06 April 2012

Passive Cooling

It's raining to beat the band.  As I sit here in the rancho, looking out over the house and its new tile roof, one can see how the passive cooling system works.

It started pouring rain HARD as soon as this storm hit.  Almost immediately, rivulets of runoff began shooting off of the rancho's metal pseudo-tile roof (the rancho has no gutters.)  Yes, there is an immediate temperature drop as the sun-heated steel roof quits radiating infrared down onto my head.  But, as soon as the rain quits and the sun hits it again, the temperature will rebound to it previous roasting temperature.

Over on the house, with the real tiles, they aren't turning shiny with rain.  I can see the quarter-sized raindrops smacking into them all over the place ... and then the drops disappear.  For at least 10 minutes, not a dribble comes out of the downspouts of the house roof gutters.  Those tiles are sponging up a third of their weight in water.

Ever use one of those clay tile wine bottle coolers?  Soak it in water ... stick the wine bottle into it ... wait a half hour ... voila, cool wine.

That's what is going on here.  For hours (or in this case, after an overnight, tomorrow morning) the wet tile will not heat up in the tropical sun.  It will slowly give back the water to evaporation and will actually be cool to the touch.

Oh, yes, I cheated a little and laid a shiny radiant barrier between the roofing beams and the tile supports but most of the reason for the cool is that tile effect.

Temperature in the rancho at the peak of sunlight today?  98F.

Temperature in the house at the same time?  80F.

Guess where I sat to read my book?

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