|Aug5-04, 08:18 AM||#1|
Sizing Secondary Systems
I would like to get some opinions on secondary circulator and piping design for heating system.
Two (2) boilers each one is 75% of building total heating load. Each with a secondary circulator pumping to a manifold into a primary loop. The return piping comes from a second manifold adjacent to to supply manifold.
Primary loop with two (2) parallel circulators moving the heating water 100% of the heating load using a 20 deg F TD to the building and through the equipment.
Okay, the boiler manufacturer suggests the formula:
Gross Output BTUH/(Temp Rise x 500) = Secondary gpm
Temp Rise = 230 deg F - Return Water Temp
I know that the boiler can handle higher flows than will be obtained through this formula (with a 70 deg Temp Rise and a 515,000 btuh boiler I only get 14.7 gpm).
So which is better, use less water at higher temperature, or use more water at lower, closer to system, temperature? Or is it best to figure a compromise and go with that? Say a 40 deg F or 50 deg F temperature rise in the boiler?
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