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 Home Brew Forums > Immersion chiller - what's best - prechiller or recirculation ?
08-15-2010, 09:53 PM   #1
DeafSmith
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 Immersion chiller - what's best - prechiller or recirculation ?

Recently there has been some discussion about using ice water with an immersion chiller to cool wort below tap water temperature. A couple of methods have been discussed: use of a prechiller submerged in a bucket of ice water to chill the tap water going to the IC; and recirculation of ice water through the IC and back to the cold water bucket or cooler by means of a pump. Either of these would presumably only be used after the wort has already been cooled to near tap water temperature by running tap water through the IC. Intuitively, I felt that the recirculation method would make more efficient use of the ice water, but I finally got interested enough to develop some equations in order to get a better handle on which method is best, and by how much. I wrote up my work in a pdf file which can be downloaded from here:

http://www.mediafire.com/?c9mkm19uxjiz9hj

I had to make some simplifying assumptions in order to be able to do this, so the equations developed won't be completely accurate, but should give a good idea of the relative benefit of the recirculation method over the prechiller method. I assumed complete heat transfer in both the prechiller and chiller; i.e., that the temperature of the liquid leaving the coil is the same as the temperature of the liquid in which it is immersed, and I avoided the complications of melting ice by assuming the use of cold water with no ice. I plotted the results of two "typical" situations, each with 6 gallons of wort at 90ºF, tap water at 80ºF, and starting with cold water at 35ºF with the only difference being the use of 4 gallons of cold water in one case and 8 gallons in the other. I hope some of you find this to be useful, or at least interesting. Sorry for the heavy math in the report, but it was unavoidable.

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08-16-2010, 09:12 PM   #2
Grasslands
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I, for one, do find this interesting. I'm considering both options at the moment. I had a question for you - taking into consideration one of my options. I have a keggle that I'm itching to use for the first time and my only means of chilling wort in the past has been through the use of a 25' x 1/4" copper IC.

To combat the expansion in size from my old kettle to the 15.5g keggle, I'm definitely going to buy/build a 50' IC (using either 1/2" or 3/8" tubing - I also don't know which is more efficient...I'm assuming the 1/2"). I'm considering using the 25' IC as a pre-feed into the 50' IC, where I'd submerge the 25' IC into a salt ice bath. Essentially it'd look like this: garden hose to 25' IC submerged in salt ice bath to 50' IC submerged in wort.

In the above scenario, is the 25' IC what you would call the pre-chiller? I'm just checking to see if my situation might be applicable to your equation.

Thanks!

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08-17-2010, 01:02 AM   #3
DeafSmith
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Yes, that's exactly what I've plotted and labeled as "prechiller". Of course, my calculations didn't take into account such things as salt in the water, or the difference between tubing sizes - to make it possible to analyze mathematically I had to make a lot of simplifying assumptions, but it does make clear that for a given amount of cold water, you can get the wort to a few degrees lower temperature by recirculating that water from the cold water tank through the immersion chiller and back to the cold water tank than what you can get by running tap water through a prechiller then to the the chiller and then down the drain. Of course the few degree difference may not justify the cost of a pump needed for the recirculation method, but if you already have a pump, then maybe recirculation is the way to go.

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08-17-2010, 03:25 PM   #4
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Quote:
 Originally Posted by DeafSmith Yes, that's exactly what I've plotted and labeled as "prechiller". Of course, my calculations didn't take into account such things as salt in the water, or the difference between tubing sizes - to make it possible to analyze mathematically I had to make a lot of simplifying assumptions, but it does make clear that for a given amount of cold water, you can get the wort to a few degrees lower temperature by recirculating that water from the cold water tank through the immersion chiller and back to the cold water tank than what you can get by running tap water through a prechiller then to the the chiller and then down the drain. Of course the few degree difference may not justify the cost of a pump needed for the recirculation method, but if you already have a pump, then maybe recirculation is the way to go.
The "few degree difference vs. cost" is the thing that I'm weighing...though technically the 25' IC is co-owned by myself and a friend - so it might make sense to get a submersible pump and recirculate. I'm currently investigating the cost efficiency of a 3/8" tube vs. a 1/2" tube.

I'm also assuming that you wouldn't start recirculating the ice water until the temperature in the wort (or at least the pumped water) drops to below 100, correct? I'm guessing that if you immediately started recirculating the water, you'd end up immediately melting your ice and turning your circulating water lukewarm.
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08-17-2010, 05:05 PM   #5
DeafSmith
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You definitely want to wait until your wort is below 100ºF before you start using your ice water - that's why my model starts with the wort at 90ºF. As to the difference between 3/8 and 1/2, you should be able to get the same amount of cooling from either, assuming that you run the water at a speed low enough for complete heat transfer to take place. Presumably the 1/2 inch tubing, or a longer length of 3/8 tubing would do the job faster, but not necessarily colder. I have a 3/8 inch, 50 foot chiller which I have been using with a 3/8 inch, 20 foot pre-chiller. Wort cooling is very fast from boiling down to a little over 100ºF, but in the summer it's very slow going after that due to the tap water temp. I don't think that going to 1/2 inch tubing would help that situation - I either need to get a longer pre-chiller and use more ice, or recirculate. I think I'm going to recirculate now that I have a pump and use my 10 gallon cooler MLT as the ice water tank instead of the 5 gallon bucket I've been using for the prechiller.

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08-17-2010, 05:13 PM   #6
Bobby_M
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My biggest beef with a prechiller is that most people use such short coils that you'd have to run your tap water really slow to get a decent temp delta. If you run 80F water through a 25' coil in 35F water at 3GPM, it's not coming out at 35F or even 40F. No math, just a bold guess from experience. The other issue is that you have to keep that bath moving to keep the warm water away from the coils. Pumping icewater puts that cold icewater into the IC without any stirring and it's always that fixed temp no matter how fast you flow it.

You CAN use it when the wort is still hotter than 100F, but you should run it a little slower and discharge the IC output elsewhere (NOT back into the ice). If you need to makeup water volume, run tap water into the ice.

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08-17-2010, 06:45 PM   #7
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I agree about needing longer coils on the prechiller - 20 feet is not long enough, in my experience. And I can tell just by feeling the chiller input line that the water is warmer than 40 degrees with my prechiller. As for keeping the bath moving, I am constantly stirring the wort (slowly, but steadily) to keep wort flowing over the coils, and once I put the ice in the prechiller bucket, I use my other hand to agitate the prechiller by lifting it up a little and letting it fall back. Kind of like trying to pat your head and rub your stomach at the same time. So that's another way recirculating would make things easier.
Still seems a good idea to wait to use the ice until wort is down below 100 to get the most benefit from the ice.

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08-17-2010, 06:51 PM   #8
maida7
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I haven't made any fancy graphs but I have used both methods. In my experience it's no contest. Recirculating ice water with a pump works several times faster then using a pre-chiller. Quite honestly, a pre-chiller has a very limited effect for me. But my tap water is way colder then 80F. Even in the heat of summer my tap water never gets above 70F.

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08-17-2010, 06:53 PM   #9
maida7
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Quote:
 Originally Posted by Bobby_M You CAN use it when the wort is still hotter than 100F, but you should run it a little slower and discharge the IC output elsewhere (NOT back into the ice). If you need to makeup water volume, run tap water into the ice.
You could but why would you want to? I think you'd be wasting your ice to use it before it goes below 100F. With either method.
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08-17-2010, 07:01 PM   #10
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Quote:
 Originally Posted by Grasslands The "few degree difference vs. cost" is the thing that I'm weighing...though technically the 25' IC is co-owned by myself and a friend - so it might make sense to get a submersible pump and recirculate. I'm currently investigating the cost efficiency of a 3/8" tube vs. a 1/2" tube.
If your cooling 10+ gallons I'd recommend 50' of 1/2" refrigeration service copper tubing. The refrigeration tubing is cheaper but it's also thinner. It says 1/2" but it solders up to 3/8" fittings. I think it's really 1/2"OD. The more expensive type L & type M are fatter, thicker walls and much more expensive. For 10+ gallons I find that 50' of the 1/2" refrigeration service copper tubing does the trick. Expect to pay between 80.00 - 120.00 depending on if you roll your own or buy one pre made.
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