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Estimating Flow & Buffer Effect

I recently posted a set of radiator surface (and some return) temperatures to correspond with a period of Vitodens operation.

Gravity conversion system with no low-loss header and only the built-in variable speed circulator.

Have been trying to estimate flow using these temperatures and estimated output. Was using the "ABCs of return temperature" to verify the computation. I know the TRUE system return temp.

No matter how I estimated the return temps of those not measured and no matter how I computed delta-t, the numbers were impossible--the system return temperature came out WAY too low compared to the actual and the flow rates were either too high or too low.

I'd forgotten something: the heat coming out of the piping! Even though it's reasonably insulated, there's certainly some heat being given off and I've also left them uninsulated inside the garage.

There was also the "little" problem of about 4,000 "missing" BTUs when comparing boiler output to estimated radiation output.

So, I assumed 2/3 of the "missing" output was being given off by the supply side and the rest by the return side.

The numbers worked both for flow and for calculating the return temp! BUT ONLY IF:

1) I give the supply piping the delta-t as measured between the difference of supply temp and that reported by the boiler.

2) I use the supply temperature that I measure for the radiation.

3) I give the return piping the delta-t as measured between the return temp near the boiler and the highest return temp measured from the radiation (only 2° BTW).

Does this "prove" that the Vitodens has turned the main piping into a buffer???


  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
    Wrong! Wrong! Wrong!

    Woke up this morning realizing that I couldn't give any flow to the mains themselves--just heat loss. UGGH! How can I be so stupid?

    Am going to make sense of these numbers yet!
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