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mbaker33 · 01-07-2013, 06:39 PM

Hi all,

I've been mulling over a fermentation chamber (basically the one on Wort-O-Matic) for a while now and the ice situation always hangs me up. I don't have the space fore a chest freezer to freeze milk jugs or anything like that and my actual fridge freezer is generally pretty packed already with general food items. So, the typical fermentation chamber doesn't really fit.

Enter the peltier, which I've been reading mixed reviews about all over the place. It seems where most people fail is when trying to attach it directly two something other than a heat-sink with a fan blowing the cool air into the chamber. I'd like to hear from anyone who has had success with these devices on sizing and design. I'd like to be able to heat and cool, and I have an Arduino with thermisters and all that. So, really, I just need the design/peltier specific plans to get my wheels off the ground.

Thanks in advance.

Mark

warthog · 01-07-2013, 06:44 PM

hi, i make precision temperature controlled enclosures for a living. we use TEC modules all the time. the thing that you have to keep in mind, is that you have to dump a lot of heat. basically you have to size your heat sink to be large enough to dump the heat you want to loose from your wort, and the heat from the electricity that you are pumping into your modules. if you don't do that, your module will quickly saturate (reach the maximum temperature differential between the 2 sides), now you have a heater instead of a chiller.

hope that helps. feel fee to get detailed.

mbaker33 · 01-07-2013, 07:20 PM

Thanks Warthog, I am aware of the heatsink concerns for sure. And I understand that's 90% of the failures. Where I struggle is making sure I don't add myself to that percentage.

Do you have any recomendations for a TEC controller/Heatsinks that will drop a chamber of roughly 24"x24"x15" to 20* below the ambient temperature? I won't need to get that low all the time, but when I want to, I'd like to be able to.

I'd also like to be able to heat using the peltier, which I understand is possible just by flipping the polarity on the voltage.

Thanks again for your input. It sounds like you know WAY more about these devices than I do for sure. I just know that the *should* work for what I want.

Mark

warthog · 01-07-2013, 08:53 PM

at this point there's some real math involved to do it right. but here's enough to select some heatsinks (your next step).
first know your heat load: that's the sum of everything that makes heat. your fermenting beverage, heat gain through the walls of your enclosure, and heat from your circulating fan (to blow all that cool you are making around). from this discussion here, your wort is giving off 20w, assuming your box is made of 1" thick blue poly foam (R6/inch), with a 20 f dT, then that's about 20w too. by coincidence, a good size of circulating fan is about 20w also. look for a heat sink that has the lowest thermal resistance you can find. it will be given in deg c/w (remember to add resistance for the interface between your TEC module and the back of the heatsink) once you have this, you will know how cold your cold side heatsink needs to be (it will be quite cold). from there, use the equation: (watts*1.76)/dT. this gives you the number of cubic feet per minute of air you need to move inside the box (find a fan that will do that, re-do the math, using the power of the real fan you will use. then look here and find a TEC module with enough umpf to do the job.
next: multiply the volts and amps of your power supply to give you watts (do not exceed vmax or imax), then add this to the cooling watts (60) to get how many watts you need to ditch. select the heat sink for your hot side (remember, that the hot side cannot get warmer than the dT number - your cold side temperature). now all you need to do is figure out how much air you need to move over the hot side heatsink, to keep the cold side cold enough to do the job (use the same formula from above). easy!

good luck. i can crunch some numbers for you if you need it

decwakeboarder · 01-08-2013, 01:10 AM

Would you need a fan in a box that small or could the TEC be mounted at the top and rely on the fact that cold air will sink?

I was looking into a TEC a while ago and the big sell for me is that I could switch from cooling to heating by just flipping the leads. The biggest downside that I saw was the inefficiencies of a TEC would waste too much power for me since I was planning on using a 7cf chest freezer...a small single bucket ferm chamber should be manageable.

warthog · 01-08-2013, 01:39 AM

it might work, but i wouldn't count on it. the heatsink will loose a lot of efficiency when air is not really moving over it. the more air the better your efficiency.

**cosmatics** · 01-08-2013, 02:16 AM

Hey warthog, some great info here, thanks. I have a few simple questions, but I figure I'll research it 1st to not be that annoying guy. But from your experience, has the peltier tech/cost made it a better solution for small chilling loads we might encounter as homebrewers?

warthog · 01-08-2013, 02:28 AM

you know, i actually haven't looked into it. single modules are pretty cheap, but add a power supply, heatsinks and fans, it all adds up. when i build these things they are used in semiconductor fabs, and nanotech labs, where conventional refrigerants are a big no no, i typically make then very big too, the last one i built had a capacity of 24,000w, and controlled to +/- 0.005c, it also cost almost $100k (whole thing, enclosure, chiller, control system etc). but i would think for small loads, less than say a few hundred watts, its probably still cheaper than buying an lg air conditioner at home depot.

**cosmatics** · 01-08-2013, 02:32 AM

Holy cow, thats a load, and slightly over my budget. Very interesting engineering.

mbaker33 · 01-08-2013, 03:28 PM

Quote:

Originally Posted by warthog

at this point there's some real math involved to do it right. but here's enough to select some heatsinks (your next step).
first know your heat load: that's the sum of everything that makes heat. your fermenting beverage, heat gain through the walls of your enclosure, and heat from your circulating fan (to blow all that cool you are making around). from this discussion here, your wort is giving off 20w, assuming your box is made of 1" thick blue poly foam (R6/inch), with a 20 f dT, then that's about 20w too. by coincidence, a good size of circulating fan is about 20w also. look for a heat sink that has the lowest thermal resistance you can find. it will be given in deg c/w (remember to add resistance for the interface between your TEC module and the back of the heatsink) once you have this, you will know how cold your cold side heatsink needs to be (it will be quite cold). from there, use the equation: (watts*1.76)/dT. this gives you the number of cubic feet per minute of air you need to move inside the box (find a fan that will do that, re-do the math, using the power of the real fan you will use. then look here and find a TEC module with enough umpf to do the job.
next: multiply the volts and amps of your power supply to give you watts (do not exceed vmax or imax), then add this to the cooling watts (60) to get how many watts you need to ditch. select the heat sink for your hot side (remember, that the hot side cannot get warmer than the dT number - your cold side temperature). now all you need to do is figure out how much air you need to move over the hot side heatsink, to keep the cold side cold enough to do the job (use the same formula from above). easy!

good luck. i can crunch some numbers for you if you need it

Holy crap, that is some amazing information. I understand the principles you discuss, but really don't know how to apply them. If you could give me a rough idea of what I'm looking for, that would make my day.

I'm actually using 2" foamboard and was going to use either a large PC CPU fan or desk fan to force the air around. I'm open to whatever is recomended, but I can't break the bank on it.

Thanks again for all your help!

Mark