Evaporator Design TD and Humidity Band
DTD = box temp - saturated suction, which sets the box humidity: <=10 F ~90% RH (produce), 12-16 F ~75-80% (meat), >16 F <70% (frozen). A 35 F box on a 25 F SST -> 10 F TD, ~90% RH; a drying 17 F suction -> 18 F TD, <70% RH. A smaller TD needs more coil. The coil rating at the design TD governs.
Formula and source
DTD = box_temp - saturated_suction_temp; humidity band by DTD (<=10 F ~90% RH ... >16 F <70% RH).
The evaporator design temperature difference (DTD) and the resulting box-humidity bands, from refrigeration coil-selection practice, by name.
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