TD and SST
SST is the saturated suction temperature: the evaporating temperature of the refrigerant in the coil. TD is the air entering the coil minus SST.
A freezer at -10°F with a -20°F SST runs at 10°F TD. Every KUHLWERX table states the SST it was rated at.
Converting to your TD
Capacity is close to proportional to TD. A unit rated 20 MBH at 10°F TD delivers about 24 MBH at 12°F TD and 16 MBH at 8°F TD.
Lower TD holds room humidity higher, which matters for fresh produce and meat. Higher TD lets a smaller unit do the job but dries the room.
Fins per inch
Tighter fins pack more surface into the same coil. Frost bridges tight fins fast, so freezers use wide spacing.
KUHLWERX tables run 6, 4, 3 and 2 fins per inch. Rooms above freezing usually take 4 to 6. Freezers usually take 2 to 3.
Fan speed and throw
Dual discharge models list high and low speed ratings. Low speed trades some capacity for lower sound and air velocity. Throw is how far the air carries, which sets how long a room one unit can serve.
| Room | Typical fins per inch | Defrost |
|---|---|---|
| Above 34°F | 4 to 6 | Off-cycle or electric |
| Below freezing | 2 to 3 | Electric, hot gas or water |
| Blast freezing | 2 to 3, or variable | Hot gas or water |