Panel Radiator Head Loss

CapeCod

I would like to determine the correct setting for my 3 speed circulator on my TriangleTube 110 Boiler.  It was left on the highest speed by my installer but I suspect that is too much.  I think I have all the formulas I need but I am unclear on the head loss thru the panel radiators.  I have a value of .45 ft head @ 1 GPM from the Myson specs but how do I extrapolate that for higher flows?  I thought I remembered from a previous life that flow is proportional to the square of pressure drop but not quite sure.

SWEI

correct setting

Is the one that gives you the desired ∆T at high fire under load.  Measure that, and adjust until you get what you want.

CapeCod

desired delta T

Thanks...I've done a little experimentation but was just looking for some math to back up my findings.  I was shooting for 30 to 40 degree delta T and have gotten pretty close by moving it to the lowest setting.  I don't have all my heat emitters on line yet so I will have to re-evaluate again when that happens.  I did have some pretty loud expansion noises that seem to have gone away with the lower setting.  Are there any warning signs / side effects if I am running at too low of a speed? LIke I said, all seems to be fine now...delta T is OK, house is warm, no funny noises from the boiler.  I still have my short cycling issue but that is less of a concern now with the colder outside temps.

SWEI

speed too low

will eventually throw an error if the boiler sees excessive ∆T.  40F across an emitter is hard to achieve.  Remember that your effective system temp is the average of the inlet and outlet temps at the radiator, and then derate the capacity of the radiator using the Heat Output Adjustment Factors table (in the Myson tech spec.)  If you can get 30F and stay warm on a design day you're doing great.  May need to increase the supply temp in order to make it work (return temp drives condensation and efficiency, so don't be afraid of using a hotter supply temp than you originally planned for if the return temp is lowered.)

CapeCod

derate the capacity of the radiator

Thanks, sounds like I am on the right track.  I was a little concerned about decreasing the radiator output when increasing the delta T but so far so good.  I just looked at it this evening and it is getting 25 to 30 degree drop and I am only 10 to 15 degrees shy of a design temp day here.