Results 51 to 77 of 77
Thread: R22 Temp To Pressure Formula
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30-03-2008, 04:17 PM #51
Re: R22 Temp To Pressure Formula
Is this formula derived from Excel, Iceman?
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30-03-2008, 04:38 PM #52
Re: R22 Temp To Pressure Formula
Originally Posted by SteinarN
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.If all else fails, ask for help.
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30-03-2008, 05:01 PM #53
Re: R22 Temp To Pressure Formula
It's impossible to make anything foolproof because fools are so ingenious...
Don't ever underestimate the power of stupid people when they are in large groups.
Please, don't teach me how to be stupid....
No job is as important as to jeopardize the safety of you or those that you work with.
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30-03-2008, 07:12 PM #54
Re: R22 Temp To Pressure Formula
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.
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30-03-2008, 07:24 PM #55
Re: R22 Temp To Pressure Formula
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!If all else fails, ask for help.
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30-03-2008, 09:52 PM #56
Re: R22 Temp To Pressure Formula
Looks like a simple Polynomial equation to 5 places
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15-04-2008, 02:31 AM #57
Re: R22 Temp To Pressure Formula
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.
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15-04-2008, 11:47 AM #58
Re: R22 Temp To Pressure Formula
mmmmmmmmmmmm nice
thanks a lot josip nice websites
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15-04-2008, 03:41 PM #59
Re: R22 Temp To Pressure Formula
Originally Posted by lwarren
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.If all else fails, ask for help.
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15-04-2008, 04:01 PM #60
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15-04-2008, 04:13 PM #61
Re: R22 Temp To Pressure Formula
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.If all else fails, ask for help.
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15-04-2008, 08:41 PM #62
Re: R22 Temp To Pressure Formula
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?
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15-04-2008, 09:44 PM #63
Re: R22 Temp To Pressure Formula
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.If all else fails, ask for help.
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16-04-2008, 02:29 AM #64
Re: R22 Temp To Pressure Formula
Thanks guys for your time and help, and special thanks to you US Iceman for producing the formula.
I will give it another try.
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16-04-2008, 03:04 AM #65
Re: R22 Temp To Pressure Formula
How can I send you the invoice?
Just kidding.If all else fails, ask for help.
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16-04-2008, 08:35 PM #66
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18-04-2008, 03:29 AM #67
Re: R22 Temp To Pressure Formula
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.
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18-04-2008, 03:47 AM #68
Re: R22 Temp To Pressure Formula
-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.If all else fails, ask for help.
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18-04-2008, 02:31 PM #69
Re: R22 Temp To Pressure Formula
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);
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19-04-2008, 03:35 PM #70
Re: R22 Temp To Pressure Formula
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.
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02-06-2008, 04:19 PM #71
Re: R22 Temp To Pressure Formula
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 sorrycomputer shooter
paul deelen
+31653300739
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27-11-2008, 12:48 PM #72
Re: R22 Temp To Pressure Formula
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)
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28-11-2008, 03:21 AM #73
Re: R22 Temp To Pressure Formula
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
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28-11-2008, 03:06 PM #74
Re: R22 Temp To Pressure Formula
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
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29-11-2008, 03:04 AM #75
Re: R22 Temp To Pressure Formula
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
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29-11-2008, 07:18 PM #76
Re: R22 Temp To Pressure Formula
I do have all the formulas in my computer for most of the refrogerants.
computer shooter
paul deelen
+31653300739
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29-11-2008, 08:46 PM #77
Re: R22 Temp To Pressure Formula
shooter, could you share the R404A formula with me?
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