Peltier controlled fermentationy device

[chris2012]

Yeah I did think about adding another one

I have seen that paper with the peltiers and the metal mount, it seems an interesting idea, alas I don't have a mill though, to
take that kind of route (or even a metal fermenter for that matter).

[BigPaw]

Chris, thanks for posting this, it's very interesting indeed!

I've been hankering after a fermentation fridge to keep things under control in the summer for a long time but at the moment don't have the space and this looks like it could be the solution.

A quick scan of ebay and I've got a shopping list coming together, something along these lines:

http://www.ebay.co.uk/itm/1-2-5x-12V-6A ... 51ba296bb0

http://www.ebay.co.uk/itm/122mmx41mmx12 ... 23431cedbb

http://www.ebay.co.uk/itm/New-60x150x25 ... 3f40cbb0ef

The problem will be finding the space and time to do some experimenting! My new born daughter and impending house extension work are conspiring to prevent any brewing related activity for the foreseeable future...

I'll be watching this thread with much interest to see how things come along - best of luck.

[chris2012]

Cheers BigPaw,

Bear in mind that you'll probably also need a fan to cool the heat sink.

I ordered the server PSU yesterday, so hopefully I'll be able to test again this coming weekend

[BigPaw]

I was wondering about that... passive cooling would be preferable but it would just depend how much heat those little things kick out! Those cpu coolers used in the link Setmash provided look pretty hefty and I was hoping it was overkill but maybe not. Might have to explore some of the PC overclocking sites for some inspiration.

I'll be interested to see how you get on with using it for the heating side of things - the ice formation on the heatsink looks pretty alarming, but I suppose it depends how long they have to run in that mode. While I like the elegance of an all-in-one solution, I guess having an stc1000 switching between running this and an alternative heat source wouldn't be the end of the world.

[BenB]

Peltiers are fairly inefficient things (to put it mildly) so they kick out a fair bit of heat. People have used them for water-cooling PCs and ended up with pumps, radiators etc etc. When you think about it, it's not surprising.

[BigPaw]

Thanks for your input BenB, I did wonder if it was all too good to be completely true...

I guess the heat output is whatever's wasted by the peltier process + however much is being moved out of the medium being cooled, kind of like the heat radiated at the back of a fridge. Which begs the question, how much energy would the peltier plates use in comparison to what a 10-15 year old gas guzzling fridge (I'm not likely to get the chance to buy and butcher a clever modern A+ rated beauty any time soon). Do you know if there're any efficiency figures out there on t'internet?

[BenB]

Depends if you believe wikepedia!

http://en.m.wikipedia.org/wiki/Thermoelectric_cooling

"Thermoelectric junctions are about 4 times less efficient in refrigeration applications than conventional means (they offer around 10–15% efficiency of the ideal Carnot cyclerefrigerator, compared with 40–60% achieved by conventional compression cycle systems (reverse Rankine systems using compression/expansion).[6])"

[boingy]

A fridge wins the efficiency battle hands down. It depends how long you expect the peltier to run for really. 200W continuous is about 5kWh per day so about 60 to 70p per day worst case, but of course that assumes it is on all the time. If your heat sinking and insulation is good enough then it should be cycling on and off to maintain a temperature (assuming you have a controller).

The big challenge is getting rid of the heat. A 200W peltier module is going to generate 200W of heat, plus the heat that it "extracts" from the cool side. If you don't get rid of it fast enough then it just conducts back into the thing you are trying to cool.

I think there is a good reason you don't see them used much.

[chris2012]

Yeah they are are definitely more inefficient. To quote wikipedia:

"Thermoelectric junctions are about 4 times less efficient in refrigeration applications than conventional means (they offer around 10–15% efficiency of the ideal Carnot cycle refrigerator, compared with 40–60% achieved by conventional compression cycle systems (reverse Rankine systems using compression/expansion)"

However you can actually get peltier fridges though.

[BigPaw]

Good to know Chris; I'll still be interested to see how you get on because even though in themselves they're less efficient, to my mind you ought to be able to utilise 90+% of that effect, rather than making use of a lower percentage of the output from a more efficient system... if I've said that right!

[chris2012]

Just been playing with the peltiers and the server PSU




I wasn't able to run it for much longer alas as I had to turn it off over night.

This wasn't using any insulation, which could maybe have helped a bit.

As you can see it's over a large time scale, so it doesn't look to great.

I'm curious to see some graphs for a fridge/freezer cooling beer, to see how fast they cool.

[boingy]

Chris, that graph looks a bit odd to me. I might be misunderstanding the experiment but shouldn't the cooling water be colder than the beer?
Maybe check the calibration and positioning of the temp sensors.
If the graph is correct then it seem to show both liquids slowly reaching ambient.

[BenB]

I have a sneeky suspiscion that tiny fan is partially the problem. A tec can generate a maximum differential between the hot and cold side of 70 degrees but it depends how much power you are throwing at it. As you near the particular tecs max power that goes down. So you need to cool your hot side as much as possible and those small fans aren't up to much. Rather than using the fan I'd try something like a hair dryer (on cool!) To blow air through the heatsink tunnel....

[BenB]

This is the air temperature inside my fermentation chamber.



Powered by a mini freezer attached to the side of an insulated chamber. The ambient on that day was about 22-23 and the chamber had 20 litres of beer that had stopped fermenting. Not sure how closely the beer temperature followed the air temperature.

[chris2012]

Boingy - yeah I agree entirely, the peltier water should be cooler than the beer temp, I'll have to double check that.

BenB - yeah that's a nice idea on using a hair dryer!

You don't happen to also have a graph showing your beer temp too per chance?