Here is a some information on two roof sprinkler systems. These systems provide cooling by spraying water on the roof surface. The water evaporates and cools the surface. They are simple, and appear to be effective, but would not be a good choice in areas where water is in short supply. One study indicates that water use is around 100 gallons per day per 1000 sqft of roof area.
John estimates that his systems saves about 5KWH per day on his cooling bill.
I'd like to hear from anyone else who has experience with these systems, or comments -- Gary.
John's description of the system:
Attached are four scanned photos of my rooftop irrigation system. A repeat cycle timer plugged into a 24 hour InterMatic timer runs the system. The system cycles about three times an hour for about six minutes a cycle. The system runs from about 8am to about 8 PM during June, July, and August. Turning off the faucet and disconnecting the hose will drain down the system for winter. The sprinkler heads and solenoid valve came from Farmtec. I got the Encore repeat cycle timer on line, I had the weatherproof InterMatic timer. I drilled out the sprinkler heads to give a little more delivery. There is a minimal amount of runoff down the downspouts which greens up the buffalo and rescue grass. The repeat cycle timer and solenoid valve was the major cost component of the system. I have less than $150 in the system. Summer time electrical rates in NE are about $0.15/kWh (so much for the myth of affordable public power). Payback should be done next year.
You can email questions about the system to:
John jjdetjr AT egavision DOT com (change the AT to an @ and DOT to a period)
Please cc me Gary
Showing the roof sprinkler pipes laid out on the roof.
2nd view of roof sprinkler pipes -- and, valve and control panel on side of house.
Close up of the timer and valve.
Close up of sprinkler head. They are drilled out for a little higher delivery.
Some additional questions and answers:
It reduces AC load by keeping the
roof temperature cooler through
You have broken the code. I consider it a evaporative cooler for the roof. Cool the roof and you minimize heat transfer through the attic insulation and through the ceiling into the house.
How do you attach the pipes and sprinklers to the roof surface?
The distribution system is 3/4" cpvc plastic pipe. It is screwed through the roof decking into the roof rafters. In the picture of the sprinkler head you can see the pipe hanger which secures the pipe to the roof deck. The pipe hangers are installed at every other roof joist. I used two 45 degree street elbows to get the sprinkler heads perpendicular to the ridgeline (a little screwing around is required to get the angles right).
Do you know roughly how much water the system uses?
I have never measured the water use since we are on our own well (Actually I didn't want to bother since these are low flow heads). The runoff from the gutter is less than three gallons per cycle. The garden gets more water than the roof.
How did you estimate the AC saving?
I have both gas and electrical receipts going back ages. Whenever I finish a major conservation project I try to estimate the actual reduction in power consumption. Since I lowered the air-conditioning set point for last summer by 2 degrees from 78 to 76 degrees the actual power savings isn't one to one. The electrical consumption differential during the cooling season from mid May through mid Sept was 528kW or 4.2kW/day. The Ave. daily temp for the period was about 2 degrees warmer. Since I don't have a wattmeter on the AC unit the 5kW a day savings is a guess but given the cooler interior temperature and hotter exterior during the period it is probably a good guess. About the only downside to the setup is the slight mineral buildup on the roof. It is more noticeable sing the shingle color is arctic white. With light tan shingles the discoloration would be less noticeable.
What kind of climate do you think this works best in? (hot/humid,
Summer humidity in this area is very low so the evaporative cooling is very efficient. If you send me a mailing address I will send you some 4x6 photos and the supplier for the sprinkler heads and timers. Fell free to ask any other questions. My next projects are a hot air collector for the basement and a hot water heater to store the thermal gains in my greenhouse (photo attached). That is how I got to your site in the first place.
North Carolina System
Here is a description of another similar system in a more humid climate from David:
David will answer email questions on the system:
David Stutts, Hampstead NC any questions email stuttsdavid AT yahoo DOT com (change AT to @ and DOT to a period).
Please cc me Gary
Gary 2/15/07, revised 3/6/07