Two 120mm Case fans

[GreatBarracuda]

I just got another 120mm thermally-controlled fan in addition to my 120mm case fan which is not thermally controlled. Now, which would be better...the thermally-controlled at the front and the non-tc at the back or vice versa? Or does it even matter?

 

[akseli]

Originally posted by: GreatBarracuda
I just got another 120mm thermally-controlled fan in addition to my 120mm case fan which is not thermally controlled. Now, which would be better...the thermally-controlled at the front and the non-tc at the back or vice versa? Or does it even matter?

You SHOULD technically run both fans at the same speed so that you don't create a vacume inside your case (more going out than coming in) in which case (NPI) you would end up with air getting sucked in through every hole (not good dust wise) ... on the other hand if you have more air getting pushed in your case than is going out, you'll end up with patches of non-moving air causing heat build up. So technically you should have the same amount of air pushed out and sucked in.
Thus, it doesn't really matter if you have the thermally controlled at the front or back as you should have it running at the same speed as the other fan in yoru case.

(altough many may argue, it is from personal experiece that I tell you, if you are to have either a vacume or an excess it is better to have a vacume as this provides better cooling -- no flamming please, this is from personal experience, many of you may have had different experiences.)

 

[GreatBarracuda]

Ok, I just found out that the rear fan (the non-thermally controlled one) which came with the case runs at 1200 rpm constant. The new thermally controlled at the front usually runs at 1500 rpm and up. Therefore according to your logic akseli, I have more air being pushed in than is going out, so there is gonna be heat buildup? Hmm... Anyone care to verify this?

 

[akseli]

Originally posted by: GreatBarracuda
Ok, I just found out that the rear fan (the non-thermally controlled one) which came with the case runs at 1200 rpm constant. The new thermally controlled at the front usually runs at 1500 rpm and up. Therefore according to your logic akseli, I have more air being pushed in than is going out, so there is gonna be heat buildup? Hmm... Anyone care to verify this?

DOn't only go by RPM, also see if you can find the CFM ratings for each fan and try to have them equal up in both directions. (sometimes you can have slower moving fans move more air due to better design)

 

[GreatBarracuda]

Good point, I totally forgot about the CFM, which is what matters! Anyway, the CFM for the tc fan is 54 and up and the non-tc fan has 56 CFM constant. So the tc fan almost always moves more air than the non-tc. So it's a good idea putting the tc at the back and the non-tc at the front...right?

 

[akseli]

Originally posted by: GreatBarracuda
Good point, I totally forgot about the CFM, which is what matters! Anyway, the CFM for the tc fan is 54 and up and the non-tc fan has 56 CFM constant. So the tc fan almost always moves more air than the non-tc. So it's a good idea putting the tc at the back and the non-tc at the front...right?

No, personally I'd put the one with MORE CFM at the back and the lesser of them at the front ... anyway, I doubt that 2 CFM will make that much of a difference so they should work both ways ... but the positive on putting the thermally controlled at the front is that you can then lessen the speed, and eventhough that would create a vacume, you would still be getting adequate cooling because the case would pull air from other holes in the case.

(personally I'm running an Antec Sonata with one 120mm fan at the rear and no intake, which means that I have a vacume in my case, but eventhough this is happening my cooling is adequate.

 

[akseli]

Ok, one correction, I don't think that you could classify it as a VACUME now that I think about it... it should be refered to as NEGATIVE PRESSURE, inside the case ... because a vacume would mean no air or anything, which obviously is not the case.

 

[xbassman]

Another thing to consider...

Most of the thermally controlled fans don't speed up until around 40-50C.
Depending on where the sensor is, it may never run higher than minimum.

 

[GreatBarracuda]

Akseli, you said: "No, personally I'd put the one with MORE CFM at the back and the lesser of them at the front". That's exactly what I suggested. Remember, the tc fan is 54 and up and the minimum rpm is 1300 rpm. And with my case temps, it runs at 1400 and up, so its CFM is likely to be more than 56 which is the cfm for the non-tc fan.

Now that we got that cleared up, is it better to have a negative pressure or a slight-heat-buildup? Because with the negative pressure (more air going out than coming in), there's gonna be more dust buildup too because of the air coming in from all the nooks and crannies. But still, there's gonna be more air which is better for cooling.

Maybe I am fussing too much over this, but then again I am taking a break at work, so

 

[akseli]

Originally posted by: GreatBarracuda
Akseli, you said: "No, personally I'd put the one with MORE CFM at the back and the lesser of them at the front". That's exactly what I suggested. Remember, the tc fan is 54 and up and the minimum rpm is 1300 rpm. And with my case temps, it runs at 1400 and up, so its CFM is likely to be more than 56 which is the cfm for the non-tc fan.

Now that we got that cleared up, is it better to have a negative pressure or a slight-heat-buildup? Because with the negative pressure (more air going out than coming in), there's gonna be more dust buildup too because of the air coming in from all the nooks and crannies. But still, there's gonna be more air which is better for cooling.

Maybe I am fussing too much over this, but then again I am taking a break at work, so

Well personally I'd go with negative pressure and a faster dust build up ... all you have to do is buy a can of pressurized air and using that clean your case ... it's not much of a fuss, maybe 30 minutes if you do it very carefully without missing a spot

 

[Davegod]

2cfm isnt exactly going to be any problem, probably your psu pushes out rather more than that anyway.

generally though I'd have more air going out than being pushed in, if not the same each way. it wont create a vacuum, computer cases arent remotely airtight, it'll just mean slightly lower preassure and air will be pulled in through any holes going.

 

[akseli]

Originally posted by: Davegod
2cfm isnt exactly going to be any problem, probably your psu pushes out rather more than that anyway.

generally though I'd have more air going out than being pushed in, if not the same each way. it wont create a vacuum, computer cases arent remotely airtight, it'll just mean slightly lower preassure and air will be pulled in through any holes going.

Yes, I know, this is what I've been saying Anyway, I corrected myself with the vacume comment, it would just create negative air pressure causing air to get sucked into the case through all the little crevices causing a somewhat larger dust buildup inside the case.