Home-made A/C Unit

[eaglebkh]

Some of you have asked about my portable A/C unit, so here is some info.  I have been very pleased with it's performance and it keeps the airplane quite comfortable in 90+ degree heat.  The parts needed are fairly easy to find, though I did not have most of them just lying around the house.  Altogether, I spent less than $100 plus about 5-6 hours labor involved. 

The basic idea is that air is sucked into the cooler and passes over 2 radiators which circulate ice-cold water.  In my design, the air is cooled twice: once as it enters the cooler and again as it is blown out.  The result is very cold air.

 

Here's the parts list (excluding various things like wiring, screws, glue, ect.):

1.  48 quart Ice Chest (size is up to you, but the more ice, the longer it lasts)

2.  Tsunami T-500 bilge pump (from Wal-Mart).  1.8 amps, 5/8" diameter outfeed.  If you can find a smaller one with a lower GPH, use it because this one really pumps too much water and melts the ice faster.

3.  2 4" computer fans, 114cfm, 0.9 amps, 12 volts (the CFM is up to you, but you'll want >90)

4.  2 heater cores.  I was able to find 2 matching ones on eBay fitting a late 80's Buick/Pontiac/Chevy car, but the important thing is the inlet and outlet diameters - 1/2" works best and fits the tubing I used.

5.  Tubing: Vinyl - 4' of 1/2" and 2' of 5/8" (available at Lowe's/Home Depot).  I also used a bicycle inner tube for the flexibility - it was a freeby from a co-worker who rides and had a flat.  The tire tube is also 1/2" inner diameter - quite convenient.

6.  Plumbing hardware: depending on your design, you'll need to reduce the 5/8" outfeed of the bilge pump into 2 separate 1/2" lines going to each heater core (refer to the next photo).  I used a 5/8" 'T' fitting, then reduced each line going to the heater cores with a 5/8" to 1/2" fitting.  Three 1/2" CPVC elbows were used to help with the bending of the tube as the lid was opened/closed.  18 hose clamps (12 5/8" and 6 3/4").  All of this can be found at Lowe's/HD

7.  2 Grills for the air intake (optional).  I used the metal screens from some old speakers.

8.  12 volt battery (optional).  I wanted to provide the possibility of using it on cigarette lighter power or battery power.

 

Construction:

The hardest part is getting the cooler lid cut into the desired form (see Lid pics) - the Drimmel and utility knife is ideal for this.  The lid from my cooler actually had some hollow thicknes (~1-2") which was great for directing and separating the inflow and outflow.  Looking at the lid, the air enters the 2 cross-wise inlets and passes over the radiator on the right looking from the front.  As the air leaves, it passes over the other radiator and through the round holes.  It was necessary to insert a divider in the lid to separate the 2 airflows (not shown).  This was done with scrap plastic from the lid after cutting up the lid.  The rectangular holes on the bottom are for the radiators (or heater cores).

The plumbing is fairly straight-forward with the only tricky part being the tube length/material (see Inside pic).  You can experiment around, but here's what I have found works.  Using the tire tubing helps prevent blockages that occur when the lid is closed and the excess tubing folds up (hence the CPVC elbows).  The length is also important because if the tubing is too long, it will bend and kink when closed, but needs to be long enough to allow the lid to fully open.  The CPVC elbows allow the tube to fold without blockage.  Each elbow has about 1" of CPVC piping added so that the tire tubing could slide over it like a sleeve.  Lastly, don't forget to hose-clamp everything.

I'm still working on attaching the radiators to the lid.  The current method of silicon and zip ties is not working.  I was out of ideas when I reached that phase of the design, but I'm going to have to use some type of brackets.  I have had to re-mount the radiators twice in the 1 year I've been using the A/C.  Also, the lid needs to be secured from folding back too far and coming off, since the extra weight of the heater cores will cause this to happen.

For the wiring, everything is contained in the area to the left of the radiators (previous photo).  You'll have to use your own expertise here, as it's hard to explain but easy in theory.  I have 2 switches on the outside for the fans and the bilge pump (in case I wanted air but didn't want to circulate the water).  The whole system pulls 3.6 amps.

 

Final notes:

With 30 lbs of ice, the A/C will deliver ~1.5 hours of cold air and should have no problem holding 40 lbs.  I have been instrument training all summer, nearly 2-hour lessons doing only approaches where the airspeed is usually at or below 90kts and close to the ground.  The A/C keeps the instructor and myself quite comfortable.  An additional 1/4" vinyl tube 7-8' long is handy for syphoning out the water at the end of the flight - makes getting the unit out of the plane much easier...

The effectiveness of the A/C can be improved if you build some type of hood of vent to set on top of the fans to direct the air forward.  I made one out of cardboard and duct tape (you know it's not a home-built unless those ingredients are present) that just sets on top of the fans and shoots the air forward.  Position the A/C in the luggage area with the right side against the pilot side of the plane and the fans will line up just right and blow between everyone's head.  The unit does however consume ~1/3 of the luggage volume, but it can always be moved to the back seat if there are no passengers.

If you have any questions, just reply or PM me.

[KSMooniac]

Brandon, thanks!  Description sounds great, but I can't see the pics on my end.  It looks like they're links to your hard-drive, so you might have to upload to this site or host them on some other site to make them show up for us.

[eaglebkh]

Fix it!  Thanks...

[Bacachero]

Nice setup!

I have a question, being that the air sucked in is in contact with the ice/water, does this blow out humid air? have you had condensation problems or the windows becoming fogged?

Thanks for sharing your ideas!

[eaglebkh]

Good question - and the answer is actually no.  As the air is leaving the unit, it is again cooled by the second exchanger.  As you know, when air is cooled the moisture condenses, so all the moisture stays in the unit.  I haven't noticed any fogging, even on the hottest, most humid alabama summer days.

I have a Word write-up if anyone is interested.  eaglebkh@bellsouth.net

 

[Stefanovm]

Basic psychrometrics. Moisture could harm the electronics, but design normally take this fact of operation into account. I second the opinion, do not worry about it.

[Bacachero]

This is not as good as brandon´s  system, but its under 40 bucks and no assembly needed.

www.kooleraire.com/