Measuring U-Value: Need Help with 3rd Grade Science Fair

Singh_3

I once met a window sales rep. who used a heat lamp to simulate heat/sun.
He compared his windows to the competition, you placed your hand on the other side if the window sample, his windows were cool, the others let the heat thru.
Perhaps you and your son could use a heat lamp, instead of window , using insulation. Sounds like fun, good luck.

larry

I was talking with my son in 3rd grade about how it might be interesting to take several different insulation building materials and try to measure which ones are most effective. He thought it was a great idea and wants to it as a science fair project.

Now I imagine the methods to do this "for real" are complicated and expensive beyond belief. Can anyone suggest a good methodology which might be intuitive enough for a 3rd grader to use and gain some insight?

Not sure if this would do it, but was thinking we might build a wooden panel the size of one of our window openings with the sample materials built into sections of the panel and then mount the panel into the window opening. Would spray paint a black target area on each material section of the panel, and then use an IR thermometer to measure the surface temperature differential across the materials.

Any and all ideas are welcome, but want him to start the project very soon as we are getting some single digit cold nights this coming week which might make for some good natural testing.

Vermonter_2

Ice

A kid I went to high school with won his science fair with this project by building a box that he could fill with ice. He could then wrap the box with the insulation he was testing, 4 inches thick (or whatever you choose) for each material. I guess you could use a glass too if you want, or a tall clear tube or... well whatever you've got around the house. If I were doing it I'd try to use something I can see through since opening a lid will make it difficult to time and will throw off the results. I'd also try to use something I had 10 or 20 of so I could test all the different materials at once.

By measuring the length of time it took the ice (12 cubes or 1 kilogram or whatever...) to melt you can figure out about how well the material insulates.

He compared the time with insulation to the time it took without any insulation.

You've just got to pay attention to a few things: the amount and temperature of ice is constant at the start of every test and the ambient temperature in the room is fairly steady too.

[Deleted User]

R you kidding me???

Somewhere, in the vast expanse of the Eatherton Archives, I have a graphic made in the fourtys that showed how to determine a walls R value based on a shielded thermistor on the inside of the wall, and a thermistor on the outside of the wall. Look pretty interesting, and actually had a formula for determining R value. Someone here on teh wall (bob warner?) donated it to the cause. Anyway, I decided to do my own study to see what R value looked like in real time, so I took one of my data loggers with 3 sensors, taped one to the inside of the outside wall, covered it with 1 square foot of R 5 XPS insulation, hung one sensor about 1 foot inside the wall, and one sensor outside the wall and set the logger to record temepratures every 15 minutes. I turned the heat source for that room off and let the data logging begin.

Attached, you can see what R value "looks like" in "real time"...

Enjoy!

ME

EDIT: EUREKA!!! Ain't the search function on these newfangled machines somethin else! See attached.

ME

larry

Thank you, but have a question...

I tried out the foam block on the wall method last night and have a question. The results of the formula aren't making sense to me.

The formula says:

R(wall) = R(foam) x [temp(inside) - temp(junction)] / [temp(junction) - temp(outside)]

I measured:

temp(inside) = 68

temp(outside) = 29

temp(junction) = 65

R(foam) = 5

Plugging this in you end up with R(wall) = 0.4

Also tried a window...

temp(inside) = 68

temp(outside) = 29

temp(junction) = 42

R(foam) = 5

This gave R(window) = 10

These are obviously not correct. What do you think I'm doing wrong?

[Deleted User]

Ya know....

I had similar experiences and gave up on the math. I know for a fact that I was dealing with an R-13 wall.

What I found most interesting was the visual fact of time lag as a constant.

Now, I didn't invent that formula, and the person who donated it to the cause would and has never steered me wrong. But, it seems to me that what you were looking at is more of a U factor than an R value. The inverse of U = R. So if we take 1 and divide it by the numbers you came up with, your wall would have an R value of 2.5 and your window would have an R value of .10.

Does this make any sense and get you any closer to what you think you have?

Math wasn't (and still isn't) one of my stronger suits...

ME

PS, If my memory serves me correctly, that forumla was provided by the manufacturer of the temperature sensor/volt ohm meter (Fluke?).

ME

realolman

I think

something like the lamp and box that you stuck your hand in, and happened fast would be the best route for 3rd graders... or corporate managers.


Sorry 3rd graders, I apologize for the insult.

mtfallsmikey

Isn't there a

Conversion chart to convert U value to R-value? I ran across this problem some years ago when trying to do a heat loss/gain on a house with fresh replacement windows.My feeble mind is going astray again, I guess!

jp_2

simpler yet mikey

R = 1/U

OR

U= 1/R

larry

Another approach

After doing some more research I saw the Rob Falke of the NCI had developed a quick and dirty method for determining R-Value based on the same three basic measurements as Mark's approach. A quick email to Rob brought a nearly instant response with some info that helped a great deal. The method of measurement is a bit different as you just shoot the surfaces with an IR thermometer (compensating for emissivity by placing tape on glass). To get room temp you take some paper and hang it at the same height near (but not touching) your wall/glass/door measurement.

We decided to do our first test on a know quantity. I cut a piece of 1" (R=5) rigid foam insulation to the same size as one of our window openings and taped it in place creating an air seal. We let it temperature stabilize for about 1 hour and then my son used the IR thermometer to shoot the surfaces. Taking the results and consulting Rob Falke's chart (uses difference between room temp and inside surface temp and outside surface temp) it plotted at R=5.5. OK, that result was WAY better than I expected. Given the simplicity of this method, rather than fabricating samples and mounting them in the window like the rigid insulation, we decided to just measure some real life stuff in our house and a neighbor's house. In a more expected manner, other measurements give a feeling for the relative material R-values and aren't as perfect as the first test. Nevertheless he is collecting a pile of data (shooting an IR thermometer is like laser tag to an 8 year old).

larry

You give corporate managers WAY too much credit.