R22 Temp To Pressure Formula

[lwarren]

I am trying to write a computer program that calculates the pressure of R22 from a given temp, just like a p/t chart.

I have searche the web an have not been able to find a formula. Does anyone know what this formula is?

Thanks

[US Iceman]

Find a set of tables for the refrigerant you want to use. Then plug the data into an Excel spreadsheet. One column for temperature and another for pressure. Then you can curve fit the data so that your program calculates the pressure from the temperature input from the instruments.

You may have to turn on the Data Analysis option in Excel, but it's in there. Look in the Help section (F1) and search for curve fitting or regression as the topic.

The temperature to pressure works out quite well, but going from pressure to temperature with this method is a little dicey.

[SteinarN]

Interesting problem. I made a heat pump where i wished to read out the condensing and evaporator temperature on the PLC from a pressure transducer. I was looking for a formula that i could program the plc with so it could convert pressure to temperature. I wasnt able to find a formula.

I doubt there exists a simple formula. At least if it should give an accurate result. If someone has a formula, simple or complicated, i'm also very interested in it.

[SteinarN]

Find a set of tables for the refrigerant you want to use. Then plug the data into an Excel spreadsheet. One column for temperature and another for pressure. Then you can curve fit the data so that your program calculates the pressure from the temperature input from the instruments.

You may have to turn on the Data Analysis option in Excel, but it's in there. Look in the Help section (F1) and search for curve fitting or regression as the topic.

The temperature to pressure works out quite well, but going from pressure to temperature with this method is a little dicey.

Is it possible to read out the actual formula from Excell? I need a formula i can incorporate in my PLC program.

[lwarren]

Is it possible to read out the actual formula from Excell? I need a formula i can incorporate in my PLC program.

That is what I am trying to do, I need to write a custom program object for an energy managment system.

I know the formula exists, because there are online caclculators that do this.

The Excel option will not work for me.

[SteinarN]

I know some compressor calculation software uses formulas and not tables to calculate capasity. Danfoss does this. You can read out the formula as well as the values for each compressor that you put in the formula (an universal formula but different values put into that formula dependent on which compressor to calculate). I tried to make a formula myself a couple year ago, but I didnt have enough time to have a serious try. Maybe i should try one more time.

[lwarren]

If you figure it out, let me know. It is not a linear formula, or it would be fairly easy.

[US Iceman]

The Excel option will not work for me.


Why? All you have to do is as I suggested and then paste the equation (that Excel generates for you) into your PLC program. It will be as accurate as you need for the program.

[lwarren]

Why? All you have to do is as I suggested and then paste the equation (that Excel generates for you) into your PLC program. It will be as accurate as you need for the program.

Sorry Iceman, I did not realize that the formula from Excel would be exposed. Thanks!

I did find the formula on Duponts site, however this site will not let me post the link to it until I get over 15 posts.

[SteinarN]

Sorry Iceman, I did not realize that the formula from Excel would be exposed. Thanks!

I did find the formula on Duponts site, however this site will not let me post the link to it until I get over 15 posts.

You'd better start posting heavily :D

Can you send the link to me directly?

[nike123]

Sorry Iceman, I did not realize that the formula from Excel would be exposed. Thanks!

I did find the formula on Duponts site, however this site will not let me post the link to it until I get over 15 posts.

Of course you could!
Write like this: smmn://zzz.refrigeration-engeineer.com

[lwarren]

Ok, here it is:

abbc://yyy.refrigerants.dupont.com/Suva/en_US/pdf/h16419.pdf

This is actually the formula for pressure from temperature, which is what I asked for. However, I actually need to convert pressure back to temp so I will have to try to figure out how to redo the formula.

[nike123]

I think that any high school pupil good in mathematics can do that for you easy. Al relationships and constants are there, and it should be easy to derive formula for temperature.

[SteinarN]

I think that any high school pupil good in mathematics can do that for you easy. Al relationships and constants are there, and it should be easy to derive formula for temperature.

Can you do it? :D

[dogma]

Interesting problem. I made a heat pump where i wished to read out the condensing and evaporator temperature on the PLC from a pressure transducer. I was looking for a formula that i could program the plc with so it could convert pressure to temperature. I wasnt able to find a formula.

I doubt there exists a simple formula. At least if it should give an accurate result. If someone has a formula, simple or complicated, i'm also very interested in it.

Hi.

Where I use to work we used a program called MSR32.

We connected 2 pressure transducers and had a ability to run 38 thermocouples through 2 data loggers. There is a formula but I neglected to write any down. Our visiting
engineer wrote them into the program.

So sorry mate. Give Solkane in germany a call. One of there engineers could help.

[lwarren]

My math is pretty rusty, but Im sure I can eventually figure it out. If I get it figured out I will post it, but if someone beats me to it please post the formula.

Hey SteinarN, I found the formula, why don't you figure out how to reverse it for temp? LOL!

[nike123]

Can you do it? :D

Yes, I can, but I will keep it for my self.:D;):p

[SteinarN]

My math is pretty rusty, but Im sure I can eventually figure it out. If I get it figured out I will post it, but if someone beats me to it please post the formula.

Hey SteinarN, I found the formula, why don't you figure out how to reverse it for temp? LOL!


Dont laugh out to loud! Maby i do reverse it :cool:

[US Iceman]

Instead of rewriting the equation why not use a loop in the program? Use the pressure as an input and continue the loop until the temperature is within 0.001 of the results.

[SteinarN]

Instead of rewriting the equation why not use a loop in the program? Use the pressure as an input and continue the loop until the temperature is within 0.001 of the results.

I had a 15 min look at the formula. It is slightly over my head to revrite it. :( Came to the same conclusion of a loop. But i will have a look at the excell option also.

[US Iceman]

It has been some time since I have looked at curve fitting the pressure to temperature. I seem to remember the accuracy was not too good, but then... how good would you need it to be?

[SteinarN]

The temperature to pressure formula from Du Pont has an average deviation of 0,11%. I would be happy if i got +-0,5C in deviation. I'ts just for information, not a part of the regulation of the heat pump.

[nike123]

I send this formula to my cousin who is doctor of mathematic science and professor of mathematic at Zagreb university. I expect his answer in few days.

[US Iceman]

I would be happy if i got +-0,5C in deviation. I'ts just for information...


Then you may be satisfied with the Excel results. It has been some time since I did this, so you might want to check it yourself.

[Pooh]

which of the formulas in the document do you want reversing as I will see what I can sort out?

Ian

[US Iceman]

Ian,

The equation he is looking for is reverse of the temperature to pressure equation with all of the log base 10 fun stuff.

They are trying to get the saturation temperature from the pressure.

[nike123]

which of the formulas in the document do you want reversing as I will see what I can sort out?

Ian

This is formula!

http://farm3.static.flickr.com/2144/2341509074_39ab7fdbcc_o_d.jpg

[SteinarN]

This is formula!

http://farm3.static.flickr.com/2144/2341509074_39ab7fdbcc_o_d.jpg

We are looking for a formula which begins like this: T=???

"T" is the temperature and is the value we want to find.

"Psat" is the saturated pressure this formula will calculate when "T" is known.

We know "Psat" and want to calculate "T".

[nike123]

We are looking for a formula which begins like this: T=???

"T" is the temperature and is the value we want to find.

"Psat" is the saturated pressure this formula will calculate when "T" is known.

We know "Psat" and want to calculate "T".

I am aware of that! Look at post 20.:rolleyes:

[SteinarN]

I am aware of that! Look at post 20.:rolleyes:

Hmmm, cant find post 20 to be relevant to your post 29.

A only tried to be helpfull. ;)

[nike123]

Hmmm, cant find post 20 to be relevant to your post 29.

A only tried to be helpfull. ;)
Yes I am aware, but you quoting me and replying to me!;)
And I knew what we (in fact Iwarren) want from this formula ( picture in my post no.27) and I said, that I send that formula to my cousin (post 23) to derive what you stated in post 28


What a mess.:D:D

I see now, you looking in linear mode and I looking in hybrid mode.
Correcting this mess....:o

Corrected!:)

[US Iceman]

You guys just found one of the interesting features of this forum. I typically use the last post first view so I can read the most current post first.

When someone refers to a post use the post number, not by relative location or we will have a big mess!!!:D

[lwarren]

I send this formula to my cousin who is doctor of mathematic science and professor of mathematic at Zagreb university. I expect his answer in few days.

Thanks nike123, I was not looking forward to trying to figure that out. I appreciate the help from everyone here.

[lwarren]

This also has me confused; if you look at the Units and Factors for that equation it says that
T = temperature in deg. R = deg. F + 459.69 deg.

[Josip]

Hi all :)


maybe to see this:

http://www.fchart.com/ees.shtml#1.1

http://www.fchart.com/eesdemo.shtml

http://www.fchart.com/eesexmpl.shtml

hope this is of some help;)

Best regards, Josip :)

[US Iceman]

This also has me confused; if you look at the Units and Factors for that equation it says that
T = temperature in deg. R = deg. F + 459.69 deg.

When you are doing gas law or thermodynamic calculations you have to use absolute pressure and temperature.

This means your pressure transducer has to be absolute pressure (which you use in the equation) and then subtract 14.69 psi from it for gauge pressure (unless you are in a vacuum) for the display.

The same thing applies to temperature. You have to add 459.69 to your temperature readings then plug it into the equation (or subtract depending on what you are doing).

And you thought this was going to be easy???:)

[US Iceman]

Hi Josip,

EES is what I use for most information and calculations.:cool: It is a very good program, but a little expensive.

[lwarren]

Hey nike123, did your cousin ever figure out how re work that formula for temperature?

[nike123]

Hey nike123, did your cousin ever figure out how re work that formula for temperature?

He didn't answered yet!
I will remind him in few days. These successful youngsters today are pretty unorganized.:rolleyes:

[lwarren]

He didn't answered yet!
I will remind him in few days. These successful youngsters today are pretty unorganized.:rolleyes:

No problem, I appreciate your help.

[nike123]

Today I have conversation with my cousin and only he could came up with this problem is that he and his colleagues cannot derive formula from this one, and he advise me to take approach with Excel as one with most likely useful for your goal.
He told me that he will try to came up with some useful solution in near future and that he will discuss this problem with his colleagues.
I will keep you posted with development on this mater.

It seems that you make some shock in mathematical community. :D:D

[mcjo tech]

Are you searching for a computer program that has the ability to convert R22 temperature to pressure correlation? If so I have it. We can convert this in F to PSIG or in C to KPA. Operates on Windows based computers with Windows .net Framework 2.0 as pre-requisite operating system. We can also convert this same calculation for 28 other Refrigerants. For blends we output both Dew Point and Bubble Point readouts.

[SteinarN]

I'm searching for a formula to incorporate in a PLC program for conversion from pressure to temperature. Do you have such a formula mcjo tech?

[mcjo tech]

StienerN
If you could please explain your application and applications needs it would help me to understand what it is you may require. Is it the formula you require? Our software does not have a basic formula. Or is it just a program that is capable of these correlations? If it is something that there would be a demand for I am sure we could produce some custom software for this application.

Joe
ExactCharge Industries,Inc.

[SteinarN]

I've made a large heat pump controlled by a PLC with a HMI panel conected. It is installed HP and LP tranducers conected to the PLC, so it is possible to read out the pressures. But I would like it to be possible to read out the condensing and evaporator temperatures also. Thats the reason I need the formula to convert from pressures to temperatures, a formula which can be incorporated in the existing PLC program.

[mcjo tech]

Thanks,

I understand you application now. Our software for Pressure/Temperature correlations is not formula based but rather logic based so we would not be able to help in your application. I am sure that there is a formula which can accomplish your needs but we do the correlations by different means. Sorry we could not be of more help.

[Josip]

Hi, :)

I believe that formula is not simple, having 4 non linear basic formulas to calculate properties charts:rolleyes:.... in other hand if its so why to loose the time to make charts :confused:.... just give few formulas and we can calculate what we need;)

..... when you read those articles with so many equations, interpolations....information

http://www.imst-art.com/ficherosdesc/interpolation.pdf

http://nii.nist.gov/srd/REFPROP7doc1.pdf (1.69MB)

http://potomac.nist.gov/srd/PDFfiles/REFPROP8.PDF



EES is what I use for most information and calculations.:cool: It is a very good program, but a little expensive.

..... agree with you, after reading above articles I understood why EES are so expensive;) a lot of efforts.... but definitely worth that money....



.....It is installed HP and LP tranducers conected to the PLC, so it is possible to read out the pressures. But I would like it to be possible to read out the condensing and evaporator temperatures also.

.... why not use those pressures and in the same row show adjacent temperature for that pressure according to charts... then install another two temperature probes and make possible to read suction and discharge superheat what is more important ....



I am trying to write a computer program that calculates the pressure of R22 from a given temp, just like a p/t chart.

I have searche the web an have not been able to find a formula. Does anyone know what this formula is?


.... seems we cannot help much...when you read above articles I believe you will realize why, but still you can use the same way....

..... seems using properties charts and normal programing procedures is inevitable process;)

.... of course I can be wrong.... just my 2pence

Best regards, Josip :)

[nike123]

I've made a large heat pump controlled by a PLC with a HMI panel conected. It is installed HP and LP tranducers conected to the PLC, so it is possible to read out the pressures. But I would like it to be possible to read out the condensing and evaporator temperatures also. Thats the reason I need the formula to convert from pressures to temperatures, a formula which can be incorporated in the existing PLC program.

I downloaded software Wolframs Mathematica today and I am going to install it, and try to came up with something.:)

[Josip]

Hi, nike123 :)


I downloaded software Wolframs Mathematica today and I am going to install it, and try to came up with something.:)

what to say.... good luck;)

maybe to use one of those ... close to CoolPack;)

http://www.et.web.mek.dtu.dk/WinDali/Files/WinDali_2.10.ZIP
http://www.et.web.mek.dtu.dk/WinDali/Files/WinDali.pdf

http://www.et.web.mek.dtu.dk/WinDali/Files/RefEqns_3.10.ZIP

all above is here...

http://www.et.web.mek.dtu.dk/WinDali/Index.html

Best regards, Josip :)

[US Iceman]

Well it seems everyone is insisting on doing this the hard way. :confused: Try this...

Temp=-8.13681513E+01+3.20065359E+00*Press-3.81813098E-02*Press^2+2.96408154E-04*Press^3-1.29284314E-06*Press^4+2.90447694E-09*Press^5-2.61193736E-12*Press^6

Temp = °F (saturation temperature)
Press = psia (valid for range of 10 psia to 315 psia)

It may not be exact to 4 decimal places but it should be close enough.

Edit: this applies to R-22 only!!

[SteinarN]

Is this formula derived from Excel, Iceman?

[US Iceman]

Is this formula derived from Excel, Iceman?


Hi,

No it was generated with the EES program Josip mentioned in one of his posts. There will be some minor deviations in the data since this is very hard to curve fit.

To see if it meets the requirements the equation can be plugged into Excel and copied down a column. Put the pressures in a column to feed the equation and then check the generated numbers (temperature) to the pressures in a PT chart.

This should be within 0.5 degree (in F scale) or less as an approximate average. At the low end (around -25°F and below) the deviation jumps up to about 1-2°.

It's not exact, but it should be close enough.;)

[Josip]

Hi, US Iceman :)


Well it seems everyone is insisting on doing this the hard way. :confused: Try this...


.....Edit: this applies to R-22 only!!

.... seems it is in our nature :confused:

.... then again convert it to *C :D

Thanks US Iceman, (that sausage is too loooong) I will stick with charts ...faster and seems even more accurate.....


Best regards, Josip :)

[lwarren]

Wow, I never figured it would be this hard to get this formula. I would certainly never have even got close to figuring this out.

If your formula is as close as you say UsIceman, that will be more than close enough for me.

Thanks everyone for all of your help.

[US Iceman]

You can get something comparable to this using Excel also. I just happen to use EES more often and can get it done faster.

I could probably fine tune the equation for better accuracy if the range were not so large. There are other ways of doing this also, but this was the fastest, since I'm working for free!:D

[frank]

Looks like a simple Polynomial equation to 5 places :D

[lwarren]

US Iceman-

Well I am sure it is something I am doing wrong, but I cannot get your formula to come out right. I have even entered it in several online formula calculators and it does not come out right there either.

[jahangir.ahmad]

mmmmmmmmmmmm nice
thanks a lot josip nice websites

[US Iceman]

US Iceman-

Well I am sure it is something I am doing wrong, but I cannot get your formula to come out right. I have even entered it in several online formula calculators and it does not come out right there either.


I checked it before it was posted.:(

If you copied the equation into a cell in Excel an adjacent cell would be the pressure in psia. For example, copy the equation into cell A4.

=-81.3681513+3.20065359*A3-0.0381813098*A3^2+0.000296408154*A3^3-0.00000129284314*A3^4+0.00000000290447694*A3^5-2.61193736E-12*A3^6

A3 would be the input pressure in psia. The value calculated in cell A4 would be the saturation temperature for that pressure listed in cell A3.

If the equation is not working then you are either using gauge pressure or the decimal point was in the wrong position in interpreting the engineering notion used in the earlier post.

Copy the equation above and try it again.;)

[frank]

I checked it before it was posted.:(

=((-81.3681513)+(3.20065359*A3)-(0.0381813098*A3^2)+(0.000296408154*A3^3)-(0.00000129284314*A3^4)+(0.00000000290447694*A3^5)-(2.61193736E-12*A3^6))

A3 would be the input pressure in psia. The value calculated in cell A4 would be the saturation temperature for that pressure listed in cell A3.

Copy the equation above and try it again.;)
It just needed some brackets adding US Iceman. Works fine now. Straight forward Polynomial :D

[US Iceman]

Ooops.

Well, that's another possibility also frank. I did not think about operator precedent.

In Excel the equation worked just fine as posted, but the precedence of the math operations (addition, subtraction, etc.) could have been over ridden and caused some real issues also.

It is always fun trying to find these sort of errors in Excel. They will absolutely drive you nuts. However, one way of watching this is in the formula bar in Excel. When you place the cursor in the formula bar, the brackets change to different colors to show the matching bracket location.;)

[frank]

When you look in the 7th segment (2.61193736E-12*A3^6) you can note that your eqation has an Error-12 but when you copy and paste the formula into Excel (or OpenOffice Calc which I've just started using) the error disappears

Don't ask me to explain that one though ;)

Anyone else use OpenOffice?

[US Iceman]

E-12 is simply engineering notation. The negative 12 simply means the decimal point should move 12 places to the left. In effect the number becomes very small.

If the notion had shown E12, the decimal point moves 12 places to the right. Therefore the number gets very large.

I suspect this is what the Doh! was all about, but thought I should mention this for others who might not be familiar with this.;)

[lwarren]

Thanks guys for your time and help, and special thanks to you US Iceman for producing the formula.

I will give it another try.

[US Iceman]

How can I send you the invoice?:eek:








Just kidding.:p

[frank]

I suspect this is what the Doh! was all about, but thought I should mention this for others who might not be familiar with this.;)
No my friend, this was because I clicked on the reply button twice and double posted. :)

Thanks for the explanation of the E-12 though - as they say, you learn something everyday.

[lwarren]

Ok, let me ask some more stupid questions because I am still not getting this to work right. Your first posted equation is like this:

Temp=-8.13681513E+01+3.20065359E+00*Press-3.81813098E-02*Press^2+2.96408154E-04*Press^3-1.29284314E-06*Press^4+2.90447694E-09*Press^5-2.61193736E-12*Press^6

Your second posted equation starts out like this:

Temp=-81.3681513E The decimal has moved one place to the right. I tried it with both with unsucessful results, but which one is correct?

Keep in mind I am trying to put this in a custom application that is java based, not excel.

[US Iceman]

-8.13681513E+01 = -81.3681513

3.20065359E+00 = 3.20065359

3.81813098E-02 = 0.0381813098

2.96408154E-04 = 0.000296408154

etc, etc.

If you are doing this like above, then the simple answer may be Java can't do math equations like this, or, something else is wrong with how the equation is being formatted in the code.

This works in Excel, it works in Visual basic or any other code I have worked in, but I can't comment about Java. Sorry.

[lwarren]

Fair enough, just wanted to make sure I had all of the entries correct.

If anyone is up on java here is the formula so far:

double a = -81.3681513;
double b = 3.20065359;
double c = 0.0381813098;
double d = 2;
double e = 0.000296408154;
double f = 3;
double g = 0.00000129284314;
double h = 4;
double i = 0.00000000290447694;
double j = 5;
double k = 0.000000000000261193736;
double l = 6;
double aa = (b*A3);
double bb = (a+aa);
double cc = (c*A3);
double dd = Math.pow(cc,d);
double ee = (bb-dd);
double ff = (e*A3);
double gg = Math.pow(ff,f);
double hh = (ee+gg);
double ii = (g*A3);
double jj = Math.pow(ii,h);
double kk = (hh-jj);
double ll = (i*A3);
double mm = Math.pow(ll,j);
double nn = (kk+mm);
double oo = (k*A3);
double pp = Math.pow(oo,l);
double qq = (nn-pp);

getOut().setValue(qq);

[lwarren]

Well through the help of someone much smarter than me, It is finally working in my program. It is very accurate from 0- 300 psia,and psig.

Thanks to all who contributed here.

[shooter]

my plc has two types of tables inside
1 for linear and one for 10 points.
and yes i did use the formulas and checked them against the ashrae books.
the formula of iceman is the one described in ashrae.
because calculating is difficult in a plc and specially when converting from one type to the other now i am using tables again. is faster as the calculation and as we only use a small portion of the big graph better precision as the formula.
i do have all these formulas in SI not in us sorry

[SteinarN]

I have figured out a formula to convert absolute bar to degree Kelvin for R404 a. It is mostly within 0,5C accuracy between -47C and +18C. It is probably possible to get it even more accurate and extend the scale by adding several more + or - (P upx x x.x)

P is the pressure in absolute Bars. The result is degree Kelvin.
The formula looks like this:

Log(P;5)x32+226,2+(P up1.8x0.58)-(P up3x0.0187)

[TXiceman]

ASHRAE published the Equations of State for refrigerants. It is a lot easier to look there rather than doing curve fitting to data.\ unless you like the math and computer exercise.

Ken

[SteinarN]

I couldn't find the ASHRAE publication. I didn't find a curve fitting function in my open office calc either.

However after I realised I had to start with a log function it's actually quite easy to extend and adjust the formula.

I have time to spare and I sometimes enjoy ponder on different mathematical challenges. And this time I did learn something in the end :)

[TXiceman]

I searched and it may no longer be produced. I have an old copy somewhere....but can't locate it. Try contacting the refrigerant vendors as they did have this data available at one time as well.

Ken

[shooter]

I do have all the formulas in my computer for most of the refrogerants.

[SteinarN]

shooter, could you share the R404A formula with me?