Danfoss ICM Suction Control

[NH3-Iceman]

I have 22 Evaporators with a Danfoss ICM on the suction outlet and regulate off of room temp the evaporators are overfed from a CPR my question is. do the expansion valves need that same amount of precision to adjust the feed rate as standard Suction Pressure Control. When the evaporators were commissioned the expansion valves were set and then adjusted to maintain room temp as far as i am told but there isn't any record for the turns open should i make an effort to get all these evaporators adjusted properly and write it down or should i go with the old saying if it ain't broke don't fix it also they are almost impossible to get to during full load. every thing in that area is built without Maintenance in mind just how many machines and conveyors can we fit in this room to give us the most use of space

[MrFreez717]

Sounds like you have 2 questions - should you put motorized valves in place of your current hand expansion valves (HEVs), and should you optimize the HEV settings. For the first question, IMO the answer is probably not. People have tried this, but the issue is: what do you use for control logic? You can't just modulate the feed valve with room temperature or with superheat, so what feedback do you use? You could try matching the feed valve opening with the suction valve opening to maintain a constant overfeed rate, but that would be hard to accomplish and of questionable value. Especially if you have VFDs on your air unit fans.

As far as optimizing HEV settings, that CAN have big dividends and IMO is well worth the effort. I actually wrote a paper about this very topic for a refrigeration conference a few years back (RETA national), and I would be happy to send you a copy if you PM me your email address.

Best regards,
MrFreez717

[RANGER1]

NH3Iceman,
Hard to justify any changes if it works.
Do you have overpressure protection for each evaporator?
Example relief valve or pressure regulator around ICM.

What brand HEV, if Danfoss reasonably easy if you have evaporator capacity, valve size & type.

[NH3-Iceman]

Yes, we have have BPRs on our all our valve groups two evaporators per control bank the defrost condensate just dumps into common wet suction header

[NH3-Iceman]

Sounds like you have 2 questions - should you put motorized valves in place of your current hand expansion valves (HEVs), and should you optimize the HEV settings. For the first question, IMO the answer is probably not. People have tried this, but the issue is: what do you use for control logic? You can't just modulate the feed valve with room temperature or with superheat, so what feedback do you use? You could try matching the feed valve opening with the suction valve opening to maintain a constant overfeed rate, but that would be hard to accomplish and of questionable value. Especially if you have VFDs on your air unit fans.

As far as optimizing HEV settings, that CAN have big dividends and IMO is well worth the effort. I actually wrote a paper about this very topic for a refrigeration conference a few years back (RETA national), and I would be happy to send you a copy if you PM me your email address.

Best regards,
MrFreez717
Everything is feed into a PLC and we use Proficy iFIX for operation the system. for me its a strange setup
because one we modulate the suction valve with feed-back from rtd in the room wouldnt you want a transducer and RTD in the suction line to modulate the suction valve and that we dont use modulation for each evaporator instead we have the same suction valve modulating two evaporators per control bank

[RANGER1]

NH3-Iceman,
I think RTD controlling room temperature is correct.
Pressure in pipe & pipe temperature don’t control room temperature if evaporator side of ICM.
You sound like you have various room temperatures that require possibly precise, or varying temperature control, otherwise, why would you just not have a mechanical back pressure regulators.
Beef chiller operation is common for ICM.

Can you tell us how, or what your plant operates.

[NH3-Iceman]

NH3-Iceman,
I think RTD controlling room temperature is correct.
Pressure in pipe & pipe temperature don’t control room temperature if evaporator side of ICM.
You sound like you have various room temperatures that require possibly precise, or varying temperature control, otherwise, why would you just not have a mechanical back pressure regulators.
Beef chiller operation is common for ICM.

Can you tell us how, or what your plant operates.

Yes, we have mechanical BPRs that go around the suction line and relief to the same suction header and we run pork processing we maintain room temps at 40 degrees on the cut-floor and we also run coolers 6 rooms that we run @ between 28 degrees and 33 degree. As well blast chiller and a freezer but that is on a separate engine room.

[RANGER1]

Thanks for information.

[NH3-Iceman]

Thanks for information.

Forgot to share brand of HEV the are all Hansen expansion valves

[RANGER1]

Forgot to share brand of HEV the are all Hansen expansion valves

MrFreeze information might help you there.
Hansen do give information, but with Danfoss & all brands need a bit of engineering data to work out theoretical settings.
Air on/off good as well, not sure that would be possible in your plant.
Like you say works okay.

[Tycho]

I agree with everything above, especially the "if it's not broken, don't touch it"

Also I'm not familiar with some of the lingo here, like CPR :) to me it means Cardiopulmonary resuscitation <- had to google that too.

but I figured as much that your evaporators are fed with what would be intermediate pressure liquid, like from a closed economizer?

The desired room temperature is 4C or 40F, plus you need rooms with -2C or 28F and 0.5C and 33F

What is the temperature of the liquid you are supplying to these circuits?


unless you need to have a central monitoring system that shows all room, the AK-cc550 is a nice room conroller
https://eurocool.co.za/wp-content/uploads/2020/07/AK-CC-550-Service.pdf

[RANGER1]

I agree with everything above, especially the "if it's not broken, don't touch it"

Also I'm not familiar with some of the lingo here, like CPR :) to me it means Cardiopulmonary resuscitation <- had to google that too.

but I figured as much that your evaporators are fed with what would be intermediate pressure liquid, like from a closed economizer?

The desired room temperature is 4C or 40F, plus you need rooms with -2C or 28F and 0.5C and 33F

What is the temperature of the liquid you are supplying to these circuits?


unless you need to have a central monitoring system that shows all room, the AK-cc550 is a nice room conroller
https://eurocool.co.za/wp-content/uploads/2020/07/AK-CC-550-Service.pdf

https://www.google.com.au/search?q=cpr+meaning+in+ammonia+refrigeration&ie=UTF-8&oe=UTF-8&hl=en-au&client=safari

Seems like a new buzz word, every region different it seems.
I thought USA called liquid overfeed vessel, or recirculator.

[MrFreez717]

In US usually a "recirculator" is a vessel with liquid refrigerant pumps, and a CPR ("Controlled Pressure Receiver") is a vessel held at an intermediate pressure and used to supply liquid via pressure differential. In the CPR system, the suction accumulator receives excess (overfed) liquid and must be fitted with a transfer system to put that liquid back into the CPR.

MrFreez717

[RANGER1]

In US usually a "recirculator" is a vessel with liquid refrigerant pumps, and a CPR ("Controlled Pressure Receiver") is a vessel held at an intermediate pressure and used to supply liquid via pressure differential. In the CPR system, the suction accumulator receives excess (overfed) liquid and must be fitted with a transfer system to put that liquid back into the CPR.

MrFreez717

MrFreeze717, would the CPR system be common, have seen on a Frigoscania (Frigo pak) -50 deg C flat bed freezer.
Not to many around Australia anyway.

Seems like CPR could be wrong terminology in original post, sounds like recirculator with liquid overfeed liquid pumps.

[frank]

I know CPR as Crankcase Pressure Regulator. Use to prevent excess pressure returning to the compressor

[MrFreez717]

Ranger1, CPR systems are not too common in northwest US, but we have a few. Mostly they are in grocery distribution centers designed by engineers from the midwest. These systems are much more common in the midwest US.

Although a matter of some controversy still, it is pretty clear that the pump recirculated systems have an efficiency advantage over the pressure-fed CPR systems. The refrigerant pump HP is nominal compared to the compressor power required to maintain the CPR vessel at a constant pressure. In addition, the liquid transfer process is inherently hazardous, as continual rapid pressure changes are required in the transfer drums.

I "assume" original post correctly refers to CPR system, as he has pressure regulators (BPRs) in the wet suction line of his evaporators. BPRs do not work in pump recirculated systems, as the inlet liquid remains at compressor suction temperature, no matter what pressure is maintained in the evaporator. Because of this a BPR in the suction line of a pump-recirculated evaporator will inevitably result in coil brining and poor performance.

Best regards,
MrFreez717

[MrFreez717]

I know CPR as Crankcase Pressure Regulator. Use to prevent excess pressure returning to the compressor

Commercial systems use "CPR" as you have stated, while industrial systems would use the term "outlet pressure regulator."

Interestingly, transcritical CO2 systems have what amounts to a CPR, but they refer to it as a flash tank.

Lots of jargon in this industry...

MrFreez717