I’ve always seen 400 cfm/ton justified by delivering about 55°F supply to hit a sensible heat ratio around 0.75 on legacy coils. Does anyone have a primary source (ratings manual or standard from the 1950s–70s) for that number — and data showing when 350 or 450 cfm/ton is more efficient once you include fan kW and latent load?
I’ve had the best luck pulling old coil tables (Trane Engineering Data and Carrier System Design Manual reprints) and plotting SHR vs cfm/ton with the unit’s fan curve; when I do that, 350 cfm/ton often beats 400 once you include fan kW in humid rooms, but 425–450 wins on dry loads — the “55°F supply” point is near the crossover. If you can get those tables for your coil, a quick spreadsheet will show net sensible kBtu per kWh at each airflow and make the tradeoff obvious.
Closest primary I’ve found is the ASHRAE 1967 Guide & Data Book (Equipment): coil tables at 80/67 show about 55°F leaving around 380–420 per ton with SHR about 0.72–0.78 — , the lack of one “origin” doc drives me nuts. For the 350 vs 450 part, run a quick bin-hour with your blower’s W/cfm; once you’re above about 0.25–0.30 W/cfm and wet-coil, 350 often wins in humid climates, while 450 can edge it in dry. @lgreen346 and here’s a starting point: Internet Archive: Digital Library of Free & Borrowable Texts, Movies, Music & Wayback Machine.
I’d look at ARI 210–69 plus the 1967 ASHRAE Guide (Equipment) — the 80/67 and 95 rating points are what anchor about 55°F supply and the familiar per‑ton airflow. Practical step: plot net EER vs airflow using your fan W/cfm and design latent; humid climates often tip it a bit lower, dry loads a bit higher, because fan watts aren’t free. Do you have fan W/cfm and target indoor RH, @olimart?