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Beat the Heat - Homebrew AC on the cheap

Thursday, July 20, 2006

It's funny what kind of ideas you can dream up when you see something get thrown away. Last summer my neighbor was reroofing his house and had a dumpster in front of his house. Peeking out of the top of it was an evaporator coil that goes on the top of a furnace in a central air condioning setup. In a nutshell it is a triangle shape coil with two sets of copper tubes running up through it. Air passes through the aluminum fins and gets cooled by the refrigerant that is circulating through the coils.

Well I walked over and checked it out, it looked in great condition with no bent fins or damaged copper tubing. So making sure no one was looking I snagged it. You are probably wondering what the heck I am going to do with it. Well it took a year to dream it all up but I finally figured it out.

I decided to make a Homebrew air chiller in my basement. Water would trickle through it and cool the fins which in turn would cool the air being pulled through it. I had a laundry chute in my house that was never getting used so I used that as a means to get the air up to the main floor.

This is a view looking down on the coil. You can see the copper coils which run through both sides of it. The two sides exit into the larger copper pipe seen on the top. I took some galvanized sheet metal and boxed it in except for the bottom.

I welded up a stand as seen here, you can also see where the water comes into the coil with two small copper tubes that feed both sides of the coil. They are shaped like an S

Here is a little better view of the in and out for the water. The top copper tube is incoming water that flows through small copper tubes to feed both sides of the coil. The larger copper tube is outgoing water coming out of the unit. The coil sits in a pan with a drain for condensation that can also be seen here.

I made some duct work and added an 8 inch inline fan from Suncourt to provide the airflow The fan is the shiny part on the top You can get these fans at Home Depot for around $30.

I found some 1/4"soft copper laying around and used that to feed the unit. I also added an inline valve to control flow. I did a temporary wiring job to power the fan.

Due to the cost of copper being outrageous I made a switch to PVC as seen here. This is the discharge water from the unit that is headed to an outside faucet to water the plants!

Here is the almost completed chiller. I added a filter to the bottom to keep the coil relatively clean and to provide filtered air to the house. I need to wire it properly and it should be all done. I made sure to make it easy to move in case major repair work had to be done to the furnace. I estimate it would take about 15 minutes to unhook some stuff and you could move it out of the way.

The discharge water exits the house here and will be used in a trickle irrigation system for the plants.

This is the old laundry chute, I had to make a grate to keep kids from throwing junk down it so I whipped out a welded design of a sunset. I haven't setup the irrigation system outside yet but I am enjoying 68 degree air being pumped out of this right now. With water trickling through I expect it to be in the low 60's temperature range. I hope to use no more than a couple gallons per hour which at less than a penny per gallon I can handle. I am being fed water from the city and they in turn get it from Lake Michigan. For some reason our water is always really cold. Cold enough to make condensation on the faucets.

I figure I have about $60-$70 into the Homemade AC with the fan, steel, sheet metal, plumbing parts, etc.

Hope you enjoyed this and have gotten a few ideas.


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  1. Anonymous Anonymous | 4:26 PM |  

    wow gold opportunity!

  2. Blogger Dubled | 4:51 PM |  

    Yea it turned out pretty cool, can't wait to show the neighbor what I did with his AC evap coil.

  3. Anonymous Tim Denike | 5:03 PM |  

    Very cool. I've heard of similar systems that used a closed-loop water system which ran under ground to dissipate heat.

  4. Blogger Dubled | 5:22 PM |  

    Yep Geothermal loop, I thought about it but could'nt warrant running a 500 plus watt circulating pump, plus I would have to dig a big hole and buy pipe. This is less than a penny a gallon from the city.

  5. Anonymous Anonymous | 4:28 PM |  

    A few gallons of water has almost no energy in it. Even if the water is at 40 degrees F from the tap, that's only a 28 degree rise to 68 degrees. Water is 4 joules/deg C/gram. Do the math and you get about 76000 joules for 5 gallons of water.

    76000 joules is 21 watt hours. You've built a 21 watt air conditoner. This is a 65 BTU air conditioner. The smallest air conditoners sold are about 5,000 BTU, meant for 150 square foot rooms.

    Your system will cool two square feet if all you feed it is 5 gallons per hour. This is still 120 gallons per day!

    There is no free lunch.

  6. Blogger Dubled | 8:30 PM |  

    Let's say that your inlet temp is 45 degrees farenheit and your discharge temp is 80. This would give you about 291 btus per gallon of water you flow through it. This converts to 291 btus per hour for one gallon. If I use 3 gallons thats 973 btus for around 3 pennies.

    It works it is blowing cold air and is costing me very little and thats the bottom line.

    I know there is no free lunch but there may be a cheaper lunch with a little effort and thats what I have.

  7. Anonymous Anonymous | 5:17 PM |  

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  8. Anonymous Anonymous | 12:13 AM |  

    I love your website. It has a lot of great pictures and is very informative.

  9. Anonymous Anonymous | 8:03 AM |  

    I like it! Good job. Go on.

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