[SOLVED] Help with airflow and fan configuration

[CapitalFlight]

I am currently building my PC now and have stumbled on a roadblock.

I have a Define R6 case and a Corsair H100i Pro AIO (2x fans 240mm radiator).

The R6 comes with 2 intake fans at the front and 1 exhaust fan at the back.

I can put the radiator on the top of the case. However if I put them as exhaust, I have a negative power balance right (i.e. 2 intake at the front, one exhaust on back, and 2 exhaust with the radiator)? But if I put them as intake, does this cause too much of a positive balance (i.e. 2 intake at front, 2 intake with radiator, 1 exhaust)?

Essentially I have 5 fans, and 4 of them are stuck in a pair of 2. Given this, what would be the best configuration?

 

[jimmysmitty]

I would probably put the radiator in front with two pulling air in then two up top and one in the rear to pull air out. That would be the ideal configuration as it would provide the radiator the coolest air while pulling the warm out up the top and back of the system.

 

[CapitalFlight]

Hey, thanks for the reply.

Would that cause negative airflow though as it is more exhaust than intake?

 

[Imacflier]

Not trying to be a smart ass, but you CANNOT exhaust more than you intake!

Larry

 

[CapitalFlight]

Isn't that what negative airflow is?

 

[Karadjgne]

Heh. No. There's enough air gaps, vents, unused fan slots, cracks etc and case fans are not that strong. If air pressure is 14.7lbs in², in a positive case it'd be @ 14.701lbs in². In a negative it'd be 14.699lbs in². Seriously only enough to slightly affect smoke tests or microparticulate dust that's near a crack.

There's also discrepancies in fans. Some have higher cfm than others at different duty cycles. Your exhausts running at 40% with total of @60cfm might very well be less than the 2x inputs at 50% and a total of 70cfm. Net result is 2x 120mm inputs are stronger than 3x 120mm exhausts. Turn the fans up higher and that will change.

Considering there's no way to tell exactly how much each % of duty cycle affects any particular fan and the fan curves it's set to (only max speed stats are given) the only way to tell overall results is a smoke test. That's where smoke is allowed to waft low in back of the pc, under the gpu slot. If the smoke does nothing but waft, it's balanced. If it drifts to the pc or is sucked inside, you have a negative pressure system. If it's blown away from the pc, you have a positive system.

I have a define R5 that used to have a nzxt Kraken X61. It's been mounted as 2x exhaust with stock FD 140mm x2 intakes, it's been mounted as intake with fans in push (stick fans as exhaust) and as intake with fans in pull (easier cleaning). Moving from exhaust to intake, gpu gained @ 2°C, cpu dropped @ 2°C. Still only used 4x fans, didn't use any rear exhaust since heat rises and a 120mm rear would do nothing but try and steal the air from the closest 140mm exhaust at 90°.

 

[CapitalFlight]

Ok cool, thanks for the detailed reply.

So in that case would you suggest the best method is jimmysmitty's suggestion, i.e. put the radiator in front with two pulling air in then two up top and one in the rear to pull air out?