Unusual compressor application, need some thoughts

[stephelton]

I'm designing a cabinet used to ferment beer. It has to be kept very cold, and I'm designing it to ferment up to 60 gallons at once, so I've chosen to use a compressor from a freezer in order to help maintain temperatures.

I'll try to explain briefly, but if you care to read more, visit my blog where I elaborate a bit more:
Removed Link, it Belongs In Your Profile



The concept is to keep a tub of liquid (water + glycol_ chilled with the compressor. the evaporator coils are (ideally) submerged in the liquid itself. Some pumps force this water into radiators in different chambers (each for a separate fermentation) over which a fan blows. Each fan and pump pair are independently controlled by a microcontroller, which monitors a series of thermometers to determine when more cooling is necessary. Likewise, the coolant temperature is monitored and the compressor is turned on/off as appropriate.

I've done some crude tests using some ghetto cardboard boxes and a cooler full of coolant, in combination with a compressor I extracted from a 2 cu ft fridge. The results were great - I was able to maintain fermentation temperatures well within the range I was shooting for, and the system was very efficient.

The problem now is that I'm designing the final cabinet, and need to support 3 fermentations at once. I was donated an old chest freezer, and took the compressor out of it, wanting to use something with a little more 'cooling' power than the 2 cu ft fridge compressor. Unfortunately, it is either very old and doesn't operate, or I may have kinked one of the pipes.

I'm open to suggestions, but I'm nearly done with the project, and I need to get on with my life, so I have to do something cheap and quick, and I have to stick closely to the designs I've already implemented.

My options are basically:

1) repair the current compressor
2) obtain another compressor
3) come up with another solution.

Thoughts?

[Senior Tech]

You have described a beer line cooler?

Look around here...

http://www.perlick.com/commercial

[stephelton]

You have described a beer line cooler?

Look around here...

http://www.perlick.com/commercial

Perlick makes very nice products, I use their spouts on my kegorator.

They have products quite similar to what I'm building, however, that doesn't help me finish the project that I'm 90% done with.

...And frankly, now I'm just discouraged; I could have just bought one of their products and been done with it...

[Wheelbaron]

If you are looking for engineering on this project you will need to post a LOT more information. It kind of sounds like you are doing this as a hit and miss type project, and as much as I hate to admit it there is in fact a time to go to one of those know it all engineers lol Using used parts and throwing things together will get you a high failure rate.....

[Shophound]

How cold are we speaking per fermentation chamber?

Is the cabinet you have constructed insulated? Is there a vapor barrier between the insulation and the interior of the cabinet?

You should definitely know the expected heat load per chamber. What advantage are you hoping for with a water/glycol heat transfer medium vs. hanging a small evaporator in each chamber? You'll need to defrost whatever form of heat exchanger per chamber you use regardless of whether it is DX or fluid, if the coils run below freezing. Will the fermenting beer off-gas any corrosive fumes, setting yourself up for coil leaks at some point?

Yep. Engineering can be a real pain at times.

[madhat]

Hmm, I know someone who did that, they just used the Chest Freezer. Removed the temperature control, installed a JCI digital readout control. (had the setpoint, T.D., Span, and actual temperature in the digital readout, little "Snowflake" that told when it was calling for cooling) Recaulked it with Aquarium RTV. They also put a Muffin fan on the compressor, thought it was running hot.

[stephelton]

Thanks for your posts, I apologize for being vague.

If you are looking for engineering on this project you will need to post a LOT more information. It kind of sounds like you are doing this as a hit and miss type project, and as much as I hate to admit it there is in fact a time to go to one of those know it all engineers lol Using used parts and throwing things together will get you a high failure rate.....

I find that if I elaborate too much, people won't read

I've thought this project out very thoroughly, and have run five test fermentations. The aforementioned compressor is the first real failure I've run in to, other than lots of software bugs here and there.

I will elaborate more at the end of the post.

How cold are we speaking per fermentation chamber?

Is the cabinet you have constructed insulated? Is there a vapor barrier between the insulation and the interior of the cabinet?

You should definitely know the expected heat load per chamber. What advantage are you hoping for with a water/glycol heat transfer medium vs. hanging a small evaporator in each chamber? You'll need to defrost whatever form of heat exchanger per chamber you use regardless of whether it is DX or fluid, if the coils run below freezing. Will the fermenting beer off-gas any corrosive fumes, setting yourself up for coil leaks at some point?

Yep. Engineering can be a real pain at times.

The main reason for using the water/glycol coolant mixture is that each chamber needs to be at substantially different temperatures. During a long lagering period, a beer may need to be as low as about 35 degrees, while certain ales may need to be fermented as high as about 70. Maintaining a large tub of coolant allows me to pipe it to each chamber individually and maintain precise temperatures in each.

I've run into frost problems. I cooled the coolant down to about 15 degrees and a thick blanket of ice quickly formed around the radiator. So I'm hoping I can get away without keeping the coolant below freezing.

That said, if each cabinet is sufficiently air tight, there should be a fairly minimal amount of moisture in the air to condense to solid anyway, most of which would have already condensed to liquid and collected on the floor of the chamber. But that's pure theory

I plan to coat each chamber with an epoxy which should yield some resistance to water vapor.

Fermenting beer yields mostly CO2 (and some unpleasant sulfur sometimes) but no corrosive gasses that I'm aware of.

A more in depth explanation of the project follows...

The cabinet is divided into four equal chambers, each of which is heavily insulated. The fourth chamber is designated to hold the coolant and the compressor, which has a divider in between. The coolant side of that chamber is very heavily insulated. The compressor side will have holes cut out and fans installed to help transfer heat out of the system.

In each chamber, there is a shelf on the bottom with a small hole cut in the middle for some air ducts which route the air back up to the top right behind a radiator. The coolant is pumped through this radiator when necessary, at which time a fan kicks in. Individual pumps allow each chamber to be cooled independently.

An Arduino microcontroller and other electronics are housed at the top of the fourth chamber. The Arduino controls circuits to turn on and off the compressor and the fans and pumps for each chamber. It also reads from small temperature probes, which are installed in the coolant, in each chamber to measure the ambient air temperature, and submerged in each beer to get a very accurate reading for the fermentation temperature. Lastly, it connects to the network and makes all these controls and information available to a computer that runs some software to manage it all.

The problem I'm having, which has driven me to post here, is that this compressor is not working. I turn it on, and the motor runs and eventually gets hot, but the evaporator coils are not getting cold, nor are the condenser coils getting hot. When cleaning off the coils, I kinked it quite a bit near the compressor. The unit is also very old (manufactured in the 80s) and although I tested it, I'm questioning how thoroughly I did so (I may have been quick to assume it was working). Any bright ideas on how I might test or fix this thing?

If I'm going to have to come up with another solution, I thought I'd post here to see if the experts on the subject had any advice.

[beenthere]

How did you determine how much refrigerant to charge it with.

[stephelton]

How did you determine how much refrigerant to charge it with.

I didn't charge it. I wouldn't expect that it would need to be charged due to anything I did; perhaps its old would likely mean it needs more refrigerant?

Is that something I can do myself? Perhaps I should fix my kink, shorten the evaporator coils (they are way too long, about 64 feet I estimate) and then charge it? Does that sound reasonable?

[beenthere]

No.

That is something you will need an EPA certified tech to do.

And from what I'm reading. You made up need evap circuits. And connected this compressor to them.
Meaning you had the system open, correct?

[stephelton]

No.

That is something you will need an EPA certified tech to do.

And from what I'm reading. You made up need evap circuits. And connected this compressor to them.
Meaning you had the system open, correct?

That's what I thought. I did not open it, I merely removed the entire unit from the freezer housing. Quite a pain that was...

[Shophound]

Well, if you don't have a clear grounding in vapor compression refrigeration theory and application, you're reduced to winging it. You might get lucky, you might lose one or more compressors before you do, you might not get there at all.

The beer, as it ferments in each chamber, I'm assuming it is in liquid form? If so, and if it is open to the cabinet, it will be a constant source of moisture to condense on any cooling coil within each cabinet. Evaporation slows at low temperatures, but does not stop. I also must ask if the fermenting process itself generates heat, as one would find in, say, a compost pile, fermenting anaerobically. In addition to the fixture temp you want in each chamber, any heat generated by blowers, lights, and the fermenting process must also be factored in.

Doggone engineering again!!

[beenthere]

You may have cracked a braze joint. And lost all the refrigerant. Have a tech check it.
And don't run it again until its checked, and or fixed.

[stephelton]

Well, if you don't have a clear grounding in vapor compression refrigeration theory and application, you're reduced to winging it. You might get lucky, you might lose one or more compressors before you do, you might not get there at all.

The beer, as it ferments in each chamber, I'm assuming it is in liquid form? If so, and if it is open to the cabinet, it will be a constant source of moisture to condense on any cooling coil within each cabinet. Evaporation slows at low temperatures, but does not stop. I also must ask if the fermenting process itself generates heat, as one would find in, say, a compost pile, fermenting anaerobically. In addition to the fixture temp you want in each chamber, any heat generated by blowers, lights, and the fermenting process must also be factored in.

Doggone engineering again!!

Fermentation is a highly exothermic process; at the height of fermentation, the beer is as much as about 4 degrees F warmer than ambient. The beer is sealed off; it is very important that fermenting beer is not exposed to oxygen (yeast can reproduce anaerobically and aerobically, the latter being undesirable). So that won't be a concern.

What I need to do is find someone who knows what they are doing who can help me in exchange for beer

Anyone in the Dallas, TX area willing to help me out for a few cases of homebrew?

[Shophound]

If you want it done right it'll cost you more than some homebrew.

If you're really serious about this, take a basic refrigeration class at a local community college, and pick the instructor's brain when he starts talking about mass flow rates and pressure-enthalpy charts.

[stephelton]

If you want it done right it'll cost you more than some homebrew.

If you're really serious about this, take a basic refrigeration class at a local community college, and pick the instructor's brain when he starts talking about mass flow rates and pressure-enthalpy charts.

Yes, I was joking. Sort of.

Good thought on taking a class, though I need to get this done quickly.

[JRINJAX]

Your best solution to a variable temp mutli station process control system would be to make a sealed glycol chilling tank with:

Internal passive cooling coil or a pump driven serpentine or plate heat exchanger. Cooling of Glycol would be controlled by a simple aquastat.

Secondary loop pump.

The multi-step sealed compartments could either use passive internal glycol coils [food-grade Prop Gly] or passive externally wrapped glycol coils. No internal copper allowed due to the sulphur [copper sulfate] or reacting with the acidic CO2.

Each step would need it's own three way mixing valve/AO DDC controller.

Insulation as necessary and a freezestat is recommended. Make sure you use a food grade dye on the Glycol to detect product contamination.