🚀 go-pugleaf

What is your reason for spraying water on your roof?


"Some Guy" <Some@Guy.com> wrote in message news:42BDB7E5.456E1146@Guy.com...
> 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? 

"Some Guy"

> 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?

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

In article <42BDB7E5.456E1146@Guy.com>, Some Guy  <Some@Guy.com> wrote:
>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?

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.

Dll wrote:
 
> "Some Guy"
> 
> > 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?
> 
> 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.  

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.

> Did your living space get cooler?  Probably not.

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.

> Would a $50 attic fan do a 50x better job?
> They do seem popular.

This is with an attic fan going.

> I suspect there is a reason the world isn't equipped with
> roof sprinklers.

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.

"Some Guy" <Some@Guy.com> wrote in message
news:42BDB7E5.456E1146@Guy.com...
> 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?

"Robert Bonomi" <bonomi@host122.r-bonomi.com> wrote in message
news:11bs1lfok861n40@corp.supernews.com...
> In article <42BDB7E5.456E1146@Guy.com>, Some Guy
<Some@Guy.com> wrote:
> >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?
>
> 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.

   Thats good advice

Phil Scott
>

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.

> Is there anything written up about residential roof cooling with water
> spray?

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

Some Guy wrote:
> 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.





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

"Some Guy"

> 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.

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

> This is with an attic fan going.

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

Vent fans are tried and true energy savers.



- Nate

Dll wrote:

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

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.

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

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.

> > This is with an attic fan going.
> 
> Vent fans are tried and true energy savers.

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.

This is a multi-part message in MIME format.
--------------060804090108010204050808
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit

Jim Baber's comments:

wkearney99 wrote:

>>Is there anything written up about residential roof cooling with water
>>spray?
>>    
>>
>
>Besides the glaring fact of WASTING WATER?  
>
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.

>Do the math on your water bill ............
>  
>
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.

>........ (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
>  
>
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.

--------------060804090108010204050808
Content-Type: text/x-vcard; charset=utf-8;
 name="jim.vcf"
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment;
 filename="jim.vcf"

begin:vcard
fn:Jim  Baber
n:Baber;Jim 
adr:;;1350 W. Mesa Ave.;Fresno;CA;93711-2008;USA
email;internet:jim@baber.org
tel;home:(559)435-9068
tel;cell:(559)905-2204
x-mozilla-html:TRUE
url:http://www.baber.org
version:2.1
end:vcard


--------------060804090108010204050808--

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

That may be true, but it's probably safe to assume that the temperature 
decrement which the gentleman read was not off by 2�C.  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 5�C 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 � Florida � 34231
877-722-8900 Sales & Tech Support
http://www.bassburglaralarms.com
=============================> 

>> Is there anything written up about residential roof cooling with water
>> spray?
>
> 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.

There's one method of using water to cool the roof/attic that can help.  I 
use solar panels to heat my pool.  The pool holds ~30,000 gallons.  There 
are eight 4'x10' solar panels on the roof.  Sunlight hitting them warms the 
pool -- not the attic.  I've noticed a significant improvement in cool-down 
cycle (time it takes to get the house cool again after we've been away) with 
the pool heater running.  Since the pool water is being circulated by the 
filtration pump during the day anyway, there's almost no *extra* cost to use 
the solar panels.

-- 

Regards,
Robert L Bass

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

Jim Baber wrote:

> >Besides the glaring fact of WASTING WATER?
> >
> Bill has a point here, but if you were to use misters

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.

> At 10.8 gal. a day for 67 days that's not much water

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

> > The various minerals causing deposits, the likelihood of algae
> > other mold/fungus growth and even it's weight are all factors
> > to consider.

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?

"Jim Baber" <jim@baber.org> wrote in message
news:orKdnX-MIND1ZiPfRVn-sQ@comcast.com...
> Jim Baber's comments:
>
> wkearney99 wrote:
>
> >>Is there anything written up about residential roof
cooling with water
> >>spray?
> >>
> >>
> >
> >Besides the glaring fact of WASTING WATER?
> >
> 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.


Misting is a vastly under used technology... sounds like you
have a great application there.    Ive been trying to sell it
to super markets with air cooled refrigeration for years... a
tough sell..but it would save them a bundle and cut repair
costs.  There are commcl systems on the market for that
application but they dont sell well.

They sell for chicken ranches and misting public areas the
desert mostly.

Phil Scott

>
> >Do the math on your water bill ............
> >
> >
> 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.
>
> >........ (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
> >
> >
> 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.
>

"Some Guy" <Some@Guy.com> wrote in message
news:42BF0BE3.2C314AE5@Guy.com...
> Jim Baber wrote:
>
> > >Besides the glaring fact of WASTING WATER?
> > >
> > Bill has a point here, but if you were to use misters
>
> Doesn't a mister waste water by atomizing it and then the
wind will
> blow it away?

     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.


>
> 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.
>
> > At 10.8 gal. a day for 67 days that's not much water
>
> That's 5.6 cents (CDN) per day, or $3.74 (CDN) for 67 days
($3.06 USD)
>
> > > The various minerals causing deposits, the likelihood of
algae
> > > other mold/fungus growth and even it's weight are all
factors
> > > to consider.
>
> 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.

Thats about right.


 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?


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.

Phil Scott wrote:

> > Doesn't a mister waste water by atomizing it and then the
> > wind will blow it away?
> 
>      The latent heat of evaporation for water ...

I still don't see an effective way to arrange a residential cooling
system based on the evaporation of water.

I don't think you can concentrate and deliver a substantial amount of
heat to a surface you can cool via evaporation.  Evaporative cooling
would be effective if the heat inside a house could be brought to an
out-door device who's surface temperature is well above boiling and
the application of water would result in evaporative cooling.  

> 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.

So what you're saying is to mistify the air circulating in a house in
order to cool it.  I don't think that would work once you've saturated
the air (ie humidity > 75%) not to mention the effects of saturated
air on items in the house, the wood, the machinery, etc.

I think only the roof makes a workable item to cool with a water
cooling.  It's designed to get wet, to collect runoff, and gets very
hot in the summer, and cooling it can lead to reduction in cooling
requirements of the house.

The only thing that makes more sense is a temporary tarp or canopy to
cover the roof during the summer (to be taken down during nasty
weather, storms, etc).

> PPS:  What are the pro's and con's of immersing your outside AC
> condensor coil in your swimming pool

Corrosion.  Air doesn't eat at the coil nearly as bad as chlorinated pool
water would.

> 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.

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.

"Jim Baber" <jim@baber.org> wrote in message
news:orKdnX-MIND1ZiPfRVn-sQ@comcast.com...
> Jim Baber's comments:

Nice bit of explanation Jim.

> 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.

True, I suppose dangerous isn't the right word.  I was thinking more along
the idea of some DIY nightmare oversaturating the roof (somehow) and
introducing problems well beyond the roof's design.  Weight, saturation,
downspout overflow, etc.

"Some Guy" <Some@Guy.com> wrote in message
news:42BF3E57.659FD057@Guy.com...
> Phil Scott wrote:
>
> > > Doesn't a mister waste water by atomizing it and then
the
> > > wind will blow it away?
> >
> >      The latent heat of evaporation for water ...
>
> I still don't see an effective way to arrange a residential
cooling
> system based on the evaporation of water.
>
> I don't think you can concentrate and deliver a substantial
amount of
> heat to a surface you can cool via evaporation.  Evaporative
cooling
> would be effective if the heat inside a house could be
brought to an
> out-door device who's surface temperature is well above
boiling and
> the application of water would result in evaporative
cooling.
>
> > 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.
>
> So what you're saying is to mistify the air circulating in a
house in
> order to cool it.  I don't think that would work once you've
saturated
> the air (ie humidity > 75%) not to mention the effects of
saturated
> air on items in the house, the wood, the machinery, etc.

I am a mechancal engineer doing these sorts of calculations
and systems for over 40 years.. and you are entirely correct
if the humidity is say 50% and the outside air is 90F... you
can cool the air to 75 or so but the humidity is then up into
the 80% range and all the problems you mention manifest.
Thats why evaportive cooling is not used in many cases.

However in areas where the relative humidity is in the 20 to
30% range, and the outside air is over 90F... then the supply
air can be cooled to 70F and 50% relative humidity..that works
very well/


>
> I think only the roof makes a workable item to cool with a
water
> cooling.  It's designed to get wet, to collect runoff, and
gets very
> hot in the summer, and cooling it can lead to reduction in
cooling
> requirements of the house.

     Its workable...but there are problems ..its seldom used
because of those problems.   You get to do whatever you wish
though its yer house.  Have fun.


>
> The only thing that makes more sense is a temporary tarp or
canopy to
> cover the roof during the summer (to be taken down during
nasty
> weather, storms, etc).

  Oh please.


Phil Scott

Don't cooling towers use evaporative cooling?

"Phil Scott" <philscott@philscott.net> wrote in message
news:d9ocdq$2hf$1@news.tdl.com...
>
> "Some Guy" <Some@Guy.com> wrote in message
> news:42BF3E57.659FD057@Guy.com...
> > Phil Scott wrote:
> >
> > > > Doesn't a mister waste water by atomizing it and then
> the
> > > > wind will blow it away?
> > >
> > >      The latent heat of evaporation for water ...
> >
> > I still don't see an effective way to arrange a residential
> cooling
> > system based on the evaporation of water.
> >
> > I don't think you can concentrate and deliver a substantial
> amount of
> > heat to a surface you can cool via evaporation.  Evaporative
> cooling
> > would be effective if the heat inside a house could be
> brought to an
> > out-door device who's surface temperature is well above
> boiling and
> > the application of water would result in evaporative
> cooling.
> >
> > > 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.
> >
> > So what you're saying is to mistify the air circulating in a
> house in
> > order to cool it.  I don't think that would work once you've
> saturated
> > the air (ie humidity > 75%) not to mention the effects of
> saturated
> > air on items in the house, the wood, the machinery, etc.
>
> I am a mechancal engineer doing these sorts of calculations
> and systems for over 40 years.. and you are entirely correct
> if the humidity is say 50% and the outside air is 90F... you
> can cool the air to 75 or so but the humidity is then up into
> the 80% range and all the problems you mention manifest.
> Thats why evaportive cooling is not used in many cases.
>
> However in areas where the relative humidity is in the 20 to
> 30% range, and the outside air is over 90F... then the supply
> air can be cooled to 70F and 50% relative humidity..that works
> very well/
>
>
> >
> > I think only the roof makes a workable item to cool with a
> water
> > cooling.  It's designed to get wet, to collect runoff, and
> gets very
> > hot in the summer, and cooling it can lead to reduction in
> cooling
> > requirements of the house.
>
>      Its workable...but there are problems ..its seldom used
> because of those problems.   You get to do whatever you wish
> though its yer house.  Have fun.
>
>
> >
> > The only thing that makes more sense is a temporary tarp or
> canopy to
> > cover the roof during the summer (to be taken down during
> nasty
> > weather, storms, etc).
>
>   Oh please.
>
>
> Phil Scott
>
>

Phil Scott wrote:

> > I think only the roof makes a workable item to cool with 
> > water cooling.  It's designed to get wet, to collect runoff,
> > and gets very hot in the summer, and cooling it can lead to
> > reduction in cooling requirements of the house.
> 
> Its workable...but there are problems ..its seldom used
> because of those problems.

Would you care to mention what those problems are?

This is a multi-part message in MIME format.
--------------020500090104060809000204
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit


Jim Baber's expanded comments:

>
> wkearney99 wrote:
>
>>> Is there anything written up about residential roof cooling with water
>>> spray?
>>>   
>>
>>
>> Besides the glaring fact of WASTING WATER? 
>
> Several people including Phil Scott have made good comments here.  I 
> feel I need to make 2 points I didn't in the earlier post. 

   1. The average humidity in Fresno CA is generally quite low in the
      daytime during the summer.  Right now it is 8:30 in the morning
      the humidity is 66%, and the temperature is only 62.8 with an
      expected high of 92 @ 17:00 pdt.  The humidity will probably drop
      to about 25 - 35% if it performs as usual. 
      This is really ideal for misting as a cooling device. 
      I just wish these temperatures would continue all summer, but we
      are supposedly going to hit 100's next week (the latest in several
      years by the way).
   2. Wind does severely reduce the effectiveness of the misting as far
      as cooling, but one of the major problems with the weather in
      Fresno is the LACK of wind in the summer. At best we can maybe get
      a 3 - 6 mph breeze and that will usually be after 7 PM. I just
      looked at my weather station again, the highest wind speed over
      the pas 24 hr was a gust to 4 mph most of the rest at 2 - 3 mph.
      with long periods without any at all.  Rather typical and boring. 
      <>
      By the way, in the 5 min. I've been typing, the Relative humidity
      dropped to 62 and the temperature went up to 64


--------------020500090104060809000204
Content-Type: text/x-vcard; charset=utf-8;
 name="jim.vcf"
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment;
 filename="jim.vcf"

begin:vcard
fn:Jim  Baber
n:Baber;Jim 
adr:;;1350 W. Mesa Ave.;Fresno;CA;93711-2008;USA
email;internet:jim@baber.org
tel;home:(559)435-9068
tel;cell:(559)905-2204
x-mozilla-html:TRUE
url:http://www.baber.org
version:2.1
end:vcard


--------------020500090104060809000204--

"Chas Hurst" <hurst1@comcast.not> wrote in message
news:0uednRz508PCbCLfRVn-1w@comcast.com...
> Don't cooling towers use evaporative cooling?


Yes they do... but they discharge 100% relative humidity
air...but its outside so its fine...the water in the process
is cooled and that cool water is used to cool most often the
condensers on large tonnage refrigerated AC systems.  that
water typically runs 65 to 80 degrees F... sufficiently cool
to cool condensers but not cool enough to be used directly for
conditioning air  (below 40F is required)

Phil Scott
>
> "Phil Scott" <philscott@philscott.net> wrote in message
> news:d9ocdq$2hf$1@news.tdl.com...
> >
> > "Some Guy" <Some@Guy.com> wrote in message
> > news:42BF3E57.659FD057@Guy.com...
> > > Phil Scott wrote:
> > >
> > > > > Doesn't a mister waste water by atomizing it and
then
> > the
> > > > > wind will blow it away?
> > > >
> > > >      The latent heat of evaporation for water ...
> > >
> > > I still don't see an effective way to arrange a
residential
> > cooling
> > > system based on the evaporation of water.
> > >
> > > I don't think you can concentrate and deliver a
substantial
> > amount of
> > > heat to a surface you can cool via evaporation.
Evaporative
> > cooling
> > > would be effective if the heat inside a house could be
> > brought to an
> > > out-door device who's surface temperature is well above
> > boiling and
> > > the application of water would result in evaporative
> > cooling.
> > >
> > > > 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.
> > >
> > > So what you're saying is to mistify the air circulating
in a
> > house in
> > > order to cool it.  I don't think that would work once
you've
> > saturated
> > > the air (ie humidity > 75%) not to mention the effects
of
> > saturated
> > > air on items in the house, the wood, the machinery, etc.
> >
> > I am a mechancal engineer doing these sorts of
calculations
> > and systems for over 40 years.. and you are entirely
correct
> > if the humidity is say 50% and the outside air is 90F...
you
> > can cool the air to 75 or so but the humidity is then up
into
> > the 80% range and all the problems you mention manifest.
> > Thats why evaportive cooling is not used in many cases.
> >
> > However in areas where the relative humidity is in the 20
to
> > 30% range, and the outside air is over 90F... then the
supply
> > air can be cooled to 70F and 50% relative humidity..that
works
> > very well/
> >
> >
> > >
> > > I think only the roof makes a workable item to cool with
a
> > water
> > > cooling.  It's designed to get wet, to collect runoff,
and
> > gets very
> > > hot in the summer, and cooling it can lead to reduction
in
> > cooling
> > > requirements of the house.
> >
> >      Its workable...but there are problems ..its seldom
used
> > because of those problems.   You get to do whatever you
wish
> > though its yer house.  Have fun.
> >
> >
> > >
> > > The only thing that makes more sense is a temporary tarp
or
> > canopy to
> > > cover the roof during the summer (to be taken down
during
> > nasty
> > > weather, storms, etc).
> >
> >   Oh please.
> >
> >
> > Phil Scott
> >
> >
>
>

"Some Guy" <Some@Guy.com> wrote in message
news:42C0095A.4263E2C0@Guy.com...
> Phil Scott wrote:
>
> > > I think only the roof makes a workable item to cool with
> > > water cooling.  It's designed to get wet, to collect
runoff,
> > > and gets very hot in the summer, and cooling it can lead
to
> > > reduction in cooling requirements of the house.
> >
> > Its workable...but there are problems ..its seldom used
> > because of those problems.
>
> Would you care to mention what those problems are?

Water is a corrosive.  Would mildly wear the roofing but with
your limited use not much...

Mineral deposits with your limited usage would be minor but
still a negative factor.

The net benefit of water cooling the roof would be close to
the benefits of attic air ventilation..attic air ventilation
would not have that set of minor problems though.

Your suggestion is workable  just not the optimum as I see it.
It would be optimum however say in the deep south west with
air temperatures over 110 in the shade...  but then mineral
content of the water is higher there and could be a very
significant problem one would have to look at...  it is
typically not done.

I might be inclined to put a spray misting system in the attic
air make up stream.  that would work.

However misting companies will not sell into a high mineral
content water area because the minerals destroy their PD pumps
and clogg the micro nozzels....thus...we see swamp coolers
used in the south west.



Phil Scott

"Phil Scott" <philscott@philscott.net> wrote in message
news:d9quua$l83$1@news.tdl.com...
>
> "Chas Hurst" <hurst1@comcast.not> wrote in message
> news:0uednRz508PCbCLfRVn-1w@comcast.com...
> > Don't cooling towers use evaporative cooling?
>
>
> Yes they do... but they discharge 100% relative humidity
> air...but its outside so its fine...the water in the process
> is cooled and that cool water is used to cool most often the
> condensers on large tonnage refrigerated AC systems.  that
> water typically runs 65 to 80 degrees F... sufficiently cool
> to cool condensers but not cool enough to be used directly for
> conditioning air  (below 40F is required)
>
> Phil Scott

Well you really lost me now. Hasn't this suggestion of water ON the roof
been about water on the outside of the house?
So the humidity created by a watered roof would be outside, just as with a
cooling tower.

Chas Hurst



> > "Phil Scott" <philscott@philscott.net> wrote in message
> > news:d9ocdq$2hf$1@news.tdl.com...
> > >
> > > "Some Guy" <Some@Guy.com> wrote in message
> > > news:42BF3E57.659FD057@Guy.com...
> > > > Phil Scott wrote:
> > > >
> > > > > > Doesn't a mister waste water by atomizing it and
> then
> > > the
> > > > > > wind will blow it away?
> > > > >
> > > > >      The latent heat of evaporation for water ...
> > > >
> > > > I still don't see an effective way to arrange a
> residential
> > > cooling
> > > > system based on the evaporation of water.
> > > >
> > > > I don't think you can concentrate and deliver a
> substantial
> > > amount of
> > > > heat to a surface you can cool via evaporation.
> Evaporative
> > > cooling
> > > > would be effective if the heat inside a house could be
> > > brought to an
> > > > out-door device who's surface temperature is well above
> > > boiling and
> > > > the application of water would result in evaporative
> > > cooling.
> > > >
> > > > > 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.
> > > >
> > > > So what you're saying is to mistify the air circulating
> in a
> > > house in
> > > > order to cool it.  I don't think that would work once
> you've
> > > saturated
> > > > the air (ie humidity > 75%) not to mention the effects
> of
> > > saturated
> > > > air on items in the house, the wood, the machinery, etc.
> > >
> > > I am a mechancal engineer doing these sorts of
> calculations
> > > and systems for over 40 years.. and you are entirely
> correct
> > > if the humidity is say 50% and the outside air is 90F...
> you
> > > can cool the air to 75 or so but the humidity is then up
> into
> > > the 80% range and all the problems you mention manifest.
> > > Thats why evaportive cooling is not used in many cases.
> > >
> > > However in areas where the relative humidity is in the 20
> to
> > > 30% range, and the outside air is over 90F... then the
> supply
> > > air can be cooled to 70F and 50% relative humidity..that
> works
> > > very well/
> > >
> > >
> > > >
> > > > I think only the roof makes a workable item to cool with
> a
> > > water
> > > > cooling.  It's designed to get wet, to collect runoff,
> and
> > > gets very
> > > > hot in the summer, and cooling it can lead to reduction
> in
> > > cooling
> > > > requirements of the house.
> > >
> > >      Its workable...but there are problems ..its seldom
> used
> > > because of those problems.   You get to do whatever you
> wish
> > > though its yer house.  Have fun.
> > >
> > >
> > > >
> > > > The only thing that makes more sense is a temporary tarp
> or
> > > canopy to
> > > > cover the roof during the summer (to be taken down
> during
> > > nasty
> > > > weather, storms, etc).
> > >
> > >   Oh please.
> > >
> > >
> > > Phil Scott
> > >
> > >
> >
> >
>
>

"Some Guy" <Some@Guy.com> wrote in message
news:42BEF3E8.85790470@Guy.com...
> Dll wrote:
>
> > The readout doesn't mean anything.  I'd bet you're getting
2 C
> > max accuracy.
>
> 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.
>
> > Pretty scientific test you had going there...not!
>
> 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.


 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


>
> 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.
>
> > > This is with an attic fan going.
> >
> > Vent fans are tried and true energy savers.
>
> 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.

"Chas Hurst" <hurst1@comcast.not> wrote in message
news:pMGdnT7ZIrKcylzfRVn-2A@comcast.com...
>
> "Phil Scott" <philscott@philscott.net> wrote in message
> news:d9quua$l83$1@news.tdl.com...
> >
> > "Chas Hurst" <hurst1@comcast.not> wrote in message
> > news:0uednRz508PCbCLfRVn-1w@comcast.com...
> > > Don't cooling towers use evaporative cooling?
> >
> >
> > Yes they do... but they discharge 100% relative humidity
> > air...but its outside so its fine...the water in the
process
> > is cooled and that cool water is used to cool most often
the
> > condensers on large tonnage refrigerated AC systems.  that
> > water typically runs 65 to 80 degrees F... sufficiently
cool
> > to cool condensers but not cool enough to be used directly
for
> > conditioning air  (below 40F is required)
> >
> > Phil Scott
>
> Well you really lost me now. Hasn't this suggestion of water
ON the roof
> been about water on the outside of the house?



> So the humidity created by a watered roof would be outside,
just as with a
> cooling tower.

correct...thats why your plan WORKS....that is...it is
VIABLE....in other words...you are NOT wrong.... said another
way...your plan to cool the roof and thus reduce attic temps
will fly like an eagle...  its FLAWLESS....

to elaborate... water cooling works GREAT... your plan it
water cooling the roof... very very good.


  Its just that an attic fan works better without whatever
problems are incurred by wetting the roof...that is why so few
people on planet earth, including the worlds best engineers
use the strategy.

  Its workable you see.... just not practical in context with
other approaches.

Phil Scott
>
> Chas Hurst
>
>
>
> > > "Phil Scott" <philscott@philscott.net> wrote in message
> > > news:d9ocdq$2hf$1@news.tdl.com...
> > > >
> > > > "Some Guy" <Some@Guy.com> wrote in message
> > > > news:42BF3E57.659FD057@Guy.com...
> > > > > Phil Scott wrote:
> > > > >
> > > > > > > Doesn't a mister waste water by atomizing it and
> > then
> > > > the
> > > > > > > wind will blow it away?
> > > > > >
> > > > > >      The latent heat of evaporation for water ...
> > > > >
> > > > > I still don't see an effective way to arrange a
> > residential
> > > > cooling
> > > > > system based on the evaporation of water.
> > > > >
> > > > > I don't think you can concentrate and deliver a
> > substantial
> > > > amount of
> > > > > heat to a surface you can cool via evaporation.
> > Evaporative
> > > > cooling
> > > > > would be effective if the heat inside a house could
be
> > > > brought to an
> > > > > out-door device who's surface temperature is well
above
> > > > boiling and
> > > > > the application of water would result in evaporative
> > > > cooling.
> > > > >
> > > > > > 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.
> > > > >
> > > > > So what you're saying is to mistify the air
circulating
> > in a
> > > > house in
> > > > > order to cool it.  I don't think that would work
once
> > you've
> > > > saturated
> > > > > the air (ie humidity > 75%) not to mention the
effects
> > of
> > > > saturated
> > > > > air on items in the house, the wood, the machinery,
etc.
> > > >
> > > > I am a mechancal engineer doing these sorts of
> > calculations
> > > > and systems for over 40 years.. and you are entirely
> > correct
> > > > if the humidity is say 50% and the outside air is
90F...
> > you
> > > > can cool the air to 75 or so but the humidity is then
up
> > into
> > > > the 80% range and all the problems you mention
manifest.
> > > > Thats why evaportive cooling is not used in many
cases.
> > > >
> > > > However in areas where the relative humidity is in the
20
> > to
> > > > 30% range, and the outside air is over 90F... then the
> > supply
> > > > air can be cooled to 70F and 50% relative
humidity..that
> > works
> > > > very well/
> > > >
> > > >
> > > > >
> > > > > I think only the roof makes a workable item to cool
with
> > a
> > > > water
> > > > > cooling.  It's designed to get wet, to collect
runoff,
> > and
> > > > gets very
> > > > > hot in the summer, and cooling it can lead to
reduction
> > in
> > > > cooling
> > > > > requirements of the house.
> > > >
> > > >      Its workable...but there are problems ..its
seldom
> > used
> > > > because of those problems.   You get to do whatever
you
> > wish
> > > > though its yer house.  Have fun.
> > > >
> > > >
> > > > >
> > > > > The only thing that makes more sense is a temporary
tarp
> > or
> > > > canopy to
> > > > > cover the roof during the summer (to be taken down
> > during
> > > > nasty
> > > > > weather, storms, etc).
> > > >
> > > >   Oh please.
> > > >
> > > >
> > > > Phil Scott
> > > >
> > > >
> > >
> > >
> >
> >
>
>