Server Closet Cooling - Intake Fan Recommendations?

[svtkobra7]

I'm not sure if this is the correct forum to post, honestly couldn't find a better option, but here is the scenario:

• I have a server closet of 59 cubic feet that I need to manage temperatures for.
• Thankfully the ceiling of that closet extends to 100" and there is a 21.5" tall plenum above it of at least 454 cubic feet.
• I plan to exhaust the warm air from the ceiling into that space using a 100 CFM Bathroom Exhaust Fan (NuTone Model # 791LEDNT) and need your help in selecting an intake fan for floor-level (living area => closet). That exhaust fan has been installed (sheet rock not yet).
• Of course quiet and high CFM don't go hand and hand so I've had some trouble finding a good pick. The best I've come up with is a Broan 512, 90 CFM / 3.5 sonnes. Which I'm not in love with - the 3.5 sonnes concerns me as it is difficult to judge how loud that will be - the ceiling fan which I have installed is 1.5 sonnes and jumping up a bit scares me as that ceiling fan noise will be insulated by the fact that it is contained in the closet, but the intake fan will be positioned to the living area of my condo.

An illustration is attached and thank you in advance.

Oh by the way, server will be mounted by way of vertical wall mount rack (closet isn't deep enough for traditional horizontal rack).

 

[scrappy]

If you're worried about noise and airflow, why not mount four 140mm PC case fans together on a wood or metal plate of sorts, then install the assembly where a bathroom fan would be and connect them all up with a 120v Molex power supply adapter?

 

[svtkobra7]

@scrappy: Thanks for your reply.

If you're worried about noise and airflow, why not mount four 140mm PC case fans together on a wood or metal plate of sorts, then install the assembly where a bathroom fan would be and connect them all up with a 120v Molex power supply adapter?

• To clarify, I'm good with the exhaust (installed ... 1.5 sonnes / 100 CFM). That sound pressure level with the door closed is nothing more than soothing white noise. ;)
• I'm looking for an intake fan, specifically a through wall fan such as the one linked (unless a better option is presented). As noted, I can't have my cake and eat it too, i.e. high CFM, low dB, so there is an optimization problem here to find the suitable balance. Surely that approach proposed for an exhaust could work as intake as well. They actually made media / home theater cabinet fans such as the one you described, but I'm hesitant to go that approach for two reasons: (a) I'm not convinced they will move enough air and (b) in case my plan does not work as intended and keep the disks cool enough, I'd like to be able to easily run ducting from the inside of the closet (fed by that intake from the living area) and direct it to the top of the server (vertical mount if you recall). Easier to do with a 6" fan as 6" ducting is readily available (not to suggest your suggestion couldn't be adapted to work). Regarding point (a) I learned all too well that X CFM /= X CFM, where X is constant when comparing fans with the chassis fans on my SC836. Please correct me if I"m off target here.

I like the creativity ... other ideas? Thanks again.

 

[Redcoat]

Why not just have a "large" (= low velocity) intake grill at a low level and no intake fan? And/or go through the wall into the dressing room closet behind the server closet and put the air intake (and fan) in that closet to take the inlet noise out of the living area.

 

[wblock]

Are bathroom fans rated for a 24 hour duty cycle?

 

[svtkobra7]

Why not just have a "large" (= low velocity) intake grill at a low level and no intake fan?

• I like it and thought about it, but after my battle with the 836 over temps I thought I would need an active/active approach (intake/exhaust).
• As to not have to rip out more drywall, feed electrical, etc. in arrears is there any way to evaluate whether this would work in advance?
• Correct me if wrong, but the exhaust is much more important than intake right?

And/or go through the wall into the dressing room closet behind the server closet and put the air intake (and fan) in that closet to take the inlet noise out of the living area.

• Good idea as well. I had considered this, except I installed custom closets which leave but a very thin intake a floor level. Also, that closet is even closer to the bedroom.

 

[svtkobra7]

Are bathroom fans rated for a 24 hour duty cycle?

Damn - didn't consider that. How can I determine the answer? Worst case scenario, it dies, convection still drives warm air out of the exhaust (back draft damper remains slightly open), so exhaust would be a small fraction of with fan on, but fan mode script pushes the fans to "full speed" mode and it should be fine. Not sure if a script can be authored to shut down the server if temps get too hot. Don't see why not ... if HDD temps can act as a trigger to change fan speed mode.

 

[Redcoat]

• I like it and thought about it, but after my battle with the 836 over temps I thought I would need an active/active approach (intake/exhaust).
• As to not have to rip out more drywall, feed electrical, etc. in arrears is there any way to evaluate whether this would work in advance?
• Correct me if wrong, but the exhaust is much more important than intake right?

• Good idea as well. I had considered this, except I installed custom closets which leave but a very thin intake a floor level. Also, that closet is even closer to the bedroom.

The performance of any fan or fan system is significantly dependent on the resistance of the flow path as well, of course, of the characteristic(s) of the fan (and the fluid - air in this case). In your instance, if the exhaust fan has sufficient capability to move "enough" air through its inlet and outlet resistances, you could use a single fan.
The resistances I envisage from your description are the inlet grille/structure, the friction and velocity change as the air passes the obstruction of the sever structure in the cross section of the server closet, the exhaust fan inlet and exhaust structures and any associated ducting, and any resistance in the balance of the discharge system from the fan.
I believe where I would start would be the mounting of the server with the drive bays facing downwards in order to have the coolest air entering at the point expected by the design of the server's cooling fan system (I looked at the chassis manual). As well as the better cooling, you won't have the added dynamic resistance of the hot air discharge flow from the back of the chassis opposing and reducing the cold air flow coming in the other direction in the closet. I realize that's not convenient for drive installation/replacement of course.
Next I would look for an inlet grille with a free area at least as large as (the cross-sectional-area of the closet) minus (the cross- sectional-area of the server and any other equipment/obstruction you will mount in the space "alongside the server"). Choosing such a grille would mean that it is not the limiting resistance of the air flow system.
If that doesn't get you enough cold air then you will have to consider positively pressurizing the closet (seal the door...) by adding an inlet fan - just volume from a "whiffler" won't do it - you have to be able to raise the pressure at the exhaust fan inlet in order to get more through the system so a ducted fan using the large inlet you already have would likely be the best option - possibly a "large cross section" axial fan mounted horizontally on the outlet of a long radius ducting bend, axis vertical discharge up (the larger the fan the lower the speed and the lower the noise generated). I suppose that you might even try a good quality large "window fan" mounted in a masonite baffle if the suction-only system performance falls only slightly short of capability.
Good luck with this project. I'm close to moving all my stuff down into my basement to keep it cool in this old house - I'm fed up with shivering year-round in my office.

 

[Redcoat]

BTW, after @wblock's good ? I looked at the fan spec sheet - it's clear that the motor is not engineered for continuous operation.

 

[svtkobra7]

BTW, after @wblock's good ? I looked at the fan spec sheet - it's clear that the motor is not engineered for continuous operation.

What makes you suggest that? I don't doubt it, two members having suggested so, just curious for my own understanding. In the process of replying to your other post (thank you btw). That stinks regarding the fan, it was a PITA to get mounted and I was literally about to sheetrock that section (this weekend). Do you have a specific alternative you might recommend (beyond what you conveyed previously)?

 

[BigDave]

Oh by the way, server will be mounted by way of vertical wall mount rack (closet isn't deep enough for traditional horizontal rack).

Hot swap trays facing up, down, or to one side? Post pic perhaps?

As far as an intake fan, my suggestion would be an in-line blower like this, with flex duct to grill @ bottom
of closet door. Mount the in-line discharge @ the drive end of chassis blowing cooler air from floor level.
If exaust fan in ceiling is 90CFM, make intake CFM 100 or higher, keeping positive static pressure within.
The ducting (5-6ft.) from in-line blower to the door will lower the audible noise heard at the intake
grill in the bottom of door and allow door to open

 

[svtkobra7]

Hot swap trays facing up, down, or to one side? Post pic perhaps?

• You know I love posting pics! ;)

https://www.racksolutions.com/wall-mount-rack.html#

• Face of hot swap drives parallel to ceiling.
• @Redcoat recommended the reverse, which I completely agree with (trays on bottom / exhaust at top), save for the fact that there would be no way to mount this particular rack and then add the server AFAIK, i.e. if the rack is 29.95" tall, I would have to mount it at least 29.95" x 2 off the floor in order to be able to insert a server into it. A structured media center box (which I have moved once already), prohibits mounting that far off the ground.
• BTW the vertical mount is necessitated by the fact that the chassis is 26" deep and the closet happens to be 25.5" deep, so I've I ever want to close the door, I have to go with an "unorthodox" mounting approach.

As far as an intake fan, my suggestion would be an in-line blower like this, with flex duct to grill @ bottom of closet door. Mount the in-line discharge @ the drive end of chassis blowing cooler air from floor level. If exaust fan in ceiling is 90CFM, make intake CFM 100 or higher, keeping positive static pressure within. The ducting (5-6ft.) from in-line blower to the door will lower the audible noise heard at the intake grill in the bottom of door and allow door to open

• I like the idea, but thinking about how to deploy I struggle to think of how to do so.
• That fan is sure to be loud so I would want to but something like Roxul sound proofing insulation in between the studs to dampen and stuff the fan in the wall.
• But since the fan is 4" in diameter and 2" x 4" studs are actually 1.5" x 3.5", I can't think of a way to accomplish that.

 

[Redcoat]

What made me suggest it?: Broan NuTone spec sheet clip for your fan says

while I noted that the Home Depot link you provided had a bullet point: "Plug-in permanently lubricated motor is engineered for continuous operation"...

I did a quick Google search on "continuous duty range hood fan" - sixth item was the Broan High Capacity where I found the Broan Losone series which does have motors rated for continuous service. That range looks like it would meet your requirements - say the smallest one - the L200L. There will be lots of others similar - these items are something of a commodity. I see that Zoro has the L200L, also Grainger (but at higher $$). Home Dept and Lowes don't seem to carry them (although Lowes has the literature in its database) - these are H&V trade items.

 

[Redcoat]

• Face of hot swap drives parallel to ceiling.

• @Redcoat recommended the reverse, which I completely agree with (trays on bottom / exhaust at top), save for the fact that there would be no way to mount this particular rack and then add the server AFAIK, i.e. if the rack is 29.95" tall, I would have to mount it at least 29.95" x 2 off the floor in order to be able to insert a server into it. A structured media center box (which I have moved once already), prohibits mounting that far off the ground.

• BTW the vertical mount is necessitated by the fact that the chassis is 26" deep and the closet happens to be 25.5" deep, so I've I ever want to close the door, I have to go with an "unorthodox" mounting approach

Ahh, now I see your mount ... I had envisaged wall mounted brackets that would allow you to slide the server directly "towards the wall", not having to slide it down as the mount requires.

 

[BigDave]

That fan is sure to be loud so I would want to but something like Roxul sound proofing insulation in between the studs to dampen and stuff the fan in the wall.

Not to be critical here but you are over-thinking this. You can't seal any fan up in the wall because ALL fans wear
out or outright fail and then need to be replaced. Even the fan you have mounted in the closet ceiling has access
for the fan motor to be replaced (at least most that I have seen)

I envisioned the in-line fan exposed on the outside of the walls. I will attempt a drawing of my proposal.

edit: add very crude drawing

 

[MatthewSteinhoff]

We have a lot of wall-mount server/network closets scattered throughout our empire. For those with 6-12U of stuff, a pretty hefty fairly conventional bathroom fan is installed but we never use an intake fan or even a ventilation grill. We cut the bottom of the door by about an inch to an inch and a half. That is our intake. We haven't done the math to see if that is enough but it seems fine - no temperature problems. Of course, the building itself is air conditioned - 72 during the day and up to 80 degrees at night.

For some of our smaller closets...



...we use passive cooling. We chop an inch to an inch and a half off the bottom of the door and another inch to an inch and a half off the top of the door. Normal convection pulls cool air from the bottom of the door while hot air exhausts out the top.

The fan noise is rarely louder than the equipment noise. We've replaced two ventilation fan motors in eight years with, I think, 11 installed.

Be sure your ventilation system doesn't have a light fixture included. No need to add worthless light and harmful heat to the room or pay for a light socket you'll never use.

Cheers,
Matt

 

[MatthewSteinhoff]

https://www.racksolutions.com/wall-mount-rack.html#

As an aside, that rack seems overkill. We use a 4U or 6U Startech wall mounts. These cost less than half what you pictured. The 6U model will hold 200 pounds of equipment.

Cheers,
Matt

 

[Redcoat]

As an aside, that rack seems overkill. We use a 4U or 6U Startech wall mounts. These cost less than half what you pictured. The 6U model will hold 200 pounds of equipment.

Cheers,
Matt

Yes, that's the picture I had in my head for the mount.

 

[svtkobra7]

As an aside, that rack seems overkill. We use a 4U or 6U Startech wall mounts. These cost less than half what you pictured. The 6U model will hold 200 pounds of equipment.

Cheers,
Matt

I appreciate the feedback. Yes, I'd absolutely prefer to spend less on a rack, but was hoping to do something like:
1. SC836 vertically mounted
2. Below that switch / UPS / etc traditionally horizontally mounted

Crude attempt to show #2 follows.

Be sure your ventilation system doesn't have a light fixture included. No need to add worthless light and harmful heat to the room or pay for a light socket you'll never use.

Sounds like that fan I choose has to go anyway, but I did purposely select one with a light, because I can't count the number of times I have been in that closet fiddling around and needed light. It is LED though so it shouldn't generate much heat.

 

[svtkobra7]

Not to be critical here but you are over-thinking this.

• I absolutely don't take your comments as such critical, but even if I designed the most bad@$$ server closet cooling system in the world (not going to happen), I'd rather hear your constructive criticism instead of commendation.
• I'd agree that I do over-analyze generally, but I do believe some thought here is necessary as when I get the server mounted in the closet, I don't want to slap myself on the head wondering why ambient is 105F and have to do any rework. I'd rather only deal with as much drywall dust as I have to. As to why I have to deal with any: As you probably know, metal studs are flimsy and there was no way I was going to attempt to mount the server on a plywood backing panel only (although it probably would have been OK). I would have only hit two studs, but had I been able to hit three, I would have probably have felt different. Point being is that I opened up the wall so that I could reinforce those metal studs with 2x4s and 2x6s to more approximately carry the load (that component of the project is complete).

You can't seal any fan up in the wall because ALL fans wear out or outright fail and then need to be replaced. Even the fan you have mounted in the closet ceiling has access for the fan motor to be replaced (at least most that I have seen)

• Good point.
• Correct, you can replace the motor without dropping the fan entirely.