Single Batch into Double Fermenters

[Crosley]

I just upgraded my fermenters from 3 bbl to 6 bbl tanks. I wanted to get back to brewing but our busy season is not quite here so I didn't want to brew a double batch and sit on it. I measured the location of the thermowell and the co2 stone and decided that I would have 8-10" above those so I should be good. I went ahead and brewed, the fermentation went fine in regards to the temp control. Once I dropped the yeast and began to crash I noticed a problem. I am down at 40 degrees but it takes about 24 hours per degree. I cant seem to be able to get it below 40 degrees.
I am wondering if this is because the majority of the cooling jacket is above the beer in the straight walled sides and just a smaller amount in the cone? These tanks are only single zones and being run by a 3/4HP glycol chiller.

Does anyone have any suggestion?

Cheers

[Crosley]

UPDATE......
I stopped brewing single Batches due to this cooling problem, but it hasn't seemed to get much better with double batches. Now I am wondering if it has to do with my chiller.
I can easily get the beer down to 3ish but really won't go any lower. I used to have a 1/3hp chiller on 3bbl tanks and it worked great, now with a 3/4hp chiller just doesn't seem enough for 6bbl. I have questioned my 1/2 inch lines from the chiller to the fermenters, I went 1/2 inch because all the fittings on the chiller pump are smaller than that.
Does anyone have any advice they might be willing to share.

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[jcastle]

UPDATE......
I stopped brewing single Batches due to this cooling problem, but it hasn't seemed to get much better with double batches. Now I am wondering if it has to do with my chiller.
I can easily get the beer down to 3ish but really won't go any lower. I used to have a 1/3hp chiller on 3bbl tanks and it worked great, now with a 3/4hp chiller just doesn't seem enough for 6bbl. I have questioned my 1/2 inch lines from the chiller to the fermenters, I went 1/2 inch because all the fittings on the chiller pump are smaller than that.
Does anyone have any advice they might be willing to share.

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Half-inch fittings will result in a pressure drop across them, when there's only a few - at the pump - this might be ok, but to plumb the whole system that way could cause a lot of flow problems. You'll often see the outlet of a centrifugal pump that's smaller than the overall piping system diameter like this http://usercontent2.hubimg.com/1745545_f520.jpg

[Crosley]

Thanks for the info. So it sounds like I need to look into redoing the entire system with 3/4 inch lines.

I have 1/2 solenoid valves, will these cause too much pressure drop or do you think I can leave these and just reduce down to them.

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[jcastle]

Well you're going to spend $40 on couplers and reducers to reduce 3/4 line to 1/2 on either side of the valve and you'll have 2x as many threaded connections to potentially leak or you can spend 40-100/valve to replace w/ a 3/4 solenoid ($40 on Amazon Industrial, 107 on McMaster).

Do the job right the first time.

[Crosley]

Jcastel,
Thanks for talking some sense into me. Since I just installed the brand new 1/2" system I was trying to save some money, but it's not worth it. I have everything on order, I will post the results.


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[jcastle]

Curious to hear the results. As long as your glycol temp is good - flow really should be the root of your problem through the jacket. If you're really curious you could put a rotometer somewhere in the line before and after the install and see a change.

[Crosley]

I'm curious as well. Glycol temp is 28 so that shouldn't be the problem.

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[jcastle]

Pumping at the same linear velocity through the lines gives you double the flowrate as the cross-sectional area of 3/4 pipe is 2.3x. How many BTU is the chiller? How many 6bbl tanks do you have crashing at once? Would 24hr to reach 40° be ideal? What's the temp at beginning of crash? I can do the math for you if I have those figures (will be approximate as would need a bunch of info about the tanks, wall thickness, jacket coverage etc).

[Crosley]

The chiller is a 3/4 hp line chiller 5,5000 btu.
Only 1 tank crashing at once, others would just be kept at temp during fermentation
The avg start temp is 67.

Thanks for all the help.

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[jcastle]

BTU/hr x System Efficiency = ((Volume*Density)*(Starting Temp - Final temp))/(Hours)

(Hours)*(BTU/hr x System Efficiency) = ((Volume*Density)*(Starting Temp - Final temp))

Hours = ((Volume*Density)*(Starting Temp - Final temp)) / (BTU/hr x System Efficiency)

8.94 Hours = ((6bbl*31gal/bbl*8.33lb/gal)*(67°F-40°F))/(5500*0.85)

Assuming an 85% system efficiency (pump heating, friction heat, not perfect tank insulation, glycol line heatup etc) and good turbulent flow in the jackets, I hope you'll be crashing in under 10 hours w/ a 5500BTU chiller.

[Crosley]

Hey that's awesome. Thanks so much. I'll report back next week.

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[Crosley]

Alright, I got the new piping installed. New 3/4 pex, new prv, more ball valves and new solenoid valves. I tried to cut out as many 90's as I could to reduce pressure loss. I got the system fired up and the tanks filled and it definitely works better.
I crashed a tank from 72 to 44 in 9 hours. By the time I came in the next morning the tank was at 35. This is way better.
Thanks so much for the info and help on this.


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[jcastle]

Glad to hear it. Sorry the solution required $ but I'm happy the math (somewhat) checked out to real-world results.

If you got from 72-44 in 9hrs @5500BTU and you were at 6BBL fill volume, you're running 88% efficiency, better than my guess! Means that to get from 72->35 your total time was just under 12hrs.