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jakb21599
17-01-2011, 04:56 PM
Hello friends, was checking to see if any of you new some allternatives i can try to do and control moisture in a cooler.(8x10x10) I know the problem is because the evaporator is way over sized for the room.( I did not install:D) Coming behind someone to see if i can correct the problem.
It maintains the temperature of 35 (F) but does not run long enough to remove moisture from the air. I have installed door flaps trying to control some of the moisture but it did not work. Other than getting the right evaporator for the room, what are some other options i can do to control the moisture in the cooler? Thanks for your help

Gary
17-01-2011, 05:05 PM
Reduce the airflow through the coil. Fan blades with less pitch maybe? If the fan motor is multi-speed, switch to the lowest speed.

What is your target humidity?

Sandro Baptista
17-01-2011, 05:05 PM
At first try to reduce the air flow (changing the motor wiring if possible or obstructing the fans) then tell me the results.

More possibilities I have in mind but first focus this one.

jakb21599
17-01-2011, 05:36 PM
i was thinking along the lines as you about changing the fan blades to a lesser pitch but was not sure if doing that would cause coil to freeze up because of less air flow. The fans are fixed speed. The evaporator has 2 fans. Would taking one fan out of service help, using only half the coil? or use both fans, just change the pitch on blades.
The target humidity i am not sure about. I know that they can load the cooler up with meat already boxed and 2 days later all the boxes have collapsed on each other from moisture. What would be a target humidity for the room?

Sandro Baptista
17-01-2011, 06:00 PM
You can use a frequency converter for the motor and try to achieve the best result. But I would first obstruct the air flow of the airflow with a kind of filter with a narrow mesh, for example.
About the boxes...are they made of cartoon?

jakb21599
17-01-2011, 06:05 PM
yes card board boxes. Your talking about putting a filter of some sort over the back side of the coil?

Sandro Baptista
17-01-2011, 06:42 PM
Yes, if your evaporator is draw type.
Then you could see the behavior/tendency of the moisture quantity on the air by observe if there were any improvements.

Have that cold room air curtains or something like that avoid the ingress of hot air?

DTLarca
17-01-2011, 06:45 PM
Hello friends, was checking to see if any of you new some allternatives i can try to do and control moisture in a cooler.(8x10x10) I know the problem is because the evaporator is way over sized for the room.( I did not install:D) Coming behind someone to see if i can correct the problem.
It maintains the temperature of 35 (F) but does not run long enough to remove moisture from the air. I have installed door flaps trying to control some of the moisture but it did not work. Other than getting the right evaporator for the room, what are some other options i can do to control the moisture in the cooler? Thanks for your help

Reading through the posts another thing you can do is reduce the amount of the coil you use - sometimes the TEV bulb can be moved further back into the coil. Other times simply raising the superheat will work and then other times the next size down orifice will work.

You could even cut every second blade off the fans though you would be busy for a while fine cutting to get them balanced :)

You could remove one or two fans and block the spigot with sheet metal.

You could even install a humidistat configured to cycle one or two of the fans.

Gary
17-01-2011, 06:46 PM
As I understand it, the maximum humidity for cardboard is 70%.

Measure the coil air in and air out temps. The difference between these two are the coil delta-T aka dT. The dT should be 8-10F.

If the air in temp is 35F, then the air out temp should be 25-27F. The lower the air out temp, the more moisture is being removed.

I wouldn't worry about frosting the coil. It will defrost itself on the off cycle.

jakb21599
17-01-2011, 07:03 PM
Thanks guys, I will try using the filter method first, if that does not work i will try the other methods you mentioned. I will post the results

Sandro Baptista
17-01-2011, 07:03 PM
Reading through the posts another thing you can do is reduce the amount of the coil you use

I you reduce the coil it would work longer in each cycle but the condensate by each second will be less. If the compressor is capacity enough to maintain an evaporating temperature of 10K below the medium air temperature it would be good have the all coil well feed with refrigerant...so more dehydrate capacity it can be gotten.

DTLarca
17-01-2011, 07:25 PM
I you reduce the coil it would work longer in each cycle but the condensate by each second will be less. If the compressor is capacity enough to maintain an evaporating temperature of 10K below the medium air temperature it would be good have the all coil well feed with refrigerant...so more dehydrate capacity it can be gotten.

The condensate might be less but the dry heat removed will be even more less - i.e. lower SHR = longer run times and a greater proportion of moisture removal.

charlie patt
17-01-2011, 08:12 PM
air off df or electric

Sandro Baptista
18-01-2011, 01:14 AM
The condensate might be less but the dry heat removed will be even more less - i.e. lower SHR = longer run times and a greater proportion of moisture removal.

I can see it that way. Please can you send me docs that proof it? I see that, (considering that the evaporating temperature is maintained), increasing superheat you will approach coil temperature of that region to the air temperature so more difficult will be the water condensation.

mad fridgie
18-01-2011, 01:30 AM
If you increase the superheat, you will effectively be reduceing the evaporation temperature (valve will be trottling down) Only part of the coil will be used for latent cooling, this gives you the impression that the air flow has been reduced (as only part of the air is refrigerated), i do not see high superheat being a problem here. The advantage of this method "if needed" is that you still have a large air throw (how far it blows), i would in this instance install a simple manual fan speed control (similar to a dimmer switch for lights) presuming that the fan moters are able to take this method. (being so small)

Gary
18-01-2011, 01:47 AM
If the coil is fed top down and the bottom of the coil is made inactive due to high superheat, then the water can run down the coil and re-humidify the air flowing through the bottom passes.

Gary
18-01-2011, 01:49 AM
In a pinch, I would flip the fan blades over to where they are backhanding the air. This would drastically reduce the air flow. If you have multiple fans, you might try flipping one blade at a time and then checking the dT.

jakb21599
18-01-2011, 01:59 AM
I put a filter on the back to see how well it works. I will check on tomorrow. If no changes in the room, then i am going to install a fan speed control for the fans and reduce the rpm. Any suggestions on as to how much to reduce the rpm. It is at 1075 rpm now. Would cutting rpm in half to around 535 rpm be to much? Or is it something i will just have to play with to find the right spot?

jakb21599
18-01-2011, 02:03 AM
In a pinch, I would flip the fan blades over to where they are backhanding the air. This would drastically reduce the air flow. If you have multiple fans, you might try flipping one blade at a time and then checking the dT.
Good idea Gary, I will do that first before putting fan speed control on

mad fridgie
18-01-2011, 02:07 AM
If the coil is fed top down and the bottom of the coil is made inactive due to high superheat, then the water can run down the coil and re-humidify the air flowing through the bottom passes.
A bit purist, "I thinks" Gary, practically not much!!!!!!!!!!

Sandro Baptista
18-01-2011, 10:28 AM
I put a filter on the back to see how well it works. I will check on tomorrow. If no changes in the room, then i am going to install a fan speed control for the fans and reduce the rpm. Any suggestions on as to how much to reduce the rpm. It is at 1075 rpm now. Would cutting rpm in half to around 535 rpm be to much? Or is it something i will just have to play with to find the right spot?

Are this cold room working alone with a compressor or is integrated on a centralized plant?

1) What's the suction pressure at outlet of evaporator and what's the refrigerant?

2) How does the evaporator defrost? By air or electric?

DTLarca
18-01-2011, 10:59 AM
I put a filter on the back to see how well it works. I will check on tomorrow. If no changes in the room, then i am going to install a fan speed control for the fans and reduce the rpm. Any suggestions on as to how much to reduce the rpm. It is at 1075 rpm now. Would cutting rpm in half to around 535 rpm be to much? Or is it something i will just have to play with to find the right spot?

If it's on a pack system you would also need to reduce the set saturation suction pressure.

The idea behind reducing air flow is simply to reduce the average coil temperature. We call the average coil temperature ADP (Apparatus Dew Point Temperature). The tips of the fins are near to room temperature, the surface of the tubes are near to refrigerant temperature. The average might be 3K above refrigerant temperature. If you had some other way to drop the refrigerant temperature then you would not need to slow the fans down. Otherwise we are slowing the fans down only because we want to drop the refrigerant temperature and the average coil temperature. Though it is also somewhat true that if you slow the air flow down the average coil temperature will also reduce even if the refrigerant temperature does not reduce, this is related to log mean TD, the main idea is to drop the refrigerant temperature.

So you want to make sure there is no EPR in action, that the head pressure control is set lower than normal etc. But you want to be watching your saturated evaporating temperature - you want to drop that a few degrees. But you also want to make sure the TEV is installed properly and set properly.

Sandro Baptista
20-01-2011, 03:11 PM
I put a filter on the back to see how well it works. I will check on tomorrow. If no changes in the room, then i am going to install a fan speed control for the fans and reduce the rpm. Any suggestions on as to how much to reduce the rpm. It is at 1075 rpm now. Would cutting rpm in half to around 535 rpm be to much? Or is it something i will just have to play with to find the right spot?

Jakb,

How is that going? Any news?

Freezon
27-01-2011, 12:08 AM
Several great idea's have been posted. Most of which will have an impact on compressor superheat(20 degrees recommended minimum) or possibly oil return. Beware!
If the compressor is indoors and not effected by ambients, you can control box temp with lo psi cut out and have little to no effect on superheat issues.
This way you can get your box much, much colder and air/defrost. I, ve done this many of times and it works like a dream. Good luck either way.