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HERMS coils length
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TheYoshi



Joined: 04 Feb 2011
Posts: 4



PostLink    Posted: Sun Apr 14, 2013 4:13 pm    Post subject: HERMS coils length Reply with quote


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Beginning a setup that will mostly be used for 5 gal batches. Wondering if anyone knows the math involved to evaluate using a 25' Herms coil over 50'. It would still be 1/2" stainless tubing. I'm wondering how big of an impact this would make in terms of controlling the mash temp. I know Kal's setup easily keeps the mash and HLT at the same temp so it feels there may be some headroom in the coil length but I'm not sure how to calculate.

Thanks

Josh
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silverspoons



Joined: 21 Dec 2010
Posts: 555
Location: Webster NY


PostLink    Posted: Mon Apr 15, 2013 12:20 pm    Post subject: Reply with quote

I use my counter flow chiller for both cooling and as a herms coil.. i believe its only around 16 feet and it works perfectly.

Silverspoons
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kal
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Joined: 12 Dec 2010
Posts: 10680
Location: Ottawa, Canada

Drinking: German Lager, Electric Creamsicle, London Pride, Kolsch, Belgian IPA, Red IPA, Russian Imperial Stout, Black Butte Porter

Working on: Weizen, Belgian Quad, Wit, English Pub Ale, Electric Creamsicle


PostLink    Posted: Mon Apr 15, 2013 2:08 pm    Post subject: Reply with quote

A counterflow chiller is a bit different. The opposite direction of flow makes it more efficient. If yours has a convoluted inner coil then it's eve more efficient.

So it's difficult to compare lengths between something like a convoluted CFC and a HERMS coil.

@Josh: I'm afraid I don't have the math behind it - sorry.

Kal

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huaco



Joined: 05 Apr 2012
Posts: 1508
Location: Burleson Texas


PostLink    Posted: Mon Apr 15, 2013 2:19 pm    Post subject: Reply with quote

Several guys in my Brew Club have 25' HERMS coils on their breweries and they make 10-12 gallon batches. They report slightly slower temp adjustments than I am getting with my 50' coil, but it is not detrimental. I would think you would be just fine.
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TheYoshi



Joined: 04 Feb 2011
Posts: 4



PostLink    Posted: Tue Apr 16, 2013 3:44 am    Post subject: Reply with quote

Thanks for the info here. I am leaning toward 25' I'll be sure to post some timings as I get things up and running
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kal
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Drinking: German Lager, Electric Creamsicle, London Pride, Kolsch, Belgian IPA, Red IPA, Russian Imperial Stout, Black Butte Porter

Working on: Weizen, Belgian Quad, Wit, English Pub Ale, Electric Creamsicle


PostLink    Posted: Tue Apr 16, 2013 12:48 pm    Post subject: Reply with quote

Just out of curiosity, why do you want to do 25'? Is it because you don't have room for 50' in the HLT?

Kal

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TheYoshi



Joined: 04 Feb 2011
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PostLink    Posted: Tue Apr 16, 2013 4:52 pm    Post subject: Reply with quote

A couple of reasons really:

1. I already have 15 gallon pots for the HLT and BK (planning to buy a blichmann MLT)
2. My HLT pot is 15 gallons, 15.25" diameter x 18.75" tall

A 50' coil at ~12" diameter would be about 9" tall, at ~10" diameter it would be 11" tall. It doesn't leave much room in the pot and requires it to be quite full to keep the coil submerged. If I go 25' those heights are effectively cut in half which gives me a ton more room and makes it easier to keep the coil submerged.

If I can still get the same, or close to the same heat transfer effectiveness I will be able to move temperatures in the HLT faster with less water in it so that appeals to me.

The cost between a 50' coil and 25' coil isn't huge so that's not really a big concern.

-Josh
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rivetcatcher



Joined: 21 Apr 2016
Posts: 120
Location: Thailand

Drinking: Timothy Taylor Landlord / Hop Candy Jr

Working on: Juicy Bits


PostLink    Posted: Sun Oct 30, 2016 9:45 am    Post subject: Reply with quote

I was thinking about this issue. I have a 25 gallon pot with a diameter of approx 19.25" and height of approx 19".

I have already ordered a 50' HERMs coil which is 10" tall. I was worried that a couple of inches at the top of the coil will be exposed when I drain my strike water from the HLT. However I don't think it will make that much of a difference to temperature.

Any thoughts on this?
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kal
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Drinking: German Lager, Electric Creamsicle, London Pride, Kolsch, Belgian IPA, Red IPA, Russian Imperial Stout, Black Butte Porter

Working on: Weizen, Belgian Quad, Wit, English Pub Ale, Electric Creamsicle


PostLink    Posted: Sun Oct 30, 2016 1:45 pm    Post subject: Reply with quote

rivetcatcher wrote:
I was thinking about this issue. I have a 25 gallon pot with a diameter of approx 19.25" and height of approx 19".

I have already ordered a 50' HERMs coil which is 10" tall. I was worried that a couple of inches at the top of the coil will be exposed when I drain my strike water from the HLT. However I don't think it will make that much of a difference to temperature.

Any thoughts on this?

Likely not a big deal. If you have any concerns, simply fill the HLT (sparge) and MLT (strike) separately at the start of the brew day such that the HLT HERMS coil is always completely submerged, and then start heating. The strike water in the MLT will heat via HERMS. Once at temperature, simply mash in. I've had to do this myself once or twice with really high (10-12 ABV%) beers where I need more total water (strike + sparge) than my 20 gallon HLT can handle. The only (minor) downside to filling the HLT and MLT separately is that if you use something like potassium metabisuphite in your water to remove chlorine/chloramine, you have to add two doses separately instead of one to the HLT.

Good luck!

Kal

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rivetcatcher



Joined: 21 Apr 2016
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Drinking: Timothy Taylor Landlord / Hop Candy Jr

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PostLink    Posted: Sun Oct 30, 2016 3:01 pm    Post subject: Reply with quote

Thanks Kal, I was thinking about doing that but may do a small experiment first to see if it really makes a difference. I was just thinking, the length of the silicone pipe between the vessels doesn't affect it then an inch or 2 of exposed herms coil shouldn't either, considering that the heat of the water in the HLT will also warm through the coil.
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kal
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PostLink    Posted: Sun Oct 30, 2016 5:02 pm    Post subject: Reply with quote

rivetcatcher wrote:
I was just thinking, the length of the silicone pipe between the vessels doesn't affect it ...

It does actually. You will lose heat through the silicone hose. This is why I recommend thicker walled 1/2" ID silicone hose (7/8" OD instead of 3/4" OD). Some that used the thinner walled stuff find that they have to offset their HLT a few degrees higher than their mash temp.

Quote:
considering that the heat of the water in the HLT will also warm through the coil.

True. In the HLT I don't really think it matters to have it exposed an inch or two.

Kal

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rivetcatcher



Joined: 21 Apr 2016
Posts: 120
Location: Thailand

Drinking: Timothy Taylor Landlord / Hop Candy Jr

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PostLink    Posted: Mon Oct 31, 2016 4:51 am    Post subject: Reply with quote

Thanks Kal
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deemo



Joined: 30 Nov 2014
Posts: 23
Location: Canada


PostLink    Posted: Thu Nov 16, 2017 5:15 pm    Post subject: Reply with quote

kal wrote:
Just out of curiosity, why do you want to do 25'? Is it because you don't have room for 50' in the HLT?

Kal


How do you feel about this experiment? Seems to show that around 8M or ~25ft is the ideal length for a coil.

https://www.brewpi.com/what-is-ideal-herms-coil-length-theory-experiments/
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kal
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Drinking: German Lager, Electric Creamsicle, London Pride, Kolsch, Belgian IPA, Red IPA, Russian Imperial Stout, Black Butte Porter

Working on: Weizen, Belgian Quad, Wit, English Pub Ale, Electric Creamsicle


PostLink    Posted: Thu Nov 16, 2017 9:45 pm    Post subject: Reply with quote

deemo wrote:
How do you feel about this experiment? Seems to show that around 8M or ~25ft is the ideal length for a coil.
https://www.brewpi.com/what-is-ideal-herms-coil-length-theory-experiments/

Careful how you interpret the results. You're only quoting part of what they wrote so your statement is incorrect. The sentence right after is very important. They wrote:

"Based on our experiments, an 8 meter coil maximizes the heat transfer. This of course depends on many factors, like the coil material, your pump pressure and other losses in the system. "

So it depends.

They don't mention what pump they use - it appears to be a really tiny DC ones with a tiny motor that isn't known to have a lot of pressure if I remember correctly. The flow slows down as soon as there's any friction or back pressure. They do mention it has 4.5m of head but that's best case with zero back pressure. Static pressure is what matters and other things connected will cause flow issues. They seem to have a ton of valves and other things (more than in my design) that may impede flow too making things worse.

Like they say, the length really depends on the entire setup. You'd have to try various lengths using your specific equipment to see what works best for you based on the exact equipment you're using.

Or just use a good pump with good pressure and go with a 50' HERMS coil. Works for me. Wink You can see how strong the flow is in the video at the bottom of this page: http://www.theelectricbrewery.com/brew-day-step-by-step?page=6

Good luck!

Kal

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Creepy



Joined: 04 Feb 2014
Posts: 130
Location: North Chicago Burbs


PostLink    Posted: Fri Nov 17, 2017 12:43 am    Post subject: Reply with quote

Not to derail the thread, but based on that experiment they also conclude wort flow in the coil should go top down. Kal, I think you run it bottom up. Any chance you have any data/experience based on your setup for that?
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kal
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PostLink    Posted: Fri Nov 17, 2017 2:00 am    Post subject: Reply with quote

As long as the wort flows in the opposite direction of the water, I don't see what difference it makes if it goes top to bottom or bottom to top if you're recirculating the HLT water correctly such that the water temp's all the same everywhere. If you use different pumps that perform poorly such that the water's hotter in certain spots, or a different setup with more restriction , or other changes then who knows.

The wort exiting my HERMS coil is at exactly the HLT water temp. That's all the heat extraction you can expect. That's what I wanted.

If your setup’s different by all means give it a go and try. Easy to do.

Cheers!

Kal

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deemo



Joined: 30 Nov 2014
Posts: 23
Location: Canada


PostLink    Posted: Fri Nov 17, 2017 4:23 pm    Post subject: Reply with quote

kal wrote:


The wort exiting my HERMS coil is at exactly the HLT water temp. That's all the heat extraction you can expect. That's what I wanted.

Kal


My wort is the same temp as the HLT as well. I have the same setup (50ft) with solid pumps. Just wondering if the temp would also be the same with 25ft. Then you would have a higher rate of flow/turnover in the mashtun at the same temp as the 50ft coil. Might result in faster temp changes. Just curious.
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kal
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Drinking: German Lager, Electric Creamsicle, London Pride, Kolsch, Belgian IPA, Red IPA, Russian Imperial Stout, Black Butte Porter

Working on: Weizen, Belgian Quad, Wit, English Pub Ale, Electric Creamsicle


PostLink    Posted: Fri Nov 17, 2017 4:35 pm    Post subject: Reply with quote

deemo wrote:
My wort is the same temp as the HLT as well. I have the same setup (50ft) with solid pumps. Just wondering if the temp would also be the same with 25ft. Then you would have a higher rate of flow/turnover in the mashtun at the same temp as the 50ft coil. Might result in faster temp changes. Just curious.

If using the pumps I recommend I don't think the flow would be much faster going from 50 to 25 given all the other restrictions (including the grain bed). I haven't tried it myself.

Kal

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Slotimes



Joined: 01 Dec 2017
Posts: 1



PostLink    Posted: Fri Dec 01, 2017 6:25 am    Post subject: Herms coil optimization Reply with quote

So I stumbled across this article the other day:


https://www.brewpi.com/what-is-ideal-herms-coil-length-theory-experiments/

The further I got into the article the more the analysis kinda irked me. They neglect an enormous amount of the true physics at play and treat many variables as fixed constants (friction coefficient and pump performance). On top of that they spit out an optimum but it is for a pump that no one here in the U.S. really uses. The problem is that the "optimum" length of your coil is massively dependent on the performance of your pump and your individual system. So I set out to do a real analytical optimization of a HERMs coil for a set up that is more like the systems that we brew on in the U.S.

This section is about the calculation, feel free to skip:

If you want a good primer on fluid flow in pipes start here:
https://www.engineeringtoolbox.com/total-pressure-loss-ducts-pipes-d_625.html

In order to solve the D'Arcy-Weisbach Equation [hloss = λ (l / dh) (v2 / 2 g) ]

We need to solve for λ a.k.a The friction coefficient can be calculated by the Colebrooke Equation:

1 / λ1/2 = -2.0 log10 [ (2.51 / (Re λ1/2)) + (k / dh) / 3.72 ]

Because the formula is recursive we will have to solve this by iteratively. I used quartic iterations. Which should yield results many orders of magnitude more precise than the Nusselt number approximations use later on later on.

I took the pump curve from March for the 815-SS available here: http://www.marchpump.com/site/files/966/148215/489110/710019/815-SS.pdf

manually copied a few of the data point and and fit the curve.

Here is the pump curve fit:


I assume for this analysis that you have 2x 4ft silcone 1/2" hoses in addition to your HERMS coil running from your pump to the inlet and exit of the HERMS coil. For minor loss calculation I assumed 1 ball valve all the way open, 4 right angle fittings, and 4 cam-lock pairs. Minor loss coefficients (ξ) can be summed and added to the major losses.

hminor_loss = ξ v2/ (2 g) (1)

where

hminor_loss = minor head loss (m, ft)

From here we have the problem of solving for the steady state system operating point. Where we match the available head from the pump with loss in the system. This must be solved iteratively as well as the losses are a function of fluid velocity and the available head is a function of the fluid velocity as well. The iterative solver will stop once the apparent error is within 0.1%.

The script will also solve for both laminar (full and partially developed) and turbulent flows and adjust the Nusselt number, the friction factor, heat transfer coefficients accordingly. (turns out that most of the flow cases with this pump and reasonable coil lengths are sufficiently turbulent (Re>10,000) but for the pump in the article and some smaller pumps that is not the case.

I swept through lengths of HERMS coils from 1 to 70 ft as well as Mash to HLT temperature deltas of 1 to 20 degrees. The results follow.

END OF METHODOLOGY

The family of curves below is for the March 815-SS pump (one of the most common brewing pumps in the US) and assumes you have two 4ft lengths of 1/2" dia silicone hose with 90 elbows and cam lock fittings, a ball valve that is all the way open on your pump, 1/2" OD stainless steel tubing for the coil (0.035" wall), and that you can maintain constant temp in your mash tun (i.e. you can provide the same heat you are extracting).

One thing the article kind of neglected is that you don't necessarily want higher HERMs outlet temps. Heat transfer is maximized when the temperature difference between the two materials is large. What that means is that the closer your wort temp in the HERMs coil gets to the HLT temp the less heat transfer into that fluid you get for the same area of heat exchanger. Additionally they neglect the fact that you don't want the wort to get above 168F at all or you will start denaturing all of your amylases. On that note, you really want to do all you can to decrease the heat load on those amylases; therefore, you really want to have as small of a HERMs outlet temp differential as possible with a high flow rate*.

The first run I just spit out the power vs. coil length but neglected the outlet temp and you get the graph below, which just says you want as big of a temperature difference between your mash temp and the HLT tempas you can get with a coil length of about 20ft.

Not_temp_restricted.jpg

The second run I killed each curve when the outlet temp increased above 165F (74C) which is why you see that strange feather shape on the left. The straight line back to zero is just a bug in how I plotted it (sorry), the curve should terminate at the top. What this says is that your maximum "enzyme safe" temp delta is 9C (16F) and at that delta T you want about 18ft of coil (yields a flow rate of ~3.5gpm**). You can technically get a higher power system with the same pump if you have a very short coil but because that slope is so steep you run the risk of easily mis-estimating the head loss and not getting much power transfer at all or cooking your wort. To me, the risk is not worth the marginal power increase from the 9C delta set up. Also, that would need a very high flow rate and I think that would probably just result in a ton of grain bed settling, restricting your flow and then cooking your wort.
Temp_restricted.jpg
About those *'s, I'm not sure that 3.5 gpm is a reasonable flow rate for most mashes. I will have to see how bad that compacts my grain bed and report back. If it proves to be too high it will push the "optimum" coil length longer.

SO,

Lessons learned:
-You don't need the expensive 50+ foot coils everyone is trying to sell you
-Next time someone asks you what the optimum length is just tell them 18 ft
-Next time I see an article about brewing that relates to “engineering” I should probably just not read it for my own sake
-Yes, I am the worst kind of person for mixing unit systems



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kal
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Location: Ottawa, Canada

Drinking: German Lager, Electric Creamsicle, London Pride, Kolsch, Belgian IPA, Red IPA, Russian Imperial Stout, Black Butte Porter

Working on: Weizen, Belgian Quad, Wit, English Pub Ale, Electric Creamsicle


PostLink    Posted: Fri Dec 01, 2017 1:19 pm    Post subject: Re: Herms coil optimization Reply with quote

Interesting info - thanks for posting!

Slotimes wrote:
About those *'s, I'm not sure that 3.5 gpm is a reasonable flow rate for most mashes. I will have to see how bad that compacts my grain bed and report back. If it proves to be too high it will push the "optimum" coil length longer.

I think that's the crux of the issue. Everyone uses different a different false bottom and every beer has a different grist (some sticky, some fine, etc). Everyone mills slightly differently. Mash *really* adds restriction to flow. I adds a huge variable such that I'm not sure how accurate the other flow modelling has to be.

I'm also not a fan of increasing the HLT well beyond the mash temp to increase heat transfer rates as eventually the two will start to equalize. The process doesn't work for me as you don't have any way of ensuring you don't overshoot the mash temp.

Cheers!

Kal

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