Altitude Attitude Adjustment

Tornado,

Thanks, I needed an intelligent second opinion, even though, it's really a fact. The last guy to confuse this issue is a ' higher up ', so the answer is very important and much appreciated. It's my opinion that many talented techs either took no physics or didn't pay attention. Often, as you say in your second sentence, they confuse the ambient atmosphere with the sealed atmosphere. I've read your stuff before, and I know you know what you're talking about. Thanks again, DRFREON.

Good Answer Tornado!

It is absolutely amazing how many people out there have practical experience with very little theoretical experience.

Perhaps it may help others who are struggling with the theoretical side to visit this site http://fridgetech.com/articles/acrnews/altitude/ and look at an article written by a very clever technician regarding the re-calibration of 'bourdon tube' gauges to compensate for changes in altitude. (There are some pictures to help those who struggle with the written word - evidenced by those who read but didn't understand the OP's question!)

I have come across this problem many times and am perfectly aware that if you want to check the pressure within the system then your manifold gauges must be calibrated (zero'd) accordingly. My experience of this ranges from sea level work on the coast, Johannesburg (on the Highveld) at 1700 mts. to 4000 mts underground (where you are in fact below sea level). Should you not recalibrate the gauges to compensate for the change in altitude you will never succeed in either charging or faultfinding the system correctly.

My suggestion to those in doubt is to redo Refrigeration 101 (maybe more than once so they understand it) and also perhaps have their keyboards and attitudes checked.

Regards, Keith

'Is the Flat Earth Society still in existence???'

Keith, right on target, thank you. I will add the link to my tech files! One I found helpful: http://www.newton.dep.anl.gov/. Thanks again.

Sounds goOd though for making excuses in the case of PresSure gauges, but how about the Temperature? SmelLs vague to me.

GA for this and for the gauge part of your explanation a post or 3 later.

& I've undone the one given for the re-author of the latter.

Just to make clear who had what right from square one, in OP terms.

And that 'one additional point' should be 'additional'.

I can not agreE, a refrigeration system is a hermeticalLy closed system

This means that the presSure outside can not directly interact with the presSuRE inside.

However, The altitude efFEct would only constitute directly to the surounding temperature.

RecalLIng Refrigeration is just the Reverse carnot engine then COP(coefF. of performance) = η-¹ ; η = 1 - Tc/Th then

COP = [1/(1-Tc/Th)]

LoOking above equation, we seE that as Th apProach Tc COP is at optimum.

Since Temperature is directly proportional PresSure (PV=RT) , lower presSURE at higher altitude corResponds a lower surRounding temperature.

Therefore, this asSertion

"At higher altitudes, compensation must be made for a refrigerant system's Pressure/ Temperature relationship." is FALSE because it would evidently make the Refrigeration system performs the betTer!

I'm sorry, but that's totally damn wrong. Go back to class.

While you're at it, fix the shift key on your keyboard. There were gazillions of miscapitalizations in that post.

Proved it then wrong, other than just by saying it. Reality bites, should the refrigerant piping be made expandable and compresSable, I wilL be convinced COMPENsation due to presSure efFECT wilL BE TRUE, but its not the case.

oH, traces of suspicious admin here, are you one of them? ThouGh seEmingly not, but your acting one of tHEm. FreEdom IS mine not yours, I DO the writing how may I may.

Actually, we already have a correct answer and correct explanation as to why from Tornado.

If you feel he's wrong, then it is up to you to write a proof here, not for any of us to prove you are wrong. We have no need or requirement.

We already know who is right and who is wrong, but we will read what you write. But your previous post made very little sense, so we are not expecting much from the next one!!

You can't type either...... Try correcting it before posting.....

Sadly, you cannot be an engineer of any sort...... or you have forgotten the basics over a long period, or you simply cannot explain well.....pick one or all.....

Yah whatever, tornado's got his big brother now, or a girlfriend or a boyfriend whatever. SeE yah somewhere we can have a healthy chitchat!

Oh yeah, ive beEN to debates with lousy physicist before, the one that can not prove me wrong definitely is out of idea. Silent answer means Yes! "damn I failed".

I did not even seE your lousy logic in here.

WelL atleast if you are fair enough and sincere of your corRECtion, you must provide answers Why it is wRONG or erRONEOUS.

Thats away science should be, I believe its you words best describe yourself giving such statement - -Mind loOking yourself in the mirRor and ask "Am i an engineER?"

You are seemingly oblivious to the way things work here.

We have a person (Tornado) that posts a proper logical Engineers assessment of the situation, showing that he has full and correct knowledge of the laws of physics that apply here.

Many (all except you?) agree with him. Myself included.

You don't.

Why should we spend any time completing your poor education? Its not as though you are pleasant & friendly!

If you want to write a calm and collected comment on what you with your own understanding of the laws of physics feel is the correct way that things work, we here are all happy to read and discuss your thoughts, but up to now, what you have written does not make sense.

It is basically badly written with bad grammar and it does not follow the generally known laws of physics which apply here as well as where you live.

You cannot even write and correct your grammar, you still have mixed up large and small characters, totally at random. We have mentioned this before, but you continue to write it like that. Start correcting please before posting, or buy a new keyboard.

So please correct your spelling, grammar and manners and then maybe we will help you further with your physics education.

Furthermore, if you don't calm down and become more mannerly and calm (and learn to write properly), I will simply report you to the people at CR4, and see what they think of you and your posts.....

It may be that you will not be allowed to post here further, though the decision does not lie with me personally in any way......but they don't like bad mannered people. Neither do we......you don't bring anything positive to CR4........please remember that.

Have a good day.

Good call. He may want to start his own engineering site: Noudgethenut79.com!

Clear your thoughts, go back to the OP's question, "Is compensation needed for P/T relationship"

The answer is NO. Have I not answer NO, or TORNADO may be you answer YES

But, unfortunately the topic has been shifted to pressure gauges which is not the main concern on OP question, though relevant but not the key points for that question.

Well, try to examine your post, who first gets offensive?Perhaps you mind your own business and say the facts other than adding up personal favor to somebody who is close to you.

I'm sad though, you presumed to be educated but not doing so, by pointing out fallacy(Education are written in boOks and now in the internet, does not have to be regional or sectorial, even monkey do learn).

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Are gauge sets that the techs use to measure system pressures susceptible to altitude/pressure changes? Typically these gauges are a bellows arrangement that pushes a geared actuator that turns the indicator needle. How much of the reaction is due to the pressure difference inside the bellows vs. ambient OR due to mechanical spring pressure on the bellows?

If it's the former, how much of an error would be caused by a change in altitude and the pressure change due to it?

Absolutely correct; airplanes/jets use absolute correcting gauges. The newest ones do the calculating for them, via GPS. I have heard that absolute gauges for the lab or field are very expensive.

some fools think the refrigerating fluid is evaporating at a lower pressure, but, as someone said, it is a sealed system, and nothing changes.

The lower density of the air at high altitude will reduce any fan or radiator efficiency, and in a vacuum they will only be able to radiate from the high temperature side.

sealed systems lack gauges, and the tech who filled a system would compensate

Thank you! Did you ever notice, people who have 90% of the facts are the most dangerous?

Save time getting out the compensation chart...charge by weight and move on to real problems.

One additional point. If you were standing at sea level and you had a set of refrigeration gauges that were open to atmosphere the gauges would read "zero". In fact they are experiencing 14.7 pounds. As you go up in altitude less pressure is exerted and the needle (assuming its a needle movement) will require adjustment to compensate. So depending on how you read the original question the tech is correct that an adjustment is necessary. But as stated this has nothing to do with the physics going on inside the system. But if a set of gauges were calibrated at sea level (or any significantly lower altitude) and then used at a higher altitude without being adjusted the readings on the system would be false.

GA

thanks :)

I would rather agreE that properties should be compensated at higher altitude for psychometric charts rather than refrigerant system.

Oh, I heard this from someone "Six months ago I could not spelL engineEr, only now I found it is getTing harder than spelLing TECHNICIAN"

2ND LAW OF (NEWTON) MOTION

"For every action, there is always an equal opPosite reaction"

Hi Noudge79,

You appear to be letting your attitude confuse your concept of what is being discussed here!

Please STOP and just consider the original statement and question:

At higher altitudes, compensation must be made for a refrigerant system's Pressure/ Temperature relationship.

Question,

Why, in anyone's (CR 4) opinion, do people think this is true?

Tornado answered by saying that the 'P/T relationship' would not alter because of a difference in altitude but then went on to explain that the pressure gauge being used to measure the system pressure at altitude should be calibrated to compensate for the lower atmospheric pressure.

Exactly what do you see as being incorrect with this answer?

The system pressure would remain the same at all altitudes (you were correct as far as that goes) but unless you calibrate your gauges you are going to be reading a completely different pressure (assuming your gauges have been calibrated for sea level and you are now checking system pressures at say 1500 mts).

If you do not understand this basic use of the test manifold guages then I suggest you seriously look at how a 'Bourdon tube' gauge works before commenting further.

Your posting of a diagram showing a very simple refrigerant circuit was very nice but completely off target - if this was a demonstration of your knowledge regarding the question being asked about altitude adjustment then I can fully understand your problem.

Surprisingly you can spell 'Psycometric Chart' but please bear in mind that this chart is absolutely no use unless the pressure readings you have taken are accurate.

Another question for you - do you find that it helps if you threaten a machine that you are working on or just explain away it's malfunction according to it's sexual orientation??

Regards Keith

PS This posting is available in lower case, upper case or a mixture of both if it helps.

Hope your abilities at 'healthy chit-chat' are better than your refrigeration knowledge.

If you mind, try to again evaluate what you reposted:

At higher altitudes, compensation must be made for a refrigerant system's Pressure/ Temperature relationship.

How do you understand the statement written in bold & italic? Does that mean pressure gauge to you?

Well, english is not my native tongue, we have 100 plus dialect in our country, I speak 4 that includes english, but I am confident with my answer to be sanely right & logical above.

Wrong!!!

Again and again. Ad infinitum.

Noudge, the comment you originated:-

"At higher altitudes, compensation must be made for a refrigerant system's Pressure/ Temperature relationship."

Is not correct. A refrigeration system is a sealed system, it has no gauges on it at all. (although gauges are employed in the initial charging of the system and although these must be properly calibrated for the local pressure, there is only a small pressure variance involved. about 10 psia from sea level to 30,000 feet).

Once a system has been setup it can then be used any where, no matter what the local pressure/altitude, subject to heat dissipation aspects that need bigger fans at higher altitudes on the radiating surfaces.

pressure vs altitude table

I personally have worked on many large systems that have factory installed pressure gauges on them.

yes, large ones will have them, but 99.9% of them do not have them, being home fridges etc.

yah,I even seen that blindfolded aurizon, thats why I didn't mind mentioning.

The pressure gauge topic was actually OT loOking at the main question the OP had. I wonder why this people here give GA where it did not the answer the question.

I'd rather rate that Pressure gauge topic of them as GOTA "Good Off Topic Answer"

And worst is, the OP compromise them, rather than try loOKing at his own question Pressure/Temperature relationship compensation-> VAGUE idea

Perhaps this chart of atmospheric pressure vs altitude will help. Note that Denver has about a three psi ambient difference. http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html If the internal operating pressure of the system is critical, this matters. Just calibrate your gauges for zero at your altitude, or don't calibrate, but compensate with a magic marker. Gauges will read higher pressure than correct at high altitudes, so a little black mark, say 3 psi lower on the gauge will do the job in Denver. Works on tires also. Might matter to a Prius driving over a mountain pass... the engine measures air MASS though.

You did not read my question acurately; it asks, why do techs think the P/T relationship INSIDE A REFRIGERATION SYSTEM needs compensation, at higher altitudes. Your answer references compensation for altitude to the MEASURING device. There is no doubt about that! Many, many techs, engineers and students misread a question; that's why the Multiple Choice Test and the Word Problem were invented. DRFREON

I'm no refrigeration technician, but I thought you used the differential pressure to determine charge, if not using weight. If you are using differential pressure, then altitude will make no difference. Because the change in atmospheric pressure has equal effect on both the suction and the discharge gauges, and you are reading the difference between the two gauges, not the gauges and atmosphere.

DRFREON the pressure in a closed system such as a refrigerantion relates to the external (ambient) pressure. Years ago we built small refrigerant air dryers (5 and 10 SCFM) with minimal compensation devices. When shipped to San Fransisco, city by the bay, the difference in refidgerant pressure/temperature caused these dryers to freeze moisture in the heat exchanger until they blocked flow.

If you are at the beach, sea level, and screw a low pressure guage into a tank or volume and be sure it is sealed tightly. Since there is no pressure in the volume the guage would show 0 (zero) pressure. Go to Denver, Colorado, the mile high city. When the volume with gauge is in normal ambient pressure the gauge will read approximately 2.5 PSIG or equivalent. Roughly 14.7 PSIA inside and 12.2 PSIA at 5,280 foot elevation.

Time to tell those intelligent persons you are sorry for doubting them.

Did you mean Noudge79 and Grand Poobah?

If you were correct, humans could not go to space. It's not the refrigerant pressure that changed. JUST BECAUSE your air dryer froze up, you are ASSUMING it was the refrigerant pressure that changed. Wrong assumption. Plus, you did not state the altitude/ location were the dryer was built! THE AIR is what CHANGED, if it was built at an air pressure significantly different than San Fran.

The reason it could have frozen up can be explained. 1. Metering device that is ambient pressure sensitive. 2. Undercharged or 3. A significant air pressure difference will affect the load on the evaporator, as the air density changes, and a compensation had to be instituted; less density - less load. A great example is obvious in the manual choke adjustments that had to be made, when starting a car engine while cold, circa 1960's and older. In modern engines, this is automatic.

You made a correction in your refrigerant charge to COMPENSATE for that part of the system open to the atmosphere - the air going through an air dryer comes from the atmosphere! That HAS to change at different elevations. (see the cooking instructions on a box of rice, for example). The "high altitude directions" require a longer cooking time because the EXTERNAL air pressure is less, lowering the boiling point, therefore, cooking time must be increased. Because the refrigerant circuit is sealed, neither the boiling point nor the FREEZE POINT will change.

In a closed system, no air can enter, nor can any refrigerant escape (unless there is a leak), therefore (I'm exhausted explaining this, as are others), the atmospheric effect is not related to the refrigerant pressure, period!

DRFREON humans use space suits. The device, expansion valve, that controls the refrigerant pressure changed and changed the pressure. The freon pressure gauges showed that the pressures had changed.

Freon pressure is reduced by adjustable (spring) force plus ambient pressure on the area of a diaphragm that is opposed by the fluid pressure.

Adjusted at sea level (14.7 PSIA ambient) the freon pressure, regulator output, would increase by 8 PSIG at 20,000 Feet where the ambient pressure is approx' 6.7 PSIA.

At risk of confusion, the freon pressure would go down if the same system were lowered under the ocean surface or taken down into a mine below death valley. It is a local external pressure issue.

Complex systems may reduce the freon pressure with greater sophistication but face the same ambient pressure issues.

The solid citizens who said freon systems need consideration for altitude are correct. I give those guys an ATTA BOY!

I believe the expansion valve used is not balanced by atmospheric pressure, or it would change at the barometer moved. I think it is a capillary attached to the high pressure side, after the radiator, and it has a needle valve adjustment in some systems. Most home fridges are on-off compressor electricity controlled.

The change in barometric pressure is slight (+/- 3/4 PSIA) compared to the change of 2.5 PSIA for an altitude change of 5000 feet not to mention outer space. The capillary device works on temperature to help prevent return of liquid freon to the compressor intake by bypassing hot freon. The home fridge has thermostatic control to turn the freon compressor on or off based upon the temperature inside the fridge. I don't believe the freon pressure is controlled electrically.

?? Yes, they control via temperature, on off to the compressor. Often you can hear the residual gas expand through the system after the motor has shut off, as it self limits. If it had a regulator it would control the low-side pressure (regulate it) from the high side pressure. Only when the high side dropped below the set pressure would the low side fall out of regulation as the expansion valve allowed gas to the low side.

I have never seen this on a home fridge, but on a large setup on a reefer ship or large cold warehouse they may have this ability to allow for faster cooling for a large fresh batch to be cooled.

Gentlemen: The "expansion valve" shown on post #3 by Noudge79 is essentially a Regulator. It reduces the liquid freon pressure to allow the change of state back to a vapor through the evaporator and before it gets to the compressor intake. Bad stuff happens if the compressor is slugged with liquid.

The Expansion Valve, Regulator, that controlls the pre-evaporator pressure is influenced by an adjustable force. In small simple refridgerant loops this is merely a screw that compresses or relaxes a spring forcing on a diaphram to change the pressure setting. IN ADDITION to the spring force the diaphragm is exposed to AMBIENT pressure. Subsequently at higher altitudes the freon pressure exiting the Expansion Valve will be higher. As stated in my post #40 we have had personal experience with the freon/altitude issue.

Energy expended being nasty does not contribute to the answer.