A typical installation is a metal-skinned warehouse-type structure, with a metal roof and no air conditioning. Repair, manufacturing, and many other functions have this kind of building—with many people working inside, in sometimes intolerable conditions in the heat of the summer.
An ingenious new solution is to install a high-tech rooftop sprinkler. These systems have sprinkler heads that emit a very fine spray on command from a computer-controlled temperature sensor. A few seconds of ultrafine spray every 30 minutes or so will (1) cool the environs of the roof by evaporative cooling and (2) simulate an insulating layer in the vicinity of the roof deck. The result is quite remarkable in some applications: a reduction in temperature inside the shed from triple digits to the high eighties. The equivalent R-value of the roof assembly approaches R-30. Furthermore, since the roof experiences fewer extremes of temperature because of the system, many roofing manufacturers will extend their warranty.
Excerpt from Save Energy, Save $$$
Residential rooftop sprinklers have been around for decades, but mostly as a one-time-use fire prevention system in areas that see a lot of wildfires (as in, like the entire Western U.S. ~ here’s the current U.S. wildfire map, showing almost 1000 active wildfires). They’re very inexpensive systems: some PVC piping, a couple of sprinkler heads, and an on/off valve. Given the savings on home insurance in fire-prone areas, the payback on your investment is very fast ~ a year or two, if that long.
Here are photos of a rooftop sprinkler on a house. I installed a SprinKool system on my house in Vicksburg, MS a few years ago. 70% of the roof was a vaulted ceiling, and there was nowhere to add extra insulation to the roof. The sprinkler system cut my summer cooling bills in half and paid for itself in just one season. I installed everything myself (not a good idea if your roof has a steep pitch).
The cooling-type of rooftop sprinkler has a valve that turns on for a few seconds when a thermostat embedded in the roof heats up. A very fine spray (water never runs down the roof) is just enough to moisten the shingles. When the water evaporates, it sucks heat out of the roof to transition water into steam (warming water takes 1 calorie per gram of water to raise 1 C; changing 100 C water into steam takes 540 calories).
Using a rooftop sprinkler for cooling, of course, depends on an inexpensive and bountiful water supply ~ okay in Mississippi, not so much in the bone-dry Western states.
A roof can reach 150 F in the summer, higher in direct sunlight for the typical dark shingles. In my Vicksburg home, there was R-16 insulation between that 150 F and the 75 F inside temperature: A 75 F temperature difference. The rooftop sprinkler keeps the roof temperature around 100 F: a 25 F difference. Since heat transfer is directly proportional to the temperature difference, the heat getting into my house was lowered by 300%.
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Excerpted from Going Green, available as an eBook at this list of eBook retailers online.