Newbie Questions. Please explain fan speed controller to me

[labpaul]

Refrigeration is not my line of work so please forgive me if I get the terminology wrong. I'm trying to better understand my setup so I can communicate better with our service people. What I'm describing is essentially from my observations over the past 3 years of ownership.

I work in a science lab and have essentially a walk-in freezer (-20 deg C) on the 2nd floor. The condenser is on the roof two stories up in an uninsulated enclosure. There are two Copeland scroll compressors connected in series (?). I say series because they don't each have their own line set to the evaporator in the cold room. One runs for 3.5 days and then it switches to the other one for 3.5 days. There are two fans on the condenser controlled by an Acontrol variable speed controller. I believe it is pressure actuated.

With the extreme cold and wind we are experiencing on the US East Coast, the 404a refrigerant has "shrunken" so much that the compressors are in a low pressure situation and can't make the cold room cold. It happens to me nearly every winter and in the summer I have the reverse situation with the system going into high pressure alarm or freezing the coil in the evaporator. Last Friday I had the local service come out to add more 404a and the system ran fine until Monday when the temps dropped even lower. Last night the temperatures warmed and the wind died down so the system is fine again.

The system was built in England and the local service company isn't familiar with all these foreign components. We are now off service contract with the English company so now we can't rely on the customer support there for help. The local service company is just who our company uses for service.

Although the service calls aren't exceedingly expensive, it is extremely inconvenient to always be worried that on very hot or cold days the system will stop cooling. The local company said they could replace our receiver with a larger one. They think ours is undersized. This, as I understand it, would provide some buffering on very hot or cold days.

Someone on another forum suggested that I focus on the fan speed controller instead to maintain the head pressure. This is where I'm confused (although you may think it happened earlier . I thought the fans were there just to cool the running compressor. The fans are variable speed. With it being so cold, the fans are spinning noticeably slower. On extremely hot days, both fans will run. So does the fan speed controller serve another function--like increasing head pressure somehow? I can't find a resource online that I understand--too technical.

One problem (of many) is the controller (Acontrol brand) is European made and displays bars. The local guy only wants to work in psi and doesn't want to do the math--it's a straightforward conversion, isn't it? It's also a controller the local company is not familiar with even though I have the manual. A few years ago I had the local guy (foreign with poor English) talk to the British support (thick ****ney accent) on a bad cell phone connection. We didn't get very far.

Can someone point me in the right direction or explain in layman's terms what the fan speed controller does and how it can be adjusted to compensate for these temperature swings without adding or taking out gas?

Thank you,
Paul

[Rob White]

.

Hi ya......

First thing first is bar to psi.

There are 15 psi (14.7 if you'r pedantic) to every bar

1 bar = 15 psi
2 bar = 30 psi
3 bar = 45 psi
4 bar = 60 psi
5 bar = 75 psi
6 bar = 90 psi
7 bar = 105 psi
8 bar = 120 psi
9 bar = 135 psi
10 bar = 150 psi And so on.............

Secondly, fan speed. To explain this in layman's terms without insulting you will be hard so
bare with me.

The condenser tends to work in ambient conditions, so in winter months as you well know the
temp is cold so the discharge / condensing temp / pressure is low. In summer months the
discharge / condensing temp / pressure is high.

The pressure / temperature of the refrigerant at this point is very important because it needs to be
about 15 degs above ambient if the ambient is low the refrigerant pressure / temperature will
also be low and if it is high the refrigerant pressure / temperature will be high, as you have found
out.

That then brings us to fan speed control. If I blow lots of ambient air over the condenser coil
the coil will give up its heat to the ambient and this is a key factor of how the thing works
because that is the temperature that the refrigerant turns from a high pressure vapour to a
high pressure liquid. We condense the refrigerant inside the condenser and it is done at about
15 degs above ambient.

If the fans are running too hard in the winter and if the ambient is too low then the refrigerant
condenses to too low a pressure for the system to work. By stopping the fans or slowing the
fans down you allow the condensing pressure to remain at a workable high level.


Regards

Rob

.

[labpaul]

Rob, thank you for taking the time to explain that. It's been a while since I had high school physics and I was pretty sure bar to psi was straightforward like that.

In a cold ambient situation is it that the refrigerant pressure is low and thus can't "prime" the compressor? Like not having my straw reach far enough into a glass to take a drink?

It doesn't seem practical to keep adding refrigerant to overcome this low pressure situation because when it warms up enough, I'll be in an over-pressure situation. Even if I could shut off the fan, my only solution would be to add more refrigerant because obviously I don't need to cool the compressor.

Does it seem reasonable to install a larger receiver to help even out the highs and lows?

Alternatively it seems like you could warm the refrigerant to overcome the low ambient situation. Is this done? The heating element would automatically adjust to compensate for ambient. In the summer it would be off, but your system would be charged for summer conditions so you'd never experience high or low pressure situations.

Thanks,
Paul

[r.bartlett]

Refrigeration is not my line of work so please forgive me if I get the terminology wrong. I'm trying to better understand my setup so I can communicate better with our service people. What I'm describing is essentially from my observations over the past 3 years of ownership.

I work in a science lab and have essentially a walk-in freezer (-20 deg C) on the 2nd floor. The condenser is on the roof two stories up in an uninsulated enclosure. There are two Copeland scroll compressors connected in series (?). I say series because they don't each have their own line set to the evaporator in the cold room. One runs for 3.5 days and then it switches to the other one for 3.5 days. There are two fans on the condenser controlled by an Acontrol variable speed controller. I believe it is pressure actuated.

With the extreme cold and wind we are experiencing on the US East Coast, the 404a refrigerant has "shrunken" so much that the compressors are in a low pressure situation and can't make the cold room cold. It happens to me nearly every winter and in the summer I have the reverse situation with the system going into high pressure alarm or freezing the coil in the evaporator. Last Friday I had the local service come out to add more 404a and the system ran fine until Monday when the temps dropped even lower. Last night the temperatures warmed and the wind died down so the system is fine again.

The system was built in England and the local service company isn't familiar with all these foreign components. We are now off service contract with the English company so now we can't rely on the customer support there for help. The local service company is just who our company uses for service.

Although the service calls aren't exceedingly expensive, it is extremely inconvenient to always be worried that on very hot or cold days the system will stop cooling. The local company said they could replace our receiver with a larger one. They think ours is undersized. This, as I understand it, would provide some buffering on very hot or cold days.

Someone on another forum suggested that I focus on the fan speed controller instead to maintain the head pressure. This is where I'm confused (although you may think it happened earlier . I thought the fans were there just to cool the running compressor. The fans are variable speed. With it being so cold, the fans are spinning noticeably slower. On extremely hot days, both fans will run. So does the fan speed controller serve another function--like increasing head pressure somehow? I can't find a resource online that I understand--too technical.

One problem (of many) is the controller (Acontrol brand) is European made and displays bars. The local guy only wants to work in psi and doesn't want to do the math--it's a straightforward conversion, isn't it? It's also a controller the local company is not familiar with even though I have the manual. A few years ago I had the local guy (foreign with poor English) talk to the British support (thick ****ney accent) on a bad cell phone connection. We didn't get very far.

Can someone point me in the right direction or explain in layman's terms what the fan speed controller does and how it can be adjusted to compensate for these temperature swings without adding or taking out gas?

Thank you,
Paul

Not to put too fine a point on it your local guy is a complete d.i.c.k

Get someone from this forum or hvactalk who is prepared to divide by 15

also post some pictures of the unit and controller we will sort it out whilst you find a decent fridgie

[Grizzly]

Well Said RB!
Well and kindly put! RW!
Labpaul.
If you do as asked and give more detail about the controller.
There is a good chance that it may be possible for it to display in Imperial measurements.

Your issue IS Highly Likely, to be a direct result of the extreme Ambient temps you explain.

So get a tech that knows what he is doing and leave the refrigerant charge alone until it is proven to be an issue!
Also there are MANY Chillers both American and European, or anywhere else in the world that are not designed to run in the low ambient high chill factor conditions you are experiencing.

If your tech is saying what you say he is then He does not know what he is doing. Full Stop!

Grizzly

[labpaul]

This is the condensing system on the factory floor in the UK. It's approximately 5'L x 3'W x 3'H. The compressors are Copeland scroll Model ZF13K4E-TF5.

Attachment 11066


Close up of Compressor 1. I don't remember now but about 2 years ago, the local company found a leak (amongst many) in the receiver (?). The current configuration has the shiny metal tank you see in the lower left swapped places with the blank tank.

Attachment 11067


Close up of Compressor 2:

Attachment 11068


High pressure gauge. System is not running:

Attachment 11069


Low pressure gauge. System is not running:

Attachment 11070

More pics in next post. Stay tuned.

[labpaul]

I don't know why the attachments aren't showing in my previous post, but they are clickable.

Acontrol model PXET6AQ fan speed controller:

IMAG1146.jpg


Danfoss pressure switches:

IMAG1147.jpg


Exterior of refrigeration control panel on 2nd floor:

IMAG1143.jpg


Interior of control panel:

IMAG1144.jpg


The local company did not build the system. They just happen to be the ones who our facility management uses to service all the lab cold rooms. This refrigeration system is actually only a small component of the unit. The cold room has 2 robots inside which are the important parts. The guys who service the robot are a different company/division from the refrigeration company and even they have trouble figuring out what everything in that panel does. I've been learning with the local guys what everything in there is for. I included the picture but I don't think it's important to this discussion. We no longer have a service contract with the robot servicers (domestic) and the refrigeration company (UK based, but under the other contract) for money reasons.

In the summer of 2011, we discovered a leak in the evaporator coil. The copper in the coil was rubbed through where it entered and exited the evaporator as it looped back and forth. Local company patched it and we were fine until the summer of 2012 when it happened again but on the other side of the coil. Local company patched us up again but I made enough of a stink that under contract we received a replacement unit--completely different model--and that has been reliable. Local company was under no obligation to do the work since we were under contract, but UK company paid for the repair and they couldn't be out here for days/weeks.

Thank you all for your input so far and your willingness to lend a hand. Please let me know if there is other information that would be helpful.

Paul

[r.bartlett]

looks a straight forward quality panel I see there is a wiring diagram so post that as well

the first set of pictures don't work for me

finally your local guy is suffering from what is describes as "Not made here" syndrome

[Grizzly]

Check out the link.
There is lots of info available, all you need is someone to explain it.
http://www.ziehl-abegg.com/ww/fans-p...rol-units.html

You can refer to the GB version of data but I expect that the run voltages are different.

Try covering your condenser coils when cold to retain the heat and enable "Lift" on start up.
You may get a hp trip as a consequence, but it will prove the influence of the cold weather / or not!

Grizzly

[labpaul]

Maybe pics will work now. I guess I haven't posted enough to be able to edit old posts.

I'll look through those documents on the Ziehl-Abegg site. I already spoke to them a few years ago but didn't get very far.

Condenser module on the factory floor in the UK. It's approximately 5'L x 3'W x 3'H. The compressors are Copeland scroll Model ZF13K4E-TF5.




Close up of Compressor 1.




Close up of Compressor 2:




High pressure gauge. System is not running but was running a couple minutes earlier.




Low pressure gauge. System is not running but was running a couple minutes earlier.




Acontrol model PXET6AQ fan speed controller:




Danfoss pressure switches:




Exterior of refrigeration control panel on 2nd floor:




Interior of control panel:

[Rob White]

In a cold ambient situation is it that the refrigerant pressure is low and thus can't "prime" the compressor? Like not having my straw reach far enough into a glass to take a drink?


Paul

No your understanding is a bit wrong.

In your photo of the gauge

https://lh5.googleusercontent.com/-a...o/IMAG1150.jpg

Do you see the scales around the out side?

Well the pressure scales are obvious

but if you look closer in you will see temperature scales for different refrigerants.

Yours is R404a so if you look at the gauge it shows about 8.5 bar pressure (130 ish psi)
and on the R404a scale that translates to a temperature of about +15 degC.

That is way too low and needs to be nearer the black marks at 16 - 17 ish bar.

It has nothing to do with the charge of refrigerant. It has everything to do with
the temperature** and your guys should Know this. I would not call him a d.i.c.k
as has been suggested but if he was a true refrigeration engineer he would know.

If you cover the condenser so air is restricted you will see the pressure start to rise,
be careful you don't let it get too high. On the high side pressure switch in the photo
it seems that the high pressure switch is set to activate at about 24 - 25 bar and it is
manual reset so if that trips the only way to get the thing working again is by manually
resetting the green button on the top of the switch.

https://lh5.googleusercontent.com/-o...o/IMAG1147.jpg

If you cover half or part of the condenser with a blanket, watch the pressure gauge
(high side) and move the blanket on or off to ensure the pressure stays near to 18 bar.

That will prove to you that the system is working OK and just needs to be acclimatized
to you low ambient temps.

Rob

**That statement is correct assuming the system is correctly charged and is working OK
under normal conditions.

.

[Rob White]

.

Ps did you notice who supplied the gauges.

Rob

.

[Brian_UK]

If it is due to the variation of ambient temperatures it might be worthwhile investigating the installation of a head pressure controlled damper across the condenser coil.

[Grizzly]

May I suggest you lag your compressors, as the start-up temperature can have a critical effect on your plant.
Especially given yours is a low ambient issue!
"WE" all noticed the Gauges Rob!
Try as suggested getting the system running with a higher discharge temp / pressure.
Plus with a higher fan speed control point the comp on start-up.
Will be allowed to develop enough temperature differential for the system to operate correctly.
If started when cold and not the system is not able to generate sufficient heat and the desired pressures.
You will fail on LP.
It is basic stuff really, which is what we are all trying to say.
Incidentally your HP cut out seems to be set rather low!
Grizzly

[FreezerGeezer]

Grizzly, I wonder if the HP on the right is actually a control instead of a safety? The combined HP/LP to the left looks to have the HP set to around 25Bar?

Labpaul, a clear photo of the wiring diagram(s) would really help please.
Comp. 1 looks like there may be / have been a leak in the area - note the oily looking patch on the side. It could be moisture though.

We used to get issues in winter on the supermarket packs since we typically ran them with enough charge to keep everything at temp, as opposed to the design charge - so less refrigerant was lost to the seemingly inevitable leak(s). In cold weather the refrigerant tended to migrate to the condensers if the liquid receivers were indoors & due to the low charge the evaporators would starve. In that case, we added enough refrigerant to overcome the issue & get things flowing.
It does sound like the head pressure control isn't set up right, or isn't performing correctly for some reason.

[labpaul]

It's all becoming clearer but it still seems like I'm in a "it depends" situation. Anyway, after the sub-zero temps of this past weekend, we have warmed enough that there have been no further issues. Now I'll wait until it gets super cold again or super hot for the next call.

I know the tech is not a "refrigeration engineer", but more of an apprentice or something along those lines. The owner of the company (presumably the expert?) has accompanied him on a few calls and understandably they are all "emergencies" so they are there to address the immediate problem--usually add or subtract refrigerant--and not really look for the long term solution so they can move on to the next call.

Now that the responsibility of service is on me and not on the original builder, I want a long term solution because these issues always arise right before a weekend or holiday, or at 5pm right before I leave work. I am in Maryland in the Washington, DC region. If you are connected with anyone in this region who you know could address the issues you all have raised, please post here or send me a private message.

Thank you,
Paul

[Gary]

You might find this helpful:

http://www.refrigeration-engineer.co...rigeration-101