Peltiers

[pablo_h]

The weather is a bit cool at the moment and I had this thought while thinking of temperature regulation. Sitting under my desk is one of those 10L peltier fridges I bought from ebay for $50 last year. It has a fan forced inside heatsink, and electronic thermostat and switches automatically form cooling to heating. Has anyone thought of making a small insulated box to fit a standard fermenter and building a peltier system (or rip out of one of these fridges).

I'm thinking it would be a great thing to use in keeping ales at 20C when the ambient is 15-25c, I'm not proposing it to run really cold or run in extreme ambients.

Mind you, the 'fridge' had no problems maintaning 7*C on hot days back in summer.

 

[LethalCorpse]

Well, technically it's possible, but you won't get much of a temperature differential to ambient. Those little peltier fridges can barely keep a few cans cool, and that's if they're cool before you put them in. Try and scale it up to a fermenter sized cabinet, and you'll manage a couple of degrees at most. Such efforts would be better spent stripping and repairing a fridge off the side of the road at your next council pickup.

 

[Hutch]

Hey pablo_h,

It can be done - I made one, and it works brilliantly. Having said that, I did not convert one of those six-pack fridges, I made mine from scratch using a couple of 40mm-squared peltiers from jaycar, and a shed-load of 70mm polystyrene foam.
A few words of advice for you:

* Use as much insulation as possible - peltiers are note the most efficient way of cooling, so any help you can give with keeping the heat in/out will help the peltier do it's job.

* Use a decent power-supply. A computer PSU is more than adequate - it needs to be capable of at least 8Amps off the 12V rail.

* Use really efficient heat-sinking on both sides of the peltier. The peltier efficiency is inversly proportional to the temperature differential between the two sides. Once the peltier reaches maximum delta-T, it no-longer pumps heat. On mine, I used a large copper heat-exchange (similar to what people use to liquid-cool computer CPUs), and pump coolant through that, and a small car radiator. Not saying you need to go to those lengths, but the better job you do of maintaining ambient temperaure on the peltier's "waste" side, the better job you'll do of temperature control.

* Expect it to work more effectively in heating than in cooling. This is mainly because the peltier acts as a heat pump and a resistive load, generating more heating than cooling. This is even more so in my system because heat rises, and my peltiers are under a large flat Aluminium plate (heat-sink) that the fermenter sits on, inside an insulated box.

* If you are going to get fancy with the electronics, I would recommend you use PWM control of the peltier. This will cause less thermal stress on the peltier device than ON/OFF control, and prevent premature failure of the peltier device.


My controller box sits outside, and in mid winter (5-15 degrees) it happily maintains a constant 20+ degress on a very low duty-cycle. In fact it would happily heat all the way to 60+degrees if I wanted, as I discovered when I had a software bug last year!
Conversely, in summer, it struggles to maintain 18-20 degrees during the warmer weather, typically running flat-out doing so.

Since making it, I bit the bullet an bought a cheap fridge, which does a much better job of cooling in summer, however the peltier box still gets good use in winter.

Hope this helps.

 

[rich_lamb]

Yep, it absolutely works and works well.

Similar to Hutch, I built a thing I call "tempsteady" which is capable of both heating and cooling around a set temperature. This is the real advantage over a fridge with a fridgemate - it works in both directions with the one device.
And mine only uses about 50W when it's going, which is much more eco-friendly than a fridge.

Mine lives inside, and is built from only thin (19mm) polystyrene which is a drawback as it can only do about 8 degC temperature differential. That works for me as I do ales in summer and my house gets to about 27 deg.

I would take Hutch's advice and use thicker insulation. This is the main point - good insulation.

My heat transfer mechanism is probably a bit less "industrial" than what Hutch has done. I use large-ish heatsinks with PC fans on them, on both sides of the peltier. One inside the box and one outside. You MUST get heat into and out of the heatsinks efficiently.

Then you have to build the circuit to control it, and I used a PC power supply too. They're good for generating the 12V you need. If you can't do this yourself you could wait a while as I'm designing a degital controller which I should be able to produce a few copies of - but I'm super busy right now so it will take a while.

My peltier is only a 48W one. I'm going to build a much more powerful version with dual 96W Peltiers and 50mm foam which should be capable of fermenting lagers for me.

Honestly, I have to bite my tongue every time I see people building fridges for temperature control. I guess I should publish the article I gave to G&G on this device. I've been holding off as I say because I'm too busy to make the "tempsteady deluxe".

 

[LethalCorpse]

erm...There's absolutely no way a peltier system will be more efficient than a fridge. A fridge draws more than 50W when it's running, but it only has to turn on for a few minutes of every hour in order to keep cold. A peltier system trying to keep the same temperature is peddling its guts out most of the time. Peltiers are notoriously, horrendously inefficient cooling devices, because so much of the energy you pump into them results in heat, and they bleed from the hot side to the cold side. Then factoring the cost of multiple peltiers (which aren't cheap), the power supply, heat exchangers, radiators, fans, heatsinks and all the materials and time for building and insulating the cabinet, against a fridge which contains all of the above and is free. The controllers are of similar complexity either way. Put all of that together and it just doesn't make sense, economically, environmentally or performance-wise.

If you wish to use the fridge for heating as well as cooling, it's a simple matter to have a heater of some description inside the fridge, and switch between heating and cooling manually or in software

 

[pablo_h]

Well, technically it's possible, but you won't get much of a temperature differential to ambient. Those little peltier fridges can barely keep a few cans cool, and that's if they're cool before you put them in. Try and scale it up to a fermenter sized cabinet, and you'll manage a couple of degrees at most.

That's all I need 5C warmer/cooler than ambient. But like I said, my fridge could run at 7C on a warm day

Such efforts would be better spent stripping and repairing a fridge off the side of the road at your next council pickup.

The problems with fridges is

i) power usage
ii) space to fit them, I need something that will fit under a bench
iii) wasted internal space( wasted freezer, can only fit 1 or 2 fermenters in it, while the same space could fit four peltier cabinets) unless you use a chest freezer which is a pain to lift fermenters in and out.
iv) only cools, need to make up strong shelving , need extra work and materials to fit a heater

Basically I was sitting here thinking it's too cold, I need to build an insulated box. Then I literally kicked my peltier fridge which is under my desk, which heats and cools, why not stick a peltier in it? I did say that I know I won't be able to brew lagers in it, or use it in extreme ambients. I just want to build something that will work in 10-25C ambients like spring/autumn weather.

 

[Hutch]

erm...There's absolutely no way a peltier system will be more efficient than a fridge.

In cooling, I agree with you. In heating, that's not true.

A Peltier used in heating mode is more efficient than a resistive load, such as a light bulb or heater belt, as you would do to warm inside a fridge.
The peltier takes heat from the cold-side, and deposits it on the hot side. It does this very inefficiently, generating waste heat in the process, which also goes to the hot side. So there is more heat being put out on the hot side than the equivalent energy into a resistive load would do.

In Cooling, well, a fridge is FAR more efficient at getting the job done for less energy.
The BENEFIT of using Peltiers in this way is that you can maintain a CONSTANT temperature (using PWM and PID control), rather than the rather crude ON-OFF control that a fridge provides. This is being a little pedantic of me, though it is a valid point to make.

And another advantage of Peltier control is that the one device can do both heating and cooling, rather than a fridge which needs to be switched to either heating or cooling, and run separate circuits to perform each task.

I prefer to use my fridge for most of my brewing now, as it is larger capacity, and more efficient in cooling.
The Peltier box was a fun project though, and I certainly have no regrets having made it.
Each to their own.

 

[rich_lamb]

Yep, as Lethal has pointed out the Peltier device is inefficient at cooling, but is still a low-power solution in that it doesn't draw the sort of power to drive a compressor (regardless of duty cycle), and as such can run off a PC power supply. Hell, you could run it off solar...

As to cost, the point about Peltiers not being cheap is actually wrong - my 50W one was $13 from Jaycar, and you can buy them for peanuts on eBay. I built my whole unit for about $100 and I actually paid for the styrene. Yes, there is going to be mucking around wiring and constructing no matter which way you go - there's no off-the-shelf solution.

The peltier solution is neat in that it's simpler (for both heating and cooling) and can be built as compact as you like. I also do not have space for a fridge, though we aren't talking about a huge space differential.
My controller is a single PCB based on a window comparator: this gives me about a 1deg deadband but I want to go to a digital version for ease of use and an even tighter deadband of about 0.5 deg.

 

[rich_lamb]

Actually, come to think of it - I'm not so sure Peltier refrigeration is that much less efficient than good ol' vapour cycle refrigeration. A couple of phase changes, and a couple of passes through heat exchangers, all run by electric motors with fluids passing around a lossy cicuit?
It's been a long time since I did thermo, but that's typically in the 40%-60% efficient ballpark right? - so many variables though, including the condition of the fridge, seals, configuration, etc.
Lethal, any info here?

I'd say the main reason we use that clunky old technology is because energy has been cheap, and its good for driving temperatures down FAST. A fridge can move a lot of heat if it has to.

The drawback of the little peltier device is it won't get your 30 degree wort down to 15 degrees: it's more for maintaining temperature. I find mine goes flat-chat for the first day as I typically pitch a couple of degrees warm and after that the fermentation is heating things.

 

[Doogiechap]

Here is a post of mine that I dug up from a couple of years ago:

I have very succesfully installed a (ex hydrocool) peltier to a fridge and control it with an oatley electronics peltier controller http://www.oatleyelectronics.com/kits/k140a.html
My ferment fridge is in my shed which has over the past 6 months had a temp range of 6 - 38 the fridge has maintained 21 +- 2 with the peltier not yet running to full capacity
The peltier I got has a heatsink and water pump integrated which is the key to good peltier use (the peltier can only transfer the heat that is applied to it so the more heat applied the more it can transfer (reverse the polarity and the heat transfer direction reverses).
I have it hooked up to an old aircon condensor with a couple of 8" fans heating/ cooling it. At max power the whole thing runs at 300mA /240V.
I'm unsure on whether you can commercially get the peltiers with the pump and heatsink but Hydrocool is still running and may be helpful ? http://www.hydrocool.com/Hydrostream.html
It took me about 8 months to get my fridge running reliably but had a whole stack of fun in the process

Now recently I have passed this on to a mate who has started brewing and have purchased a freezer which I run off a Fridgemate. I miss the excellent stable temperature control I had particularly in winter for warming but love the ability to cool of my fermenter to pitching temps which was pretty difficult in the height of Perth Summers. I would love to rehash the setup in a smaller fridge to get some better control over my starter temps on the stirplate.

 

[pablo_h]

All this is food for thought. I notice you've already planned you project Doogiechap
Basing one on a bar fridge makes sense, it's already insulated. On that note, there's no point is butchering my peltier fridge, as it would be handy for starters as it is. It's not a "6 pack" peltier fridge, but a 10 or 12L fridge that could fit many starters ( I do 3 at a time as I have 3 fermenters, and it would fit them in easily).
On top of that, it would be no problem for me to fix up a busted bar fridge and use refrigeration instead of peltiers. I'm more able to do that than design and program a circuit to control peltiers. I was just thinking of heating more than cooling, and also the fact most bar fridges aren't large enough for some fermenters. I'll have to look around the tip for a bar fridge big enough that only has a faulty controller, relay or simple compressor burnout and re-evaluate a heating system.

 

[pablo_h]

I've got an old 4 door kitchen cabinet that fits my three fermenters plus room for a heat source.
It fits my purpose because there's heaps of room inthere even after insulating, and I can use the benchtop as a work bench too.
So where can I get sheets of insulation to line the inside?
I was going to use a moisture sealer, layer of plastic, 2" of insulation, then colourbond or melamine inside lining and all sealed up with expanding foam. Going all out because later on I could add proper doors and a drop-in/cassette style refrig unit.

 

[Hutch]

So where can I get sheets of insulation to line the inside?

I scrounged mine from a skip near work (you often see large offcuts at construction sites).
Clarke Rubber, has it in various sizes too.

I effectively built an oversized minibar fridge, with 70mm polystyrene walls (including the door), and lined the lot with 3mm white ABS sheet from one of the commercial suppliers (can't remember the name).