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kengineering
21-02-2008, 11:44 PM
A 404 open merchandiser. suppy air 29 to 31*f; inside case air temps 35 38. but the product temps after 24 hrs. won't fall below 42*f; There are no drafts and the ambient is 69*f with low humidity. Just not sure where to begin

Toosh
22-02-2008, 03:45 AM
HI Kent I presume you have had your guages on, tis the best way to analyse the system and it gives us something to work with

Regards Norm

Electrocoolman
22-02-2008, 09:32 AM
This definitely looks like airflow problems....
Check that the cabinet fan plate has been correctly installed.
I've found several times that the shop has had the cabinet apart for cleaning and have assembled the fan baffle/mounting plate incorrectly so that there is hardly any airflow thru' evap and not enough blow to distribute cold air up to shelves and overhead discharge.
Base deck will often be cold with rest of cabinet a lot warmer.

Gary
22-02-2008, 02:20 PM
A 404 open merchandiser. suppy air 29 to 31*f; inside case air temps 35 38. but the product temps after 24 hrs. won't fall below 42*f; There are no drafts and the ambient is 69*f with low humidity. Just not sure where to begin

I'm having trouble visualizing this system. Is this open top or open front? Single deck or multi-deck? Single fan or multiple fans? Connected to a rack or self-contained? TXV or cap tube? What type of defrost?

In your description it sounds as if the product is surrounded by cold air, yet its temperature refuses to drop. That doesn't seem possible.

Exactly where and how are you measuring these temperatures?

Always begin with air flow. Are all fans running properly? Is the coil clear? It may (or may not) be necessary to have all or part of the products removed from the case in order to visually inspect the fans and coil.

kengineering
23-02-2008, 01:31 AM
I hastily put this up and I should give you all the complete situation.

I work for a small case manufacturer who's specialty is very custom oriented. We have had an open merchandiser that needs an up dated appearance. Our cases to this point have been simple. R-22, morrell evap motors, paragon defrost timer all run by a low pressure control. They work fine but the sales are driving us to technology.
I am not an engineer but, in charge of production, I have designed most of our projects.
The company has had an associate change all the components. A 404A condensing unit, GE Benoit fans, different coil design, electronic temp/defrost control and a slightly different cabinet shape which changed the way air moves in it. It is multideck open front
With temperture probes and a fluke unit the temp readings are ; Coil temp 4*f, return air 33*f , shelf air temp 36-38, but the bottle of water right next to the shelf temp won't go below 41*f . This is puzzling and dosent seem possible

I would like to help him solve the problem and have suggested we check super heat and sub cooling but my input is not taken.
Shouldn't there be some definite numbers to expect in a correctly working 404A Txv open beverage case? Not just SH SC but air velocity as well an whatever standard expectations ther should be

Thanks, Ken

The Viking
23-02-2008, 01:42 AM
Considering that you are a manufacturer and that it seems like if you invested some money in designing a new system....

Why don't you get a proper, hands on, refrigeration engineer in to give it a once over and evaluate the whole set-up?

powell
23-02-2008, 04:36 AM
With temperture probes and a fluke unit the temp readings are ; Coil temp 4*f, return air 33*f , shelf air temp 36-38, but the bottle of water right next to the shelf temp won't go below 41*f . This is puzzling and dosent seem possible

Not enough btuh or air flow problems.

Gary
23-02-2008, 04:46 AM
Sounds like a frozen coil to me... definitely an airflow problem... could be something as simple as one of the new fans running backwards... or insufficient defrost.. or a baffle out of place... or... or...

The air enters the coil at 33F. It must exit the coil at something substantially less than 33F, yet the shelf is running 36-38F. The cold supply air isn't getting to the shelf.

When there is an airflow problem in a multi-deck, the cold supply air doesn't reach the top shelf, the coil temperature drops, and the coil freezes... but not necessarily in that order.

Gary
23-02-2008, 02:46 PM
Here's another possibility: Fan blades flipped over so that they backhand the air instead of scooping the air.

paul_h
23-02-2008, 05:17 PM
Agree, it sound like there is cold air, just not enough of it to get product cold, so check coils for icing, fans for operation, ductwork for airflow, coil for being the right size, refrig charge for being correct, and all components operational and the right size.

Another thing, don't reach ins rely in heaters for an air barrier? Never worked on them, so I don't know what effect non operational heaters have on them.

edit: wait, so you're not an engineer, but you are designing new systems. And when they don't work, you want someone to check the refrig system charge, and whoever is in charge is ignoring you?
Not being nasty, but ask the people who are ignoring you* how to fix.


*You're suggesting something they are ignoring, so there's no fault with you, but then again any troubleshooting we do with you is wasted time on our part since they might ignore you with our suggestions.

kengineering
24-02-2008, 10:54 PM
i did find some ice on the coil from 48hr. of run time so Changing the defrost termination is in order. I havw just found out that the condensing unit is a nominal1.25hp.404A we previously have used a 3/4 hp. R-22 unit. Could oversizing case preset the problemm, perhaps the super cold coil that satisfies before the products give it up? Is that possible?
The fans were checked and changed to the morrill 9W and the results are simular only noisier which is why wer're changing them.
As far as my associate I could care less if he gets it, I'm not here to help him I'm one who just needs to know for my own head. I had an instructor who used to say " Be the refrigerant" if ya know what I mean. Thanks, Ken

Pooh
25-02-2008, 01:00 AM
Ken
just a basic question but was the system charged with liquid or vapour from the bottle initially?

Ian

kengineering
25-02-2008, 01:35 AM
404a Liquid only to satisfy a full sight glass. tommorrow I will change the condensing unit and txv to a smaller size.
Question: if super heat is very low, because the coil is flooded, and I close the valve-doesn't the coil pressurre fall further wont the SH get lower?
Ken

Gary
25-02-2008, 05:58 AM
Regardless of any other suspected problems, the bottom line is that the cold air leaving the coil is not getting up to the top shelf. That's an airflow problem and nothing is going to work right until this is resolved.

Gary
25-02-2008, 06:01 AM
Hmmm... I recall working on a multi-deck freezer that had an ice build-up inside the back wall (supply air duct). The coil was clear, but no air could get through. Something to think about.

Gary
25-02-2008, 06:13 AM
404a Liquid only to satisfy a full sight glass. tommorrow I will change the condensing unit and txv to a smaller size.
Question: if super heat is very low, because the coil is flooded, and I close the valve-doesn't the coil pressurre fall further wont the SH get lower?
Ken

No... the pressure drops and the superheat rises.

If the superheat is low, that's because you have an airflow problem. Don't even think about superheat until you have good airflow.

Always start with airflow. Insufficient airflow affects everything else, throughout the system.

Be the airflow... then be the refrigerant.

kengineering
26-02-2008, 01:58 AM
No... the pressure drops and the superheat rises.

If the superheat is low, that's because you have an airflow problem. Don't even think about superheat until you have good airflow.

Always start with airflow. Insufficient airflow affects everything else, throughout the system.

Be the airflow... then be the refrigerant.

I found the problem with coil freezing . The fins were flat on the deck and the coil was defrosting but not draining well and refreezing probably increasing in size each time.
I did a smoke test that appeared airflow was good but compared to what I'm not sure. No baseline info. Is there a velomiter or magnehelic reading I colud take that is ideal or expected?
When I was in school one of the subjects that was skipped was Pychometrics. "You guys will never need to know this so were just gonna skip this stuff". Actually the school I attended was full of "either you go to school or you go to jail " kinda guys so I never felt challenged and have really learned through self study and practice with some mentoring from this site. Help Mr.Wizard
Thanks,
Ken

Gary
26-02-2008, 04:44 AM
Measure the temperatures of the supply air (as close to the coil as possible) and the return air.

The difference between these two temperatures should be no more than 20F. More than 20F means there is not enough airflow.

In addition, there must be enough airflow to bring the top shelf down to temperature.

Gary
26-02-2008, 04:57 AM
I did a smoke test that appeared airflow was good but compared to what I'm not sure.

Did you get plenty of smoke up to the top shelf? Cold air falls, so if the top shelf is well fed the rest of the case will be happy, too.

kengineering
27-02-2008, 01:48 AM
I will check the TD of the evap tomorrow for the 20 degrees. The smoke seemd to be well distributed and stay in the cabnet. since some changes maybe another test would be in order. Question? The new coil
design has a staggered coil vs. or old design with inline tube and fin. The belief was a more effecient coil with the staggerd one. Could this change have effected the airflow causing this rude behavior.
Ken

Hey Gary how's the fishin?

Gary
27-02-2008, 05:32 AM
I will check the TD of the evap tomorrow for the 20 degrees.

The air in/air out temp difference is called the delta-T or dT.

The TD is the difference between air in and saturated suction temp.


The smoke seemd to be well distributed and stay in the cabnet. since some changes maybe another test would be in order. Question? The new coil
design has a staggered coil vs. or old design with inline tube and fin. The belief was a more effecient coil with the staggerd one. Could this change have effected the airflow causing this rude behavior.

We'll find out when you measure the dT.


Hey Gary how's the fishin?

Not my thing... but the riding is great... good weather and lots of twisty back roads. When I get old, maybe I'll try fishing... LOL

Gary
27-02-2008, 06:52 AM
I take it this is a prototype case?

What is your target temperature and humidity?

750 Valve
01-03-2008, 12:21 PM
Just a few side questions here...

What angle are your shelves on? And do they stick out beyond the air curtain formed by the front air disharge grille?

Flat shelves are easy to refrigerate, angled shelves will show up any shortcomings in air volume a lot quicker.

Is your rear air distribution duct fully perforated or are there holes cut at different levels for the individual shelves.

If you have done wholesale changes to fans and coil it sounds like an airflow prblem has occurred. Try measuring air velocities on an older non refurbished case and compare them to your new setup, I'll bet there is a difference in air volume that the fans are moving or static pressure developed by new fans is now less and can't overcome losses in air side pressure drop in new coil.