Air flow questions on Antec P182

[mis33]

I am building a new PC with Antec P182. It comes with 3 Tri-Cool fans and I think the air flow should be:
1. Top of the back panel - Exhaust
2. Top panel - Exhaust
3. In the lower chamber behind the PSU - ???

I plan to add a 4th fan in the top HDD cage to move air inside the case. How should I set the 3rd fan, exhaust or intake?

 

[ivanski]

Intake

 

[Russsl1]

I have the P180 and have four WD 320 GB drives mounted in the lower HDD bay. I have the third fan in the lower bay drawing over the HDDs and exhausting into the PSU. The PSU fan then exhausts out the back of the case.

I thought of using a fourth fan in the upper HDD compartment, but didn't add it. Having two fans drawing air in and I thought they would draw more air than the fourth could provide and maybe cause grill noise. I figured that I would have to decrease the upper and back fan speeds and increase the fourth's speed to balance the air flow. Also, having that fourth fan just inside the front of the case running full speed, I was more worried about the noise this fan would create.