What should my Delta T be ???

Norm Harvey

Couple of questions.

How are you measuring your domestic water temp?


Have you tried pulling the aquastat well out for inspection of the well, and as much of the coil as you can see? (I bought the testo combustion analyzer that came with the free fiber optic scope and it is awesome for stuff like that) I am wondering if you have any buildup on your coil preventing heat transfer.


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Shaun Anderson

What should my Delta T be ????

I have a Vitodens boiler, 15-60, hooked up to a Bock 119CT and I have a few questions. Tank setpoint is set @ 136 degrees and feeding the indirect with just 167 degrees max. We drained the tank 3/4 of the way down and filled it back up, tank temp was 73 degrees when I started my testing and with a Fluke temp guage on the supply and reurn my Delta T was just at best 9 degrees. Should I be seeing a better Delta T ?? In 40 minutes my tank temp went from 73 to 106 degrees all while my Delta T dropped. When the tank gets above 115 degrees the Delta T is no more than 2 degrees !!!! The reason for this post is because the Bock is always calling for heat and we can't find out why. Maybe some of you wallies can help me out.
This job is around three years old and on well water.

Thanks

Shaun Anderson

Mike T., Swampeast MO

Sounds to me like the indirect has FAR less heat transfer potential than the Vitodens "wants" to see.

Since it's a 15-60 without the built-in variable-speed circulator were you careful when it came time to mate the circulator with the specifications of the indirect? I kind of hate to say this, but could you even find specifications for the indirect germane to the operation of the Vitodens?

I'm going to paraphrase a bit here but Dan Holohan (owner of this website) once publically commented about the "worst" problem with Vitodens boilers and indirects is that typical North-American indirects lack the heat transfer ability ASSUMED by the Vitodens. The Vitodens really wants an indirect capable of INSTANTLY absorbing its MAXIMUM output. If the heat exchange ability of the indirect falls short the control system looses it...because it's A-#1 goal is efficiency. How do you efficiently deliver energy to an inefficient device?

Shaun Anderson

These reading are from the supply and return of the heat exchanger. The well for aquastat is replaced with Viessmanns DHW sensor and the boiler was reading tank temp while I was checking the temp through the heat exchanger. When we did drain the tank some sediment came out but very little. I was thinking the heat exchanger could be calsavide but I have no one to check. Any ideas ???

Shaun Anderson

Shaun Anderson

Grundfos UP26-64F is what both Bock recommends and Viessmann also for their equipment. We plan on replacing the tank with Bocks new SideKick unit. I have other jobs with the same boiler but 80CT and they work just fine. Could the heat-exchanger be caked with sediment on the outside of the heat-exchanger ???

Shaun Anderson