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Estimating Flow & Buffer Effect
Mike T., Swampeast MO
Member Posts: 6,928
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 lowloss header and only the builtin 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 deltat, the numbers were impossiblethe 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 deltat 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 deltat 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???
Gravity conversion system with no lowloss header and only the builtin 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 deltat, the numbers were impossiblethe 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 deltat 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 deltat 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???
0
Comments

Wrong! Wrong! Wrong!
Woke up this morning realizing that I couldn't give any flow to the mains themselvesjust heat loss. UGGH! How can I be so stupid?
Am going to make sense of these numbers yet!0
This discussion has been closed.
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