As it dawns on me–the volume is constant, since the length and size of the loop are constant, I dont have to divide the volume by 2 when the pump is halved. The average temp in the pipe, 113 with valve open, 123 when halved, represents the relative amount of btus transferred. The measurements say the water is hotter in the pipe when the pump is slowed.
But then you say
Hotter water is run through the system by speeding up the pump.
which contradicts the evidence: the ave temp is 10 deg hotter when the valve is halved.
It needs 30 degrees differential to work.
My system has worked during all but the coldest weather without that, but I’ll accept it as a standard.
What you want is to move water slowly enough so it allows stratification to exist in the tank and to ger a 30 degree differential between water leaving the tank and water returning to the tank. That should keep the tank firing…
At coldest outdoor temps it’s what I want, but at 30 deg, which is most of the winter, it gets too warm and I’m saying (please correct me) that speeding the water and reducing the ave temp in the loop might be more suitable at 30 deg outside.
Thanks again, Larry, for your expertise and forbearance. I’ve learned a bit that I will soon put to use and I agree that the terminology is the biggest block.