Fin spacing
Also known as: fin pitch
Short definitionThe gap between two fins of an evaporator or condenser, in millimetres. The colder the room, the wider the spacing; close fins for chill rooms, wide fins for freezer rooms.
Thin aluminium fins threaded onto the tubes enlarge the heat transfer surface. The closer the fins, the more surface fits in the same casing and the higher the capacity. With wide spacing there is less surface, but there is room for frost and air passes more easily. Evaporators use between 3 and 12 mm. A condenser does not frost, so its spacing is 2–2.5 mm.
The evaporator is chosen by room temperature. Rooms above 0 °C take 4 mm fins, rooms between 0 and −20 °C take 6 mm, and blast freezers and −30 °C rooms take 8–12 mm. The capacity of the same casing changes with fin spacing, so the quote must read the capacity of the right series. Put a close-finned evaporator in a freezer room and the fins fill with ice within hours and the capacity is lost.