Not sure I understand proper probe placement with HERMS...

Been doing a lot of research lately on building an electric HERMS setup, but the one thing I'm not sure I "get" is where the mash temp probe should go. It seems to be that the commonly accepted locations are the HLT itself and at the point at which the wort re-enters the MLT from the coil (am I right to think this is generally accomplished with a T-fitting?)

What I can't get my head around is why the MLT probe isn't in the main vessel itself. Is there not a significant temperature difference between the wort as it exits the coil and when it it is finished running through the fittings/tubing/return system and is sitting back in the main liquid volume?

It seems to me that putting the probe in the MLT itself would possibly cause the HLT to heat up more than it would in the "typical" situation, as it would be trying to heat the entire volume of the MLT based on the feedback from the probe; this would likely mean a significant higher temperature of returning wort as it leaves the coil.

I've also thought that you could run TWO probes -- coil exit and MLT main -- and "average" them using logic in BCS; "splitting the difference," as it were.

Does anyone have some insight for a very confused HERMS newbie?

I have the sensor in the hlt. It works great that way. I also have a sensor directly in the mash but just to check temps. It does not control anything.

HERMS coil exit is the most accurate location to identify actual wort temperature. Mash Tun Kettle is the most accurate location to measure actually mash temperature.
3 sensors would be the best scenario: HLT kettle, HERMS coil exit, MT kettle. The purpose of the PID is to prevent temperature spiking so that the HLT does not overheat.

Thanks for the input, guys. OHG, do you have any experience with BCS builds? Would the logic run that the average of Coil Exit Temp and Mash Temp (say, 158 and 150, averaging 154) would control the HLT's heating element to keep the HLT temp at whatever might be appropriate (say, 166) in order that the "average" temp stayed steady at 154 -- which, let's say is your desired mash temp.

Yes, we have done a few BCS systems. RIMS and direct fire. So far, no customers have actually ordered a HERMS system manual or otherwise.
I think averaging the Coil Exit and the grain temperature would be better. It's the actual grain temperature that is the final target.

What would really be nice is to have the funds to test different scenarios.

In practice what I've found is that monitoring the HEX out/mash in is the most accurate as it's the highest temp your wort will be in the process.

Measuring the MT or averaging would be innacurate as when you do ramps there's a natural lag time between changing the wort in temp and seeing it trickle down through the mash.

Rice hulls, stirring during ramps, and thinner wort are how you minimize the issue.

I don't seem to have a problem with using the probe in the hlt. The mash is 1 degree cooler than the hlt so it's easy to dial in a temp. When ramping I do watch the temp display for the mash tun because it does not heat up as fast as the hlt.

JRems said:

I don't seem to have a problem with using the probe in the hlt. The mash is 1 degree cooler than the hlt so it's easy to dial in a temp. When ramping I do watch the temp display for the mash tun because it does not heat up as fast as the hlt.

Click to expand...

That makes sense. Does that mean that your controller (BCS, PID, etc) monitors the HLT probe and cycles the element to maintain that temp? So if you wanted to mash at 152, you'd just set your HLT for 153?

I have been using a HERMS for about a year. I built my system to incorporate constant recirculation. While helping a pro brewer in town I noticed how clear his wort was going in to the boil kettle and he attributed it recirculation. I have a copper coil in my HLT with an analog thermometer monitoring the water temp in the HTL. I am using a Gott 10 gallon cooler with a copper baffle as my mash tun. The tun has an analog thermometer that monitors aprox the middle of the grain bed. The HERMS uses two 12V DC valves that are controlled with a PID. The valves allow me to control the flow of wort through the coil or bypass depending on the temp of the mash. This allows me to do step mashes rather easily. I can strike to hit 122deg mash and then run the HTL up to 177 - 180 while the mash is resting at 122. All the while recirculating. When the the rest is finished (15 -20 min) the valves open and allow the wort to pass though the coil. At 180deg HTL I can usually hit 152 in the mash tun in 10 - 15 min. (all depends on the mash volume). I usually run a thinner mash then 1.3 qt/p after reading a lot of info posted by Kai.

I will say that after reading a ton of info over the past few weeks I am going to move my probe to the output side of the HEX. For some unknown reason I put it on the output side of the tun. It works "ok" but I feel I get a little bit more temp lag then I would if I monitored the output of the HEX but I have no proof to back that up. I think I am going to move the probe and see what the difference is. I will say that I don't think I would build a system without a way to monitor the middle of the mash. After all it is the grain that is doing the conversion. I have a system that allows for full auto or full manual control. This way is something goes aery I can quickly take full control.

I really don't think there is a right way or a wrong way just YOUR way. As long as you get the results YOU want then you are doing it right.

Geordan said:

That makes sense. Does that mean that your controller (BCS, PID, etc) monitors the HLT probe and cycles the element to maintain that temp? So if you wanted to mash at 152, you'd just set your HLT for 153?

Click to expand...

Yes correct, if I want my mash at 152 I will set the pid to 153. It's usually about 1 degree difference at most 2. I have a temp probe in the mash tun just to make sure. I constantly re circulate and have found a thinner mash easier to work with. Also rice hulls do help.

I have been using a HERMS for about a year. I built my system to incorporate constant recirculation. While helping a pro brewer in town I noticed how clear his wort was going in to the boil kettle and he attributed it recirculation. I have a copper coil in my HLT with an analog thermometer monitoring the water temp in the HTL. I am using a Gott 10 gallon cooler with a copper baffle as my mash tun. The tun has an analog thermometer that monitors aprox the middle of the grain bed. The HERMS uses two 12V DC valves that are controlled with a PID. The valves allow me to control the flow of wort through the coil or bypass depending on the temp of the mash. This allows me to do step mashes rather easily. I can strike to hit 122deg mash and then run the HTL up to 177 - 180 while the mash is resting at 122. All the while recirculating. When the the rest is finished (15 -20 min) the valves open and allow the wort to pass though the coil. At 180deg HTL I can usually hit 152 in the mash tun in 10 - 15 min. (all depends on the mash volume). I usually run a thinner mash then 1.3 qt/p after reading a lot of info posted by Kai.
I will say that after reading a ton of info over the past few weeks I am going to move my probe to the output side of the HEX. For some unknown reason I put it on the output side of the tun. It works "ok" but I feel I get a little bit more temp lag then I would if I monitored the output of the HEX but I have no proof to back that up. I think I am going to move the probe and see what the difference is. I will say that I don't think I would build a system without a way to monitor the middle of the mash. After all it is the grain that is doing the conversion. I have a system that allows for full auto or full manual control. This way is something goes aery I can quickly take full control.

I really don't think there is a right way or a wrong way just YOUR way. As long as you get the results YOU want then you are doing it right.

Click to expand...

msjulian
I know this is reviving a pretty old thread, but I was wondering how your sensor placement worked on the coil exit with the PID controlled HERMS bypass, I made a very similar system and am struggling to get my PID dialed in correctly. I am using it in on-off mode. Would you mind sharing your hysteresis and cycle time settings? Thanks!

Since moving the RTD probe to the HTX output things have started to run really smooth. Just as JRims stated in his last post, with the HLT water held @ 170 deg, I set the PID to 153 deg to hold a 152 deg mash. After dough-in the controller switches the valves very frequently and after about 10 min the grain temp has settled in and the valves slow down considerably. I can hold the temp in the tun to +/- 1 deg for 90 min with no intervention on my part at all.

I am running the PID in on/off mode with a 0.2 hysteresis. I have just switched out my 10 gallon gott cooler for a keggle and plan to brew the christening 10 gallon batch this week so I will see if I need to make any changes to the PID to keep things where I want them.