HERMS temp measuring questions

[drkwoods]

I have searched the board and it seems that measuring the temp at the HERMS exit is the best approach. I went ahead and ran a test measuring at three points every minute with the HLT burner on medium flame.. My system is a 3 sanke systme with 50 feet of copper coil tubing heat exchange in the HLT. The MLT has no direct heat source. I have calibrated the thermometers which are mounted in the MLT and HLT at the same place. I measured the HERMS exit with an instant read digital thermometer at the exit of the hose where it would attach to the sparge arm..

My concern is the big differences in the MLT and HERMS exit temps.. I knew the HLT would be hotter. What should I rely on and how should I run this set up??

I enclosed a graph of my findings and pics of my system

 

[stevehaun]

Looks like you have a great system. Your data is exactly what I would expect. You should have a temperature gradient between HLT and HERMS coil and between HERMS coil and MLT.
In my system, I put the temp probe from the temp controller between the HERMS coil and the MLT. I measure the temp at the output of the MLT and I also put a floating thermometer in the mash. I have to set the temp controller 4F above mash temp to maintain the desired mash temp. There usually is a 1-2F gradient between mash temp and MLT output temp.
It looks like you would need to maintain your HLT temp about 10F above desired mash temp. Alternatively, you could maintain your HERMS exit temp about 5F above desired mash temp. Good luck and go make some beer!

 

[drkwoods]

so the temperature that counts the most is one from the MLT. If I want to hit 154 I need that thermometer to read 154. It looks like my gradiant is about the same as your 4 degrees. Im curious if the floating thermometer would be any different then the temp down at the Blichman Dial thermometer probe? Also..What if I add a wool insulation jacket around my MLT do you think that would alter the gradiant or would it simply save me heating my HLT more often?

 

[stevehaun]

Yes, the mash temp is what you are attempting to control. I am not sure you need more than one thermometer in your mash tun. I measure the temp of the mash tun output (bottom drain) and the temp of the upper part of the mash with a floating thermometer. The gradient between the top and bottom of the mash will be directly proportional to thermal mass of the mash/flow thru HERMS. A large mash with low flow thru the HERMS will lead to a larger gradient than a small mash with high flow thru the herms. Your 50 foot coil is probably much longer than needed. The longer the coil, the higher the resistance. Higher resistance = lower flow rate. What is OD of your coil?

 

[drkwoods]

its 50 ft of 1/2" copper tubing (an old immersion chiller)

thanxxxx for your help

I want to hit mash temps right on and not have big flucuations in the grain bed. I wasnt sure if the mash while running through the coil was the temp I want to hit or if the grain bed was what I want to hit for a 154 degree mash.. Cause the temp is rising above the Mash temp while flowing thru the coil..

Next I need to decide if I want to control the pump automatically or the HLT flame. Im going to go ahead and add the insulation on the MLT to reduce heat loss and then retest everything.

 

[jvino]

Just to clarify, is the grain bed or the hex output monitored as the "mash temp"??

 

[drkwoods]

my first batch I monitored the grain bed thermometer in the MLT. But when I ran these tests I noticed how much hotter (~5 degrees) the Hex out put thermometer was reading and got to wondering which one is giving me my "true" mash temp.. I suppose its the obvious, the MLT prob at the bottom? (which in the first pic is the middle keggle). the shorter one)

 

[jvino]

I wonder if the temps would equalize within a reasonable amount of time?? I always thought that people monitored the hex output and called it the mash temp. Now I'm confused. I was planning on monitoring both temps in the BCS anyway but which is right??

 

[stevehaun]

I control the hex output but I measure the mash temp. Because of heat loss, most people need a small gradient 1-4F between the hex output temp and the desired mash temp. At the end of the day, what matters is the mash temp.