Build Your Own Freezer With Thermoelectric Coolers

Freezers are highly useful devices. You can preserve food, stop a dead animal from stinking out your apartment, and keep your vodka at the optimal drinking temperature. Of course, most of us bought ours from the local whitegoods store, but [Tech Ingredients] set out to build his own (YouTube, embedded below).

Unlike your freezer at home, this build doesn’t use the typical heat pump and refrigeration cycle with a compressor and expansion valve and so on. Instead, this freezer uses thermoelectric devices to pump heat, in combination with a glycol cooling circuit and fan-cooled radiators.

It’s not the most efficient or practical way to build a freezer, but it is functional and the device demonstrably works, making ice cubes over the course of a few hours. Performance can be further improved by moving the radiator assembly outdoors to make the most of the low ambient temperatures.

[Tech Ingredients] has further plans to experiment with a dessicant-based refrigeration system, and reports that initial results are promising. We’re eager to see how that goes; we’re fans of any rig that can cool a beer down in no time flat. Video after the break.

37 thoughts on “Build Your Own Freezer With Thermoelectric Coolers

  1. I’ve seen TEC fridges in hotel rooms, improperly enclosed in cabinets that trap heat. With the cabinet door closed they work poorly without the ventilation required for the heat to get away.

    1. These are poor refrigerators in general – very energy-inefficient, and even when working properly they won’t get cold enough to make ice. Most hotels I’ve been in have gotten rid of them (and I don’t see them for sale in big box stores these days either) as more efficient vapor-compression systems are now price-competitive.

      1. Yeah, I saw an article some years ago by some well-intentioned students proposing getting rid of the “mechanical and therefor inefficient” air conditioning systems in cars and using thermoelectric elements. Simple tunnel vision and a lack of basic research.

      2. They’re mostly poorly designed and built by cheap companies that don’t know what they’re doing and are simply copying someone else’s design. TECs are relatively cheap, and aluminum heatsinks are plenty, so everyone can make one with relative ease – it’s just a box and some fans, and since the closest competition (proper fridges) cost proper money you can sell one for much more than it’s worth.

        Result: lemon market. All the products are bad, because people have too many bad experiences and so putting proper money into making a proper TEC fridge doesn’t pay. People would rather buy a “real” fridge than risk it.

        That said, the guy in the video is half-correct. Running peltiers gently makes them more efficient due to proportionally lower losses, but what makes them really efficient is reducing the dT across the junction. If you cascade them, you get to low temperatures with higher efficiency, but then the price goes up because now you’re double doubling the number of elements and half of them need to be bigger to deal with the extra heat given off by the other half.

        If your temperature difference is only a couple degrees, TECs can be surprisingly efficient. If you run a dT of 10 C at around 10% of the rated current, you can pump about 3 times as much heat compared to the input power. For very small dT around 2-5 C the coefficient of power can be 4-6 easily, so stacking peltiers and running them at very small powers can be efficient – you just don’t move a whole lot of heat and that’s why nobody builds them like that.

        1. Also, Peltiers are terrible insulators, so you have to include a mechanism for isolating the hot side from the cold side whenever you’re not running them. If you have a wall of peltiers on your fridge, that’s essentially like having a wall with no insulation.

          Similarly, a common mistake is to add a big heavy heatsink, which gets hot, and then when you finally reach the low temperature you wanted and turn off the TEC, the heat just instantly flows back and warms your cooler just as hot as it was when you started. It’s like trying to bail the water out of a well.

        2. Cascading TECs does increase the maximum delta-T you can achieve, but does NOT improve efficiency. The reason is, each TEC has to pump not only the heat that you’re pumping, but also the heat produced by the upstream TECs (on its cold side). [Tech Ingredients] goes through all of the math on this in a separate video that’s a prequel to this one: https://www.youtube.com/watch?v=aSGwaQWA05U (start at 2:17).

          1. Yes, if you run it over a greater dT – the point splitting the difference between the elements.

            I can find a case where the optimum CoP goes from 1 to 2.7 as the dT drops from 30 to 15K and 1 to 4.4 as the dT drops from 30 to 10K. That means the power consumption of a single device would be 1W per 1W and two stacked would turn out 0.88W per 1 W of heat. Stacking three would get you:

            0.222 W used to pump 1 W
            0.278 W used to pump 1.222 W
            0.341 W used to pump 1.5 W
            Total used: 0.841 W or -16% over the single device.

            It’s this non-linear change in the CoP is what makes the stacking work, but you have to size the TECs just right (or run them at the correct power level, which isn’t 9000) so they achieve their optimum coefficient of power.

    2. The TEC fridges have pretty much fallen out of favor for almost everything. They are especially bad in anything that is AC powered as any ripple causes them to create heat making them even less efficient than they already are. I have a car unit. It draws over 8 amps and on a hot day just manages to keep cold things cold. The savings grace is that there is no need for ice. It is nice having a dry cooler. Soggy sandwiches suck.

      1. Open it up and be surprised. I had one too. It was so shoddily made that there were deep grooves in all of the heatsinks, and they had actually stacked flat bars of aluminum to space the heatsinks apart, and just slopped thermal grease in to fill the gaps. It could barely keep cool because it essentially didn’t work for s**t.

        Seriously. These things are typically very very badly made, and the ones that aren’t, you won’t find in a regular hardware store or camping appliances shop etc. because they’re too expensive for most people.

  2. at tec will only drop a specified degrees below ambient temp ? ,so how do you get it to freeze if you have a 30 c temp out doors or even higher ?, it wont work ??

    1. The TECs I’ve seen can manage 40degF differential, but they’re even less efficient (like 10%) in that condition. Basically, the higher the temperature difference, the lower the efficiency. So no, you don’t get any ice in the summer, but he didn’t test this in the summer, did he? See the snow outside?

    1. IT WoZ A GREAT LAB QUALITY PRESENTATION WITH A CONTROL USED , I BELEIVE IT IS OF ARCHIVE QUALITY REPRESENTATION OF CURRENT TECH , WHICH WILL BE BENEFICIAL IN TIME TO SHOW HOW A LAB TYPE EXPERIMENT SHOULD BE SHOWN A CONDUCTED FOR EDUCATIONAL PURPOSES AS I WOULD LOVE TO DO ONE ON MY OWN EXPERIMENTS AS WELL.

  3. What I would like to see is a company that lets me take advantage of the outside temps vs inside temps to heat/cool things. With a switchable cooling system that could perhaps pump heat out in the winter to the local room, but in the summer pump that extra heat outside.

    1. That’s called a heat pump. I have one on my home here in Florida that uses a ground loop cooler buried out back. Relying on a traditional radiator for HVAC is not efficient in our new climate.

    2. It’s called a heat pump. What you are looking for is actually available, and been available by all major HVAC manufacturers, for decades. In the mid to southeast most homes come equipped with them because it never gets extremely cold. They actually don’t pump heat outside, rather they move the home temperature refrigerant outdoors and compress it, blow ambient air outside over it and release it back into the house side. In the winter it does the opposite, attempting to extract what little energy in the air outside there is and move it into the house. They stop being effective below 40 degrees Fahrenheit, which is why you only see them in temperate zones.

      1. Modern air-air heatpumps are useful all the way down to 0F and even when it’s couple degrees below they’re still marginally better than direct electric heating.

        I mean, people in Sweden use them with success. If they didn’t work below freezing, what would be the point?

  4. Peltier coolers while inefficient do have there niche. I think that there’s definitely potential in employing them where they can take advantage of preexisting temperature deferentials as stated above. Anybody know if anyone’s incorporated Seebeck Effect adapters into a geothermal system?

  5. Peltiers are only good for directly cooling what they are touching. They do not produce enough BTU for the amperage being fed into them. Basically, they are great for cooling chips. They are used in CPU coolers, camera sensors, thermal cores, etc. Using them to cool down a large volume is only going to work so much. It would be smarter to invest more research into Stirling Cycle engines, as they are more efficient than the Rankin cycle and can be produced of very small sizes (to compete with peltiers!).

  6. Years back there was a company that sold a unit and they came up with a more efficient grid design. Units you rip out of department store fridges and coolers are just good enough to pass QA..

  7. It seems to me that a hybridization of TEC with absorption refrigeration might be a good thing. Absorption fridges use a cycle of hydrous and anhydrous ammonia with a heat source to produce cooling. This is the typical “RV” or even some off-grid units that use propane. The excess heat from the hot side of the TEC can be used to boil the ammonia, or at least pre-heat it, potentially using less propane to achieve the desired cooling. Couple that with a nice solar panel and propane use goes way down when sun is available, and likely when the most cooling is needed.

  8. I found it highly amusing to see somebody talking about building a fridge that keep things cool inside by placing the radiator outside where it is much colder (showing snow in the background)… and then mentions efficiency.
    Hmmm… if you really care for efficiency, wouldn’t it make more sense to place the box outside?!?! Just like grandma did… But perhaps add a small heater for when it get’s too cold.

    Pumping your coolant through long hoses seems like fun but is harder then you think as it is just another heat leak in the system. These peltier elements are fun for cooling really small things, where a conventional cooling system would be to large and make the setup otherwise impractical perhaps. But also the current reversal of a peltier element could make it act like a heater. Think of cooling/heating a piece of circuitry for a test setup (like crystals, to determine the s-curve), did that once, worked like a charm.

  9. Curious… I just happened to be repairing a small TEC fridge when I see this artivle (high resistance in heat – cool swich burnt switch up, also had a bad power cord connection.)

    Anyway, the only real problem I have with TEC based coolers is their horrible insulation characteristics should power be removed. I live totally off grid, running generator about 50% of day. I need a fridge that will cool down while power is available, but will then maintain that cold while power is off. Have thought about using two stage system. But a mechanical linkage that dropped foam insulation over inside surface might work better.

    1. That’s correct. Most manufactured TEC coolers are engineered for minimum cost, and they’re having to compete with passive ice chests, which have very low manufacturing costs. As such, they have to compete based on how much food/beverage you can put in them, compared to the overall size. This leads to using the minimum amount of insulation that will allow them to keep food acceptably cool, and very few customers have the means or interest to measure the power consumption. They care about two things in judging a camping cooler: 1) did it keep the food cool?, and 2) did it run the vehicle battery down so far that the engine wouldn’t start? As long as the power consumption isn’t high enough to fail the second criterion, the cooler is judged to be effective.

      This is where any DIYer who DOES care about power consumption can improve, and the biggest target for improvement is to the insulation. I mean, if you start off with cold food, and your insulation is perfect, the efficiency of the cooling unit becomes moot, because the only heat it has to remove is the warm air that enters when you open it to grab a beer. Which by the way, argues for using a top-opening cabinet rather than front-opening, and many camping refrigerators are now moving over to top-opening. With a front-opening cabinet, it only takes a few seconds of open door for ALL of the internal air to be replaced with ambient air, just from convection. A top-opening unit can be left open much longer, since natural convection will tend to keep the cold air in the cabinet, and the only airflow you get is displacement for the volume of the food removed, and whatever air gets moved by turbulence of opening and closing the door. But then, cooling the air isn’t the major task – removing the heat that leaks through the insulation is really the job of the cooler. So minimizing that is the most important design consideration if you care about power consumption.

  10. A box that size that is well insulated should be able to achieve a delta T of > 30C (54F) with a small air to air assembly consisting of two single stage TE coolers. It will draw about 80W of power, so not very efficient compared to a compressor system, but it can get the job done and make you ice provided your room isn’t above about 30C (86F). The benefit of a TE cooled fridge is that through PWM control you can keep the internal temperature very precise, probably within 0.1C, whereas a compressor would be cycling on and off. You may not need this to keep your beer cold, but it can be critical for some medical storage units.

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