Slashdot Log In
Homebrew Air Conditioning for Under $25
Posted by
timothy
on Mon Jun 13, 2005 05:42 PM
from the ice-is-free-after-all dept.
from the ice-is-free-after-all dept.
inkey string writes "Summer has arrived, and I've been busy slowly overheating in my student house without central air.
I decided to put my thermodynamics classes to work however, and produced this ~24$ homebrew air conditioner. It'll cool a room to a comfortable level in 15-20 mins, and will run for a few hours on a garbage pail full of water.
It's cheap, environmentally friendly (just fire the waste water off to your garden), and makes a good one hour project for a quiet evening."
This discussion has been archived.
No new comments can be posted.
The Fine Print: The following comments are owned by whoever posted them. We are not responsible for them in any way.
Full
Abbreviated
Hidden
Loading... please wait.
Its going to be hot soon (Score:5, Funny)
Re:Its going to be hot soon (Score:5, Insightful)
It's actually a University of Waterloo server. I'm sure the sysadmin is gonna love this sudden DDOS.
Parent
Re:Its going to be hot soon (Score:4, Funny)
Parent
And you can place it... (Score:4, Funny)
Re:And you can place it... (Score:5, Funny)
By placing the garbage pail full of water in your garden, you ensure that within five minutes of the link going live on Slashdot, you'll have several gallons of piping-hot vegetable soup!
Parent
Air Conditioning for $1500/month (Score:5, Funny)
Today it hit 70F, and the news stations are talking about "the heatwave of 2005".
Re:Air Conditioning for $1500/month (Score:5, Funny)
I repeat my assertion that since 31 Octobher, 1995 (the last Oingo Boingo show) the state has had no redeeming value.
Parent
Re:Air Conditioning for $1500/month (Score:5, Funny)
Hey! California has amazing redeeming value. Without it, all those idiots would be living with the rest of us!
Parent
Re:Air Conditioning for $1500/month (Score:5, Funny)
Parent
Re:Air Conditioning for $1500/month (Score:5, Funny)
Parent
Re:Air Conditioning for $1500/month (Score:3, Funny)
Californians raise our power rates by buying ours, we don't mind.
Californians make more money, we don't mind.
Californians drive up here and buy houses at HUGE prices, we don't mind.
Californians steal our nice Oregon springs leaving us more drenched than usual, we want better environmental laws or blood.
Re:Air Conditioning for $1500/month (Score:3, Funny)
KFG
Re:Air Conditioning for $1500/month (Score:4, Informative)
Parent
Re:Air Conditioning for $1500/month (Score:4, Interesting)
Ah well, if you aren't lucky you learn something new every day.
I'll make two notes though, Twain was a public speaker, and just because this particular witticism can't be found in his writtings is not actually an indication that he didn't say, and even orginate, the quote, it simply means it can be proven from the written record. There is such a thing as oral history. Many things I have orginated and said are not recorded in print, despite my post count, and the printed version of not a few things has been lost even to myself.
The second note though is my observation (and I believe that of others before me) that sooner or later every American will attribute every witticism to Twain, especially as he often used the witticisms of others, often without direct attribution since the people of his time were well aware of their actual origin.
KFG
Parent
Minor nit (Score:5, Insightful)
Re:Minor nit (Score:3, Insightful)
Re:Minor nit (Score:5, Insightful)
Parent
Re:Minor nit (Score:5, Funny)
If he wants to be cheap, why not just take an old fridge ($20), remove the doors, and use the fridge to block the door to his room? Leave the coils facing out into the hallway, and his room becomes cooler - plus the light will always be on, so he can see wtf he's doing.
Parent
Re:Minor nit (Score:5, Insightful)
The work has been shown multiple times in the various threads, but since you seem to be slow to catch on...
Starting state:
1) Room: temperature x (warm)
2) Water: temperature y (also ~room temp)
Net heat: x + y
Step 1:
Water gets put in fridge. Heat is pumped from water to room.
Result from Step 1:
Call the change of heat in the water z.
(Water gets colder. Room gets hotter. Even heat levels from that part.)
Inefficiency in the fridge adds net heat to room.
The inefficiency heat is i.
Net heat = (x + z) + (y - z) + i = x + z + i
Net Result: increased temperature from inefficiency.
Step 2:
Cold water from fridge is used to run through piping/fan to cool room. It's not done by swamp or other methods. The only thing going on is the warm air is blown past the tube of cool water, bringing the temperature of the room down, and the temperature of the water up. (The water doesn't go through any phase changes through the tubing or anything; it's simply equalizing the temperature)
Result from Step 2:
Heat n is transferred from the air to the water.
Room is warm and so is the water once again around room temp (going out the window now).
Heat m is added from the inefficiency of the fan.
(x + z - n) + (y - z + n ) + i + m
Net Result: (original heat)+ (excess heat)
x + y + i + m
We started with x + y. Now we have x + y + i + m.
Seeing the problem yet?
The water going through the tubing is *not* superheated. It's not warmer than the room air. At the very best it's the same temp as the room. That's if he gets complete transfer. No net heat is removed. It's added.
Water y gets dumped out the window. What are you left with? x ++
Please show your math for your strange theory that makes this perpetual motion machine work, and show how the water in the tube is well above room temperature in order to decrease the net temperature of the room.
And thanks for playing.
Parent
Re:Minor nit (Score:3, Funny)
I suppose it might still work running on cold tap-water, but then that could make for an expensive water bill. Although not nearly as much as running your freezer with its compressor
Re:Minor nit (Score:5, Informative)
This is exactly how a good thermal heat-pump operates. However, a few "upgrades" would make this perfectly viable for a home of 1500+ sq. feet.
1: Make it a closed-loop system, or even a dual-loop system.
2: Use a good radiator and heat-block. Think of a water-cooling rig on a PC, but in reverse and a much larger scale.
3: Use the earth, itself, as both the source and destination of heat.
Most people that have done this for their homes use the earth as a natural heat sink. If it's new construction, they typically dig shallow, but wide. In a retro-fit, they'll drill deep and narrow. Either way, the earth holds a pretty steady temperature below 6-8 feet or so. All that's needed is a way to put heat into it when you want to cool off and a way to get heat out of it when you want to warm up.
This way, all that you spend money on is the electricity to pump the heat-carrying fluid/gas/whatever into and out of the tubes in the ground. If that isn't enough, a small furnace and/or A/C unit can supplement, if need be. Either way, the energy consumed from the utility companies is a fraction of "normal".
I have plans to build a new home in the next 3-5 years, and I'm looking at all sorts of alternatives to just about everything that consumes energy in a home.
1: Geothermal heat pump(s) for climate-control.
2: On-Demand, CNG water heater (i.e.: no tank to keep warm)
3: Solar-powered radiant heat (suplements forced-air from #1)
4: On-Demand lighting (sensors that detect room occupancy)
I'm missing a number of other things I could do, but the goal is to have a home with all sorts of modern conveniences while trying to reduce the energy usage associated with most of them. It's tempting to add a water-cooling loop to the climate-control system for the comptuers. They're already producing heat, so why not just send it directly to it's destination and avoid that pesky conversion to heated air?
Getting back on-topic, this guy hasn't done anything new. In fact, it's rather wasteful to just use a coil of copper tubing tied to the back of a fan. The fact that he's using ice water (as mentioned in other posts) does nothing to save energy costs. After all, he's got to power a freezer to make the ice to begin with, which offsets most of the savings. Never mind that the heat from the water (plus the heat from the machine, itself) went into the living space that he's trying to cool.
And that he's a student, and *probably* not paying for much, if any, of his utility costs. But I digress...
Parent
Thinkcycle (Score:3, Informative)
Siphoning (Score:3, Funny)
sorry...
MirrorDot (Score:4, Informative)
http://www.mirrordot.org/stories/5cb66a4a72a5269b
Congrats on making your PH.d. pay for itself! (Score:5, Insightful)
Canada (Score:5, Funny)
Now you just have to figure out how to keep the snow off of the carpet.
Re:Canada (Score:5, Informative)
Parent
Re:Canada (Score:4, Informative)
weekend? Ontario's been a rotten b*stard for the last week - 30 Celsius + humidity every day.
I'm sitting between two fans, beer in hand, AC cranked. My effing hydro bill is going to make me cry...
Parent
Re:Canada (Score:4, Informative)
Parent
Re:Canada (Score:3, Funny)
Can't wait until August, when it really gets hot.
Environmentally friendly? (Score:5, Insightful)
Unless you have a solar or wind-powered refrigerator, I suspect that the overall system is not actually all that environmentally friendly. What is the energy efficiency of the system?
Re:Environmentally friendly? (Score:4, Funny)
Ice Pixies magic it up, so he doesn't have to run a refridgerator/freezer to make the ice. Because, you know, those actually produce heat inside the house, which he is trying to get rid of... Pixies. Yeah, that's it.
Parent
Beer (Score:5, Funny)
Congratulations (Score:5, Informative)
It didn't seem all that likely that most /.ers would care about evaporative cooling, since even in Arizona they only work part of the year (like now, although today the Phoenix dew point got up to 10C. I woke up just knowing it had gone up because the cooler was blowing full speed and it still wasn't all that cool.) Never mind next month when the monsoons start. AC time then for sure.
Swamp Coolers... (Score:4, Interesting)
Newer homes never have them, but the older house that I bought (built in 1979) had a monster one installed on it. During the early parts of summer (when the humidity is low) I can keep my house at 72 degrees when the outside temp is about 100 and my electricity bill is $65/mo.
If I ran my AC unit and kept the house equally as cool with it, I would be looking at no less then a $150 in early summer and $200+ as the temp gets into the range of 110+.
At this point, what I would love is a thermostat that runs both my swamp cooler and AC unit and can determine when to use one versus the other and switch automatically between them. Anybody know of such a device?
cheers.
Parent
Re:Swamp Coolers... (Score:4, Informative)
what I would love is a thermostat that runs both my swamp cooler and AC unit and can determine when to use one versus the other and switch automatically between them. Anybody know of such a device? Nope, and you won't find one. It's a fast way to kill your AC.
I had a tenant who manually switched between AC and evap every day, when we were in one of those "not quite dry enough for evap" months. Her theory was that in the PM, when the RH was low, she could use the evap, then use the AC the rest of the time. Then she called me because the AC was not working.
The first day or so of an AC switchover from evap is when the AC has to remove all that moisture left by the evap. The tenant had been switching often enough that the humidity removed made a sheet of ice on the coils and the AC died. Because it wasn't cooling rapidly enough, she cranked the T-stat down as low as possible, which made the icing worse. Fortunately, there was no permanent damage ot the AC, but she had to swelter with no cooling until the ice caking the coils melted. She wasn't willing to pay the AC guy his hourly to stand there with a blow dryer and melt yhe ice.
Parent
thermodynamics? (Score:5, Funny)
hmmmm.... (Score:5, Insightful)
#2 even if you used the house freezer, you shut the door and basically you're pumping heat away from the bedroom into the kitchen, obviously you won't get huge temperature differentials, but 5-6C feels very noticeable when you're trying to fall asleep and it's too hot to do so.
Parent
costs (Score:4, Insightful)
The store needs to make a profit on top of the cost of the electricity to maintain the machine, and the ice...
...supplied by the ice company which bought the machine, maintains it, and freezes the ice, and trucks it to the store from their "plant"...and make a profit.
You do realize that 1kW/hr costs about 22 cents, whereas a 20lb bag of ice costs about $5, right?
You have to move 330J of energy to freeze one gram of water, basically. We'll assume a 50% efficiency here (pretty poor, I believe). A bag of ice, say, 20lb- would need about 3 million joules (watt-seconds), or 6 million watt-seconds of electricity. That's 1662 Watt-hours, roughly.
Or about 36 cents.
#2 even if you used the house freezer, you shut the door and basically you're pumping heat away from the bedroom into the kitchen, obviously you won't get huge temperature differentials
Most refrigerators are virtually incapable of pumping that much heat (there's a reason they're insulated), and furthermore, are designed to work at a temperature range 60-90 degrees cooler than what you're asking of it. Ever noticed that a fridge takes forever to get from room temperature down to operating temperature?
This idea is so stupid, I can't believe I just wasted 5 minutes on this post. I want that 5 minutes of my life back.
Parent
Re:thermodynamics? (Score:3, Insightful)
While I agree that there are far more elegant ways to do this, You can still cool a room this way and not disobey the laws of Thermodynamics.
The heat generated by the Fridge stays in the Kitchen. Close the door and now you have effectively transfered heat from the cool room (bedroom or livingroom) to the kitchen. It is now far easier to relax.
Think it through before calling someone a moron.
Most enviro friendly method to not overheat (Score:3, Interesting)
this will result in you using about 1/8 the electricity to get the same light, but drop the heat output from lighting - a major contributor to household heat - to virtually nil.
I used to have a problem in my new house with having to get a fan until I realized it was mostly heat from lights that was making it hotter than a normal open window breeze could cool. Then I replaced my incandescent bulbs (well, most of them) with flourescent bulbs and suddenly it was cool enough I didn't even need a fan at all.
Now, if the external temperature is above about 98 degrees Fahrenheit (30 C, I think), you may still need to do the water evaporator you describe, but the energy used by it will still be lowered by switching to compact flourescent bulbs for lighting.
Oh, and get a flat panel LCD monitor - that will save a lot of energy usage and heat output as well.
Save the fan to cool off your computer, not your room.
addressing all the flames/legitimate concerns... (Score:5, Informative)
which addresses the why no recirculation/you need an infinite supply of ice criticisms. this was designed to cool me off before bed, so i could fall asleep without wanting to kill myself. once the bucket runs out of water/ice, it just becomes a regular fan which is fine once the house cools off in the wee hours. plus i dont have to worry about knocking anything over in a morning daze.
ive rigged it up to a slowly flowing garden hose which will keep things cool indefinitely, but i find it easier and a bit cooler to just pick up a big bag of ice and dump it in when it gets really hot.
anyways, take it or leave it. and to the graduating chemmie that said he was ashamed to call me a student - come visit me at my office by the weef lab (e2-1311), im sure i can address any of your concerns to my satisfaction.
CostCo $50 for 5000 BTU (Score:5, Informative)
It's $99.99 with an instant $50 off rebate at the register.
Less work too.....
Bend the copper using sand (Score:5, Informative)
While the freezer probably isn't the best way... (Score:5, Interesting)
1) Get a second trash can. Drain to trash can number 2. This will allow you to save water, plus:
2) Put salt in the water. The ice and chilled water mixture gets colder with salt.
You probably don't want to drain salt water to the yard.
You can run from one trash can to the other, then when it's done draining, swap one can for the other and ice down the other can. If you've got some freezer space to dedicate to the project, the bottles of ice are probably an excellent idea-- have a set in the freezer and one in the heat pump.
Coral Cache (Score:5, Informative)
Will someone edit the submission to replace the URL, please? Sheesh.
Parent
No, it isn't (Score:5, Informative)
Parent
mirrordot (Score:5, Informative)
Parent
Re:Fan? (Score:3, Interesting)
Probably some other factors as well, I had a bit of a dumb thermodynamics teacher (not to mention it was over 10 years ago and haven't used it since!).
Good show, but not a great idea... (Score:5, Informative)
Air conditioners are unbelievably cheap and unbelievably efficient nowadays.
As others have said, this setup has all sorts of problems, from a reliance upon a source of ice that may very well be dumping more heat into the local environment than it saves, to wasting water.
Though this system doesn't use a pump, a recirculating system with a small electric pump could end up creating more heat than it saves.
If you're really bent upon saving energy in a cost-effective fashion, adding insulation is almost always efficient. Good blinds on the windows are also a great investment.
Parent