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Gary
05-07-2009, 05:21 PM
I was thinking it might be a good idea to set up a basic thread to send the newbies to:

Refrigeration 101:

Let's start from the beginning:

Wet your finger and wave it in the air. What you are feeling is a refrigeration effect. When a liquid turns to a vapor it absorbs heat. In this case it is sucking the heat out of your finger.

The opposite is also true. If that vapor then loses that heat, it will turn back into a liquid.

In a refrigeration system, we force a liquid to become a vapor in the evaporator, thus absorbing heat from the refrigerated space.

We then use a compressor to pump that vapor to the condenser.

In the condenser we force that vapor to reject the heat and thus turn back into a liquid so that we can re-use it.

We then meter the liquid back into the evaporator to complete the loop and do it all over again and again and again.

How do we force a liquid to become a vapor?... or a vapor to become a liquid? By manipulating its boiling point.

The boiling point is the temperature at which the liquid turns to vapor when heat is added. It is also the temperature at which a vapor turns to liquid when heat is removed.

Boiling point = saturation temp = evaporating temp = condensing temp

When we think of the boiling point of a liquid it is the boiling point at zero psi pressure. If we increase its pressure we raise its boiling point. If we decrease its pressure we lower its boiling point.

In the evaporator we force liquid to become a vapor by lowering its pressure until its boiling point/evaporating temperature is lower than the air it is trying to cool.

In the condenser we force the vapor to become a liquid by raising its pressure until its boiling point/condensing temperature is higher than the air it is trying to heat.

Different substances have different boiling points at different pressures.

We can tell what the boiling point/saturation temp/evaporating temp/condensing temp is at various pressures for common refrigerants by checking a pressure/temperature chart.

Okay... let's go a step further: Superheat and subcooling.

If we boil off a liquid into vapor and then add heat to that vapor its temperature will rise above the saturation temperature. This is called superheating the vapor. When its temp is 10 degrees above the saturation temperature it is superheated 10 degrees. When its temp is 20 above saturation it has 20 degrees of superheat, etc, etc.

Similarly if we condense a vapor into liquid and then further cool the liquid this is called subcooling. When the temp gets 10 degrees below saturation it has 10 degrees of subcooling. When its temp is 20 degrees below saturation it has 20 degrees of subcooling.

Refrigerant flows very rapidly through the evaporator coil into the suction line. Many people believe that you can't have superheat until the liquid has all turned to vapor, but this is not true. Because of the velocity of the refrigerant flow it is possible to have liquid droplets surrounded by superheated vapor at the outlet of the evaporator... and in fact this is what happens. All of the liquid droplets are gone by the time there is 5-10F/3-5.5K superheat.

We want the superheat at the evaporator outlet to be low enough to ensure that we are fully utilizing the coil, thus maximizing its ability to absorb heat, but we do not want liquid droplets to be sent back to the compressor.

Similarly, it is possible to have vapor bubbles surrounded by subcooled liquid at the outlet of the condenser. All of the vapor bubbles disappear at about 10-15F/5.5-8.5K subcooling.

We want the subcooling to be high enough to ensure that we are sending sufficient liquid to the metering device, but not so high that we are backing up liquid into the condenser, thus reducing its ability to reject heat.

On a cap tube system there is a fixed amount of liquid flowing into the evaporator. When the load is heavy there is warmer air flowing through the coil and thus the liquid is all boiled off long before it reaches the outlet of the coil, thus the superheat is high when the load is heavy. If properly designed and charged, the superheat will be just right when the design temperature (design load) is reached.

Many people believe that a TXV will maintain a fixed superheat, regardless of load. This is just simply not true. When the load is heavy the superheat rises and more liquid is fed to the evaporator. The superheat remains high as long as the load remains high. And again, the superheat is just right when the design temperature (design load) is reached. But the design temp will be reached sooner because of the extra refrigerant feed.

As we see, when the load decreases the superheat decreases... so what happens when the filter gets dirty, or the evap coil... or the blower wheel? Less airflow means less load therefore the superheat drops, even though the refrigerated space may be at design temp.

When the load is high the superheat is high, and when the load is low the superheat is low... even with a TXV.

Everywhere, throughout the system, there are opposing forces balancing against each other, and it can be very difficult to tell which of these forces is out of balance.

And yes, there is more... much much more... but that's enough for now.

Grizzly
05-07-2009, 06:05 PM
Very nicely put Gary.
Should be helpful to anyone who has a grey area!
Very easy to understand terminology as well.
Grizzly

chillyblue
05-07-2009, 06:10 PM
Great one mate.

Just one question.



Many people believe that a TXV will maintain a fixed superheat, regardless of load. This is just simply not true. When the load is heavy the superheat rises and more liquid is fed to the evaporator. The superheat remains high as long as the load remains high. And again, the superheat is just right when the design temperature (design load) is reached. But the design temp will be reached sooner because of the extra refrigerant feed.

As we see, when the load decreases the superheat decreases... so what happens when the filter gets dirty, or the evap coil... or the blower wheel? Less airflow means less load therefore the superheat drops, even though the refrigerated space may be at design temp.

When the load is high the superheat is high, and when the load is low the superheat is low... even with a TXV.

As you say the superheat will be high when the load is high (thats why they say you should only set the valve at design temp).
scenario, Your client is complaining of high room temperatures, So you check everything and you've got good sub-cooling, everythings is running well, but you have high air on temps and high air off temps and your superheat at the evap oulet is also high as you said.
What actions do you take??? or where do you start to confirm that there is not a problem, it's just high superheat due to pull down. I think most engineers would assume the TEV requires opening to reduce the superheat,

Like with the cappillary system, you arrive on site cabinet temps high, suction superheat high what are you checking for to confirm there is not a fault.

I'm sure you'll have the answer for us and i'm sure i missing something totally obvious.

CB

Gary
05-07-2009, 06:27 PM
I first check the delta-T's to confirm adequate airflow through both coils.

Then I check for high subcooling.

Then I check for low superheat.

Then I check for low subcooling.

Then I check the condenser TD to see if the high side is rejecting a heavy heat load.

If the high side is rejecting a heavy load, then the low side must be absorbing a heavy load.

Adjusting a TXV aka TEV is almost always a mistake, especially when the refrigerated space is above design temp.

Gary
05-07-2009, 06:48 PM
Here is a list of the temps/pressures needed to troubleshoot a system:

Evap air in temp
Evap air out temp
Low side pressure or saturation temp
Suction line temp at evap outlet

Cond air in temp
Cond air out temp
High side pressure or saturation temp
Liquid line temp at receiver or condenser outlet

The more information provided the more accurate the diagnosis.

chillyblue
05-07-2009, 07:01 PM
I first check the delta-T's to confirm adequate airflow through both coils.

What would you expect these to be during high loads, do they differ from when the load is low???

Gary
05-07-2009, 07:12 PM
Assuming a fixed speed compressor, only insufficient airflow can raise the delta-T beyond normal limits.

chillyblue
05-07-2009, 07:29 PM
If the superheat is high would the delta-T be much higher than when you have a normal superheat??

Am i correct in saying you should have approx (commercial refrigeration) 3 to 6 Deg C temp difference (air on to air air off)

Would the temp difference (air on to air off) be the same regardless of the high or correct room temp???

I.e design room temp 0 deg C
will the air on-off temp still be 3- 6 deg C difference when the room temp is 20 deg C
And will it still be 3-6 deg C when the room is at 1 deg C

CB

Gary
05-07-2009, 07:37 PM
Delta=T upper limit differs for various types of systems as well as for different design temperature and humidity requirements. And this goes beyond the scope of "Refrigeration 101".

Suffice it to say that if you are familiar with the delta-T limit for a particular type of system, anything above this limit is an unambiguous indicator of an airflow problem.

Excessive delta-T can ONLY be caused by insufficient airflow.

nathan...
06-07-2009, 12:29 AM
hell yeah. this is the good stuff
keep it coming

Magoo
06-07-2009, 05:28 AM
Hi Gary
A good post, should benefit alot of people.
I have this " pet " thing, that a large percentage of service tech's do no understand TEV superheat, let alone how to test and adjust. But then again I am old.
I have a fail proof test procedure that I stated years ago on this site, only works if designer was worth his salt.
Do you have a similar procedure.
What I use is good for pull-down performance or at design, but takes time.
magoo

desA
07-07-2009, 08:12 PM
Thanks Gary - excellent stuff. :)

I'd appreciate if you could touch on refrigerant charge determination, at some point in the thread.

Gary
11-07-2009, 05:47 PM
Thanks Gary - excellent stuff. :)

I'd appreciate if you could touch on refrigerant charge determination, at some point in the thread.

Think of the system charge as consisting of low side charge and high side charge.

Assuming there is proper airflow through both coils (and that everything else is functioning normally):

On the low side, at design refrigerated space temp, if the coil outlet superheat is right, then the low side charge is right.

Coil outlet superheat varies with type of system. Generally speaking, a freezer should have 6-8F/3.5-4.5K superheat, a cooler should have 8-10F/4.5-5.5K superheat, and an A/C should have 12-16F/6.5-9K superheat.

On the high side the subcooling should be no more than 15F/8.5K because this is the point at which liquid will start to back up into the condenser.

On a cap tube/fixed orifice system, if the superheat is right (at design space temp) and the subcooling is not more than 15F/8.5K then the system has the right charge.

Note that minimum subcooling is not a factor on cap tube/fixed orifice systems. They are critically charged.

On a TXV system there is a minimum and maximum charge. When the superheat is right (at design space temp) and the subcooling is not more than 15F/8.5K then there is enough refrigerant in the system to do the job. This is the minimum charge.

Additional refrigerant can then be added to bring the subcooling up to 15F/8.5K. This is the maximum charge.

It is good practice to bring the charge up to maximum because vapor bubbles flowing through the TXV will wear out the needle and seat. This also provides additional refrigerant for heavy loads.

Gary
11-07-2009, 06:14 PM
OR

You can weigh in the charge as marked on the nameplate.

The manufacturer has done all of the work for you, setting up the system under tightly controlled conditions, determining the right charge, and then pulling all of the refrigerant out, weighing it and marking that weight on the nameplate.

desA
12-07-2009, 08:30 AM
Thanks so much, Gary.


Coil outlet superheat varies with type of system. Generally speaking, a freezer should have 6-8F/3.5-4.5K superheat, a cooler should have 8-10F/4.5-5.5K superheat, and an A/C should have 12-16F/6.5-9K superheat.

What figures for evap outlet superheat & condenser sub-cooling should be used for an air-to-water heat-pump?

At what operating temperature would the refrigerant mass charge determination be most appropriate - startup Tc,sat 35'C; or hot end Tc,sat 70'C?

I have no given mass charge to work off in this case & have to determine it in-house.

Gary
12-07-2009, 03:32 PM
Thanks so much, Gary.



What figures for evap outlet superheat & condenser sub-cooling should be used for an air-to-water heat-pump?

At what operating temperature would the refrigerant mass charge determination be most appropriate - startup Tc,sat 35'C; or hot end Tc,sat 70'C?

I have no given mass charge to work off in this case & have to determine it in-house.

You should start a new thread for this, as it is specific to your particular system.

philfridge
12-07-2009, 07:04 PM
Seems like Gary knows his stuff on paper but anygood in the field ?

Karl Hofmann
12-07-2009, 07:20 PM
Seems like Gary knows his stuff on paper but anygood in the field ?

Of course he's not.... He aint REFCON certified..;););)

Gary
12-07-2009, 07:27 PM
Worse yet... I'm retired.

... after 40 years in the field.

nike123
12-07-2009, 09:01 PM
Seems like Gary knows his stuff on paper but anygood in the field ?




Always hold your head up, but be careful to keep your nose at a friendly level.

Always keep your words soft and sweet, just in case you have to eat them.


.........................

waisk
15-07-2009, 11:18 AM
In the condenser we force the vapor to become a liquid by raising its pressure until its boiling point/condensing temperature is higher than the air it is trying to heat.


Hi, Gary, I am new here and as well new to refrigeration. I have a couple of question about the condenser. Because as I know, the refrigerant pump out from the compressor is in high pressure, then I am confuse after I read through your article. As you said, "need to raise its pressure in condenser until its boiling point temperature is higher than the air"... what exactly is this mean and how to do that actually?

Ps*I am a student which involves in a project which needed to build a refrigeration system, and the part that I am responsible to, is design an air cooled condenser which do not have a fan to cool it, because the system is an outdoor unit, so we plan to use natural wind to cool it, and I do not have any clue on how to start.. can you guide me?

Gary
15-07-2009, 05:34 PM
Hi, Gary, I am new here and as well new to refrigeration. I have a couple of question about the condenser. Because as I know, the refrigerant pump out from the compressor is in high pressure, then I am confuse after I read through your article. As you said, "need to raise its pressure in condenser until its boiling point temperature is higher than the air"... what exactly is this mean and how to do that actually?

The compressor raises the pressure and this raises the boiling point/condensing temperature.

Gary
15-07-2009, 05:37 PM
Ps*I am a student which involves in a project which needed to build a refrigeration system, and the part that I am responsible to, is design an air cooled condenser which do not have a fan to cool it, because the system is an outdoor unit, so we plan to use natural wind to cool it, and I do not have any clue on how to start.. can you guide me?

This is beyond the scope of "Refrigeration 101" so you should start a new thread for your project.

Design is not my forte, but you will find there are others on this forum more qualified than I to guide you.

gwynn jones
15-07-2009, 06:14 PM
SNIP............Adjusting a TXV aka TEV is almost always a mistake, especially when the refrigerated space is above design temp.

Oh I very much agree -I work with a few lads who will fiddle with the TEV every call - makes even more trouble

gwm121
17-07-2009, 11:50 AM
very nocely written. Where can we find a book written like this for a guy with experience ONLY on small splits who neds to raise knowledge to pass the 2079 test...?? Oh im confused by the sample question raie evap temp 1 degree and achieve eff increase 3 degres... why not 2 degres, 3 degres 4 degrees....

Josip
17-07-2009, 12:08 PM
Hi, gwm121 :)


very nocely written. Where can we find a book written like this for a guy with experience ONLY on small splits who neds to raise knowledge to pass the 2079 test...?? Oh im confused by the sample question raie evap temp 1 degree and achieve eff increase 3 degres... why not 2 degres, 3 degres 4 degrees....


.... they want to show how much you can save changing evaporator temp for 1 degree only ...



Yes, you are right, Gary is making those things very simple in the best possible way ... regarding a good book refer to Gary;)

Best regards, Josip :)

chillyblue
27-07-2009, 05:13 PM
I first check the delta-T's to confirm adequate airflow through both coils.

Then I check for high subcooling.

Then I check for low superheat.

Then I check for low subcooling.

Then I check the condenser TD to see if the high side is rejecting a heavy heat load.

If the high side is rejecting a heavy load, then the low side must be absorbing a heavy load.

Adjusting a TXV aka TEV is almost always a mistake, especially when the refrigerated space is above design temp.

What would be high and low???????

chillyblue
27-07-2009, 05:21 PM
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

superswill
27-07-2009, 05:42 PM
very nocely written. Where can we find a book written like this for a guy with experience ONLY on small splits who neds to raise knowledge to pass the 2079 test...?? Oh im confused by the sample question raie evap temp 1 degree and achieve eff increase 3 degres... why not 2 degres, 3 degres 4 degrees....

try

http://techmethod.com/

a link to gary's web site

Gary
28-07-2009, 08:06 AM
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
28-07-2009, 09:48 AM
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

lowcool
28-07-2009, 01:12 PM
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?

luckee
28-07-2009, 01:51 PM
Very nicely written Gary. Thanks for taking the time to write this thread.

chillyblue
28-07-2009, 05:35 PM
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!!!!

Gary
28-07-2009, 06:24 PM
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
28-07-2009, 06:52 PM
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
28-07-2009, 07:36 PM
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

Gary
28-07-2009, 07:42 PM
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.


Just the opposite. High load increases SCT and low load decreases SCT... and SCT above ambient (cond TD) should remain within the 11-19K range.

Gary
28-07-2009, 07:46 PM
I'm also assuming that under high conditons your subcooling will be less and with low load conditions your subcooling will more

There will be relatively little change in subcooling as the liquid line temp will tend to rise and fall with the SCT and a TXV system stores sufficient surplus liquid refrigerant to compensate for variations in load without substantial changes in subcooling.

chillyblue
28-07-2009, 09:17 PM
Just the opposite. High load increases SCT and low load decreases SCT... and SCT above ambient (cond TD) should remain within the 11-19K range.

If the ambient air onto the condenser remains the same and the sct decreases with low load then the cond td must get bigger.
If the ambient air onto the condenser remains the same and the sct increases with high load then the cond td must get smaller.

do you mean that with a high load the cond td would be around 11k (smaller) and low load would be around 19k (larger)

CB

Gary
28-07-2009, 09:27 PM
If the ambient air onto the condenser remains the same and the sct decreases with low load then the cond td must get bigger.
If the ambient air onto the condenser remains the same and the sct increases with high load then the cond td must get smaller.

do you mean that with a high load the cond td would be around 11k (smaller) and low load would be around 19k (larger)

CB

No... No... and No.

Let's say the ambient is 25C and the SCT is 36C. The TD is 36-25=11K.

The SCT then rises to 40C. The TD is 40-25=15K .

chillyblue
29-07-2009, 07:01 AM
Thats right, thanks

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

CB

Gary
30-07-2009, 04:34 PM
Oh I very much agree -I work with a few lads who will fiddle with the TEV every call - makes even more trouble

In another thread Magoo has offered a rule for judging TXV superheat. He says the superheat should be 60-70% of the TD. This makes very good sense. I like it... a lot. :D:

Frikkie
01-08-2009, 10:27 PM
Very helpful and very nicely written. Thank you Gary.

gazsweet
10-08-2009, 04:37 PM
Excellent, great to read. just need an apprenticeship now. its so hard to find!!!:rolleyes:

Rich1281
12-08-2009, 04:40 AM
Hi Gary, it’s been a long time since we had lunch in Michigan at Bob Evans :-) Hope you have been well.
Quote:
Originally Posted by Gary


Coil outlet superheat varies with type of system. Generally speaking, a freezer should have 6-8F/3.5-4.5K superheat, a cooler should have 8-10F/4.5-5.5K superheat, and an A/C should have 12-16F/6.5-9K superheat..

We installed a Russell freezer system last week and I thought of you. They are saying Copeland now wants 30F superheat at the compressor MINIMUM. They don't seem to care about the superheat outlet at the coil. What happened to Copeland’s 12F standard?



On the high side the sub cooling should be no more than 15F/8.5K because this is the point at which liquid will start to back up into the condenser.

I have yet to see a system that can obtain a 15F sub cooling, the most I have seen ever was 10 and the newer systems seem to be around 4f. Is this due to a design issue? I always test a system before leaving to make certain it can pump down under load and not be a problem. Over 10f sub cooling I have yet to see possible. ?????

Also, I'd like to mention to newbie’s that these numbers may not be obtainable on converted systems. On a converted system you may have an overly charged system trying to obtain even small sub cooling temperatures. Also, one must be concerned with pump down capacity where LONG liquid lines are used and the solenoid valve is located inside the condenser. I have one customer with a 7/8 liquid line where the original installer put the solenoid valve at the unit and the line was over 100 actual feet. Needless to say, we moved the solenoid valve to the evaporator and the systems pump down capacity was ample since we didn't have the entire refrigerant in the liquid line pumping into the condenser.




......Additional refrigerant can then be added to bring the sub cooling up to 15F/8.5K. This is the maximum charge.

Is this a new standard? Like I stated, I've seen systems overcharged at 10 Sub Cooling.

Eagerly waiting for your guidance.

Richard

Gary
12-08-2009, 06:34 AM
Hi Gary, it’s been a long time since we had lunch in Michigan at Bob Evans :-) Hope you have been well.

Hi Rich. A very long time. Nice to hear from you again.



We installed a Russell freezer system last week and I thought of you. They are saying Copeland now wants 30F superheat at the compressor MINIMUM. They don't seem to care about the superheat outlet at the coil. What happened to Copeland’s 12F standard?

As far back as I can remember, Copeland has called for a minimum of 20F superheat and a maximum of 30F superheat at the compressor inlet.

Being a compressor manufacturer, their primary concern is the superheat at the compressor inlet rather than the evaporator outlet. No surprise there.


I have yet to see a system that can obtain a 15F sub cooling, the most I have seen ever was 10 and the newer systems seem to be around 4f. Is this due to a design issue? I always test a system before leaving to make certain it can pump down under load and not be a problem. Over 10f sub cooling I have yet to see possible. ?????

Are you measuring subcooling on the liquid line near the receiver?... or on the drip leg between the condenser and the receiver?

keepmecool
14-08-2009, 12:40 PM
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

chillyblue
16-08-2009, 10:55 AM
Are you measuring subcooling on the liquid line near the receiver?... or on the drip leg between the condenser and the receiver?

Does this make a difference?? if so why??



I have yet to see a system that can obtain a 15F sub cooling, the most I have seen ever was 10 and the newer systems seem to be around 4f. Is this due to a design issue? I always test a system before leaving to make certain it can pump down under load and not be a problem. Over 10f sub cooling I have yet to see possible. ??????

I've seen this, but i am very doubtfull how the system will cope when the ambient air into the condenser reaches 32 deg C (design temp) I can see hp switches tripping.

CB

Gary
16-08-2009, 02:56 PM
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.

mk98064
18-08-2009, 06:41 PM
you are an author of tech methods books?

Toosh
18-08-2009, 11:51 PM
you are an author of tech methods booh?

I find your remarks rather strange as its your first post

Toosh

eamonn493
19-08-2009, 07:25 AM
I first check the delta-T's to confirm adequate airflow through both coils.

Then I check for high subcooling.

Then I check for low superheat.

Then I check for low subcooling.

Then I check the condenser TD to see if the high side is rejecting a heavy heat load.

If the high side is rejecting a heavy load, then the low side must be absorbing a heavy load.

Adjusting a TXV aka TEV is almost always a mistake, especially when the refrigerated space is above design temp.
Hi Gary
Brilliant artical !!! Iam new to this A/C but I find it very interesting. One problem I do have is some of the Buss words you experienced engineers use.
eg delta T, TD. pulldown etc could you explain some of the more basic ones for me please. Also we had a leak on a compressed air cooling system last week all the 407 gas had been lost. repaired the leak and recharged every thing ok now,but noticed a bypass valve had been fitted to the system,how do I know if this valve is working?
One last point could I have lost some of the oil from the system,how do I check it.
Regards Eamonn

nike123
19-08-2009, 09:00 AM
Hi Gary
Brilliant artical !!! Iam new to this A/C but I find it very interesting. One problem I do have is some of the Buss words you experienced engineers use.
eg delta T, TD. pulldown etc could you explain some of the more basic ones for me please. Also we had a leak on a compressed air cooling system last week all the 407 gas had been lost. repaired the leak and recharged every thing ok now,but noticed a bypass valve had been fitted to the system,how do I know if this valve is working?
One last point could I have lost some of the oil from the system,how do I check it.
Regards Eamonn

Delta t ( Δt) is difference between two temperatures of same media.
For example, air entering and leaving condenser, or air entering and leaving evaporator, or water entering and leaving condenser, or water entering and leaving evaporator.

TD is difference in temperature of two different media.
For example, difference between saturation evaporation temperature of refrigerant in evaporator and evaporator air entering temperature or difference between condenser air entering temperature and condensation saturation temperature.

http://www.refrigeration-engineer.com/forums/showpost.php?p=92775&postcount=5

Pull down is time period passed from starting equipment to reaching design condition.

For your problem please post question in new thread since that is not refrigeration 101.

Ration_Tea
19-08-2009, 02:45 PM
Thanks for the info! I read it three times!

Fett
20-08-2009, 12:26 AM
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
20-08-2009, 12:42 AM
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
20-08-2009, 10:43 AM
Some terminology clarification:
http://sporlan.jandrewschoen.com/ColdWAR%20January%202006%20Unique%20Terminology.pdf

http://sporlan.jandrewschoen.com/ColdWar%20September%202007%20Cold%20WAR%20The%20First%20100%20Terms.pdf

Gary
20-08-2009, 07:09 PM
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
20-08-2009, 08:06 PM
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
20-08-2009, 08:49 PM
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
20-08-2009, 09:48 PM
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
20-08-2009, 10:11 PM
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.

hd88
20-08-2009, 11:42 PM
Gary,you are a legend in your own mind. heheh!

Gary
20-08-2009, 11:49 PM
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
20-08-2009, 11:55 PM
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 !!!!!!!!!!!!!!!!!!!!

hd88
20-08-2009, 11:58 PM
I got that at a week long Manitowoc factory school in Manitowoc, Wisconson, in 1996 and it is so TRUE.

hd88
21-08-2009, 12:01 AM
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
21-08-2009, 12:09 AM
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.

Gary
21-08-2009, 12:32 AM
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. :)

Fett
22-08-2009, 12:29 AM
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.

Ration_Tea
22-08-2009, 03:10 AM
Seems like Gary knows his stuff on paper but anygood in the field ?

I'm laugh so hard at the Avatar you have. :D

I didn't see that last time.

Fett
10-09-2009, 02:00 AM
Hey Gary,

What are the effects of excessive superheat/subcooling and lack of superheat/subcooling.

Perhaps we can run a few example system diagnoses here.

Example:

Time of Day: Noon
Type of System: Rooftop Packaged
Outside Air Temp: 103F
Indoor Air Temp @ Return:86F
Indoor Air Temp @ Supply:83F
You inspect each section of the system visually.

Indoor Coil is clean and clear of obstruction and the air filter is new and clean.

The Outdoor coil is slightly soiled, but nothing to be seriously concerned about.

Outdoor Fan: Operating
Indoor Fan: Operating
Compressor: Operating


Complaint: The unit is blowing warm air.



This should be a pretty simple one... you don't need superheat or subcooling to figure it out.
Here in Arizona one out of five calls is this problem in my experience.


-Fett

Gary
10-09-2009, 03:02 AM
Hey Gary,

What are the effects of excessive superheat/subcooling and lack of superheat/subcooling.

Perhaps we can run a few example system diagnoses here.

Example:

Time of Day: Noon
Type of System: Rooftop Packaged
Outside Air Temp: 103F
Indoor Air Temp @ Return:86F
Indoor Air Temp @ Supply:83F
You inspect each section of the system visually.

Indoor Coil is clean and clear of obstruction and the air filter is new and clean.

The Outdoor coil is slightly soiled, but nothing to be seriously concerned about.

Outdoor Fan: Operating
Indoor Fan: Operating
Compressor: Operating


Complaint: The unit is blowing warm air.



This should be a pretty simple one... you don't need superheat or subcooling to figure it out.


Yes... you do.

Could be undercharge, could be restriction, could be blown valves in the compressor.

You might think you know what the most likely problem is, but you don't really know what the problem is until you check the subcooling and the superheat.

While you're at it, check to see what type of metering device you have.

Slother
10-09-2009, 11:36 AM
Hi All;
enjoy the site, I'm a sparky working on hot water heat pumps and have a couple of questions regarding fundamentals.

We were called to a fault, the outlet from the TX valve was frosting up. The fridgie explained that the TX valve was the problem.

The unit was working fine, the reported fault (rattly). Both pressures LP and HP were a little low, there was some oil but no leaks could be found. I suggested topping up refrigerant, it was explained that doing this would only put more refrigerant into the TX outlet (and frost it up more).

I have read some posts about checking superheat temp in the fault finding of a TX, not sure how this is done. If someone could give me advice on checks to carry out if TX valve outlet frosts up (including adjustment) I'd appreciate it.

nike123
10-09-2009, 01:14 PM
Hi All;
enjoy the site, I'm a sparky working on hot water heat pumps and have a couple of questions regarding fundamentals.

We were called to a fault, the outlet from the TX valve was frosting up. The fridgie explained that the TX valve was the problem.

Frosting of valve outlet at air-con unit could indicate at problem, but at refrigeration unit that is normal. What is that unit used for?


The unit was working fine, the reported fault (rattly). Both pressures LP and HP were a little low, there was some oil but no leaks could be found.If there is oil, there is leak!
How much low, we need numbers?
We also need temperatures of air in and out of evaporator and condenser to tell if pressure is low or not.
Also we need pipe temperature at evaporator outlet, compressor inlet, condenser outlet.



I suggested topping up refrigerant, it was explained that doing this would only put more refrigerant into the TX outlet (and frost it up more). Topping up refrigerant could be done only after is established that refrigerant missing.That is done by measuring what I said above and judging from acquired measurements.
If measurement say that subcooling is low, than refrigerant is missing in condenser. It could be leak or restriction on low side. If you have oil spots and nobody before is not added refrigerant you are probably short of refrigerant.
If you have sight glass, than you will be having lot of bubbles in glass.


I have read some posts about checking superheat temp in the fault finding of a TX, not sure how this is done. If someone could give me advice on checks to carry out if TX valve outlet frosts up (including adjustment) I'd appreciate it.Please do not touch TXV before we establish that it is cause of trouble, especially, do not adjust it.

Fett
11-09-2009, 08:53 PM
Yes... you do.

Could be undercharge, could be restriction, could be blown valves in the compressor.

You might think you know what the most likely problem is, but you don't really know what the problem is until you check the subcooling and the superheat.

While you're at it, check to see what type of metering device you have.


Aye, you may be right, but for the problem I have suggested it is not necessary.

But say we plug in 18-20F superheat and lets say 3-4F subcooling.

Would you say it is undercharged or just a high heat load on the system?

I think that alot of people overcharge systems before considering other factors. A system at proper charge should have no problem bringing down the temp from 86F to 78 or 80 in an hour to an hour and a half. Think of a company that just installed a brand new unit with new ductwork on a relatively old house (35-40 year old house). So they get done on the install and all the ductwork was run. Maybe two or three weeks goes by and a 2x4 which is part of the roof support breaks away from its mounting and falls on some ductwork tearing a hole in it. So now the unit is sucking in that hot air inside the attic and fails to cool the home. Or maybe the installer stretched the duct too much and didn't fasten it together very well and the joint seperated.

Having that hot air will give you a high superheat, well assuming that its a cap tube system but even a TXV would open up pretty wide to compensate for the added heat load.

ewart
13-09-2009, 09:24 PM
Hey Gary
How would you determine the correct refrigerant charge in a water cooled system when water flow is controlled by a water regulating valve and it depends on head pressure to regulate. Say we are working with R404 and condenser water temp. of 50F?????

nike123
14-09-2009, 08:02 AM
Hey Gary
How would you determine the correct refrigerant charge in a water cooled system when water flow is controlled by a water regulating valve and it depends on head pressure to regulate. Say we are working with R404 and condenser water temp. of 50F?????

If you have regulated condenser water flow than your condenser water out temperature should be at or more than cca 70°F. Why that low? Or you are speaking about water in temperature?

vishal
15-09-2009, 07:56 AM
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
22-09-2009, 11:55 AM
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
22-09-2009, 04:23 PM
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!:D
Check his profile!

Maximo111
25-09-2009, 04:49 AM
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
30-09-2009, 09:07 AM
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
07-10-2009, 08:47 PM
Thanks Gary. This has been very helpful. I definitely needed it.

ianparker0801
14-10-2009, 11:03 AM
Hi, I'm new to all this. have found the forum amazing usefull, having been sent on a couple of basic courses, which mainly teach you all the legislation, then left a static sight with no guidense or help. I have a slight confusion which is probably easy to resolve. After reading the guide to calculating superheat and subcooling (which made alot make sense) I use my companies service sheets to record the information needed, but instead of asking for liquid line temp. and press. they ask for discharge temp, press to be recorded. I would have assumed discharge would suggest after the compressor, are they the same thing or is this more likely because the sheets are incorrect. This probably seems like I'm being pedantic but untill I found this forum it was causing me all kinds of confusion.

Gary
14-10-2009, 08:34 PM
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.

SANJAYKHETRAPAL
15-10-2009, 08:35 AM
now only i become the member & i am so happy to see how Gary has made the refrigeration subject so simple & interesting .I will like to see many more knowledgable issues in future .Once again i appreciate the gary's effort.very well done.
cheers.

ianparker0801
15-10-2009, 09:57 AM
Thanks for you help gary, it all helps when trying to apply the theory to practical application. My next question is about high pressure and low pressure cut outs. How do you go about testing these safety features, on both courses we were told to check these but noone has ever said how.

mad fridgie
15-10-2009, 10:14 AM
Thanks for you help gary, it all helps when trying to apply the theory to practical application. My next question is about high pressure and low pressure cut outs. How do you go about testing these safety features, on both courses we were told to check these but noone has ever said how.
Pressure switches can be tested with a nitrogen via a regulator/gauge, Raise pressure until switch changes. make a note of actual pressure, then slowly release until switch changes back. Adjust until you reach desired set points. "Note" the scale are indicators only, for rough adjustment.
On site, you sort of break a few rules, for HP (discharge) you "slowly" close discharge valve, keeping a very close eye on your gauge. Hp switch will trip (at some set point). (if manual reset then no other settings to check) if auto reset then watch as the pressure drops note switch change, for LP similar process but switch is is opposite direction

goshen
15-10-2009, 05:22 PM
hi garry very nice thread should answer a lot of newbies questions!!!

Gary
15-10-2009, 07:10 PM
Don't forget to click the reputation button. :D

Uni
18-10-2009, 01:12 AM
It's really useful, Garry. After 1 year of self-learning, you give me have a chance to review what I have been done and believe were right or not.

Can you write something about system balancing (using captube) and how to get the max cooling capacity out of the component we have? Or say how to tune a unit?

How the excessive Cond airflow and/or Evap airflow can bring the Capacity down? It looks like I have more SC, lower HP, so I can add more charge to control SH after drawing the Capacity line against charge amount. But it made no sense as I did not get what I had.

Capacity has always been a problem of mine since I started playing :confused:

Thanks, Gary

Gary
18-10-2009, 04:15 AM
Insufficient (not excessive) airflow brings down capacity.

shaafeq
24-10-2009, 06:25 AM
In Freezer with capilary as metering devices, how to determine if the system is overcharged or less charged with a refirgerant? Can we decide this base on the suction line temp., discharge line temp./ before filter dryer temp.?

shaafeq
24-10-2009, 07:14 AM
Hi Gary,

I've a question for you. In Freezer system, how we can determine whether the system is overcharged or less charged base on the suction line temperature (evaporator in / out), accumulator out temperature, before filter dryer temperature, discharge line temperature? Let say the system is unsing capilalry as the metering device. Hope you can give me some hints regarding this.

nike123
24-10-2009, 08:30 AM
In Freezer with capilary as metering devices, how to determine if the system is overcharged or less charged with a refirgerant? Can we decide this base on the suction line temp., discharge line temp./ before filter dryer temp.?

Before/or filter dryer temperature will tell the difference.


In a system that is short of refrigerant the condenser would have a gradual change in temperature from the top all the way down to the strainer. In fact the strainer will be slightly above room temperature.

In a system that is overcharged strainer will be at same tamperature as lower part off condenser.

http://www.supco.com/images/pdfs/Manuals-Instructions/Cap%20Tubing%20Manual.pdf

Gary
24-10-2009, 04:05 PM
Most accurate would be to weigh in the charge.

james1234
23-11-2009, 06:19 AM
thanks for directing me to your thread on the basics. It really brings it all together for me in plain simple language. Much appreciated!

ice_cold
29-11-2009, 04:29 PM
Hello,
Here is a question from a newbie of both the forum and the world of refrigeration!
You see the terms evaporating temperature, condensing temperature in the literature. My question is where exactly these values are measured from? For example if we take the evaporating temperature; is it measured from the entrance or the exit of the evaporator?
Thanks in advance!

Gary
29-11-2009, 11:06 PM
Hello,
Here is a question from a newbie of both the forum and the world of refrigeration!
You see the terms evaporating temperature, condensing temperature in the literature. My question is where exactly these values are measured from? For example if we take the evaporating temperature; is it measured from the entrance or the exit of the evaporator?
Thanks in advance!

The evaporating temperature is the saturation temperature which corresponds to the low side pressure on a pressure/temperature chart.

The condensing temperature is the saturation temperature which corresponds to the high side pressure on a pressure/temperature chart.

ice_cold
30-11-2009, 08:22 AM
The evaporating temperature is the saturation temperature which corresponds to the low side pressure on a pressure/temperature chart.

The condensing temperature is the saturation temperature which corresponds to the high side pressure on a pressure/temperature chart.

thank you, appreciated!

oogene
30-12-2009, 08:14 PM
yes! I have one of Gary's TECH books and they cut to the chase to real t/s, a great purchase if u can!!!

Sridhar1312
08-01-2010, 03:33 AM
Respected Gary
Where I can get the books Tecch method troble shooting? Is there any agent in India?

Gary
08-01-2010, 03:53 AM
http://prostores1.carrierzone.com/servlet/techmethod_com/StoreFront

exhussmann
25-01-2010, 04:07 PM
This thread is a wealth of good information. It is a shame that the people who need this info the most do not look at / subscribe to free sources of education such as this web site.
Thanks
From the west side of the pond.

ianparker0801
16-02-2010, 09:04 AM
Hi, I have a quick question about connecting gauges, don't think it has been asked before. I always seem to release alot of gas when connecting guages to split A/C systems. Is there a nack to it, like pumping down a system before hand. Is it best to connect when the system is running or off, both high and low sides.

nike123
17-02-2010, 07:11 AM
Turn unit on cooling, close partially valve on smaller pipe and when pressure falls to around 1 bar disconnect your gauge. Open valve fully and put valve caps.

Or buy Refco Quick Couplers.

moideen
17-02-2010, 11:17 AM
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
28-02-2010, 07:21 AM
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
01-03-2010, 04:54 PM
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.

Philip
03-03-2010, 03:26 AM
Gary,you're a legend.I always follow your post since i become a member and your ideas are great.

Gary
03-03-2010, 03:44 AM
I'm a legend in my own mind... lol

nike123
03-03-2010, 04:02 AM
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/products/diagnosis/sherlock-2000.html

Gary
03-03-2010, 06:04 AM
Something like this:
http://www.ecotechnics.it/en/products/diagnosis/sherlock-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.

tctarunchauhan
22-03-2010, 02:54 PM
i thnk a cooling effect on d finger will appear...due to d reason- d water on d finger will absorb latent heat of vapourization nd will vapourize...as a result d temp. of d finger will fall nd a cooling effect will b produced...

Nicholas
31-03-2010, 07:41 PM
good explanation welldone

simon@parker
13-04-2010, 08:29 PM
hi guys this is a great idea love it:):) i will have to read the technical stuff again cos some of it leaked out my head already an i have learned some things as well an only been in game 20 plus yrs if i may be so bold as to make a small contribution even though most of you are super technical more than me not enough engineers stop and actually look at what there working on an do the stuff i was taught look at it listen to it and feel it there the most important tools we have you can see a design floor in a system and adjust for it you can hear a compressor straining under excessive load and you can feel if an evap is fully wet all the way accross and then ya can break out the super tools to fix it ;)

Gary
25-04-2010, 05:56 PM
There seems to be a great deal of confusion about subcooling, so let's take a closer look:

The vapor loses its heat and turns to liquid as it moves very rapidly though the condenser. This does not happen all at once, it is a gradual process.

There is a point where the last vapor bubbles disappear and the mixture becomes solid liquid. Let's call this the "solid liquid point" or SLP.

Technically, if there is enough refrigerant to modulate the superheat at the evap outlet, then the system will function properly, but this is not the full story. Vapor bubbles travelling through the TXV orifice over a long period of time will wear out and distort the orifice, so to ensure long life for the TXV we want solid liquid at its inlet.

So... our minimum charge would have the SLP at the TXV inlet.

At the other extreme, we do not want liquid backing up into the condenser as this takes up condensing space and drives up the high side pressure.

So... our maximum charge would have the SLP at the condenser outlet.

The problem with the minimum charge is that changing conditions could have vapor bubbles at the TXV inlet. The problem with the maximum charge is that changing conditions could have liquid backing up into the condenser.

So... the ideal charge would have the SLP somewhere in between the TXV inlet and the condenser outlet. Thus, we want the SLP to be at the receiver outlet... which is why the sightglass is normally placed there, and why we want to measure subcooling there.

If we monitor the subcooling while observing the sightglass, on a wide variety of systems, we will find that the last vapor bubbles disappear at about 10-15F/5.5-8.5K subcooling. Thus we can identify the SLP by measuring the subcooling at the receiver outlet, ensuring that (with all else functioning properly) we are neither undercharged, nor overcharged.

Rayin
26-04-2010, 02:14 PM
Respected Gary,
Thank you very much for your "Refrigeration 101", the highly informative article.
May I ask you how can we check the heat absorbing capacity of a fin and tube evaporator, if we do not have any product details on it? Just we have the physical size of tube diameter, distance between end fins, fin spacing, fin thickness, number of tubes, number of elbows, fin width, refrigerant temperature, and cabinet temperaure. Also we know the fin and tube material, refrigerant and its properties. (forget about the oil film on the inner wall of the tube).
Wishing you all the very best:)
Thank you
Rayin

sors
28-04-2010, 11:39 PM
Gary that all sounds good there are actually 2 kinds of superheat evaporator and suction vapor since you failed to mention that. But lets do some
transmission heat load calculations:
If a wall has a u factor of .114 area of 90 square feet with a inside temp of 80 degrees what would the heat transmission be gary? In btu/hr

Gary
29-04-2010, 02:08 AM
There is only one kind of superheat... but lots of different places to measure it.

Heat load calculations are outside the scope of this thread.

If you would like to start a thread about heat load calculations... go for it. :)

jakabus
17-05-2010, 10:12 AM
I was thinking it might be a good idea to set up a basic thread to send the newbies to:

Refrigeration 101:

Let's start from the beginning:

Wet your finger and wave it in the air. What you are feeling is a refrigeration effect. When a liquid turns to a vapor it absorbs heat. In this case it is sucking the heat out of your finger.

The opposite is also true. If that vapor then loses that heat, it will turn back into a liquid.

In a refrigeration system, we force a liquid to become a vapor in the evaporator, thus absorbing heat from the refrigerated space.

We then use a compressor to pump that vapor to the condenser.

In the condenser we force that vapor to reject the heat and thus turn back into a liquid so that we can re-use it.

We then meter the liquid back into the evaporator to complete the loop and do it all over again and again and again.

How do we force a liquid to become a vapor?... or a vapor to become a liquid? By manipulating its boiling point.

The boiling point is the temperature at which the liquid turns to vapor when heat is added. It is also the temperature at which a vapor turns to liquid when heat is removed.

Boiling point = saturation temp = evaporating temp = condensing temp

When we think of the boiling point of a liquid it is the boiling point at zero psi pressure. If we increase its pressure we raise its boiling point. If we decrease its pressure we lower its boiling point.

In the evaporator we force liquid to become a vapor by lowering its pressure until its boiling point/evaporating temperature is lower than the air it is trying to cool.

In the condenser we force the vapor to become a liquid by raising its pressure until its boiling point/condensing temperature is higher than the air it is trying to heat.

Different substances have different boiling points at different pressures.

We can tell what the boiling point/saturation temp/evaporating temp/condensing temp is at various pressures for common refrigerants by checking a pressure/temperature chart.

Okay... let's go a step further: Superheat and subcooling.

If we boil off a liquid into vapor and then add heat to that vapor its temperature will rise above the saturation temperature. This is called superheating the vapor. When its temp is 10 degrees above the saturation temperature it is superheated 10 degrees. When its temp is 20 above saturation it has 20 degrees of superheat, etc, etc.

Similarly if we condense a vapor into liquid and then further cool the liquid this is called subcooling. When the temp gets 10 degrees below saturation it has 10 degrees of subcooling. When its temp is 20 degrees below saturation it has 20 degrees of subcooling.

Refrigerant flows very rapidly through the evaporator coil into the suction line. Many people believe that you can't have superheat until the liquid has all turned to vapor, but this is not true. Because of the velocity of the refrigerant flow it is possible to have liquid droplets surrounded by superheated vapor at the outlet of the evaporator... and in fact this is what happens. All of the liquid droplets are gone by the time there is 5-10F/3-5.5K superheat.

We want the superheat at the evaporator outlet to be low enough to ensure that we are fully utilizing the coil, thus maximizing its ability to absorb heat, but we do not want liquid droplets to be sent back to the compressor.

Similarly, it is possible to have vapor bubbles surrounded by subcooled liquid at the outlet of the condenser. All of the vapor bubbles disappear at about 10-15F/5.5-8.5K subcooling.

We want the subcooling to be high enough to ensure that we are sending sufficient liquid to the metering device, but not so high that we are backing up liquid into the condenser, thus reducing its ability to reject heat.

On a cap tube system there is a fixed amount of liquid flowing into the evaporator. When the load is heavy there is warmer air flowing through the coil and thus the liquid is all boiled off long before it reaches the outlet of the coil, thus the superheat is high when the load is heavy. If properly designed and charged, the superheat will be just right when the design temperature (design load) is reached.

Many people believe that a TXV will maintain a fixed superheat, regardless of load. This is just simply not true. When the load is heavy the superheat rises and more liquid is fed to the evaporator. The superheat remains high as long as the load remains high. And again, the superheat is just right when the design temperature (design load) is reached. But the design temp will be reached sooner because of the extra refrigerant feed.

As we see, when the load decreases the superheat decreases... so what happens when the filter gets dirty, or the evap coil... or the blower wheel? Less airflow means less load therefore the superheat drops, even though the refrigerated space may be at design temp.

When the load is high the superheat is high, and when the load is low the superheat is low... even with a TXV.

Everywhere, throughout the system, there are opposing forces balancing against each other, and it can be very difficult to tell which of these forces is out of balance.

And yes, there is more... much much more... but that's enough for now.
I didn't think starting a new thread for my mind blank was a great idea, and this was the closest thread i could relate my thread too.

I am new into the refrigeration industry and I can't remember what a capillary system is.

I have done a small search on google and have not made sense of the results. I was wondering if some one could explain a simple capillary system. Thanks...

nike123
17-05-2010, 08:14 PM
http://tinyurl.com/3a4mexj

jakabus
18-05-2010, 08:47 PM
capillary...

Somewhere in the coil the flow of refrigerant is slower and also the pressure drops over the distance it has to traval? right?

so does it travel this distance loosing pressure in a small coil pipe in hopes when the refrigerent gets to the evap (larger pipe coil) its lost enough enough pressure to have a zillion vapour droplets colleting heat? like a thermal expansion valve, but with out the sensor or valve?

chancie owens
19-05-2010, 02:07 AM
great job gary, i liked what i read.

Deniver45
24-05-2010, 06:57 AM
Gary,

When you say "Generally speaking, a freezer should have 6-8F/3.5-4.5K superheat, a cooler should have 8-10F/4.5-5.5K superheat, and an A/C should have 12-16F/6.5-9K superheat."

At what abient temp are we talking here?

75 degree's?

Gary
25-05-2010, 06:05 AM
Gary,

When you say "Generally speaking, a freezer should have 6-8F/3.5-4.5K superheat, a cooler should have 8-10F/4.5-5.5K superheat, and an A/C should have 12-16F/6.5-9K superheat."

At what abient temp are we talking here?

75 degree's?

Normally, the ambient temp would have relatively little effect on the superheat.

Aik
27-05-2010, 07:30 PM
In another thread Magoo has offered a rule for judging TXV superheat. He says the superheat should be 60-70% of the TD. This makes very good sense. I like it... a lot. :D:
Acording Braydert's " Designing refrigeration installations" error-free performance of evaporator possible only with 0.5...0.7 of the TD.

desA
28-05-2010, 01:29 AM
If we monitor the subcooling while observing the sightglass, on a wide variety of systems, we will find that the last vapor bubbles disappear at about 10-15F/5.5-8.5K subcooling. Thus we can identify the SLP by measuring the subcooling at the receiver outlet, ensuring that (with all else functioning properly) we are neither undercharged, nor overcharged.

How does SLP concept this relate to the concept of 'liquid cooling'?

Where : LC = Tc,sat - Txv,in

A few points to note:
1. LC will vary as Tc,sat varies over the cycle range;
2. The allowable subcooling (SC = Tc,sat - Tc,exit) differs for different condenser types. SC of 5.5-8.5K will be a problem for plate condensers (2-4K), & air-cooled condensers (~ 0K).
3. In the quest for increased SC, be careful of not pushing up Tc,sat. Basically, Tc,sat levers up off the cooling medium temperature. There is a happy balance point for each system.

desA
28-05-2010, 06:56 AM
Normally, the ambient temp would have relatively little effect on the superheat.

In my heat-pump trials, I have observed an influence on evaporator SH, due to ambient air temperature movements.

If Ta,in falls during the range of test, SH will roll down a little more than if Ta,in is constant.

If Ta,in rises during the range of test, SH can often end up being almost constant over the test duration.

The influence can be in the range of ~ 1-3K, depending on the operating SH of the machine.

Gary
28-05-2010, 08:07 AM
In my heat-pump trials, I have observed an influence on evaporator SH, due to ambient air temperature movements.

If Ta,in falls during the range of test, SH will roll down a little more than if Ta,in is constant.

If Ta,in rises during the range of test, SH can often end up being almost constant over the test duration.

The influence can be in the range of ~ 1-3K, depending on the operating SH of the machine.

In your heat pumps, the ambient air would be the air entering the evaporator. As I interpreted the posters question, I believe he was referring to the air entering the condenser.

Gary
28-05-2010, 08:19 AM
How does SLP concept this relate to the concept of 'liquid cooling'?

Where : LC = Tc,sat - Txv,in

A few points to note:
1. LC will vary as Tc,sat varies over the cycle range;
2. The allowable subcooling (SC = Tc,sat - Tc,exit) differs for different condenser types. SC of 5.5-8.5K will be a problem for plate condensers (2-4K), & air-cooled condensers (~ 0K).
3. In the quest for increased SC, be careful of not pushing up Tc,sat. Basically, Tc,sat levers up off the cooling medium temperature. There is a happy balance point for each system.

There is no doubt an ideal balance for each specific system... and I would not recommend SLP at the condenser exit for any system.

What I have found works reasonably well for refrigeration systems in general is to have the SLP in between the condenser outlet and the TXV inlet.

Generally, I would want the SLP to be near the receiver outlet and this is where I measure the SC. I suspect this is the very reason sightglasses are usually mounted near the receiver outlet.

desA
28-05-2010, 08:22 AM
Gary,

When you say "Generally speaking, a freezer should have 6-8F/3.5-4.5K superheat, a cooler should have 8-10F/4.5-5.5K superheat, and an A/C should have 12-16F/6.5-9K superheat."

At what abient temp are we talking here?

75 degree's?

This is the post I was referring to, Gary. There is a mix of applications & conditions here.

It could be useful to split the air-breathing evaps from the closed-space evaps, in regards to the SH question - it will be less confusing.

:D

Gary
28-05-2010, 08:31 AM
This is the post I was referring to, Gary. There is a mix of applications & conditions here.

It could be useful to split the air-breathing evaps from the closed-space evaps, in regards to the SH question - it will be less confusing.

:D

I agree... both the question and the answer could have been more specific.

:D

desA
28-05-2010, 09:21 AM
Originally Posted by desA
How does SLP concept this relate to the concept of 'liquid cooling'?

Where : LC = Tc,sat - Txv,in

A few points to note:
1. LC will vary as Tc,sat varies over the cycle range;
2. The allowable subcooling (SC = Tc,sat - Tc,exit) differs for different condenser types. SC of 5.5-8.5K will be a problem for plate condensers (2-4K), & air-cooled condensers (~ 0K).
3. In the quest for increased SC, be careful of not pushing up Tc,sat. Basically, Tc,sat levers up off the cooling medium temperature. There is a happy balance point for each system.
There is no doubt an ideal balance for each specific system... and I would not recommend SLP at the condenser exit for any system.

Gary:
What I have found works reasonably well for refrigeration systems in general is to have the SLP in between the condenser outlet and the TXV inlet.

Generally, I would want the SLP to be near the receiver outlet and this is where I measure the SC. I suspect this is the very reason sightglasses are usually mounted near the receiver outlet.

Based on thousands of experimental test points over the past few years, I would venture to say, in a direct system (no receiver), if no bubbles are present, then the system will be over-charged.

Sub-cooled boiling & gas evolution in direct liquid lines are part & parcel of a liquid line's behaviour (R-134a). This may be different for a receiver-based system.

The limiting system mass charge will be the one at which the Tc,sat value either jumps by 1-2K (non-linear jump), or where Tc,sat begins to climb rapidly. At this same instant, the pressure drop on the low-side reduces rapidly. These effects can be observed during refrigerant charge-determination trials. This seems to be a switch-over point from an evaporator-dominated system, to a condenser-dominated system.

I'd say that basic rules-of-thumb are useful for field applications, but, for new designs, the system characteristics for each case, will need to be carefully evaluated.

desA
28-05-2010, 02:11 PM
Acording Braydert's " Designing refrigeration installations" error-free performance of evaporator possible only with 0.5...0.7 of the TD.

This will very much depend on the magnitude of the TD itself.

For instance:
TD=10K ; SH = 0.5*10=5K; SH = 0.7*10=7K
TD=20K ; SH = 0.5*20=10K; SH = 0.7*20=14K
TD=30K ; SH = 0.5*30=15K; SH = 0.7*30=21K !!!

That's asking for a fair-sized SH. In all likelihood, you'd have a tremendously high Tc,discharge temperature.

The Magoo rule seems to be applicable in low TD applications & may need to be adjusted for high TD applications.

Like everything in the rhvac game, some level of sound engineering judgement will need to be made in each specific application.

silva.foxx
29-05-2010, 12:18 AM
Gary...

may I first thank you for posting this "refresher" and secondly thank you for continuing your input to the Refrigeration world after your "semi-retirement".

I'm no fridgey...but at 33 and experienced it for 8 years, no quals gained, your "basics" brought it all back and has really urged me to follow the trade.

I'm an automation eng by trade, I experienced 8 years as a services eng with ammonia gas in a food factory, working with Frick and Grasso screws in pumped overfeed systems to blast & spiral freezers plus -26c cold-storeage. Looking back I loved it! It was like a black art: food at 60+ degrees going into a box and coming out frozen!!! A magic box that I knew the code of; well I assumed I did. I was working in a role that I wasn't qualified for, had no proper experience of yet getting by... really dangerous looking back. Stupid or getting by? Stupid I'd say, but someone was assessing my skills and passing me capable!

eggs
29-05-2010, 01:08 PM
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.

Gary, do you still have copies of these programs?

Is there any chance of a copy?

Eggs

aaronh
31-05-2010, 11:19 AM
With regards to this thread which I think has been very interesting t read, I am extremley new to this forum and to refrigeration all together. You seem to mention a lot about different heat loads, can someone please explain to me what a heat load is and how it would effect the refrigeration system?:confused:

cool tool
06-07-2010, 02:17 AM
I am in school for HVACR, I will be graduating in Oct. I have used this site many times for research, and I am pleased with all of the info. I am struggling with the wiring diagrams (showing sequence of operation), any link you may have on basic wiring would be extremely helpful Thank You for your time Russell Peters (Cool Tool)

macrylinda1
02-08-2010, 12:34 PM
OR

You can weigh in the charge as marked on the nameplate.

The manufacturer has done all of the work for you, setting up the system under tightly controlled conditions, determining the right charge, and then pulling all of the refrigerant out, weighing it and marking that weight on the nameplate.
At what operating temperature would the refrigerant mass charge determination be most appropriate - startup Tc,sat 35'C; or hot end Tc,sat 70'C?

I have no given mass charge to work off in this case & have to determine it in-house.

Heeellp
28-08-2010, 02:39 AM
That maybe true, but I am impressed. Gary, I have several quick questions if I may (homeowner). I know this is installation specific so I will try to keep it concise and compact. It deals with a problematic installation (as most do) and a dealer who can't seem to get it right. Can you try to steer me right? Thanks.

3 ton heat pump (two speed ultra tech scroll compressor) split system. 95 % AFUE variable speed furnace matched coil System has had MANY problems since installation. TXV and heat pump replaced due to non-condensibles. Manual states: subcool 5-7 (no plus or minus for two speed pumps) and superheat values of 7-9 (no plus minus). After two years of somewhat adequate cooling I noticed it started running longer than usual cycles. Tech reluctantly came out again. Checked subcool (10-11) and superheat of 20. He added refrigerant until subcool was 9-10 and superheat was 10. He stopped. Please understand, I am a layman so go easy. Unfortunately I do no have the delta T for you. Ambient was around 80-82 degrees and compressor was on low speed. System runs way too long for these values (based on previous years of usage). It simply does not cool the house like it once did (added 44 bags of cellulose insulation in attic). Any ideas? Please?

Found the issues as suspected. Techs would not adjust TXV. Field rep did. System runs much better. Thanks.......

sajinraj
21-09-2010, 11:07 PM
i would like to ask one question sir i have one refrigeration compressor make sabroe modl tsmc 108s using refrigerand 22 now adays it have loding problam it dosend get safishnt pumbing, then i open the compressor icant find eny mager problums but its oil pressur getting 4.5bar

paul441
22-09-2010, 06:23 PM
Hi Gary
Good post,i could do with you in my tool bag so i can just pull you out and help me when im on site,im new to fridge game and im working on dryers mainly atlas copcos but it proving hard to get my head round and sort problems, cheers

daviddwilson
04-10-2010, 04:01 PM
Just the opposite. High load increases SCT and low load decreases SCT... and SCT above ambient (cond TD) should remain within the 11-19K range.
There will be relatively little change in subcooling as the liquid line temp will tend to rise and fall with the SCT and a TXV system stores sufficient surplus liquid refrigerant to compensate for variations in load without substantial changes in subcooling.

Memo275
04-10-2010, 09:56 PM
Refrigeration System

1/Refrigeration system overview
*Propane Chiller: 57% Level
*LPG OH Condenser: 80% Level, LPG T°: -36°C
*Propane Economizer: 40% Level, PCV: 6 Bar, T° Gas: 9.5°C
*02Propane Compressor:
-PRO “A” -PRO”B”
.Capacity Control:
Set point (Bar) O.5 0.5
PID Out: 100% 100%
.High Stage Capacity Control:
Set point: 3.5 3.5 Bar
PID Out: 100% 100%
.Moy Amperes (Amp) 60.2 58.5
.Suction Pressure (Bar): 0.82 O.91
.Suction Temp (°C) : -41.3 -41.2
.Suction SH (°C): 5.0 3.3
.Intermediate Pressure (Bar): 4.0 4.4
.Intermediate Temp (°C) : 50.8 49.2
.Intermediate SH (°C): 55.5 51.6
.Discharge Pressure (BAR) : 13.5 13.8
.Discharge Temp (°C) : 74.0 72.1
.Discharge SH (°C) : 34.7 31.8
→Bypass Propane Condenser used in manual 0%
*Propane surge drum:
.Pressure: 14.5 Bar
.Level: 52%
*Gas Propane Exchanger:
.Propane T°: 34.75°C
.Gas T°: 29.25 °C
2/ Refrigeration Skid:
*Inlet Cold Separator: 26.4c°C
*Outlet Cold Separator: -28 °C
*Level Cold Separator: 40%
*Set point TCV: -45 °C (Bypass Cold Separator)
*Gas / Liquid Exchanger :
. Gas T°: 36.75 °C
.LPG T° : 8.85 °C
*Gas / Gas Cooler :
.Gas T° to sweet / sales gas Exchanger : 4 °c
.Gas T° to propane chiller: -16 °C
→*we can’t attend the cold Temperature -45°C
*Same times we have carryover of liquid on Propane Receiver
Please help me to identify the problem and correct them.

janroy
06-10-2010, 04:49 PM
hello im a newbie..i'll will enjoy this such a helpful tips on my work and profession..

DannyHR
15-10-2010, 02:42 PM
Hi, i am just starting to learn about refrigeration and how it all works, although i am unsure of how positive and negative air pressure will affect a refrigeration system i was hoping that some1 could help me out with this.
I am currently designing a filtered positive air system for a food production plant, up to now the positive air systems i have installed have been fed from the outside ambient air. on this system as the production room is to be kept at below 12degrees celsius and is 700cubic metres, going on the basis of using 8 air changes per hour. i am hoping to use two feeds with dampers, one from the outside and one from the refrigerated garage store next door to the production room which is kept at 5 degrees is 2,800 cubic metres. Will the negative air pressure created in the refrigerated garage area (which is 4x the size of the production room) affect the evaporators in this room, apart from making them work a little harder?? i am sorry if i havn't explained this very well this is my fist time writing a post. i can give more details if needed. Hope some one can advise. Thanks

nicehitsam
19-10-2010, 03:17 AM
Think of the system charge as consisting of low side charge and high side charge.

Assuming there is proper airflow through both coils (and that everything else is functioning normally):

On the low side, at design refrigerated space temp, if the coil outlet superheat is right, then the low side charge is right.

Coil outlet superheat varies with type of system. Generally speaking, a freezer should have 6-8F/3.5-4.5K superheat, a cooler should have 8-10F/4.5-5.5K superheat, and an A/C should have 12-16F/6.5-9K superheat.

On the high side the subcooling should be no more than 15F/8.5K because this is the point at which liquid will start to back up into the condenser.

On a cap tube/fixed orifice system, if the superheat is right (at design space temp) and the subcooling is not more than 15F/8.5K then the system has the right charge.

Note that minimum subcooling is not a factor on cap tube/fixed orifice systems. They are critically charged.

On a TXV system there is a minimum and maximum charge. When the superheat is right (at design space temp) and the subcooling is not more than 15F/8.5K then there is enough refrigerant in the system to do the job. This is the minimum charge.

Additional refrigerant can then be added to bring the subcooling up to 15F/8.5K. This is the maximum charge.

It is good practice to bring the charge up to maximum because vapor bubbles flowing through the TXV will wear out the needle and seat. This also provides additional refrigerant for heavy loads.
Yes sir I'm a newbie but I like this, this is really great stuff.Thanks for all u do.

nicehitsam
19-10-2010, 03:16 PM
Gary this is great info I do appreciate it could you tell me what is meant by " if the superheat is right at( design space temp) and the subcooling is not more than 15F/8.5K then the system has the right charge.

anil0000
02-11-2010, 04:26 AM
It is reaaly nice way you put up required basic information of refrigeration...!!! Good one...!!!

daviidwilson
02-11-2010, 08:14 AM
If the superheat is high would the delta-T be much higher than when you have a normal superheat??

Am i correct in saying you should have approx (commercial refrigeration) 3 to 6 Deg C temp difference (air on to air air off)

Would the temp difference (air on to air off) be the same regardless of the high or correct room temp???

I.e design room temp 0 deg C
will the air on-off temp still be 3- 6 deg C difference when the room temp is 20 deg C
And will it still be 3-6 deg C when the room is at 1 deg C

CB
Delta=T upper limit differs for various types of systems as well as for different design temperature and humidity requirements. And this goes beyond the scope of "Refrigeration 101".

Suffice it to say that if you are familiar with the delta-T limit for a particular type of system, anything above this limit is an unambiguous indicator of an airflow problem.

chandramouli
02-11-2010, 02:02 PM
Sir,

I am a commer to this site, well your version of refrigeration is so simple as it is communicable to every one.

Thanks

:) Chandramouli.G

femalerotor
11-11-2010, 09:39 PM
Thanks...I follow the reasoning...it helps to grasp the basic concept(s)...you're an excellent teacher...(where would we be without IT...finding such good answers from someone on the other side of the globe, with the click of a mouse)

hbguy
19-11-2010, 04:25 AM
Oh I very much agree -I work with a few lads who will fiddle with the TEV every call - makes even more trouble
I remember working for a parts house where about 40-50% of the tev's we sold went to ONE tech.

Bones
29-12-2010, 12:55 PM
You dont sell/supply parker valves do you?

It is true, txv rarely seldom need adjusting. Only adjusted maybe 2 from STD setting after installs, all rest had to be adjusted because last bloke wound it silly for who knows why...

Is there any good threads about superheat checking/adjustment on multi evap systems? Seem to do alot of them where I'm at ATM mostly single evap/cond units previous.

I have been using evap outlet shraeder valve for evap pressures where available and pipe temp probe at bulb location for each evap coil on system - but as not all systems have evap coil access can you use sst at comp?

Steve Wright
30-12-2010, 07:07 PM
Gary I have been using your TECH method for years it is really great especially when you are having a bad day and can't identify a starting point.

I would encouage folk to get it and practiace it.

Steve Wright CMS

PRESS
12-01-2011, 05:45 PM
Hi Guys,

You might be interested in the two e-books which I posted on the forum today for further reading. check them under refrigeration books.

www.isentropictemptech.com (http://www.isentropictemptech.com)

crfugate
14-01-2011, 02:34 AM
I am new to the HVAC field. I am an electrician by trade and have just recently complete an Associate Degree in HVACR at a local community college. I have currently started a new position in the Refrigeration Department in the chemical plant at which I work. I was recently asked to look at a Trane VAV that has no HIM on the unit. The others in the shop tell me that the Trane Techs can interface with the VAV with a laptop. I would applicate any information that may help me trouble shoot this piece of equipment. Thanks!!

Benners
19-01-2011, 06:51 PM
Hi Gary ,
I havn't been a member long and am currently in an apprentaship in the trade, i have about 6 months experience and things are clicking into place for a newby if that makes sense ha. I just want to say that your postings are brilliant and are helping me alot. Looking forward to reading some more many thanks
Ben :)

Gary
02-02-2011, 03:45 AM
There seems to be some confusion about saturation, so perhaps some clarification is in order:

For a given pressure, every liquid has a boiling temperature.

For example, at atmospheric pressure (0 psi) water boils at 100C/212F. We could say this is it's "boiling temperature", or since we are turning it into a vapor we could say this is it's "evaporating temperature", or since vapor bubbles are forming we could call this it's "bubble point temperature". All mean the same thing.

If we take hot steam at atmospheric pressure (0 psi) and cool it to that same 100C/212F it condenses to a liquid, so we could call this it's "condensing temperature", or since it is forming liquid droplets (dew) we could call this it's "dewpoint temperature".

All of these terms describe the same temperature point for water at 0 psi, but also describe whether we are adding or removing heat.

What if both liquid and vapor are present and we are neither adding nor removing heat? What do we call this temperature then? If we are simply describing the temperature at which the process could be driven in either direction (liquid to vapor or vapor to liquid) for water at 0 psi, we call this it's "saturation temperature".

Which terminology we use depends on whether we are simply describing the temperature point or also describing the process... so...

The saturation temperature for water at 0 psi is 100C/212F.

The evaporating temperature for water at 0 psi is 100C/212F.

The condensing temperature for water at 0 psi is 100C/212F.

Gary
02-02-2011, 04:11 AM
Taking this a step further, "dewpoint temperature" and "bubble point temperature" are terms we use to describe a mixture of refrigerants which have different saturation temperatures (zeotropic mixture).

Let's say we have two refrigerants.

The saturation temperature for refrigerant "A" at 0 psi is 10C/50F.

The saturation temperature for refrigerant "B" at 0 psi is 15C/59F.

If we mix these two together and are in the process of adding heat (at 0 psi), the mixture will start to bubble at 10C/50F and will finish evaporating at 15C/59F.

If we are in the process of removing heat from the mixture (at 0 psi), it will start to form dew at 15C/59F and finish condensing at 10C/50F.

The bubble point for this mixture at 0 psi is 10C/50F.

The dewpoint for this mixture at 0 psi is 15C/59F.

The difference between bubble point temperature and dewpoint temperature is called the "glide" which in this case is 5K/9F.

Note that evaporating finishes at the dewpoint temperature, so when looking at the low side pressure, we want to know the dewpoint.

Note also that condensing finishes at the bubble point temperature, so when looking at the high side pressure, we want to know the bubble point.

Gary
02-02-2011, 04:15 AM
And then there is pressure.

If we raise the pressure, we raise the saturation temp. If we lower the pressure, we lower the saturation temp.

The pressure/temperature (P/T) chart (aka comparator) for our refrigerant tells us the saturation temp for a given pressure. Or for zeotropic refrigerant mixtures, it tells us the bubble point and/or dewpoint.

For those who confuse zeotropes with azeotropes, here's how I remember which is which:

Just as theist means with religion and atheist means without religion, zeotrope means with glide and azeotrope means without glide.

desA
02-02-2011, 05:51 AM
Thanks Gary - excellent. :)

faiaz
14-02-2011, 07:47 AM
Re. Refrigeration 101
great information...,would you like to emphasize some thing on setting the superheat on a refrigeration system.
Fai

Indy2010
15-02-2011, 05:40 AM
Excellent explanation, thanks Gary

nike123
16-02-2011, 04:43 PM
If I recollect correctly, it is already explained as "Magoo rule" of 0,65xTD
But more detailed is here:
http://www.kueba.de/en-us/Tools/Küba-Expansion-Valve-Calculator/Pages/default.aspx

joe magee
25-02-2011, 10:28 PM
I will concur with Gary. Keep away from the expansion valve. I've been at this a long time and have started up many supermarkets with long line ups of cases. very rarely do I have to touch a valve. Whats nice now is that some of the cases have sensors on the inlet and the outlet of the coil and supply and return air sensors. Back at the E-2 you can read superheats and splits. Makes it very convenient.

datsmad
26-02-2011, 03:44 AM
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

mickel
04-03-2011, 01:31 PM
Refrigerant flows very rapidly through the evaporator coil into the suction line. Many people believe that you can't have superheat until the liquid has all turned to vapor, but this is not true. Because of the velocity of the refrigerant flow it is possible to have liquid droplets surrounded by superheated vapor at the outlet of the evaporator... and in fact this is what happens. All of the liquid droplets are gone by the time there is 5-10F/3-5.5K superheat.

We want the superheat at the evaporator outlet to be low enough to ensure that we are fully utilizing the coil, thus maximizing its ability to absorb heat, but we do not want liquid droplets to be sent back to the compressor.

Similarly, it is possible to have vapor bubbles surrounded by subcooled liquid at the outlet of the condenser. All of the vapor bubbles disappear at about 10-15F/5.5-8.5K subcooling.

We want the subcooling to be high enough to ensure that we are sending sufficient liquid to the metering device, but not so high that we are backing up liquid into the condenser, thus reducing its ability to reject heat.

conair chris
03-05-2011, 08:46 PM
Thanks for such an informative post, I am new to the field and any advice and information is greatly appreciated :)

Windseeker
17-05-2011, 06:15 AM
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.

Windseeker
20-05-2011, 11:59 PM
On a cap tube system there is a fixed amount of liquid flowing into the evaporator. When the load is heavy there is warmer air flowing through the coil and thus the liquid is all boiled off long before it reaches the outlet of the coil, thus the superheat is high when the load is heavy. If properly designed and charged, the superheat will be just right when the design temperature (design load) is reached.

AH-HA Moment. Thank You, Thank You, Thank You.

Now, I know why I over-charged the system during pull-down and found 350 PSI hi pressure and frosted lines when I came back.

Naeem
30-05-2011, 05:33 PM
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

patrickj
08-07-2011, 10:47 AM
Dear Gary,
I have been encountered with aproblem of Oil nonreturning back to the compressor in an R22 system connected to an flake ice plant evaporating at -20C.The flaker is fed through 7nos TXVs and a hand regulating valve.I recon itis an TxV problem and what sort of superheats should yu allow. At the moment ir is set at 7 C.
patrickj

Rich1281
24-07-2011, 02:13 PM
Are you measuring subcooling on the liquid line near the receiver?... or on the drip leg between the condenser and the receiver?

On AC systems its the outlet side of the condenser, on refrigeration units its usually at the drip since I ususally can't get onto the outlet of the condenser. Wouldn't the liquid line just outside the reciever be the larger/greater subcooling difference?

BTW, someone stoll my books, where can I get replacements?
Rich

Gary
24-07-2011, 05:38 PM
BTW, someone stoll my books, where can I get replacements?
Rich

Just click on my signature line. :)

Gary
25-07-2011, 12:54 PM
Subcooling should be measured on the liquid line after the receiver. Keep in mind that the liquid line cannot be cooler than the air surrounding it. If the liquid line is in the hot air stream leaving the condenser, it will measure abnormally high.

Move down the liquid line until it enters an area that is surrounded by ambient air. That's where you measure the subcooling.

exxu
18-08-2011, 10:27 PM
First of all thank you Gary and all of you for sharing your knowledge.

Second of all, picture this:
- a sistem used in air conditioning: 5 C evap, 40 C cond, txv with no MOP, runing, in normal conditions with SH = 5k and SC = 4K, about 30 kw compressor capacity (it's a purely ipotetic system), R407c
- according with txv producer (let's say Danfoss - TEZ 5 with orifice no.2), the valve has a capacity of 30 kw at a TXV DP of about 12bar; the capacity rises with the TXV DP rise
- with a high load, the superheat rises, the txv opens and the TXV DP decreases thus it's capacity decreases, so the sistem capacity decreses too, leading to a increasing suply air temperature.
What is wrong ?

Gary
19-08-2011, 02:59 PM
I think you are confusing TXV capacity ratings with system output.

Let's say an elevator has a capacity rating of 10 people. Does that mean there are 10 people on the elevator? Nope.

exxu
23-08-2011, 03:37 PM
I'm well aware that the things are not going that way. The txv will open to increase the system capacity, to reduce the superheat and the thv dp will decrease. Then what is the table i've attached from Danfoss doc. saying ?

Gary
23-08-2011, 04:06 PM
The table is telling you the maximum flow (valve wide open) for a given dP... and you are still confusing capacity with output. Opening the TXV does not increase the capacity of the system, it increases the flow and thus the output.

chillerman2006
23-08-2011, 04:19 PM
Subcooling should be measured on the liquid line after the receiver. Keep in mind that the liquid line cannot be cooler than the air surrounding it. If the liquid line is in the hot air stream leaving the condenser, it will measure abnormally high.

Move down the liquid line until it enters an area that is surrounded by ambient air. That's where you measure the subcooling.

Question Sir <Gary>

Liquid line (on water chiller) should be subcooled liquid coming from condensor

Sun beating down on tube-work

I am expecting now saturated liquid (lots of flash gas)

Could you explain for me please (technically or simply put)

What is in this liquid line now ?

R's chillerman

Gary
23-08-2011, 04:52 PM
Question Sir <Gary>

Liquid line (on water chiller) should be subcooled liquid coming from condensor

Sun beating down on tube-work

I am expecting now saturated liquid (lots of flash gas)

Could you explain for me please (technically or simply put)

What is in this liquid line now ?

R's chillerman

I think you are grossly overestimating the solar input.

chillerman2006
23-08-2011, 05:04 PM
Question Sir <Gary>

Liquid line (on water chiller) should be subcooled liquid coming from condensor

Sun beating down on tube-work

I am expecting now saturated liquid (lots of flash gas)

Could you explain for me please (technically or simply put)

What is in this liquid line now ?

R's chillerman


I think you are grossly overestimating the solar input.

Hi Gary

could you explain further for me

& obviously others would benefit from your expertise here

R's chillerman

Gary
23-08-2011, 06:08 PM
Given the curvature of the liquid line, along with the reflective properties of the metal and the relatively small size, I suspect the solar heat gain would be negligible. I would certainly not expect lots of flashing.

chillerman2006
23-08-2011, 07:20 PM
Given the curvature of the liquid line, along with the reflective properties of the metal and the relatively small size, I suspect the solar heat gain would be negligible. I would certainly not expect lots of flashing.

Thankyou very much Sir,

you have put to bed, once & for all a miss-conception which has been argued back & forth for far too long !

R's chillerman

Uni
06-09-2011, 01:49 AM
A basic question, Gary.

Given a system running in Cooling mode, how to raise evaporating temp (or pressure)? Different ways to do so?

My condensing ~50C but evaporating ~ -3, quite low for an A/C.

Try to open the TXV apperture until getting low limit SH but failed to raise Tevap muchly.
Anything to do with indoor air flow rate? I was trying to maintain a 10% lower air flow rate than initial calculation for noise benefit.

Gary
06-09-2011, 04:45 AM
A basic question, Gary.

Given a system running in Cooling mode, how to raise evaporating temp (or pressure)? Different ways to do so?

My condensing ~50C but evaporating ~ -3, quite low for an A/C.

Try to open the TXV apperture until getting low limit SH but failed to raise Tevap muchly.
Anything to do with indoor air flow rate? I was trying to maintain a 10% lower air flow rate than initial calculation for noise benefit.


Given a fully active evap coil, the pressure/temperature will depend upon the amount of heat being transferred from the air to the refrigerant. The more heat transfer, the higher the pressure/temperature.... and vice versa. The rate of heat transfer depends upon the surface area, the volume of air flowing through the coil and the temperature of the air flowing through the coil.

It is a mistake to believe that a pressure/temperature is, in and of itself, too high or too low. In truth, the temperature/pressure may or may not be too high/too low for a particular design under a given set of conditions.

In this case, the evap being the outdoor coil, on a cool day -3C is probably not low at all. It depends.

Gary
06-09-2011, 05:05 AM
Anything to do with indoor air flow rate? I was trying to maintain a 10% lower air flow rate than initial calculation for noise benefit.

Thereby throwing the entire system out of balance. Air flow is IMPORTANT. Earplugs are cheap.

Uni
06-09-2011, 06:10 AM
Thanks for your insights, at least I know that my thought was not far off to explain the situation.
Agree with you, airflow is so important and I hate forcing myself reducing it. But have to factor in noise level, can't make it quiet, cant sell.

I considered Tevap low compared to initial calculated system balance. Such a low evap temp will affect system efficiency as well. Small compressor is now designed for high efficiency and is most efficient at approx Tevap ~ 5C or more. Stucked with airflow and coil size so could not improve it. And if you read my other post, it affects heating mode as well (high head pressure). Too much compromises just for noise.

chillerman2006
08-09-2011, 12:49 AM
Off topic - needed removing

texas64
18-10-2011, 02:26 PM
Gary, what do you think about using compressor superheat to analyse system performance? Checking discharge line temps and subtracting saturated liquid pressure. Something like 50 to 70 degrees as normal range.

Gary
18-10-2011, 11:29 PM
Gary, what do you think about using compressor superheat to analyse system performance? Checking discharge line temps and subtracting saturated liquid pressure. Something like 50 to 70 degrees as normal range.

Discharge superheat is directly related to compressor inlet superheat. The higher the inlet superheat, the higher the discharge superheat... and vice versa. I use inlet superheat and it tells me what I need to know. I don't know much about discharge superheat, because it is not something I use.

spoon man
25-10-2011, 11:04 PM
Sorry to but in. I work on chillers for industrial. Supplying cooled water for various machines. A sub cooling of 15oc should be acheavable with any system there or about and 5oc superheat give or take. If you are not acheiving this its the same route. Gas charge/condensor fault/evap fault/ tev fault/ and abnormal ambient range. Your gauges are your friend and a simple logical reason. Look for signs like liquid return to compressor(bottom iced up) or tev iced up, mass dt across evaporater, low diff across condenser etc

spoon man
25-10-2011, 11:10 PM
Oh and possibly water blockage on water side or pump failure all water / process side. Anything slowing down heat exchange

spoon man
25-10-2011, 11:11 PM
In that case check pump curves - completely different game but very easy to grasp.

chillerman2006
25-10-2011, 11:17 PM
Sorry to but in. I work on chillers for industrial. Supplying cooled water for various machines. A sub cooling of 15oc should be acheavable with any system there or about and 5oc superheat give or take. If you are not acheiving this its the same route. Gas charge/condensor fault/evap fault/ tev fault/ and abnormal ambient range. Your gauges are your friend and a simple logical reason. Look for signs like liquid return to compressor(bottom iced up) or tev iced up, mass dt across evaporater, low diff across condenser etc

Spoon Man

a condensor has 3 jobs to do when rejecting heat

de-superheating (specific heat rejection)
condensing (latent heat rejection)
subcooling (specific heat rejection)

the last subcooling depends if the coil has been sized accordingly to subcool the refrigerant and to what degree, industrial refrigeration will subcool the already de-superheated/condensed refrigerant but most package chillers dont subcool to 15*c, in fact many struggle to reach 6*c

Exactly what make/model are you referring to ??? @ 15*c many will be overcharged

R's chillerman

Gary
30-10-2011, 10:32 PM
Subcooling at 15K is way too high, causing liquid to back up into the condenser, reducing it's effective area and therefore it's efficiency. I would recommend max 8.5K/15F subcooling or clear sightglass, whichever comes first.

corkman
01-11-2011, 10:14 AM
i like this post

L-PLATES
01-11-2011, 11:18 PM
Hello everyone i am new here and have just passed my 2079 and good to be one of the lads now
this is a great site and really look forward to making new friends