Hydronic System Flow from Load and Delta-T
The most fundamental hydronic number, which every balancing valve, pump, and pipe size starts from: GPM = Q / (500 dT) from Q = 500 GPM dT for water, or the chilled-water shortcut GPM = 24 tons/dT. A 10-ton coil at a 10 F design delta-T needs 24 GPM; a 100,000 Btu/h boiler at a wide 20 F delta-T only 10 GPM - the delta-T is the lever that shrinks the pump and pipe for the same load. Pure water at the sea-level factor (adjust for glycol); full load on the delta-T. A design aid; the mechanical engineer of record governs.
Formula and source
Q_btuh = (unit == tons) ? load x 12,000 : load; GPM = Q_btuh / (factor x dT); chilled-water shortcut GPM = 24 tons/dT (water).
The water-side sensible-heat transport Q = 500 x GPM x dT and its rearrangement to the design flow, with the chilled-water 24 tons/dT shortcut and the glycol-lowered factor, a standard hydronic relation, by name.
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