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Thor

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Reply with quote  #21 

"Magic 1.08"

all based on being- @ sea level, @70 degrees F, @ zero humidity. 

The 1.08 multiplier is based on the weight of standard air (0.075 pounds of air per cfm) x the specific heat of air (0.24 Btu per pound) x minutes in an hour (60). For best accuracy, this 1.08 multiplier does need to be adjusted for higher elevations and temperatures above or below 70°F.

The number is not really constant because the volume of the air varies with altitude, temperature, and humidity. A change in any of these variables changes the density of air, which in turn changes the "magic number." The factor 1.08 in this formula is only accurate for dry air at 70°F at sea level. For example, 1.08 really does not work with flue gas or airflow in freezers because the air volume has changed, which changes the convenience factor. Similarly, 1.08 does not work in Denver because the altitude changes the air pressure, changing the density. Even the relative humidity changes the factor. Changing the relative humidity to 50% changes the air volume, which changes the factor.

Lets look at some examples. 0°F air at sea level has a density of 0.086 pounds per cubic foot, while 300°F air at sea level has a density of 0.052 pounds per cubic foot. Instead of the commonly quoted 1.08, these densities produce factors of 1.24 for 0°F air and 0.746 for 300°F air. If the air is 70°F but at 5000 feet elevation, the factor becomes 0.9 because the air density has changed due to the increased elevation. Even changing from 0% relative humidity to 50% relative humidity changes the density to 0.0741 instead of 0.0745 (the 0.075 for 70°F air is rounded). This changes our convenience factor to 1.07.

https://wahiduddin.net/calc/calc_da.htm


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My little boy calls me Thor! [biggrin]
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gbwillson

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Reply with quote  #22 
Thanks for the detailed explanation Thor. I know of 3 ways to calculate BTU output and they all give pretty much the same results, even the various fudge factors. 

Greg in MN
Julian Jameson

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Reply with quote  #23 
Quote:
Originally Posted by gbwillson
Thanks for the detailed explanation Thor. I know of 3 ways to calculate BTU output and they all give pretty much the same results, even the various fudge factors. 

Greg in MN


Some of the associated math is listed on the company's website, if you're interested in having a scan it's here: http://www.greenhillenvirotechnologies.com/about-closed-loop-solar-air-heaters/solar-heating-math
mranum

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Reply with quote  #24 
Thanks for the link. That helps explain things for me. [thumb]
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gbwillson

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Reply with quote  #25 
Julian-

The link takes me to a page with a calculator, but doesn't allow any data to be entered. 

Greg in MN
Julian Jameson

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Reply with quote  #26 
Quote:
Originally Posted by gbwillson
Julian-

The link takes me to a page with a calculator, but doesn't allow any data to be entered. 

Greg in MN


The calculator should be listed at the bottom of this page: http://www.greenhillenvirotechnologies.com/android-and-java-apps/okapi-viewer-apps/solar-heater-output-calculator

That calculator is one that you have to download to use. Right at the bottom of the page, you should be able to see a link to download the SolarHeaterOutputCalc.jar file. To download it you have to click on the tiny blue arrow on the right. As it runs in a Java environment, you'll also need the correct version of Java installed on your PC (if it's not already there). 
Bert

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Reply with quote  #27 
Matt,

Your project looks very well done and seems to be going along fast.
Looking forward to seeing how it performs for you.
I will be starting my first ZP in a few weeks or so.
Good luck!

Bert

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Bert K.
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gbwillson

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Reply with quote  #28 
Thanks Julian-

For anyone like myself who is running on a Mac or just wants an Excel format, use the file below:

Greg in MN

xlsx SS SAH Output Calculator.xlsx     

It may look complicated, but the only cells you need to fill in are the 4 orange ones.

mranum

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Reply with quote  #29 
Thanks Bert. One thing is for sure the results are pretty impressive. Its no "furnace" but it does exactly what it is intended to do, be an economical suplimental heat source.

I encourage you to post your progress. Very cool to follow along with people and see their individual results. [thumb]

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Bert

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Reply with quote  #30 
Great to hear the results.

BTW I will be posting as I go on my next collector. It will be fun. I have to keep pitching the benefits to my wife. She's mainly onboard.

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Bert K.
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