HERMS Coil

Yeah, I have a 3 keggle, 3 PID, E-HERMS setup. After 3 years, 2 moves, birth of my children, one deployment and the purchase of my first home, I finally finished it last month. I will be posting a full build thread after I get home from being out to sea. I left Mattawan in 2001 when I joined the Navy. My HLT PID controls the HLT element by sensing the HLT temp through the HLT outlet (8" RTD probe). My MASH PID controls the HLT element on the return to the Mash Tun. I'm using a 25' 1/2" SS coil inlet on top, outlet on bottom.

 

Interesting. Will be looking forward to your post about it. I am experimenting with the no sparge method with a 32 ga Brute as my MT.

 

So i have one probe with my PID controller, is it possible to do HERMS by setting temp in HLT to desired mash temp or do i place it in the mash & let it turn on element to heat up HLT water more?

I know....ultimately a new controller that has 2 inputs & outputs is optimum but i dont have that extra money to get one now.

Any feedback would be appreciated!


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In my system the temperatures will eventually equalize between the HLT and MLT, but it can take around 15 minutes for that to happen. Say I go to mash out. I turn the HLT PID up to 169. It takes about 15 minutes for the MLT (which was previously sitting at 153) to come up to that temp. Without the sensor in the MLT I wouldn't know when that had happened so I would have to assume. As long as you made your process repeatable by using the same time intervals each time then I would think it would be a workable solution without a MLT sensor, but not ideal.

 

I think with only one probe the best choice is to put it in the HLT. From what I've read if you control the HLT element with a probe in the MT you'll have some pretty big swings and likely overshoot your temperatures quite a bit. Just double-check your mash temps with a handheld thermometer, depending on your system you should find your mash equals your HLT temp or maybe is always 2 or 3 degrees lower due to heat loss. Then you can set your PID at say 156 instead of 154 and nail your temps everytime.

 

If I only had one probe I'd also put it in the HLT.

Like Setesh, I have two probes - one at the MLT output, one at the HLT output. The HLT output probe is used to maintain HLT temp which in turns heats the MLT through the HERMS coil.

The probe in the MLT simply lets me know how far behind the mash is lagging. The time can vary too - for example, the time to heat the HLT from mash to mashout may only be 15 minutes or so and fairly constant (since the amount of HLT water is about the same), the time for the mash to follow up to that temp will vary as sometimes I have 12 lbs of grain, sometimes 25 lbs.

I have an example video of how the two work during mashout here:

Kal

 

Yes, in the MT is bad. In the HLT is good, but in my opinion, at the MT inlet is the best. That way the water you put back in the MT during recirc is exactly what you want your mash temp to be. It is a good idea to monitor the inside of the mash or the MT outlet with a thermometer, but you definitely should not control element firing at these points.

 

I am designing an external counter-flow HERMS coil using rigid pipe, so I wrote this script.

I set the HEX mash inlet temp (147), HEX water inlet temp (150), and the desired HEX mash outlet temp (149) and it tells me the required length, based on the design and water properties.

I used those numbers because I figured if it can raise 147 up to within 1 deg of the mash, as it circulates the temperature in the mash should track within 1 deg of the HLT, more or less.

Here's the script:

clear all; close all; clc;

% known inlet temperatures
Ti_c = 147;
Ti_c = (Ti_c-32)*5/9; % convert to C

Ti_h = 150;
Ti_h = (Ti_h-32)*5/9; % convert to C

% 'required' outlet temperatures
To_c = 149;
To_c = (To_c-32)*5/9; % convert to C

% flow rates
VFR_h = 10; % hot side volumetric flow, in gpm
VFR_c = 2; % cold side volumetric flow, in gpm

MFR_h = VFR_h * 3.7854118 / 60; % mass flow rate in kg/s
MFR_c = VFR_c * 3.7854118 / 60; % mass flow rate in kg/s

% pipe geometries (meters)
OD_i = 0.0127;
ID_i = 0.01143;

OD_o = 0.022225;
ID_o = 0.0205994;

% constants for ~60 C water
Cp = 4180;
rho = 983;
mu = 467E-6;
k = 0.65;
Pr = 2.99;

% calculated required heat transfer
q_req = MFR_c * Cp * (To_c - Ti_c);

% calculated heating water outlet temp
To_h = Ti_h - q_req/(MFR_h * Cp);

% calculate the log mean temp delta
delT = ((Ti_h - To_c) - (To_h - Ti_c)) / log((Ti_h - To_c)/(To_h - Ti_c));

% calculate reynolds number
Re_c = 4*MFR_c / (pi*ID_i*mu);
Re_h = 4*MFR_h / (pi*(ID_o - OD_i)*mu);

% calculate nusselts number
Nu_c = 0.023 * (Re_c^0.8) * (Pr^0.4);
Nu_h = 0.023 * (Re_h^0.8) * (Pr^0.4);

% calculate convective coefficient
h_c = Nu_c * k / ID_i;
h_h = Nu_h * k / OD_o;

% overall heat transfer coefficient
U = 1/(1/h_c + 1/h_h);

% calculate required length
L = q_req / (U * pi * OD_i * delT);

% required length in feet
L = L * 3.28

 

if you don't have matlab, Octave is a GNU alternative to matlab that it should run on.

And a quick shout out to all my fellow matlab jockeys...

 

edit: accidental dual post

 

Best placement of probe in hlt? Using an element to heat.


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In process control systems that involve fluid recirculating, temperature monitoring is usually done in the plumbing instead of in the kettle. This helps avoid temperature misreads due to stratification (layering).

So put it in the HLT kettle output, and recirculate all the time when heating.

Kal