HERMS temp probe placement? Help!

[Push Eject]

(snippage)
If i mount the temp probe at the sparge arm i would get the temp correct there but i am worried about denaturing the enzimes in the HE.

You will not denature enzymes in the wort from passing it through the HE coil. The heat gained by the pass through the coil is in turn passed in to the mash in a matter of a couple of seconds.

In general, for a TYPICAL HERMS and mash, the best placement of the sensor is either in the mash, near the FB/manifold, or at the MLT wort OUTLET. For larger mash tuns, like 125+ quart coolers, you can add a second sensor to the Ranco ETC (see wiring in operating instructions) to get an average mash temp. Placing it at the wort return will lead to very long ramp times. Note that I specified TYPICAL HERMS setups, with a fixed HLT setpoint, in which the controller swithes the pump or valves. There are designs in which the HLT temp is the controlled variable, in which case the wort return may make sense.

The keys to efficient heat exchange and being able to ramp up in a reasonable amount of time are delta T and flow rate. Assuming equal flow rates, the control scheme using a higher delta T (i.e. higher HL temp) will have shorter ramp times. I run my HL at 190 F until halfway through the ramp up to mash out. Then I lower the setpoint to sparge temp (170), and top off HLT with a small amount cold water if needed to get down to it.

Excellent post, Fletch. I'm going to recongieviate my rig based on this.

[fastdogbrewing]

(snippage)
If i mount the temp probe at the sparge arm i would get the temp correct there but i am worried about denaturing the enzimes in the HE.

You will not denature enzymes in the wort from passing it through the HE coil. The heat gained by the pass through the coil is in turn passed in to the mash in a matter of a couple of seconds.

In general, for a TYPICAL HERMS and mash, the best placement of the sensor is either in the mash, near the FB/manifold, or at the MLT wort OUTLET. For larger mash tuns, like 125+ quart coolers, you can add a second sensor to the Ranco ETC (see wiring in operating instructions) to get an average mash temp. Placing it at the wort return will lead to very long ramp times. Note that I specified TYPICAL HERMS setups, with a fixed HLT setpoint, in which the controller swithes the pump or valves. There are designs in which the HLT temp is the controlled variable, in which case the wort return may make sense.

The keys to efficient heat exchange and being able to ramp up in a reasonable amount of time are delta T and flow rate. Assuming equal flow rates, the control scheme using a higher delta T (i.e. higher HL temp) will have shorter ramp times. I run my HL at 190 F until halfway through the ramp up to mash out. Then I lower the setpoint to sparge temp (170), and top off HLT with a small amount cold water if needed to get down to it.

Excellent post, Fletch. I'm going to recongieviate my rig based on this.

Agreed, though I still contend that the temp at any point in the fluid path is not an accurate place to take the measurement. Let's say you read 154deg at some point. Once the fluid had reached the grain the temp may change. Now if you can calculate for this than you will be fine, but you do have to take into account the thermal losses. All of this added up to the process I chose. I measure at one point, the HLT, for control and monitor in the grain bed of the mash.

What it comes down to really is that any point you measure will require some level of compensation for thermal losses and gains. As long as you have figured out what they are for your system and have been able to get them to be constant you should be fine.