Hard to keep proper temp. in Cold storage

[stanthonycold]

Hi,

We are trouble getting the temp in our CS down to around -27.We have 2 sabroe 125 hp screw compressors with 3 evaps.We are having a lot of door openings and our evaps are in the wrong place (one is right above the CS door !!!)My question is now that our cold storage is practically full of product(frozen fish/shrimp) this should make a difference with temps correct?We are drawing 3-4"hg ,discharge 140-150 psi.Would love to get it down to -27 but i dont think it will happen as long as we are having door openings and full load of product.Any suggestions?

[Grizzly]

Place mobile fans in the aisles to assist with air flow to maximise heat transfer,
I assume you have auto closing doors on timers and strip curtains as a minimum.
You don't say what refrigerant you are running on.

Irrespective of the product temperature the movement of product frequencies and door opening frequencies.
Will reduce the cooling effect.
Why are you trying to maintain -27?
That sounds way to cold. Or are you trying to freeze the product ?
Grizzly

[Sandro Baptista]

Firsts very important questions:

Where do you have the temperatures probes installed? How much do you have?

What's the minimum temperature you can reach?

[Magoo]

What refrigerant is the system operating on.
What ever refrigerant, try running at +32> 35 'C condensing, to get flow rates in the correct range, that will feed the coils to get performance. With the CS full, product will act as a huge heat sink, so all you are dealing with is panel and door opening loads plus fan motor heat.

[Sandro Baptista]

What refrigerant is the system operating on.
What ever refrigerant, try running at +32> 35 'C condensing, to get flow rates in the correct range, that will feed the coils to get performance. With the CS full, product will act as a huge heat sink, so all you are dealing with is panel and door opening loads plus fan motor heat.

I would say that 25ºC condensing temperature still will give good pressure difference (we are talking about cold store -25ºC, more or less) . At +25ºC condensing temperature the compressors will give more capacity and less shaft power absorbed...and less wearing of the mechanical parts.

[Sandro Baptista]

Stanthonycold, any news?

Please give us data so we can give some ideas.

[stanthonycold]

Stanthonycold, any news?

Please give us data so we can give some ideas.



yes i calibrated suction/discharge sensors and seems to working ok..BUT i have 2 compressors running now and one compressor is saying that operating pressure is 65 psi while the discharge pressure is 130psi,,on the second compressor both pressures are about the same..whats up with that ?Im green to this profession to by the way..Thanks for help appreciate it

[Sandro Baptista]

Let see step by step:

You told at first that you have problems with the temperature:

1) What's the set point you have defined?

2) Where do you have place the probes temperature sensors and how much they are?

More questions/analysis will be done...further

Regards

[stanthonycold]

Let see step by step:

You told at first that you have problems with the temperature:

1) What's the set point you have defined?

2) Where do you have place the probes temperature sensors and how much they are?

More questions/analysis will be done...further

Regards

discharge temp is 88 degrees C,discharge pressure is 120 psi,,operating pressure is 70 psi,compressor slide valve is 100% 1.3 inches of mercury,, ST is -29.0 degrees C.This compressor is not working properly.

The compressor that we have that is the same model and is working correctly has a discharge temp of 69 C ,discharge pressure 120 psi,operating pressure of 120 psi,3-4 inches mercury ST is -29.0 C.

Im new to this profession and appreciate all help and advice.

[Sandro Baptista]

discharge temp is 88 degrees C,discharge pressure is 120 psi,,operating pressure is 70 psi,compressor slide valve is 100% 1.3 inches of mercury,, ST is -29.0 degrees C.This compressor is not working properly.

The compressor that we have that is the same model and is working correctly has a discharge temp of 69 C ,discharge pressure 120 psi,operating pressure of 120 psi,3-4 inches mercury ST is -29.0 C.

Im new to this profession and appreciate all help and advice.


1) Discharge pressure 120 psi and operating pressure 70 psi (discharge pressure??) » I'm not understand...

2) ST -29ºC you meant suction temperature, right? or saturated temperature from LP side?
You talk about 1,3 inches mercury and 3-4 inches mercury. Is this suction pressure? If it is it doesn't match with -29ºC even if it is saturated temperature.
The system works with R717, right?

3) You started this thread talking about difficulty on getting the temperature you want for the cold store. Please answer first to my previous post.

[stanthonycold]

Firsts very important questions:

Where do you have the temperatures probes installed? How much do you have?

What's the minimum temperature you can reach?

In the cold storage on the wall about 40 feet directly below 3 evaps.Yes we r using ammonia,yes inches of mercury im referring to is suction pressure.Minimum temp i have seen in cold storage is -27.5 C.

[stanthonycold]

1) Discharge pressure 120 psi and operating pressure 70 psi (discharge pressure??) » I'm not understand...

2) ST -29ºC you meant suction temperature, right? or saturated temperature from LP side?
You talk about 1,3 inches mercury and 3-4 inches mercury. Is this suction pressure? If it is it doesn't match with -29ºC even if it is saturated temperature.
The system works with R717, right?

3) You started this thread talking about difficulty on getting the temperature you want for the cold store. Please answer first to my previous post.


St = suction temp

[Sandro Baptista]

In the cold storage on the wall about 40 feet directly below 3 evaps.Yes we r using ammonia,yes inches of mercury im referring to is suction pressure.Minimum temp i have seen in cold storage is -27.5 C.

1) If the temperature transmitter is below the evaps (near the door) is normal the air temperature rapidly increases and stay high during the doors are open. Try do move way the probe from the door or...use a product simulation compound surrounds the sensor element ensuring response time as EN441-13. It's a case where is the probe that is fill with specific gel. It will have a delay in response like the shrimp.

2) Does the doors is equipped with air curtains or strips to reduce the infiltrations of air and moisture? Or better an dehydrating systems like Munters? Maybe if the cold store has a lot of service it would be nice to install them or one of them.

3) You said the minimum temperature reached was -27,5ºC. What's the set-point (I still could get this answer from you)? If it's -25ºC and your average temperature is -25ºC with a deviation of 2K from the set-point it's nice (of course when you open the door and because you have the probe just near the door the temperature ups).

4) What's the temperature of the shrimp when enters in the cold store?

5) Why the compressors, is they are in parallel, working for the same circuit have so much difference on the discharge pressure and suction pressure? Are transmitters well calibrated?

[Sandro Baptista]

Sorry, where I wrote "What's the set-point (I still could get this answer from you)?" I meant: "What's the set-point (I still couldn't get this answer from you)?"

[Sandro Baptista]

Stanthonycold,

Any news?

[Sandro Baptista]

Stanthonycold,

Because you so far you not told us anything else I hope your problem be resolved. I hope our advices at RE had help.

Regards

[yorkman_gr]

Also hi was not tel what type of system it is, direct expansion or with a suction drum using 717 pumps to circulate the ammonia inside the evaporators,also hi was not telling if drain oil out oh his system,and so far i understood his is talking about cold storage but to me seem a freeze tunnel, because one u freeze your shrimps on about -30 for at least 4 hours u don't have to to keep it in that low temperature any more,and i mean in so low temperature cool storage