DIY AC For The Hot Shop

Working out in the shop is usually super fun but if it’s summertime, watch out, it can get hot! We’ve all been there and we’ve all wished we could do something about it. Well, woodworker and general DIYer [April] has stepped up to the plate and built a portable low-buck AC unit to cool her shop down to an acceptable temperature.

The unit is very simple and starts off with an old thrift store cooler. A hole is cut in the back of the cooler to make room for a fan that is directed to blow air inside the cooler and across blocks of ice. The air cools down as it passes over the ice and leaves out the top of the cooler through five 90-degree PVC elbows. After all the inlets and outlets were caulked, the entire unit was given a monochromatic black paint job.

[April] says you can feel the cool air blowing from about 5 feet away from the unit. She has measured the output air temperature to be 58-62ºF. If using loose ice cubes, the unit will work for 2-3 hours. Freezing milk jugs full of water gets about 5 hours of use.

73 thoughts on “DIY AC For The Hot Shop

  1. Yet another thermodynamics fail.

    Freezing two gallons of water releases 0.9 kWh, or conversely, melting 2 gallons of ice draws 0.9 kWh of heat, which spread over 5 hours equals a cooling power of 184 Watts.

    Which is about a quarter to a fifth of even the smallest commercial portable A/C unit. A typical mini portable unit removes 600-1000W

    The main effect of this device is the fact that it blows air at you – not that the air is significantly colder than the surroundings anymore once it reaches you 5 ft away.

      1. Those cheap desk fans are so inefficient that a PC case fan powered off a wall wart is easily 2-4 times as efficient. To put it simply, shaded pole motors are a really ugly hack and multi speed PSC is almost as bad.

    1. When shopping for an A/C unit, you might see a rating in Refrigeration Tons. 1 Ton is equivalent to 12,000 BTU/h or about 3.5 kW, and represents the cooling power of 1 ton of ice melted per day. That 600-1000W unit is about a quarter ton of ice per day (500 lbs or 225 kg).

      1. Yeah. Just that in metric countries we’re used to just Watts instead of tons or btus. Then people get confused of the difference between the input power and the cooling capacity.

        And though I try, the smallest I’ve actually managed to find online is a 1500 Watt (500W) window mounted unit. Those are basically only good to cool down a one-room apartment.

          1. They’re compressor based, so if you use a VFD it’ll either not turn or it will break the compressor. It’s not designed to run at an arbitrary speed.

        1. Not inefficient, but ineffective.

          It would probably perform as well if there was just a mesh of wet cotton threads inside the box for the air to travel through before exiting the pipes.

          That reminds me: if the air is already humid, then a great deal of cooling power is lost by condensation of moisture from the air on the ice.

          1. Actually, that’s part of the “cooling” , Dry air tends to let sweat evaporate more easily, increasing the cooling efficiency of our own natural system. Any AC system uses this effect.

        2. Depending on the relative humidity of the entering air, you might get very little drybulb cooling effect from a swamp cooler. It might work in Arizona but don’t try it in Florida.

          1. Unless you separate the evaporation system from the cooling system.

            Have a larger outdoor unit which evaporates a large pool of water over a running wick based system (to provide as much evaporative capacity as possible), and then pipe that water indoors and through a radiator. That way there’s no humidity increase inside.

            Having said that, this is still useful in situations where you either don’t have an enclosed room (so a regular A/C would be pretty useless), or require a very low (localized) power usage. It’s about blowing a little bit of cool air on the person, not cooling an entire room. Switching to a much higher efficiency 12V fan would allow portable use as well.

            Think of the ice like a thermodynamic battery.

          2. Forced evaporation coolers spray water mist down a tube while air travels in the opposite direction, and the water collected at the bottom is used for the coolant.

            A 10 Watt aquarium pump and a drip system with cocentric tubes for a heat exchanger might work too. Water in at the top, air in at the bottom, whatever drips through you recirculate.

          3. In order for these to work you’d need ambient wetbulb temperatures in the upper 40s to lower 50s since your approach is going to be on the order of 5 degrees F.

  2. Maybe more interestingly, assuming that buying a real AC may not be an option, does this design have any advantage over just putting a bag of ice in front of a fan?

    I guess that having the ice in the box may slow the melting process compared to having it out in the open, but then the air flow is designed to maximize heat transfer, so I’m not sure that effect is actually desired… It might be slightly more effective at directing the cold air to where it is wanted than just an open fan, though.

    Any ideas on this?

    1. I suspect it’s because a bag of ice with a fan has an undirected cooling effect on the whole room. Ducting and blowing directly on _you_ has a localized cooling effect, which is more important than cooling the entire room.

    1. I thought that too. I wonder if you could do the same style setup, but the fan in front of the ice pulling air instead of behind it, with the vents for intake on the same side as the fan. Basically mimicking the way window A/C units operate, but using ice instead.

        1. I wouldn’t be concerned. There’s nothing to lower the temperature after going over the ice to cause the evaporated water to condense out of the air. What you are describing is the difference between draw thru and blow thru. The difference being that draw thru makes the fan heat supply side load which increases the supply air temperature (allow other things being equal, which they’re not, but for the sake of discussion…)

  3. I’m surprised by the nay-sayers on this one. Seriously, a thermodynamics fail? It works! Just because it’s simple and not as efficient as some refrigeration systems (it isn’t? assuming an ambient temp of 85F, it’s showing a dT of 25F! That’s as good as can be expected of a run-of-the-mill A/C system!), doesn’t mean that it’s a fail. Quite the opposite.

    1. >”it’s showing a dT of 25F! That’s as good as can be expected of a run-of-the-mill A/C system!”

      Yes. At the outlet, but you could get any temperature there by just pushing more or less air through.

      It “works” in the sense that it cools air, but that small amount of air is mixing with the ambient air, heating up and the amount of cooling you get diminishes to nothing but a little waft of ever-so-slightly cooler air.

      A regular desktop PC blows more heat faster out of the back than this thing can remove.

      1. You missed the point: It works.
        Just because it doesn’t have the sheer cooling volume of a 3-ton household cooling system doesn’t mean it’s not effective at doing precisely what it’s designed to do: Provide a spot of cool air in an otherwise hot work shop.

        Sheesh, I’ve never seen such a bunch of people so negative about a hack that does exactly what it was supposed to do… Oh, wait. I have, actually. Right here on this web site.

        Free advice for all who want it: Go ahead and spend a few hundred dollars on a window-shaker, or spend a few thousand dollars on a mini-split, or even more on a whole-house cooling system if you want to. However, if all you want is a bit of cool air for cheap money, give this a try. It might just surprise you.

          1. Experiential comparison.

            Having used actual A/C units with several times the power, I can estimate that it’s not doing much more than blow air at you.

        1. In order to determine how “it works” or “is cheap”, you want to consider its economic efficiency over time. A typical window style AC unit designed for a 15sq ft space costs around $160, but may have a yearly operating costs of ~$40 worth of electricity. Over 5-10 years, you will spend more on electricity than the unit itself.

          For this cooler, you want to look not just at the upfront cost, but also the cost of operation. Since the system is not particularly efficient, the cost to continually freeze water and operate the fan will not be trivial. It would be interesting to compare the lifetime cost and resulting performance of both units.

          1. Well, for starters the window A/C unit operates over a smaller temperature differential because it isn’t trying to freeze water, so it’s going to have a higher coefficient of power, or more heat removed per input power.

        2. Saying something “works” and not thinking about anything else is just the thing perpetual motion enthusiast’s say.

          Does a match work, when you’re trying to heat a room?
          If you measure the ΔT on the output, YES.
          If you just think for a moment, like a grown-up. No…

  4. you stand in front of it and get a nice cool breeze, total success if you ask me.

    Nobody is going to use this unit to cool a room, so all that thermodynamics mumbo-jumbo is completely irrelevant here.

    1. It’s the breeze that cools you down much more than the slight temperature drop 5 ft away from the device. That’s the point.

      If you can hold up a dry thermometer 5 ft from the device and measure even 5 F decrease in temperature, I’ll eat my hat.

        1. I might, but I know how it will end up.

          I know this because I’ve used a commercial A/C unit which outputs several times the cooling power and it was still very feeble. There is no way something with less than a fifth the capacity will work any better than simply running a fan to your face.

  5. Seems as if many people here have never used a block of ice to cool down an area before. I used to dump buckets of ice on the floor of my patrol craft, it certainly helped in the hot months. I would argue that she needs to design a heat exchange system that will allow the moisture to remain in the cooler, also a drain that would allow condensate to run out. I could see good use for this with a 12 volt fan that one could run overnight camping. even a small change in temperature with the air circulation may have a desirable effect.

        1. I’ve already given the evidence and stick by it.

          The smallest commercial units are around 900 Watts cooling power as far as I can tell, and these struggle to cool anything. Two gallon jugs of ice melted over 5 hours gives 160-180 Watts cooling power.

          To make a more intuitive comparison, those amounts compare to trying to stay warm in the winter by huddling around two lightbulbs instead of a small space heater.

  6. Whenever I see these home made “air conditioners” I think that it’s probably a waste freezing the ice, melting the ice, freezing more ice when you could use that same electricity to run a real A/C unit, what somebody needs to hack together, to put into a DIY A/C is an IcyBall, check out the link…

    http://en.wikipedia.org/wiki/Icyball

    Make one of these, now that would be a cool hack!

    1. Ammonia is not very hacker friendly but there is something oddly compelling about ice from fire. Something you could run by burning wood in the middle of nowhere.

    2. This is more suited for lifehacker. This isn’t a technology hack, it’s redneck engineering. It takes more energy to freeze the ice. A window cracked on one side of the house and a window open wide on the other would provide a high velocity airstream. Pressure differences and the venturi effect. Oh and that’s free.

  7. I live in Florida and frequently work in areas without electricity. I use a system exactly like this using a 12 volt D/C auto fan hooked too a battery or solar power. Guess what the system works. Don’t care about the thermodynamics of how or why just know it reduces the heat factor enough to make it feel cooler.

    1. Well you might care if you’re paying the ice for nothing, where the fan alone would do almost as well.

      It’s the “I know it works because I just feel it working” that gets people to buy magnetic bracelets and magic salt crystals.

  8. Would do better with an opening low on a north wall and another high on a south wall, with a fan blowing out the high opening. That would draw air in from a slightly cooler shaded area. Having grass or other vegetation on that side and heat absorbing and re-radiating stuff like concrete nowhere near the inlet would be best.

    Anyone old enough to remember double hung windows where the top went up close to the ceiling? Same principle. Pull the top sash down on the sunny side and lift the bottom sash on the shady side. Could also pull the top sash down on the shady side. Convection pulls cooler air in the bottom as the warm air goes out the top.

    ‘Course even though you may try it, convection cooling does not work if you also design the building like a giant friggin greenhouse, like the Sandra Day O’Connor Courthouse in Arizona. http://www.architectmagazine.com/technology/sandra-day-oconnor-federal-courthouse-cooling-technology-cant-keep-up_o

    What sort of idjit builds a greenhouse in ARIZONA without any air conditioning, then expects people to work in it?

  9. I did something similar a few years back.

    http://imgur.com/a/GLgCw

    It’s powered by a battery and will run for about a day. The chilled water is pumped into a heater core which the fans pull air through, and the water is returned to the reservoir. I use 2 batteries so one can trickle charge from a solar panel while the other is in use. The only operating cost is a few bags of ice from the corner store. It was nice to have when we lost power one summer after a hurricane, made going to sleep possible by cooling down the bedroom.

      1. I didn’t notice the date when I looked at her website. I wonder if it’s still in use and working.

        And yes, it’s nothing new. The instructions I based my design off of were from the late 90s.

        1. ..and what the ‘duh but thermodynamics’ crowd are missing is it’s not to cool the shop, it’s to cool you.

          As far as thermodynamics is concerned a normal fan is useless as all it does is move air around while adding more heat – but you’ll still stand in front of it on a hot day – good thing humans sweat, eh?

          This is no different, except the air being blown at you is less than ambient.

  10. Despite all the thermo-nazi comments on here there are very relevant uses for this. If you wanted to cool a small area (like a tent) it would certainly work. With a 12v fan and a battery it could be used where generators were not allowed like at historical reenactments (SCA etc.) or anyplace where the generator noise is unacceptable. In these types of situations the poor efficiency doesn’t mean squat. When I was in the SCA it easily could have been made to look “period” and Ice was readily available. Believe me a little cool air in the middle of a hot July night makes a world of difference.

    Oh by the way, just leave the ice in the bag if you don’t want extra moisture.

    Good Hack.

    1. You can’t really provide any sort of localized cooling because the air is free to flow around and mix.

      See how dyson bladeless fans work; the small breeze from the tubes moves a larger amount of air which dilutes the cold air coming from the device and by the time it reaches you 5 ft away it’s already nearly as hot as before.

  11. The problem isn’t the people for or against the redneck air conditioner. The problem is that it’s 2015 and hackaday is publishing an article about something that’s been done about a million times already. Let’s just say we are all little scientists, some of us may be real ones, yet this is like discovering that wind will turn a propeller and do work, and then hackaday publishes an article about it like it’s never been done before.

    Instead of repeating old crap to fill a daily quota, I’d rather get just one hack per day that is actually based on new ideas and ‘hacks’. I’m slowly starting to think I won’t be coming back here. If I wanted to read crap like this I’d go to instructables.

  12. I built a swamp cooler with some 2x3s, a 20″ box fan, swap cooler mesh, and a swamp cooler pump. I’m in San Diego, California so the air is nice and dry here. Waiting for it to heat up around here again then I’ll see how well it actually cools.

    I tried freezing blocks of ice and blowing air over at last summer. it’s horribly inefficient because I was spending more time and money freezing blocks of ice than I was cooling down your living room. I had a big deepfreezer dedicated to tge freezing process also. With a swamp cooler all you’re doing is refilling it with room temperature water. The only energy that is wasted is the energy the fan is consuming.

    I’ll try and post my project once it warms up and I can test it out.

    This is the project I copied. I sealed up the edges with duct tape to force air to enter through the mesh.

    https://youtu.be/J_ubf0zqvSQ

  13. I work for a blood bank that does mobile blood drives. When a donor isn’t feeling well during a donation or you’ve been on your feet for 4 hours in a lab coat working on people being able to provide a “colder than a fan” area is a big plus. It doesn’t have to be the whole room, they’re usually very big rooms we’re in.

    I’ve been refining a design on one of these for us to use regularly for this situation. Similar to camping a portable ac unit isn’t viable and too expensive and we already use ice machines in all our facilities for shipping the blood so the cost of coming the ice also isn’t an issue.

    These aren’t magic, but given the right use case they work very well for what they are.

  14. Very funny and fancy but.. if it works? as well as a fan with a dropwise system in front..

    It adds humidity, and a false sensation of cold.. in a 10 ou 12 square meter room the ice systems can drop some 3 to 5º Celsius, with some drawbacks, you have to have ice (produce it, buy it, whatever.. ) and de effect is very low, at a long term it is cheaper to buy a AC unit. For a shorter period well, you can drink more water and get used to it.

    The only situation i can see this is really usefull is when you move from place to place in small periods, and you dont have a eletricity grid, so you need any kind of batteries.

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