R you with me... (ME)

Mark Eatherton1

I put the Hobo data colector back to work last week, and just got the chance to interpret the data and convert it to graphic form.

I'm still struggling with the formula portion of it (math was NOT one of my strongest suites in school) and will forward that information to you as it becomes more clear.

In the mean time, I graphed the temperatures of the OSA, a North R-12 (approx.) walls "shielded" surface, and the room air temp of a relatively unheated (NE corner) room of my home.

I used my infrared scanner to make sure the "wall temp" sensors were placed in the very middle of the stud bay, and not near any structural influences (studs) that might affect the actual surface temperature.

The sensor was covered by 1" of foam (r-5), 1 foot square with the sensor placed in the very center to make sure it was seeing a true, un-influenced (relatively so) wall surface temperature.

The room air temp sensor was suspended about half way between the ceiling and the floor, about 1 foot from the outside wall.

One of the interesting things that shows is the lag in temperature movement of the room air and wall surface temperature compared to the outside air, which is the major driving influence on the wall and room air temps.

I guess this is what "R value" looks like in real time. I think it is also influenced (obviously) by the flywheel mass effect of the room as a whole.

In calculating the R value based on the formula that was given here at the wall (R wall = R foam x inside temperature - junction temperature divided by junction temperature - outside temperature), it varies all over the place between fractional numbers, all the way up to 3. something as it got warmer outside.


I'm digging into the formulas provided by ASHRAE in the 1989 Fundamentals book, but if there is some engineering type out there that would like to look at the raw digital data, please feel free to drop me a line and I'd be glad to let you cross your eyes over this thing...

Any input Wallies?

Graphics didn't transfer as clearly as I would have liked, so...

Blue = OSA
Purple = wall surface temp
Yellow = room air temperature

ME



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Dave Yates (PAH)

Humnnnn

Interesting graph. You mentioned this is an unheated space and it looks like the MRT slightly offsets the wall deviations, which doesn't surprise but, rather, confirms previously held gut feelings regarding heat losses and their progression. It would be interesting to compare with a heated space and a monitor recording lead/lag on Btu loading needed to offset the outdoor temps while maintaining the greater delta-T that the wall divides. Then again, maybe I'm missing the point?

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[Deleted User]

You da straw!!

Thanks for your input Dave. Funny how we think alike eh...

I can turn the heat on in this room, only problem is, I can't reproduce the OSA conditions.

But if you ask, I can do...

And thank you for asking!!

I wish I had about four more HOBO's, then I could look at what the over all contribtution of the heated wall connections to the unheated space contribution really are.

Funny what happens when you let the mind roll...

ME

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Bob Tonner

It seems to me...

It seems to me that your data supports my argument that outside air is not neccesarily the only criteria that should be taken into consideration with regard to boiler reset. More specifically, that heat-loss (Dynamic Demand) should be the only critera for resetting a boilers operating limits and differential.

Thanks for the research Mark. I normally have to pay expensive engineers and lab time for this kind of information. If you are willing to share, I would love to get a copy of your spreadsheet file.

Best regards

Bob Tonner, President, InfinityLab Inc.