Larry Fishel wrote:

I have a temperature sensor mounted about 1" under the plywood
roof deck in the attic and it went from about 120F to about 100F
during the watering.

The temperature at this point may be misleading (most affected by the
sun, least affected by venting).

I don't agree.

Air currents in a soffit-ventilated attic will flow primarily from the
intake point (the soffits) up along the underside of the decking to the
peak where the exhaust fan is located.

By placing the sensor mid-way up this path, on the underside of the deck
(but not touching it) I'll get a good sense as to the heat load that the
shingles are transfering to the attic space - in terms of the
ventilation system's ability to remove this heat.

Because the water was able to carry away the heat from the shingles, the
ventilation system was able to bring the attic temperature very close to
ambient during the time that the water was being applied, and even for a
short time after the water had been turned off and evaporative cooling
was happening.

If I had the time, and a backhoe, I'd create a water storage reservior
in the ground near my house, probably lined with concrete, maybe
insulated, and circulate water from that reservior to my roof and back
again, storing heat energy to heat my home in the winter. I'd put pipes
in my driveway and melt the winter snow with this heated water, and by
next spring the water would be cold and ready to absorb the next
summer's heat.

Anyone know how much water would be necessary to store enough heat to
heat a typical house in the winter? Say, in Chicago, Detroit, Buffalo
or Toronto? Say if you started with a water temperature of maybe 175
degrees and by the end of the winter it was down to 70 degrees? (no
heat pump involved that is).