Calculating water temps for radiant heat(not using the charts)

Josh_10

Let's just say out of the hydronic heating "Bible."

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Greennmann

calculating water temps for radiant systems(not with the charts)

Is there a easy to use formula that I could plug these variables into to find the water temp required for a radiant system? Required space temp, Temp below the radiant floor, R value above pipe, R value below pipe, BTUH per ft2

Brad White_9

One easier way

is to use the Rad Pad. I recently posted a reply extolling the virtues of this tool.

So many of the variables are interactive so it is difficult to find a "simple" formula that gives a direct answer. Change one variable (tube spacing, intermediate R-value for examples) and the other variables change as well. Type of tubing and how employed also are important factors.

Josh_10

I'll add my endorsement to what Brad just said. Get a Rad Pad.

http://www.heatinghelp.com/shopcart/product.cfm?category=5-40

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Greennmann

I'm going to get the rad pad it look pretty cool. But I'd still like to know that formula with all the variables well defined.

If I know my thermal transfer coefficient will that help?
2 btu/h/ft2/f*

Also I'm only interested in three tube spacings 7", 8", 12"

Josh_10

Boy... I am un-aware of any "simple" formula. There are way too many variables. I have enclosed a spreadsheet that you are welcome to use. Maybe after seeing it you will understand how many variables there actually are.

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Brad White_9

Without 'enabling' you

What is your BTU per SF calculated load? Your target space temperature?

Say you want to maintain 68 degrees F. and have a BTU per SF load of 25 with a floor R-value of 2.0 above the tubes (and assuming well insulated to say R-19 below):

According to my Rad Pad, your floor temperature would need to be 81 degrees F. To achieve that floor temperature with an intervening R of 2.0, you would need a water temperature of 118.2 degrees F.

There is a snapshot and possible place to start...

Greennmann

thanks man that exactly what i needed i'll be able to use that sheet.

the youngster haha i bet i got you beat i'm 23

Greennmann

thanks everyone i'm good now the youngster hooked me up with a spread sheet that clarified this subject for me

Brad White_9

But still buy a Rad Pad you cheapskate

Help Dan deliver the Dowry!

Cheers!

Brad

Josh_10

That's great! I bet you are starting to become a great installer. Keep going man. This site is great for someone like yourself. Just remember to stay humble and listen and you will get alot out of being a "Wallie." These guys are like big brothers to me.

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Unknown

What assembly conductivity does the radpad assume?

Is that appropriate only for slab? Obviously your suspended tube vs your slab system are going to use different water temps.

Unknown

Josh,

Where are you getting the K-values on page two? You have interested me mightily there...

Brad White_9

Depends

You have to figure that out for each project. While they do give guidelines, I use ASHRAE data myself. There is a slide/curve for that portion of the work, if I grasp your question correctly. The Rad Pad is a good generic tool. If using a system like Upponor/Wirsbo, I would defer to the manufacturer-specific information where available.