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

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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?

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?


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



"Some Guy"

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Funny thing is that a coworker tried this.  He said it made his shingles
look really old quickly and didn't really do a whole lot other than that.

Perhaps you are good (or bad) at math.  You might start by looking at the
accuracy of your thermometer.  Only a few I know will discern accurately the
1.6 degree drop in temp you say, and they are expensive.  In other words,
the temp could well have gone up with the measurement error added in.
Another thing to consider is the heat capacity of the water, and where that
BTU capacity is best used - perhaps not cooling your roof.  Did your living
space get cooler?  Probably not.  Would a $50 attic fan do a 50x better job?
They do seem popular.  I suspect there is a reason the world isn't equipped
with roof sprinklers.


- Nate





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


Dll wrote:
 
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The thermometer I'm using is similar to this one:

http://tinyurl.com/d2u7x

It's an older version of the one on that page, except mine is
temperature only (so it shows simultaneous temps of both the sensor in
the unit and a remote sensor on the other end if a wire attached to
the unit).  Mine also shows the temp with 1 decimal place resolution.
When the remote sensor is brought close to the unit and left to
equilibrate for 10 minutes both readings agree with each other to
within about 0.5 degree.

Whether or not it is off by a few degrees compared with a calibrated
thermometer is not really the point.  If it shows a daytime attic temp
of 120 degrees and then later 74 degrees at night, and if other
sensors I have are telling me that it really is 74 degrees outside,
then I think I can rely on it.

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Hard to judge, given the fact that my thermostat is on the main floor
and is regulating the AC based on the temp it is seeing on the main
floor.

It seems obvious that an attic with an air temperature of 100 degrees
would present a much better thermal load on the air space of the house
below it vs 120 or 130 degrees in the attic.

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This is with an attic fan going.

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Houses aren't equiped with a lot of things - today or 10 years ago or
30 years ago.  My house was build in 1976 and (as I have discovered)
has 1/2 inch drywall panels directly behind the aluminum siding on the
second floor (no foam-board or styrofoam insulation panels).

But getting back to roof-mounted sprinklers, something like that will
never become part of standard residential construction because if it's
not done right it will more of a liability than an asset (freezing or
bursting pipes or condensation in attic, need for a good control
system, etc).

There is no doubt that water-cooled roofs in industrial/commercial
situations have been proven to be useful and cost effective (according
to some google searches I've done).  I can't find anywhere where
they've tried it in a residential situation.


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


Probably another reason why you don't see this in residential
settings:

Patent 4175703: Spray cooling system for gable roof

http://www.freepatentsonline.com/patents/us/417/4175703/4175703.pdf

In the USA, you can patent almost anything, regardless if it is
similar to what is already in practice, or what is generally "known to
those skilled in the art".

In this case, the above patent (granted in 1979) at the time the use
of evaporative roof cooling was well known for industrial / commercial
flat roofs.  How this guy got a patent for use on a gable roof is
beyond me.

The patent office is full of examples of things we don't see as
consumers because some bone-head thought he could get rich by
patenting something trivial and obvious.  All he ends up doing is
wasting his money on a patent.

I would think that the patent has now expired.


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




Some Guy wrote:
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BTW:

In searching for the roof spray patent I found this:
http://www.freepatentsonline.com/patents/us/417/4173930/4173930.pdf
http://www.freepatentsonline.com/patents/us/417/4173930/4173930-002.tif

That may be prior art that precedes one of the latest patents from NASA
--- its for a golf ball that has aerodynamically more efficient
ellipsoidal dimples. The wonder of socialism at work In America !!!


.........

The water spray idea could be a nice product business where there is
plenty of water. There may be room for some new inventions there.


BTW, If you are working on an idea, write me, and I'll get you in touch
with the right people. Do talk to your Patent Agent first or we'll help
you to find one, and do not talk to others regarding your idea. Least of
all on Usenet. No, you don't pay anyone to market your ideas - that's a
scam. We help you to get your idea developed, drawn, patented,
prototyped, and presentable. Sometimes we can help you to find capital
for you for your development purposes, or more importantly, we are a
self-help forum for technical ideas of all sorts.


Ralph Hertle
Vice President and Trustee
National Society of Inventors


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



"Some Guy"

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The readout doesn't mean anything.  I'd bet you're getting 2 C max accuracy.

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Pretty scientific test you had going there...not!

Vent fans are tried and true energy savers.



- Nate






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


Dll wrote:

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I'm satisfied that when I bring that particular unit (with it's
internal and external transducer) along with several other (different)
units together in the same place, and see them display a temperature
within 1 degree (F) of each other, that there's little chance that
they're all out of whack by the same amount.

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My hypothesis was that spraying water on the roof would cause a
decrease in attic air temperature.

My temp display before applying the spray was showing 120+ degrees
(f).  Within 1/2 hour of applying the spray the temp went to 100
degrees and leveled off to about 98 degrees after an hour.

This was scientific in that

- I had reasonable confidence in my measurement device
- I varied only 1 parameter during the study
- there were no other variables that could have affected the
  results (like a change in outside temp, cloud cover, etc)

During the entire time the roof-mounted exhaust fan was running.

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I don't know what the temp would have been without the spray and
without the fan running, but I agree that a vent fan (combined with
proper soffit ventilation) is absolutely necessary to prolong shingle
life and reduce the heat load to the house.


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



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2 C
it's
(different)
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temperature
chance that
cause a
degrees
100


 no suprise...sure water cooling works...did you say that was
on an 85F day?     so you cooled the roof to within 15
degrees.    Venting with enough air would have taken the attic
temp closer to the air temp that was used for venting.  as a
wild guess your load vs the cfm....90 deg F. maybe 98 or even
warmer...depends on how big fan is and type of roof
construction.

again. its the temp inside the first 1/2 inch of attic
insulation thats most relevant.

You have 'what works' confused with whats practical.

Phil Scott


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running.
and
(combined with
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prolong shingle




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


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That may be true, but it's probably safe to assume that the temperature
decrement which the gentleman read was not off by 2ēC.  Even assuming the
"before" and "after" temperature readings were off by a degree or two, the
delta reading was probably accurate to within a small fraction of a degree.

That said, I'm not sure this is an optimal use of natural resources.  Where
I live (southern Florida and northern Brazil at various times during the
year) water is more expensive than electricity.  A good fan can bring the
attic temperature to within 5ēC of the outside air temperature.  Operational
costs are minimal.

In Sarasota private well water cannot be used for this purpose for two
reasons.  First it's usually full of sulfur and iron deposits which would
stain the roof horribly and stink like rotten eggs.  Second, it's illegal.
We have strict environmental laws here to keep anyone other than strip
miners from wasting natural resources and destroying the ecology.

--

Regards,
Robert L Bass

=============================>
Bass Home Electronics
2291 Pine View Circle
Sarasota ˇ Florida ˇ 34231
877-722-8900 Sales & Tech Support
http://www.bassburglaralarms.com
=============================>




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


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Hoo boy, and does it STINK.  I was appalled visiting a friend's place some
years ago at how badly the water stank of sulfur.



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


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One of the worst things is getting hit with spray from a lawn sprinkler
while bicycling.  :(

--

Regards,
Robert L Bass

=============================>
Bass Home Electronics
2291 Pine View Circle
Sarasota ˇ Florida ˇ 34231
877-722-8900 Sales & Tech Support
http://www.bassburglaralarms.com
=============================>



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


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Back in the days before ubiquitous A/C, and when 'skimpy' insulation was
commonplace, "watering the roof" was a _common_ method of making things
inside a bit more livable.

The idea being to just wet down the roof, and have the water _evaporate_
to carry off the heat.   evaporating water pulls off hundreds of times as
much heat energy as does just warming the water up does.

'Evaporative cooling' is one of the most energy efficient cooling methods
known.  However, there are a whole bunch of limits as to how much cooling
you can get that way.  The higher the ambient 'relative humidity', the
less cooling you can produce.  The lower the temperature, the less cooling
you can produce.  And, of course, you have to have a means to 'discard'
the 'used up' air.

As a practical matter, you "don't care" how hot the attic air is _near_the_
_roof_, if the temperature just above the insulation to the inhabited space
stays rational.  Decent 'convection' air-flow, possibly with power-assist
does a good job of _that_.

Also, if you have 'good' insulation between the inhabited space, and the
attic, a 'spike down' in the attic temperatures will -not- make a noticable
difference in the inhabited space thermal load -- takes too long for the
change to 'penetrate' all that insulation.


I'd try putting some temprature sensors at, or even a little ways _into_
the top of the insulation at the attic *floor*, and see how bad the
temperatures get there.  And then try to optimize the air-flow to get
those readings close to 'in the shade' outdoor temperatures.



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



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outdoor
humidity.
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about 36' x
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Soffits are 2
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along 1 side
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space to
powered with
underside of wood
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decking but
I rigged up
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achieve
exiting
the touch
100
is 98.4
total
pot-lights,
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stuff into the
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be "cool"
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couple of
I could
with water
increased shingle
spray if the
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of the
insulation was
making things
_evaporate_
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hundreds of times as
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cooling methods
much cooling
humidity', the
the less cooling
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to 'discard'
air is _near_the_
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inhabited space
power-assist
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space, and the
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make a noticable
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long for the
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ways _into_
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bad the
air-flow to get
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   Thats good advice

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


What is your reason for spraying water on your roof?


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



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outdoor
humidity.
color) on a
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about 36' x
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Soffits are 2
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along 1 side
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to
powered with
of wood
decking but
rigged up
achieve
exiting
the touch
100
98.4
total
pot-lights,
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stuff into the
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be "cool"
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couple of
could
with water


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
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increased shingle
spray if the
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the




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



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Besides the glaring fact of WASTING WATER?  Do the math on your water bill
(or the electric to pump your own well water) and you'll probably find it's
a helluva lot cheaper to just leave the roof alone.  If anything, put in an
attic vent fan.  Water's not as harmless a material as one might imagine.
The various minerals causing deposits, the likelihood of algae other
mold/fungus growth and even it's weight are all factors to consider.  Enough
that unless the roof was designed with in mind would make it not only a bad
idea but a potentially dangerous one at that.

-Bill Kearney



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


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Jim Baber's comments:

wkearney99 wrote:

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Bill has a point here, but if you were to use misters (like I do between
my solar panels and my roof), you might see the same kind of drop in
attic temp that I have had.  My roof that has my solar system is a 6:12
pitch facing due south.  I have noticed a 10 degree reduction in the
attic temperature just due to the shading by my solar panels, down from
160 to 150 deg. on a 100 degree day.

I installed those commercial cooling misters for patios and yards,
behind my solar panels to cool the panels themselves, figuring that I
did NOT want mineral deposits on the front.  I was not to worried about
roof deposits, because I intended to only run the misters on days over
90 when I had measured a drop in power generated by the panels because
of temperature degradation above 95 degrees.

This supposedly only uses about 2 gal. an hour per the Mfg. claims, and
has not deposited significant or noticeable minerals in 2 years of
operation.  The roof does get damp sometimes but not usually, since
there is considerable convection air flow upwards behind the panels that
evaporates most of the mist before it wets the roof.  I do use a
demineralizing cartridge in the supply line, and they are available
where I got the misters.

When I turned on the misters behind the solar panels the temperature
dropped an additional 30 degrees in the attic to 120 degrees.  This
isn't cool by anyone's idea, but I noticed that the A/C has reduced the
number of minutes the it runs each hour by about 15% on those 100 degree
days we have too many of here.

By the way the misters also accomplished what I wanted in the first
place, I got back the 0.83 kW of peak solar production I had lost
because of the solar cell heating. (that's about $1.62 for any day over
90)   All in all I found it to be a very worthwhile effort since we had
67 days over 90 last year for an additional estimated $108.00 worth of
power we produced.  I have not estimated how much the reduction in A/C
time was worth but I could from the cost of running it vs not running it.

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At 10.8 gal. a day for 67 days that's not much water, but I can't put a
value on it since we are not metered at all.  You could put a value on
it at your cost, but I can't even make a guess as to that.

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I can't see how it would be dangerous, in fact in So. Calif. some people
do this for protection from brush fires,  and I would do it here if I
still had a shake shingle roof.

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


Jim Baber wrote:

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Doesn't a mister waste water by atomizing it and then the wind will
blow it away?

I would think the ideal way to cool something with water would be to
completely wet the surface of something you want to cool with a low
volume of flowing water.  That would avoid staining from minerals in
the water.  The heat you're taking away is the difference between the
inflow and outflow temp multiplied by the volume flow rate.  Some
evaporation will also happen.

I know that water can cool best if (all of) it evaporates, but that
will leave mineral stains, and also it probably won't get you down to
the low temps you can reach by continuous flowing water.

My tap water comes from lake Huron and is probably around 50 degrees
(f).  I pay 3.86 cents (CDN) per cubic foot (3.165  USD).  I think
that's about 0.516 cents (CDN) per US gallon (or 0.423 cents USD).

I pay 5 cents (CDN) per kWh for the first 750 kWh (per month) and 5.8
cents per kWh after that.  That's about 4.1 and 4.8 cents USD
respectively.

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That's 5.6 cents (CDN) per day, or $3.74 (CDN) for 67 days ($3.06 USD)

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Deposits, yes - but perhaps negligable if the water is not allowed to
evaporate.  Mold/fungus - I'm thinking no because this would only be
used on mostly sunny days for maybe 1/2 hour to maybe 2 hours of the
day.  When the water is turned off, the roof will dry up and I
wouldn't think that would give any mold or fungus any ability to grow
given that the shingle temp would probably climb back to well over 100
degrees.  A thin layer of flowing water on the roof is equivalent to a
gentle spring or fall rain shower and nowhere near the weight of the
snow loads we see during the winter.

PS:  Given gasoline costs at $2 to $3 per gallon (or $1 CDN per liter)
what are the costs to generate electricity (on a kWh basis) using a
gasoline powered generator?

PPS:  Are there gasoline or propane-powered AC units, and are they
more economical to run vs electric?

PPS:  What are the pro's and con's of immersing your outside AC
condensor coil in your swimming pool (and therefor doing away with the
cooling fan) ???  Heat your pool and remove heat from the coils much
more efficiently?


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



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wind will

     The latent heat of evaporation for water is somehing like
970 btu's per lb... one gallon of water is 8 lbs...so its
about 7800 btu's of heat required or the equivalent amount of
*sensible heat removed from the air to evaporate a gallon of
water.  Thats equivalent to about 3/4 of a ton of
airconditioning  (average home takes about 3 tons).

So you would have to evaporate about 4 gallons of water an
hour to cool the average home in a very dry climate... say 10
hours a day.. thats 40 gallons a day,..or 1200 gallons a
month.    The average home uses about 500 gallons of water a
day the bill is say 25 dollars for that 15,000 gallons a
month.   So the water used in 100% evap cooling sells for
around 3 dollars a month. or lets say 10 dollars max.

Cooling the house with refrigerated HVAC will cost 200 to 300
dollars a month or more.



The cost of a gallon of city water is less than a cent...so
its a very good deal cost wise.. and ecologically much better
than running a one HP motor (approx HP required to deliver 3/4
ton of cooling if you count the fans).   That power is
generated by burning foscil fuels in most cases.

Evaporative cooling would be limitlessly popular if it did not
add an equal amount of humidity in the form of 'steam' to the
air it was cooling to *sensibly lower termperatures.     There
is sensible heat, measured with a thermometer, and Latent heat
thats water vapor in the air..it takes about 100 times as much
heat to create steam as it does to raise the same amount of
water 1 degree F.

So latent heat is a big deal in humid climates... in dry
climates you can use evap cooling to take advantage of the
situation.


 The human body feels both this humidity and the sensible
temperature as one...so evaporative cooling only works in very
dry climates where an acceptable rise in humidity fits well
with human comfort requirements.

It will become a lot more popular in commercial buildings in
the south west shortly..as fuel prices go up.  Right now its
straight refrigerated air.


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would be to
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with a low
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minerals in
between the
Some
but that
you down to
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degrees
think
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month) and 5.8
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USD
($3.06 USD)
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algae
factors
allowed to
only be
hours of the
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I
ability to grow
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well over 100
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Thats about right.


 A thin layer of flowing water on the roof is equivalent to a
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weight of the
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per liter)
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using a
are they
AC
away with the
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coils much


That would be what is called a 'ground water sourced heat pump
system' those work very very well.  And are popular.    For
some reason you dont see them piped to pool water very often.
But its workable....to a limit.   Depending on the size of
your pool, in the summer the system would warm the pool...but
you wouldnt want it to go over 85 degrees or so...then it
would have to switch back to air cooled or a ground loop.

In the winter you would be cooling the pool while heating the
house... the pool temp would then drop to 40F or so and start
absorbing heat from the surrounding ground in most climates...
and if the pools was large enough and had a pool cover .. it
would make a good heat source for winter heating...but of
course then too cold to swim in..

so for that reason pipes burried in the ground are common.
The engineering and install can screwed up easily and often
is..then its a mess.  If done right its a very good deal.


On the attic temps though the poster who mentioned temp at the
top of the insulation had the best response.. myself in your
case I would not wet the roof.  I would ventilate the attic
with a fan.



Phil Scott
Mech Engr HVAC contractor since 1829.




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



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Evaporative cooling must do wonders for longevity.


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