes, this is typical compressor pack / multiplex system. When the last of compressors stop, it is a common practice to stop it on a low pressure switch. This is referred as pump down procedure. At restart, when the SV opens, refrigerant fills up the vacuum created by the pump down, and the result is liquid hammering.

Ok, but when there's several rooms and only one room stops it's the same hammering and no compressor stops, so no pump down is happening there, right? I think the only solution for this is to install the SV near the TEV...




Register yourself and download the programmable controllers brochure form www.dixell.it (http://www.dixell.it) . You can have a slight glance of the new ideas for the refrigeration sector
Thanks for that link, I will look into it.

Peter_1
23-07-2010, 05:59 PM
....
If one wants to control a room temperature, for what good dam reason does one control the suction pressure? ...
When cold rooms (0°C) an processing rooms are connected to the same pack which is often the case, evaporating at -10°C, then an EPR could prevent icing up the coils in the processing rooms, or increase latent heat of the blown air so that there are less cold draft complaints from peoples working in those rooms or an EPR could be used to increase RH an a central manifold.

Peter_1
23-07-2010, 06:01 PM
...At restart, when the SV opens, refrigerant fills up the vacuum created by the pump down, and the result is liquid hammering.....
Not if teh SV is mounted just in front of the TEV.
Carrefour , Colruyt and Delhaize, big Belgium supermarkets describe in their manuals you have to install the SV's as close as possible to the TEV.

georgedvf
23-07-2010, 06:42 PM
Just to get it right, so when using Parallel Compressors Rack and several rooms yo DO use SV neear as possible from the TEV to stop refrigeratn flow when set temperature is reached or defrost is required, right??

NoNickName
23-07-2010, 09:59 PM
Not if teh SV is mounted just in front of the TEV.


It doesn't matter. It probably is worse when the SV is near the TEV. Same hammering in less volume.

NoNickName
23-07-2010, 10:00 PM
Just to get it right, so when using Parallel Compressors Rack and several rooms yo DO use SV neear as possible from the TEV to stop refrigeratn flow when set temperature is reached or defrost is required, right??

That's the general idea. Your mileage may vary.

littleyapper
23-07-2010, 10:18 PM
i'm with sv at exp vlv...... or just to throw a right spanner use danfoss elect vlv's :) should i duck now

Peter_1
23-07-2010, 11:17 PM
It doesn't matter. It probably is worse when the SV is near the TEV. Same hammering in less volume.

I totally disagree with this statement, the closer the better, if installed besides each other no hammer effect at all what DP you anyhow may see across the valve.
I had a judicial case about this with a loss of goods of over 250.000 € due to the long distance between SV and TEV.
We did measurements in both cases and DP can go to 100 bar.
It's also mentioned very clearly in the recommendations of Danfoss.

NoNickName
24-07-2010, 11:42 AM
Again, mileage may vary. Loss of goods is always the case when no backup and no spare parts are available. Blame is put on the producer of the equipment, as always.
I got a court case, because a close control unit went down and the server room of a bank stopped. They were transacting 1millionGBP per second. They had a loss of few billion GBP, all because of a 5 years old fan that burnt and no spares on site.
They got kicked and ashamed by the judge.
If you want to avoid hammering between the SV and the TEV, put the drier in between.

Peter_1
24-07-2010, 04:56 PM
Again, mileage may vary. Loss of goods is always the case when no backup and no spare parts are available. Blame is put on the producer of the equipment, as always.
I got a court case, because a close control unit went down and the server room of a bank stopped. They were transacting 1millionGBP per second. They had a loss of few billion GBP, all because of a 5 years old fan that burnt and no spares on site.
They got kicked and ashamed by the judge.
If you want to avoid hammering between the SV and the TEV, put the drier in between.

Came the judge to that decision without appointing first a judicial expert?

Putting the drier between SV and TEV, that need some clarification because the drier has almost no volume where velocity can decrease and avoid pressure build up

NoNickName
24-07-2010, 05:42 PM
The judge refused the case and didn't appoint any expert.

It depends on the drier. There are driers with plenty of volume inside. Anyway the core is able to slow the hammer, I think.

georgedvf
26-07-2010, 02:35 PM
Thanks to all.

I have one more question.

What would happen if no SV's are used and only EPR's are installed?

What happens to rooms temperatures?

What happens when defrost is needed?

Ok, there was three more questions....;)

Thanks!

Peter_1
26-07-2010, 02:47 PM
The judge refused the case and didn't appoint any expert.

It depends on the drier. There are driers with plenty of volume inside. Anyway the core is able to slow the hammer, I think.

In Belgium, a judge can't refuse a case, this is against the defense of whom who started the case.
There has to be anyhow a case with lawyers, eventually without the appointment of a judicial expert. But I'm sure, both parties (defended/offended) can give statements/arguments which justify that and why they're right and why the other was wrong.

NoNickName
26-07-2010, 02:56 PM
In Belgium, a judge can't refuse a case, this is against the defense of whom who started the case.


This is singular. What if a case is clearly unfounded?
Do they have so much money and time in Belgium?

In Italy, he is called GUP (judge of preliminary hearing).
E.g. there had been a case of a terminally ill man who refused being treated. The hospital wanted him to be forcefully treated (to avoid him self killing) and called him in judgement. The GUP refused the case because everybody is free to take or refuse medicines upon his/her only free will, which is a Constitutional Right.

But this is clearly off topic here. :off topic:

D.D.KORANNE
27-07-2010, 12:42 PM
FURTHER INPUT ON THIS SYSTEM :
1) THE LOAD OF THE LOWEST TEMP EVAP SHOULD BE AT LEAST 60% OF THE TOTAL LOAD .
2) HIGH TEMP EVAP SHOULD HAVE EPRs
3) LOW TEMP EVAP SHOULD HAVE A CHECK VALVE IN SUCTION LINE .
4) SOL VALVES FOR EACH EVAP NEAR TO TEX VALVE AS DISCUSSED IN THIS THREAD BY VARIOUS CONTRIBUTORS

Peter_1
27-07-2010, 08:25 PM
This is singular. What if a case is clearly unfounded?
Do they have so much money and time in Belgium?

I...

It has nothing to do with money nor time but about legal rights. How can a judge class a case as unfounded if the problem relates to a technical matter? He can't know all the details to do this, especially the technical ones to make the right decision.
It's also complete unthinkable that politicians can interfere or change laws that put them outside that law. Especially if there are presumptions that a politician broke the law. The politician will then temporarily placed outside his/her political immunity.
Law and politics are clearly separated here.
But as you said :off topic:

suny
18-08-2010, 12:59 PM
If you install a SV far from the TEV, you can brake the TEV due to liquid hammer.
You have to install the SV as close as possible to the TEV.
Installing all the SV's in the machineroom is a very bad practice.

Thank you Peter_1. I will redesign all my equipments & install the SV close to the TEV. After long period of time the TEV is not working properly. So we had to replace them after some time.