Fermentation Temperature Controller

This is a project that I have been working on for some time. The goal is to heat/cool any fermentation vessel easily using a solid-state peltier device.

To accomplish this, I used an Arduino and some computer cooling components along with simple plumbing and brewing accessories.

If you’re interested in creating something like this, please view the project details on this page. Total cost is about $150. Please let me know what you think.

[u]>>LINK TO DETAILS<<[/u]

Thanks and happy brewing!

This is the whole setup. Yes, it’s very prototype-y, but it works great! The XBee, Arduino, and relay module is in the foreground. The CPU cooler/pump/fan/heatsink is in the mid-ground and the carboy insulator with tubing is in the background. The mini-barrel is just for demo purposes.

The Arduino, XBee, and SainSmart 4-Relay Module. Note that the pump/fan relay is wired in series with the heat/cool relays. This ensures that the pump and fan are running if the peltier device is running. Yes, this should probably be on a breadboard, but this was just a proof-of-concept.

The peltier device is sandwiched between the Antec Kühler H2O 620 and the CPU cooler. Some long bolts and wing nuts hold the three components together.

Two adapters (1/4" barb to 1/4" MPT and 1/4" MPT to quick connect) are used to allow the flexible tubing to mate to the Kühler 620 native tubing.

The carboy insulator is lined with the flexible plastic tubing and taped to the inside with foil tape. The mini-barrel was just a convenient prop, not an actual fermentation vessel. Hold the insulator closed around a carboy or plastic bucket using tape or a bungee cord. The tubing will transfer heat either to or from the vessel based on heating or cooling mode.


Download the two files attached. You’ll need to update the paths in the #include statements to match your system. Then upload the sketch to your Arduino.

To set the target temperature, type ‘s’ followed by the desired temperature. The default temperature scale is Centigrade, although it can be changed to Fahrenheit by typing ‘f’. For example, to set the target temperature to 20°C, type ‘s20’ and then press Enter. The default target as 25°C. Your settings will be saved in the EEPROM so that a power failure will not affect your settings.

The hysteresis can also be set by typing ‘h’ followed by the hysteresis value. To turn the system off, type 0 followed by Enter. To turn it back on, type 1 followed by Enter. For help, type ‘?’ Enter.

The startup as seen form the Arduino IDE serial interface. The interface will update with the current temperature and heating/cooling mode every second.

The debug screen showing the temperature settings, total cooling and heating time. This can be seen by using an XBee module wirelessly connected to the device or directly connected to the Arduino via a USB cable. Simply type ‘d’ followed by Enter to see this info.

Please let me know what you think.

Thermostat.ino (10.8 KB)

EEPROMplus.h (589 Bytes)

Peltier cooling is very inefficient. The device creates a lot of waste heat. And the waste heat is going straight into your room, ( and not "outside" somewhere ). The overall effect is heating your room and your beer keg, more than offsetting the cooling effect.

It is like trying to cool down your kitchen by leaving the refrigerator door open. It doesn't work.

Peltier cooling is very inefficient. The device creates a lot of waste heat. And the waste heat is going straight into your room, ( and not "outside" somewhere ). The overall effect is heating your room and your beer keg, more than offsetting the cooling effect.

I do agree with what you have said; but from the picture I can notice he tried to thermally insulate the keg from the rest of the room. How efficiently he did it? I don't know.. Maybe he just opened the insulation to take the picture???. Depending on the quality of the job, the insulation will delay heat transfer back to the keg. If there is AC in the room (probably the case) and if efficiently done, the AC unit will extract the heat from the room faster than it can reach back into the keg surroundings or the "mini room" created by the insulation. I think it has some chances of working that way; but he will get a higher electricity bill. Placing the element outside as you have suggested by simply extending the coolant hoses, is way more efficient.

I didn't specify in my post how easy it would be to adapt this to a more efficient design, but here you go... Find a big cooler. Drill two holes for the in and out hoses. Route hoses through cooler wall. Put keg, growler, bottle, barrel, etc. in cooler...and voila! Now 99% of the heat pumped out of the cooler will stay out of the cooler. I find that the convenience of being able to simply wrap the insulator around something outweighs the efficiency loss.

True, peltier devices are about 4 times less efficient than compressor-based systems for cooling, however they are actually more efficient than standard resistive heaters for heating! Granted, cooling is generally more important than heating to most brewers, but some tasks do require heating.

People are very quick to discount peltier devices because of their low cooling efficiency, but we must consider some other factors:

  • They're very small.
  • The are very inexpensive
  • They're silent
  • They require low voltage
  • They do not require any refrigerants or high pressure tubing.

If I wanted a dual mode heat pump (compressor-based) to do what this project can do, I would have to spend a couple grand and it would be much much larger and heaver. It would also not be very DIY-friendly since the piping couldn't be modified without evacuating and recharging the system with refrigerant. I'm betting I could run this device for several years straight before I racked up an electric bill that even approached the cost of a compressor-based system.

Then here's the final thing to consider about electric efficiency...and it's an important one: I live in the American Midwest where the majority of our climate control expense is due to heating, not cooling. I also tend to do most of my brewing in the winter. So even if I only get 10-15% efficiency out of this system for cooling, the extra heat simply offsets my furnace's heating load. So in reality, the energy used is nearly free. It's all about moving heat to where it's needed...and away from where it's not.

Just for clarification, in normal use, the insulator is wrapped around a 6 gallon bucket or carboy so that it seals all the way around (yes the top and bottom are open). The mini-barrel was just a prop to keep the insulator open for the photo.

BTW, the analog about leaving the fridge door open to cool the room...doesn't quite fit. It would be more akin to leaving the fridge door open to cool things in the fridge. It will work, just not at high efficiency.

I didn't specify in my post how easy it would be to adapt this to a more efficient design, but here you go...

If that's regarding me, I was just trying to help your point, for 2 main reasons: I like the project and its obvious to me that you know what you are doing. If you look to the left under your screen name, there you have a karma. I gave it to you.

I had originally planned to list out some ways that the device could be easily improved, but I didn't get around to it. Michinyon's comment about leaving the fridge door open reminded me that people may not see some of the simple modifications that could easily change the characteristics of the device to suit varying needs. I appreciate your reply though and thanks for the karma point!

All that being said, let's move on in a positive way. Why don't you use the cooler you know will give a better efficiency? On the other hand, people living in hot weathers like myself may want to build your project. I'm particularly interested on this because I have been thinking for a while now on building a temp chamber to test many of my own projects behavior with temp. That's a constant need for me. The cooling system which I need for sure in this hot climate I live in, has been the major obstacle preventing me from starting that. I was of the impression a Peltier based cooling system for that will not have the necessary heat extraction punch I might need and the compressor type option will have required modifications and refrigerant recharging tools and equipment I don't have as you pointed out. I had a bad experience with a small Peltier based fridge I bought once and it was simply not cooling enough for my needs; but that was a particular case. Anyways, I have other concerns and suggestions though. -If you use plain water as the coolant and since this is a close circulation circuit, there is the possibility of bacteria and algae grow, which might end up clotting the pluming system in the long term. In this system, the temp (I think) will never reach high enough to kill them and keep the system sterile for long periods of time. The use of the transparent hose helps photosynthesis to take place and algae may thrive. This is something I've seen happening even in very sophisticated machines and chemicals had to be added periodically to prevent that as part of the regular maintenance. That takes me to the conclusion that since you might end up using a cooler, it will also be a good idea to place the Peltier element in direct contact with the interior which will benefit your project as you will not have the algae grow problem, will not need the pluming system, circulation pump and special coolant. Also, it will further increase the energy efficiency of your system by eliminating the heat transfer loses the coolant system introduces and the energy required for the circulation pump. This is just a suggestion for your consideration. -The next concern/suggestion is regarding the heat pumping action of the Peltier element in use. If the heat production rate (Watts) of the brewing surpasses the heat pumping action of the Peltier element or if it is close to it, the system will not be able to lower the temp or only a few degrees at best. That, as you know, depends of many factors like size of the brewing, ingredients, volume of the chamber, Peltier element size and power, etc. This is not the case of a hot object placed inside a fridge for cooling and does not have an energy source to sustain heat production. In this case, it keeps generating heat by the energy released in the chemical reactions taking place in the brewing process. Therefore, long exposure to the cooling process will not be sufficient to lower temp as it would otherwise be with a massive; but passive object by slowly extracting the heat. The suggestion then, is to place a sample temp sensor inside the brewing to collect data from it, another sensor inside the chamber and another outside. You already have at least one of them to perform the temp control. The data collected from them will give a better idea of the cooling effect and operation of the system. Although I believe you have performed at least some preliminary measurements, that data will help to figure out what is really happening there. Anyways, I still think you've done a great project; but like almost anything else it can be improved little bit here and there. This project has made my mind clear that what I really need for my temp chamber is to modify an existing working mini fridge by adding a heating system. That will be way easier than adding a cooling system and resistive heating to a non working microwave oven being used as a the chamber, as I was wrongfully thinking. That will make that project way simpler and doable. I take the opportunity to offer this idea as a project to do to anyone interested. I'll give it try myself one of these days... Thanks and Good Luck!

I would definitely add some form of coolant mixture into your water to prevent the growth of things. I know there are some fairly inexpensive non-toxic ones we use at work for our few compressor based cooling systems.

Hi BlakLite,

This is something I am looking into and have taken great inspiration and encouragement from your design and build. My initial design is to connect the pump to stainless steel tube that is inserted into the fermenter. I am wondering the kind of temperature drops from ambient you can get from your setup. Would this setup be able to cool 20L from 20 deg C to 10 deg C? Many Thanks

I am not convinced by your assertion that in heating mode, the peltier device is more efficient than regular resistive heating. How is this possible ?

I came accross a very interesting website with more info on this product: http://www.directindustry.com/industrial-manufacturer/temperature-regulator-60923.html