To TXV or not to TXV? that is the question

[BigBadger]

The idea of a TXV (Thermostatic eXpansion Valve) in my refrigeration system seams pretty appealing. It should help prevent slugging (liquid return to compressor) and should also give me a bit of adjustability in the system where a capillary tube does not.
I rushed around my local refrigeration dealer and bought this:
http://www.steve.bage.btinternet.co.uk/TXV.jpg
It's a Danfoss type 'TS2' TXV. I also got a size '00' cartridge for it.

Question is does anyone have any practical experience with TXV's? Are they a good idea or bad idea, and any advice on installation and set-up?
The cost of the valve is irrelevant because as you see I’ve already bought one!!!

[|PuNiSh3R|]

I am guessing you paid 30.00 dollars (USD) or so right?

You got it now.. so use it.. should of asked the local refrigeration chump how to use it.. No instructions came with it?

Those are the best expansion valves you can buy.. Danfoss brand that is..

[|PuNiSh3R|]

Oh, yea.. what kind of digital camera you use?

[BigBadger]

There are some instructions with it but pretty basic stuff. I'll install it and see how it performs....fingers crossed.

the camara is a Fuji 4900Z...nice piece of kit.

[naTTen]

is it worth it to get one of those?

[|PuNiSh3R|]

Depends on the complexity of your system young naTTen.. If you can afford it.. yes go for it.. it's not NEEDED.. but they sure do make things easier.

[bowman1964]

YOU MUST MOUNT THE VAVLE AS CLOSE TO THE EVAPERATOR AS YOU CAN.BEACUSE FROM THE EXPANSION VAVLE FOWARD TO THE EVAPERATOR IT WILL FREEZE.ANY WHERE BEHIND THE EXP VAVLE IS A LOW PRESSURE SIDE AND THAT IS WHERE IT WILL START TO BOIL AND REMOVE THE HEAT.THAT IS WHY I HAVENT USED ONE MYSELF.I HAVE A SHELF FULL AT WORK OF DIFFERANT EXP VAVLES.THEY WORK GREAT BUT BIG DRAW BACK IS HAVING TO BE SO CLOSE THE EVAP DIE.SECOND YOU NEED A RECIEVER TO STORE THE FREON SO WHEN THE VAVLE OPENS UNDER LOAD IT DOESNT RUN OUT OF FREON LIQUID.NOW IF I WAS BUILDING A CHILLER ONLY UNIT I WOULD USE THE EXP.BUT ON DIE EVAP COOLING IS ALOT HARDER TO GET IT TO WORK PROPERLY.

[BigBadger]

Originally posted by bowman1964
YOU MUST MOUNT THE VAVLE AS CLOSE TO THE EVAPERATOR AS YOU CAN.BEACUSE FROM THE EXPANSION VAVLE FOWARD TO THE EVAPERATOR IT WILL FREEZE.ANY WHERE BEHIND THE EXP VAVLE IS A LOW PRESSURE SIDE AND THAT IS WHERE IT WILL START TO BOIL AND REMOVE THE HEAT.THAT IS WHY I HAVENT USED ONE MYSELF.I HAVE A SHELF FULL AT WORK OF DIFFERANT EXP VAVLES.THEY WORK GREAT BUT BIG DRAW BACK IS HAVING TO BE SO CLOSE THE EVAP DIE.SECOND YOU NEED A RECIEVER TO STORE THE FREON SO WHEN THE VAVLE OPENS UNDER LOAD IT DOESNT RUN OUT OF FREON LIQUID.NOW IF I WAS BUILDING A CHILLER ONLY UNIT I WOULD USE THE EXP.BUT ON DIE EVAP COOLING IS ALOT HARDER TO GET IT TO WORK PROPERLY.

That's just the sort of advice i was looking for.
The liquid reciever is no problem because my system has one built in. The need to place the valve close to the evaporator was something i'd thought about, the conclusion i came to was i could perhaps use the TXV and a short cap tube together in series. The TXV would be mounted after the liquid receiver then would lead into a short cap tube (about half of the normal length) this way the 'boiling' would not occur at the TXV outlet but at the end of the cap tube.
Any thoughts?

[bowman1964]

ok well i have thought about that too but only one problem and it can be a big one.after the freon leaves the offrice inside the vavle it will be released to a low pressure area (even if you attach the capillary tube right to the vavle there is a pocket inside the vavle itself)that the freon liquid will start its process of boiling...there is no way you can stop it.to a small degree.this boiling how ever small it might seem will be more than enough to disrupt to flow of liquid freon in the capillary tube.causing a lot of headaches trying to figure out what is going wrong.it will cool but not anywhere where it should be at.sorry to tell you that but you should be aware of that happening.

[BigBadger]

I guess the only way to tell for sure is to build it and see how it goes......I'll let you know

[|PuNiSh3R|]

Heh.. I am gettin so sick of working on my system.. it's been to long now.. I now have to fix leaks in my reservoir.. grr.. just pissin me off..

I'd like to put in some type of sub-cooling so I don't need to run the condensor fans so fast.. any idea's??

I am still seeing high side pressures.. that are to .. high.. heh.. I don't understand it.. althought I have a few thoughts..

[BigBadger]

How high is too high???? My system is speced to run 210psia on the high side and 19psia low side.

[|PuNiSh3R|]

heh.. well from what I believe your standard soft 1/4" copper tubing bursts at 500PSI.. for this type of setup you shouldn't have a high side more then 225.. that's pretty high.. Want to keep it between 150 and 200.

Low side.. whatever works best.. somewhere between 0 and 20.. or if you got a really good compressor maybe you'll be in a vacuum..

[BigBadger]

Originally posted by |PuNiSh3R|
heh.. well from what I believe your standard soft 1/4" copper tubing bursts at 500PSI.. for this type of setup you shouldn't have a high side more then 225.. that's pretty high.. Want to keep it between 150 and 200.

Low side.. whatever works best.. somewhere between 0 and 20.. or if you got a really good compressor maybe you'll be in a vacuum..

I'm using some tecumseh software to work out the pressures and heat load.
Generally low evap temp/low heat load = low pressure (both high and low side). High heat load/high evap temp = high pressure both sides. If my system (R404A) was designed for a -10C evap temp the high side pressure would be over 400psia !!
My R404A system would use higher pressures than a R134A rig anyway because the boiling temp of the refrigerant is higher so there is no need to be aiming for a vacuum on the suction side unless your looking for temps below -50C. Running a suction vacuum is VERY inefficient and would give a very small heat load capacity. As far as the compressor goes the higher the suction pressure the better it works.

[aenigma]

Running a vaccum on low side is not ineffeciant if you have a strong compressor to back it up.But I think you were talking about your system.
I agree 19psi is a bit high for a low side temp.

To get below -50c you dont need to be in a vaccum,about 0psi or so would be sufficient as long as your system is capable of saturating the evap with liquid.Although I am talking about r290,so with R404a technically you should get even lower.
But it all depends on your system.Your system while at 0psi might not have much of a heat capacity,but I am sure it would have enough of a capacity at 0-5psi....

[BigBadger]

The pressures I'm quoting are 'absolute' so 19psia (a=absolute) is equal to a gauge pressure of 4.5psig (g=gauge).
Atmospheric pressure = 14.5psia.

Running on a suction vacuum is inefficient for any compressor however with a big enough compressor then yes, you can still achieve a reasonable heat load.
Basically the reason why a refrigeration system can move more heat when the suction pressure is high is because the higher the suction pressure the more efficient the compressor (theoreticaly up to the point where the motor torque is insufficient to compress the gas any further or the discharge pressure exceeds the rating of the unit).
This is all pretty academic for our use as we need to run low suction pressures to get the temperatures we want.

[aenigma]

Originally posted by BigBadger
The pressures I'm quoting are 'absolute' so 19psia (a=absolute) is equal to a gauge pressure of 4.5psig (g=gauge).
Atmospheric pressure = 14.5psia.

Running on a suction vacuum is inefficient for any compressor however with a big enough compressor then yes, you can still achieve a reasonable heat load.
Basically the reason why a refrigeration system can move more heat when the suction pressure is high is because the higher the suction pressure the more efficient the compressor (theoreticaly up to the point where the motor torque is insufficient to compress the gas any further or the discharge pressure exceeds the rating of the unit).
This is all pretty academic for our use as we need to run low suction pressures to get the temperatures we want.

Yeah if the compressor is efficient running a vaccum will not hurt heat capacity enough to matter.But most average small compressors like 1/2hp cant really run a vaccum while maintaining a good high side pressure.So you dont get a good flow of refrigerant.
But my system for example will run good in a vaccum because it is dual stage.It will run around 150psi high side while in about 10 inches of vaccum on low side while maintaining a pretty high flow of liquid refrigerant.But at about 0psi the evap is heavily saturated with liquid refrigerant and yields evap temps below -60f with a nice heat load capacity.

I need a nice quiet compressor that will give me 200psi high with low side at about 25 inches of vaccum :D

[bowman1964]

BigBadger
I'm using some tecumseh software to work out the pressures and heat load


well i have the program you are using.TECUMSEH called diskette_uh and one from danfoss called rs+program.i like the tecumseh better.but these programs ar not even designed to be used for what we are doing.they dont give data going down low enough in temps.but they will get us close in capillary tube size.i am trying to make a chart using those two programs plus some other documents to make a chart by hp and temp line.to hopefully get with in a near perfect capillary size and lenght.for a given temp and hp.i hope i get it figured out before i have to start cutting my new rolls of tubing.

[BigBadger]

Is that Diskette_uh the downloaded version?....I've got a program simply called 'Tecumseh Europe Selection Program' it came on CD with my compressor and is much better than the downloadable program.......I could burn you a copy if you tell me whare to send it.

[bowman1964]

WELL THAT IS WHAT MY PROGRAM SAYS WHEN I START IT UP 'Tecumseh Europe Selection Program' . I DID DOWNLOAD IT FROM THE SITE.WOULD BE NICE TO HAVE A FULL COPY, BUT IT IS TOO MUCH TROUBLE FOR YOU TO SEND IT TO ME IN THE US.BUT I REALLY APPRECIATE THE OFFER.ANY TIME YOU NEED SOME HELP JUST GIVE ME A YELL.

:toast: :toast: :toast: :toast:

[dmitriyaz]

okay,
another n00b question coming up:
TXV usues a "bulb" right bofore the compressor to measure the temperature of incoming refrigirant and accoringly adjusts the diameter of the capilary hole to make sure the pressure is correct for all the refrigirant to evaporate before entering the compressor.
one thing i just thought of: on different systems, the suction line has different pressure. and while it one system, a particular TXV would work fine, in another system, where the suction line pressure is higher, the same particular TXV would still allow the slugging.
pressure and boiling point are dependant on each other, and i am failing to see how a TXV can work correctly while only knowing one of these parameters.
i know a am wrong here somewhere, please enlighten me! :help:

[BigBadger]

TXV's are usually adjustable. The one i bought can take variouse sizes of orifice to suit different flow rates and the 'set-point' can be adjusted (there is a screw-in adjuster under the brass cap)