Wasting water like this is prohibited...Insulation is much cheaper, and just as effective...

it's not really a waste per se but I would agree on improving your insulation first before doing your water cooling plan. It's not a common one, which means you might end up spending more.

Roof Cooling

Effective roof insulation & water proofing is one of the better options to reduce roof load. Roof Gardening is another suggestion to reduce roof load on A.C system.

Central Building Research Institute in India had conducted experiment in this regard. They had covered the roof of R.C.C building with Jute Bags and sprinkled water on these bags. There was significant drop in temperature due to evaporation on the water. It was cheaper alternative to expensive air conditioning of the buildings.

I've used this ceramic paint additive in our house, applied to the ceilings and exterior walls with a minimum of 2 coats. There was a marked decrease of inside air temperature of about 25% less then the previous year, using nearly identical outside ambient air temps, humidity and amount of sunshine. It's expensive and a PIA to apply, but it does work! The stuff was originally developed for NASA.

I would have applied it to the roof shingles, but alas I could not.......first there's solar panels on the southern half of the roof. Second, applying the paint would have voided the 30-year asphalt shingle warranty on a roof that was installed 2 years prior.

Painting the roof or ceiling?

Too much maintenance if you are painting the roof.

1) use the collected heat for something (hot water preheat?)

2) don't waste the water (recirc or garden plot?)

3) how much does the evaporation (if any) increase water cost (or electricity to pump in makeup well water)

4) how much energy cost does the pump require?

5) how much heat does the pump generate if in the house (counterproductive?)

6) consider unintended consequences (does it shorten life of the roof?, etc)

7) consider other approaches to success (plant fast-grow shade trees, reflective roof, collect solar energy and make electricity, roof vents to move hot air out by convection, air vent fan, air condition the house, roof-top deck or garden, insulate attic, etc etc etc)

just a few thoughts

I tried this some years ago. Made a manifold of PVC pipe that straddled the roof peak. Then used "leaky" hose to dribble water down the roof. Water that made it off the roof was really hot. The tradeoff would be what the water costs versus HVAC savings. But the wife didn't like it and I took it down before I could get any data.

I like the idea. I've been tempted to do this myself using a hose from time to time. But long term I think it could be trouble. Maybe it would be something to use only in extreme circumstances.

In Arizona they use a foam spray about 6 inches and then paint it white.. works very well

Near where I live, the unthinking politicians demanded wooden shake roofs on houses, thinking it would make the neighborhood look classier. The unintended (?) consequences were larger fire depts. and higher insurance premiums. In that context, or in places where brush or forest fires are a problem, a roof wetting system might really pay off. Locally, water conservation is not a big issue; Kansas City advertises itself as the "city of fountains" and the grass median strips are irrigated by sprayers.

I pulled this off the net as an example..................

Whether you are currently planning new construction or reroofing an existing roof, Spray Polyurethane Foam Roofing and Lapolla White Reflective Coatings are for you. This is because it lends itself well to all types of roofing situations, from traditional flat roofs to unusual designs. Foam roofing systems can be applied rapidly, with little or no disruption to the facilities. In most reroofing situations there is not even a need to remove the existing roof.

Spray Polyurethane Foam has been used as a roofing and insulation material for over 40 years. At one time it was considered to just be an alternative to built-up roofing; foam roofing now protects a wide range of buildings. During this time, foam roofing systems have proven themselves through comprehensive, independent studies to be dependable, long lasting, and very affordable. Today there are foam roofs that have been in place for over 4 decades, and by all appearances they should be able to last indefinitely as long as they are properly maintained.

Because of its light weight, Sprayed Polyurethane Foam Roofing can be applied over already existing roof installations. It can be applied directly over asphalt, shingles, built-up roofs, clay tile, concrete, metal, and wood. This saves the need for tear-off, reducing the amount of time, disruption to the business, even the debris in landfills. The roof has to be properly prepared by cleaning off any loose debris and aggregate, and by making sure that it is completely free of moisture.

Here hot weather is also fire season. I have simply put a submersible pump in my raimwater tank and a sprinkler system on the roof. The runoff goes back into the tank. due to the high volume there is little evaporation and good cooling.

Quote: Here hot weather is also fire season. I have simply put a submersible pump in my rainwater tank and a sprinkler system on the roof. The runoff goes back into the tank. due to the high volume there is little evaporation and good cooling.

Thats what I had in mind!

Norm

Good thoughts, but careful!!!!

When there is a fire large enough to think to use this system, there is usually significant wind and the water is blown away from the building. Sprinklers at the perimeter of the yard might be more effective in cooling the incoming embers and the air stream also.

If you want to use it for fire suppression, then you will need to get sprinklers that do NOT have rubber seals or similar components and the hose will need to be repalced with hard pipe.

Fire control is serious stuff and it needs to be VERY carefully thought through.

Beware of concentrating and cultivating air-borne bacteria in that lovely warm water tank with such a system, particularly legionella pneumophila.

How about a Solar powered attic fan. Zero energy costs the same result. No mold, or maintenance required. When it breaks throw it away and replace it. We have used this company below on our projects in the past for warehouse ventilation along with some good fans from the Bigass fan company.

http://www.atticbreeze.net/zephyr.htm

http://www.bigassfans.com

No piping just one hole and go!!!!!

you "MUST" have ventilated soffit with a roof vent "ridge cap". the air flow between the soffit and vent can't be blocked by insulation. never insulate the the roof. turbine ventilators might also be needed. make sure the attice floor insulation is about r-30.