TL;DR: need to build a grid of Peltier or Peltier || Resistors to heat\cool a beer fermenter, looping the control on a temperature reading. Power output is 500 W. Point me out!
By one of those curious coincidences that happen rather often in science, in spite of living on opposite sides of the globe, both me and BeerPal had the idea of building a digital fermenter for beer brewing using Arduino. You can find his topic here: http://forum.arduino.cc/index.php?topic=260582.0.
While I thank you for the help you have indirectly given me by answering that post, I come to you with more questions about a specific problem: temperature control.
Temperature is one of, if not the most, critical parameters in brewing beer: while chemical composition can, at least at the start, be accurately controlled by simple measurings, temperature control depends heavily both on the fermentation process and the ambient temperature . Thus, a dynamic temperature control will, in my opinion, be much more suitable than the average "brewbelt", basically a large resistor.
Given the ability to measure temperature, for which the aforelinked post is an excellent source of knowledge, I have come up with two ideas, but you are more than welcome to contribute more if you know more efficient ways to achieve the same result.
1- Two distinct branches, only one active at a time (selection by a switch), one made up of resistors and one of Peltier modules on parallel branches: being on parallel branches, given equal impedance\peltier coefficient they will give an ideally uniform heating\cooling. Resistors, furthermore, are relatively inexpensive. The cons are the use of DC, branch selection and current control: I would like to implement Arduino for the latter point, but I am at a loss as to how apply it.
2- Only one branch, of parallel Peltier modules. The Peltier effect is dependent on the current flow direction and intensity, so in line of principle I could select heating or cooling through a flow direction selection and the heat\cooling power flux by current control. While the circuit mesh would be easier than #1, I recognize Peltier modules are more expensive, and I am entirely blind as how to implement a switch on the current direction: I live in Europe, and my wall output is 220V AC, at a frequency I have long forgotten. Maybe I could make a switch\diode selection for the current direction?
As for the magnitude of the power output, I have done some basic math, without looking too much into the transfer coefficients of a system that has, to my knowledge, not been implemented in literature of chemical engineering before.
The heat capacity of beer is roughly the same as that of water: 4181 J/kg. Doing away with temperature dependance, small on modest temperature differentials, I have the consider the quantity of brew I will produce. As the fermenter is 50 l in volume, and one third has to be leaven for air, I have 33.3 l of fermentation solution. With a specific density of 1.06, but considering 1.2 for a safety factor, I have 5.017 kJ/l of brew solution, thus 167.24 kJ of energy required.
I'd like this energy to be given off in 30 minutes, assuming a temperature difference of 5°C : that makes it a power output of 464.6 W Let's make it even at 500 W.
So, why did I write this post? I am looking for: - ideas, comments, and improvements on the proposed circuits - explanations, tutorial links on how to build the proposed circuits - kudos for the upcoming guide, in the remote ( :P ) event of success, for any kind of fermentation solution: help everyone make better wine, beer and liquors! (Distillation may be coming too, if this project works)
And thank you for reading through this gargantuan post!