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12-04-2002, 08:18 PM #1
Endless Freezer as Endless Cooler (10 door)
Mr. customer said "I'm buyin' two (used) 5-door (glass) merchandisers, and I need you to provide a condensing unit and do the install." They're endless glass door merchandisers. He's buyin' used (refurbished) equipment after turning down my quote for NEW MasterBilt brand matched cases and C.U.
So, I use my guidebook thingy, and determine a required capacity of about 12,400 btuh @20degF SST. I make a selection and get it coming via the distributor.
And guess what? Two 5-glass-door freezers arrive!!!! Now according to my guidebook thingy, I estimate the required capacity of these cases to be about 17,000 btuh @ -15degF SST, or perhaps 1,133 btuh/degFTD, assuming a 15degF TD. Whereas I assumed a evaporator capacity of about 820btuh/degFTD for the 12,400btuh rule-of-thumb load.
I decided, no problem, I'll just disable a couple of (the 10) evaporator fan motors in order to decrease NRE of the evap. In doing so, I decided that I could de-rate the unit about 20% in order to see a 15degFTD (desired 20degF SST) in order to maintain humidity, SH's, etc.
When we started it up, box coming down to near temp, we were running a 23degF SST, thereabouts and SH was a bit high at the evap outlets. I told my tech NOT to fuss with TEV adjustment before "knockin' out" a couple of the evap fan motors. That brought our SST down to 20degF at a 36degF box!!!!!! Great!!
BUT.... the new C.U. (Trenton EH200H2) has a 17 pound receiver. IT'S NOT ENOUGH!! Head pressure rises on pump-down..... and it's no wonder, because we've got more than 17 pounds of gas in the unit.
? Is the discrepancy due to increased evap volume for the higher capacity and lower temps of the freezer app that the cases were designed for?
Should the mfgr standard receiver provided for rated capacities be adequate in most of applications?
Does the endless merchandiser application typically require more than standard receiver capacities (refrigerant charges)?
I've had one other instance, exactly the same with this customer and his piece-a-meal equipment. Freezer cases as cooler cases, and had to re-fit a larger capacity receiver. However, I've applied condensers with properly utilized cases.....NO PROB.
I told Mr. customer that he bought freezers! He called Johnny (refurbished equipment supplier) back, and Johnny said that they were multi-purpose cases! yeah, right.
Of course, we wouldn't be going through this if "Mr. customer" wasn't tryin' to save the buck on the wrong end of the stick.
Also, I'm concerned that my HP is real low. These evaps are fitted with liquid subcoolers before and after the TEV. I don't like it.
What do you think?Last edited by herefishy; 15-04-2002 at 04:18 PM.
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12-04-2002, 11:57 PM #2
Herefishy, one of the reasons that the load is higher are the heated frames and glass that the low temperature cases require. You could likely disable the glass heat with no problem. Maybe even the door frames too.
Off the shelf condensing units generally will have too small a receiver for endless display cases - freezers or otherwise. I just installed one for a gravity coil service case and had the same problem. One way around it is to disable pumpdown, the other is to install a larger receiver. Yes, its the evaporator size that does you in - especially with supermarket reach-ins built in the last 15 years. You might have been better off starving the evaporator to a 15 deg F TD, to utilize the small receiver, as opposed to reducing air flow.
I am not sure if the evaporators are larger for freezers than for coolers, I think most manufacturers use the same evaporators... the difference being the anti-sweat heat and electric defrost necessary for the freezers.
Not sure I understand the subcoolers before and after the TEV. Is it possible that these cases came from an Albertson's and what you are describing is the Alco ALLS?
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13-04-2002, 12:17 AM #3
YES!!!!!!!! The Alco thingies!!!!
I have disabled the defrost heaters.........
The door frame heaters..... we were going to see how hot they got or burned up. Hunidity level may be a little high in the store, and I was assuming that they may be thermostatically controlled, and perhaps may not even come into play.
I have no doubt that my load calculation is correct. There is no problem with obtaining temp. I am concerned with compressor lifespan. The receiver capacity thing is the primary issue regarding the current situation.
Your response is helpful. what do you think of the
Alco thingy in the MED. temp app?
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13-04-2002, 12:19 AM #4Originally posted by Dan
Herefishy, one of the reasons that the load is higher are the heated frames and glass that the low temperature cases require.Last edited by herefishy; 13-04-2002 at 12:22 AM.
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13-04-2002, 12:21 AM #5Is it possible that these cases came from an Albertson's and what you are describing is the Alco ALLS?
Disabling the two evap fan motors will likely increase the refrigerant mass in the evaporators.Prof Sporlan
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13-04-2002, 12:24 AM #6
Okay guys....... fill me in on the ALLS..... y'all are responding faster than I can grab the Alco book (which is way behind the Sporlan book (Certified I might say)).
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13-04-2002, 12:25 AM #7Originally posted by Prof Sporlan
Disabling the two evap fan motors will likely increase the refrigerant mass in the evaporators.
Aside from the receiver capacity issue, of course.Last edited by herefishy; 13-04-2002 at 12:28 AM.
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13-04-2002, 12:30 AM #8
By the way, Prof... I'm intending to go to the Supermarket REF seminar in Arlington (TX), on the 17th. If there's still room. I'll call in Monday.
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13-04-2002, 12:33 AM #9
The fact that you have a subcooler ahead of the TEV makes the ALLS redundant... the ALLS is a variation of your standard suction/liquid line subcooler, and both are used to assure flash-free refrigerant ahead of the TEV. The difference is the suction/liquid line subcooler can also help flash off minor slugs of liquid before they reach the compressor. The ALLS does its subcooling using refrigerant before it enters the evaporator.
Larger evaporator + 2 deactivated evaporator fan motors = greater refrigerant mass in the evaporator = a larger receiver necessary.....Prof Sporlan
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13-04-2002, 12:36 AM #10Originally posted by Dan
One way around it is to disable pumpdown
You've got a long row to hoe in getting me to do that.
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13-04-2002, 12:36 AM #11By the way, Prof... I'm intending to go to the Supermarket REF seminar in ArlingtonProf Sporlan
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13-04-2002, 12:42 AM #12Originally posted by Prof Sporlan
The fact that you have a subcooler ahead of the TEV makes the ALLS redundant... a larger receiver necessary.....
Was the Albertson's thing an overengineering nightmare that troubled all of the manufacturers involved?
I would like to remove BOTH subcoolers, because I typically rate my TEV' under such conditions (without subcooling). for the two cases, I determined to require 6,200 btuh, I fitted (2) BFVE-AA-C TEV's. My concern with all this subcooling, was that the sub-cooling is de-rating the valves (too much). because when I did the calculation thingy, The valves came out at 52% rated capacity, at the (normal) conditions that I spec'd.
...New (additional) receiver.... DONE DEAL!!! I just wanted to make sure that the increase in receiver capacity was technically justified, and not some jackleg workaround a serious problem.... Thanx, Prof.!!!Last edited by herefishy; 13-04-2002 at 12:47 AM.
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13-04-2002, 12:48 AM #13Do you think my course of action appropriate? And the net result an end to it's means?
Your course of action, in the Prof's opinion, is fine. Unfortunately, it will require a larger receiver. Removing the ALLS probably won't change this situation. Might be inetersting to see what would happen if you reactivated one of the evaporator fan motors.....Prof Sporlan
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13-04-2002, 12:50 AM #14Originally posted by Prof Sporlan
Tell John Murray (our Manager of Supermarket Refrigeration) you know the Prof!
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13-04-2002, 12:53 AM #15Originally posted by Prof Sporlan
Might be inetersting to see what would happen if you reactivated one of the evaporator fan motors.....
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13-04-2002, 01:03 AM #16Was the Albertson's thing an overengineering nightmare that troubled all of the manufacturers involved?
I would like to remove <i>BOTH</i> subcoolersProf Sporlan
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13-04-2002, 01:09 AM #17Originally posted by Prof Sporlan
Subcooling will actually increase TEV capacity, as the lower liquid temperature increases NRE.
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13-04-2002, 01:11 AM #18I'll hunt John down.Prof Sporlan
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13-04-2002, 01:12 AM #19
I think the system would be most efficient at a minimum of sensible subcooling. I think that sensible gain is a lower input vs. output relationship. A waste of time and money.
I.E., a system at 1degF subcooling is more efficient that a system with 10degF sub cooling.
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13-04-2002, 01:28 AM #20the latent heat of the refrigerant is what makes the system desirable.... so why would one want to put so much into the sensible?
The efficiency effect of a suction/liquid line heat exchanger is a bit more complicated to analyze. But if you flash ahead of the TEV without it, then it becomes a no-brainer.
I think the system would be most efficient at a minimum of sensible subcooling.Prof Sporlan
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13-04-2002, 01:30 AM #21
The professor is a knowledgeable spokesperson for the Alco products.LOL
I categorically refuse to operate without a pumpdown.
You've got a long row to hoe in getting me to do that.
Well, since you have disabled the fans and need more refrigerant in the system, you may have a point there.: On the other hand, you could likely get by with a lot less refrigerant if you starved the coil (ie: making it about the size of a coil manufacturers used to make for these cases 20 years ago) and let a bubbly sightglass happen (especially with the ALLS in place... you could possibly halve your refrigerant charge and get by nicely without a pumpdown.
If it is an outdoor unit, I would stick with the pumpdown. I think you would be surprised how many refrigeration condensing units are out there doing quite nicely without a pumpdown, however.
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13-04-2002, 01:50 AM #22
If you go without a pumpdown, the next best is to cycle the LLS with the compressor.
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13-04-2002, 02:03 AM #23
If you have multi-circuit coils, another possible solution would be to eliminate the top circuit, effectively downsizing the coil. Then turn the fans back on (which someone is going to do sooner or later).
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13-04-2002, 03:39 AM #24
Gary, that's good advice. Hussmann reach-ins, for example have 3 circuits feeding 3 parallel rows. If you valved off the middle row, you would effectively have 2/3 of the coil operating, and the TEV would most likely achieve good control. These coils are vertically positioned in the rear wall, these days. But not always.
I favor stealing from the middle row because it seems to me to hold the advantage of the secondary surface for heat transfer and latent heat removal.
But you have me thinking.
Regardless, the evaporators are larger these days than in the past both in fridge and A/C. I would expect that if you cut a third out of the evaporator that you would have to operate about 5 def F colder to achieve a given temperature.... whether in low temp applications or in medium temp applications.
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13-04-2002, 03:58 AM #25
I'm thinking you're probably right about taking out the middle row, Dan. That makes sense.
It should be a simple matter of taking a pinch-off tool to the feeder line.
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13-04-2002, 11:04 AM #26
Hi, what about reducing the air flow through the evaporator by changing all the evap[ fan blades, this would give a more satisfactory result evening out the load about all the coils. For the pumpdown thing will all the cases be pumped out at the same time? Stagger the defrosts, and the thermostats, but I suppose the only real answer is a larger receiver?
Regards. Andy.If you can't fix it leave it that no one else will:rolleyes:
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13-04-2002, 05:14 PM #27Originally posted by Andy
what about reducing the air flow through the evaporator by changing all the evap fan blades,
Mind you, I estimate the evap coil capacity in the (freezers) to total 1,130 btuh/degFTD (in consideration of the (10) fans, assuming a 15degF TD. When I started the C.U. selection I assumed a 820 btuh/degFTD NRE, assuming a 15degFTD at a design 35degF box.
It was an 80degf day at start-up, and my head (R-22) was 190psig. would the redundant subcoolers cause the (what I consider) low head? Or does the liauid temperature reduction not translate into lower pressure? I HATE subcoolers!!! My personal opinion is that they are work-arounds for poor engineering and crummy pipe sizing.
I appreciate the comment about lettin' the bubbles flow in the sightglass. It makes me feel better. My tech was getting a little punchy with R-22 can. I told him to put that sucker away, we're not putting anymore gas in the system until I figure this thing out. The box was at temp already, anyway and we're not able to fit another receiver until after the weekend..
At start-up the superheat was high at evap outlet. Would it be advisable to remove the ALLS prior to fiddlin' with SH adjustment? I think that the ALLS' may be applying a load to the TEV capacity that I have not accounted for.
Is the redundant subcooling perhaps beneficial for the low temp application that the cases were originally designed for, but may be working against me in the MED temp app?
Just for clarity, the cases are Tyler brand (It's fuzzy to me at the moment, but I beleive Tyler is out of business). Two 5-door cases with one evap each, that I'm feeding with (2) BFVE-AA-C TEV's. The coils are mounted in the bottom of the cases. I calculated load at 6,200 btuh per coil @20degF SST. My new C.U. is a Trenton EH200H2 that rings in just over the 12,400 btuh mark at 110degF ambient. Yes, the C.U. is outdoor (roof).
If I cut out an evap circuit, would it be likely that I may be effectively reducing the average coil surface temperature (LMTD?) of the evap, and even though I am running a 20degF SST, the net coil temperature may be above that and reduce my latent work and result in higher than design humidity and damage to the cardboard packaging of the product? Trane did that with their (A/C) evaps in some applications, it was a no-latent-work-high-humidity nightmare (particularly in Houston and Corpus Christi).Last edited by herefishy; 13-04-2002 at 05:19 PM.
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13-04-2002, 07:27 PM #28
Hi, I would remove the heat exchangers, are these ALLS suction liq exchangers? Too much subcooling would account for the high mass of refrigerant in the evap's, you may get away with out changing the receiver yet. Also the head is low for the ambient maybe more liquid is backed into the condenser, I would cycle one fan off, I assume there is more than one cond fan, this elevated head will push out liquid from the condenser, it will also reduce the units capacity which may not be entirly what you want. My feelings are that the system has a large mass of subcooled liquid lying in various parts, this will reduce the heat exchangers capacity, cond and evap, this would be detrimental.
Also what about using a different refrigerant, one which would evaporate a little lower with increased refrigeration effect, one way of incresing the units capacity or lowering the SST.
Regards. Andy.If you can't fix it leave it that no one else will:rolleyes:
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13-04-2002, 08:34 PM #29At start-up the superheat was high at evap outlet. Would it be advisable to remove the ALLS prior to fiddlin' with SH adjustment?
I think that the ALLS' may be applying a load to the TEV capacity that I have not accounted for.
With a suction/liquid line heat exchanger, things are a bit more complicated, and are affected by TEV sensing bulb and the heat exchanger location. If the sensing bulb is located upstream of the heat exchanger, and the heat exchanger is outside of the case, the TEV will not see the heat exchanger load, and one should account for the lower liquid temperatures the TEV will see when sizing it.
If the heat exchanger is within the case, then assume the case manufacturer has accounted for the added load in their case ratings, and size the TEV based on the liquid temperature entering the case, not ahead of the TEV, and place the sensing bulb at their recommended location.
The Prof, however, prefers placing the sensing bulb upstream of any suction liquid line heat exchanger. In that way, you don't get into a problem of having liquid enter the suction line between the evaporator and heat exchanger, and creating possible hunting problems.
Is the redundant subcooling perhaps beneficial for the low temp application
(It's fuzzy to me at the moment, but I beleive Tyler is out of business).Prof Sporlan
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13-04-2002, 08:43 PM #30I don't understand why either a suction/liquid heat exchanger or an evaporator/liquid heat exchanger should increase evaporator refrigerant mass. Because of the liquid subcool, how so?
In the case of the ALLS, it's effect would probably be minimal, unless it is affecting refrigerant distribution.Prof Sporlan
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13-04-2002, 10:13 PM #31I don't understand why either a suction/liquid heat exchanger or
an evaporator/liquid heat exchanger should increase evaporator
refrigerant mass. Because of the liquid subcool, how so?
Well, if subcooling or reduced air flow lowers superheat, then I guess it is a safe assumption that we have more mass in the evaporator?
Beyond that, I really don't have a theory. But back to Herefishy's puzzlements.
That was certainly a primary option. The customer was HOT to
get his product back into the case, so I expedited the coil NRE by
disabling 20% of the fans in order to evaluate the effect. My
presumption appears to be correct, due to the fact that I reduced
my SST from 23degF to 20degF. 20degF TD being the target.
Mind you, I estimate the evap coil capacity in the (freezers) to
total 1,130 btuh/degFTD (in consideration of the (10) fans,
assuming a 15degF TD.
When I started the C.U. selection I
assumed a 820 btuh/degFTD NRE, assuming a 15degFTD at a
design 35degF box.
It was an 80degf day at start-up, and my head (R-22) was
190psig. would the redundant subcoolers cause the (what I
consider) low head? Or does the liauid temperature reduction not
translate into lower pressure? I HATE subcoolers!!! My personal
opinion is that they are work-arounds for poor engineering and
crummy pipe sizing.
I appreciate the comment about lettin' the bubbles flow in the
sightglass. It makes me feel better. My tech was getting a little
punchy with R-22 can. I told him to put that sucker away, we're
not putting anymore gas in the system until I figure this thing
out. The box was at temp already, anyway and we're not able to
fit another receiver until after the weekend..
We left the case at temperature and with bubbles in the sightglass and a pumpdown control system in place. Bubbles ain't Pacman. They might be in the sightglass but not necessarily at the TEV.
At start-up the superheat was high at evap outlet.
Would it be
advisable to remove the ALLS prior to fiddlin' with SH
adjustment? I think that the ALLS' may be applying a load to the
TEV capacity that I have not accounted for.
Is the redundant subcooling perhaps beneficial for the low
temp application that the cases were originally designed for, but
may be working against me in the MED temp app?
Just for clarity, the cases are Tyler brand (It's fuzzy to me at the
moment, but I beleive Tyler is out of business).
Two 5-door
cases with one evap each, that I'm feeding with (2) BFVE-AA-C
TEV's. The coils are mounted in the bottom of the cases. I
calculated load at 6,200 btuh per coil @20degF SST. My new C.U.
is a Trenton EH200H2 that rings in just over the 12,400 btuh
mark at 110degF ambient. Yes, the C.U. is outdoor (roof).
If I cut out an evap circuit, would it be likely that I may be
effectively reducing the average coil surface temperature (LMTD?)
of the evap,
and even though I am running a 20degF SST, the net
coil temperature may be above that and reduce my latent work
and result in higher than design humidity and damage to the
cardboard packaging of the product? Trane did that with their
(A/C) evaps in some applications, it was a
no-latent-work-high-humidity nightmare (particularly in Houston
and Corpus Christi).
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14-04-2002, 12:00 AM #32
Let's start over. The head pressure would seem to indicate low load. If the fans were re-connected, the load should be just about right. So, what's the problem?
This is difficult for me, because I have little faith in guidebooks and calculations. That's not the way I do things. I don't calculate and predict. I measure and analyze. And I would certainly never try to make a system fit someone's predictions. A measurement beats a prediction every time.
In order to do this right, we need to hook the fans back up and take the following readings, preferably near cut-out temp:
evap air in temp
evap air out temp
SST
coil outlet suction line temp
compressor inlet suction line temp
cond air in temp
cond air out temp
SCT
receiver outlet liquid line temp
TXV inlet liquid line temp
Discharge line temp near compressorLast edited by Gary; 15-04-2002 at 10:09 PM.
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14-04-2002, 01:16 AM #33Tyler is definitely not out of business anymore than Alco is. But I find it funny that a Hussmann fellow and a Sporlan fellow are the only willing speculators regarding competitive equipment.... which really ain't all that badProf Sporlan
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14-04-2002, 03:33 PM #34
Hi, It is possible to have too much subcooling, with TEV's anyway (and this is only my veiw) especially with valves which are probabely not sized for the extra subcooling. I have seen supermarket cases where the refrigerant was changed and the suction/liq heat exchangers were short circuited to reduce the suction superheat and also to reduce the capacity of the evaporators, is this not what we want to acheive in this case. A lower SST is required to lower the humidity in the case. Iwould look at what this unit and case configuiration would do on a different refrigerant i.e one traditionally used for deep freeze work.
Also a beleive that the subcooled liq will require a greater amount of heat to boil it off and that there will be less flash gas in the evaporator initiating this boiling process, so we will retain more refrigerant in the evaporator.
To sum it up I would consider a different refrigerant one more suitable to the original configuration of this case.
Regards. AndyIf you can't fix it leave it that no one else will:rolleyes:
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14-04-2002, 04:02 PM #35Hi, It is possible to have too much subcooling, with TEV's anyway
If the TEV is sized properly, the TEV doesn't care how much subcooling exists in the refrigerant, as long as some subcooling exists to prevent flash gas.
The problem with highly subcooled liquid is it will lower the refrigerant velocities in the evaporator coil, possibly to the point you no longer get good wetting along the insides of the evaporator tubes. In effect, you get "sewer flow" which will reduce the effectiveness of the evaporator surface. Low refrigerant velocities can also cause refrigerant trapping within the coil, particularly with bottom fed coils which are common with reverse cycle defrost systems. Liquid trapping can actually assist with the effectiveness of the evaporator surface, but then the coil holds greater refrigerant mass, and the trapped liquid will often cause some TEV hunting when liquid slugs form.
Also a beleive that the subcooled liq will require a greater amount of heat to boil it off and that there will be less flash gas in the evaporator initiating this boiling process, so we will retain more refrigerant in the evaporator.Prof Sporlan
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15-04-2002, 04:04 PM #36
The reason that I say NRE is that by reducing the airflow, I am reducing the refrigerating effect of the coil. Such as in the case of a low velocity unit cooler which has more coil area than an equivalent rated standard velocity unit. So, perhaps my terminology sucks!
I am used to the high superheat at start-up. I don't know why I brought it up, except only to illustrate that I was not going to tamper with the TEV's until I have a grasp of all the issues.
I derived my C.U. capacity requirement by referencing Masterbilt eng. data for similar equip. I derived the estimated capacity of the (freezer) equipment via the same manner.
The unit appeared to have been utilized in a low-temp R-22 application in previous life (referencing particular concerns regarding what refrigerant being used), because BFVE-A-Z valves were fitted. Johnny-used-equipment-salesman shipped the reincarnated equipment with BFVE-AA-C valves. He was going to ship BFVE-A-C valves, but I told him if he did that, I would not utilize them. When I used my confuser program (Sporlan), the AA's came in at 52% of valve capacity.
The ALLS' are located at the TEV outlets! (between TEV and evap)
My point regarding receiver capacity, is I assume that this freezer has a greater evap coil VOLUME than a comparable case designed for medium temp.
I like to keep my HP high, in order to maintain PD across valve. In Central Texas, we hit 110degF for month (in August). I don't like to see my condensing temperature fall much below 100degF, because the swing in PD across the valve in the highest vs. the lowest ambients that are expected seem to me to not be within the range of any particular TEV selection.
I am in contact with Tyler Refrigeration Corporation. I'm awaiting a call back from Wes Swank.
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15-04-2002, 04:23 PM #37Originally posted by Dan
Herefishy, one of the reasons that the load is higher are the heated frames and glass that the low temperature cases require.
I selected a C.U. rated at 12,400btuh+ @110degF ambient for the 10-door (glass) case.
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15-04-2002, 05:14 PM #38
Okay, I just finished talking to Tyler.
The freezer and cooler cases (of the same type) do use the same evaporator coil and fan configuration. Each of the 12' case evaps will contain about 9# of (evaporating) refrigerant R-22.
Tyler rates the freezer cases @ 7,000 buth @-16degF suction (14,000btuh total for the 10 doors I now have).
As a cooler, the cases are rated 6,600 btuh @20degF suction (13,200btuh for the two cases I now have)
Tyler recommended a 26# capacity receiver @80% for the two cases (24').
So..... I'm going to fit an additional receiver, re-employ the evap fan motors that I disabled, and I'm going to stop worrying about everything else!
and the Supermarket Seminar in Arlington is BOOKED and there's no space for me!!!!
Maybe the Prof. can pull some stringsLast edited by herefishy; 15-04-2002 at 06:17 PM.
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15-04-2002, 09:09 PM #39So..... I'm going to fit an additional receiver, re-employ the evap fan motors that I disabled, and I'm going to stop worrying about everything else!
You may (or may not) find that the system has humidity problems, because the slightly undersized CU gives it a higher ADP. If this is the case, the best solution might be new fan blades with a little less pitch. Which means you were right in the first place.
On the other hand, the longer run time (more time to de-humidify) may make up for it.Last edited by Gary; 15-04-2002 at 09:40 PM.
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15-04-2002, 10:06 PM #40
I don't think that I'm that far out of the ballpark on the C.U. sizing. Of course if I would've called the mfgr before I ordered the C.U., I may have made a different selection. But at 90'F amb, the 2-horse that I've got on there 'll do 14,527btuh. At 105'F, it's rated at 12,898btuh.
Tyler is comfortable with the 2-horse, is the jist I got from the engineer that I talked to this morning.
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15-04-2002, 10:14 PM #41
I don't think you're out of line at all, and in fact slightly under gives you a little more run time, which is better for removing humidity. And slightly under with less airflow would maximize humidity removal (lower ADP and longer run time).
Last edited by Gary; 15-04-2002 at 10:18 PM.
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15-04-2002, 10:17 PM #42
Gary, I'm going to the jobsite. I've got a couple of men down there right now trimmin' out the cases, and fitting the receiver. I'll get those temps for you.
see, ya.
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15-04-2002, 11:00 PM #43and the Supermarket Seminar in Arlington is <i>BOOKED</i> and there's no space for me!!!!Prof Sporlan
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16-04-2002, 12:39 AM #44Originally posted by Prof Sporlan
The Prof suspects if you were to show up at the seminar on time, (and that you advised John Murray that you know the Prof), a spare chair will be found....
The Fish suspects that the Prof. advised Mr. Murray, that if there is anyone in the state of Texas, or the international forumn in which he participates, there is no one more in need of the information provided by the seminar!
I will likely roll the dice on the Professor's assurance and "crash the party"!
Gary, I went out to the site as I said, when I said. When I arrived, the evacuation process was just being completed. The case was at about 46'F - 47'F, so SH readings/adjustment did not commence. The case is full of product, and we decided to let it pull down overnight before fiddlin' with it.
But, the HP was at 210psig
SST at 26'F (49'F case)
Just because I was there, the liquid line temp entering the box from the C.U. was 104'F
Having my meter in the case to check case temp, I measured entering evap temp @ 47'F, air exiting at back wall of case 43'F.
We are anticipating needing to decrease superheat setting tomorrow morning.
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16-04-2002, 12:56 AM #45
I suspect the outdoor temp was 80ish?
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16-04-2002, 01:00 AM #46Originally posted by Fridgetech
...coil capacity is about
kW/mē.K
Where
kW = Capacity potential
mē = total surface area or for a certain coil block the face area
K = LMTD otherwise TD for constant air volume
A variable constant?
Maybe you could say NO because the reduced volume results in increased TD (LMTD... whatever. I haven't bought the book yet) If that is the case. I haven't really thought about it like that. But the increased TD (lower SST) results in lower C.U. capacity.
Again, I envision the low velocity unit cooler with more coil surface area than an equivalent rated standard velocity unit cooler.Last edited by herefishy; 16-04-2002 at 01:20 AM.
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16-04-2002, 01:07 AM #47Originally posted by Gary
I suspect the outdoor temp was 80ish?
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16-04-2002, 01:14 AM #48
Pulling a pretty good load then. I suspect you won't need to adjust the TXV's. The low delta-T means it's sucking up lots of humidity. So far so good.
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16-04-2002, 01:16 AM #49
Gary,
Tomorrow I'll fill you in on the final readings. I've never concerned myself with dT, so I'm real interested in your evaluation of those numbers.
Thanx,
Mark
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16-04-2002, 02:08 AM #50
Here's what we know so far:
Normal load is SCT about 20-35F above ambient, 20F being a light load, and 35F being a heavy load.
At 28F over ambient, this condenser is getting rid of a fairly heavy load of heat. Where does that heat load come from? The evaporator.
If the TXV's weren't somewhere in the ballpark, it would not be able to pick up this much load.
The evaporator coil does two things. It cools the air (sensible load) and it de-humidifies the air (latent load). It isn't picking up much sensible load (low dT), so it must be picking up a heavy latent load (lots of humidity).
Make sense?Last edited by Gary; 16-04-2002 at 02:35 AM.
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