Step 2: Theory of Operation

There's some awesome scientific stuff that makes our Solar Air Conditioning Unit possible!!  The three major principles at work are convection, evaporation, and adhesion-cohesion.

1.  Convection:
     But what does that mean!?  Hot air rises.  As the hotter air rises, it can draw cooler air up with it.  Convection cycles can occur when hot air rises, and draws cooler air from lower elevation.  When the hot air rises and loses energy it begins to fall.  This is the bare bones explanation.  There's a ton more information out there from people who know more than I do.  I did a lot of reading before starting this project, and I'd encourage you to do likewise.  I've listed some sources for more information at the end of this step for your convenience : )

2.  Evaporation:
     We are using water in this project as our cooling agent.  Evaporation is when a substance changes from liquid to gas at it's surface.  Links to fun evaporation information down below.

3.  Cohesion and Adhesion:
     Cohesion and Adhesion are two properties of water, and closely related.  Cohesion means that water tends to stick to itself, or try to stick together.  You can see this by placing small drops of water onto wax paper.  You'll notice that the drops tend to ball up.  This is because of the strong polar bonds in the water that attract individual molecules to one another.  Adhesion means that water sticks to other stuff.  This effect is best seen by dipping part of a paper towel into a small amount of water, and watching as the water makes its way up the paper towel.
(*7/23/2012: shannonlove was nice enough to point out that a more accurate term for this water property is "capillary action".  I was going from what I remembered in my chemistry classes, however doing a search for "capillary action" may lead to more helpful information.)

These three principles make the Unit what it is.  The sun will shine on the unit and heat the air at the bottom of the shaft.  The air will rise, and also draw in more air from the bottom.  As the air rises, it will cause water in a small chamber to evaporate.  When the water evaporates, it will take energy away from the heated air in order to change from a liquid to a gas.  This will cause the surrounding air to get cooler.  The water is brought into contact with the moving air by a piece of fabric.  The fabric will pull up water from the chamber to increase the surface area of the water with respect to the moving air.  As the water evaporates and the fabric gets dry, more water will be drawn up the fabric due to the awesomeness of cohesion and adhesion.

Got it?  Awesome.  Let's get building!
Jump over here (step 11) to see my video on how it works: http://www.instructables.com/id/DIY-Solar-Air-Conditioning-Unit/step11/Videos/
More on Convection:
More on Evaporation:
More on Cohesion/Adhesion:
Awesome idea and great video production. Unfortunately it's not at all safe to use while driving.
How about a small solar panel powering a computer fan to speed the heat transfer?
<p>HOW DID IT DO</p>
<p>Does this really work? I feel like putting solar panels on would just make it hotter. Thanks for sharing though, it's a clever idea. <br><br>Dorthy Packer | &lt;a href='http://www.eastcoastair.net.au/residential-air-conditioning' &gt; http://www.eastcoastair.net.au/residential-air-conditioning&lt;/a&gt;</p>
<p>Don't you feel this product is incompetent of satisfying the cooling needs of a modern home that only <a href="http://creightonlaircey.net/" rel="nofollow">traditional air conditioners that take less to repair and prepare </a>can satisfy with their extraordinary performance?</p>
Thanks for sharing this information! I have been looking into <a href="http://esconow.com" rel="nofollow">air conditioning salt lake city ut</a> and where to get some help. Can you tell me more tips of how to choose a air conditioning company? Thanks again for sharing!
This is awesome! I've been looking for place that can work on my <a href="http://esconow.com" rel="nofollow">air conditioning in Salt Lake City</a>, and am glad I found this. I'm gonna have to try it out. Thanks for sharing!
I have previously asked for the videos for some clarification, and happy to find it now. I couldnt start the project without it. Thanks....I will update after i try.. <br> <br>Also expecting your updates about any improvement or addition..
This is a fantastic idea. I went to <a href="http://WWW.ramelectricsummerville.com" rel="nofollow">HVAC Summerville</a> and they said they hadn't heard of anyone successfully doing this, so I'm excited to try this out.
That is a really good idea. I think that all of us have walked back to our car and have been hit by a heat wave when we open the door. Having a solar <a href="http://independentacinc.com" rel="nofollow">air conditioning</a> unit running like this looks like an excellent way to keep your car cool when you have it parked. Thanks for sharing this with us!
Im glad your using your brain and trying to thinks of idea. Even though this might not be the easiest and simplest idea. you can take what you learnt from it and use it in the future for something else. You got some handyman skills there. <br>I was thinking Get some kind of air scoop so when you drive it directs the wind inside the car. Then have a wet medium infront of it . And mybe a bottle of water and a pump which sits under the seat and pumps new water to the unit. <br>The car would cool down pretty fast after a few mins of driving . <br>IF you have any questions im an air conditioning mechanic .
Author: What do you think about this idea? <br>
Wow this is very cool! I would have never thought to do anything like this to my cat! But it is totally awesome cause that is the worst part about cars, how hot they are when you get in after it had been sitting in the sun for so long! I have been talking to <a href="http://www.manwill.net/cooling.php" rel="nofollow">salt lake city air conditioning</a> companies to see if there was anything that could work for me! I just wonder, can you make it smaller so it doesn't take up the whole window? Thanks for sharing!
I wouldn't worry about high precision in this case. Getting down to the nearest degree is more than sufficient. Don't do more work than you have to. Adding needless precision also adds the risk of additional error. Learned that one the hard way after mis-measuring hundreds of blue crabs with needlessly precise calipers which I misread. <br> <br>I would recommend cooking thermometers like the kind they sell to make candy. They have a wider upper range than weather thermometers, they are more durable and, most importantly, you can calibrate them using boiling water (corrected for barometric pressure of course.)
Hi there!! : )<br><br>I considered using candy thermometers, however they can be $10 or more, and so I didn't want to buy them when I'd only really be using them for these measurements.. I also wasn't sure how accurate/reliable they would be hanging in air, as opposed to being submerged in a syrup.<br><br>Thanks for the read and the comment!! : )
I use the ~ $5 digital food thermometer in Walmart's kitchen accessories section. Unless you are working with serious critical chemical reactions, their accuracy probably is good enough for the home shop. Good instructable, but a project I would duplicate, you gotta be tough :) Currently it's 102 F outside at a time when are having record triple digit highs. I live in the part of KS swamp cooling works well most days.
That's not a bad idea. I actually got a candy thermometer yesterday, so I'll be able to take some measurements soon.<br>: )
$10 bucks is $10 bucks, especially when you are a young student as I remember all to well. Back in my day, $10 bucks was 2 hrs labor at my minimum wage college jobs. However, I also remember wasting a lot of time, money and effort because I guessed at something instead of measuring.<br><br>All science begins with measurement. If you can't produce repeatable measurements, whatever you're doing isn't science and probably not even useful inventing/engineering. You can easily end up pursuing dead end design paths because you had to guess whether any particular design or change was really producing the results you thought they did. <br><br>I always recommend to people building anything whether woodworking, electronics, software, cooking etc to spend money first on measuring tools. It's the traditional, &quot;measure twice, cut once&quot; wisdom. <br><br>Check around. You can get relatively descent infrared thermometers for $20 bucks or so. Also, remember you can borrow tools. Make friends, schmooze and help other out and they will return the favor. When you're working on a shoestring friends are more important than cache.
That's right, and I've been working 2-3 jobs all summer trying to save for all the upcoming expenses.. That said, you have a good point about the importance of measurements.<br><br>Thanks for your input and comments!! Your help and interest is appreciated : )
Temperature is temperature, be it in a solid, liquid or gas. What would change would be the time taken to get a distinct reading. The candy thermometers I've seen are heavier than house ones, inside a steel casing with a window to see the temperature, and that would take longer to warm up or cool down in air compared to a plain household bulb thermometer on a plastic mount.
You are correct that it would seem like the increased mass of the candy thermometer would make them less reactive but I haven't noticed any issues with them. <br><br>Candy thermometers are quite reactive because candy making requires precision as some task like chocolate making will fail if the temperature goes outside a 4F/2C range. On the other hand the thermal mass of water, solids and sugar is enormous so they might be slow measuring just air. I have used them for a surprisingly wide variety of task e.g. checking engine temps (but please don't tell my significant other) and they seem very reactive. <br><br> Their major advantage vs weather thermometers is their upper range. Most weather thermometer peg out at around 120F/49C making them useless for measuring any temp you couldn't touch with bare hands anyway. The second advantage is that you can calibrate them with boiling water.
Thanks for your input!! I may try to look for some decent thermometers later today!<br><br>Thanks again!<br>: )
Won't work here in Florida, to much humidity. But putting this thing on every day is easier than a foil reflector?
RIght, certainly no help to Florida, unfortunately : )<br>It's not hard at all to put on, however I can't really say whether or not it's &quot;easier&quot; since I haven't tried a foil shade. It's certainly more fun and fulfilling to put on to say the least : )
Don't worry that you've &quot;reinvented&quot; the swamp-cooler - These are very good and very efficient. I had a whole house &quot;air-conned&quot; with one on the roof when I lived in Riyadh, Saudi Arabia, where (being basically in the centre of a large desert) it was hot (up to 115 degrees F or even more) and very dry. <br> <br>Compared with a &quot;compressor-type&quot; air-con, they cost pennies to run, and made he place more comfortable with the humidification or the air indoors. <br> <br>I like the idea too of making it &quot;dual purpose&quot; to heat the car in the Winter before driving off - I'm currently doing something a bit similar to stop my workshop in the garden getting too cold and damp at night in the Winter by fitting a &quot;Solar Collector&quot; on the South end, blowing air heated by the sun in the day through a THICK insulated concrete base, which should radiate into the workshop at night and keep the conditions in there a lot nicer.
Thank you!! I did have hotter and more arid regions in mind when I thought about the possibility of scaling this project!<br><br>Your garden heating project sounds awesome! A great idea for passive solar heat.<br><br>Thanks for the read and comment!! : )
Hi Fozzy, It's not strictly speaking a &quot;passive solar&quot; system - that's where you just use a large area of South-facing glass (or polycarbonate) to heat the internal structure of a building directly by the sun. It's &quot;active&quot; because I will be using a fan to circulate the hot air captured in the solar collector and circulated through a base of rammed earth and concrete (about 100 cubic feet in my project) which is insulated from the ground below it.<br> <br> The thermal mass of this base is intended to store that heat and to radiate it from the floor into the building once the temperature inside starts to drop at night. Yes - I've been taking pictures as I've been going, and it will be submitted as an instructible when it's finished . . . . But that won't be for several months as I won't need the heating until later in the year when it starts to get colder at night. I've been neglecting a lot of other chores since I started which I'll have to catch up on!<br> <br> I've built the workshop with stud wall, OSB skin inside,&nbsp; which will have the space between the studs insulated with glass wool insulation and twin-wall plastic cladding outside, while the roof is OSB, covered with glass wool and another layer of OSB over that. Should be nice and cozy!<br> <br> Stu
Respectfully your definition of passive is much stricter than it is in the general community. In using a solar chimney to create a cooling breeze in a building wouldn't be passive given how you define passive. For most. passive solar means using solar without any other additional energy input to complete the desired task. In the event you could design it to use heat from the sun to circulate the air through the thermal mass in your project it would then be %100 passive.
I did think about that for my project, and &quot;hot air rises&quot; - yeah? So if the cold air comes into the bottom of the collector, and goes out of the top, then a pipe from the top of the collector should connect to the top of the concrete storage slab, circulate through it, drop to the lower area of the slab (as it cools, giving up heat to the slab), circulate and then return to the bottom of the collector.<br> <br> I agree it would work - to a degree, but I'm putting in a &quot;muffin&quot; fan to be able to get the airr to circulate better.<br> <br> Of course, I MAY find that it circulates enough without the fan, and that will save me having to provide a small power source (probably solar PV) to run the fan during the day.<br> <br> In fact, I have the air planned to go to the bottom layer of the slab first, as this way the heat should take longer to transfer to the top of the slab (and hence into the structure above, in order to achieve my aim of keeping the building warmer during the <em>late</em> part of the night (electronic equipment does not like cold, damp atmosphere), but it still may work . . . . (?)<br> <br> Stu
If your muffin fan were powered by a solar panel, would that be considered passive? <br> <br>Gordie
Good question Gordie - But I really don't want to get into a lot of semantics. Yes, the muffin fan will probably be powered by solar. I intend to have a small solar PV (about a 10-watt panel) to charge a &quot;float battery&quot;, but mainly to allow me to use my ham radio gear in an emergency (I'm a member of the UK ham emergency volunteers) should we have a total power failure. The fan will be powered from that battery-backed supply.
Ah! I called it &quot;passive solar&quot;, since I thought that term applied to systems that stored solar energy in stone, or in your case concrete.&nbsp; I guess it does make sense that it's not truly passive if there's a fan involved.<br> <br> An awesome project nonetheless!&nbsp; Can't wait to see it!<br> <br> Thanks! : )<br> <br> <sub>(My good friend, the &quot;vote&quot; button, gets forgotten and feels unloved)<br> : )</sub><br>
Nicely done. When I was a kid in Arizona &quot;swamp coolers&quot; for houses and even cars were common. There was also flax bags: You would saturate them with water, then fill them up. Hung on your car outside the grille, after driving awhile the water would be ice cold! <br> <br>The idea of using your apparatus dry creating heat might be useful in the winter.
Flax bags sound interesting!! And I'm excited to try using it for heat as well! Thanks for the read and comment!! : )<br> <br> <sub>*casually points to the &quot;vote&quot; button in the upper right* : )</sub>
You can still buy flax bags:<br>http://www.lifestylestore.com/details/ls_detail_6058.html<br><br>This is about Trombe walls: Same effect as using your device dry:<br>http://en.wikipedia.org/wiki/Trombe_wall
The water bags I recall had a canteen like neck <a href="http://www.epier.com/product.asp?1479334" rel="nofollow">http://www.epier.com/product.asp?1479334</a> . In the process of keeping the water cool, water in the bag was consumed by evaporation. While they keep the water refreshingly cool, it certainly isn't&nbsp; ice cold as the other commenter stated.
They're not perfect devices, but I recall using them in 90-100 degree heat in Arizona resulting in very cold water. The basic principle remains the same: Cooling by evaporation.
Just a note about MDF. <br>-very susceptible to moisture, and it will swell up to maybe 3 times its size. Not desireable. <br>-the strength on the face of it is very good, i.e. you want to walk on it or rest things on it. I built a medium duty workbench with it, works wonderful, nice flat surface. I built utility shelves with it, very nice. I did all the wood work in my house with it... OUTSTANDING. <br>-but it is not structural in that it has very little span, not good on its edge, won't hold a screw (or nail) very well in the edge or even on the face to well, suggest glueing along with screwing/nailing. <br>-absent of moisture it is extremely stable. <br>-MDF is VERY heavy <br> <br>For this project I would almost suggest some type of foam board with hot glue gun. Easier to work with, more resistant to moisture and very economical
Yes MDF is heavy and susceptible to moisture. /You can use GatorBoard foam at 1/2&quot; thickness to construct a rigid, lightweight more waterproof housing. Should paint it. It is a phenolic resin paper sandwich with a styrofoam interior. styrofoam interior wither different than FoamCore.
Is GatorBoard available at your average home improvement store at a reasonable price? I'm definitely interested for future projects.<br><br>Thanks for the read and comment!! : )
I was thinking more of R-Max 1/2&quot; <br> <br>This stuff doesn't have a rigid outlayer but has a somewhat rigid inner core between some silver reflective paper. It has a less than 2% water absorbtion. It is just $9.48 at Lowes. I put this on my basement ceiling and had a ton of big scraps leftover, some of which spent a couple of weeks out in the weather and it came in still in good shape. I read they do a lot of modeling with that gatorboard and perhaps it is a tad more permanent but this R-Max 1/2&quot; would be great for proof of concept projects and I even believe it would hang in there for a good deal of years outdoors, but I can't be certain.
I guess it is also called R-Matte Plus 3 and I looked up the specs and it is &lt;1% water absorbtion, and can be used between -40f and 250f <br> <br>It is NON-structural. but for small boxes etc I would try it. I'm thinking of trying a dual chamber swamp cooler using this material.
With that low of water absorption and wide temperature range, I could easily look past the &quot;non-structural&quot; label, especially for a project like this.&nbsp; For this specific application however, the 1/2&quot; thickness would be a bit of an issue, since my car window is thinner than that, but the 1/4&quot; fit very nicely.<br> <br> I can't wait to see your cooler!<br> <br> Thanks! : )
This is used in Graphic Arts or TradeShow/ Exhibit displays. Photographers use it for mounting. You might find some scraps or used panels if you check around local companies. <br> <br>The price is rather high, but here are some sources for single sheets. <br>Paint edges with latex or acrylic! Maybe 3/16&quot; would be sturdy enough for your use... <br> <br>GatorBoard <br>http://www.foamboardsource.com/ <br>http://www.artsuppliesonline.com/catalog.cfm?cata_id=6044 <br> <br>UltraBoard is similar but with plastic surfaces (I haven't tried it): <br>http://www.tri-dee.com/Ultra%20Board%20Panels.htm
Ah, okay, it's too bad that it sounds hard to find. It's good to know it's around though so I can look for it.<br><br>Thanks! : )
I didn't know MDF was so susceptible to moisture! I chose it because I thought it was made of sawdust and a sort of resin, which I assumed would be more resistant to moisture than plywood. <br><br>I don't know if foam board would be quite sturdy enough for this project though, but it wouldn't hurt to give it a shot.<br><br>Thanks! : )
great idea,and a well executed instructable.two thumbs up!!!
Thanks for the kind words, as well as reading and commenting!! : )
Could the effectivness of your design be increased by using a small solar powered fan? I just curious. <br>:-) <br> <br>
Yes! It would just need to be placed at the bottom near where the air intake would be. <br><br>Thanks for reading and commenting! : )

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Bio: I am currently a mechanical engineering student at the University of Toledo, and the founder of the University of Toledo Maker Society. I have a ... More »
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