Panasonic S-36PU1E5A Technical Data & Service Manual page 385

Restriction on the number of passes of the heat exchanger hairpin
Minimum number of passes
= Number of steps × Distance between tube sheets × Number of rows × 1.5 ×10
<For example>
Number of steps :
Distance between tube sheets
Number of rows :
Minimum number of passes = 12 × 1000 × 3 × 1.5 × 10
12
: 1000 [mm]
3
-4 = 5.4 < 6 passes
1-375
-4
1