frost top construction ???

**herefishy** · 24-06-2003, 01:37 PM

Originally posted by Tom Richardson
.... EPR adjusting......

errrrr.... EPR removal....... that should be

**Gary** · 24-06-2003, 02:18 PM

If he removes the EPR, the SST will run about 0-5F, dropping below zero each time the coil cycles off, because the compressor is too big. This isn't necessarily a bad thing (we can downsize the condensing unit), but I'm not convinced that the frost top shouldn't be under its control, at least for the time being, so we can see what its TD is and determine what size compressor is needed.

I would agree with adjusting the cold control 'off' setting to 24F in order to stop the rapid cycling, though (assuming humidity control is not needed). We need to see the frost top TD under stabile operation.

I would like to see both suction lines connected at the EPR inlet, and the EPR remain at its 55psi setting. We can then stabilize operation, regulating the frost top temperature by adjusting the EPR, and judge relative compressor sizing by the SST at compressor inlet.

At that point Tom gets to make executive decisions. He can have smaller condensing unit or faster pulldown. He can have rock steady frost top temperature or eliminate the EPR and let the frost top temperature swing with the coil cycles.

**herefishy** · 24-06-2003, 02:30 PM

What I don't understand, is it is assumed that we have a 6,000btuh load. the bohn is what, a 430btuh/degFTD? And we had derived that @ a 10degF TD (although I say the design should be a 15F T.D.) we would employ a 4,300btuh load, and allow the remaining 1K+ capacity for the frost top.

One thing I was going to point out earlier though, Gary, is that you demonstrated that the forced air coil superheat is 20F to 30F. I think that this may be a key in the non-performance of the system a this time. I think if the superheats get set properly that we will see a good 20F suction throughout the system (without EPR).

If the three-quarter is now being employed, it is rated up to a 30F SST.

**herefishy** · 24-06-2003, 02:50 PM

If I refer to the 3/4 horse performance chart, @ 0F SST, we could conclude that we are doing 4,318btuh ??

**Gary** · 24-06-2003, 02:53 PM

I don't doubt that the EPR may be eliminated, but with it we can get both coils under control and see what the actual loads are rather than depending upon assumptions, calculations, and predictions. A measurement beats a calculation every time.

**Gary** · 24-06-2003, 02:56 PM

It is my understanding that the 1/2 hp unit is currently being used, but I may be mistaken.

**herefishy** · 24-06-2003, 03:01 PM

Well, if it's the 1/2 horse, then we're doing approx 3,110btuh @ 0F.

**Gary** · 24-06-2003, 03:01 PM

I don't think we can draw any conclusions concerning btu until we have proper orfices, correct superheat settings, and stabile operation.

**DaBit** · 24-06-2003, 04:01 PM

Originally posted by Andy
Maybe not I have quoted figures for the more common TE2 type NOT the horrible TUAE.

Besides it being a brazed valve instead of a flared valve, what is wrong with it? I am currently using one (TUAE R404a #0), and it seems to work very good, even when too little load is put on it.

Besides, here in The Netherlands it is not allowed to use flare connections when a brazed alternative is available.

**Andy** · 24-06-2003, 04:39 PM

Hi Dabit

the brazed type is preferable on HFC refrigerants, but still a pian if you have to change it!
I supose I am harking back to the good old days when flare was the way to go

Don't forget that the majority of the world is still installing R22 quite merrily, only the EU has banned it

R22 to date has not a satisfactory replacement in all situations. i.e. flooded operation or water chilling.
Regards. Andy

**angryk** · 25-06-2003, 01:42 AM

Too young to miss R12, but I sure am going to miss R22

**Tom Richardson** · 25-06-2003, 06:45 AM

We have the 3/4 hp installed. The boss wants to test some more with the 3/4. He is very concerned - new ground and all. We are going against all he is being told by 'his experts'.
I changed the evap coil TEV orifice, installed the #2. This caused the on/off time to go from 2on/3off min to 2.75 on / 3 off. A move in the right direction.
Next, changed the thermostat sensing temp (herefishy) from 32 to 36 deg F. to 30 to 36 deg F. This had a positive effect on the evap cycle. It went to 4.5 min on / 3 min off. This unit runs for 14 hours straight, and freezing up has been a problem in the past. (could be the engineering - compressors to big or something like that....)
continued.

**Tom Richardson** · 25-06-2003, 06:49 AM

resumming..
One change @ a time. I ordered the #0 orifice for the frost top today.
EPR is set @ 60 psig from the original 55 psig. I really didn't see any great change here. I would like to eliminate the EPR altogether - it is a pain to pipe in. Explain the problems to be overcome by eliminating the EPR and maybe installing a CPR @ the compressor instead. Would / could this work? Can the EPR be adjusted such that it appears 'out of the circuit', like @ 70 or 75 psig? It is going to be a pain to remove, and a bigger political move. (service. service. service)
Superheats? Adjusting expansion valves? Guys, I am only an IMPROVING POSTER, everything I have read says "the last thing to adjust is the expansion valve, if it is ever adjusted at all." (I always wondered why the adjusting screw was there if this was a true statement???? )
Dan, is anybody close you know of ???
continued...

**Tom Richardson** · 25-06-2003, 06:50 AM

resumming...
Today's work plan:
Replace frost top TEV orifice,
work toward the evap coil cycle, would like to see 7-10 min on / 1 min off (if possible),
and work on the political side of this project - I like the mechanical & philosophical aspects of this work, having to convince the boss to go against everything we have done in the past - wish me luck, I will need it.
Overall, the #$&*%@ thing is "way too cold" and I think everyone(here) can see that now! The longer it runs, the colder it gets. The frost top is going from 15 to 19 deg F. Too cold. The air out of the evap coil is good at 33 to 35 deg F out and 39 to 40 deg F. back in. This is the best air curtain we have seen for a shallow unit. The pressures @ the compressor are: 16 to 21 psig @ return and 160 to 195 psig out. (with evap off/on.)

Thanks guys, you don't realize how much help this forum has been, first to me, second to my company. There are a lot of 'experts' out there that.........sorry.
Tom

**Gary** · 25-06-2003, 07:56 AM

I would like to eliminate the EPR altogether - it is a pain to pipe in. Explain the problems to be overcome by eliminating the EPR and maybe installing a CPR @ the compressor instead. Would / could this work?

How about installing the EPR @ the compressor instead? I would like to use it in the common suction line and adjust it to control the frost top temperature.

Can the EPR be adjusted such that it appears 'out of the circuit', like @ 70 or 75 psig? It is going to be a pain to remove, and a bigger political move. (service. service. service)

To make it appear out of the circuit you would take it in the other direction, down to minimum psig setting.

Today's work plan:
Replace frost top TEV orifice,
work toward the evap coil cycle, would like to see 7-10 min on / 1 min off (if possible),

Adjust the cold control to 24F off 38F on.

Move the EPR downstream from where the two suction lines come together.

Adjust the EPR to regulate the frost top temperature. Higher psi to raise the temp, lower psi to lower the temp.

Take a full set of temperature readings so we can see what it is doing.

**Andy** · 25-06-2003, 08:04 AM

Hi Tom

on the EPR, for the meantime just screw of the spring pressure exerted on the EPR, setting the pressure higher is not what you want on the evap coil. I would possibly run a while like this, just I still think you may need the EPR on the frost top.
I wouldn't fit the CPR with the EPR in use on say both circuits, but you could fit it if only one was thru the EPR (the different regulators would fight one and another)
What gas are you using? That head seems low for R404a, but about what R22 should be

Regards. Andy

**Gary** · 25-06-2003, 08:21 AM

Andy, with the EPR in the common suction, we can simulate the effects of a smaller compressor (raise the common SST), and adjust the EPR to control the frost top. Once we have the frost top temperature we want, we can see by the compressor inlet SST exactly what size compressor would be needed to match the simulated SST.

**Andy** · 25-06-2003, 08:26 AM

Hi Gary

fitting the EPR on the main suction would be a step forward.

why was it fitted to the evaporator for the well???
Come the day when a smaller compressor is fitted, we could then explore fitting a CPR for pulldown

By the way where has all the excessive head pressure went

Regards. Andy

**Andy** · 25-06-2003, 08:34 AM

Hi Tom

"the last thing to adjust is the expansion valve, if it is ever adjusted at all." (I always wondered why the adjusting screw was there if this was a true statement???? )

Time to think about adjusting those valves

Regards. Andy

**Gary** · 25-06-2003, 09:26 AM

fitting the EPR on the main suction would be a step forward. why was it fitted to the evaporator for the well???

I have no idea. I had assumed it was for humidity control, but apparently that is not the case.

Come the day when a smaller compressor is fitted, we could then explore fitting a CPR for pulldown

Once we get the orifices right, I doubt that the CPR will be needed. And in fact, when all is said and done, we may be able to get rid of the EPR as well.

**herefishy** · 25-06-2003, 03:08 PM

I think that the primary difficulty with all this, is that Tom Richardson (or the powers that be) had insisted that they needed a 6,000btuh capacity condensing unit. I think it is obvious (since the 3/4 horse is now in) that the actual required capacity is nearer to 3,500btuh @ 20degF SST. But all of us at this forumn assumed that there was some science behind the 6K figure... NOT!

The High head disappeared because the three quarter got put in. NOT becuase the 3/4 is a larger capacity unit, but because it is rated at a max. evap temp of 30F. the 1/2 horse was rated at a max evap temp of 25F.. which is why it couldn't handle the pulldown at a 35F evap temp.

I am beginning to think that a proper 1/2 horse of a true medium temp rating (the one they are using is rated med/low) might do the job, meaning perhaps a unit with a max evap temp rating of at least 30F... 35F would be preferrable, and would help assure long and prosperous compressor life (this is NOT a low temp application). If my assumptions are correct regarding the "real" capacity requirement, I might recommend a:

FTAH-A050 R-134A whose max evap temp is rated 45F (you'll never overload that sucker.. 3,300btuh @ 20F SST

or

F3AH-A050 R-22 whose max evap temp is 45F and 3,570btuh @ 20F SST

Also, the massive Bohn 430 coil that is in that box seems inapprpriate. Do we need all that CFM produced by it? A Bohn TL-21 or any evap near a 200btuh/degFT T.D. would seem appropriate. but if the airflow is a requirement, it is not an issue (it's more expensive), and the result is merely a low TD (ahem, higher SST referencing failure of 1/2 horse that cannot stand SST over 25F)

Of course that is assuming that the current 3/4 hp is as unloaded as it appears to be.

I don't think anyone in Tom Richardson's presence on this project is able to set the TEV (superheat), much less know what superheat actually is. Maybe he needs some direct instructions in how to perform the task (PS: always put the cap back onto the stem when monitoring the effects of an adjustment

)

But I swear!!!! If someone doesn't reset that d*mn cold control to a 24deg cut-out, I'm going to hop a plane, and go do it myself!!!!

Tom, The refrigerant that is boiling in the evaporator is approximately 19degrees, according to the information that you have provided. The coil must always be colder than the temperature of the space that you are cooling. Typically a refrigeration system is designed for the coil to be 10 degrees colder than the design space temperature. At a 35F space, the coil will be 25F. Because of system design T.D. (Temperature Difference between coil and refrigerated space) we can control space temperature by monitoring coil temperature (which is 10 degrees colder) and insure coil deforst if things go awry and the space is not at design, but the coil gets too cold (freezes).

Got it?

**herefishy** · 25-06-2003, 03:14 PM

Checking the cheat sheet on system size selection, I might equate the refrigerated space (cabinet storage) to perhaps a 6' backbar refrigerator. My cheat sheet recommends about 1,060btuh. An 8' backbar refrigerator is recommended at 1,416btuh.

Add to that the presumed 1Kbtuh for the frost top, and maybe another 1K for the infiltration from the air curtain.....

**herefishy** · 25-06-2003, 03:39 PM

But anyway... I'm not suggesting that we change course now. Let's get what we've got tuned up, and then we have these observations to refer to, upon evaluation of the conclusions of the current activity.

**Gary** · 25-06-2003, 03:50 PM

But all of us at this forumn assumed

I think not.

If my assumptions are correct regarding the "real" capacity requirement, I might recommend a:

FTAH-A050 R-134A whose max evap temp is rated 45F (you'll never overload that sucker.. 3,300btuh @ 20F SST

or

F3AH-A050 R-22 whose max evap temp is 45F and 3,570btuh @ 20F SST

Why are you so anxious to jump straight to the finish line? This is a prototype. We don't want to make it work. We want to perfect it, fine tuning each aspect of its operation, step by step.

Also, the massive Bohn 430 coil that is in that box seems inapprpriate. Do we need all that CFM produced by it?

An excellent question.

**Tom Richardson** · 25-06-2003, 05:14 PM

As to the 430 Bohn, much too big. The fans are running @ 50% speed & it is only on 1/2 the time. The whole project is over engineered. I believe the 1/2 hp compressor was 'on the shelf'. I told them what I thought I needed. This low - medium - medium low range stuff, I am understanding now ??????? I know the 1/2 hp compressor cost $100.00 more than the 3/4 hp.
Going to adjust the thermo down to 28deg F., now we are @ 30 to 34 and working great, no freeze ups. Will try 28 to 34. (thanks mr. herefishy, I know you say the ice will hold, but let me take small steps. Cold swimming is not my thing)
two things have changed from the original calculations:
1. the 3/8" copper lines for the frost top are working better than expected.
2. the deeper frost top is allowing the capture of more refrigerated air than before, causing the evap coil to work less.

Thanks guys,
Tom

**herefishy** · 25-06-2003, 05:46 PM

Originally posted by Tom Richardson
Will try 28 to 34.

I suggested 24F cut-out and 38F cut-in. NOT a 34F cut-in. Please adjust cut-in to 38F, okay 37F if you want to make small steps and not swim cold, but 34F is too low cut-in.

**Gary** · 25-06-2003, 06:32 PM

I agree. The cut in should be 38F and the cut out should be 24F.

**herefishy** · 25-06-2003, 07:00 PM

Originally posted by Tom Richardson
fans are running @ 50% speed & it is only on 1/2 the time....

My motto is, "the only stupid question is the one not asked."

The fans themselves, are running continously though, right?

**Tom Richardson** · 25-06-2003, 07:10 PM

Mr herefishy,
My error, the fans are on all the time, running @ 50% speed.
Thermo settings: 28 to 34. Testing now for ice buildup.
4 1/2 min on 4 1/4 min off??
Tom

**herefishy** · 25-06-2003, 07:11 PM

set cut-in to 38, not 34.

**herefishy** · 26-06-2003, 03:44 AM

Originally posted by Tom Richardson
the fans are on all the time, running @ 50% speed.

How did you get the fans to run 50% speed? Actually that is good for our current situation, because you have essentially derated the evap to about a 200btuh/degFT.D. which is the observation that I had made in an earlier post. However you did it, if indeed you did, is advantageous to our current endeavour.

By the way, Andy I apologize for the Mr. comment in the earlier post. I was being "cute", but of course now, it seems that I am the butt of my own "cuteness".

Regards, ... the fish

**Andy** · 26-06-2003, 08:11 AM

Hi Mr Herefishy

all taken in good fun

Regards. Andy

**Tom Richardson** · 26-06-2003, 05:33 PM

Mr. Herefishy,
Well, we are finally down to 26 to 34 deg F for the thermo setting - and like you were saying, IT WORKS GREAT AND NO NO FREEZING. The fan speed was increased to 60 %, using a rheostat control. The main improvement was now the evap coil is on for 8 min and off for 2 min. The air temp is 32.8 to 36.1 deg F., well within our design specs.
We are testing product temps now . Boy when you are right, you are right!!!
Thanks,
Tom

**herefishy** · 26-06-2003, 05:38 PM

sheesh!!!!!

LOL!!

Now set the cold control cut-out to 38 degrees!

You want cold control range to be 24F cut out, 38F cut-in.

PLEEEEZZZZ.

**Gary** · 26-06-2003, 05:58 PM

ROFLMAO !!!!

**herefishy** · 26-06-2003, 06:37 PM

Tom Richardson,

If you have time, maybe you could read this thread

http://www.refrigeration-engineer.co...&threadid=1099

I feel it may instill a little more confidence in you reagarding Gary's and my insistance on the cold control setting.

I still do not like you 8degF differential (26F - 34F), which is an improper application that can result in compressor damage over a period of time.

I am recommending 12degF differential (24F - 38F), which is what I consider to be a (more) proper application of the process.

(sometimes I don't think this is for real, ya' know.... like someone is just toying with me, and none of you "posters" really exist. Kinda' like the Matrix

)

**Tom Richardson** · 26-06-2003, 06:50 PM

IT'S REAL, BELIEVE ME.
That's why the first Matrix (movie) program did not work - there were no 'issues' everyone was TOO happy. haha
Thanks so much,
Tom

**Gary** · 26-06-2003, 08:53 PM

(sometimes I don't think this is for real, ya' know.... like someone is just toying with me, and none of you "posters" really exist. Kinda' like the Matrix )

I often think of the internet as the twilight zone. Damn, I'm old.

**Gary** · 26-06-2003, 09:38 PM

Herefishy, in looking through that thread I agree with almost everything you said, except that I don't share your faith in the manufacturers.

**herefishy** · 26-06-2003, 10:22 PM

Gee, Gary ............. thanks

It isn't a matter of "faith" that I have in the manufacturers, because mind you I have re-engineered some equipment (particularly in the matter of temperature control in small boxes as we are discussing now, and previous)

But only in extreme circumstances (which actually are primarily due to the misapplication of the equipment in the first place). The customer bought the equipment because of it's capabilities and features, then misapplies it against the manufacturer specification or recommendations.

But in the long run, my attitude is that the customer purchased the equipment because of the features, characteristics, quality, and perhaps (unfortunately) the economy that a particular machine provides. I take upon myself (when I walk onto the job anyway) to re-establish the original design and operation of the equipment as the mfgr. intended, that being perhaps the reason the customer owns it.

**Tom Richardson** · 27-06-2003, 11:56 AM

Friday.
WE DO WANT THIS UNIT TO WORK, BUT IT IS A PROTOTYPE.
We also have lights, 385 watts that were added today.

Ran the unit 12 hours Thur. and after the 9th hour, evap coil started freezing. By 12th hour, about 50% of coil blocked with ice. We are running with 32.2 to 36.0 deg F. air out, this is colder than required, but we are testing. We added approx. 8# of glycerol based media @ 85deg F to the frost top, and only saw a 2 deg rise to frost top temp. Pre-cooled to 40 deg media is all that we recommend to add - but you know in operation, the customer can do anything. The media got TOO cold & that was observed by the powers to be..... This is the first time we have ever had a TOO cold condition. It is very easy to 'warm it up'.
Condensor in temp 77 deg F. (ambient air temp), out temp 84 deg F. (at compressor), could the combined work being done be calculated from this?

Thanks guys,
Tom

**Gary** · 27-06-2003, 12:15 PM

It is getting too cold, therefore by definition, too much work is being done. Install the EPR in the common suction line and use it to regulate the frost top temperature. Once all of the temperatures are right, then we can see how much work is being done, and what size compressor is needed to do that amount of work.

The coil froze because the cut-in temperature is too low. It needs to be 38F to completely defrost the coil on the off cycle. Then regulate the minimum air temperature with the cut-out setting.

**Tom Richardson** · 27-06-2003, 12:47 PM

Gary,
If I take to cut-in temp up to 38 deg F, will the air out exceed the 38 deg maximum air temp desired?
EPR valve is installed & set @ 60 psig, to give approx 25 deg. for the evap coil.
Tom

**Gary** · 27-06-2003, 01:09 PM

The cut-in setting must be high enough to completely defrost the coil on the off cycle. The coil froze, therefore the setting is not high enough.

Unless we are trying to maintain high humidity, the air coil does not need the EPR. The air coil is regulated by the cold control. At 60psig, the EPR is fighting the cold control.

By installing the EPR in the common suction line, we can regulate the frost top temperature and also simulate reduced compressor size, thus telling us what size compressor is needed.

**Gary** · 27-06-2003, 03:34 PM

BTW, only half of the coil froze because only half of the coil is being fed refrigerant. Why? Because you still haven't adjusted the superheat on the TXV.

**herefishy** · 27-06-2003, 03:51 PM

Originally posted by Tom Richardson
We are running with 32.2 to 36.0 deg F. air out, this is colder than required,

The "air out" is not what you should be analyzing. It's the "air in" that indicates what the temperature (of the refrigerated area) is.

...and as Gary and Andy have been saying, NOW IS THE TIME TO ADJUST YOUR TEV SUPERHEAT !!

Gary, I'm plumb worn out from jumping up and down over the cold control setting, so now you have to fuss about the superheat adjustment, okay.

As a matter of fact, and relative to the superheat discrepancy, I just had a job this week, whereas an open merchandiser kept freezing up (unevenly). It was a cold control application just like Tom Richardson's. BTW the cold control is set at 18F cut-out, 38F cut-in.

The TEV superheat was 23F. I adjusted the valve 1-1/4 turn to obtain approx. 8-9F superheat... all okay.

**Andy** · 27-06-2003, 08:18 PM

Tom,
please set the cold control to cut back in at 38 deg F, or you will have one very agitated irish man to deal with and you don't want that do you

If your need that close a control on the air off, you need to change from air to electric heater defrost, with a pumpdown cycle.
Set them valves.
Have you both a pressure and a temperature reading point at the evaporator outlet?? If so read the pressure, convert to temperature and ten read the temperature at the outlet. I would be looking for the outlet temp to be 10 deg F above the saturation pressure (warmer) that would be 10 deg F superheat. That is a starting point, you may be required to go up a little to acheive a good even setting with no "hunting" but you will soon find this out for yourself.
Regards. Andy

**Dan** · 28-06-2003, 12:08 AM

Whew. Lot's of posts. I have been away too long to advise. But questions I am good at.

Is one of our problems that we want frost on the plate but not on the coil?

Is the chief concern now with short-cycling the compressor?

Is off-cycle defrosting even an important issue with a machine that will be turned off for at least 8 hours every night? Maybe just size the coil and fins to run constantly?

Is the mandate still to make the refrigeration components as small as possible, and the cost as little as possible? (I get confused, since it appeared that managers opted for compressors too large for the duty, if I understand my quick reads correctly.)

I guess I only have one question: Is all this fine advice from Herefishy, Gary and Andy the right answers to the wrong questions?

I cannot wait until I revisit this thread next time in town and read about how we are sizing the cap tubes.

**herefishy** · 28-06-2003, 12:29 AM

Thanx, Andy

Dan, I suggest you get a six pack, read the entire thread, and decide for yourself !!!

BTW: The cap tube application DID cross my mind today. But we haven't gotten the current configuration entirey figured out yet.

**Tom Richardson** · 28-06-2003, 09:40 AM

Hey Guys,
Friday was a lost day - tested all day per Owner's suggested thermo settings - 27° to 34°. FAILED COMPLETLY! I tried to tell him it was not going to work, but ......
Today(6-28-03) I am going to a 26° to 38° setting (or 25° to 38°). Keep in mind EPR is set to 60psi which converts to ~25° F for evap coil. Can not acheive 24° setting, 25° is tough. Can I?
Superheat: In side after TEV @ frost top, 20 psi in, temp measurement is -4°. Is this superheat of ~ 10° F.?
*With the temps I am trying for, is R404a the correct refrigerant??
Thanks,
Tom

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