# ASHRAE Superheated tables



## sayed (Oct 20, 2017)

i was working on the PPI practice book and it has a solution that simply goes "using super heated table for ammonia.."

where is this table? MERM does not have it. And i could not find it on the ASHRAE books (i have all four)

any help?


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## Slay the P.E. (Oct 20, 2017)

You can find that in the back of some thermodynamics textbooks.  If you don’t have any, then use a P-h diagram which is more easily available than a table.

We have one here for free https://www.slaythepe.com/free-resources.html


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## MikeGlass1969 (Oct 21, 2017)

If you must have a table the iiAR.org ammonia refrigeration data book would have this information.   BUT it is expensive.


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## sayed (Oct 21, 2017)

Slay the P.E. said:


> You can find that in the back of some thermodynamics textbooks.  If you don’t have any, then use a P-h diagram which is more easily available than a table.
> 
> We have one here for free https://www.slaythepe.com/free-resources.html


the P-h diagrams don't have entropy. It makes me wonder how the problem was solved. This was Q6 in chapter 33



MikeGlass1969 said:


> If you must have a table the iiAR.org ammonia refrigeration data book would have this information.   BUT it is expensive.


this is insane. $2500 for a book?


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## sayed (Oct 21, 2017)

the HVAC board is very lonely here

i guess it's not too hard since 80% pass :mellow:


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## P-E (Oct 21, 2017)

I looked in my fundamentals handbook 2005 chapter 20.  There's a p-h graph that shows superheated region for R717 aka ammonia.


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## sayed (Oct 21, 2017)

P-E said:


> I looked in my fundamentals handbook 2005 chapter 20.  There's a p-h graph that shows superheated region for R717 aka ammonia.


thanks

in my edition it has "space air diffusion" info

i suppose the p-h diagrams should suffice. maybe that was just a weird ppi problem


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## Slay the P.E. (Oct 21, 2017)

sayed said:


> the P-h diagrams don't have entropy. It makes me wonder how the problem was solved. This was Q6 in chapter 33


P-h diagrams do have lines of constant entropy. You use them to represent the compression process. The one in our website is color coded so you can find the constant entropy lines easily.


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## sayed (Oct 21, 2017)

Slay the P.E. said:


> P-h diagrams do have lines of constant entropy. You use them to represent the compression process. The one in our website is color coded so you can find the constant entropy lines easily.


thanks

not sure how i missed that. I guess that's something that the ppi class didn't go over (using s on p-h diagram)


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## MikeGlass1969 (Oct 21, 2017)

sayed said:


> the P-h diagrams don't have entropy. It makes me wonder how the problem was solved. This was Q6 in chapter 33
> 
> this is insane. $2500 for a book?


Just $200...   PSM and RMP are they expensive ones...

http://www.iiar.org/IIAR/WCM//ItemDetail?iProductCode=01BOO-EN0101


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## MikeGlass1969 (Oct 21, 2017)

People make hundreds of thousands of dollars off those PSM and RMP books, every year....   $2500 seems like a good investment


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## Slay the P.E. (Oct 21, 2017)

sayed said:


> thanks
> 
> not sure how i missed that. I guess that's something that the ppi class didn't go over (using s on p-h diagram)


Please don't walk into that test room without knowing how to represent a simple vapor compression refrigeration cycle in a _P-h_ diagram. This is an absolute must for both the Thermal Fluids &amp; Systems and the HVAC&amp;R exams.


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## sayed (Oct 21, 2017)

Slay the P.E. said:


> Please don't walk into that test room without knowing how to represent a simple vapor compression refrigeration cycle in a _P-h_ diagram. This is an absolute must for both the Thermal Fluids &amp; Systems and the HVAC&amp;R exams.


yeah, going through these problems, i definitely need to keep in mind what process it is. i kept assuming it remained saturated and was getting the wrong answers.

cranking out some more problems should get me ready


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## sayed (Oct 21, 2017)

MikeGlass1969 said:


> People make hundreds of thousands of dollars off those PSM and RMP books, every year....   $2500 seems like a good investment


probably a huge volume on info no one reads or uses


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## Audi Driver P.E. (Oct 23, 2017)

There is a chart in my thermo book.  I definitely recommend bringing course books to the exam with you.


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## NHEngineer037 (Oct 25, 2017)

ASHRAE Fundamentals Chapter 30 has all the charts you need for refrigerants... all of them.

When I start a refrigeration problem, the first thing I do is sketch the shape of the process that you would on the P-H curve, on my sheet of scrap paper.  You know...a rectangle with the right side of it sloped.  Then as I read the problem, I quickly jot on the diagram the temperatures given, the pressure (corrected for psia if given in psig) and make note of superheat or sub cooling by putting a little tick on the drawn box with an arrow pointing to it saying something like "20 F superheat".  Depending on the question, I figure out what enthalpy values I need to figure out and I write them out on my diagram.  Then I find the appropriate chart in ASHRAE Chapter 30 and just figure it out.  The quick napkin sketch makes messing up or forgetting some provided information a non-issue.  They are pretty simple once you get the hang of it.


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## namod65 (Oct 25, 2017)

NHEngineer037 said:


> ASHRAE Fundamentals Chapter 30 has all the charts you need for refrigerants... all of them.
> 
> When I start a refrigeration problem, the first thing I do is sketch the shape of the process that you would on the P-H curve, on my sheet of scrap paper.  You know...a rectangle with the right side of it sloped.  Then as I read the problem, I quickly jot on the diagram the temperatures given, the pressure (corrected for psia if given in psig) and make note of superheat or sub cooling by putting a little tick on the drawn box with an arrow pointing to it saying something like "20 F superheat".  Depending on the question, I figure out what enthalpy values I need to figure out and I write them out on my diagram.  Then I find the appropriate chart in ASHRAE Chapter 30 and just figure it out.  The quick napkin sketch makes messing up or forgetting some provided information a non-issue.  They are pretty simple once you get the hang of it.


Pretty much exactly what I've been doing. I have a digital copy of the the Fundamentals and printed out the refrigeration diagrams chapter and bound it separately for quicker use. I can't imagine you'll need anything more than this. It even has the superheated data tabulated for R-134a which could make it easier to find those enthalpy points at the compressor. It's sometimes hard to get accurate when following the constant entropy lines up to the compressor discharge.

I hope there's a ton of these problems on the test Friday, like on the practice exams. They're super easy once you do a few.


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## NHEngineer037 (Oct 26, 2017)

namod65 said:


> Pretty much exactly what I've been doing. I have a digital copy of the the Fundamentals and printed out the refrigeration diagrams chapter and bound it separately for quicker use. I can't imagine you'll need anything more than this. It even has the superheated data tabulated for R-134a which could make it easier to find those enthalpy points at the compressor. It's sometimes hard to get accurate when following the constant entropy lines up to the compressor discharge.
> 
> I hope there's a ton of these problems on the test Friday, like on the practice exams. They're super easy once you do a few.


There are super heated tables?  What page are those on in Fundamentals?


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## namod65 (Oct 26, 2017)

Page 30.18 of the 2013 edition. But it's just for R-134a. So we have to do it graphically for any other refrigerant.


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