32ft herms coil sufficient for step mashing?

[luckybeagle]

I'm contemplating a 32 ft herms coil, which will sit in my 15g HLT powered by 1x5500w electric element. I occasionally like to do 10 gallon batches and am curious how this might fare with step mashes? I know most opt for 50ft of 1/2" diameter coil, but I'd much prefer one that I don't need to bend into shape or deal with compression fittings. Is 32ft length sufficient or is there a significant difference in stepping up with the the 50ft?

 

[stevehaun]

32 feet will work fine. Mine is 25 feet.

 

[Bobby_M]

It should work just fine. Be careful drilling the holes for the weldless fittings, they have a pretty small range of acceptable hole diameters before the oring falls into the hole. You want it just barely big enough for the threads to pass through which is 13/16 exactly.

 

[WesBrew]

32 feet will work fine. Mine is 25 feet.

Good to hear. I got a 25’ brewzilla replacement. Haven’t tested yet.

 

[day_trippr]

Obviously, a 32' 1/2" hex will work. "Fine" will be up to the user.

fwiw, I'm running a 50' 1/2" ss hex in a 20g hlt (needing just over 11 gallons to fully immerse it) and ramping hlt and mash to mash-out & sparge temps (roughly 18°F) takes a good 20 minutes for my typical ~24 pound mash, and 40 minutes for my (massive) stout with nearly twice the grist. So roughly 1°F gain per minute per 20 pounds.

Losing nearly half of the length is definitely going to slow ramps down significantly, no way around it without repealing thermodynamics laws...

Cheers!

 

[sicktght311]

it really more has to do with how quickly you can make temperature changes in your HLT than the size of the coil. 25 feet is more than long enough to quickly change temperature of the liquid running through it. No it wont change it by 10 degrees in one pass, but if you can realistically increase your HLT from like 145 to 160 in like 10 minutes, then the liquid passing through the Herms coil should respond fairly quickly as well

 

[day_trippr]

Actually, the hlt bath really isn't germaine at all wrt hex length vs time to hit a step.
One does not measure "step time" on how long the bath took to make a step

As long as the hex is fully submerged and the bath is at the prescribed step temperature, the rest is totally about the hex length...

Cheers!

[ps] One could run the hlt hotter, but unless the batch was full-volume mash, one will lose that time on the back side waiting for the hlt to cool down to sparge temperature...

 

[stevehaun]

I think that ramping is more limited by flow thru the mash than by heat transfer in the herms coil. With my 25 foot coil, the temp at the output of my herms coil rapidly reaches the set temp and then I wait for the mash temp to slowly catch up. I don't understand how a longer herms coil will speed up the process. Only two ways to speed it up: 1) increase the delta between set temp at herms coil output and mash temp or 2) increase flow thru the mash.

 

[day_trippr]

[...]Only two ways to speed it up: [...] or 2) increase flow thru the mash.

And that's where a longer coil wins...

Cheers!

 

[stevehaun]

And that's where a longer coil wins...

Cheers!

You lost me there. How will a longer coil increase flow thru the mash?

 

[WesBrew]

I think that ramping is more limited by flow thru the mash than by heat transfer in the herms coil. With my 25 foot coil, the temp at the output of my herms coil rapidly reaches the set temp and then I wait for the mash temp to slowly catch up. I don't understand how a longer herms coil will speed up the process. Only two ways to speed it up: 1) increase the delta between set temp at herms coil output and mash temp or 2) increase flow thru the mash.

ok good. ‘25 is enough for the HERMS output to reach set temp in the hlt . You’re saying the limited amount of wort flow going back into the tun is where lag is in raising the temp in that vessel.

 

[stevehaun]

ok good. ‘25 is enough for the HERMS output to reach set temp in the hlt . You’re saying the limited amount of wort flow going back into the tun is where lag is in raising the temp in that vessel.

Yes. For example, if I want to raise my mash temp from 145 to 162F, I set my PID to 164F. I measure wort temp as it enters the top of the mash tun and as it exits the bottom of the mash tun. The temp at the output of the herms coil rapidly reaches 164F and then I wait for mash temp to slowly come up to 162F. In my system, my ramp time is more limited by the rate of flow thru the mash than the time it takes for the temperature of the wort exiting the herms coil to reach the set point.

 

[day_trippr]

You lost me there. How will a longer coil increase flow thru the mash?

A longer coil enables a faster flow rate at the same exit temperature...

Cheers!

 

[stevehaun]

A longer coil enables a faster flow rate at the same exit temperature...

Cheers!

That would only be true if heat exchange is not complete in the shorter coil. It is not true if the temp of the wort exiting the shorter coil has equilibrated with the water temp in the HLT. Plus you have to take into consideration the resistance of the coil. A 50 foot coil will have twice the resistance of a 25 foot coil. For a given pressure drop, a 25 foot coil will have twice the flow compared to the 50 foot coil.

 

[day_trippr]

Not sure you're getting the inescapable point that regardless of resistance if one is indeed able to pump a longer coil faster while still hitting the desired exit temperature the thermal exchange at the mlt is improved. I mean, would you argue a 5 foot coil is just as good as a 50?

Your first point is correct - if the recirculation is at its maximum. If you have to slow the flow to hit that exit temperature because the coil isn't long enough then obviously transfer efficiency is commensurately reduced...

Cheers!

 

[stevehaun]

Not sure you're getting the inescapable point that regardless of resistance if one is indeed able to pump a longer coil faster while still hitting the desired exit temperature the thermal exchange at the mlt is improved. I mean, would you argue a 5 foot coil is just as good as a 50?

I understand and agree with your point. Somewhere between 0 and 50 feet of 1/2" OD SS tubing, there is an optimal length for heat exchange, given the flow generated by typical homebrew pump (5-7 gpm). If the coil is shorter than the optimal length, time for heat exchange will not be adequate and you will have to slow your flow. However, if the coil longer than optimal, you will not get any additional heat exchange and you will not be able to generate as much flow because of added resistance. What neither of us has shown (because neither of us know) is what the optimal length actually is. The other variable is the flow through the grain bed. I venture to guess that most people using a herms system do not run their pump wide open because of compacting the grain bed. Personally, I crack the valve on my pump about 1/3 to 1/2 open. Do you run your pump wide open during the mash?

 

[day_trippr]

^All true^. I'm going on intuition and common sense, I wouldn't know how to "math" the problem
I run recirculation as fast as the grain bed allows, typically between 2 to 3 gpm, roughly 30-40% of the pump's rated throughput...

Cheers!

 

[Elky]

One could run the hlt hotter, but unless the batch was full-volume mash, one will lose that time on the back side waiting for the hlt to cool down to sparge temperature...

You can always cool down the HLT by either running it through the chiller hex (if this is something you plan to do, just leave it hooked up to the counterflow through the whole mash but only flood it with cold water after your mash is at final step temp, would only take a minute) or just by adding cold water to the HLT. If you're treating your sparge water though you will have to pre treat the whole batch, then run off the cold bit prior to heating anything up, so it would take more prep.

 

[day_trippr]

Right. A pita time-sink no matter how it's sliced...

Cheers!

 

[Staticsouls]

With a 50 ft coil what ever the wort temp is, it is coming out at the hlt temp.

 

[Dustin_J]

Some food for thought https://www.homebrewtalk.com/forum/threads/optimization-of-herms-coil-length.639634/

TLDR: 18-20 ft is suggested, along with thorough mixing if the HLT. The Brewpot article mentioned in this link suggests about 25 ft as ideal given their assumptions, FWIW so you're probably in good shape.

 

[SloTimes]

Some food for thought https://www.homebrewtalk.com/forum/threads/optimization-of-herms-coil-length.639634/

TLDR: 18-20 ft is suggested, along with thorough mixing if the HLT. The Brewpot article mentioned in this link suggests about 25 ft as ideal given their assumptions, FWIW so you're probably in good shape.

@Staticsouls is 100% correct. I would actually advise you against getting the 50ft.

Happy to answer questions about the assumptions made in that post.