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Tom Richardson
26-04-2003, 06:38 PM
This is my first post, and the syntax may not be proper, please bear with me.
My company builds mechanical frost tops (chill plates) for salad top displays, and have been for the past 35 years.
We are introducing a new product, a frost top with a diverted cold air supply. View at: http://www.allsouthern.com/other.html
My problem is: I need to increase the efficiency of the unit to allow the use of a smaller compressor.
If you are interested in discussing this project with me, I will provide you with complete technical specifications of the components now being used and product requirements.
I would be interested in hearing from anyone who has frost top experience.
Thank you,

frank
27-04-2003, 12:12 PM
Hi Tom

I've only built one "frost top" which was for a "real ale" pub to cool the glasses after they come out of the glasswasher. It didn't have the cool air facility you describe. What temps are you achieving at present/what refrigerant/compressor etc?

frank

Prof Sporlan
27-04-2003, 04:14 PM
Perhaps the first place to start is to determine to operating TDs for both the condenser and evaporator. If these TDs can be reduced, compressor efficiency will increase.

Tom Richardson
27-04-2003, 05:48 PM
See the attached jpg of a single unit with the top up.
I am not sure of this reply, but we are trying to hold the product (salads, etc. for a salad bar operation) between 33 & 39 deg F. The cold air from the evaporator (Bohn 4300 BTU) is being monitored with a set point of 32 deg F, with a 4 degree differential, and using variable speed fans. We are using R-404A refrigerant, a 12000 BTU compressor, DanFoss thermostic expansion valves with replaceable orfices, Orit 6 EPR valve. The frost top uses 43 feet of .187" ID copper, strapped to the 304 ss pan with full length copper straps, with thermo mastic liberally applied to the entire surface.
My first concern now is "How to improve the efficency of the frost top."
1. I need a procedure for measuring what I have now, in some form, jouels, watts, BTUs: something.
2. As stated earlier, I am new to this area, totally out of my element, "what is ment by TDs"? :(
Thank you for taking the time to reply.

frank
27-04-2003, 08:04 PM
Tom

To measure the duty of the frost top you need a Mollier chart.

You can make measurements from the equipment and plot them on to the chart which will give you an indication of the refrigeration effect.

The compressor and evaporator seem to be mis-matched? any reason for this.

Gary
27-04-2003, 08:38 PM
Low side:

Evap air in temp
Evap air out temp
SST (saturated suction temp) or pressures (before and after EPR)
Suction line temp at coil outlet
Suction line temp at comp inlet

High side:

Cond air in temp
Cond air out temp
SCT (saturated condensing temp) or pressure
Liquid line temp at cond outlet
Liquid line temp at TXV inlet

Piping and wiring diagrams would also be helpful. The pictures are nice, but mechanics like to peek under the hood.

Prof Sporlan
27-04-2003, 09:54 PM
We are using R-404A refrigerant, a 12000 BTU compressor, DanFoss thermostic expansion valves with replaceable orfices, Orit 6 EPR valve.
The Prof appeciates the use of his ORIT-6. Mmmmmm... might have to do something with the Danfoss TEVs... :)


2. As stated earlier, I am new to this area, totally out of my element, "what is ment by TDs"?:(
"TD" simply means "temperature difference". In the case of the evaporator, it is entering air temperature minus the evaporating temperature. In the case of the condenser, it is condensing temperature minus ambient temperature. You may hear of the term: "log mean temperature difference (LMTD)" when one desires a more precise means of evaluating coil capacity, but the above is fine for our purposes.


To measure the duty of the frost top you need a Mollier chart.
Or to be more precise, a p-h (pressure vs enthalpy) chart. :) A Mollier chart is technically an h-s (enthalpy vs entropy) chart, though the term is loosely used. The Prof has seen h-x (enthalpy vs humidity ratio) psychrometric charts referred to as Mollier charts.


The compressor and evaporator seem to be mis-matched?
The Prof assumes the 43 feet of 3/16" OD tubing is operating at common suction, and the ORIT-6 controls the 4300 BTU/hr coil. The common suction pressure at with the 3/16" OD tubing must run at to achieve desired frost top operation is key here. Also, the pressure drop across the 3/16" OD tubing may well be a bit excessive. The million dollar questions at the moment: what is your common suction pressure during normal operation? What is you pressure at the TEV outlet feeding the 3/16" OD tubing? These numbers will give us a handle on the "TD" of the 3/16" OD tubing, and if you are running excessive pressure drop across it.

Tom Richardson
28-04-2003, 02:02 AM
I want to thank everyone that has replied to my problem.

Suction pressure @ EPR 55psig with evaporator solenoid open and 41 psig with evap. sol. closed.

I will post a schematic of the system on 4-26-2003 by 12:00 noon EST.

All the replies have been very helpful.

I know the compressor is "over powered" for the system, that is one of the things I am trying to prove.
We have a heat problem, the compressor is mounted inside the cabinet, a self contained unit. It is very difficult to vent the hot air without causing a lot of noise. The excessive heat (as high as 105 deg F.) causes the compressor to loose efficiency, so we just used bigger and bigger.......until we overpowered the heat issue. Not the most logical solution, but there was a time deadline, also.
Again, thank all of you so much.

herefishy
30-04-2003, 02:33 PM
Very respectfully, I submit that your delimna is common in your industry (manufacturing). Take Delfeild, for instance - They had built a freezer cabinet with the condensing unit coil facing the back of the machine. When the machine was set it place at the end-user's facility, it was naturally set against a wall!!!!

The condenser was three inches from the wall and in consideration of the rest of the construction the condensing temperature was astronimical and you couldn't service the dern thing with 300lbs of product in it. Of course the unit was only rated for a 90F ambient.

When I talked to the "Old Timer" at the plant, he indicated that "I know, I kept telling 'em". It seems that these plants are hiring kids that know little about the refrigeration process or related service and use, but are really good at operating CAD software and drawing little pictures.

First of all, changing your compressor is not going to improve your condensing temperature heat gain. It is a cabinet design problem. You are "Wagging the Dog" if you intend to address your (ambient heat gain) problem by re-engineering the refrigeration system. Get back on the CAD machine and redesign your cabinet, or reposition your condenser.
Or perhaps you could edit your installation specifications to reflect proper application of the equipment.

In answer to the specific question that you pose however, I will offer that minimizing the capacity of the compressor may best be obtained by employing a compressor whose maximum evaporating temperature is the design temperature of the appliance, and then employing a crankcase pressure regulator (CPR) valve to protect the compressor from the higher pressures that it would be exposed to. There are other considerations, but I'll leave it at that for now.

:)


1. I need a procedure for measuring what I have now, in some form, jouels, watts, BTUs: something.

I think that with compressor or condensing unit information and pressures/temperatures of an operating system we could determine that amount of work that is being done.

If we knew the mass, thickness and surface area of the chill top, we could come close to some kind of load data, also.

Tom Richardson
02-05-2003, 11:50 AM
Still in the frost top issues...
Attached is the spec sheet for the materials used in the construction of the frost top.
Questions:
1. Which style would be most efficient?
2. How to measure required compressor size?
3. Does anyone know of a better way to transfere the heat from the s.s. pan to the copper tubes?


An additional post will be the same drawing, zipped including .dwg & .png

thanks,:)

Tom Richardson
02-05-2003, 11:52 AM
This is the .dwg & .png files for the frost top construction.

Thank You,:D

herefishy
02-05-2003, 02:35 PM
Tom Richardson,

Before we go through some extensive exercise, could you please once again indicate why it is that you are trying to decrease the compressor "size"?

Prof Sporlan
02-05-2003, 03:08 PM
The Prof is concerned that the 1/4" OD circuit tube size might be a bit small here, even with the two circuit design. The heat exchange load is a bit of an unknown here.

You will want to use the 2 circuit design if pressure drop across the single circuit design is excessive at design conditions, let's say anything above about 3 psi.

Pressure taps will help determine best design.

Tom Richardson
02-05-2003, 03:15 PM
I want to reduce the compressor size to cut down on the 'noise' that three 1 hp compressors make inside an enclosed cabinet.
I am now using Copeland F style 1 hp compressors. I want to go to Copeland M style 1/2 hp compressors. The smaller compressor will allow:
1. More room inside the cabinet. This will allow an elaborate air ducting system for the air in and out.
2. The smaller compressor will NOT generate as much heat.
3. The smaller compressor will run quieter.
4. The smaller compressor cost less$$$$.

Until we reduce the noise, the product is not acceptable to the customer!

Thank you,

herefishy
02-05-2003, 03:19 PM
The smaller compressor will not generate as much heat, because it will not "absorb" as much heat from the cabinet (less refrigeration).


please list the model numbers of the condensing units for each of the (3) applications, and the desired temperature of each of the spaces (or plates) to be cooled.

Tom Richardson
02-05-2003, 05:23 PM
1 unit consists of:
1 Frost top, 1 evaporator coil, 1 compressor

Complete salad bar consists of 3 units in one cabinet approx. 17 feet long.
We are not refrigerating any enclosed areas, only moving cold air over the product, and collecting about 50% of the 'refrigerated air' for the next cycle, with an influx of 50% ambient air @ 70-75 deg F.
The pan is well insulated from the compressor. The heat problem is inside the cabinet, with temperatures above 100 deg F. in the compressor area.
________________________________
Frost Top:
Temperature desired: 28-32 deg F.

Evaporator:
TA43AF Bohn, 4300 BTU w 750 cfm.
Air Temp. moving out of coil to be 32-36 deg F., thermostatically controlled.

Thank you,:)

herefishy
02-05-2003, 06:58 PM
First of all, without doing a load calc or even speculating, why are we not redesigning the cabinet to adequatley reject the heat, rather than just deciding to do "less work"? Of course, due to the improperly designed compressor compartment, we are doing less work (higher condensing temperature), but decreasing capacity, in my humble opinion, will result in doing even less, "less work". :confused:


________________________________________

The Bohn '43 evaporaotr is not 4,300 but/h. it is 430 btu/h per degree TD. Typically in this type of application (if properly engineered, we don't know) you would run about a 15F TD or approximately a 20F saturated suction temperature (coil temperature) and as such the "load" or heat transfer rate of the evaporator would be approximately 6,450 btuh. Though actually it would probably be more... we would need to know exactly what the parameters are... such as the questions that Gary keeps asking.. air in, air out, yadda yadda yadda....... but the 6,450 btu/h figure serves me well at this point.

If we assume the "rule of thirds" and apply it to your 1hp condensing unit (compressor), we would be in the ballpark if we assumed a capacity (at a 20F S.S.T.) of approx. 9,000 but/h which would indicate a reserve of approx 2,500 btuh/ serving the chill plate.

Sounds to me like you don't have much to play with. We could decisively make that decision, if we had all of the temps, pressures and other operating characteristics of the machine as it is running.


:)

Tom Richardson
03-05-2003, 01:44 PM
I want to thank everyone who has replied to my project. ALL replies have been very informative.

If anyone cares to go farther with me, I have attached scaled .dxf & .dwg drawings of a cross-section of the salad top.
If you need more information to clear up what I am trying to communicate, please contact my email.
Again, thank everyone for their replies:)

Gary
03-05-2003, 07:36 PM
On your website it says a remote condenser model is available. You might want to design that first. This will tell you what size is needed to do the job. Then figure out how to put it in the cabinet.

All of the engineering calculations can get you in the ballpark. The air in air out yadda yadda yadda can fine tune it for you. :)

herefishy
05-05-2003, 02:41 PM
I can't open a ".dwg" file. What program is that?

As far as "going further with you", do you have any more questions? Have we answered any of yours?

I am interested in your response to my pointing out that the Bohn '43 evaporator is NOT 4,300 btuh. How did that strike you?



:)

Andy
05-05-2003, 08:38 PM
Hi Herefishy, dwg is a CAD drawing file, most likly of the autocad variety, if it was dxf you could open it with most CAD programs, but in this case I assume you require some form of autocad.
Regards. Andy:(

Tom Richardson
06-05-2003, 11:56 AM
The DWG file is AutoCad, but also included in the zip file is the DXF version that can be opened (imported) in most cad software and some photo editing software.

The 430 btu / 1 deg specification for the Bohn, well this whole forum has been VERY informative and educational. Like I stated earlier, I am very new to this field, we had this job 'engineered' by people who are professionals, and it appears there are quite a few 'gray areas' that can be explored (expanded on) in this particular application.

We have a product that needs some 'tweeking' before the customer will accept it. The noise the compressors make is one issue. Gary wrote in about the remote compressors, well we just did that to a store at the end of April, moved the compressors out of the cabinet and up to the roof - and it worked like a charm, and that is where it showed up that we have 'too much' compressor.
The remote compressor will not work in a store that is located in a mall, we can't have access to the outside....

It was suggested to 'redesign the cabinet'. We have to go with the design that we have now (outside look) to match the theme of existing stores. The inside is a different matter. The new M style compressors will allow some 'fancy ducting' to keep the air moving in a more controlled manner.

Again, many thanks for your replies and question / answers.
:confused:

herefishy
06-05-2003, 03:06 PM
As far as the noise issue, I would suggest some acoustical material be applied to the compressor compartment walls. Perhaps fiberglass duct board? Or in the case of your "ducting" of the condensing unit airflow... investigate the acoustical qualities of whatever you may propose to use.

:confused: I do not understand what symptom causes you to conclude that you have "too much compressor". I have not heard any information to lead one (or myself) to such a conclusion. I initially thought your premise that the compressor(s) is too big was because it is hot in your poorly designed cabinet. But now you say that it was the operation of the remote units that the oversized conclusion was derived.

Please explain. Were evaps freezing up?... Was the salad freezing up?

:)

Dan
07-05-2003, 12:18 AM
Nice thread. Herefishy, try the demo at this site: http://www.cadopia.com/demo/demo.asp it was free for me and it is darned good for viewing CAD drawings.

Richard, I think after looking at the pictures, that you are discharging refrigerated air over the product. It appears you have a large discharge moire' in the rear. If this is so, quit worrying about the cold plate, unless you are concerned that it is not developing a cosmetic frosting. Here is what I am thinking:

You are trying to achieve a product temperture below 41 deg F because of the new food codes. So you developed an air over system to maintain this.

I think you could afford to abandon the cold plate piping. All you need is a surface equal to the temperature of the air you are distributing over it.

A key thing you want to measure is the difference in temperature of the air discharging from the evaporator and the air that is returning to the evaporator. This is a measurement that both Gary and The Professor were alluding to. And it can tell you how effective your refrigeration is in the display area.

Another key thing you want to measure is the effect of air velocity on this change in temperature. Let's call this change in temperature the Delta T, as opposed to TD which is the difference in temperature between the evaporating temperature and the air temperture.

Herefishy's point regarding the capacity of the Bohn coil you are using is right on, too. It's capacity will change as the TD's and Delta-T's change, as will the compressor's capacity! Which is what we all can see can be improved.

So... just where is your air return located and how warm is that air? I think we can improve on that.:)

Tom Richardson
07-05-2003, 12:17 PM
Dan, very interesting, and you are just across the Bay....
The incomming air runs approx. 45 to 48 deg F. The air after the evap. coil is 32 Deg F. The fans are controlled by a variable speed controller.. too much air flow, the air temp is too high, too little air flow, the coil freezes up!
(see attached .zip)

The frost top is for 'cosmetic frosting' and we are experiencing some 'very cold' conditions with it. I do not have a working model in the shop now, to give exact temps, I am working from my notes.

The air intake has been an issue, we are loosing a large percentage of our 'refrigerated' air and drawing in ambient air from the store (70-75deg F.). A deeper pan helps this condition, and we have used the deeper pan for some other jobs, but we have restrictions on this unit design, and that is what I am working toward.

Dan, we are just a few miles from Tampa...

Thanks guys,:D

herefishy
07-05-2003, 02:46 PM
Originally posted by Tom Richardson
The incomming air runs approx. 45 to 48 deg F. The air after the evap. coil is 32 Deg F.

If your S.S.T (suction temperature or "evaporator coil temperature") is 25degF, at a 45degF return air, the capacity of the Bohn '43 evaporator is approx. 8,600btuh ! :D

At 48degF, 25 degF coil temperature 9,890btuh. This is not in consideration of any latent load, but I think we could assume a 50% RH of the infiltrating air, and at a 20degF to 23degF TD, I would assume that the latent load is negligible.

If you could provide the exact manufacturer model # of the condensing unit, I could get a better idea of precisely what your evaporating temperature is when servicing the Bohn '43 coil :)

Someone would be better than I, to calculate the work done @ 750 cfm of air at 50%RH with a DT of 13 to 16degF, 45-48degF air leaving.


OH!, Tom Richardson, in regard to your coil freezing up - I was pondering what kind of thermostatic control you were using. I suggest NOT controlling the refrigeration via air temperature. Apply a coil sensing cold control, whereas the machine cycles on the coil temperature, not eh air temperature which varies greatly in your application. Call REfrigeration Hardware Supply and order a stock # 60-260. Insert the coil of the sensing capillary into the outlet of the coil fins. I assure you that you WILL NOT have any more coil freezing up problems. :)

frank
07-05-2003, 07:35 PM
A "dwg" file is an Autocad File

Frank

Dan
07-05-2003, 11:43 PM
Hello neighbor:) I think I would play with the air feed and return. Also, since your design will not permit you to lower the surface (which was my next suggestion) you could try putting up a small barrier around the circumference of the display area - keeping the return air flue on the inside of the barrier. The taller the barrier, the better, but even a 2-inch plexiglass barrier would help a lot, without being objectionable, I would think

Try covering most of the lower holes in the discharge area, and put the fan on the lowest speed you can live with. Then smoke test the air discharge and play with aiming the air toward the return air flue.

As you lower the air volume, the compressor will run at a lower suction pressure. This is one reason you are icing up the coil. But that's okay. You are wanting to put in a smaller condensing unit, and icing up the coil is telling you that you are achieving what you desire.

The next thing you might wish to try for testing purposes is to install a CPR valve on the compressor. This will enable you to adjust the suction pressure to simulate a smaller compressor.

Once you have an evaporating pressure that you are satisfied with, you can look at the suction pressure at the compressor. If you look up the capacity of that compressor at that suction pressure, you will know the capacity of the compressor you need at the evaporating pressure you adjusted the CPR valve to.

Herefishy's advice is excellent for this application. I wouldn't let the fact that you ice up the coil be a distraction. The icing of the coil only applies to the condensing unit that you are trying to make smaller.

Tom Richardson
06-06-2003, 10:39 AM
I want to take this oppoertunity to THANK everyone who has participated in this discussion - thank you very much.

I have learned quite a bit!!!

We are building a new unit, with 3/8" od copper pipe for the Frost Top, a deeper pan to catch more of the 'refrigerated air' from the evaporator, to lower the evaporator's TD, and a completly new cabinet design, to facilitate air into & out of the cabinet.

I am trying to find the proper compressor - this is a job. Everyone wants to go 'big', for safety. I am 'just' looking for a unit that will give me a max of 6000 BTUs....

I will post test results, I hope, by the end of next week????
Again, Thank all of you so much,
Tom

herefishy
06-06-2003, 02:22 PM
Hi Tom Richardson,

If your company is making this thing, You should be an "OEM" purchaser, and your condensing unit/compressor mfgr. has an engineering department that will also assist you with your selection and design ;)

By the way... you forgot to mention that you are also going to employ a "coil temperature sensing" temperature control in order to assure proper defrosts.

see ya'

Dan
07-06-2003, 11:09 PM
I am glad you paid attention to the airflow. I thought that was the biggie.:)

Tom Richardson
09-06-2003, 12:52 AM
Hello,
A while ago you asked about a look 'under the hood'.
Well the attached .DXF file is a look.
We are building another test unit now, I will have some results by this weeks end. I hope.

Thanks again to all,
Tom

Tom Richardson
21-06-2003, 10:01 AM
:)
For those who have been following my Frost Top work, we installed the 1/2 hp condensing unit (5900 BTU, low temp copeland) and it is working GREAT. All required temps are holding, noise is around 55 db, heat discharge is acceptable.

There is one problem: START UP
If the ambient temp is above 83 deg F., the refrigeration process will NOT take place. High head pressures (350 psi) & high return pressures (90 psi). Below 82 deg F., I have complete frost coverage within 45 minutes, at 75 deg F. startup, complete coverage in 30 min. (Above 83 deg F., the #$%@ thing just needs to be 'push started'.)

We are now in the 'fine tuning' phase, testing & recording. With all the new modifications we have incorporated into this unit, this is our 'BEST' one yet!!!

I really want to thank ALL who have replied to my postings and I appreciate your sharing of knowledge with me.
Thanks again,
Tom
:D

Andy
21-06-2003, 11:37 AM
Hi Tom,
fit a simple crankcase regulator, this will restrict the pressure in the suction line entering the compressor and thus the head pressure during start-up.
Regards. Andy:)

Dan
21-06-2003, 03:29 PM
Yep, Andy, that should do it. If that fails to build the frost in the desired time, I would further recommend putting the fans on a pressure control or time delay to keep the load off the compressor until the frosting is established.

herefishy
21-06-2003, 05:47 PM
Well, Tom.. y'all are obviously low-balling this thing. :(

You have applied a compressor in which it's maximum rated suction temperature is probably 20degF, I assume. This is a common misapplication in refrigeration (utilized by the low-bidder to get the job, employing the 1/2 hp instead of the required 3/4). The only time that the compressor is going to be within the manufactorer's specified application range.. Is when the thermostat is satisfied, and the compressor turns OFF ! ! !

The problem that you will experience is slow pull-downs, and a rash of compressor failures, warranty claims, and customer complaints. What's more expensive?... the three-quarter horse?.. or maintaining an equipment line with a misapplied condensing unit? Go figure.

A btu is a btu is a btu. The amount of work done equates to the load. The only variable (the way I see) is the THR affected by the heat gain of the compressor itself, but if you are rejecting a 6,000btuh heat load, the heat rejection will be 6,000btuh + the heat of the motor (machine).

PS... I would have to see the spec's to actually beleive that you have a 1/2HP that has a capacity of 5,900btuh @ 20degF SST (or furthermore, under what conditions this capacity is derived) :rolleyes:

Dan
21-06-2003, 08:36 PM
Herefishy, I have to disagree. Pull down loads on self-contained equipment are not necessarily how you want to size self-contained equipment.

Remember, the size of the condensing unit is a driving force in self-contained equipment, as is noise.

Most all manufacturers of self-contained equipment get dispensation from Copeland, for example, to operate compressors outside the normal parameters for remote equipment as long as they use devices such as EPR valves or MOP TEV's. Now that I think about it, I hope Tom has checked with Copeland to see if they will warrant his application.

I think Tom is on the right track. The service tech in me agrees with the spirit of your ripost, though, Herefishy.

How often have we attempted to replace a misapplied compressor through the wholesaler only to find out that it is warranted by Copeland only through the manufacturer? After much grief and wasted time.:(

Gary
21-06-2003, 08:49 PM
Overload on pulldown is the obvious assumption and CPR the obvious solution. Do we really want to assume that it is not overloaded throughout its cycle? Shall we assume that the charge is right? Shall we assume that it has sufficient airflow?

As usual, we gather as little information as possible and jump to conclusions.

This system will spend the vast majority of its life working within a few degrees of setpoint, and what really matters is the details of its performance under these conditions.

Dan
21-06-2003, 10:06 PM
Damn. There is always Gary. He has a whistle with a bead in it. He requires proper data. He is relentless.

I ignore him. It is not so simple to take a temperature of something. It is surprisingly difficult.

But, if you are inventing.. constructing... compromising... and discovering... well, then, you just have to let it fly.


As usual, we gather as little information as possible and jump to conclusions.


To make sense of what Gary is saying, I think that if you have a fire under you, you should not necessarily jump offf of it. Don't ask me! Ask Gary! My ass is burning.

Gary
21-06-2003, 10:17 PM
Perhaps after he gets a rash of compressor failures, he will graduate from meaningless descriptive phrases such as "working GREAT", "heat discharge is acceptable", and "our 'BEST' one yet" to giving us actual meaningful numbers.

I should not single out Mr. Richardson in this. Our entire industry somehow manages to stay afloat on a vast sea of WAG (Wild Assed Guess) and SWAG (Scientific Wild Assed Guess). It's a wonder that anything works.

Tom Richardson
22-06-2003, 02:48 AM
We all realize the 1/2 is working above what is determined to be 'normal' (about 88% w/evap & frost top & 45% w/ frost top only), but you do have a recommended RANGE from Copeland, the high point in the range, compressor may not last as long - the low end of the range, the compressor may last forever, or blow up tomorrow.
The 1/2 hp was an experiment - one that will work, it opened the door for further research.

All kidding aside, we installed the 3/4 hp unit today, realising that we do warranty this unit for four years and the SERVICE is very important to us. We sell to customers many times - not one time flash in the pan sales - we expect REPEAT sales! The 3/4 is running about 66% & 34%. The overall noise is about the same, and no difference in heat output.

The big test will come when three units are together and measuring the amount of noise they produce.

With all the improvements in this unit, we are experiencing 'very low' temps with both units. R404a may be too much for this application. Next week is going to be a fun week, try this and see what happens!!! This is definitly different that trying to 'get it colder', which is what we have been doing in the past.

In one of my earlier postings, I mentioned that it is very difficult to get the condensing unit you want - or think you want. We are working with Copeland now to become an OEM, and utilize their brain power for some of these projects.
The CONDENSOR models are: (from memory - which is fleeting.)
both 115vac 60cycle
FJAF-A059-CAV-101
FJAF-B078-IAA-201

Again, many many thanks to you'll,
Tom
:D :D

Gary
22-06-2003, 03:01 AM
What's wrong with a MOP valve?


There is nothing wrong with MOP or CPR if overload during pulldown is the only problem. But that's a rather large IF.

Dan
22-06-2003, 03:03 AM
I can only smile seeing Gary holding his grand-daughter as he ponders the miracle of anything working. We have WAGS and SWAGS and WMD's. Then, of course, there is Tom Richardson.

Thank goodness, Tom, that you don't know better.

Dan
22-06-2003, 03:15 AM
As usual, we gather as little information as possible and jump to conclusions.

Not entirely so, Gary. Efforts were made to diminish the air flow. The frost top is a rather stable load by my experience. The goal and efforts were to diminish the load and reduce the compressor size. Apparently, some progress was made, despite a lack of good measurements.

As usual, we use what little information that is gathered, and invite conclusions to jump into our lap so we can pet them for a while.

Tom Richardson
22-06-2003, 10:00 AM
Sometimes,
you have to 'look outside the box' to see the box.

MEASUREMENTS:
Now that I have a working model,
what measurements and from where, would be helpful? I have access ports & thermocouples mounted in various places.

One thing of interest, the pressure/temperature at the gage verses the temperature reading from a thermocouple at the same place do NOT always read the same temperature!!!

Thanks so much,
Tom

Gary
22-06-2003, 02:55 PM
MEASUREMENTS:
Now that I have a working model,
what measurements and from where, would be helpful? I have access ports & thermocouples mounted in various places.


Low side:

Evap air in temp
Evap air out temp
SST (saturated suction temp) or pressures (before and after EPR)
Suction line temp at coil outlet
Suction line temp at comp inlet

High side:

Cond air in temp
Cond air out temp
SCT (saturated condensing temp) or pressure
Liquid line temp at cond outlet
Liquid line temp at TXV inlet


One thing of interest, the pressure/temperature at the gage verses the temperature reading from a thermocouple at the same place do NOT always read the same temperature!!!


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

herefishy
22-06-2003, 06:38 PM
FJAF-0056-CAV @ 20F SST (90F ambient) = 5,340 btuh - maximum rated evaporating temperature is inducated up to 25F :(


FJAF-A078-IAA @ 20F SST (90F ambient) = 6,727btuh - maximum rated evporating temperature indicated is up to 30F :)


... the three-quarter is a much better selection.

in the R-22 department, I would recommend a F3AM-A078 :)

Tom, I probably could really tear you apart (help), if you told me what expansion valve(s) y'all are using... becuase I would bet that that is an improper application.

Hint: sporlan "1/2" expansion valve does NOT = 1/2 ton :p If such a misapplication of the expansion device exists, that may be cause for the discrepancy in the operation of the 5,200btuh condenser (1/2 hp). :) .... Of course your suction pressure and related temps could demonstrate that.

Dan
22-06-2003, 10:49 PM
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?

Tom Richardson
22-06-2003, 11:59 PM
All comments are very helpful, I am a much too old dog to $&@$ in someone else's yard, and not realize the repercussions of those actions. We all, @ my company really appreciate the help.
We paid a lot of money to have this unit ENGINEERED by professionals. We spent a lot of $$$ replacing parts. They started us with a 3/4 hp, then 1 1/4hp, then a 1 hp. So, I got on the internet and started reading, and asking 'stupid' questions, and then I found you guys.
Thank Heaven.


Current measurements:
I took the day off today, so this info is strictly from memory!!! This could be a bad thing. (Exact measurements will come tomorrow.)

Frost top:
TOO COLD, APPROACHING ZERO......AND BELOW.

air in evap: 41 deg F.
air out evap: 36 deg F.
(new pan design catches much more of the refrigerated air.)
Pressure into & outof the frost are within 1 to 2 pounds of each other, and they vary with the state of the evap coil. However, the temps seem to be out of phase with the pressures. This is normal I would imagine.

condensor air in: 75 deg F. (air being picked up from the floor.)
condensor air out: 85 deg F. ???
Orit 6 EPR @ evap coil.
w/ evap coil ***** flowing, 55 psig.


Expansion valves are Danfoss, with replaceable orifices.
Type: TEB w/ #2 orifice for frost top , & TEBE w/ #3 orifice for the evap coil. (They could be TUB, I have both, will post tomorrow.)

* I would like to replace the #2 with a #1 orifice @ the frost top & replace the #3 with a #2 @ the evap coil.
Please comment.

Special notes: evap coil sensor mounted inside coil is set to turn ***** flow off @ 32 deg F, and turn on @ 36 deg F.
* The coil stays on for approx. 3 minutes & off from 3 to 4 minutes. I am not sure, but I think THIS IS BAD. I think this means the coil is getting too cold. I would like to see more on time, with much less off time.
Please comment.

Thanks again, I will be waiting for your replies,
Tom
:D

Gary
23-06-2003, 12:49 AM
The frost top approaching zero degrees would imply that the SST is below zero, while the main evaporator is being held at a higher temperature by the EPR. Being that the frost is cosmetic, I see no reason the suction line from the frost top can't be connected upstream from the EPR, subjecting both to the controlled limit. But perhaps others may disagree. The downside is that this would slow the formation of frost, and could in fact eliminate it under extreme conditions.

Since the main evaporator refrigerant flow is being cycled on coil temperature, this would imply that the EPR is set too low. Raising this would increase the on time and decrease the off time.

Of course we may see more fundamental causes given a full set of numbers.

So far, it doesn't look like the compressor is undersized at all.

We can't tell much about the orifice sizing without further information.

And accurate measurements are essential to accurate evaluation.

Gary
23-06-2003, 09:36 AM
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
23-06-2003, 09:54 AM
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
23-06-2003, 10:51 AM
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
23-06-2003, 11:13 AM
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
23-06-2003, 02:19 PM
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
23-06-2003, 03:04 PM
How did I know the TEV's were wrong?:p


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
23-06-2003, 03:15 PM
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
23-06-2003, 03:30 PM
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
23-06-2003, 03:55 PM
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
23-06-2003, 03:55 PM
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
23-06-2003, 04:17 PM
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 :rolleyes:

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?:confused:

herefishy
23-06-2003, 04:28 PM
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
23-06-2003, 04:51 PM
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:D

Gary
23-06-2003, 04:56 PM
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. :D


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
23-06-2003, 05:04 PM
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: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:D

Gary
23-06-2003, 05:27 PM
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
23-06-2003, 05:31 PM
Inquiring minds want to know..... what is the desired frost top temp?

Andy
23-06-2003, 05:47 PM
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
23-06-2003, 05:54 PM
Hi Andy :)

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

Tom Richardson
23-06-2003, 07:25 PM
A lot of data comming back:eek:

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
23-06-2003, 07:40 PM
Rip the EPR out of the system, and use it for a paperweight. :p

Okay, then.... do it carefully.

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

:)

Andy
23-06-2003, 07:42 PM
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:D
Regards. Andy

Andy
23-06-2003, 07:45 PM
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
23-06-2003, 07:46 PM
Hi Andy, I may be incorrect, but I believe that there may be a mandate in regard to mechanical connections in assembled equipment.

:)

herefishy
23-06-2003, 07:51 PM
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
23-06-2003, 07:56 PM
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:mad:
Regards. Andy.:)

herefishy
23-06-2003, 07:59 PM
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 :p

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

;)

Tom Richardson
23-06-2003, 08:15 PM
NEW ORIFICES ARE ON THE WAY!!
Tom

herefishy
23-06-2003, 08:22 PM
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? :confused:

Tom Richardson
23-06-2003, 08:47 PM
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
23-06-2003, 08:56 PM
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
23-06-2003, 09:03 PM
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
23-06-2003, 09:12 PM
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
23-06-2003, 09:22 PM
Mr. Herefishy,
That would be a great thing...
smaller evap coil....
smaller comp.....
Let me hear what you are thinking?
Tom

Tom Richardson
23-06-2003, 09:24 PM
Question:
What does this IMPROVING POSTER" mean?
Who decided that I was improving????
Tom

herefishy
23-06-2003, 09:30 PM
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
23-06-2003, 09:33 PM
Do you think this will freeze the evap coil?
Tom

herefishy
23-06-2003, 09:41 PM
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
23-06-2003, 10:39 PM
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. :D

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
23-06-2003, 11:01 PM
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
23-06-2003, 11:19 PM
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
23-06-2003, 11:47 PM
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
23-06-2003, 11:49 PM
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
23-06-2003, 11:50 PM
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 :p

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

herefishy
23-06-2003, 11:57 PM
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). :p

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
23-06-2003, 11:59 PM
Who decided that I was improving????


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

Gary
24-06-2003, 12:04 AM
The readings are comming from thermocouples strapped to the lines.

Are they insulated?

herefishy
24-06-2003, 12:04 AM
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
24-06-2003, 01:14 AM
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
24-06-2003, 10:47 AM
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

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. :D

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:D
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:o
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:D
By the way where has all the excessive head pressure went:confused:
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:D
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..... :D

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. :D


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. :D

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". :p

Regards, ... the fish

:)

Andy
26-06-2003, 08:11 AM
Hi Mr Herefishy:D
all taken in good fun:eek:
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!!!!! :rolleyes: 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. :D

Gary
26-06-2003, 05:58 PM
ROFLMAO !!!!

herefishy
26-06-2003, 06:37 PM
:p


Tom Richardson,

If you have time, maybe you could read this thread

http://www.refrigeration-engineer.com/chat/showthread.php?s=&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. :eek:

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 :eek: )

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. :D

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. :D

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:D
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 :D

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

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

Tom Richardson
28-06-2003, 10:00 AM
Additional information:
My current job at this company is Systems / Oprerations Manager.
I am responsible for the computers, software & hardware, the operating systems for the company, inventory, the production workers (40), electrical trouble shooter, and blablabla. My degree is is Business Administration. You are prob. wondering - Why the @&*% are you working on something you don't know the first thing about??? We have gone thru three(3) Ref. Companies plus the original designers. There was no one left! I worked with the last guy for 2 days in Feb. on another unit - I saw a lot of guessing on his part - things you do not do in electrical / electronic trouble shooting, and we were paying $100.00 per hour.
So you see, this forum has been a tremendous help to me. You have cleared up so many issues.
Thank all who have participated so very much,
Tom

Andy
28-06-2003, 07:10 PM
Tom:)
What refrigerant are you using R404a??
20 psig OUTLET pressure on the evaporator would be a saturation pressure of about -26.4 deg C (about -15 deg F) if your temperature at outlet is -4 deg F your superheat is about 11 deg F, or near enough to start with.
Regards. Andy:)

herefishy
28-06-2003, 10:18 PM
Tom Richardson,

In re: to superheat, read this:

http://www.hvacwebtech.com/trouble.htm

or this:

http://www.refimax.com/docs/therm_exp_valve.htm



Measure your suction line temperature exiting the evaporator (or cold plate).

Measure your suction pressure.

Refer to the "satuaration" temperature of your pressure reading on your pressure/temperature chart.

Subtract your saturation temperature of the refrigerant pressure (chart temperature reading) from your suction line temperature and the result is the superheat (the degrees above the boiling point that the refrigerant is at as it leaves the heat exchange device, evaporator or cold plate).

For medium temp, typically you want to be at about 7-9degrees, but in your close-coupled system a little bit more is not bad. You can adjust the responsiveness of your cold control scenario by relocated the cold control sensing location. For more positive reaction (defrost) you would locate the sensing location closer to the inlet of the evaporator. :)

herefishy
28-06-2003, 10:24 PM
Originally posted by Tom Richardson
*With the temps I am trying for, is R404a the correct refrigerant??

...More acurately, the condensing unit you are utilizing is designed for 404A, as such that is what you need to be using. The "type of refrigerant" is NOT an issue. You should use the refrigerant that the condenser is designed for, as long as you are using the proper TEV thermostatic element for that refrigerant.

I.E., don't waste your time thinking about it. Actually, medium temp R-404A applications are becoming more common.

:)

Gary
29-06-2003, 08:48 PM
Tom, you need to go to my website and purchase the "TECH Method Lesson Series: ACR Trouble Shooting". It will help you a lot, although you also need hands on experience to go with it.

Gary
29-06-2003, 09:01 PM
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?


The cold control and the EPR are fighting each other. Move the EPR to the common suction line and adjust it to control the frost top temperature.

If you find that the new control settings DO NOT get you where you want to go, I am going to tell you to move the EPR to the common suction line and adjust it to control the frost top temperature.

If you find that the new control settings DO get you where you want to go, I am going to tell you to move the EPR to the common suction line and adjust it to control the frost top temperature.

And either way, I will keep telling you to adjust the TXV superheat.

Gary
29-06-2003, 09:19 PM
If you want to do the whole thing in steps, here is the first step:

1. Move the EPR to the common suction line and adjust it to control the frost top temperature.

2. Adjust the TXV superheat.

3. Adjust the cold control.

4. After each step, give us a full set of pressure and temperature measurements all over the system, so we can see what it is doing. We can't see the system from here. We can only see your description of it and the temperature measurements you report to us.

You are trying to do step number 3 before you do steps 1 and 2. That is not the right way to do things. The sequence is important.

condenseddave
29-06-2003, 11:19 PM
This certainly is not the first one of this type of box to be introduced. I've worked on this design from at least three other manufacturers.

All that I have seen thus far have the EPR controlling the fan coil, while letting the ice rail run wild.

It's the crappiest way to refrigerate that I have seen yet.:mad:

Tom Richardson
30-06-2003, 10:55 AM
Mr Condenseddave,
Where have you seen a unit like I have described?
Who makes it?
What is a better way?
-----------------------------
Mr Gary,
You say move the EPR to a 'common line' with both evap & frost top, same line ??
-----------------------------
Sunday, The unit ran very well with temp setting of 26°F. and 34°F. for the air out temp. The frost top temp floated about 6°F., but this was not a problem, the media being tested kept at a controlled 33° to 36°. No Ice accumulated on evap coil!!!
The air out measurement is for reference, this is how 'they have always' measured the performance of an air over model.
Thanks guys,
Tom

Gary
30-06-2003, 11:07 AM
You say move the EPR to a 'common line' with both evap & frost top, same line ??


Yes, the common suction line that goes to the compressor.

Tom Richardson
30-06-2003, 11:44 AM
Gary,
What psi setting on EPR ??

Can EPR physically be located @ the compressor area???

What will take place when the evap cycles off??

Tom

Gary
30-06-2003, 11:59 AM
What psi setting on EPR ??

Whatever setting maintains the frost top at the temperature you want. The lower the setting, the lower the frost top temperature. The higher the setting, the higher the frost top temperature.


Can EPR physically be located @ the compressor area???

Yes.


What will take place when the evap cycles off??


I assume you mean the air evap? The air evap coil will defrost itself. The frost top will maintain the same temperature.

herefishy
30-06-2003, 07:06 PM
Hi Gary,

I'm am trying not to confuse the issue as much as possible (so I'm trying to keep my mouth shut when someone hits a good point, and something is being accomplished ;) )

But, I might make the observation, that I believe that Tom Richardson stated that he was looking for a 30F cold plate temp. :eek:

Gary
30-06-2003, 07:57 PM
I know just what you mean, Herefishy. It would be very easy to jump ahead and throw in a lot of things that we can see coming. But Tom is new to this and we need to do it a step at a time, in a logical sequence.

Tom Richardson
01-07-2003, 12:14 AM
Note: In order to work correctly, we have to hold the frost top to 20°F. to 25°F., mistake on my part.
NEW BUG:
Changed the EPR to common suction. Everything worked fine for 3 hours, held temps, everything 'appeared' fine.
Then we opened the unit to check for ice. one of the 4 fans had quit working - there was ICE. We repaired the fan & decided to turn the fan speed up to 70% to defrost the coil faster. Wo and behold, I could never get the suction pressure below 65psi, and the frost top begain thawing. Turned the fans back to their 60% and the pressure started comming down! WHAT HAPPENDED??
WHAT TO DO NOW?
HELP!
Tom

Gary
01-07-2003, 03:10 AM
Leave the fans at 60%.

Does the frost top temperature get to where you want it now?

What was the EPR setting when everything was working fine and the frost top temperature was where you wanted it?

condenseddave
01-07-2003, 06:24 AM
Originally posted by Tom Richardson
Mr Condenseddave,
Where have you seen a unit like I have described?
Who makes it?
What is a better way?
-----------------------------


Convenience stores up and down the East Coast have units similar to this to use as prep tables for sandwich sales. One chain that comes to mind is WaWa food stores in the Northeast. I believe that Randall manufacturing is one, and another name that escapes me. (The one that I cannot remember the manufacturers' name bears the model number of simply "wawa", which indicates that they are most definitely custom units.)

I may be wrong, but I believe Hussmann made these for a period, also, possibly in Brantford or Gloversville? Dan?

Gary
01-07-2003, 06:32 AM
What are the following?

Evap air in:
Evap air out:
Pressure:
Suction line temp @ coil outlet (near TXV bulb):

Frost top temp:
Pressure:
Suction line temp @ coil outlet (near TXV bulb):

Low side pressure @ compressor:
Suction line temp @ compressor:

Cond air in temp:
Cond air out temp:
High side pressure:
Liquid line temp @ cond outlet:

condenseddave
01-07-2003, 06:32 AM
Oh, yeah, no "Mr.", just Dave is fine. I'm not even related to anyone living who is a "Mr.":D

I'll call a friend int he morning who still services wawa to see if he can remember the mfg, or look at one in the next few days.

They're using 22, with an EPR on the blower coil, and a pressure control to cycle the compressor. The "Ice Rail", as I've always been led to call them, run in the neighborhood of +10 degrees F.

The name "Bloomington" rings a bell.

herefishy
01-07-2003, 02:52 PM
Tom Richardson, I am interested in the superheat conditions relating to the coil icing. Instead of using temperature/pressure superhaet reading method, apply a temp sensor at the TEV outlet, and another at the evap coil outlet (line temp before and after evaporator coil). What is the difference in temperature in and out.

If your icing condition is not smooth and even (like you would want to skat on it), you are not properly feeding your coil.

Do you still have the cold control at the improper cut-in setting of 34F ?

Gary
01-07-2003, 03:50 PM
Now that the EPR is in the common suction line and controlling the frost top temperature, there should be a lot less confusion. Being controlled by the EPR, the frost top is no longer a problem area, we know exactly what the low end SST is for both coils, and the EPR compensates for the oversized compressor so we can set that issue aside for the moment.

We can now focus on the air coil without all of the side issues to confuse things.

As soon as we get a full set of pressure and temperature readings from Tom, we will know exactly where we stand and what we need to do next.

herefishy
12-07-2003, 01:32 AM
Gee willickers.... :p

We haven't heard from Tom Richardson in awhile...

Did we scare him off ?


:confused:

Dan
12-07-2003, 01:59 AM
Good question. I sent him an e-mail a few weeks ago offering to stop by and take a look at his prototype because I was scheduled to be in town this week. He never replied. Maybe his bosses didn't like the idea. The offer is still open, Tom. Apparently I am permitted to remain at home for another week.

Gary
18-08-2003, 09:26 AM
Apparently Mr. Richardson either figured it all out or gave up on us. :(

It's a shame. We were just starting to get somewhere. With the EPR controlling the frost top, we could tell what SST is needed. With the fan speed control at 60%, we can see that the evaporator is oversized. Once we get that sorted out, we can tell by the pressure entering the compressor exactly what size compressor is needed.

condenseddave
18-08-2003, 04:12 PM
Maybe they didn't realize that this had been done already.

He seemed sort of surprised that this was not an original idea...