Need Advice on HERMS

[BBL_Brewer]

Im thinking about going HERMS and was wondering how big of a coil you guys think I need in my HLT. I brew 30 gallon batches. I have a well insulated mash tun that holds temp just fine, but I have a hard time hitting my mash temps right on the button (usually on the low side). I would like to simply dough in and then recirculate until I hit my desired temp and then rest. Not a true HERMS I guess but I don't need to recirculate continuously.

Also, is anyone using SS tubing for this instead of copper?

 

[blaze379]

Here is my HTL coil..... it's made from 50ft of soft copper. My mash keeps its temp by controlling the temp of the HTL.

 

[BBL_Brewer]

Sounds cool, thanks for sharing. However, it doesn't really help me with my question. How big is your MLT? Do you think 50 ft of tubing will be sufficient to bring my mash temps up in a reaonable amount of time? I typically have 60-70 lbs of grain @ ~1.5 qt/lb.

 

[audger]

depending on the actual setup, longer doesnt necessarily mean better.

the longer your piece of tubing, the more time the wort will spend inside the HLT being heated. if your HLT is hotter than your mash, it could be overheated durring its travel. a hotter HLT/HEX temp means that there is a larger HLT:mash temp delta. a larger temp delta means energy will flow across the heat exchanger at a higher rate.

if you want to impart the most amount of energy possible in a single pass thru the HLT, go with a longer tube legnth. the input and output temperature delta will be greater. this could cause overheating though, and could denature active protiens in the wort as it went thru.

a shorter legnth of tubing will not heat in one pass as much, but prevents overheating more. it still takes the same amount of energy to heat the same amount of wort, so wether you heat some of it faster, or all of it slower, it really evens out in the grand scheme of things.

i would go with a shorter legnth (10 to 20 feet) because i like very tight temperature control. in my heat exchanger (separate, not in my HLT), i only use maybe 5 to 8 feet of 1/2" copper pipe. it can heat a max of +5.1 degrees per pass (input and output delta), but it can change temperature without overshooting at all.

so tl&dr:
shorter legnth = tighter holding tollarances, less overshoot, much flatter heating curve (very linear rate of temperature change right up to the setpoint)

longer legnth = greater single-pass heating, wort spends more time in the heater, larger hysteresis band, more logarythmic heating curve (faster initially, then tapering off as it reaches setpoint)

both = same total amount of heat imparted

 

[JuanMoore]

To add to what audger said, you're probably going to want to maximize flow with a 1 bbl batch size since it will take longer to circulate the entire volume and make temp changes. For this reason, the ID of your HEX coil will also be an important factor. What's the ID of your pump outlet and your plumbing? And yes, there are a lot of people using SS HEX coils.

And FWIW I use a long coil but keep the temp differential between the HLT and desired mash small to avoid temp overshoots, which enables me to also use the HEX efficiently as a chiller.

 

[blaze379]

Sounds cool, thanks for sharing. However, it doesn't really help me with my question. How big is your MLT? Do you think 50 ft of tubing will be sufficient to bring my mash temps up in a reaonable amount of time? I typically have 60-70 lbs of grain @ ~1.5 qt/lb.

Sorry, Here is a pic of my setup... MLT is 40 Gallons, same as HTL and Boiler

 

[Lost]

I'd think 25 to 50 ft of copper would be fine. The diameter of the coil should match your pump so that it is not a restriction.

You have two options which would impact the length of the coil.
1. You have a separate heart exchanger heated to a temp far above mash temps. It should be small to permit rapid temp changes for step mashes and such. Here a short coil is preferred to avoid temp over shoots. You'll also only recirculate when you need to raise the mash temp.
2. You put the coil in the HLT and heat that to mash target temp. This is a simpler system and the one I prefer. Here you want enough length to permit the wort to match the temp in the HLT. I don't think you need a crazy length though. I bet 25 feet would be enough and 50 at most.

You have to think about the temp difference between the HLT and the wort which probably won't be much so you don't need a long contact time for them to match. You also have to think about your pumping speed which is really limited by grainbed compaction and the capacity of your pump.

I also don't see a downside to constant recirculation, you'll get clearer wort that way.

 

[BBL_Brewer]

Thanks for the advice everyone, that gives me something to chew on for a while.