Posted by VaTom on March 06, 2014 at 11:49:49 from (70.32.203.33):
In Reply to: Re: Solar heating? posted by Bret4207 on March 06, 2014 at 09:39:23:
Excellent questions Bret.
I know Nori (Washington state), far as I know she never convinced her husband into a PAHS build. She was shocked when I mentioned that I quantify heat for PAHS, she'd never heard of that. I know her through alternative-architecture circles. That excerpt is out of the book I mentioned.
Wish I could tell you exactly how the Missoula house worked. Unfortunately, John Hait never provided enough data. He said it was due to summer heat going into the mass. Missoula only has 256 cooling degree-days.
You're correct, the only way to determine what's happening is to quantify the heat movement. My engineering manual's old enough to use BTUs.
If I was only charging my mass during sunny days, it wouldn't work very well. I have 1131 cooling degree-days, which puts heat into my mass 24/7 all summer, while everyone else is buying electricity for air conditioning.
This is precisely why I mentioned that the design needs to be tweaked for the local climate, preferably even the micro-climate of the house site. I go month by month to determine which direction heat is flowing, and quantifying it.
PAHS is a heating/cooling system that, like any other heating/cooling system, should be sized to the application. Hait did not do that. I do. I built my place on the assumption that no matter what I got it would likely be better than anybody else's around here. That proved true, but the houses I help design work better than mine.
Out of fear of mold incubation, I didn't use earth tubes. The house still works. I'm simply charging my mass, and depleting it, through my buried walls, floor, and roof. Earth tubes are actually more effective in low-mass houses. I'm no longer afraid of them in a hot humid climate, but that required some experience. The Atlanta house got them.
Hait made some errors, assumptions (I think) that were not based on empirical evidence. One I recently corrected for a guy in New York wanting to sell geodesic dome kits for PAHS use (www.domeanddirt.com) was about Hait's insistence on small glazing.
Glazing is always the trouble area, any house, any heating system. One size does not fit all in usual terms of % of floor area. Hait said 6% max. As you said, "tiny". He doesn't live with my wife, we have 26% of floor area in glazing.
I have 250 sq ft of south-facing glass, enough to grossly over-heat a low-mass house this size. No problem for a high mass house, though we do effect .5 ACH with an HRV. Our glazing you'd have no problem believing we get a lot of heating. However, summers we have no direct sun entering the house, and the warming of the mass continues at an increased rate because the indoor temps are higher.
Again, this is not a short-term system. It relies on annual effects. Why Hait called it Annual Heat Storage. Your assumptions are not wrong, just not applicable to PAHS as a whole.
Many have asked why the stored heat did not always flow in one direction, to the cooler adjoining earth. I didn't know until an aerospace engineer explained sinusoidal damping to me. PAHS houses take 2-3 years to stabilize, far longer than the 6 months Hait observed heat took to move through his rule-of-thumb 20 feet of dry earth storage. Hait apparently didn't know why that stabilization took so long, simply what he observed.
Too much history. We've probably already put everyone else to sleep so if you'd like more we might take this off-forum.
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