I recently completed my latest creation. It's a very different design from what I had previously. This version attempts to deal with the small issue I encountered with my last design with regards to condensation buildup in the heat exchanger. Depending on how humid it is, you will get water pooling on the bottom of the heat exchanger (bottom of the "U"). This happens when the exchanger walls are at or below the dew point temperature. The level of water condensing isn't a lot, certainly not enough to block the flow of air, but I got around half a glass or so which I have to pour out after a day of use. Not a big deal, but it got me thinking on how I can modify the design so that I wouldn't have to bother with that. This led me to constructing a horizontal heat exchanger as shown in Figure 1-3. It's basically a flattened tube constructed out of the usual aluminum sheet I've been using so far.
The construction was fairly simple. It only took me a few hours. I used a 20 litre plastic container to house the heat exchanger and also hold the cooling medium which is ice-water in this case. I made the heat exchanger roughly 7 mm (0.7 cm) wide and 20 cm high to promote a high rate of cooling, and also to compensate for a shorter flow length than was used in the previous version. To prevent leakage the gaps were sealed with silicone (which happens to be DAP 100% silicone for this particular project - great stuff and it cures fast!).
The heat exchanger is tilted slightly downwards so that the end where the air exits is slightly lower than the intake end. This allows the condensate to flow "downhill" and into a small container I conveniently place just underneath the mouth where the air exits. See Figure 4.
The intake end (where the fan sits) was a little trickier to construct as I had to create an opening for the fan to fit snugly inside and transition that to the narrow intake gap. To do this I attached a flexible rubber funnel constructed out of silicone baking mats (left over from another project) and joined that to a sheet aluminum ring using a strip of old table cloth. See Figure 5-7. Everything was sealed and joined together with silicone as it's a great adhesive.
I measured the level of cooling to be slightly less than with the previous version. This was a bit surprising for me, especially given that the internal gap was a lot smaller than in the previous version. Also, the exiting air temperature distribution was quite uneven from top to bottom with the top being around 2 degrees Celsius cooler than the temperature of the air exiting at the bottom. The reason for this is twofold. First, the water pressure tended to push the two sides of the heat exchanger together creating a slight "pinch" at the middle. This separated the flow somewhat into two streams above and below the "pinch" region, resulting in poorer mixing (less heat transfer), especially for the bottom stream. And secondly, the flow length was somewhat short and straight. This discourages mixing and heat transfer as well. With the previous version there was a longer flow length and the air was additionally forced around a bend (bottom of the "U") which encourages mixing/cooling and also results in a more even air temperature distribution at the exit - there was less than a 1 degree difference between the center and the two ends, with the center being cooler.
To reduce the "pinching" due to water pressure I filled the container with water only up to the top edge of the heat exchanger (Figure 8).
With a cooling medium (water) temperature of 16 degrees Celsius, and an ambient air temperature of 26 degrees, the air was cooled to roughly 22-23 degrees on average, between inlet and outlet.
Regardless, this version is decent enough, although you do have to turn the fan speed to maximum (or use a more powerful fan or blower) to get appreciable air speed coming out the exit (the air speed is less than with the previous version at the same fan setting). And the fan running at maximum is pretty loud which is a bit of a disadvantage. In the previous version, I can turn the fan on low and still get good air speed coming out. Good air speed is important because it helps cool the room faster.
If you're looking for something better than a stand-alone fan but maybe not quite as potent as a store-bought A/C, then this type of unit can work well. It probably works best if it's in close proximity to you, such as when you're sitting or sleeping.
Have a look at Cost To Make Ice For Homemade Air Conditioner.
Other related post:
Homemade Air Conditioner Version 1
25 comments:
I have got one better for ya.
metal duct.. fan that fits into the duct.. bucket full of ice water with a small water pump sending the cold water thru copper pipe coiled inside the duct.
mount the duct ontop of the bucket (or better yet... a cheep $5 cooler) and not only is it more portable... but with a little work you could make the condensation drip right into the bucket
Cool idea.
I imagine there is significant stratification of water with the warmer water on top. If you flip your heat exchanged horizontal near the bottom I'd bet it would work better.
Also there is probably a fine line between turbulent air flow and air flow that is too fast to dump the heat.
What about running separate discreet tubes through the buck like a tube steam boiler? Copper might be too expensive but perhaps some foot long pieces of galvanized iron water pipe would work.
I think that might work better, better heat transfer and slower airflow.
jon,
That sounds like a good idea. The cooler will certainly reduce heat infiltration from the outside. Maybe I can find one that is the same size as the container I'm using for version 3.
I actually experimented with using ice water running through 10 feet of coiled copper pipe. It gives very little cooling, maybe 1 degree cooler downstream. There just isn't enough heat transfer area relative to volume of air flow, to result in serious cooling. But on the plus you preserve good air speed. And that's part of the trade off, balancing desirable air speed with desirable cooling, which is all related to the resistance to air flow through the heat exchanger. The more resistance (the narrower the air passage-way) the more cooling you get, generally. Coiled pipe won't usually cool very much because it doesn't "constrict" the flow enough. That's why I opted for internal flow heat exchangers, where I can narrow the gap accordanly.
I feel I've basically maxed out the design and the level of cooling/good air speed with version 3, using the fan I have.
Flipping the heat exchanger horizontal might work better, but I decided against that as it would mean making a large horizontal cut across the container which could weaken it a bit too much.
I'm not sure the stratification explains why the top air stream was cooler than the bottom. It seems to be a consequence of the flow physics more than anything.
Using horizontal pipes might work better. It would help keep the flow uniform anyway. I would need a lot of them though, like a tube bundle basically. And I may have to flatten them in the middle to improve cooling. Copper pipes would probably be better for this as they're easier to flatten :)
Hello, saw this posted over on MAKE: and got me to thinking. But first off, great idea you have here, it's quite interesting to see how people deal with the heat of summer and I find that when you get others to think it's an even more valuable idea.
Well, here's what I was thinking. I notice that your heat exchanger is a straight line, more or less. True, you get better heat exchange with a smaller channel for your forced air, but how about surface area?
For instance, have you tried corrugating your aluminum exchanger? Putting in a bit of a wave to increase the surface area and therefore the rate of heat exchange?
You could also use copper, much better at this than aluminum (though more expensive). If you were to take a number of small copper tubes that roughly equaled the height of your aluminum "U" and then coiled them through the cooling medium, you could easily increase the amount of exchange due to the greatly increased surface area. Though I'm unsure how this would affect the airflow...
Along those same lines, if you were to place water on the outside of the coil and a bucket of ice on the inside of the coil, how would that affect the duration of the cooling ability of your HAC?
Have you thought of buying a few, cheap, Styrofoam coolers, breaking them down into their constituent pellets, and then gluing them on the outside of your bucket?
Just ideas that popped into my head after I'd read about what you did. :)
Good job and keep the ideas flowing! heh
Or...you could reverse the design, and use an old car radiator. Pump the chilled water through it and have a much higher airflow.
curt, I have thought of using corrugated sides. It might help the mixing along the flow length, especially if the corrugations are lined up against the flow. Maybe the next version :)
Those are interesting ideas you mentioned. I'll keep them in mind thanks!
Do you have any insight how "green" this is compared to a commercial air conditioner? I'm thinking it must be really hard to beat the efficiency of a well-engineered A/C, which uses a better coolant than water. If you add up all the energy this thing uses, including the power needed to make the ice-water, how does it compare in terms of power required for a certain amount of cooling?
It is greener and uses a lot less energy than a commercial a/c, if you use ice made during the cold winter months and store it in the freezer, which I did, or if you just use water out of your tap (assuming it's cold enough), or by cooling it with a low cost means (e.g. running it through underground pipes or leaving it out at night).
But yeah, it is not as effective as a store bought unit. No one is arguing that.
This reminds me a lot of the home made fog chillers that are used in haunted houses. They chill the hot fog coming out of the fog machine so it lays along the ground nice and scary like. Really easy to make too.
Sure, I wouldn't expect this type of system to be as effective as a commercial unit either. But how many WattHours does this spend per degree you make your room cooler? How does this compare to a store bought A/C? I'm not trying to diss your solution, which is a great project, but I'm thinking about making my own cooling solution as well, and I'm simply not convinced doing it this way will ultimately save power. Even if you make ice during the winter, you have to 1) make a massive amount to last the summer and 2) keep it frozen al the time. Particularly 2) means you're pretty much just moving the power consumption from the A/C to your freezer (Unless you have a pre-fridge-era freezer stuck in a cave/deep cellar in which a large amount of ice will last a long time).
Good questions. All I can say for sure is that the way I have it set up now uses a lot less power. The fan is maybe 100 W max. The cooling medium for the time being can just be tap water which is about 14 deg C in my area - basically free.
As for Watt-hours per degree cooling per "x" size room, I don't have any data right now. But I can say that it's better than having just a fan blowing, and if you put it beside you then it's a good source of local cooling. I would suggest that you build one anyway and see how it goes. And I can link to it :)
I appreciate the effort you went to on this idea.
The biggest problem in the A/C is I think getting the heat out of the air. Here is an idea that i have had which might work.
I have heard that if you dig into the ground about three feet or more, the temperature is always about 55F.
If this is true, why couldn't you figure out a way to (1) send hot air into the ground for cooling and then return to the surface, or (2) put some water down there and use a little pump to recirculate the cool water through a Honda auto radiator, which is designed to cool water, and blow the hot air into the radiator fins and into the room?
Each room in the trailer could have it's own Honda radiator and water pump.
-30
Alfred E. Neumann
In my house I run the central heat/air fan all the time to increase curculation and help clean the air. What if you rigged something similar to this on one of the output vents of a central air system? You would not be using any additional energy but would be "treating" the air coming out. Or perhaps it could be a had on the air return side. Just throwing out ideas here.
What if you tried to circulate alcohol cooled with dry ice? I'm not sure on the cost effectiveness, but you can get way cooler than 0 Celcius. I want to say you can possibly achieve -50 degrees C. NOW that's some potential for awesome heat exchange. You may be able to get 5 gallons of isopropyl alcohol for ~90 USD and this would last most of the summer. Not sure on the price of dry ice.
I'm seriously contemplating a home made cooler... something like this but running a copper coil off the cold water supply to the hot water tank to cool a long, narrow tank of water that acts as ambient source of cool air.
I'd have a cover on the tank with a 2" or 3" PVC pipe coming out each end - one end would have a small ventilation fan and the other I'd route into the air supply duct for the central HVAC and it would all be insulated.
I'd also have a float valve in the narrow tank to keep the water at correct level, and a drip pan underneath to catch condensation or accidental overflow.
If working efficiently this would also have the effect of preheating the hot water tank a little, using the slightly warmer air of the furnace room to warm the long narrow water tank.
The nice thing about the water supply line is that is always cold. Also having this cooler in the furnace room means access to electrical for the fan and a floor drain for the drip pan.
My biggest concern would be getting enough flow through the copper tubing to cool the tank water without reducing the hot water pressure too much - I'd probably run a parallel line rather than route all the water going to the hot water tank through the coil.
My other concern is whether or not blowing the cool air into the supply duct would actually help cool the house or if it would just blow back into the basement from the cold air return.
Very cool idea... I guess you can also video the steps you did onto youtube or something so that people can get a feel of what you're doing...
Keep it up ;)
This will 'not' gonna work. A normal room will not be cooled with this, you need many many more cooling powers then this.
The easiest and most efficient way of providing cooling to the air is by evaporative cooling of misted water. First and foremost, you don't run up your electric bill making ice in the freezer. Second, you don't need to dig a trench. Third, you don't need to use city water - any water source will do.
Simply put: spray water, make a fine mist. Ever stood within 100 - 200 feet of even a small waterfall? You can provide about 16 degrees (Fahrenheit) of cooling this way, and you don't need an electric pump either. Let gravitation do the work.
Elevate a rain barrel, and run a rigid tube from the bottom down to ground level. This will provide the pressure. You don't need a large flux of water through the spray nozzle - just the tiniest of flows. The spray nozzle must provide a very fine mist in an enclosed chamber through which air circulates (make the air outlet at the TOP of the chamber and of sufficient height that mist will not appear at the end. If you don't want increased moisture content in your air then you need a heat exchanger, but the principle is the same. Personally, I don't mind the increased moisture content, because the air is sufficiently cool that it feels rather good.
To have better, and colder cooling add salt to the ice water. depending on how much you put in you can make it about 10-15 degrees (Fahrenheit) cooler.
Cool stuff. I love repurposing old items. Just a thought. What about using an old motorcycle radiator as the heat exchange?
Just to address some of the comments:
- using evaporative cooling probably wouldn't work very well where I am (southwestern ontario) as it gets very humid here, usually coinciding with the hot days
- adding salt to cool further would work, but I would need a lot. Now rock salt (winter deicer) is fairly cheap. But there is the corrosion problem. My container + heat exchanger may not hold up well to a salty environment.
- a radiator may work well but I would probably need a stronger fan or a blower to "push" the air through with enough velocity. The reason I opted for a homemade heat exchanger is because I can narrow the "gap" according to the fan power I have available.
I appreciate the comments!
I have a different idea. I'm looking at a burying a 100' by 6" plastic tube in the ground. I'm going to take the air in from one portion of the house and put it into another portion of the house.
I talked to the plastic tube people and they said people had done this in the past, however, they were just drawing the air in from outside. I figure that would cause very high humidity.
I figure by taking the already cooler house air into the tube I can work with a lower temperture air to start with and lower humidity to start.
The tube has no holes or opening except the ends.
Can anyone tell me how much air I can expect to get from this? The 6" measurement is I.D. Should I use 2 pipes of 6" or should this be enough to help the air conditioner.
I was planning on forcing air through the tube and then use the air circulating air feature on the air conditioner.
Any thoughts?
goodh2o
^^^ I think you might have an issue with water condensing out of the air as it flows through the pipe(s). And since it's underground there could be a problem drying it out. And there's also the risk of mold growth.
From what I know about ground-source cooling, an anti-freeze type liquid is circulated/pumped in closed circuit underground pipes which feed into and out of a heat exchanger (like a radiator). The heated liquid coming out of the radiator then rejects the heat it gained to the ground, and the cycle repeats. And the process can be reversed in the winter where the ground acts as a heat source instead of a sink. It's basically a heat pump set up.
In your case you may be able to use the pre-cooled air coming out of the radiator to take some of the cooling load off your A/C if it's not cool enough by itself, which may be less expensive than installing a full-blown geothermal heat pump system.
I have done a little playing around with some home-made AC ideas. Mine is not really the same concept as this one but let me know what you think: http://eewannabe.wordpress.com/ I am working on a better one. I should be done in a couple of days. All comments are appreciated.
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