Roof Sprinkler Cooling system

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's Nebraska System

 

David's North Carolina System

 

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.

 

Nebraska System

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.

The parts supplier for the sprinkler heads is FarmTek.com 1-800-372-6835.  There are two sprinkler heads a 360 degree (wf4070) and a 180 degree (wf4070).    The microspray adapter (wf1022) is used to connect the sprinkler heads to the plastic pipe.  The cost will be about $3.00 per sprinkler head -cheap.  The solenoid valve (wr1220) is a little pricier (about $42.00).   These folks have a very nice catalogue which they mail out several times a year.
 
I did a web search for the Encore repeat cycle interval timer and found it for $63.00 last spring.  All the rest of the plastic parts were picked up (purchased I mean) at a discount home store.  If I remember correctly the weather proof 24 hour timer was about $20.00 as a True Value  bargain of the month.  This timer serves a winter function as the timer for my home made insulated, heated water bucket for the dogs.

 

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
evaporation?

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,
hot/dry, ...)

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.

Update from John -- January 2014

Just thought I would update you on my evaporative has for the roof.

The system is still running.  About the only maintenance required has been soaking the emitter heads in CLR  in the spring to dissolve the calcium deposits.  I have had to replace several of the emitters.

I have to clean the rain gutters in the fall.  I guess I remove about 5 gallons of sludge from the gutters.  I use a 4" spatula for this tedious task.

The system runs unattended all summer long.

The main downside to the system is the hard-water build-up (Calcium salts) on the shingles.  If I had used a color other than Arctic White for my shingles it would be much less noticeable.

John

North Carolina System

Here is a description of another similar system in a more humid climate from David:

 

Hi,
A comment on roof evaporative cooling system.  I was involved back in about 1984 on a roof top system here near the coast of NC with a similar, although simpler and cheaper system which I will attempt to explain in detail.
 
This was done on insulated poultry houses and my home. The timer set up was similar with the exception of we ran for approximately 3 min out of 15 and adjusted for max benefit. We attempted to have zero run-off to maximize the water to heat removal ratio -- this would be adjusted for your area etc. I don't remember the exact timer used but it was a one hour repeatable timer -- very inexpensive. We ran from water supply with 1/2 pvc to peak of roof.  The pipe was then run across peak of roof using plastic conduit clamps.

Before putting the pipe on roof we perforated it every 3 ft with a NAIL.  We found the easiest way was to use a drill press turned off and press the nail point until it just perforated the pipe (this took time but after depth was determined, it went quickly).  I actually used a bench grinder and flattened out the flat sides effectively sharpening the edges on a number 8 nail before use. This created a diamond shaped pattern which caused the water to fan out somewhat instead of a stream. We experimented with hole placement at different pressures etc and achieved some dramatic results from this. The 300 ft poultry houses saw an "attic" temp decrease, measured at peak of roof, of an average of 30 degrees during a 20 day period in July- August when roof temps were 115 -120 degree avg. My home which I ran slightly longer cycles due to black shingles I ended up running about 3 min in 10 and saw dramatic attic temp drops which I don't have documented but I remember being in the same range as poultry house but having more effect inside the house due to different cooling types. This was very inexpensive I actually used a defrost timer from an old refrigerator and cut notches with grinder to activate solenoid. Use this and experiment and let us hear results.

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