Refrigeration 101

[chillerman2006]

Off topic - needed removing

[chillyblue]

TEV adjustment is chicken & egg.

Do you open the tev to get the duty from the evap to get the room temp or do you wait for the room temp to come down before opening it (which may never happen).

If the superheat is high and the room temp is high! where do you start??

CB

[Gary]

TEV adjustment is chicken & egg.

Do you open the tev to get the duty from the evap to get the room temp or do you wait for the room temp to come down before opening it (which may never happen).

If the superheat is high and the room temp is high! where do you start??

CB

You start by leaving the TXV adjustment alone. Don't even think about it. Adjusting a TXV is almost always a mistake. They do not get out of adjustment... unless somebody screws with them.

If the room temp is high, the superheat is supposed to be high. That's how a TXV works. If the room temp doesn't come down, then something else is wrong.

TXV's should be non-adjustable.

[chillyblue]

If the room temp is high, the superheat is supposed to be high. That's how a TXV works. If the room temp doesn't come down, then something else is wrong.

How high is high, 8, 10 ,20, 30, 50???????????
and if it is high what indication can you get from the evap that it is performing correctly,
Some rooms i've worked on can take hrs to pull down, there must be some indication via evap td or air dt that indicates correct operation.
Mistakenly so i've always gone by evap superheat, and now i'm trying to correct myself and an understanding of why is always helpful.

Thanks CB

[Gary]

How high is high, 8, 10 ,20, 30, 50???????????
and if it is high what indication can you get from the evap that it is performing correctly,
Some rooms i've worked on can take hrs to pull down, there must be some indication via evap td or air dt that indicates correct operation.
Mistakenly so i've always gone by evap superheat, and now i'm trying to correct myself and an understanding of why is always helpful.

Thanks CB

Let's say you have a room that is very warm. You increase the orifice size and you turn the adjustment screw out until you have what you believe to be the right superheat at the bulb. You have matched the refrigerant flow to the heat load.

You are currently overloading the compressor and condenser by absorbing a very heavy heat load in the evaporator. But if the compressor can handle the overload, the room temp will drop quickly, leading you to believe that you have done the right thing.

As the room comes down to its design temperature the TXV starts hunting (oversized orifice) and flooding (incorrect TXV adjustment). Why? Because the heat load is now insufficient to boil off the excessive flow of liquid refrigerant through the TXV.

If you have already left the job site, you may not even be aware that the system is hunting, flooding, flushing the oil out of the compressor and potentially going into self-destruct.

[Gary]

How high is high, 8, 10 ,20, 30, 50???????????
and if it is high what indication can you get from the evap that it is performing correctly,

Your indication comes from the condenser. Given a normal load, and assuming good condenser airflow, the SCT should be 20-35F/11-19K above the ambient (condenser air in) temperature (20-35F/11-19K cond TD), depending upon the relative coil sizing. If the heat load being rejected by the condenser is normal, then the heat load being absorbed by the evaporator must also be normal.

[chillyblue]

Your indication comes from the condenser. Given a normal load, and assuming good condenser airflow, the SCT should be 20-35F/11-19K above the ambient (condenser air in) temperature, depending upon the relative coil sizing. If the heat load being rejected by the condenser is normal, then the heat load being absorbed by the evaporator must also be normal.

Thanks Gary, thats great help thanks.
could you confirm what happens if you have a high load and a low load??
I'm assuming with a high load the SCT will reduce below 11-19K above air on to condenser and with a low load the SCT will increase to more than 11-19k above air on to cond.
I'm also assuming that under high conditons your subcooling will be less and with low load conditions your subcooling will more

[lowcool]

mate if you fit tev with changeable orifice and open or close it as to what oneself might think it should be.near to required value why not,apart from experience,where is the bible that says every valve matches every coil?

[chillyblue]

mate if you fit tev with changeable orifice and open or close it as to what oneself might think it should be.near to required value why not,apart from experience,where is the bible that says every valve matches every coil?

Thats a great explanation mate!!!!

[luckee]

Very nicely written Gary. Thanks for taking the time to write this thread.

[chillyblue]

Thats right, thanks

I assume that is the same with your evap the
high load big td
low load small td

CB

[Frikkie]

Very helpful and very nicely written. Thank you Gary.

[gazsweet]

Excellent, great to read. just need an apprenticeship now. its so hard to find!!!

[keepmecool]

Gary, thanks for directing me to your thread on the basics. It really brings it all together for me in plain simple language. Much appreciated!
Michael

[Gary]

I apologize for the confusion. It seems further clarification is needed here:

Subcooling is the cooling of liquid below saturation. In order for this to occur the liquid must be subjected to a temperature that is below saturation.

In order for the subcooling to be 15F/8.5K the liquid must travel through an area where the temperature is at least 15F/8.5K below the SCT or the desired subcooling cannot be achieved.

If the receiver outlet is directly in the path of the air leaving the condenser, then the surrounding air is not cool enough to sufficiently subcool the liquid.

In this case, the liquid line temperature must be measured further downstream where the surrounding air is cooler.

Similarly, in order to achieve sufficient superheat at the TXV bulb the vapor must travel through an area where the temperature is sufficiently high to cause that superheating. If the suction line is directly in the path of the air leaving the coil, then the surrounding air temperature will not be warm enough to achieve the desired superheat.

Hope this helps end the confusion.

[Fett]

In order for the subcooling to be 15F/8.5K the liquid must travel through an area where the temperature is at least 15F/8.5K below the SCT or the desired subcooling cannot be achieved.

If the receiver outlet is directly in the path of the air leaving the condenser, then the surrounding air is not cool enough to sufficiently subcool the liquid.

In this case, the liquid line temperature must be measured further downstream where the surrounding air is cooler.

Hey Gary,

Would it be incorrect to measure the liquid line temperature a few inches upstream from the TXV/TEV?

It would seem to me that area would be a good spot to measure, but I could be wrong.

[Gary]

Hey Gary,

Would it be incorrect to measure the liquid line temperature a few inches upstream from the TXV/TEV?

It would seem to me that area would be a good spot to measure, but I could be wrong.

No, it would not be incorrect, but it may not tell you what you need to know.

The ideal is to have solid liquid at the TXV inlet, but to not back liquid up into the condenser.

Since there is solid liquid at 10-15F/5.5-8.5K SC, we can tell where along the liquid line there is solid liquid and where there is excess SC.

Excess SC is fine at the TXV inlet, but if there is excess SC at the receiver outlet, then we start backing liquid up into the condenser, which drives up the high side pressure.

Measuring SC at the TXV inlet can tell you if there is sufficient refrigerant to feed the coil, but it doesn't tell you if the system is overcharged. That's why I want to check it closer to the receiver.

[nike123]

Some terminology clarification:
http://sporlan.jandrewschoen.com/Col...erminology.pdf

http://sporlan.jandrewschoen.com/Col...00%20Terms.pdf

[datsmad]

G'Day its my 1st post to this sight , fairly new to the game , i am looking for a table of how many joules of energy each metal will absorb , i'm fairly sure there is something in arac but i can't find it , basicly table should state copper ***Kj per sq meter . Can any one help me
Thanks

[conair chris]

Thanks for such an informative post, I am new to the field and any advice and information is greatly appreciated

[mk98064]

you are an author of tech methods books?

[Toosh]

you are an author of tech methods booh?

I find your remarks rather strange as its your first post

Toosh

[Ration_Tea]

Thanks for the info! I read it three times!

[Gary]

Take note that all useful information about a system comes from subtracting one temperature from another temperature.

I can't think of any single temperature or pressure anywhere on any system that tells me what I need to know about that system.

But given temperatures at various points in the system, we can subtract different combinations of temperatures to figure out exactly what the system is doing or not doing.

[Fett]

Take note that all useful information about a system comes from subtracting one temperature from another temperature.

I can't think of any single temperature or pressure anywhere on any system that tells me what I need to know about that system.

But given temperatures at various points in the system, we can subtract different combinations of temperatures to figure out exactly what the system is doing or not doing.

Just out of curiosity, has any manufacturer ever made a system with sensors in the suction line and liquid line to give you this info.

[Gary]

There has been a big move towards self-diagnostic systems in recent years, but as far as I know they haven't gotten it right yet... apparently their computers haven't learned how to subtract yet.

On the other hand, I am retired now, so maybe things have changed since then.

[Fett]

Hmm it just seems like there is enough technology now that they should be able to at least design a simple system to read subcooling and superheat at a pre-determined point.

But then again they probably don't do this because we still need jobs. hehe

[Gary]

Hmm it just seems like there is enough technology now that they should be able to at least design a simple system to read subcooling and superheat at a pre-determined point.

But then again they probably don't do this because we still need jobs. hehe

So... the options are, the manufacturers do not make systems truly self-diagnostic because:

A. They are concerned about you keeping your job.

B. They don't know how to do it.

I vote for B.

[Fett]

So... the options are, the manufacturers do not make systems truly self-diagnostic because:

A. They are concerned about you keeping your job.

B. They don't know how to do it.

I vote for B.

Well, I think I do... Stick a thermistor in the suction line at a pre-determined spot and one in the liquid line at a pre-determined spot. Then stick a calculator inbetween the two, and WHALA self diagnosing.

Well... not self diagnosing but at least it would tell you the temps and the difference between them.

[moideen]

There has been a big move towards self-diagnostic systems in recent years, but as far as I know they haven't gotten it right yet... apparently their computers haven't learned how to subtract yet.

On the other hand, I am retired now, so maybe things have changed since then.

Hi gary sir
Before 25 years ago self diagnosing systems are in market!! Ex: carrier 30 GT chiller. Now all commercial chiller manufactures are designing self diagnosing based refrigeration fundamentals. Some sample alarms such as- low suction super heat, high saturation suction temperature, low discharge superheat…………….etc.
Your 101 is very useful, thanks a lot

Moideen-dubai

[Gary]

Before 25 years ago self diagnosing systems are in market!! Ex: carrier 30 GT chiller. Now all commercial chiller manufactures are designing self diagnosing based refrigeration fundamentals. Some sample alarms such as- low suction super heat, high saturation suction temperature, low discharge superheat…………….

Something like e.g. - low suction superheat - is a symptom, not a diagnosis. In my opinion, these systems are not self-diagnostic.

When they can say things like - insufficient evap airflow, or liquid restriction, or refrigerant overcharge, or inefficient compressor, etc, etc. etc... then I will be impressed.

[Gary]

Something like e.g. - low suction superheat - is a symptom, not a diagnosis. In my opinion, these systems are not self-diagnostic.

When they can say things like - insufficient evap airflow, or liquid restriction, or refrigerant overcharge, or inefficient compressor, etc, etc. etc... then I will be impressed.

BTW, I know this can be done. I wrote a program to do this back in the 1980's. Nobody was interested.

[nike123]

When they can say things like - insufficient evap airflow, or liquid restriction, or refrigerant overcharge, or inefficient compressor, etc, etc. etc... then I will be impressed.

Something like this:
http://www.ecotechnics.it/en/product...lock-2000.html

[Gary]

Something like this:
http://www.ecotechnics.it/en/product...lock-2000.html

Yep... something like that.

I had a couple diagnostic programs that I marketed on floppy disks back in the early 1990's. One for refrigeration and the other for A/C.

Crude but effective. Programmers would have a good laugh, but it told you what was wrong with the system.

Then they started putting USB connectors on printers and the printer function no longer worked. Started getting complaints that my programs wouldn't print the results, so I discontinued the products. I'm a service tech, not a programmer.

[Windseeker]

There has been a big move towards self-diagnostic systems in recent years

Funny you say that. I'm a sailboat owner. 5 years ago, my refigerator/freezer was not working on my boat. I pulled into a large and respectible marina and asked them if they would take a look at it. Well, they did not have time, but recommeneded that I replace the entire system from and air cooled condensor to a keel (water) cooled condensor. {hmm, a wholesale changeout on a system that is roughly 5 years old.} No, I'll pass. I ended up recharging it and made it work for another couple of seasons anyway. I now own a 30 lb can of 134a, gauges, nitrogen bottle w/ regulator, electronic leak detector and still cannot find the leak! Anyway, it's down to the bathtub pressure test.

Aside from all that good fun, the refigeration concepts have been facinating to me have lead me on a pursuit to make a better refigeration system. As I dig deeper into this topic, I find myself refering back to the Enthapy charts. It seems as though only when you know the exact pressure and temperature do you know the state of the substance.

To Gary's comment, my thought is that even though it is technically feasible to design a system that would diagnose itself, I doubt the Product Management or Marketing Department would allow it due to expense. That is my OPINION. Would you agree? I think we could have the ideal system if we could monitor and control the proper parameters. It is possible, and I just might do it with some help.

[Naeem]

hey,

im pretty new this forum, and i dont know how to create my own thread. anyway...im a student in my final year of my degree in construction project management, and i am doing a dissertation on air conditioning, but i dont know what to talk about. the title will most probs be "Air conditioning and Environmental issues" but i seriously dont know what to talk about, so i would appreciate if you guys could give me some advice, and point me the right direction?

thank you
Naeem

[hd88]

Gary,you are a legend in your own mind. heheh!

[Gary]

Well... that's true enough... lol

The manufacturers don't know how to troubleshoot because that isn't their area of expertise. Their area of expertise is design.

[hd88]

Here is a lesson for you. Commercial refrigeration is a science of vague assumtions, based upon debatable figures, taken from inconclusive experiments, performed with instruments of problematical accuracy by persons of doubtful reliability and questionable mentality !!!!!!!!!!!!!!!!!!!!

[Gary]

Here is a lesson for you. Commercial refrigeration is a science of vague assumtions, based upon debatable figures, taken from inconclusive experiments, performed with instruments of problematical accuracy by persons of doubtful reliability and questionable mentality !!!!!!!!!!!!!!!!!!!!

I won't argue with any of that. I can't speak for others, but my mentality is certainly questionable.

[hd88]

I got that at a week long Manitowoc factory school in Manitowoc, Wisconson, in 1996 and it is so TRUE.

[hd88]

I see you all over this forum, and just wanted to mess with you. no harm intended bro. just from one old tech to another. hd88

[Gary]

I see you all over this forum, and just wanted to mess with you. no harm intended bro. just from one old tech to another. hd88

No offense taken.

[vishal]

Dear Gary sir,
You are really a genius, The way you have explained Refrigeration to newbies, this was very useful as a beginner for me. Thanks a lot.....

[tomlinson3553@h]

Hi Gary, i am currently at college doing my level 2.

Do you know of any books etc that will help me along the way?

many thanks

Colin

[nike123]

Hi Gary, i am currently at college doing my level 2.

Do you know of any books etc that will help me along the way?

many thanks

Colin

I am sure that he knows at least one book!
Check his profile!

[Maximo111]

wow.I been doing trailers for five years. Never had info like this. I can take a compressor out and replace it with a new one, go through all the steps to have a good working reefer unit. I have replaced a condenser and an evaporator, pressure tests and evacuation on these things. But I never, never had it explained like this. Just by what you shared it makes me think like I dont know much about these things. Can I be your son?! Thank you very, very much.

[Sridhar1312]

Respected Gary Sir

Simple and easily understandable. Thanks a lot for enlightening us.
the makes my job simpler to make the architects and other new entrants easily.

Regards Sridhar

[Ivan006]

Thanks Gary. This has been very helpful. I definitely needed it.

[Gary]

Compressor discharge temp is measured on the discharge line about 6 inches from the compressor.

Superheated vapor enters the compressor and is compressed, which adds to its heat content, which in turn gives us higher discharge temp along with the higher pressure.

In general, the higher the compressor inlet superheat, the higher the discharge temp as they go up and down together.

However, if the discharge temp rises without a corresponding rise in inlet superheat, this would indicate a possible problem with the compressor.

So... we might say that the discharge temp, in combination with other indicators, gives us a very general feel for the overall health of the system.

That said, I prefer to look much closer at system performance and do not view discharge temp as an important indicator. I very rarely bother measuring it.