Passive Carboy Cooling - Heat Pipes

In the DIY Fermentation Chamber thread, I started to muse about using heat pipes for carboy cooling. I started this thread because it was a wild tangent and may be worth its own discussion.

Has anyone tried cooling a carboy using heat pipes? If so, what setup, what experience as a result?

I did do some searching and found the following three chats on the topic:
Heat Pipe Cooled Fermenter
heat Pipe Cooled Fermenter Followup
The Cold Box *Cool!*

I was thinking that there are three ways a heat pipe rig could be set up. 1) internal, 2) external, 3) combination. I believe each has its own benefits and drawbacks. However, I am going to first explain the rig I am thinking about and then the pros/cons of each method.

The Rig:
Thin, hollow, metal tubing. Type - depends on if internal or external, cheap but decent conductivity would be ideal, would need relatively decent structural stability. Vertically connect the tubing to a heat sink that is chilled to the desired temperature. Chilling of the heat sink can be as easy as a block of ice in a cooler (enter piping through valve). Or as complex as a peltier coolant assembly. I think simpler is better.

Basic description:

Take hollow tubing, crimp and seal on one end. Fill approximately 1/10 full with distilled water. Chill below the vapour point of the water at the goal vacuum pressure / vapour density. Rent, borrow, acquire a vacuum unit, create vacuum inside tube, crimp and seal opposite end (this is likely the most difficult/expensive part of this idea). Thread one end through a heatsink of some type. Repeat for as many tubes as you want - there is a maximum length/exchange rate at some point, I do not know what it is.

If for external use, spiral from base to top of carboy - keep it tight to the carboy. If internal, thread through carboy stopper, consider convoluted piping to maximize surface area, probably run three or four separate tubes out the top. Either way, the heatsink goes up top (higher than the rest of the tubing).

You could run it a bit of extra distance for setting on/near a shelf unit, or attach with a wood/metal shelf unit around the carboy.

Several ways to keep the heatsink cool. I rather like the box of ice in a cooler, it would last for a few days unless it was really hot out. The other is to run it into a kegerator or anything else that would help keep things cold. Or, if you have cold enough nights, you could run it like the Cold Box linked above into the night air. I believe if the top of the heat pipe is hotter than the bottom, it transfers very little heat down. But, once the top is cool again the heat exchange will restart.

The Science:

Heat pipes work by putting a small amount of a liquid within a small diameter tube that has a relatively decent vacuum in it. Water will boil at 273K (31.73F) if it is in a vacuum. While ethanol could be used at a lower vacuum rate. Either way, the amount of vacuum affects the boiling rate of the contained liquid. These charts Vapor Chart or other charts and formulas or Water Vapor Pressure Chart or Wikipedia show that for 60F you need a saturated vapor pressure of about 149.4 mm Hg. By comparison, normal boiling 212F is 760 mm Hg. This seems achievable without too much cost. Plus, here are two $20 vacuum pump creation instructions: Cheap Little Sucker - made with a beer keg cooler - or Bicycle Pump. Of course, anyone with access to refrigeration repair equipment should have available some type of decent vacuum pump.

What happens is at the temperature correspondent to the vacuum, the water (or alcohol, but I prefer water) turns into vapor (steam) and floats up to the top of the tube. Once at the top, it cools, condenses, and drops back down as a liquid. This cycle continues and results in a nice chilling effect. The temperature achieved should be near the temperature that the vapor turns to steam, perhaps a bit warmer. The temperature required for the heatsink is only slightly lower than that of the liquids condensation point (although, colder will result in greater cooling). Thus, a nice, simple heat exchange.


Variations:
So, internal versus external?

Internal you have the problem of an acidic medium corroding whatever metal you have used and subsequent off flavors. There are some metals that could be used that could avoid this, but what a pain. On the other hand, internal also achieves a more consistent temperature as compared to external only. However, internal is also limited by the size of the carboy opening - unless you permanently install it, which is then a PITA to clean!

External you have the problem of the center/top of the wort not equalizing to the temperature, but over time this will not be a problem. This seems like the best all around solution. The other problem with external is you will need more piping. The optimal solution would be several vertical lattices, latched together. However, it could also be done with one or more spirals, but the spirals would be less efficient overall.

Combination - all the drawbacks of internal, but all the awesomeness of superior cooling.

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So, what do you think, possible? Energy efficient? (I think it might be). Fun looking project? Cost estimates? (I think it could be done cheaply with the right tubing, the vacuum tube is the most expensive part.)

Thank you for the input -


M.

DO IT!!! You would have the most awesome passive cooler on the forum if you successfully pulled it off.
If not, you could tell us where you screwed up so we don't make the same mistakes trying to copy you. C'mon, you want to be the guinea pig, you know you do....

On the vacuum unit, Harbor Fright has one for AC that works off an air compressor. Maybe a foodsaver would work as well.

I think that an internal stainless setup would be ideal.

The only obvious drawback I see (if I understand the idea correctly) is that once you crimp the tubing and establish the vacuum level, you're stuck with one temperature setting (corresponding to your preset vacuum). If you want a different temp for a different fermentation, do you have to reconstruct the tubing setup?

As far as the internal/external problem, I think the best solution might be an external rig, encased in a simple insulated box (like the "cold box" you linked). for carboy-sized volumes, I don't think the benefits of internal cooling are worth the additional hassles.

Bike N Brew said:

The only obvious drawback I see (if I understand the idea correctly) is that once you crimp the tubing and establish the vacuum level, you're stuck with one temperature setting (corresponding to your preset vacuum). If you want a different temp for a different fermentation, do you have to reconstruct the tubing setup?

As far as the internal/external problem, I think the best solution might be an external rig, encased in a simple insulated box (like the "cold box" you linked). for carboy-sized volumes, I don't think the benefits of internal cooling are worth the additional hassles.

Click to expand...

I was thinking I would put a charge valve onto it, that would also simplify the filling, setting pressure, and crimping. And would simplify recharging.

I don't know if it would work. However, I was thinking of either doing a dual-liquid system - if I could find two liquids that responded to two decent temperatures, that do not mix, that could co-exist peacefully in the same pipes. Or, do two sets of tubes, one with a lower pressure than the other. Set one for around 35F, the other for 60F. Then as long as the temperature of the radiator is above 35F it would stay at 60F and if below, it would drop below 35F.

And, the more I think about it, the more a cool box like you are suggesting would make sense. At that point, I could do one box at 35F the other at 60F and have one for lagering and one for ales. I think that would be the ideal solution.

Now, I wonder if there is a way to use passive heating in conjunction with this to guarantee it stays within a 5 degree range of temperature - just below the vapour point, but just above the coldest I want it at. I am not sure I could do the heating passive - but an electric heat blanket set to turn on at a reasonable point would work.

The other thing I am not sure of, yet, is if the top is too cold - say the radiator hits 32F up top - will the liquid condense fast enough that it doesn't drop much below the 60F internally, or will it drop to the 32F and thus overchill? I think it is time to call my ex-physicist father-in-law.

Finally, you are correct, internal cooling wouldn't make as much sense unless I was doing huge batches. Something to keep in mind then!

maztec said:

... I think it is time to call my ex-physicist father-in-law.

Finally, you are correct, internal cooling wouldn't make as much sense unless I was doing huge batches. Something to keep in mind then!

Click to expand...

Ok, after reading for about 2 days on this, external does make more sense.
maztec- get on the phone !!!

If I have this right, the device essentially stops cooling when the top reaches the designed temperature.

So, for the sake of discussion, say I have a heat pipe with distilled water @ 9.2psi. My carboy is generating 72* heat, and the ambient temp at the top of the pipe ( or manifold to some other exchanger) is 60*, I would get a drop to 60* right?

Then if the ambient temp (outside the fermentation chamber) was higher than the design temp of 60*, I would need to combine with some type of additional heat exchange (peltier, radiator, etc ).

Did I get these concepts right?

Looyville: You are correct. Things I am not 100% sure on is if it is above 60* will it rise to meet that, or gain heat at the rate it is insulated. I suspect the latter, but am not 100% sure. This can be countered with some form of external heat exchange as you suggested, but could be made efficient if it only used a set amount of the cooling unit. Other cooling options include connecting it to a cold water pipe or using natural cold air at night. However, both would be dependent upon daytime heat exchange - if any.

Then, if outside temp is much below 60*, it shouldn't drop below 60* until the heat exchange through the insulation allows it to continue dropping temperature. However, that can be cured with a heater on a trigger ... I am still puzzling if there is a passive way to do that.

Spoke with the father-in-law, he thought the idea sounds solid. He also had some great ideas for cooling, that require more house construction that I want to do on a rental. Albeit, installing a cool cupboard was a great idea - but not feasible in this situation.

However, the conversation did lead to me realize that the heat pipe idea is good - but has the same problem of all ideas, what to do for cooling of the top of the pipes. So, what type of external radiator/cooler/heat exchange am I going to use. One idea was awesome - big cool mass of water that cycles onto the roof at night. But, alas, way too much construction!

I think I am going to go with a radiator and ice-drip assembly that sucks the cool from the ice put into one unit, lets it melt slowly through the radiator, and exposes the warming water to a lower radiator as it goes into a separate water collector. Put a slow drip on it. It should help preserve the ice longer by maintaining the cold mass and putting off the warm mass.

One other thought of his, was to use some type of salt additive to the ice, so it has a different solidifcation point for the liquid and thus retains a greater amount of cold. Similar to what some of the fancier ice packs do. I suspect I might just look to see how much longer those last and might buy a few and drain them for some ice supply. We'll see.

So, that is the update. We will see where this takes me over the next few months, but SWMBO has put a small halt on my brew related expenses.

any further progress?

I specced it out, but ended up buying a house and suddenly didn't have time or money to finish it. And now have different problems - namely, I don't have a place to brew beer in my new house :\. Which i something that will be fixed soon as SWMBO gets her stuff out of my brew space and I build myself a new brew electric brew pot.