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subzero*psia
30-03-2001, 07:19 PM
What valve would this be... it was found on a unit used to quick-chill chocolate in a cooling tunnel. There has been some discussion on it, it was found in the suction line between the compressor inlet and the evaporator outlet. The valve was fed directly off the liquid line and when open it apparently fed the liquid straight into the suction line. Everyone is of the opinion that it was to desuperheat the suction gas possibly but the operation of the valve "ORO" was the confusing part along with its application. Ever heard of it??

Dan
31-03-2001, 03:09 AM
I worry that I am not navigating this site well, or wonder if this is a new question to an old post?

I don't know of any valve that opens on rise of outlet.

Dan

Gary
17-04-2001, 01:05 AM
Chocolate tunnels are a special case. The faster it chills, the shinier the chocolate. The shinier the chocolate, the better it sells (strange, but true). The better it sells, the friendlier your customer is.

Since high superheat is generally associated with low pressure, ORO would seem odd (unless we are talking about outlet temperature rise).

Where was the valve in relation to the TXV sensing bulb? Upstream or downstream?

Gary


[Edited by Gary on 17-04-2001 at 01:30 AM]

subzero*psia
17-04-2001, 01:35 AM
Well, it was used on a cooling tunnel for chocolate. It was a post on one of fridgetechs pages... different site. Anyway a few of us were trying to figure out what the valve may have originally been.

It was being used to desuperheat the suction gas was the general consensus. It was fed directly off the liquid line and into the suction line after the evaporator and before the compressor.

Mike Hopkins
07-11-2001, 01:34 AM
Subzero,
Bit late here, but was browsing the posts and found this one.
I had brought that subject up in Fridgetech. That was a custom built unit, and as I found out was using a type of valve in a rather unorthodox application. The valve is normally used as an expansion valve. Parker states when used as the liquid metering device it regulates the rate of liquid flow to the evaporator at a constant outlet pressure, exactly matching the compressor's capacity. Seems to me it limits the load on the compressor to keep from overloading. However, the intent of the designers of this particular system was to provide suction gas cooling to the compressor. They failed to consider how the valve would react in it's intended application though. A constant pressure valve will actually close on rise of outlet pressure. Thus the designation of a pressure limiting valve. My original thoughts on this valve were wrong and I admit it. Apologies to all who may have been misled.
But hey don't we all learn something at least everyday? The designers would have done better to install a thermostatic valve with a solenoid controlled by a sensor in the suction line.
The little unit is still running though and does it's load with no complaints. Once again, sorry for the confusion there Subzero.

Mike Hopkins

subzero*psia
07-11-2001, 11:11 PM
Maximum Operating Pressure type valve... sounds like an automatic expansion valve.

Thanks for clearing that up... it was buggering me with the ORO description!




;)

herefishy
15-02-2002, 03:16 PM
Parker? My guess is it a constant pressure expansion valve Type "A", maybe? If we're looking at the valve, I'm sure we could find out.

It's application? Humidity is a very bad thing for chocolate. Typically design T.D.'s are high to produce low humidities in the refrigerating air that contacts the chocolate. My guess is the valve serves to "unload" the system, as stated previously, and prevent the system from cycling off in order to maintain constant evaporator temperature under low load conditions and eliminate swings in dew point during the curing process.

However, just utilizing the constant pressure valve as the "only" refrigerant control could possibly affect evaporator NRE under high load conditions, perhaps?

I'd sure like to have Prof. Sporlan's input on the subject.

Andy
15-02-2002, 08:29 PM
Hi, I think the idea of the valve is to simply de-superheat the suction vapour before entering the compressor, remember to have chocolate fluid it's temperature is quite high, this will lead to very high suction superheats. I have seen a few variations of system using this type of aditional suction cooling, for products from butter to gravy for pet food. Some systems even include a vessel like an intercooler on the suction line fitted prior to an evaporator pressure regulator, holding the evaporator pressure higher than the main suction line. The EPR is there to maintain a constant evaporation and also to intoduce a pressure drop in the suction line to create flow out off the cooling vessel for both refrigerant and oil. Oh and mostly the expansion valve used on this aplication is controlling the liquid level in the vessel. A heater is attached to the phail of the expansion valve, no liquid and the phail is heated opening, liquid present and the heat is not dissipate and the valve remains shut. (Sporlan level master)
Regards. Andy.

Mike Hopkins
16-02-2002, 12:41 AM
This system was on a small cooling tunnel, maybe 14" X 14" and 6 feet long. Standard air cooled condensing unit mounted underneath running R-12, since converted to an alternate. Evaporator was fed by standard TXV, no hot gas, no defrost. The suction line where it left the box had a tee in it and was connected to the outlet of the constant pressure valve (Parker). I believe it was an A-4 valve. Liquid line coming up from condensing unit on it's way to TXV had a tee also and was connected to the inlet of the constant pressure valve but also had a hand valve inline to regulate flow to the constant pressure valve. Control was simple on\off thermostat in return air path of evaporator. Definitely the designer's intent was for it to be used for de-superheating of the compressor return gas. But I really saw no use for it as the condensing unit handled the "load" quite well and superheats never rose much above 14* F. It may have been
over kill on the designers part or that the unit was at one time exposed to conditions requiring de-superheating. The valve being used in this application simply maintains an outlet pressure equal to whatever you set it for, we have used the same valve to maintain 45-50 psig suction pressure, it won't go above that but may go below if there was say a feed problem, very similar to a crankcase pressure reugulator but before the evaporator instead of after it. Now, not related to this valve we are speaking of but who was it that said they never heard of a valve that opens on rise of outlet? Check Sporlan bulletin 90-30 and read about the OROA head pressure control valve. Opens on rise of outlet. Never say never.

Mike Hopkins

Mike Hopkins
16-02-2002, 01:09 AM
One other thing in regards to chocolate. The main importance of getting the "hardness" of the chocolate occurs before it enters the cooling tunnel and is called tempering. When you go to make a certain type of candy be it bar or whatever, how hard or soft it will be is entirely dependent upon the temperature you hold it at prior to molding it. 86.0*F and 88.0*F will produce drastic differences in the temper. Once it begins to cool it's all over. Making it colder after the fact or changing the humidity is a mute point. As long as you don't take it above the temperature it was
molded at it will stay where it was. The reason cooling tunnels are used is to at least get the product temperature below what it was molded at before wrapping, etc. Anywhere you see a cooling tunnel for chocolate there will also be a tempering unit holding the chocolate at an exact temperature before gets to the cooling tunnel. These units are very precise in temperature and will maintain within a tenth of a degree if they are worth their salt and the product is to be consistent. Humidity comes into play because you want the dewpoint in the manufacturing area much lower than the product. Unless you are dealing with a very delicate process you won't see much humidity control on a tunnel.
The process area yes, it will be humidity and temperature controlled. What it comes down to in this game of the fridge is to know your customers process. If you don't know that then you are lost at the gate and might as well leave. Tweak the fridge all you want but you have to know what they are doing with the product, all else is futile.

Mike Hopkins

Prof Sporlan
16-02-2002, 01:46 AM
Check Sporlan bulletin 90-30 and read about the OROA head pressure control valve. Opens on rise of outlet. Never say never.
That's correct! there is at least one <b>O</b>pen on <b>R</b>ise of <b>O</b>utlet valve on the market. The Sporlan OROA valve is a head pressure control valve that regulates head pressure by backing up liquid in the condenser when ambients drop.

This valve actually senses receiver pressure at its outlet connection. As receiver pressure rises above the the valve's setting, it moves to a more open position, reducing the amount of liquid it has backed up in the condenser, and thus head pressure. Conversely, as receiver pressure falls below the valve's setting, it moves to a more closed position, increasing the amount of liquid it has backed up in the condenser.

An <b>O</b>pen on <b>R</b>ise of <b>O</b>utlet valve is not very common. More common is an <b>O</b>pen on <b>R</b>ise of <b>I</b>nlet valve, e.g., your EPR valve and perhaps the more common way you can do head pressure control valves. And the <b>C</b>lose on <b>R</b>ise of <b>O</b>utlet valve, e.g., your CPR valve. The automatic expansion valve and hot gas bypass valve are also examples of <b>C</b>lose on <b>R</b>ise of <b>O</b>utlet valves.

herefishy
16-02-2002, 05:51 AM
Prof, I am interested in your input, however maybe you did not read the whole thread, Liquid control does not seem applicable to the conditions.

I do not understand why de-superheating would be required if the sytem design/TEV application was correct.

If the TEV is set for proper superheat, and the system is not overloaded or disfunctional, why do you need to de-superheat?

This is a medium temperature application, and it is not like a Low Temp coming out of defrost.

Prof, it has been verified somewhat that this valve may be a Parker "A" constant pressure evaporator regulator ... A-4..... per Mike.

Excuuuuuuussssssse mmmmmeeeee, but curing chocolate at a 90% relative humidity (typ. 10degF T.D.) seems detrimental, regardless (or inconsideration of ), of the atmosphere that it enters and exits into....!!!!

Maybe that's my opinion, but I personally would take it into consideration in system design, Mike. Of course that is neither here nor there in the issue at hand.

Have you determined the design T.D. in the existing system by relating the evaporator capacity to the condenser capacity? I'll bet you that I'm right....furthermore, I bet you that system design is 15degF T.D. min. Furthermore, humidity control in the tunnel is inherent to the evaporating temperature of the evaporator.

Prof Sporlan
16-02-2002, 05:45 PM
Prof, it has been verified somewhat that this valve may be a Parker "A" constant pressure evaporator regulator ... A-4..... per Mike.
If an A4 is the valve in question, it is an automatic (constant pressure) expansion valve, a close on rise of outlet valve.

One could use this valve as a desuperheating valve, though one can easily argue a TEV is better suited for this purpose.

I do not understand why de-superheating would be required if the sytem design/TEV application was correct.
Long suction lines, low temp R-22 applications, a unit employing an EPR which causes the compressor to operate at low suction pressures, or for that matter, any system control scheme which causes the compressor to operate at low suction pressures would be candidates for a desuperheating valve. If this unit employs a despuerheating valve, one can guess the unit does operate at high superheat/low suction pressure at the compressor at least part of the time.

herefishy
19-02-2002, 01:49 AM
Thank you, Prof.

It appears that Subzero is only speaking of some hypothetical scenario that he saw on a web page. But, you have enlightened me to the application of desuperheating applications

The long suction line scenario is particularly interesting.

I am familiar with the Copeland electronic control that I have seen applied in a blood bank freezer condenser utilizing R-22, in which the de-superheating liquid is injected into the crankcase (Copeland Sentry?).

Do people visiting this forumn actually work in the field at all?

Prof.,
However, how well can you do by adjusting the superheat setting of the controlling device (TEV), by monitoring the superheat at the compressor. ..i.e., setting the superheat to within allowable tolerances for the entering gas conditions at the compressor? Could you be affected adversley by changing ambient conditions that the suction line is affected by?

I have taken the action of adjusting the TEV superheat setting to a higher setting due to very short linsets on 10HP low temp applications at the meat plant.

I do have applications for Ice Cream merchandisers that seem to have a higher gas temperature at the compressor than desired, and I'm considering adjusting the TEV according to my readings at the accumulator (approx. 20degF superheat), and doing so regardless of what my evaporator outlet temperature may be (within reason).

What do you think?

Prof Sporlan
19-02-2002, 04:39 AM
However, how well can you do by adjusting the superheat setting of the controlling device (TEV), by monitoring the superheat at the compressor.
It is not good practice to set the TEV by monitoring superheat at the compressor. The problem is the TEV may have to control a very low superheat, or zero superheat for that matter, to obtain the desired superheat at the compressor. The TEV can only control superheat at its sensing bulb location. The TEV must have some reasonable operating superheat for it to control as the TEV, by design, cannot control a zero superheat. In fact, a fixed restriction can be expected to control a zero superheat better than a TEV.

The correct method is to set the TEV to control superheat in the normal range while the system is operating at design conditions. Normal superheats are as follows:

low temp: 4-6F
medium temp: 6-8F
high temp, a/c: 8-12F

If superheats at the compressor are excessive despite the fact that the TEV is controlling proper superheat, then a desuperheating TEV should be used.

If the intent is the increase superheat at the compressor by adjusting the TEV in so that it controls superheat above the normal range, this can be done as long as it is understood the higher superheat control will reduce evaporator capacity.

frank
19-02-2002, 09:47 PM
I've discussed superheat measurments with quite a few "engineers" and there seems to be various interpretations. Can anyone state how superheat should be measured on a system given that there are high, medium and low temp systems?

Prof Sporlan
20-02-2002, 01:16 AM
The preferred method for measuring the superheat that the TEV controls is to take a pressure reading at or near the sensing bulb location.... and accurate gauge is recommended... :) convert this pressure to the saturation temperature of the refrigerant, and subtract this value from a temperature reading taken at the bulb location.... an accurate electronic thermometer is recommended... :)

The aformentioned superheat values can be used if recommended values are not available from the equipment manufacturer.

Gary
20-02-2002, 04:14 AM
I would add that if the TEV is adjusted properly and the compressor inlet superheat is high, the first thing that should be checked is suction line insulation. If the insulation is sufficient, then de-superheating is needed.

Simply stated, superheat is temperature above saturation. Saturation temperature is that converted from pressure using a PT chart, and the difference between the saturation temperature and the temperature at any given point on the suction line is the superheat at that point, i.e. coil outlet superheat, compressor inlet superheat, etc.



low temp: 4-6F
medium temp: 6-8F
high temp, a/c: 8-12F

It cannot be overemphasized that these are the settings AT DESIGN TEMP. If the refrigerated space is warm, a properly adjusted valve will show a higher superheat, and below design temp it will be lower.

The most important thing to remember is to NEVER use your calibrated tongue to measure coil outlet superheat.

frank
20-02-2002, 08:54 PM
Thanks Guys - that concurs with my interpretation but I am astounded by how many different ways I've heard from so called engineers. Any thoughts on measuring superheat at the discharge pipe - just for the record obviously! (my calibrated tongue doesn't read high temps)) :D

william_wye
01-03-2008, 07:07 AM
[QUOTE][/The correct method is to set the TEV to control superheat in the normal range while the system is operating at design conditions. Normal superheats are as follows:

low temp: 4-6F
medium temp: 6-8F
high temp, a/c: 8-12F
]
Why is there a need for different levels of superheats for different applications

william_wye
01-03-2008, 07:13 AM
[QUOTE][/The correct method is to set the TEV to control superheat in the normal range while the system is operating at design conditions. Normal superheats are as follows:

low temp: 4-6F
medium temp: 6-8F
high temp, a/c: 8-12F
]


Why is there a need for different levels of superheats for different applications

william_wye
01-03-2008, 07:16 AM
The correct method is to set the TEV to control superheat in the normal range while the system is operating at design conditions. Normal superheats are as follows:

low temp: 4-6F
medium temp: 6-8F
high temp, a/c: 8-12F



Why is there a need for different levels of superheats for different applications??

william_wye
01-03-2008, 07:18 AM
Finally figured out how to use quotes..lol

nike123
01-03-2008, 11:39 AM
Finally figured out how to use quotes..lol
Now, figure out how to delete your posts, if you want to delete previous wrong ones.:)

nike123
01-03-2008, 11:46 AM
I think, because at lower temperatures lower is density of air and refrigerants, and also ability of evaporator to transfer heat and if this superheat is high, than much of evaporator would be vacant to evaporate refrigerant.