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 ModelAFan 07-16-2013 04:05 AM

Refrigeration Terms - I need help

I'd like to learn more about refrigeration, especially the terms. I want to learn what "superheat" and "subcooling" means. I'd also like to learn how technicians figure superheat and subcooling. Please help and any help is appreciated.

(Also, I don't want to work on my own equipment. I'm just interested in learning refrigeration.)

 raylo32 07-16-2013 05:05 AM

Start by reading something like this. A basic book on thermodynamics is also helpful.

http://www.achrnews.com/articles/the...geration-cycle

 ModelAFan 07-16-2013 05:45 AM

So, here is what basically happens:

At the evaporator coil, the high-pressure liquid (refrigerant) picks up heat then turns into a low-pressure vapor. Then, it is pumped through an accumulator (if the unit has one) and the filter drier by the compressor. Then it is pumped through the condensing coil, where the heat is dispersed, then the vapor turns into a liquid and returns to the evaporator coil via the suction line. The TXV (thermal expansion valve) allows a certain amount of refrigerant into the evaporator coil.

But I always thought that the suction line (the big line) carried the liquid back to the evaporator coil. But then why is the smaller line called the "liquid line?" Also, how does the TXV work? I think that it senses the temperature of the (liquid line?) and when the temperature of the (liquid line?) increases, it increases the flow of refrigerant (allowing more refrigerant into the evaporator coil.)

Sorry, I'm new at this, and I want to learn as much about refrigeration as I can. But, I'm thinking I'm starting to learn something here! :thumbup: But, I still don't understand subcooling.

I think I know what superheat is. It says that it is the amount of heat added to the refrigerant in order to turn it from a liquid to a vapor at the evaporator?

 Marty S. 07-16-2013 06:13 AM

Refrigerant p/t charts show saturation where there's vapor and liquid. Superheated means it's warm enough to be all vapor. subcooled means it's all liquid.

 ModelAFan 07-16-2013 06:18 AM

Quote:
 Originally Posted by Marty S. (Post 1216567) Refrigerant p/t charts show saturation where there's vapor and liquid. Superheated means it's warm enough to be all vapor. subcooled means it's all liquid.
So, superheat means the refrigerant is warm enough to be all vapor. And subcooled is the opposite (means it is cool enough to be all liquid.)

I don't understand it. They have high-pressure vapors and liquids, and low-pressure vapors and liquids.

 raylo32 07-16-2013 07:06 AM

Superheat is the increase in temperature of the vapor above the saturation temperature based on its pressure. Subcooling is the decrease in temperature of the liquid below the saturation temperature based on its pressure. Vaopr in the big line, liquid in the small line... makes sense if you think of mass flow rates and density.

You should just google this stuff and spend some time reading up on it... then come back with practical questions.

 ModelAFan 07-16-2013 10:08 AM

Quote:
 Originally Posted by raylo32 (Post 1216580) You should just google this stuff and spend some time reading up on it... then come back with practical questions.
Thank you. I tried to google subcooling and superheat and did not understand it, that is why I came here.

 HVAC1000 07-16-2013 11:15 AM

Quote:
 Originally Posted by ModelAFan Thank you. I tried to google subcooling and superheat and did not understand it, that is why I came here.
If you want to learn about this stuff it's not all about the refrigeration process you have to understand the electric and the controls side of it too.

 beenthere 07-16-2013 03:41 PM

Quote:
 Originally Posted by ModelAFan (Post 1216618) Thank you. I tried to google subcooling and superheat and did not understand it, that is why I came here.
When a refrigerant is super heated. It is heated/has absorbed enough heat energy no liquid can still exist at the pressure it is contain at.

When a refrigerant is subcooled, heat/heat energy has been removed to the point that no vapor can exist in it at that pressure.

 hvactech126 07-16-2013 05:51 PM

Pay to go to school to learn like most of us did? Or start an apprenticeship to learn the trade on the job or maybe the employer would send you to school.
If you are trying to learn just to do side work or work on your own equipment then go to school.

 FClef 07-17-2013 01:15 AM

Just one simple principle will explain refrigeration work:

Heat always goes to cold. It is a basic physics law and the basis of the fundamental cooling and heating systems everywhere.

How it happens is for another chapter.

But yes, get some schooling and read a lot if you want to learn the trade.

 ChantryOntario 07-17-2013 07:39 AM

Ok, here's the semi-blind leading the blind.:whistling2:

The way I see it, and I'm sure I'll be corrected if I'm wrong, is.....

Mechanical refrigeration as we know it today is largely possible because of the principle stated in Boyle's law.

As the pressure on a liquid increases, it's boiling point increases.

You can't boil water at 212 degrees if it's under pressure. You can superheat water to 500 degrees if it's under enough pressure in a pipe or containment vessel, and it still won't boil, because there's nowhere for it to expand into gas or vapors. If you did that, the water would technically be superheated 288 degrees, or it's heated 288 degrees past it's normal boiling point. The same applies to r-22 or any refrigerant. Refrigerants have vastly lower boiling points than water, which makes them suitable for absorbing more heat under less pressure, then releasing it in good amounts by simply lowering the pressure outside of the area to be cooled..

If we can get a refrigerant to absorb a lot more heat that it normally would, by keeping it in a pressurized system, then we can transfer that superheated refrigerant to another area, lessen the pressure on it, say by allowing it to expand through a txv, and it will boil into gas, and release it's heat, or a lot of the heat anyway.

Remember that boiling, or turning into vapor and gas, releases heat from whatever's boiling. That allows us to release the heat from your fridge interior into another area, say your kitchen, by compressing the refrigerant enough so that it absorbs heat from the interior of the fridge, putting the refrigerant in a superheated condition,then allowing it to boil and release its heat outside the fridge, like from the coils on the back of your fridge. The txv or whatever valve is used on your fridge is the way to control the boiling/expansion of the superheated refrigerant coming from the inside of your fridge.

Air conditioning uses the same principle, but collects the heat in your room, superheating the refrigerant because its in a pressurized line, then moving the refrigerant outside your room and allowing it to naturally expand and release its heat outside.

 hvac benny 07-17-2013 10:11 AM

Quote:
 Originally Posted by ChantryOntario Ok, here's the semi-blind leading the blind.:whistling2: The way I see it, and I'm sure I'll be corrected if I'm wrong, is..... Mechanical refrigeration as we know it today is largely possible because of the principle stated in Boyle's law. As the pressure on a liquid increases, it's boiling point increases. You can't boil water at 212 degrees if it's under pressure. You can superheat water to 500 degrees if it's under enough pressure in a pipe or containment vessel, and it still won't boil, because there's nowhere for it to expand into gas or vapors. If you did that, the water would technically be superheated 288 degrees, or it's heated 288 degrees past it's normal boiling point. The same applies to r-22 or any refrigerant. Refrigerants have vastly lower boiling points than water, which makes them suitable for absorbing more heat under less pressure, then releasing it in good amounts by simply lowering the pressure outside of the area to be cooled.. If we can get a refrigerant to absorb a lot more heat that it normally would, by keeping it in a pressurized system, then we can transfer that superheated refrigerant to another area, lessen the pressure on it, say by allowing it to expand through a txv, and it will boil into gas, and release it's heat, or a lot of the heat anyway. Remember that boiling, or turning into vapor and gas, releases heat from whatever's boiling. That allows us to release the heat from your fridge interior into another area, say your kitchen, by compressing the refrigerant enough so that it absorbs heat from the interior of the fridge, putting the refrigerant in a superheated condition,then allowing it to boil and release its heat outside the fridge, like from the coils on the back of your fridge. The txv or whatever valve is used on your fridge is the way to control the boiling/expansion of the superheated refrigerant coming from the inside of your fridge. Air conditioning uses the same principle, but collects the heat in your room, superheating the refrigerant because its in a pressurized line, then moving the refrigerant outside your room and allowing it to naturally expand and release its heat outside.
Boiling absorbs heat, and superheat applies to gas/vapor.

OP, if you really want to learn, you should look into a basic refrigeration course. Or, if you're interested in mechanical systems altogether, take a first level instrumentation course which will give you a solid foundation of the principles behind mechanical systems.

 beenthere 07-17-2013 03:08 PM

Quote:
 Originally Posted by ChantryOntario (Post 1216990) Ok, here's the semi-blind leading the blind.:whistling2: The way I see it, and I'm sure I'll be corrected if I'm wrong, is..... Mechanical refrigeration as we know it today is largely possible because of the principle stated in Boyle's law. As the pressure on a liquid increases, it's boiling point increases. You can't boil water at 212 degrees if it's under pressure. You can superheat water to 500 degrees if it's under enough pressure in a pipe or containment vessel, and it still won't boil, because there's nowhere for it to expand into gas or vapors. If you did that, the water would technically be superheated 288 degrees, or it's heated 288 degrees past it's normal boiling point. The same applies to r-22 or any refrigerant. Refrigerants have vastly lower boiling points than water, which makes them suitable for absorbing more heat under less pressure, then releasing it in good amounts by simply lowering the pressure outside of the area to be cooled.. If we can get a refrigerant to absorb a lot more heat that it normally would, by keeping it in a pressurized system, then we can transfer that superheated refrigerant to another area, lessen the pressure on it, say by allowing it to expand through a txv, and it will boil into gas, and release it's heat, or a lot of the heat anyway. Remember that boiling, or turning into vapor and gas, releases heat from whatever's boiling. That allows us to release the heat from your fridge interior into another area, say your kitchen, by compressing the refrigerant enough so that it absorbs heat from the interior of the fridge, putting the refrigerant in a superheated condition,then allowing it to boil and release its heat outside the fridge, like from the coils on the back of your fridge. The txv or whatever valve is used on your fridge is the way to control the boiling/expansion of the superheated refrigerant coming from the inside of your fridge. Air conditioning uses the same principle, but collects the heat in your room, superheating the refrigerant because its in a pressurized line, then moving the refrigerant outside your room and allowing it to naturally expand and release its heat outside.

Don't take this wrong. But please don't try to explain the refrigeration cycle again, until you actually learn it.

 yuri 07-17-2013 05:00 PM

If you really want to learn about refrigeration go to the library and get a book/textbook "Fundamentals of Refrigeration". You also need to understand basic thermodynamics and psychrometric properties of air. Also need to know some of the basic gas laws like Boyles and Charles laws. Put that together and you get an idea what the Pros went thru.

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