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

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.

Nice bit of explanation Jim.

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.

Evaporative cooling must do wonders for longevity.

the

cooling

amount of

cooling

brought to an

boiling and

cooling.

house in

saturated

saturated

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/

water

gets very

cooling

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.

canopy to

nasty

Oh please.

Phil Scott

Don't cooling towers use evaporative cooling?

Jim Baber's expanded comments:

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

Would you care to mention what those problems are?

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

Are you sure about that? I use much less than that, even with lawn sprinklers and a 15,000 gallong in-ground pool to maintain.

Where I live it's a good deal more costly than that.

True, so don't count on any incentives coming from the present administration either. :)

15000 gallons is about 2005 cubic feet. It would cost me $77 CDN ($63 USD) for that much water.

Cheap water could become thing of past as supplies dwindle The Arizona Republic Jan. 22, 2003

"It may not seem like it when you write the check to pay the bill every month, but water is cheap in the West. Not only do Arizonans pay some of the lowest residential rates in the nation - in one survey of big cities, only San Antonio charged less - the state's farmers tap into reliable, subsidized sources that allow them to survive a shifting economy. The Salt River Project collects about $10 per acre-foot from its municipal customers, a rate that hasn't changed much in years. The Central Arizona Project, a $4 billion canal that brings water to Phoenix from the Colorado River, charges cities about $105 per acre-foot. An acre-foot is about 326,000 gallons, or enough to supply a five-person household for one year. Tribes have been reluctant to talk price publicly, but one attorney told a group of city officials that the cost could start as high as $1,100 per acre-foot."

$10 per acre foot is practically free. Are there no carrying or pipe-line charges? That wouldn't even support routine maintenance.

An acre-foot is 326,000 gallons, or about 43580 cubic feet.

$100 per acre foot is 0.23 cents per cubic foot. $1000 per acre foot is 2.3 cents per cubic foot. That's still almost half of what we pay (but then some of our costs include sewer surtax).

So what does the average home owner in San Antonio pay for his water?

Given the risk of damage to property and loss of life due to improperly installed water heaters I'd say it's perfectly reasonable to insist a permit be issued. As for your permitting people being lazy, that's certainly worth a call to the newspapers. Call them anyway, if just to give the Metro section reporters something to write about.

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

then

residential

substantial

Evaporative

in a

you've

of

calculations

correct

you

into

to

supply

works

a

and

in

used

wish

or

during

runoff,

to

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

Jim, watch what you're doing. I don't need your posted response as an email with an attachment. Reading the newsgroup is just fine.

R

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

2 C

it's

(different)

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

running.

and

(combined with

prolong shingle

process

the

cool

for

ON the roof

just as with a

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

be

above

if it

form of

lower

circulating

once

effects

etc.

90F...

up

manifest.

cases.

20

humidity..that

with

runoff,

reduction

seldom

you

tarp