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Old 10-25-13, 06:28 PM   #8
Lex Parsimoniae
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Join Date: Feb 2009
Location: Woburn, MA
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Default Solar? Too many clouds!

The forecast didn't work out.. Maybe tomorrow we can get some real sun..

Pretty cool and cloudy for most of the day. The PV heated water tank climbed in unison with the attic.
But, it didn't cool off as fast. Again, the basement temp was pretty flat.
I was able to tweak the program a bit and got the fans turning off & on nicely.
I used a setpoint with only a 3 deg differential (warmer in the attic)
and tried a 5 deg diff later in the afternoon. I can see that a higher
number is going to be needed.. Maybe 8 or 10 degs F.
Air that is just slightly warmer than the basement has very little impact.
I could feel very little warmth down there. Barely noticeable.

I can't wait to see 80s or 90s in the attic. That's going to warm up the basement stairs, at least.

I did some measurements of the slab.. It's pretty uniformly cold <60F.
Warming up the air in the basement looks like an uphill battle..

I've had the A7 unplugged, for a few days, and with little sun to heat the
water tank, it's been dropping a lot. But, it's a good indicator of sunshine.

One thing surprised me. Even when the sun was dim, sucking the air
out of the attic, didn't really drop the temperature up there very much..
I had expected to see a pretty rapid drop in air temp (in the peak area)
when the blower started moving 200cfm downstairs..

But, that wasn't the case. The temp drop was pretty slow.
I think the main reason it dropped below the set-point,
was due to the lack of solar..

Yesterday, early in the morning, when the sun first hits the roof, I was out there with my IR scanner.
I measured 85F on the singles. But, when I went inside and scanned the
attic boards near the peak, they were only in the 50s..
This lag-time (plus the observation above) leads me to think
my roof is a pretty good thermal mass.

~~~~~~~Edit 9:43 AM
It's sunny now, but it looks like a ton of clouds are rolling in..
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My hobby is installing & trying to repair mini-splits
EPA 608 Type 1 Technician Certification ~ 5 lbs or less..

Last edited by Xringer; 10-26-13 at 08:44 AM.. Reason: Weather report
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