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Author Topic: Indoor & Outdoor air enthalpy  (Read 382 times)

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Offline HilltopJim

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Indoor & Outdoor air enthalpy
« on: November 28, 2017, 01:08:18 PM »
Could we have WD report indoor and outdoor air enthalpy? Is there a way that one can enter a complicated function into WD and have the result reported? Or could a tag be created that reports enthalpy.
Using the difference between the two one can decide whether to open the windows or run the air conditioning. I'd also like to see how the enthalpy effects comfort.  #-o
Jim

Offline Weather Display

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Re: Indoor & Outdoor air enthalpy
« Reply #1 on: November 28, 2017, 11:31:46 PM »
do you have any formulas?

Offline niko

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Re: Indoor & Outdoor air enthalpy
« Reply #2 on: November 29, 2017, 12:30:40 AM »
I thought you had done something with indoor/outdoor temp difference before, but I don't find a tag or the thread on here :?

Enthalpy in wikipedia.
« Last Edit: November 29, 2017, 12:33:11 AM by niko »

Offline Weather Display

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Re: Indoor & Outdoor air enthalpy
« Reply #3 on: November 29, 2017, 08:30:29 PM »
I don't think WD can work out the energy of a system

Offline niko

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Re: Indoor & Outdoor air enthalpy
« Reply #4 on: November 29, 2017, 11:08:20 PM »
That was my reaction after reading up on enthalpy  :(

Offline HilltopJim

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Re: Indoor & Outdoor air enthalpy
« Reply #5 on: November 30, 2017, 02:21:30 PM »
Thanks to all who have tried to help. I found this for having Excel calculate an approximate enthalpy. I have it entered in a spread sheet. I have WD sending current indoor and outdoor temperature and humidity to my own website. The spreadsheet scraps the indoor and outdoor  temp and humidity from the website and calculates the entropy.
Here is the article I found on the internet:
temperature and relative humidity.

    By Engineer Joe, www.mrexcel.com
    View Original
    July 29th, 2015

    This isn't actually a question. I worked for a while to come up with a feasible formula working between 0 and 100F to provide an enthalpy value based on dry bulb temperature and relative humidity. It uses a polynomial model to match Psat to temperature in order to avoid referencing a table (I wanted it to be able to work by a simple math equation...no steps.) You can see the polynomial in it's own bracket with several terms raised to the 4,3,2,1st order. That's the approximation model. It's >99% accurate between 0 and 100F. I'm posting here so that if someone googles the key terms, maybe this will pop up for them. I've googled this several times before with no results that were any good. So, future HVAC/excel users, here ya go!

    h = 0.24*OAT+(0.6219)*(0.01*(0.000000007401234*OAT^4 - 0.000000493526794*OAT^3 + 0.000071281097208*OAT^2 - 0.000489806163078*OAT + 0.039762055806989)*RH)/(14.7-(0.01*(0.000000007401234*OAT^4 - 0.000000493526794*OAT^3 + 0.000071281097208*OAT^2 - 0.000489806163078*OAT + 0.039762055806989)*RH))*(1061.2+0.444*OAT)

    Entalpy: h is in btu/lb(dry air)     

    OAT: Temperature in F     

    RH: Relative Humidity as a percentage. (e.g. 40% RH would just be 40, not 0.40)

    Obviously, plugging this into excel, you would replace references to OAT and RH with cell references.

    Have a nice day! And yes, I'm aware I didn't need to use 15 sig figs. i went into the trend in the chart and just started clicking the decimals button until i got tired and then copy/pasted.


Offline niko

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Re: Indoor & Outdoor air enthalpy
« Reply #6 on: November 30, 2017, 02:48:00 PM »
Thanks  :)  I'll work through that after breakfast and a few coffees...

Do you have a website? If so you could easily calculate/display that with a small .php program which would get the data from the clientraw.txt file.

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Re: Indoor & Outdoor air enthalpy
« Reply #7 on: November 30, 2017, 05:23:59 PM »
it looks similar to the heat index formula at first glance

Offline niko

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Re: Indoor & Outdoor air enthalpy
« Reply #8 on: November 30, 2017, 05:30:15 PM »
Watch out for Excel's order of operations  :wink:

Offline niko

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Re: Indoor & Outdoor air enthalpy
« Reply #9 on: November 30, 2017, 05:50:45 PM »
Do you have a working link to the mrexcel article? I couldn't find enthalpy, entropy, or temperature and relative humidity in the search on that site  :(

Offline Murry Conarroe

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Re: Indoor & Outdoor air enthalpy
« Reply #10 on: November 30, 2017, 07:46:48 PM »
Do you have a working link to the mrexcel article? I couldn't find enthalpy, entropy, or temperature and relative humidity in the search on that site  :(

https://www.mrexcel.com/forum/excel-questions/871843-excel-formula-calculating-airs-enthalpy-dry-bulb-temperature-relative-humidity.html
Murry

Offline niko

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Re: Indoor & Outdoor air enthalpy
« Reply #11 on: November 30, 2017, 08:18:25 PM »
Thanks Murry  :D