DIY Solar Air Conditioning Unit

The sun is great, and vital to nearly all of Earth's processes.  What bothers me is that the sun also makes the air really hot!  As a result, millions of people turn to air conditioning to cool their homes, cars, offices, etc.  Traditional air conditioning units use massive amounts of energy, making electricity bills skyrocket in the summertime. 

What if there was a way to cool your home, car, or workplace without the need for a big, loud, and energy-hungry machine?  What if this device also was entirely solar powered with no moving parts?  Sound to good to be true? 

This Instructable will cover the method I used to build a prototype Solar Air Conditioning Unit.  This unit is a prototype, and was only ever meant as a proof of concept that my idea could work.  There is a lot of testing that needs to be done to see how this idea can be used in more practical applications.
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Index:

• Introduction
• "Why?"
• Theory of Operation
• Gather Materials
• The Build Pt. 1 - Cutting Wood
• The Build Pt. 2 - Gluing
• The Build Pt. 3 - Metalwork
• The Build Pt. 4 - PVC
• The Build Pt. 5 - Miscellaneous
• Using the Unit
• Going Further and Conclusion
• Videos!

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.:| This Instructable was intended to be entered into the Green Technology Contest.  However, because this project uses no electronics, it was not accepted.  I entered this into the Hurricane Laser Contest instead, and if you like this Instructable, it would be awesome if you would vote for it in the contest!  Having a laser cutter would be awesome because it would allow me to build things better and more quickly to be able to share them with the community! |:.
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7/17/2012:  Thanks so much for the feature!!

Step 1: "Why?"

I wanted to try to keep the Intro fairly short and sweet, and more formal.  But why build this, at a personal level?

-I'll take this point to say that if you don't care about specifically why I built this, then move on to the next step, no hard feelings : )

My car sits in the sun all day, and has a black interior.  I'm sure you already know that dark colored things tend to get hotter when they sit in the sun than lightly colored things.  Additionally, windows do a funny thing when light hit them, and serve as a sort of insulation, so that the air in my car actually gets hotter than the outside air temperature.  Both of these factors cause me to start sweating almost immediately upon entering my car, which isn't very attractive when going to work, nor very comfortable.

Therefore, I was thinking of different ways I could cool down my car while it sits in the driveway.  Leaving all my windows down isn't very practical for safety reasons and letting bugs in.  A foil sun shade that would sit on my windshield would be annoying to put up and take down.  I also had a vague idea of how a Solar Air Conditioning Unit could work, and decided that a car would be the perfect test medium for my concept!  The car would allow me to attempt to cool a small amount of space, in a fairly controlled setting, and potentially save me from a very uncomfortable commute.

Comments

[aniltvmin]

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..

Also expecting your updates about any improvement or addition..

[Redstormx1]

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.
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.
The car would cool down pretty fast after a few mins of driving .
IF you have any questions im an air conditioning mechanic .

[Ranie-K]

Author: What do you think about this idea?

[shannonlove]

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.

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.)

[fozzy13]

Hi there!! : )

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.

Thanks for the read and the comment!! : )

[static]

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.

[fozzy13]

That's not a bad idea. I actually got a candy thermometer yesterday, so I'll be able to take some measurements soon.
: )

[shannonlove]

$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.

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.

I always recommend to people building anything whether woodworking, electronics, software, cooking etc to spend money first on measuring tools. It's the traditional, "measure twice, cut once" wisdom.

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.

[fozzy13]

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.

Thanks for your input and comments!! Your help and interest is appreciated : )

[bpfh]

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.

[shannonlove]

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.

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.

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.

[fozzy13]

Thanks for your input!! I may try to look for some decent thermometers later today!

Thanks again!
: )

[rhooie]

Won't work here in Florida, to much humidity. But putting this thing on every day is easier than a foil reflector?

[fozzy13]

RIght, certainly no help to Florida, unfortunately : )
It's not hard at all to put on, however I can't really say whether or not it's "easier" since I haven't tried a foil shade. It's certainly more fun and fulfilling to put on to say the least : )

[StuNutt]

Don't worry that you've "reinvented" the swamp-cooler - These are very good and very efficient. I had a whole house "air-conned" 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.

Compared with a "compressor-type" air-con, they cost pennies to run, and made he place more comfortable with the humidification or the air indoors.

I like the idea too of making it "dual purpose" 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 "Solar Collector" 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.

[fozzy13]

Thank you!! I did have hotter and more arid regions in mind when I thought about the possibility of scaling this project!

Your garden heating project sounds awesome! A great idea for passive solar heat.

Thanks for the read and comment!! : )

[StuNutt]

Hi Fozzy, It's not strictly speaking a "passive solar" 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 "active" 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.

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!

I've built the workshop with stud wall, OSB skin inside,  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!

Stu

[static]

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.

[StuNutt]

I did think about that for my project, and "hot air rises" - 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.

I agree it would work - to a degree, but I'm putting in a "muffin" fan to be able to get the airr to circulate better.

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.

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 late part of the night (electronic equipment does not like cold, damp atmosphere), but it still may work . . . . (?)

Stu

[GordieGii]

If your muffin fan were powered by a solar panel, would that be considered passive?

Gordie

[StuNutt]

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 "float battery", 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.

[fozzy13]

Ah! I called it "passive solar", since I thought that term applied to systems that stored solar energy in stone, or in your case concrete.  I guess it does make sense that it's not truly passive if there's a fan involved.

An awesome project nonetheless!  Can't wait to see it!

Thanks! : )

_{(My good friend, the "vote" button, gets forgotten and feels unloved)
: )}

[dll932]

Nicely done. When I was a kid in Arizona "swamp coolers" 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!

The idea of using your apparatus dry creating heat might be useful in the winter.

[fozzy13]

Flax bags sound interesting!! And I'm excited to try using it for heat as well! Thanks for the read and comment!! : )

_{*casually points to the "vote" button in the upper right* : )}

[dll932]

You can still buy flax bags:
http://www.lifestylestore.com/details/ls_detail_6058.html

This is about Trombe walls: Same effect as using your device dry:
http://en.wikipedia.org/wiki/Trombe_wall

[static]

The water bags I recall had a canteen like neck http://www.epier.com/product.asp?1479334 . 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  ice cold as the other commenter stated.

[dll932]

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.

[tafelice]

Just a note about MDF.
-very susceptible to moisture, and it will swell up to maybe 3 times its size. Not desireable.
-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.
-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.
-absent of moisture it is extremely stable.
-MDF is VERY heavy

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

[albeem]

Yes MDF is heavy and susceptible to moisture. /You can use GatorBoard foam at 1/2" 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.

[fozzy13]

Is GatorBoard available at your average home improvement store at a reasonable price? I'm definitely interested for future projects.

Thanks for the read and comment!! : )

[tafelice]

I was thinking more of R-Max 1/2"

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" 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.

[tafelice]

I guess it is also called R-Matte Plus 3 and I looked up the specs and it is <1% water absorbtion, and can be used between -40f and 250f

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.

[fozzy13]

With that low of water absorption and wide temperature range, I could easily look past the "non-structural" label, especially for a project like this.  For this specific application however, the 1/2" thickness would be a bit of an issue, since my car window is thinner than that, but the 1/4" fit very nicely.

I can't wait to see your cooler!

Thanks! : )

[albeem]

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.

The price is rather high, but here are some sources for single sheets.
Paint edges with latex or acrylic! Maybe 3/16" would be sturdy enough for your use...

GatorBoard
http://www.foamboardsource.com/
http://www.artsuppliesonline.com/catalog.cfm?cata_id=6044

UltraBoard is similar but with plastic surfaces (I haven't tried it):
http://www.tri-dee.com/Ultra%20Board%20Panels.htm

[fozzy13]

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.

Thanks! : )

[fozzy13]

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.

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.

Thanks! : )

[isaacwilk]

I agree with tafelice's comment on using MDF - it's pretty terrible when it comes to waterproofing, and will swell up and turn to mush if exposed. I'd at least paint it, or coat it with something waterproof.

Great idea and instructable though!

[fozzy13]

I will have to do that!! It wouldn't take much to get some clear coat or something of the sort to make it more durable.

Thanks for reading and commenting!! : )

[kjemielity]

great idea,and a well executed instructable.two thumbs up!!!

[fozzy13]

Thanks for the kind words, as well as reading and commenting!! : )