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I hope I am not beating a dead horse.
This delta-T circulator question.
I admit that within a certain range of supply and heat loads, a delta-T pump can maintain that delta T. But I still do not understand why one would want to maintain a fixed delta T, or any other delta-T other than what would normally come out of a system.
I just calculated a little system that operated at 10 F delta T and at 1F delta T.
The results were as shown in the attached spreadsheet, if I can get it in here.
It shows that running with a lower delta T actually puts out more heat than at the higher delta T. A corollary is that for the same amount of heat as the 10F delta system puts out, you could run a fixed speed system at a lower supply temperature.
It says my .pdf is not a valid .pdf file. So here it is as straight text. I divided a 11 foot piece of baseboard into 11 1-foot pieces and calculated the temperature of each piece separately. I then looked up the BTU/hr/ft output from each section at that temperature. I had to interpolate (linearly) the in-between temperatures, since the charts do not show things that fine. So there as slight errors because the loss is not quite linear. But the errors should not be enough to upset the results very much.
Segment T BTU/hr/ft Segment T BTU/hr/ft
120 200 120.0 200.0
119 195 119.9 199.5
118 190 119.8 199.0
117 185 119.7 198.5
116 180 119.6 198.0
115 175 119.5 197.5
114 170 119.4 197.0
113 165 119.3 196.5
112 160 119.2 196.0
111 155 119.1 195.5
110 150 119.0 195.0
10 1925 1 2172.5
DeltaT BTU output Delta T BTU output