Boiler supply temperature sensing

gpjazz

This is in regards to a recent job that has been completed. I have 3 boilers connected to a single zone system for the building, and have a Tekmar 294 boiler control system.

The system is working well overall, but on occasion, it seems that the supply temperature reading displayed on the Tekmar is a bit off.

So on the attached drawing, where should the sensor be located for supply water temperature ??

boilers and piping.pdf

gpjazz

This is from the Tekmar manual…
The Universal Sensor should be placed downstream of a pump
or after an elbow or similar fitting.

And also from manual…

The included Universal Sensor can measure the boiler supply temperature of water coming from the boiler
system. This sensor should be installed on the supply pipe ahead of the tees supplying any loads.

hot_rod

with those bypass valves on the boiler supply, I would put the sensor downstream of those check valves.

They should have insulation over the also.

gpjazz

Let me clarify… There is only one single supply temperature sensor for the Tekmar to monitor "SYSTEM" supply water temperature. So the sensor should be somewhere on the main piping, or technically the "secondary" loop. Isn't that correct? My question is where on the main piping

hot_rod

Looks like only one sensor, boiler sensor which would go on the piping at the top of the drawing.

But one drawing in the manual seems to show sensors at all the boilers?? Where would those wire to?

As for the two loops. The loop that has the expansion tank connected is the primary loop. So the boilers are actually secondary loops.

jesmed1

I just installed a Tekmar 256 on my sister's boiler. The Tekmar 256 is a simpler version of the 294 with the same sensors. If you read page 8 of the 294 installation instructions, it says:

"The Universal Sensor should be placed downstream of a pump
or after an elbow or similar fitting. This is especially important if
large diameter pipes are used as the thermal stratification within
the pipe can result in erroneous sensor readings. Proper sensor
location requires that the fluid is thoroughly mixed within the
pipe before it reaches the sensor."

This may be your poblem, that you have piping in the main circ loop big enough that thermal stratification is happening, throwing off the temp reading. So you want to follow their instructions and place the sensor just after the main circ or an elbow in the main loop. The circ will cause turbulence that disrupts any stratification, creating a uniform average temperature of the supply flow right after the circ. So that's the best place for the sensor. The next best place would be just after an elbow, which will also cause turbulent mixing that breaks up stratification. (You'll notice that all the diagrams in the manual show the sensor installed right after an elbow.)

As others say, cover it with zip-tied pipe insulation. In that location and covered with insulation, it will give good temp readings of well-mixed supply water that hasn't been stratified.

I would also mention that even with the sensor in the correct location, you may see a 10-degree or more difference in the Tekmar sensor temperature vs. the boiler tridicator temp reading. On my sister's boiler, the tridicator reads 10 degrees or more higher than the Tekmar sensor that's right at the boiler supply output. I actually trust the Tekmar sensor more than I do the tridicator, because I know the tridicator pressure gauge is also not very accurate. So if you see a (for example) 10 degree difference between the boiler gauge and the Tekmar reading, that doesn't necessarily mean the Tekmar sensor is wrong. You can double check the Tekmar sensor by wrapping black electrical tape around the (presumably copper) pipe next to the sensor and shooting the tape with a cheap IR thermometer. You should get pretty close to the same temp reading as the Tekmar.

jesmed1

109A_5

One sensor, I would say here.

EBEBRATT-Ed

I would put it next to the High Limit

109A_5

https://forum.heatinghelp.com/discussion/comment/1907531#Comment_1907531

Why ? The manual clearly shows it before the main circulator and after the closely spaces tees and after the elbow. Maybe between the 2nd elbow and the main circulator would be better.

hot_rod

Downstream of the loop pump would be my choice, so the circ stirs the blended temperature happening at the close tees

You may have more purge ports than you need? Upper left you could pump into, purge from upper right.

EBEBRATT-Ed

Just makes sense to me to put the operating control next to the high limit so they sense the same temperature.

109A_5

Having a high limit down stream from a circulator that could fail seems a bit curious to me.

That High Limit connects to what ? Some burner control loop for all the boilers. I don't see a High Limit on the Tekmar 294.

hot_rod

https://forum.heatinghelp.com/discussion/comment/1907584#Comment_1907584

yeah, I don’t see the purpose of the high limit. I would guess the boilers include that function in their control string.