Water Shed Air Conditioner

Insulate and ventilate instead, unless you want lots of bug growth in that rainwater butt!

Insulated as much as possible considering and I have enough large fans and windows to make a hurricane movie....still extra HOT after 1 PM.

No clue what you mean. No help from a search.

Do you intend to run water over the roof and collect it for recirculation?

Spray water onto the roof and collect it?

Have you considered the water load and rust potential?

I'd insulate or bury the tank.

Lynn could this be some version of a swamp cooler. When my wife and I were visiting a friend in Tuscon we saw several cooling system close to this, they constantly had to add chemicals to the system to keep the biologicals at bay. Duke

What works in Tuscon is not necessarily viable in Cajun country.

I would add in new water each day or so.... I have "city" chlorinated water plus iron heavy water well water.

I have a commercial steel roof with 20oz. vinyl tarp over the steel to keep that cool.

Still it is too hot in the afternoon. I have too many cracks and gaps to air condition.

I was just looking at this green house and the system did cool the building.

I used a swamp cooler before with very little effect.

Just a thought on this....I am not dead set on THIS project.....just asking around first.

Thank you for the input.

You could try using one of your fans to blow some air between the tarp and metal roof.

Come on, tell the truth. You just like the sound of rain on a metal roof so much that you want to hear it all the time.

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With the humidity and rain frequency in Louisiana, I'm surprised you want to dribble extra on your roof. Mosquitoes, rust, humidity, algae, gutter clogs and leaks, etc....

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You can get a larger improvement for the same cost, or a similar improvement for a lower cost by using a cool high reflectivity paint on the roof and/or adding insulation and a radiant barrier below.

Yes! I can work extra long during a good rain storm. . . lightning and all.

...and there can't be any more bugs than there already are!

"...and there can't be any more bugs than there already are!...."

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It may not be wise to tempt the fates.

Board insulation is not prohibitively expensive, requires little maintenance and lasts for a long long time....The system you have posited is rife with problems, high maintenance, dubious effectiveness, and possibly illegal....You might consider polyurethane spray insulation...

http://agua2009.info/metal-roof-insulation/#.U5Ozp_ldWSo

http://www.spraypolyurethane.org/

http://www.amazon.com/FOAM-Polyurethane-Spray-Foam-Insulation/dp/B00597CCUU

I have 1" board insulation under the roof. It helps some.

Try 10in of mineral wool insulation instead!

What is that and how would I attach it to bare rafters?

Paint the roof white first, to reflect away sunlight.

Then insulate the roof and whichever walls get a lot of sunshine.

I just insulated the south-facing wall of my tool shed plus most of the south-facing portion of the roof with R-13 fiberglass batt insulation. The thermometer I've kept in there indicates a 15 degree F drop in the inside temperature at 2PM compared to before installing the insulation.

Roof is white already, with a white 20 oz. heavy duty vinyl tarp over the steel.

Some help, but not enough.

The roof is white....I'll hazard a guess that the tarp is a dark color? It might be useful to measure the temperature at different places around 1pm. The highest point below the insulation, justt above the insulation if possible, just above the metal roof, and just above the tarp.

Tarp is black on the roof side and white on the sunny side. I know all about dark colors in heat environs.....

One of the funny things about surfaces behave with thermal radiation is that high reflectivity surface are low emissivity, and the opposite is true as well. The end result being, the black surface may be radiating heat more heat down to the conductive metal roof than the white side is radiating back up. If the tarp is right on the metal roof, the metal roof won't act as a radiant barrier very effectively.

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Not all white or seemingly highly reflective surfaces are cool. Ever been to a white beach where the sand is scorching hot, or on white concrete that is exceedingly hot? The same principle is behind the use of aluminum foil under infrared lamps, it may reflect a large percentage, but it emits less than it absorbs in the short term, i.e. a form of selective surface.

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Measuring temperatures between the tarp and the roof, above the tarp and at places below the roof would be helpful in knowing exactly where the problem lies.

Oh Oh! The tarp is laid straight down on the roofing. It is screwed down to the metal.

The inside is jet black, the outside (sunny side) is bed sheet white.

I can not touch the metal roofing at 1 PM for more than a few seconds... under the tarp I can touch the metal for as long as I want. Its warm but not blistering hot.

Under the roof, on the rafters inside the shop I have 1" insulation board nailed about 6" from the metal roof ( on the 2x6 rafters).

The heat is now unbearable for me due to health issues. Years back you could not burn me out with napalm...but after that last kidney surgery, I am now just a big Candy A$$ .

• Do you think that tarp is hurting the situation?
• Will this misting plan alleviate any of this? If I can knock 10 degrees off, I'd consider this a success.

An AC man I trust, said it would take 8K of insulation and new windows/ doors to even think about running a 3-5 ton unit. that will not happen in the near future. I just need to knock off 10 degrees from 1 PM through 5PM and all will be good in Cajun land!

Get that tarp lifted off the roof so air can flow between the roof and the tarp. Since it is a sloped roof, If it is open at the top and bottom, there will be natural convective circulation of air carrying heat away.

Better still, as someone else suggested, construct a form of manifold to force air through that space and use one of your fans. The manifold could be constructed of the same tarp material.

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• Do you think that tarp is hurting the situation?..."

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It might be, but I don't think that is very likely. What is more likely is that it isn't helping very much.

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Far more valuable than my guesses from afar, would be a quick test. Uncover a couple rafters worth of the full slope, from the low side to the high side. Make some temperature measurements BELOW the metal roof but above the insulation. Compare those temperatures to comparable area of a section that remained covered...but not double covered with the tarp pulled back from the test area...

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Getting actual temperature measurements will give you a much better indication. There are a lot of factors that can affect our sensation of heat. Think about how room temperature metals feel cool. Metals that are hotter than body temperature feel in a similar way feel 'hotter' than similar temperature non-metal materials. This is mainly due to thermal conductivity. The reason I bring this up is, putting your hand on top of the tarp and trying to judge if it is as hot as the bare roof, may be misleading.... for a couple reasons.

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dkwarner has some good ideas on this. Lifting the tarp off the roof will help in a couple ways. Creating channels will encourage convection to cool down the tarp and the roof so that not so much heat continues downward. Moving the tarp a couple inches away will also allow the metal roof the possibility of acting as a radiant barrier as well. If you an get the channels a couple inches wide, with large entries and exits, you might not even need a blower. A smooth transition to a vertical section off the high side would obviate the need for a blower with natural circulation.

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That same idea is important to consider for the space below the metal roof above the insulation. If you have vents to outside air on the low side and high side of those channels, it will be significantly cooler than without. make sure the exit on the high side takes the hot air clear of the side of the building and of any overhangs.

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One last thing on that question...back to the tarp. I'm not sure black on the underside is a good idea. Black generally absorbs thermal radiation well, but it radiated thermal radiation equally well, and that isn't what you want on the back side of the surface facing your heat source if you are trying to cool things down. Consider coating the underside of the tarp with low emissivity coating/paint.

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"....

• Will this misting plan alleviate any of this? If I can knock 10 degrees off, I'd consider this a success...."

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There are a lot of variables here. Can you knock 10 degrees off? Almost certainly. If you have adequate well water, pumping enough between the tarp and roof or even on top of the tarp could make it much cooler. Well water is bound to be many tens of degrees below the hottest temps on the roof. The downside of course is it might be a lot of water and some electricity as well. If you have a use for that much warm water in a day, it might be an option, just set up a big collection tank just off the roof.

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Recirculating water might help for a short time in the morning, but pretty soon that water is going to get hot. In arid places, latent heat of vaporization can provide a lot of cooling, but Louisiana is not arid. It will make the air around their about as humid as it can get as well. Think of those really hot days when it rains for just a moment and the water steams up off the asphalt and it is actually hotter than before....that is a possibility.

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I think you should:

-Make sure your channels beneath the metal roof and above the insulation are well ventilated. adding a blower to push outside air between those channels is something to consider.

-Raise the tarp off the roof a few inches and leave the high side and low side open to encourage convection.

-Paint a section of the bottom of the tarp and a different section of the top of the metal roof, and a third section of both...with a high reflectivity/low emissivity coating/paint. Measure temperatures to see what works best.

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Another consideration in making a space tolerable or even comfortable is humidity. Dehumidifying might be a worthwhile consideration....there might even be ways to put that hot roof to work dehumidifying your space.

It would help to fill the space between the white tarp and the steel with almost any kind of insulation; fiberglass, blown-in, or rigid foam panels.

....that is a possibility also..... just sandwich it in-between???

Some years ago, I lived in a house with an un-shaded, un-insulated 30' x 12' screen porch.

I rigged up a pipe system with misting nozzles on the roof. I designed the nozzle spacing by testing actual coverage per nozzle based on my house water pressure.

I would turn on the system for a couple minutes, then off for 20 or so. It would lower the screen room temperature by about 20 degrees.

1. If it works in FL, it will work in LA.

2. I don't think you need a pump.

3. A little water goes a long way if your design is sound.

4. If you use misting nozzles, you might not need a collection return tank.

Misting might just be the better answer...no pump... mist pulls off more heat than does running water?

Yes, with misting there is more surface area to the water = more heat absorption per unit of water.

http://www.aeromist.com/mist-nozzles/low-pressure-anti-drip-nozzles-10-24.html

Like this??

Heat Reflective Paints - Eco Evaluator may be an option.

Running water over the hot roof may help a little.

Spraying a mist onto the roof would be better. Turning liquid water into vapor removes heat.

LOCKDUKE, swamp coolers work best in very low humidity areas. They also add humidity to the air from outside as it is cooled. Not good for netmaker's shop, which is humid already.

I'm just leery of cascading water over the roof. Of course, if NM uses his well water, his roof will turn red from the iron in the water.

Still curious if this is a mist or liquid water?

A red roof might look pretty down here.

I am leaning toward this misting thing. Mist will pull off more heat than running water?

Mist is better. Your roof will be the temperature of the water running over it. Evaporation of the water (heat removal) will be at the water surface, not the roof surface.

The mist will land on the roof and evaporate from the roof surface, giving better roof cooling.

That's the way I see it.

Should I remove the tarp?

Go online and do a search for ceramic powder. You add it to paint and put a coat on the roof. It will keep 80% of the heat from penetrating the roof. You can walk on it at noon in your bare feet. I have painted paint (with ceramic powder mixed in the paint) 7 mils thick on steel pipe that was at 400degrees F and you could lean against it and not get burnt. I have tested it on several different hot surfaces and it does work. Do a search and check it out. When you paint it on a roof you have to be careful that it doesn't cause it to rain on the inside of the building due to condensation.

Thank you. that is yet another solution in case I need to go to plan B. The idea of condensation build up is so very real. It is always humid down here already. I am not sure of what the misting thing will do, however I can cut that off quickly. Thank you for the ceramic idea though....it might be worth a trial on a section .

I was going to ask about humidity, the cooling effect of the water flowing on the roof results from evaporation of the water, it works in dry places but not in high humidity.

...even if it's really HOT????

At any interface between air and water (like the surface of a wet object or a droplet of water), there is always a balance between evaporation and condensation. It takes energy for a molecule to evaporate (move from the liquid phase to the vapor phase), and that energy is taken from the remaining liquid water and/or other objects in contact with that water, lowering the temperature. When a vapor molecule condenses (moves from the vapor phase to the liquid phase), the energy is returned to the liquid and those other objects, increasing the temperature. If the relative humidity at the interface is less than 100%, then more evaporation than condensation will lower the temperature of the surface until that surface is at the dew point temperature

If the roof is significantly hotter than the surrounding air, then evaporation will be greater than condensation and some cooling will occur. The rate of energy exchange is highly dependent on the humidity of the surrounding air; if the humidity is low (like the 5-15% common in places like Arizona), the cooling will be rapid and efficient. If the humidity is high (like it commonly is in your area) the cooling will be slow and inefficient.

And if the water is deeper than, say 1/8 inch, the cooler surface water will be carried away before it can remove any heat from the underlying mental roof.

That's why a mist is more effective, I think.

How do you keep, say 1/8 inch of water on top of a mental roof?

A mist has a very large surface-to-volume ratio, so can evaporate rapidly IF the humidity is low.

Just going by the sketch. It appears that there is water cascading down the roof to a gutter.

Average Humidity will be around 70%...seldom lower. If humidity will affect the misting, then we have a problem.

With that said, my wife found THIS . It would be the "O" type for Outdoors....not the "I" type for indoor ( winter).

What do you all say about this kind of Shade Sail? I make these things already out of 70% sunlight blocking, woven PP and they do a great job of making a patio or deck area a lot less hot.... This material is the same but has some differences as it is aluminum. What do you all think of a shade sail made to cover most of the shop as the 1 PM sun's position lines up on it????

Having a shade that is distant from the roof will help a lot, and the composition of the material becomes far less critical. It would be better if the material reflected most of the radiation, but even if it absorbed it and got hot, the distance would minimize conduction and convection to the roof and would substantially cut the radiation to the roof.

A well lined trench on the south face of your building with running species of timber bamboo could have your place well shaded but it would take two years at a minimum.

If you just lift the existing tarp high enough off the roof to allow plenty of air circulation between the tarp and the roof, you'll essentially have a shade sail.

I have the impression that the low side of your shed is the south side. If so, extending that tarp 2 or 3 feet beyond the bottom edge of the roof will shade the south wall in the summer, and increase the chance of catching any natural breeze. Since you are in hurricane country, the whole tarp should be mounted in such a way as to be easily and quickly removed, and later replaced.

I only briefly looked at the article your wife found, but I suspect that it is aluminized (something else coated with aluminum), not aluminum. Years ago I tried using aluminized mylar as a solar reflector, but it did not last long in the sun. (but then very few plastics do last long in full sun. The major exception I'm aware of is Teflon. I have Teflon antenna insulators (homemade) that have been out in the sun for over 50 years, and still look like new. Does anyone make fabric of Teflon?

This is another good point. The south wall can be a huge source of heat. Overhangs on the south side and awnings over windows on the south side help a lot. where overhangs on the south side are not feasible, consider more insulation behind that potion of the south wall.

Overhangs and awnings on the east and west sides help somewhat, before and after noon, respectively.

The south side is protected by huge trees. I have shade from them until right before noon. Its that 11 AM to 4-5PM sun light from the west that kills us.

The tarp is very heavy. Lifting it off the roof will be near impossible without a major frame work. However, the Shade Cloth I do have as well as this Aluminet both have UV inhibitors and are rated at full sun for 5-8 years.

Just getting something to cast a shadow will do it you think?

If it is not close enough that heat exchange by conduction and convection are negligible, and it isn't radiating a lot of heat toward the building, shade will be very effective.

I've been mentally picturing a 2x4 or 2x6 on edge at every 2nd or 3rd ridge of the roof. Something like this:

Obviously the shading object will be heated by the sun. As long as there is sufficient space between the shading object and the roof, for the air to carry away most of that heat, then that heat will indeed be carried away and not reach the roof.

Note that, once installed, this requires no energy, while any water system does.

It is resting on the roof right now, the spacers you use to lift it off the roof can rest on the roof as well if aligned properly. Something as simple as 30' pieces of pipe secured at intervals overhanging the 28' dimension of the roof a little on each end, with the tarp tensioned in the 50' direction could work. depending on the tension you can use, you may not even need very many pieces of pipe.

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You might even have material laying around the shop that could do the job reasonably.

Well, I did deal with the temperatures in Houston, for a while. Under the asphalt shingles the temperature at 14:00 in July rises to 150°F. I painted, first, the shingles with paint specially made for this purpose. I did attach to the ceiling of the cathedral ceiling boards of 2 inch foam, and painted over. I have rolled Rxx (I don't remember the ratings) of insulation, in the attic, where I could reach (the crawl area is very small and I am....not small). I have created a porch on the North side with apertures and I installed a temperature activated fan, so it would be a draft of air taken from the North side (shaded) to the upper side of the attic.

It didn't work very well untill...I have mounted on wooden blocks, 2x4x6 doubled, insulation boards, 8x4 ft, with one side covered in aluminium foil. I have covered all the South slope of the roof. The 31/2 inch between the roof and the board kept the roof at the ambient temperature (the max 100°F). That worked fine! Air was able to cool the living bellow 80°F and I felt like an...engineer. Until, not you didn't guess! Until Ike came. Before that were winds, rained a lot and I didn't have any problems. But you cannot fight Ike.

So, for a secondary roof, placed 6 to 10 inch on top of the existing one, you can have the very low electric bill during the summer. Combined with a good isolation in the attic, is economic all year long. Now, with an electric bill of $400 in the summer time on one hand, and the cost of the second roof (I guess closed to 10 grand) It is possible that in 15 years you break it even...

I heard that the radiant barrier is doing fine, too. On the inside of the roof. Stapled on the rafters. It is even cheaper and doesn't care IKE.

P.S. I haven't patented it...yet!

Thank you.

I have replaced maybe 4 or 5 roofs due to hurricanes.... I know about that all too well.

I understand your comments...

Thank you for the information.

What if I were to scrap the heavy tarp entirely. It weighs about 80 lbs....and replace it with one of my Shade Sails ( rectangles) made with either a 70% sun block or that aluminum coated heat shield that is 80% sun block.The shade sail could be as much as 30-40" off of the roof. It would also weight in at about 25 lbs. max. and would allow air to pass through...very importnat with our summer squalls around here.

Lyn has a point....well water will rust...even misting water will have some drops left and the work to set that up might not justify the end results.

After reading through all the questions and answers, I don't see the subject of cross ventilation addressed.....It seems you have taken adequate measures to mitigate the heat from the roof, but the second part of that equation is adequate ventilation, you need air movement across the working environment....You should have garage doors on all 4 sides and some of those 3' or 4' floor fans to force ventilate when there is no adequate breeze blowing through....Even with a ton of insulation, with air trapped inside, the temperatures will rise...

http://www.bvc.com/farmventilation.html

This is what you need...

Instead of re-inventing the wheel, why don't you try this:

http://www.coolerado.com/

The system works by saturating a working air stream with moisture, while the split off cooled air stream is cooled by the latent heat of evaporation on the back side of the media. The cooled off air stream does not become more humid, but will cool off to within 1 degree F of the local dew point. If you live in a climate where the humidity is already above about 60% on average, this might not be a great option, and you will be better off installing some form of refrigeration cycle, or even geothermal heat pump.

Thank you for the link. This does seem to be a uniquely new product. They do not include Louisiana as one of their covered areas. They only allow their people to install and their quote , if they could/would do it, is way out of my budget.

I'd still need serious renovations to seal off all of the old windows and other air leak areas.

Thank you for the link anyway.

If you are not air conditioning the work space, you need to do the opposite of sealing leaks. Improving air exchange efficiency and increasing ventilation will make it much easier to work in the space. It may seem funny to insulate and seal off the roof and walls, but then open the windows, but outside air will be cooler and less humid than air sealed inside if refrigeration of some type is not used.

A while back I took to my WEST wall with a serious Makita sheet metal cutter and put a 5'x5' hole. . . . . this in addition to the 10- 3x3 windows all around and the 8x8 Dutch doors. I am wide open .

* realistically, I am just fighting health issues (which are compounded by the heat), that should have put me on my @$$ for the rest of my days. I just do not want to stop working and I have a limited expense account for building work..... its called getting old! ha ha!!!

If this is a health related issue, as you describe, you need to air-condition the place, and get rid of humidity that contributes to black mold possibility. I know it is hotter than a water less place in Louisiana when the sun is shining and humid. I reckon that a solar-powered heat collection system on the tin roof of that barn would provide enough heat to easily drive an ammonia absorption refrigerated air system. You can put the whole system outside so that in the event of any ammonia leak, it will dissipate away from you. Run a cold water loop inside the barn, and collect the condensate from it to a drain, but it will be relatively pure water.

Use the pump you were going to pump just water with, only heat this water and let it work on the ammonia solution. You might have to add a fan to drive off the waste heat from the chiller.

Your last sentence is key! NetMaker is in Louisiana.

I'm sure the Coolerado is cheaper to operate than a refrigeration unit, in climates where it is appropriate, but I do see a few limitations.

1. It uses 100% outside air. That means it has to cool all of that air all the way down from outside temperature to below room temperature. In the times you really need it, it must cool the air from 100 or 110° (or even higher) down to roughly 60°. (To remove heat from the room, the incoming air must be below room temperature.) I haven't done any of the related math, but I don't see that happening.

While it is desirable to bring in some new outside air to help get rid of the CO₂, H₂O, etc. we breath out, it would be much more efficient if at least half of the air were recirculated, so it only has to cool from room temperature down to 60°.

2. While the system does have separate paths for the moist and dry air, unless the moist air is exhausted a significant distance from the inlet, some of that moisture will get sucked back into the inlet, increasing the humidity of the 'dry' air stream.

3. While this is clearly superior to a 'swamp' evaporative cooler, which raises the inside humidity significantly, it still does not remove any moisture from the air. A significant amount of the comfort provided by refrigerative air conditioning is due to the lowering of the inside humidity, thereby increasing the evaporation rate from our skin.

4. Assuming that the filters remove all of the dust from the atmosphere, (which I doubt), there is still going to be a buildup of minerals in the ducts from the evaporated water. Most hot places don't have naturally soft water. These units are definitely going to require periodic maintenance, annually or more frequently. Of course I've changed the filters many times, but my A/C has been serviced exactly twice in 47 years of operation. OK, make that three times - I did have to replace the compressor fan motor.

You do understand the difference betwee latent and sensible heat, do you not? The air is split into two streams. The cooled stream does not gain moisture, but is cooled to very near the dew point (below the wet bulb temperature). Quick calculation:

105 F, 50% RH, 30.00 in Hg atmospheric pressure results in d.p. of 82.6 without increasing the humidity in the room being cooled, thus increasing the relative comfort level. I do not think it is much worth it above 50% RH though, just as others have pointed out.

If this is way above his price range, the best he can do is swamp cooler with a very uncomfortable cooling effect. He would be far better off water fogging his whole area, and shading the roof, etc. OR get a solar ammonia absorption cooler.

Just measured the temps on the naked metal inside and outside. The INSIDE of the naked metal roof is hotter than the OUTSIDE temp.

Learn something new again on CR4.

There's your sign!

A little more detail, please. Your first sentence implies that you were measuring the inside and outside of the metal, presumably the roof (bottom and top), and presumably while the sun is shining on it. But I don't think the inside of the roof will be hotter than the top of the roof.

Now your second sentence seems to indicate that you were comparing the inside of the roof to the outside air temperature... Of course the roof is going to be hotter than the air; that's why every once in a while we read about a child or pet dying because they were left in a car on a hot day. It can easily reach 150°F inside a car, or other closed space, like your shed with no windows or doors open.

If you don't already have one, get an infrared (remote sensing) thermometer to compare different areas. With that, you can measure the temperature of the roof while standing on the floor. But do remember that the indicated temperature of a surface depends on the emissivity of the surface; A flat black hot surface will indicate hotter than a glossy black surface having the same temperature.

Will do. I have a podna that has one right down the road...

Maybe a different approach is called for.....how about a personal cooling device?

Just too "cool" for an ol' goat like me!

If I understand you correctly, this indicates your priority should be ventilating the space below the metal roof above the insulation.

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It sounds like painting the lower surface of the metal a white/light low emissivity color would be helpful as well if accessing it can be done easily. However, ventilating the channels should be done whether or not you can paint the underside of the metal.

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Shade that is removed some distance from the roof as discussed earlier is also a good idea.