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Thread: frost top construction ???
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26-04-2003, 06:38 PM #1
frost top construction ???
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,
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27-04-2003, 12:12 PM #2
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
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27-04-2003, 04:14 PM #3
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.
Prof Sporlan
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27-04-2003, 05:48 PM #4
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.
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27-04-2003, 08:04 PM #5
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.
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27-04-2003, 08:38 PM #6
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.Last edited by Gary; 27-04-2003 at 08:57 PM.
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27-04-2003, 09:54 PM #7We are using R-404A refrigerant, a 12000 BTU compressor, DanFoss thermostic expansion valves with replaceable orfices, Orit 6 EPR valve.
2. As stated earlier, I am new to this area, totally out of my element, "what is ment by TDs"?
To measure the duty of the frost top you need a Mollier chart.
The compressor and evaporator seem to be mis-matched?Prof Sporlan
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28-04-2003, 02:02 AM #8
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.Last edited by Tom Richardson; 28-04-2003 at 02:06 AM.
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30-04-2003, 02:33 PM #9
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.
If we knew the mass, thickness and surface area of the chill top, we could come close to some kind of load data, also.Last edited by herefishy; 30-04-2003 at 02:49 PM.
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02-05-2003, 11:50 AM #10
frost top
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,
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02-05-2003, 11:52 AM #11
follow-up more pictures
This is the .dwg & .png files for the frost top construction.
Thank You,
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02-05-2003, 02:35 PM #12
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"?
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02-05-2003, 03:08 PM #13
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.Prof Sporlan
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02-05-2003, 03:15 PM #14
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,
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02-05-2003, 03:19 PM #15
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.
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02-05-2003, 05:23 PM #16
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,
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02-05-2003, 06:58 PM #17
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".
________________________________________
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.
Last edited by herefishy; 02-05-2003 at 07:06 PM.
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03-05-2003, 01:44 PM #18
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
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03-05-2003, 07:36 PM #19
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.
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05-05-2003, 02:41 PM #20
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?
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05-05-2003, 08:38 PM #21
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
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06-05-2003, 11:56 AM #22
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.
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06-05-2003, 03:06 PM #23
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.
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?
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07-05-2003, 12:18 AM #24
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.
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07-05-2003, 12:17 PM #25
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,
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07-05-2003, 02:46 PM #26Originally posted by Tom Richardson
The incomming air runs approx. 45 to 48 deg F. The air after the evap. coil is 32 Deg F.
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.Last edited by herefishy; 07-05-2003 at 02:54 PM.
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07-05-2003, 07:35 PM #27
A "dwg" file is an Autocad File
Frank
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07-05-2003, 11:43 PM #28
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.
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06-06-2003, 10:39 AM #29
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
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06-06-2003, 02:22 PM #30
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'
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07-06-2003, 11:09 PM #31
I am glad you paid attention to the airflow. I thought that was the biggie.
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09-06-2003, 12:52 AM #32
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
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21-06-2003, 10:01 AM #33
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
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21-06-2003, 11:37 AM #34
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
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21-06-2003, 03:29 PM #35
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.
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21-06-2003, 05:47 PM #36
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)Last edited by herefishy; 21-06-2003 at 05:52 PM.
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21-06-2003, 08:36 PM #37
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.
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21-06-2003, 08:49 PM #38
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.Last edited by Gary; 21-06-2003 at 09:10 PM.
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21-06-2003, 10:06 PM #39
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.
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21-06-2003, 10:17 PM #40
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.Last edited by Gary; 21-06-2003 at 11:10 PM.
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22-06-2003, 02:48 AM #41
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
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22-06-2003, 03:01 AM #42What's wrong with a MOP valve?
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22-06-2003, 03:03 AM #43
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.
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22-06-2003, 03:15 AM #44As usual, we gather as little information as possible and jump to conclusions.
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.
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22-06-2003, 10:00 AM #45
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
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22-06-2003, 02:55 PM #46MEASUREMENTS:
Now that I have a working model,
what measurements and from where, would be helpful? I have access ports & thermocouples mounted in various places.
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!!!
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22-06-2003, 06:38 PM #47
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 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.
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22-06-2003, 10:49 PM #48They are not supposed to read the same. In fact, those differences are the whole point of the exercise.
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22-06-2003, 11:59 PM #49
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
Last edited by Tom Richardson; 23-06-2003 at 12:04 AM.
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23-06-2003, 12:49 AM #50
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.Last edited by Gary; 23-06-2003 at 01:22 AM.
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