frost top construction ???

[Gary]

I have little experience with Danfoss valves, but those orifice sizes seem oversized for the application. Perhaps someone out there is more familiar with the Danfoss products?

If this is the case, it could account for the overload on pulldown. It is definitely NOT a condenser airflow problem.

[Gary]

They are not supposed to read the same. In fact, those differences are the whole point of the exercise.


Few words, there, Gary. What is the exercise?

A refrigeration system is a series of heat transfers. By looking at temperature differences (dT, TD, SC, SH, etc.), we can evaluate how effectively heat is transferred each step of the way, and thus pinpoint specific problems, as well as fine tune the system.

[Andy]

Hi
55psig is below freezing, which is about 60 psig, I would set the EPR to this.
Oriface sizing:
#1 = 2.5kW or 8532 btu
#2 = 3.5kW or 11945 btu
#3 = 5.2kW or 17747 btu
These are nominal values, not corrected for exact conditions. These values would indicate that your orifaces are too big, especially on pulldown, possibly causing the high head problem.
Regards. Andy

[Gary]

Thanks, Andy

It seems that even switching to the #2 and #1 would be excessive, although much better. What would the #0 be rated at?

On the EPR setting, I think I would bring it up a little at a time, lengthening the on cycle, aiming for a steady air out temp of about 33F, with maybe an occasional off cycle.

[Andy]

Hi Gary,
yes on reflection 60 psig is probably too high, I would gradually raise the set point to acheive the designed air off. Is the frost top tru the EPR or just the holding area below? This would have been better tru the EPR, the only problem is with on EPR it could shut starving the compressor of vapour.
What about two EPR's set for each application?
Orifaces:
#0x = 0.5kW or 1706 btu
#00 = 1.0kW or 3112 btu
Regards. Andy

[herefishy]

How did I know the TEV's were wrong?


Also, Tom Richardson... your cold control settings are very incorrect.


With properly applied expansion devices for your application, you want the cold control to cut out the compressor (or solenoid valve, whichever applies) when the coil temperature reaches about 22degF, if I recall our previous discussions regarding the system balance (condensing unit capacity divided by unit cooler capacity @ 1degF T.D.)

Set the cold control to cut out @ 22-24F, and cut in @ 38F (the cut-in being your highest desirable temperature that youwant to maintain). Your differential on the cold control is going to be about 16 degrees F.

It seems perhaps y'alls reasoning of setting the cut-out @ 32F was to prevent a frosted over coil. The coil is a air defrost coil. Yes, frost is going to form. The off cycle is what defrosts it.

[Gary]

Is the frost top tru the EPR or just the holding area below? This would have been better tru the EPR, the only problem is with on EPR it could shut starving the compressor of vapour.
What about two EPR's set for each application?

This being a relatively minor problem, I think any decision on this would best be put off until we see how everything balances out.

It seems as if the #01 and the #00 would be about right here. On the other hand #02 and #01 would provide a faster pulldown if the system can handle it.

Set the cold control to cut out @ 22F, and cut in @ 38F (the cut-in being your highest desirable temperature that youwant to amintain).

The EPR tends to complicate this, as the coil temperature cannot possibly drop below EPR setting. We need to get the EPR setting right before adjusting the control settings.

[herefishy]

Is the 55psig the evaporator pressure setting of the EPR (19degF)? That sounds fine to me.

What is the compressor seeing in the suction pressure department?... I wonder

[Gary]

Is the 55psig the evaporator pressure setting of the EPR (19degF)? That sounds fine to me.

It's a question of strategy. We could have the coil drop to a lower temperature and then cycle to defrost, or we could maintain the coil temperature a little higher, minimizing the formation of frost with a defrost cycle backup. Maintaining a higher coil temperature will give us a higher humidity. The main thing is to not have the two fighting each other.

What is the compressor seeing in the suction pressure department?... I wonder

Apparently low enough to bring the frost top down near 0F, down around 30-35psi or thereabouts. We will no doubt get a clearer picture with a full set of real numbers.

[Tom Richardson]

To Herefishy,
As I mentioned earlier about 'working from memory', the expansion valves are TUA w/#2 orifice @ frost top &
TUAE w/#3 orifice @ evap coil.
Thanks

[herefishy]

If we increase the coil temperature, we decrease the amount of heat transfer (work)

If we are at 0 suction at the compressor, the 1/2 horse is rated at approx 3,250btuh, the 3/4 is rated 4,318btuh.

Gary, does the compressor capacity at the evaporating temperature of the compressor relate directly to a load being served a differing evaporating temperature (in the case of an EPR)? I always wondered

Has anyone explained the temperature differences that Tom Richardson concerns himself with, in terms of superheat? ... or did Gary not want to open that can of worms, LOL !!!

Oh, and one thing that comes to mind... if a 20deg cold plate is adequate (or even desired), I assume the design Evaporating temp of the forced air unit cooler to be approx. 20F, why are we employing an EPR?

[herefishy]

Originally posted by Tom Richardson
To Herefishy,
As I mentioned earlier about 'working from memory', the expansion valves are TUA w/#2 orifice @ frost top &
TUAE w/#3 orifice @ evap coil.
Thanks

Mr. Andy appears to be the Danfoss Guru on this thread. Nonetheless, the orifice figures are what are relevant, and the valve body nomenclature is not of any concern in examining capacities.

[Andy]

Mr. Andy appears to be the Danfoss Guru on this thread.

Maybe not I have quoted figures for the more common TE2 type NOT the horrible TUAE. Iwill check and re-post.
Regards. Andy.
P.S what's with the Mr

[Gary]

If we increase the coil temperature, we decrease the amount of heat transfer (work)

By means of EPR adjustment, true.

If we are at 0 suction at the compressor, the 1/2 horse is rated at approx 3,250btuh, the 3/4 is rated 4,318btuh.

Gary, does the compressor capacity at the evaporating temperature of the compressor relate directly to a load being served a differing evaporating temperature (in the case of an EPR)? I always wondered

Yes. The mass refrigerant flow entering the compressor is the total system flow at that point in time, representing the work being done by the system. Somewhat less than 1/2 ton, I would say.

Has anyone explained the temperature differences that Tom Richardson concerns himself with, in terms of superheat? ... or did Gary not want to open that can of worms, LOL !!!

One can of worms at a time.

Oh, and one thing that comes to mind... if a 20deg cold plate is adequate (or even desired), I assume the design Evaporating temp of the forced air unit cooler to be approx. 20F, why are we employing an EPR?

Because the actual load is somewhat less than 1/2 ton? Because we want to maintain high humidity? Because we want our frost top at a lower temperature?

[Andy]

Hi
#0 = 0.6kW or 2047 btu
#1 = 0.9kW or 3072 btu
#2 = 1.3kW or 4437 btu
#3 = 1.8kW or 6143 btu
Why fit the brazed/sealed type when you are not using any leaky HFC refrigerants?
The world's gone mad
When I first started refrigeration, we carried six expansion valves in the van R22 R502 R12 internal and external variety. And two of each oriface, there was not a fridge or display cabinet we couldn't change the valve on.
Regards. Andy

[Gary]

Those numbers look much better, but the conclusion is the same. The 3+2 combination overloads the compressor, the 2+1 combination should take care of the overload while maximizing pulldown, and the 1+0 is probably the right combination for the application.

[herefishy]

Inquiring minds want to know..... what is the desired frost top temp?

[Andy]

Hi
also worth commenting on is the use of a TUA on the frost top (internally equalized) and a TUAE (externally equalized) on the evap coil.
Why use an internal valve??? is the pressure drop that small in the frost top? I would doubt that
Regards. Andy.

[herefishy]

Hi Andy

I think Tom Richardson stated a 1-2psi drop across the frost top circuit.

[Tom Richardson]

A lot of data comming back

Desired frost top temp:
30 deg F. +- 1 deg
current temp:
19 deg F. TOO COLD...

evap air in: 40 deg F
evap air out: 35 deg
SST before & aft EPR: ??
suction line temp @ coil outlet: 53 deg
suction line temp @ comp inlet: 47 - 55 deg

cond air in temp: 73 deg
cond air out temp: 78 - 82 deg
SCT or pressure: ?? explain-
liquid line temp @ cond outlet: 86 deg
liquid line temp @ TXV inlet: 84 deg

evaporator
in
29 deg (***** on)
39 deg (***** off)
out
55 deg (on)
53 deg (off)

frost top:
in
24 psi
-9 deg wo/evap
8 deg w/evap

out
21 psi
4 deg wo/evap
38 deg w/evap

compressor
suction
17psi (evap off)
37 psi (evap on)
high
185 psi (evap off)
215 psi (evap on)

condensor
line temp in: 111 deg

Please expand on the Danfoss exp. valves "horrible"?

Thanks so much,
Tom

[herefishy]

Rip the EPR out of the system, and use it for a paperweight.

Okay, then.... do it carefully.

Do you have a thermostatic control for the frost top? I would sense suction outlet temperature.

[Andy]

Please expand on the Danfoss exp. valves "horrible"?

Manufacturers fit these nice looking "solutions" from a book, how often have you tried to change one of those brazed in valves in the field without burning either the cabinet or yourself!
If you are not using HFC refrigerants consider fitting a SAE flared valve, the guys working on the cabinet will thank you for it
Regards. Andy

[Andy]

Hi,

Rip the EPR out of the system, and use it for a paperweight.

or fit it to the frost top instead to control the low temps you are experiencing.
Regards. Andy

[herefishy]

Hi Andy, I may be incorrect, but I believe that there may be a mandate in regard to mechanical connections in assembled equipment.

[herefishy]

Originally posted by Andy
Hi,
or fit it to the frost top instead to control the low temps you are experiencing.
Regards. Andy

Hi Andy, that crossed my mind too, however a common 20F to 25F suction should be fine.

I would try it without any evaporator control, then consider it on the frost top, if I still was not happy with the results. Definitely, the frost top is the "TOP" condidate for evaporator pressure control in this application.

[Andy]

Hi
what the heck! try it without the EPR, things are way to much off/on at the moment and if in doubt fit smaller orifaces on the valves, if you find extra load being added by the evap, due to nothing being held back by the EPR.
Regards. Andy.
P.S. still think those welded valves are a poor excuse for a valve
Regards. Andy.

[herefishy]

Tom Richardson.... the orifices must be changed.... do not fail to do this.

.....do not fail to do this

....do not.... Okay, I'll stop

Andy... those figures were for R-404A, right? At what SST?

[Tom Richardson]

NEW ORIFICES ARE ON THE WAY!!
Tom

[herefishy]

Tom Richardson,

Due to my extensive befuddlement of your cold control setting, which I have been contemplating until my head hurts....

You should consider the "air in" temp of the evaporator the temperature of the conditioned space not the air exiting temp. So you want to cycle off when the "air entering" (i.e. space or load temperature) is ... 35F.

I seem to interpret your settings as you're satisfied with the 35 F air temp leaving the evap, as such the discrepancy in your run times...

Does this seem an accurate view of what you're doing?

[Tom Richardson]

Mr Herefishy,
We tried to measure the incomming air, and we froze the evap coil - soild. Moving the temp sensor to the exhaust side of the coil and imbeded into the coil has solved the 'freezing up' problem.
The air moving over the product needs to be 40 - 33 deg F., in this range. The frost top actually keeps the product at temp. The air is an air curtain.
Tom

[herefishy]

I was referring to your temperature readings measurement that you were relaying.

I was not referring to the cold control sensing bulb location.


You measure.... the control senses.

I understand the application... (just so we don't get sidetracked on any issue of qualifying one's understanding). "The space" is a figurative term that I use with a broad brush, I do not wish to confuse you.

[Tom Richardson]

Mr. Herefishy,
Sorry, a mis-communication!!!
The air exiting the evap coil is at an acceptable temp. The new deeper pan design has allowed us to catch more refrigerated air than before. Temps of air enterring before were 55 deg F. A major improvement.
Tom

[herefishy]

Very good, sir. Now, back to my point, I was trying to see if you would consider getting the "air IN", returning to the coil into that acceptable range to which you refer.

[Tom Richardson]

Mr. Herefishy,
That would be a great thing...
smaller evap coil....
smaller comp.....
Let me hear what you are thinking?
Tom

[Tom Richardson]

Question:
What does this IMPROVING POSTER" mean?
Who decided that I was improving????
Tom

[herefishy]

Originally posted by Tom Richardson
Let me hear what you are thinking?
Tom

What I am suggesting, is set the cut-out of the cold control to 24degrees.

[Tom Richardson]

Do you think this will freeze the evap coil?
Tom

[herefishy]

NO.

when the coil gets to 24 degrees, the stat will cycle off, and will not "call" (come back on) until the coil temperature is 38 degrees or whatever your cut-in is set at (the "high event", at which point no ice will exist at atmospheric pressure).

That is the purpose of the "cold control".

Try it... it will work.

[Gary]

Air evap temps:
evap air in: 40 deg F
evap air out: 35 deg
SST before: 55psi = 20F SST
& aft EPR: 37psi = 4F SST
suction line temp @ coil outlet: 53 deg
suction line temp @ comp inlet: 47 - 55 deg

Frost top evap temps:
surface temp: 19F
SST: 21psi = -15F SST
suction line temp @ coil outlet: -9F

cond air in temp: 73 deg
cond air out temp: 78 - 82 deg
SCT or pressure: 215psi = 94F SCT
liquid line temp @ cond outlet: 86 deg
liquid line temp @ TXV inlet: 84 deg

Just trying to get it all sorted out.

If you convert low side pressure to temperature on a pressure/temperature chart, the temperature is SST (saturated suction temperature)

If you convert high side pressure to temperature on a pressure temperature chart, the temperature is SCT (saturated condensing temperature).

[Gary]

The air evap TXV superheat is 33F. This is much too high. Someone no doubt adjusted it in an attempt to compensate for the orifice being much too large.

Hmmmmm... Now that I think about it, more likely 53F is not the true coil outlet temperature. The outlet temp is probably right around air in temp, which would give us 20F superheat, which is still much too high.

The TXV setting on the frost top looks to be okay. The TD is somewhere between 39F and 15F. Difficult to tell with all the cycling.

What product is being cooled? Does it need high humidity?

[herefishy]

Hi Gary,

Typically in this type of application, the storage is short-term and space is a factor (relating to coil size). So the units are usually rated at a 15F T.D. or so. Product is not anticipated to be in the refrigerated (or display) space for very long, so degredation is not a primary factor/criteria.

My assumtions in regard to some of our discussions have been based on this "concept".

[Gary]

This being the case, there is no need to keep the coil temperature high. However the frost top TD is a big IF at this point. And it's temperature will take a nosedive each time the air coil is cycled off.

First, the orifices need to be changed, then the TXV superheats checked and adjusted if needed.

We can tie the suction lines together before the EPR and set it to maintain correct frost top surface temperature. The air coil 'off' temp can then be set slightly above this. That way the frost top temperature won't be jerked around by the cycling.

I'm thinking without the EPR, the SST will be considerably less than the 20-25F you are anticipating. This being the case, we could further reduce compressor size. Of course we can't tell for sure until we see what the changes give us.

[Tom Richardson]

None of the exp. valves have been adjusted, they are new out of the box.
The readings are comming from thermocouples strapped to the lines. They were all tested prior to installing.
The product is salads, and there is a quick turn-around-time.
Tom

[herefishy]

Originally posted by Tom Richardson
Question:
What does this IMPROVING POSTER" mean?
Who decided that I was improving????
Tom

I'd tell you.... but, then I'd have to kill you

Just think of it this way... It's better than being a PROVING IMPOSTER !!! LOL

[herefishy]

Hi Gary,

Actually for this application, I was anticipating about an 18degF SST on the forced air coil at spec temp. But really, the TD is a result of the system balance inherent in the coil surface area and the condensing unit capacity, unless of course as you pointed out, the possiblility of "starving" the coil by increasing the superheat.

Tom Richardson, TEV settings (superheat) must always be checked. There is no such thing as a "pre-set" valve. Out of the box means that it has never been set properly (or setting confirmed).

My initial feeling, is that the system should be entirely controlled by the forced-air coil thermostat (cold control, excuse me). Let the frost top just "lag" the air cooling. I think it'll do fine, particularly if the top has a considerable thermal mass.

....okay, maybe it's worth a try, anyway

[Gary]

Who decided that I was improving????

The same people who decided I was a VIP... LOL

[Gary]

The readings are comming from thermocouples strapped to the lines.

Are they insulated?

[herefishy]

Originally posted by herefishy
Tom Richardson, TEV settings (superheat) must always be checked. There is no such thing as a "pre-set" valve. Out of the box means that it has never been set properly (or setting confirmed). :

Oh, I take that back. once you have set a valve to your required settings, you can send the set valve in to the mfgr, and order all valves at that spring tension (setting). Then as a mfgr, you don;t have to fuss with it. .... Of course that is if you are utilizing a Sporlan, right Prof.?

[Prof Sporlan]

Oh, I take that back. once you have set a valve to your required settings, you can send the set valve in to the mfgr, and order all valves at that spring tension (setting). Then as a mfgr, you don;t have to fuss with it. .... Of course that is if you are utilizing a Sporlan, right Prof.?

The Prof is happy to verify Sporlan TEV settings, and manufacture subsequent valves to that setting...

If a manufacturer is building many indentical units, this is the way to go. If the manufacturer builds primarily custom units, then ordering TEVs at the factory setting is the best way to go, and adjust when necessary.

[Tom Richardson]

First, all thermocouples are insulated. I am going to check all thermocouples @ ambient temp & in a cup of ice water.
Next, Florida is a nice place to live, a heavy need for 'store bought air' & some good fishing........
Second, orifice changing, EPR adjusting, more measuring.
Thanks for all the info,
Tom