Return Line Radiator?

JohnLaPlante

Hi all,



While calculating the total radiation I have for another thread, I came across something interesting...



One of my radiators is not fed by the main steam supply header.  It is fed by a return line from one (or two, I can't tell) radiators from the upstairs.  The line going in to the radiator does not have a steam supply valve like the other rads...the pipe goes into the bottom of the radiator and exits the other side, again at the bottom.



What kind of radiator is this?  I can hear rushing water in the pipe that feeds this rad, so I'm thinking it's water in there.  It sure makes sense, but it was something I wasn't ready for. 



Would this kind of radiator count towards the EDR of the system?

Brad White

If it is

below the waterline, yes, just a way to squeeze more useful heat out of a system, to heat the caretaker's apartment or workshop for example.  I would think of it as a bulge in the return line, sort of an after-cooler for the condensate which will help heat a space on the way back to the boiler.



If you are using your radiation measurements (EDR) to size a new boiler, I would first take this one as a hot water radiator sized for hot water (150 BTUH per SF at 170 average water temperature), because it does impose a heating loss to the system, even if on the sensible side.  At the least, you will know what capacity it would give to your space.



If a single radiator do not see it having so great an effect on your total boiler EDR however, because sensible heat (the water side in a steam a boiler system) is only worth 142 BTU's per lb. whereas on the steam/vapor side it is worth 970 BTUH, more or less, per lb.  (The 142 is the temperature difference between 70F in a room and 212 being the boiling point).



EDIT: More accurately, the actual load in BTU per lb. of the condensate would be even lower, because the returning water would never be cooled to room temperature (say 70F), but would probably be 140 to 160 depending on flow rate at the time. Thus your actual BTUH per lb. of the water-side might be half of what I stated,  say 72 BTUH per lb.) Another reason to not worry as much about this load vs. the boiler steam side.





If in doubt, figure it both ways, (as if steam-side and then not) and see if it brings you over to the next size. Even if it did, the losses happen on the water or sensible side of the process. I would not be concerned about it, if only one radiator. It would be absorbed into that 1.33 IBR factor.