ADPI Room Air Diffusion Selection (ASHRAE)
Whether a supply outlet will actually mix the room, by the ASHRAE Air Diffusion Performance Index: the ratio of the catalog throw T to the room's characteristic length L predicts the ADPI, and each outlet type and cooling load has a T/L for maximum ADPI and a band over which ADPI stays above the comfort threshold. A round ceiling diffuser peaks at T/L = 0.8 (ADPI 88 at a 40 Btu/hr-ft^2 load); a high sidewall grille wants ~1.8 but a heavy 80 Btu/hr-ft^2 load caps it at ADPI 68 no matter the throw - the load, not the outlet, sets the ceiling. Reproduces the ASHRAE Fundamentals selection table (Miller/Nevins, throw per Std 70, ADPI per Std 113). A selection aid; the manufacturer's data and the design engineer govern.
Formula and source
ratio = throw_ft / char_length_ft; look up the ADPI table row for the outlet type and nearest cooling load (20/40/60/80 Btu/hr-ft^2); in_band = band_lo <= ratio <= band_hi; target_throw = opt_ratio x char_length_ft.
ASHRAE Handbook -- Fundamentals, Space Air Diffusion chapter, the ADPI (Air Diffusion Performance Index) Selection Guide table (throw per ASHRAE Standard 70, ADPI per ASHRAE Standard 113; the Miller / Nevins Kansas State research), by name.
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