Frigoscandia spiral freezer

[ASAD]

Hi to all,

A client of ours, has a Frigoscandia spiral freezer.

Model – GC 400-06-25-06 NS CCR.

The evaporator is a flooded type.

Working conditions: (-40) / 45.

refrigerant- R-22.

A rack/stand, with two handbell screw compressors: RC12 + RC11.

Attached are two sketches that describe the system.

I have a few questions regarding the system:

1. We want to change the refrigerant (R-22) to a different type, which would you recommend?

2. How would you call the tank that is by the evaporator (figure 1)?

3. The valve that is located after the solenoid (figure 2) is a globe type. It is not a regulation valve. When the solenoid valve is opened, all the refrigerant runes to the evaporator, without going through the expansion valve (Danfoss TEX-2) of the compressors economizers. (the easy way), which means we are losing capacity.

What do you think about that?

4. We would like to increase the capacity and we thought about cooling the liquid that enters the evaporator by adding a heat exchanger.

We thought about doing that in two different ways:

a. With an external cooling unit, by cooling the liquid down to (-40).

b. Like an economizer – the liquid will cool down by itself.

What do you think about that?

[RANGER1]

Hi to all,
A client of ours, has a Frigoscandia spiral freezer.
Model – GC 400-06-25-06 NS CCR.
The evaporator is a flooded type.
Working conditions: (-40) / 45.
refrigerant- R-22.
A rack/stand, with two handbell screw compressors: RC12 + RC11.
Attached are two sketches that describe the system.
I have a few questions regarding the system:
1. We want to change the refrigerant (R-22) to a different type, which would you recommend?
2. How would you call the tank that is by the evaporator (figure 1)?
3. The valve that is located after the solenoid (figure 2) is a globe type. It is not a regulation valve. When the solenoid valve is opened, all the refrigerant runes to the evaporator, without going through the expansion valve (Danfoss TEX-2) of the compressors economizers. (the easy way), which means we are losing capacity.
What do you think about that?
4. We would like to increase the capacity and we thought about cooling the liquid that enters the evaporator by adding a heat exchanger.
We thought about doing that in two different ways:
a. With an external cooling unit, by cooling the liquid down to (-40).
b. Like an economizer – the liquid will cool down by itself.
What do you think about that?

ASAD,
Never seen a Frigoscandia plant this small!

1/ Don't know of any good replacement for R22 flooded evaporator that could recommend.

2/ Tank/accumulator beside evaporator could be called suction slop pot or compressor protection vessel.
Any liquid is separated before enters compressor.
Usually liquid line runs through in a separate coil it to boil of anything that enters it on a plant start up etc.

3/ Valve after solenoid would imagine is a manual expansion valve.
It is opened enough to to maintain liquid level in evaporator when level float switch energizes solenoid valve.
In operation solenoid will open & close when level switch call for it to open.
Solenoid should be energized 60-70% of the time under full load.

4/ Economizer subcools the liquid line, which is to the right of each compressor.
So if working cannot see reason to add in another one.

Could not see a liquid receiver anywhere in your drawings

[Tycho]

1. We want to change the refrigerant (R-22) to a different type, which would you recommend?
Can't answer this
2. How would you call the tank that is by the evaporator (figure 1)?
LP Receiver/suction drum
3. The valve that is located after the solenoid (figure 2) is a globe type. It is not a regulation valve. When the solenoid valve is opened, all the refrigerant runes to the evaporator, without going through the expansion valve (Danfoss TEX-2) of the compressors economizers. (the easy way), which means we are losing capacity.
What do you think about that?

You are going to have to be more specific, can you mark the solenoid on the drawing?
I can't see any globe valve after a solenoid valve on drawing 2.

4. We would like to increase the capacity and we thought about cooling the liquid that enters the evaporator by adding a heat exchanger.
We thought about doing that in two different ways:
a. With an external cooling unit, by cooling the liquid down to (-40).

No


b. Like an economizer – the liquid will cool down by itself.
What do you think about that?

Yes.

------------------------------------------
Don't know how the economizer ports are regulated on this plant, but I am guessing the solenoid that feeds the economizer side of the heat exchanger only opens when the compressor is above 80% capacity.

Making this plant more efficient is going to take a major redesign and rebuild and is going to be very costly.

Replacing the R-22 with one of the new "Hubba Bubba" refrigerants with a large glide may make your plant less efficient...

I would take this problem to an engineer, and not base a rebuild on the input from some random, though very knowledgeable guys, on an internet forum

------------------------------------

Top tip:
I installed two identical RSW plants with R-427a, first one, the suction temperature was determined by pressure calculated to temperature, and it was very erratic, a change of 0,1 bar had a huge impact on the calculated temperature.

Caused me a lot of headache...

On the second one I said... you know what, this refrigerant is s**t, with the glide and we have no idea what the temperature relay is... why don't we put a temperature probe in the refrigerant and read the real temperature.

So we did... and the regulation was the most stable I have seen in 20 years...

[ASAD]

To Tycho, much thanks for your replay.

1. We want to change the refrigerant (R-22) to a different type, which would you recommend?
   Can't answer this
   2. How would you call the tank that is by the evaporator (figure 1)?
   LP Receiver/suction drum
   3. The valve that is located after the solenoid (figure 2) is a globe type. It is not a regulation valve. When the solenoid valve is opened, all the refrigerant runes to the evaporator, without going through the expansion valve (Danfoss TEX-2) of the compressor's economizers. (the easy way), which means we are losing capacity.
   What do you think about that?
   
   You are going to have to be more specific, can you mark the solenoid on the drawing?
   I can't see any globe valve after a solenoid valve on drawing 2.

You are definitely right; you can see the solenoid in figure 1.
rephrase my question. Do you think there is a difference between DX system and flooded system?
In regard, to how much liquid will pass through the expansion valve of the economizer.
4. We would like to increase the capacity and we thought about cooling the liquid that enters the evaporator by adding a heat exchanger.
We thought about doing that in two different ways:
a. With an external cooling unit, by cooling the liquid down to (-40).

No


b. Like an economizer – the liquid will cool down by itself.
What do you think about that?

Yes.



So, what you are saying basically is that as long as we cool the liquid that goes into the evaporator it will increase the capacity. so the question remains- how can we do it properly? if that so why not work with option A?
------------------------------------------
Don't know how the economizer ports are regulated on this plant, but I am guessing the solenoid that feeds the economizer side of the heat exchanger only opens when the compressor is above 80% capacity.
Very true. The compressors achieve 100% capacity immediately and remains so during the whole process.
Making this plant more efficient is going to take a major redesign and rebuild and is going to be very costly.
will appreciate if you could expand more.
Replacing the R-22 with one of the new "Hubba Bubba" refrigerants with a large glide may make your plant less efficient...

I would take this problem to an engineer, and not base a rebuild on the input from some random, though very knowledgeable guys, on an internet forum [IMG]file:///C:/Users/USER/AppData/Local/Temp/msohtmlclip1/01/clip_image001.png[/IMG]
Of course, but from all my teachers, I’ve learned.
------------------------------------

Top tip:
I installed two identical RSW plants with R-427a, first one, the suction temperature was determined by pressure calculated to temperature, and it was very erratic, a change of 0,1 bar had a huge impact on the calculated temperature.

Caused me a lot of headache...

On the second one I said... you know what, this refrigerant is s**t, with the glide and we have no idea what the temperature relay is... why don't we put a temperature probe in the refrigerant and read the real temperature.

So we did... and the regulation was the most stable I have seen in 20 years...
Last edited by Tycho; 06-05-2020 at 09:31 PM.
-Cheers-

Tycho

[ASAD]

To ranger, much thanks for your replay

ASAD,
Never seen a Frigoscandia plant this small!

1/ Don't know of any good replacement for R22 flooded evaporator that could recommend.

2/ Tank/accumulator beside evaporator could be called suction slop pot or compressor protection vessel.
Any liquid is separated before enters compressor.
Usually liquid line runs through in a separate coil it to boil of anything that enters it on a plant start up etc.
You can see the accumulator in figure 1
The vessel that I have asked about is in figure 2

3/ Valve after solenoid would imagine is a manual expansion valve.
No it is not manual expansion valve.
It is opened enough to maintain liquid level in evaporator when level float switch energizes solenoid valve.
In operation solenoid will open & close when level switch call for it to open.
Solenoid should be energized 60-70% of the time under full load.
can u Please expand more?

4/ Economizer subcools the liquid line, which is to the right of each compressor.
So if working cannot see reason to add in another one.

Could not see a liquid receiver anywhere in your drawings.
You are right. There is a condenser between the oil separator and the dryer.

[RANGER1]

Asad, what type of condenser do you have if there is no liquid receiver?
Is it a shell & tube condenser?

Also what temperature is high pressure liquid line before & after economiser.
This determines if economisers are working.

[sterl]

Any "Glide" or zeotropic refrigerant is not going to be suitable for evaporators fed by a gravity drum. (the vessel beside the evaporators....). The economizer arrangement is highly effective at near full compressor capacity providing the heat exchangers are large enough to keep the temperature differences low but, in reality, the HP liquid flow through 2-separate ecomizer exchangers is always going to be out of balance considering the rest of the arrangement: arranged in parallel with no managing restriction, the pipe and accessory pressure differences, and that through the individual heat exchangers, play a big role in the path liquid will follow. Tendency would be, one compressor does the majority of the economising while the other receives very little vapor via the side port.

Flash type economizing would releive that effect, and the temperature difference required by the heat exchangers (the approach) would largely reduce to nothing: but those represent the entire gain, at the loss of the driving pressure through the liquid line to the makeup solenoid at the gravity vessel and the rectifier at that vessel is going to act differently as well....In fact, the rectifier probably acts pretty strange on start up when both the oil and the refrigerant are warmer than normal.