Solar Cooling

Swamp Coolers, Cooler Management, Dry Ice, Misting Systems, and just plain how to beat the heat.

Solar Cooling

Postby kman » Wed Jun 30, 2010 5:51 pm

I almost posted this in the HexaYurt thread, but realized it probably applies more than just yurt dwellers who would bother reading that thread. :)

I'm interested in nailing down cooling ideas my yurt (or your van, or tent or whatever) ... preferably those that don't involve responses like "buy an AC and a generator or banks of batteries", since that's not an option. I've read FigJam's thread on a swamp cooler with interest, but (a) that's not an option for everyone, and (b) there's still the power issue to resolve. Not to mention the extra water that has to be hauled out to the playa to feed the cooler.

Ideally, I'd like to be all solar, if that's not an improbable dream, and I've been trying to figure out how the heck I can get some moderately reasonable airflow through the yurt without spending many hundreds on big spendy solar panels. The combination of low budget and solar is tricky, I know. There are tons of killer commercial solar attic fans that might do the trick nicely, but they seem to start above $200 and climb rapidly from there. Plus they're one-trick ponies. :)

Any thoughts? I was looking at eBay, which has some pretty sweet looking 40w solar panels for $100 ($120 w/ shipping) that seems like it might be strong enough to push a 12v fan (like perhaps the endless breeze fan, the best I've found) without needing any supplemental power sources. My buddy has been cooling his yurt with a pair of car radiator fans connected to a deep cycle marine battery, but I'm trying to avoid that route if possible, since recharging the battery remains an issue. And even if I had both the battery and the 40w panel, at that level it starts to get a lot more complicated, needing battery charge control modules to avoid overcharging, etc. Direct power seems so much more simple... if it's enough.

Any thoughts? I'm sure there are a number of experts on the topic here, and I'd love to pick your brains a bit, and comb the collective mind for great ideas I'd never come up with on my own. :)
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Postby capjbadger » Wed Jun 30, 2010 10:23 pm

First things first:

Amps x Volts = Watts
Figure your power draw and go from there. :)

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Postby Token » Wed Jun 30, 2010 10:39 pm

Cooling by heating a phase change liquid has been around for a long time.

Propane refrigerators in RVs use that method and do fine.

There are simple devices that can be built from regular plumbing parts that do this with ethanol or similar and a solar collector.

Google it for some plans n kits.
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Postby kman » Wed Jun 30, 2010 11:48 pm

capjbadger wrote:First things first:

Amps x Volts = Watts
Figure your power draw and go from there. :)


Well, if FigJam measured the fan as drawing:

"Low 250cfm 1.44amps, mediem 500cfm 2.08amps, high 900cfm 2.95amps"

... then the solar panel I linked, pushing out 2.3amps per the specs listed, should be able to push the fan at Medium or low, but perhaps not high? (at least at max output, which, I'm guessing is most of the day on the playa)

I'm not sure where voltage plays into that, exactly, however. Also not sure if I should worry about what I've read about startup amperage being a lot higher for fans when they try to spin up.

I guess I can always try it and hope for the best! Worst case, the solar panel should be helpful for recharging a battery, if I decide to cheat.
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Postby gyre » Thu Jul 01, 2010 12:38 am

http://en.wikipedia.org/wiki/Windcatcher
http://en.wikipedia.org/wiki/Stack_effect
http://en.wikipedia.org/wiki/Natural_ventilation
http://en.wikipedia.org/wiki/Solar_chimney

Stack effect uses solar power (heat) to remove air with vents at low and high positions.
Every house using air conditioning needs to be properly set up to use this in the attic.
Few are.
It is extremely effective.
Vent location is crucial.

Wind can sometimes be used as a substitute for stack effect, which is self powered.

I think all you need in this case is an attic or wall providing shade with a vented or open area between it and the main structure, acting essentially as a heat shield.

Additional cooling could be done with an air conditioner or the chemical heat driven devices mentioned.
Those sound intriguing.

The evaporation coolers work, even in crude form.
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Postby gyre » Thu Jul 01, 2010 12:46 am

kman wrote:
I'm not sure where voltage plays into that, exactly, however. Also not sure if I should worry about what I've read about startup amperage being a lot higher for fans when they try to spin up.

I guess I can always try it and hope for the best! Worst case, the solar panel should be helpful for recharging a battery, if I decide to cheat.

Start up draw isn't an issue with a small fan.
The supply needs to be able to maintain voltage on start up.
Easy to check.

Harbor freight has had voltmeters on sale for $3, even with back light.

Radiator fans are high draw.

Small high end muffin fans are made in high flow and high efficiency versions, and different voltages.
Blowers (cages) can be quieter and more efficient.
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Postby gyre » Thu Jul 01, 2010 12:58 am

FYI, I am finding the same incorrect explanation of cross ventilation being parroted all over the net.

Wind does not effectively "push" hot air out.
Cross ventilation is a design approach using stack effect and window location to pull warm air out of a building.
In some climates, wind may be used to draw hot air out.
There are even chimneys designed to achieve this.

"Cross ventilation" as used with identical windows at the same height is recognized as totally ineffective.
Small vents located at upper and lower heights creates far more air flow than huge windows of this type.
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Postby Captain Goddammit » Thu Jul 01, 2010 6:50 am

kman wrote:
capjbadger wrote:First things first:

Amps x Volts = Watts
Figure your power draw and go from there. :)


Well, if FigJam measured the fan as drawing:

"Low 250cfm 1.44amps, mediem 500cfm 2.08amps, high 900cfm 2.95amps"

... then the solar panel I linked, pushing out 2.3amps per the specs listed, should be able to push the fan at Medium or low, but perhaps not high? (at least at max output, which, I'm guessing is most of the day on the playa)

I'm not sure where voltage plays into that, exactly, however. Also not sure if I should worry about what I've read about startup amperage being a lot higher for fans when they try to spin up.

I guess I can always try it and hope for the best! Worst case, the solar panel should be helpful for recharging a battery, if I decide to cheat.


Volts figures in here:
If you compare power levels looking only at Amps it's meaningless unless Volts is the same in each case.
2 Amps at 120 volts is ten times the power (which is expressed in Watts) as 2 Amps at 12 Volts.

Something to keep in mind is that solar panels are usually rated at absolute maximum ideal conditions and rarely achieve more than half to 3/4 of their rated output in real-world use.

I think you should think more about a swamp cooler. They really work! They don't need any more power than any other fan setup, and the water you'll need to bring is worth it! You could also bring some $$ and buy lots of ice at Camp Arctica and use that instead of hauling your own, and it'll be colder too.
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Postby Token » Thu Jul 01, 2010 6:56 am

The art of rising hot air convection in architecture has been used for thousands of years.

Ancient Romans took it even further by digging basements that were flooded with water and placing the low vents down there where they had a big no moving parts swamp cooler.

Nifty part is they figured all this out back in the days of the abacus. And they built these vast buildings with a hammer and a piece of string.
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Postby ygmir » Thu Jul 01, 2010 7:02 am

wasn't the abacus from China?...............

but, string, plumb bob, and square............those nutty Masons...........
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Postby FIGJAM » Thu Jul 01, 2010 7:04 am

The amp draws you quoted are with the pump hooked into the power system. The fan by it self is 1.18, 1.68, and 2.50amps. You can run the pump on a small solar panel, The sight says it uses .23amps.
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Postby FIGJAM » Thu Jul 01, 2010 7:53 am

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Postby FIGJAM » Thu Jul 01, 2010 8:14 am

If I understand gyre correctly, useing a 3 or 4 foot pipe sticking up out of a sealed structure will draw air in where ever you put a vent into the space. So if you just have a wet pad over that vent, the ventury effect of pipe with wind blowing across the top could possibly replace the need for a fan?
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Postby gyre » Thu Jul 01, 2010 8:23 am

Yes, but that's running ac with the windows open.

Unless the outside is cooler than the inside, a bad approach.
Stack effect works best for cooling the attic area.

If the outside air is cooler than the inside, like in a very moderately hot area like the bay, or after nightfall, it is useful for the inside.

But blocking the heat is the first part of it.
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Postby gyre » Thu Jul 01, 2010 8:27 am

FIGJAM wrote:If I understand gyre correctly, useing a 3 or 4 foot pipe sticking up out of a sealed structure will draw air in where ever you put a vent into the space. So if you just have a wet pad over that vent, the venturi effect of pipe with wind blowing across the top could possibly replace the need for a fan?

The intake vent should be as low as possible.
And it is possible to make the intake vents too large.
Not usually an issue with the exhaust part.
Venturi effect is part of the equation.
And distributing the air makes a difference with heat in attics.

Not sure how the venturi effect would play into using it with evaporative cooling.
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Postby FIGJAM » Thu Jul 01, 2010 8:34 am

With evap cooling you need to change the air in the space so the humidity doesnt build up. A box with alot of pad exposure and no fan will work at the same 30 degree temp reduction, but your dependant on the wind created by the ventury effect for cerculation to move the air. I would think a 4" pvc stack 4ft long would create quite a suction.
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Postby gyre » Thu Jul 01, 2010 8:41 am

I didn't think it took much outside ventilation to keep it working?
And more humidity should be of benefit, isn't it?

Stack effect doesn't rely on venturi effect to operate, but it enhances airflow or effectiveness.

A windcatcher is a different thing though.

I think there are chimney stacks that utilize venturi effect, but they have to be directional usually, and therefore smaller than possible with a static vent, so I haven't explored them.
And we have very low wind here.
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Postby FIGJAM » Thu Jul 01, 2010 8:50 am

The air from the cooler is very cool and moist, but the humid air absorbs heat fast. So the cooler is changing the air in the structure constantly. Thats why you cant recurculate the air. The humidity will build up and the cooling action from evaporation stops.
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Postby kman » Thu Jul 01, 2010 9:05 am

FIGJAM wrote:The amp draws you quoted are with the pump hooked into the power system. The fan by it self is 1.18, 1.68, and 2.50amps. You can run the pump on a small solar panel, The sight says it uses .23amps.

Which pump are you using, in this example? Did the nice little solar fountain pump from harbor freight work out, or did you end up using a different, higher powered pump (drawing from the battery)?

Basically, I'm trying to create a self-sustaining system so my battery can last all week. I'd expect to use the swamp cooler (if I go there) and fans for a few hours per day, so without a way to recharge the battery from a generator, I'm trying to stay solar as much as possible. Any power sources will probably also run some small interior lights, too (type to be determined), so we can see well in the yurt (when not sleeping).
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Postby gyre » Thu Jul 01, 2010 9:16 am

Harbor freight has a discount on a 45 watt panel.
No idea on quality, but it's chinese, so low.
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Postby FIGJAM » Thu Jul 01, 2010 9:21 am

The solar pump from harbor freight is fine for the bucket cooler (42gph). The box is a little bigger, so is the pump (80gph) and can be powered with a battery or solar panel. I just hooked the fan and pump both to the battery.

http://www.siliconsolar.com/solar-fountain-pumps.html

scoll down the page, the pump is $14.65
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Postby FIGJAM » Thu Jul 01, 2010 9:28 am

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Postby kman » Thu Jul 01, 2010 11:05 am

gyre wrote:Harbor freight has a discount on a 45 watt panel.
No idea on quality, but it's chinese, so low.

Yeah, I'd been eyeing that. I think, though, given my budget, I'm looking more at the many 40w panels I see on eBay for $100, rather paying $160 for the extra 5w:

40W 40 Watt Solar Panel Cells Made in Japan Quality

40W solar panel,40 watt solar panel Special On sale!

40 watts Mono Solar Panel $2.50/W UL 25-Year Warranty

The downside to a bigger panel is, if I want to use it to charge the battery (rather than just push the fan directly), I'd also need a charge regulator ($25-30 more). Not the end of the world, but man, all this is adding up...
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Postby kman » Thu Jul 01, 2010 11:08 am

FIGJAM wrote:The solar pump from harbor freight is fine for the bucket cooler (42gph). The box is a little bigger, so is the pump (80gph) and can be powered with a battery or solar panel. I just hooked the fan and pump both to the battery.

http://www.siliconsolar.com/solar-fountain-pumps.html

scoll down the page, the pump is $14.65


Simple is good. I'm leaning towards the bucket cooler, if anything. With the solar fountain pump and a panel to push the fan directly, I wouldn't need any batteries, or any power source other than the sun. And water, of course.
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Postby gyre » Thu Jul 01, 2010 11:20 am

The hf kit has a frame and some extras.

You need to look very closely at any solar panel.

Obsolete and used models may be relatively inefficient or overpriced.

I wouldn't go solar for this or buy unknown ebay panels when I do. but a purpose that only is used during sun is efficient.

Sharp just made their 2 millionth panel here.
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Postby FIGJAM » Thu Jul 01, 2010 2:56 pm

What battery are you going to use? If your just useing the 107cfm fan it only uses .5amps. A 55amp hour battery will run that fan for 50 hrs and be 50% discharged. Thats a deep cycle battery. Best for this purpose. Car batteries are not made for this purpose and it will shorten thier life or kill them.
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Postby kman » Thu Jul 01, 2010 3:47 pm

FIGJAM wrote:What battery are you going to use? If your just useing the 107cfm fan it only uses .5amps. A 55amp hour battery will run that fan for 50 hrs and be 50% discharged. Thats a deep cycle battery. Best for this purpose. Car batteries are not made for this purpose and it will shorten thier life or kill them.

Yeah definitely deep cycle if I get one at all... I'm sort of trying to see if I can avoid it and drive things directly from the panels, but we'll see. As funds permit I'll buy bits and pieces and play with them on my roof patio to see how well they work.
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Postby FIGJAM » Thu Jul 01, 2010 4:07 pm

Calculate the cubic footage of your yurt. How many minutes is it going to take for the cooler replace all the air? This will determine how much cooling you need to stay comfortable. I figure Im going to be out and about so much that the cooler may get 2 or 3 hrs use a day.
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Postby Captain Goddammit » Sat Jul 03, 2010 12:01 pm

If you want as much power as cheaply as possible, I think you should consider the simplest solution - just get a deep-cycle battery and charge it by running your car a while every day. Your car's alternator makes a HELL of a lot more current than any of those wimpy solar panels, and you already have it.
You can just hook jumper cables up to charge, but it will work better if you cut off the alligator clamps and install some proper cable fittings of whatever type works with your car's battery at one end, and whatever type fits your deep-cycle at the other end.
Simply bring extra gas so you're sure to have plenty to get off the playa.

I know, this isn't solar, but like others have said, solar isn't efficient if all you're buying the hardware for is this one week on the playa.
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Postby kman » Sat Jul 03, 2010 12:53 pm

That's a really good idea, Capn... keep them coming, everyone!

Personally, I decided to bite the bullet. I picked up the Harbor Freight 45w solar kit, which is on sale, a 105 amp hour deep cycle marine battery from Costco, and the endless breeze 12v fan. I may or may not make the extra effort to add the swamp cooler this year, we'll see how funds are doing after my yurt is built and all the other necessities have been dealt with. Worst case, I should be fine with the inherent coolness of the yurt plus the fan. With a 45w array to keep the battery topped off, I should have no problems running it anytime I'm actually hanging out in the yurt (which probably won't be all that much, other than sleep).

I hope. :oops:
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