Endless Freezer as Endless Cooler (10 door)

[herefishy]

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?

[Dan]

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?

[herefishy]

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?

[herefishy]

Originally 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.

The load has been correctly calculated, and furthermore, the load is not a problem (in the current medium temperature application). I understand that the evap rating is higher for the low temp app. That is the "variable" that I quander in the current application, because the evap coil volume and surface area is designed for that low temp (higher capacity) application.

[Prof Sporlan]

Is it possible that these cases came from an Albertson's and what you are describing is the Alco ALLS?

That would be the Prof's guess.

Disabling the two evap fan motors will likely increase the refrigerant mass in the evaporators.

[herefishy]

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)).

[herefishy]

Originally posted by Prof Sporlan
Disabling the two evap fan motors will likely increase the refrigerant mass in the evaporators.

Do you think my course of action appropriate? And the net result an end to it's means?

Aside from the receiver capacity issue, of course.

[herefishy]

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.

[Prof Sporlan]

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.....

[herefishy]

Originally posted by Dan
One way around it is to disable pumpdown

I categorically refuse to operate without a pumpdown.

You've got a long row to hoe in getting me to do that.

[Prof Sporlan]

By the way, Prof... I'm intending to go to the Supermarket REF seminar in Arlington

Tell John Murray (our Manager of Supermarket Refrigeration) you know the Prof!

[herefishy]

Originally posted by Prof Sporlan
The fact that you have a subcooler ahead of the TEV makes the ALLS redundant... a larger receiver necessary.....

10-04 Prof.

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.!!!

[Prof Sporlan]

Do you think my course of action appropriate? And the net result an end to it's means?

The Prof sees he is quickly falling behind in his post counts to herefishy...

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.....

[herefishy]

Originally posted by Prof Sporlan


Tell John Murray (our Manager of Supermarket Refrigeration) you know the Prof!

I'll hunt John down. I'll tell him to tell you that he met "herefishy". then he can report what an ugly cuss I am!!!!!

[herefishy]

Originally posted by Prof Sporlan
Might be inetersting to see what would happen if you reactivated one of the evaporator fan motors.....

Well, I know what will happen..... my SST will increase.... I will exceed my design criteria for the TEV's..... because my SST increases, I will close in on a 10degF TD, and the beer cartons will be saturated from the 90% RH.......

[Prof Sporlan]

Was the Albertson's thing an overengineering nightmare that troubled all of the manufacturers involved?

If the Prof recalls correctly, the ALLS heat exchanger was developed by an individual who had some association with Albertsons. Sporlan was originally asked to manufacture the device. For various reasons, we declined, and Alco elected to manufacture the device.

I would like to remove <i>BOTH</i> subcoolers

Removing both subcoolers could help reduce refrigerant mass in the evaporator, but the larger receiver will resolve the problem. The Prof doesn't mind having one subcooler present to assure vapor freee refrigerant to the TEV. Subcooling will actually increase TEV capacity, as the lower liquid temperature increases NRE. Interestingly, the ALLS is a bit of a trade off for the TEV. You get lower liquid temperatures at the TEV at the expense of an increased load for the TEV.

[herefishy]

Originally posted by Prof Sporlan
Subcooling will actually increase TEV capacity, as the lower liquid temperature increases NRE.

This is a concept that I just do not get.... I mean I understand it, but the sub-cooling is sensible. Why would you short circuit the refrigeration circuit (evap) for sensible gain, at the expense of (what I consider) the "power" of the latent heat of evaporation. the latent heat of the refrigerant is what makes the system desirable.... so why would one want to put so much into the sensible?.... doesn't sound sensible to me.

[Prof Sporlan]

I'll hunt John down.

It should be easy... he'll be the master of ceremonies at the seminar. You might be interested to know that the Prof assisted in his training when he was a young sales engineer for Sporlan..

[herefishy]

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.

[Prof Sporlan]

the latent heat of the refrigerant is what makes the system desirable.... so why would one want to put so much into the sensible?

In the case of the ALLS, you are truly trading Btus. What you gain lowering liquid temperature you lose with the higher load. In theory, you don't gain anything, unless you would be flashing ahead of the TEV without it

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.

For the above methods of subcooling, that is a fair statement. If we are talking about mechanical subcoolers (separate refrigeration system for the purpose of refrigerant subcooling), these systems can show significant efficiency gains if applied correctly. The reason here is the compressor on a mechanical subcooler can operate more efficiently than, say, the compressors on a low temp compressor rack.

[Dan]

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.

[Gary]

If you go without a pumpdown, the next best is to cycle the LLS with the compressor.

[Gary]

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).

[Dan]

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.

[Gary]

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.

[Andy]

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.

[herefishy]

Originally posted by Andy
what about reducing the air flow through the evaporator by changing all the evap fan blades,

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..

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).

[Andy]

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.

[Prof Sporlan]

At start-up the superheat was high at evap outlet. Would it be advisable to remove the ALLS prior to fiddlin' with SH adjustment?

First, make sure your case temperature is reasonably close to desired temperature before adjusting the TEV. Setting the TEV during pulldown can result in a low superheat or flooding condition when the case reaches desired temperature.

I think that the ALLS' may be applying a load to the TEV capacity that I have not accounted for.

With the ALLS, the TEV sees the added load of the ALLS, but in return, the TEV gets lower liquid temperatures which increases its capacity. The net effect on the TEV sizing is essentially nil. But the Prof would use the liquid temperature entering the ALLS, and not the TEV, to size the valve.

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

Subcooling via suction line heat exchanger or ALLS is fine for maintaining vapor free liquid at the TEV. But once this has been achieved, you're essentially trading Btus. Having added subcooling provided by a separate refrigeration unit, however, can provide added efficiencies if properly applied.

(It's fuzzy to me at the moment, but I beleive Tyler is out of business).

Nope. They're making cases in Niles, MI, and cases and racks in Waxahachie, TX. They're owned by United Technologies--Carrier.

[Prof Sporlan]

I 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?

Greater subcool would reduce refrigerant velocity in the evaporator coil, assuming the subcooling load is not being seen by the TEV (heat exchanger outside of the case). Lower velocities would promote greater refrigerant mass in the evaporator. Cutting out evaporator fan motors would likely have a greater effect, though.

In the case of the ALLS, it's effect would probably be minimal, unless it is affecting refrigerant distribution.

[Dan]

I 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?

Originally I speculated that reducing the air flow would increase the refrigerant mass in the evaporator. Your question is to the same point, though, isn't it?

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.

Nothing you did changed the net refrigeration effect. You managed to lower suction pressure because you removed a proportion of the heat load when you disabled fans.

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.

I don't know how you got there, but you are a tad light for a freezer load, even though I have seen such numbers published. Reach-ins are a peculiar sort. If you keep the doors closed and never change product all you have to do is weigh the heat of motors, heaters, and conduction. I would guess that would be a load of about 500 Btu/hr.

When I started the C.U. selection I
assumed a 820 btuh/degFTD NRE, assuming a 15degFTD at a
design 35degF box.

The TD has little to do with the load. So little, I would call it "nothing" and risk criticism.

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.

LOL. I don't see the head pressure as being low. And no, I don't think in your instance the additional heat exchangers are making more work for the compressor. More often than not, heat exchangers of any sort improve compressor performance.

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..

I had mentioned my most recent undersized receiver incident with the service case and a gravity coil. What I failed to mention was that we were brought in to replace a compressor that failed. The likely cause of failure was charging the unit until the bubbles disappeared from the sightglass.

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.

Get used to that.

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.

Nah.... I am sort of partial to the ALLS, to be honest. Heat exchangers do not add load.. they just swap it back and forth. The load is indifferent to what we do with heat transfer within the walls of pipe.

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?

Nope.

Just for clarity, the cases are Tyler brand (It's fuzzy to me at the
moment, but I beleive Tyler is out of business).

Tyler 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 bad.

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).

How are you calculating?

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,

I have to interrupt... yes.

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).

I really didn't do any good for you Herefishy with my responses, but I did enjoy myself. Remember the Alamo. In fridge terms it was improved when the holes went in. There are those who would argue that Willis Carrier and General Santana have much in common. Fortunately, most of them are dead, except me.

[Gary]

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 compressor

[Prof Sporlan]

Tyler 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 bad

Only goes to show that Hussmann and Sporlan have folks who keep a proper eye on the competition...

[Andy]

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. Andy

[Prof Sporlan]

Hi, It is possible to have too much subcooling, with TEV's anyway

The greater subcooling increases TEV capacity because of the increased net refrigerating effect of the refrigerant <b>AND</b> the greater density of the liquid refrigerant entering the TEV.

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.

Your thinking on this subject is quite good...

[herefishy]

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.

[herefishy]

Originally 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.

Just for clarity, Dan. The load is not higher. The case is designed for a higher load at the (originally intended) lower case temperature. In the Med. temp app., the load is lower than the load of the low temp application.

I selected a C.U. rated at 12,400btuh+ @110degF ambient for the 10-door (glass) case.

[herefishy]

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 strings

[Gary]

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!

I would still like to see a complete set of temps for this system when you are done.

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.

[herefishy]

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.

[Gary]

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).

[herefishy]

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.

[Prof Sporlan]

and the Supermarket Seminar in Arlington is <i>BOOKED</i> and there's no space for me!!!!

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....

[herefishy]

Originally 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.

[Gary]

I suspect the outdoor temp was 80ish?

[herefishy]

Originally posted by Fridgetech
...coil capacity is about

kW/m².K

Where
kW = Capacity potential
m² = total surface area or for a certain coil block the face area
K = LMTD otherwise TD for constant air volume

Marc, isn't airflow (volume) involved in the equation? Would the "constant air volume" be a variable? i.e.,... a variable as opposed to a constant?

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.

[herefishy]

Originally posted by Gary
I suspect the outdoor temp was 80ish?

yeah, I think about 77'F

[Gary]

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.

[herefishy]

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

[Gary]

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?