Electricity-free way to cool a home?

What are things that you do? We don't have air conditioning, but do have ceiling fans which I would prefer to not use. We live in a garage and it gets HOT. Hopefully we will be insulating the ceiling soon, but I doubt that will help much with the heat...

Here are a lot of ideas: http://www.builditsolar.com/Projects/Cooling/passive_cooling.htm

Shade
Earth contact
Earth air tubes
Water flow
Air flow
Solar chimney
Simple chimney effect
Lunar cooling panels
Thermal mass
High ceilings

Cheers,

-Walter Jeffries
Sugar Mountain Farm
Pastured Pigs, Sheep & Kids
in the mountains of Vermont
Read about our on-farm butcher shop project:
http://SugarMtnFarm.com/butchershop

Check out our Kickstarting the Butcher Shop project at:
http://www.kickstarter.com/projects/sugarmtnfarm/building-a-butcher-shop-on-sugarmountainfarm

Walter Jeffries wrote:
Lunar cooling panels

Do you have any links or other information about this?

Tyler Ludens wrote:

Walter Jeffries wrote:
Lunar cooling panels

Do you have any links or other information about this?

Unfortunately no, I don't have a link because I haven't written the article about it yet. I invented them. The idea is simple though so let me give you the short version: A lunar panel is the opposite of a solar panel. With a solar panel you capture the light of the sun and turn it into heat energy which you then pump into a storage vessel. Rewind. With a lunar panel you take the heat from a vessel and run the fluid up through the panel pointed at the darkest part of the night sky (not actually the moon) and the heat radiates away. The now cooled fluid is denser so it falls back down into the vessel (your house, concrete slab, water tank, etc) and picks up its next load of heat. Once it is warmed it rises back up through the up side of the tubing to the lunar panel where it once again releases it's load of heat. Presto: Lunar Cooling Panels. I like passive systems that use thermosiphons so it has no motor burning energy but you could build it with a motorized pump if you were upside down (e.g., you were sending the heat down into a pond or the ground.)

Cheers,

-Walter Jeffries
Sugar Mountain Farm
Pastured Pigs, Sheep & Kids
in the mountains of Vermont
Read about our on-farm butcher shop project:
http://SugarMtnFarm.com/butchershop

Check out our Kickstarting the Butcher Shop project at:
http://www.kickstarter.com/projects/sugarmtnfarm/building-a-butcher-shop-on-sugarmountainfarm

I worked for a solar pool heater company and they suggested doing just as Walter detailed to cool off the pool if temps got too high. Just run the panels at night-- doesn't matter if the moon hits them or not. It really works.

Seren Manda wrote:I worked for a solar pool heater company and they suggested doing just as Walter detailed to cool off the pool if temps got too high. Just run the panels at night-- doesn't matter if the moon hits them or not. It really works.

Exactly. The moon has nothing to do with it. I just like calling them Lunar as opposed to Solar. Technically, the darkest part of the sky would be best.

Cheers,

-Walter Jeffries
Sugar Mountain Farm
Pastured Pigs, Sheep & Kids
in the mountains of Vermont
Read about our on-farm butcher shop project:
http://SugarMtnFarm.com/butchershop

Check out our Kickstarting the Butcher Shop project at:
http://www.kickstarter.com/projects/sugarmtnfarm/building-a-butcher-shop-on-sugarmountainfarm

You can use pex tubes with sprincklers on the roof, one pump takes the water in a well or in a rain water collector, a timer or an appropriate thermometer drives the pump and it goes; water that has not been evaporated comes back by gutters. Now you have the biggests , the cheapest but efficient air conditioner in the neighborhood!

Dude, a swamp cooler is your best option and it does not not take a lot to run one. I lived in the high desert and in the top of the summer day I would spray my roof with water. It cooled the roof off to mitigate the heat gain. Have you thought of a tarp that is wet? Cal usually has dry wind. The effect of the evaporation will cool you off inside it. Misters too work, same principal.

Just get a cheep above ground pool and use it.

Also, you need to vent the roof heat will rise and cool drops.

we have an indoor outdoor battery thermometer that we keep an eye on..if the temps outside are cooler than the temps inside and not forcasted to drop TOO cold (like 40's or so)..we open every window in the house and let the colder air inside..then before the temps are equal inside and out, while it is still cooler outside..we close all the windows and pull the blinds if the sun is out and the forcast is for very very hot weather..thus trapping the cold air inside and keeping the warm air outside..we only pull the blinds on the sunny side of the house in order to still allow plenty of light in the north and non sunny areas..only preventing the sun from getting too hot inside.

we avoid anything that produces heat in the heat of the day here, attempting to do any laundry, run dishwasher, cook, etc..inside during hot days..we plan cold meals or cook outside on the grill.

also remember to dress in light colored clothes outside in hot weather and there is a new item for heat rashes that appears to work it is Gold bond friction stick..like a deoderant stick that you use where you get heat rashes..(which i get badly in the summer ..also get heat stroke)..i tried it and so far since i've used it, no heat rashes..woo hoo..they can be very painful.

also switch to LED lights where you can to cut back on heat..if you have fans use them only to circulate air when it isn't blowing hot air on you.

unfortunately we had to lose a huge tree in front of our house that provided shade all summer long to our home..which is gone now..so we are planting more trees..that will take a while.

you could grow vines up the outside of your house to shade the house as well..including things like green beans up string..

apologize for not taking time to read all the tips..just don't have the time right now

did you find out about the old burlap coolers?

basically a window box with burlap hanging down like a screen, and soaking up and evap'ing water. what they used to use out here in the southwest.
works best in windows the wind is blowing into, especially a high one.
] EVAPORATIVE COOLER

http://forums2.gardenweb.com/forums/load/strucs/msg051951147967.html

http://h2othouse.com/html/cooling.html








seach for burlap cooler, burlap icebox , and burlap cold storage


got a solar panel?
http://www.swampy.net/evapcool.html


http://www.provident-living-today.com/Alternative-Refrigeration.html


can also build up a stack of bricks, or blocks, higher than the window opening, on the sunny side.
spray em down, inside, and out, and the air on the inside will be much cooler than the outside.
put a couple potted plants on top to help out more.

and solar electric
http://www.ssrsi.org/sr2/Heat/cooler.htm

Evaprative cooler work well in dry climates. They compound the problem in high humidity areas.

Soak some thin blankets in water and hang them in front of windows/doors.

Hose off your roof to cool it off.

Hello. I have looked into such things before. Have a look at this...

http://en.wikipedia.org/wiki/Absorption_refrigerator

Particularly the part about "Water spray absorption refrigeration". I could easily see this being AC built cheap and easy. All you need is salt, water, heat, and ingenuity.

Edit: It's not unlike a "Swamp Cooler" Only these will work in wet climates where the former will not.

I had a garage that heated up to 120 degrees in the summer. I insulated the ceiling with styrofoam up against the UPPER
attic rafters. This allowed the heat to rise UP and then
OUT of the garage through a roof-turbine vent. After insulating the walls, this garage rarely went above 82 degrees
during hot summer days even with NO AIR CONDITIONER. Another method of accomplishing this is to simply paint
the roof white. I found a way to do this at a cost of less than 20 dollars. You can read about this on the
website "builditsolar.com" here is the link ..... http://www.builditsolar.com/Projects/Cooling/WhiteRoofExperiment/WhiteRoof.htm
These methods work VERY well and have minimum cost. The attached picture shows attaching styrofoam sheets
to the upper attic rafters in process (not completed).

Our kitchen opens out to a 12 metre x 12 metre combined nursery and artificial wetland greywater treatment pond. On a hot day we open up an upstairs window, and cool air is drawn inside from the nursery. I really should do a thread on that nursery.

Heat rises. Anything you can do to drive heat up and out of your house works great.

At one point we lived in OK where it was 100 plus degrees all summer.  We had a very small one room air conditioner in the bedroom. That was it. By driving heat up and out with fans we were pretty cool. We had a fan that drove the air into the attic and then another that exhausted the heat from the attic.

My Hubby is more heat sensitive than me or would never have air conditioning.

Best,
Lil

Jason Silberschneider
QUOTE: “I really should do a thread on that nursery.”

Please do .... id love to see pics and read about it !

Although hubby and I have and use a/c on occasion (health problems) we have used a technique similar to one posted above using fans. First thing in the morning (or even during the night if we get up), hubby fastens a large box fan into the screen door . As a self-storing storm door, it has a bar horizontally about half way up the screen part, which is ideal.  The fan is positioned to blow outwards, which creates a slight vacuum throughout the house. So then we open windows to allow the cooler outside air to flow in. The trick is - the outside air has to be at least 5*F cooler than the internal house temps. As soon as the sun comes over the mountain, outside temps warm rapidly and we close everything up, pull shades and keep the cool air in. Obviously you can't keep the house cool with people running in and out; so limit your exiting to doors on the shady side.  In another situation, we installed the same fan face down into the attic opening, and exhausted the hot air upwards as the cooler air was drawn through open windows. Mostly the fans are limited to nighttime and early morning use, but they do make a difference for a good morning. I forgot to mention that the room in which the fan is found is the last to cool, which might be a consideration as to the fan's placement.
Sorry, not electricity-free, but still good to know. Oldtimers used evaporative cooling to keep their watermelons and other produce fresher by covering them with wet blankets and wetting them down periodically in the shade.

I have been chewing on this recently too, what with summer heat and all.  I think the white roof idea might be the best bang for the buck and effort (esp. ongoing effort....aka none).  I have read the article on Build It Solar and there was also another good DIY white-roof article there.  Permies tend to like long-used traditional methods......I think whitewash qualifies!

Here's the way I like to look at these things - simplified model - your house is like a cell phone or laptop with a battery.  Heat, or cool if you want to look at it the other way, is like the charge in your battery.

To keep the amount of charge (heat/cool) within certain limits, you can -

Charge the battery more (frequently or faster)

Discharge the battery less (frequently or faster)

Or get a bigger battery

Charging, during summer, might be removing heat / adding cool.  That's all an A/C does - pumps heat from inside to outside, using electricity.  Ventilating at night, as others have mentioned, is a decent, less expensive method (removing heated air).  

Discharging less might be limiting the heat gain in summer (lower your loss of cool).  Shading, cool roof, attic insulation / ventilation, etc. can be examples.

A bigger battery would be more thermal mass - like the RMH concepts.  Actually I think an RMH could be a good addition to a cooling plan too, if done well.  Of course, you still have to charge your battery / mass (get the temperature down, e.g. by night ventilation) if you want it to last.

So look at controlling building comfort in a from that perspective - think through what the heat gains / losses are, and what you can control most easily.  And of course just reverse things for the cold season.

And remember the three modes of heat transfer - conduction, convection and radiation.

Walter Jeffries wrote:

Tyler Ludens wrote:

Walter Jeffries wrote:
Lunar cooling panels

Do you have any links or other information about this?  

Unfortunately no, I don't have a link because I haven't written the article about it yet. I invented them. The idea is simple though so let me give you the short version: A lunar panel is the opposite of a solar panel. With a solar panel you capture the light of the sun and turn it into heat energy which you then pump into a storage vessel. Rewind. With a lunar panel you take the heat from a vessel and run the fluid up through the panel pointed at the darkest part of the night sky (not actually the moon) and the heat radiates away. The now cooled fluid is denser so it falls back down into the vessel (your house, concrete slab, water tank, etc) and picks up its next load of heat. Once it is warmed it rises back up through the up side of the tubing to the lunar panel where it once again releases it's load of heat. Presto: Lunar Cooling Panels. I like passive systems that use thermosiphons so it has no motor burning energy but you could build it with a motorized pump if you were upside down (e.g., you were sending the heat down into a pond or the ground.)

Hey Walter, have you done much work with your Lunar Cooling Panels?  Are you referring to two-phase thermosiphons?  I have been interested in toying around with a TPTS night sky radiative cooling device for a few years now.  There are many other important projects to get underway first, like a passive refrigeration system to make ice in the winter, similar to the Scott Nielsen version.  

Love to see a DIY radiative panel example.  It would be neat to continue ice production in air temperatures above 0 Celsius, assuming clear skies!  

John Polk wrote:Evaprative cooler work well in dry climates.  They compound the problem in high humidity areas.

Amen, brother!  Thanks for pointing out the other half of the story.

hannah ransom wrote:...We live in a garage and it gets HOT. Hopefully we will be insulating the ceiling soon, but I doubt that will help much with the heat...

Actually, insulating your ceiling is the single simplest and most important thing you can do.  The greatest heat gain/loss of any building is through the roof, not the walls or windows.  I would highly recommend installing a radiant barrier as well as traditional insulation.  I have them and they are amazingly effective.  However, make sure that you understand how they work so that you can see that they are installed correctly.  I am astounded at the number of people I've come across - including professional builders who were installing them on jobs - who DON'T understand the (pretty simple) physics behind how radiant barriers work, and install them incorrectly!

The easiest way to install a radiant barrier is during new construction.  That's what I did.  Every 4'x8' sheet of OSB for your roof sheathing, you can get with the foil barrier already attached.  That increases the material cost from maybe $5 per sheet to $8 per sheet.  But then your barrier is installed when you sheath the roof, and you haven't spent one extra minute doing it!  Otherwise, there are plenty of aftermarket barriers you can retrofit onto the undersides of existing roof sheathing.  But the reflective foil side MUST face down into the attic space, and you MUST have an air gap immediately below that, preferably coupled with plenty of roof ventilation.  Without an air gap, the heat you're trying to keep out simply bypasses the radiant barrier via conduction and you have achieved nothing.

This works great for an attic with insulation on the floor.  If for some reason you feel you must insulate the roof of the attic - or if you have no attic and the roof is the same as the ceiling of your living space - then you will either have to build a double ceiling so as to have the roof and radiant barrier, then a ventilated air gap, then insulation and the inner ceiling, or you will have to forgo the radiant barrier.

Walter Jeffries wrote:

Tyler Ludens wrote:

Walter Jeffries wrote:
Lunar cooling panels

Do you have any links or other information about this?  

Unfortunately no, I don't have a link because I haven't written the article about it yet. I invented them. The idea is simple though so let me give you the short version: A lunar panel is the opposite of a solar panel. With a solar panel you capture the light of the sun and turn it into heat energy which you then pump into a storage vessel. Rewind. With a lunar panel you take the heat from a vessel and run the fluid up through the panel pointed at the darkest part of the night sky (not actually the moon) and the heat radiates away. The now cooled fluid is denser so it falls back down into the vessel (your house, concrete slab, water tank, etc) and picks up its next load of heat. Once it is warmed it rises back up through the up side of the tubing to the lunar panel where it once again releases it's load of heat. Presto: Lunar Cooling Panels. I like passive systems that use thermosiphons so it has no motor burning energy but you could build it with a motorized pump if you were upside down (e.g., you were sending the heat down into a pond or the ground.)

@ Walter Jeffries - Walter, I find your concept of a lunar panel fascinating.  Very creative.  But I am confused about something: what about your system do you feel is an advantage over a classic passive solar cooling ventilation scheme?  Have you done a study on the thermodynamics that suggests it is worth the extra cost and trouble?  I'd really like to know.  Like you, I am fascinated by the simple elegance of passive systems.

To elaborate my question... You are proposing a fluid loop powered by thermosiphon effect that transfers heat collected from the living space (via a radiator-type fixture, I presume) to a panel, from where the heat is radiated to the outside.  So that requires two heat exchange fixtures (one inside, one on the roof), plus fluid, plus piping.  Whereas at night (or whenever it is cooler outside than inside), I instead open my clerestory windows and my lower room windows and let the hot air exhaust from my house, drawing a steady flow of cooler air in at the ground level. This also works on a thermosiphon effect, but my heat transfer fluid is just air, and my heat exchange fixtures are just open windows (one high, one low).  Yours is a closed loop system, whereas mine continually exhausts the cooling fluid.  But then air is free.  Clearly my system is simpler, lower cost, and more foolproof since there is no apparatus to require maintenance.  But that doesn't necessarily mean it is more effective.  Also, if one didn't build a clerestory into one's home, an exhaust fan would be needed instead, which then introduces an apparatus to break down as well as electricity to burn.

Interested in your opinion.  Thanks!

Wind tower, they are used across the middle East, Pakistan etc I have built them

FWIW, the concept of "lunar cooling panels" is more commonly referred to as "Night Sky Radiant Cooling", you'll have a lot more luck researching if you use those terms in your search engine.

NSRC has been used for thousands of years and there has been a fair amount of research into it recently including a TED talk I saw recently where they had developed a selective material that allowed them to do radiant cooling even during the daytime.

Without using the expensive selective materials NSRC works best on clear nights with low humidity.   Too much moisture in the air will absorb and re-radiate the heat back towards you instead of allowing it to radiate out into space.  The research I'd read indicated that NSRC panels can reach temperatures almost as low as the local dew point.

Some thoughts on modeling performance:
http://www.solarlogicllc.com/Articles/pe07_2010%20extracted.pdf

A description of a NSRC system built in New Mexico:
https://aceee.org/files/proceedings/2006/data/papers/SS06_Panel3_Paper12.pdf

Matthew Nistico wrote:
@ Walter Jeffries - Walter, I find your concept of a lunar panel fascinating.  Very creative.  But I am confused about something: what about your system do you feel is an advantage over a classic passive solar cooling ventilation scheme?  Have you done a study on the thermodynamics that suggests it is worth the extra cost and trouble?  I'd really like to know.  Like you, I am fascinated by the simple elegance of passive systems.

To elaborate my question... You are proposing a fluid loop powered by thermosiphon effect that transfers heat collected from the living space (via a radiator-type fixture, I presume) to a panel, from where the heat is radiated to the outside.  So that requires two heat exchange fixtures (one inside, one on the roof), plus fluid, plus piping.  Whereas at night (or whenever it is cooler outside than inside), I instead open my clerestory windows and my lower room windows and let the hot air exhaust from my house, drawing a steady flow of cooler air in at the ground level. This also works on a thermosiphon effect, but my heat transfer fluid is just air, and my heat exchange fixtures are just open windows (one high, one low).  Yours is a closed loop system, whereas mine continually exhausts the cooling fluid.  But then air is free.  Clearly my system is simpler, lower cost, and more foolproof since there is no apparatus to require maintenance.  But that doesn't necessarily mean it is more effective.  Also, if one didn't build a clerestory into one's home, an exhaust fan would be needed instead, which then introduces an apparatus to break down as well as electricity to burn.

Interested in your opinion.  Thanks!

I tend to agree, there are so many other options for expelling heat, or avoiding it in the first place.  Night sky radiative cooling is a neat technology, and if properly applied, it has the potential of dissipating more heat than other passive systems, or even active ventilation schemes.  I've seen systems applied in the tropics that cooled water on the roof at night that could absorb heat in the ceiling during the day, after insulation was re-applied in the morning.  The version I would like to play with would use a simple two-phase thermosiphon loop containing a volatile refrigerant that naturally circulates between a heat source and the radiative panel.  The size of such a system to cool a home down is impractical in my view, as you would need a rather large surface area, as well as pretty clear and dry skies, and few terrestrial sources of heat like trees.  

White roofs, radiant barriers, natural ventilation at night, and shade should be more effective and cheaper to install.  There's no substitute for good basic design, unless you want to brute force cooling with heat pumps.

In case anyone hasn't seen the recent TED talk on radiant cooling

Not necessarily modern suggestions, but a book by John S. Taylor, A Shelter Sketchbook, provides a section on how many folks in many cultures around the world have included designs/features in their shelters to keep cool.

Built one of these for my kids dorm room.  It worked pretty good for a small space and a few hours of relief and a nap.  You can sub a small fan that runs off a solar cell in for the plug in electric one shown in video.  Happy Nappies ya'll

I'm under the vague impression that if you dig a basement below the frost line it will reach the geothermal layer, and your house will stay around sixty degrees year round as long as it is totally insulated.  I thought I read that a year or two ago when I was researching earthbag domes.  Am I off?

Rob Lineberger wrote:
I'm under the vague impression that if you dig a basement below the frost line it will reach the geothermal layer, and your house will stay around sixty degrees year round as long as it is totally insulated.  I thought I read that a year or two ago when I was researching earthbag domes.  Am I off?

You don’t even need to be below frost line; you can create an insulation ‘umbrella’ around the perimeter of the house. You simply need to be below grade, ie- lower than the top of the ground. As to 60 degrees, that will vary depending on location, but typically is 45-65 in most places. In the far north or far south one would need to go deeper or insulate more. Whether that will heat/cool the above grade part of a house depends on a lot of other factors. But earthbag homes have a lot of thermal mass in the walls which tends to stabilize temperatures for longer time periods.

Julie Reed wrote:As to 60 degrees, that will vary depending on location, but typically is 45-65 in most places. In the far north or far south one would need to go deeper or insulate more.

Very true, Julie. This page at "Build it Solar" has a chart showing mean soil temperatures at a 30-foot depth. That's considerably below anyone's frost line, but it gives an idea of what's possible in one's location.

Timothy Dowty wrote:

Built one of these for my kids dorm room.  It worked pretty good for a small space and a few hours of relief and a nap.  You can sub a small fan that runs off a solar cell in for the plug in electric one shown in video.  Happy Nappies ya'll

Thanks for posting!  I was well aware of this concept - portable, fan-powered, ice chest coolers - but this is the best construction guide I've yet seen.  I plan to make one of these for myself, as it will be considerably cheaper than fixing the AC in my car!

Every prepper living in a hot climate (as I do) should make several of these for emergencies.  During an extended summertime power outage, you could run an ice-maker for a couple hours off of a generator or solar array, but good luck trying to run your central AC, or even ceiling fans.  Especially if you could make them with battery-powered fans, each person carrying one of these around to wherever in the house they are working could be a good solution.

I note that evaporation-based coolers are simpler, cheaper, and less energy intensive, since you don't have to make ice.  And they work great... if you live in a desert.  If you live in a sauna, you have to go an extra length to create cool air.  This seems like an excellent path to get there.

Here is a good tip to augment your home cooling strategies, which I don't think anyone has yet mentioned.  This could be a great addition to a passive solar home design, even one off grid.  A couple of caveats, first:

1) I present one version that IS electricity free.  BUT it assumes you are hooked up to city water (or else that you have a well with a strong pump... which uses electricity).
2) I present a second version that is NOT 100% energy free, but can be implemented off-grid.  It does use minimal electricity to pump water against gravity, but reasonably small amounts of water, so we're talking about electricity that shouldn't max out your generator or solar array.
3) I've not yet implemented this design myself, so can't verify just how well it works.  Totally plan to, so will post an update whenever I do.
4) This is not my own idea.  I heard it advanced on TSP by alternative energy and prepping guru Steven Harris, who has more detailed info on his various websites... BUT as I write this all of his websites are off line.  I have no idea why or for how long.

The basic concept is to hook up a hose to your outside spigot, snake it up your wall, and attach it to a dispenser that runs along the ridge of your roof.  That dispenser could be assembled out of materials from a drip irrigation system, or it could be as simple as a cheap garden hose with carefully-spaced and -positioned holes poked into it.  On hot, sunny days, the spigot is turned on so that water dribbles down evenly over the surface of your roof.

This system recognizes that the majority of any building's heat gain or heat loss occurs through the roof.  That is why even conventional, energy-stupid homes have more insulation in their attics than in their walls.  In terms of summertime heat gain, with which we're currently concerned, a cooler roof means a cooler attic, and a cooler attic means a cooler home!

Obviously, you would only run this system during the day, not at night, and particularly during the hottest and sunniest hours of the day.  I believe the idea is to fine tune the flow of water so that only enough comes out to coat the roof - you want the majority to evaporate on the surface and not run into your gutters.  This could be done with a flow restricter built into the rooftop dispenser, or by adjusting the spigot to optimize the flow.  I imagine that it would take a little trial and error to fine tune the settings, and perhaps even those settings might need tweaking to adjust to the difference between a milder day and a true scorcher.

So this is essentially an evaporative cooler for your building.  But it has two huge advantages over traditional swamp coolers, as I see it, both of which advantages boil down to the same effect: this system should work even in humid climates.  Such as my own climate in the South!  Swamp coolers in a dessert make your house cooler.  But if the air is already heavily humid, they just make your house swampier!  Whereas the proposed system cools your building, not your interior air; all of the extra humidity created is outside.

Also, swamp coolers don't work efficiently in humid air.  They just don't evaporate enough water to do much cooling.  But the proposed system should work regardless, because it is powered by the 140 degree (or hotter!) temperatures on your sun-baked roofing material.

And I don't see why it shouldn't work on any conventional roof material: asphalt shingles, slate shingles, metal panels, or tiles.  It wouldn't work on a green roof, but those are already plenty cool.  It also won't work on a flat roof, like the tar or gravel roofs of some commercial buildings, or on the flat roof of an RV.

Another advantage of this system is that it doesn't interfere with the basic functioning of your home.  It doesn't have to be designed in.  It can easily be retrofitted with cheap, DIY materials, depending to some extent on how much you care about appearances.  It need not take the place of your attic insulation, or your radiant barrier, or your attic ventilation scheme, but rather works complimentary to all of those.

As described above, the system is powered only by the pressure of your water line.  If you are not hooked up to city water, you could still easily run the same system out of a rain barrel, but you will need a small pump (AC or DC, depending on your set up) to lift that water up the hose to your roof.  On the plus side, the water being used is free, at least until the rain barrel runs dry.  Then you'd have to refill using whatever source of water your house relies on.  One interesting idea for this kind of off-grid application would be to set up a small solar panel dedicated to running the rain-barrel roof pump, which in this scenario would be a DC pump.  It would only run when the sun was shining brightest, but then those would be the hours when you most need the system to work.

Plus, with that setup you can never forget to turn it off and leave it running through the night!  If running your pump off of household AC power, you could still set up a timer to control when the water flows and how much flows, perhaps pumping water to the roof intermittently during morning and evening, continuously through the afternoon, and off at night.  Either way, none of this would be terribly expensive to set up, nor too technical for the average permie to master.

As I said, I've not built this yet myself, so I can only guess at how effective it is - Steven Harris claims it is highly effective! - or how much water it consumes.  Or how much juice it uses if you require an electric pump.  I imagine these factors would depend on a number of variables, such as just how hot and sunny your summer days are, what color and material is your roof, and even what slope is your roof.  As they say, your mileage will vary, LOL!

I'd love to hear back from anyone who has actually implemented such a system!

Interesting idea, it would use a LOT of water,  so maybe best to set it up as a grey water system?  It would essentially be like watering your lawn all day on hot days. I'd like to know how much water is used on an average day.

Water use maybe more or less of an environmental issue depending on where you live. I know on my block we actually get water quality problems from too LITTLE water usage (sediment builds up), so this might be worthwhile for my house.

Mk Neal wrote:Water use maybe more or less of an environmental issue depending on where you live...

Excellent point!  I still feel confident predicting that, even if the system I proposed uses as much water as you suggest, and even assuming drinkable city water were used, the household would come out on the positive side, dollar wise.  Particularly when you consider that reducing extreme surface temperatures is going to extend the life of a shingle roof, a very expensive and wasteful item to replace.  (Not that this matters to me; I have a metal roof.)

Dollars can be used as an equivalent to estimate energy and materials consumption between various human activities.  But it is a very rough estimation.  And as you point out, there are other factors beyond energy consumption that comprise total environmental impact.

Where I live, water is plentiful.  I am a couple hours away from a temperate rain forest.  And I otherwise use very little water on my property: I have no lawn, and as my permaculture systems mature, I almost never irrigate any more.  Maybe one month a year in a bad year.  Plus I was born missing the gene that causes most Americans to develop a fetish over the appearance of their automobile.  Mine gets washed once a year, and surprisingly it still drives just as well.

Also, even while I'm hooked up to city water, I already have 900 gallons of rain water harvesting capacity, so I'd probably try to use that first.

If I lived in the desert, on the other hand, I might well reconsider the pros and cons of the system I proposed.  But then again, if I lived in a desert other simpler evaporative cooling techniques, like swamp coolers, would be viable options!