Buffer Tank with Distribution-Loop Credit

Gross V = on_time x (source_min - zone_load) / (500 x delta_T), loop water = 0.0408 x d^2 x L gal, net = max(0, gross - loop). A fat, long common primary loop already holds gallons that count toward the anti-short-cycle volume, so the tank you actually buy is smaller -- or unnecessary. A sizing aid, not the manufacturer's data.

gross_buffer_gal = min_on_time_min x (source_min_btu - zone_min_load_btu) / (500 x delta_t_f); loop_volume_gal = 0.0408 x pipe_id_in^2 x loop_length_ft; net_tank_gal = max(0, gross_buffer_gal - loop_volume_gal).

ASHRAE / Idronics (Caleffi) anti-short-cycle buffer-tank practice, by name.

The buffer-tank sizing relation and the pipe-volume geometry are standard hydronic design practice; the equipment minimum-cycle data and the manufacturer govern.

Estimate. AHJ and licensed professional govern.

Field names used by the API: min_on_time_min, source_min_btu, delta_t_f, pipe_id_in, loop_length_ft, gross_buffer_gal, loop_volume_gal, net_tank_gal

• Loop coupled to buffer credit only the water in a common primary loop hydraulically coupled to the buffer; a decoupled secondary does not countIdronics / Caleffi
• 0.0408 gal/ft/in^2 pi/4 x (1/12)^2 ft^2 x 7.48 gal/ft^3 = 0.0408 gal per ft per square inch of internal diameterpipe geometry