737 aircon recirculation fans (fuel consumption?, hold temp?)
Looking in the MEL, there is no performance penalty if the recirculation fan is inoperative. That despite the system description says it lowers the bleed demand and hence fuel consumption.
For lack of better, the 737.org.uk website has the following information:
A pack in HIGH flow will produce more cold air than normal, but has a 25% higher bleed air demand ..... The recirc fan will switch off if either pack is in high flow, giving a net reduction in the ventilation rate of 15%, so best cooling is achieved with pack(s) AUTO and recirc fan(s) ON.
So the big question is does it lower the fuel consumption during flight at all?
Or does it only increase the cooling capability and possibly fuel consumption when a high cooling demand (normally on ground) is needed? Consequently, during flight with a low cooling demand, does it make a difference if it's on or not?
The other question is how the temperature in the forward hold (for our four-legged friends) is influenced by the recirculation fan? Would it be warmer, colder or no difference with the fan off?
Any sources for reading, experience with the matter or logical reasoning appreciated...