Re: Cooling attic (and home) by spraying water on roof (shingles) - good/bad?

["Phil Scott" <philscott@xxxxxxxxxxxxx>]

"Some Guy" <Some@xxxxxxx> wrote in message
news:42BDB7E5.456E1146@xxxxxxxxxx
> It's a mostly sunny day here (SW Ontario) and the mid-day
outdoor
> conditions are about 87 degrees and 50 to 55% relative
humidity.
>
> I have new shingles (100% asphalt, relatively light in
color) on a
> roof (pyramidal) with a 4:12 pitch covering an area that's
about 36' x
> 40'.  Large vent fan and 3 passive vents near the peak.
Soffits are 2
> foot wide on all 4 sides (but ventaliation is only good
along 1 side
> for the moment). Small fan is jury rigged in the attic space
to
> provide forced air circulation of the attic space and is
powered with
> the main roof fan.
>
> Temperature sensor is positioned 1/2 inch from the underside
of wood
> deck - so I can read the air temp immediately under the
decking but
> not the actual deck or exterior shingle temperature.
>
> Around 1 pm today the attic temperature read 120 degrees.  I
rigged up
> some garden sprinklers on the roof and adjusted the flow to
achieve
> maybe 1 gallon per minute total flow.  Naturally, the water
exiting
> the roof through the downspouts was warm to medium hot to
the touch
> (didn't measure the temp).
>
> Within about 15 to 25 minutes the attic air temp was about
100
> degrees, and it's almost 4 pm as I type this and the temp is
98.4
> degrees (outside temp is about 87).  I'm sure I don't have
total
> coverage of roof with water spray.
>
> Since I'm currently re-working the soffits (adding
pot-lights,
> speakers, cables for CCTV, etc) I'm going to be running
stuff into the
> attic from the basement.  I'm thinking that maybe it might
be "cool"
> to run a copper water line as well and permenantly mount a
couple of
> sprinklers that would give proper coverage to the roof and I
could
> turn on manually or automatically.
>
> Is there anything written up about residential roof cooling
with water
> spray?


Its done very rarely but is a good idea in hot climates...
especially as we are going to time of use billing on
residential shortly... with roof cooling you could keep from
running the AC so much under peak conditions and save a nasty
demand charge billing.

Using city water though leaves mineral deposits that embed
into the roofing and are probably not real good for most roofs
over time.  thats why its not more common.

If enough water can be used so that the roof stays wet and
runs off then mineral deposits are less but its still an
issue...some areas a big issue... others not.

Poultry farms use 3000 psig water atomizer units  (pumps as in
pressure washers) to force water through tiny nozzels so it
evaporates completely in the air...cooling the air and any
mineral deposits come out as solid particles and land on the
ground.

You could cool your attic that way and get good results..
those are fairly expensive systems though.

Or you could use an evaporative cooler to cool the attic.  1/6
hp fan motor... would save about 3/4 hp of cooling load.  No
mineral depost issues... but then you have a swamp cooler to
maintain.

Phil Scott
>
> Are the benefits (reduced interior cooling load and
increased shingle
> longevity) outweight by (maybe) shingle dammage by water
spray if the
> water is used on the hottest, sunniest days in the middle of
the
> summer?