Closet cooling and fan static pressure

[kaspor]

Hello

I have a closet which is approx 2.7m high by 1m deep by 1.2m wide. I have l equipment in there that needs to sit at max 30degC. There are two double doors on the closet.

In order to keep it at 30degC I’ve installed 4 extraction fans on a thermostat. The fans draw air in through gaps in the doors and from underneath and exhaust it at the top. The fans are similar to these

S Series 100 Wall/Ceiling Exhaust Fan – White - Universal Fans

The Fanco S Series exhaust fan is a small yet capable fan. It features a simple design and can be mounted on the ceiling or wall. It can also be connected to duct so the air may be exhausted out of the house.

universalfans.com.au

The problem is the noise. They’re generation 30dba each. I’ve insulated them as much as I can but they’re still loud.

So I then started looking at quieter fans such as these

NF-S12A FLX

The NF-S12A marks the third generation of Noctua’s signature S12 series quiet case fans, which have received more than 250 awards and recommendations from the international press. Featuring a further refined blade design with Anti-Stall Knobs that works in tandem with the new AAO (Advanced...

noctua.at

They have a much lower db but looking at the performance curve it looks to have a much lower static pressure rating

NF-A12x25: performance comparison to NF-F12 and NF-S12A

Designed in Austria, Noctua's premium cooling components are renowned for their superb quietness, exceptional performance and thoroughgoing quality.

noctua.at

Does this mean they will inherently take longer to get the temp in the closet down as they are not able to draw the same amount of air in?

I’m worried that if I change the fans over that the newer fans will be useless as they won’t be able to draw air in like my current ones.

Also cutting holes or vents for intake isn’t an option unfortunately.

 

[HVAC-Novice]

Thanks for the reply. Power ratings would probably an inaccurate way to do a heat load calc as much of this equipment is sitting well below its full capacity. I can measure the power draw, but the whole closet is probably drawing no more than 1.2kW (electrical)

What are you running in your HOME? Are you crypto mining, or what?

If it draws 1.2kW, it dissipates 1.2kW (minus what dissipates in the spaces if you have PoE)

imagine running a 1kW space heater all year, that closet would be extremely hot. I doubt you actually draw 1.2 kW. But I don't know what is going on....

 

[3DDave]

Where you live may not make some legal distinction, but physics says that connection would make a chimney to route smoke and fire through the flooring and will accelerate the ability to die if a fire breaks out either in the closet or in the area under the closet.

Frankly, your wife should be more concerned about the problem of creating a smoke stack than a bit of humming sound.

Adding forced ventilation to add more draw to a fire below the floor makes it far worse - it will be distributing carbon monoxide.

The one who commented about "air registers" is an air head. Those are typically attached to closed ductwork that prevent movement of fire from one area to another, mainly by not supporting combustion in the ductwork.

 

[kaspor]

What are you running in your HOME? Are you crypto mining, or what?

If it draws 1.2kW, it dissipates 1.2kW (minus what dissipates in the spaces if you have PoE)

imagine running a 1kW space heater all year, that closet would be extremely hot. I doubt you actually draw 1.2 kW. But I don't know what is going on....

Yeah a poor guess on my part. I went and measured it. Getting around 150W at the moment.

Where you live may not make some legal distinction, but physics says that connection would make a chimney to route smoke and fire through the flooring and will accelerate the ability to die if a fire breaks out either in the closet or in the area under the closet.

Frankly, your wife should be more concerned about the problem of creating a smoke stack than a bit of humming sound.

Adding forced ventilation to add more draw to a fire below the floor makes it far worse - it will be distributing carbon monoxide.

The one who commented about "air registers" is an air head. Those are typically attached to closed ductwork that prevent movement of fire from one area to another, mainly by not supporting combustion in the ductwork.

Ok I see your point and appreciate the feedback, but the likelyhood of a PC or an NVR catching fire is extremely low. I am not running a data center here lol. I have been in the electrical and construction business for 40 years and tbh I have never seen this happen. And even if they did catch fire, the abutting bedrooms are more of a concern than the floor below which is a hallway. That's why the law here mandates safety switches (residual current devices) on all mains power + smoke detectors throughout the home which are interlinked. Plus the amount of internal protection on modern electronics would also add another barrier to this happening. There also holes in the subfloor for all types of services. HVAC risers, water, sewer and vent stacks. If this were a real concern, then we'd be fire sealing these penetrations too. Granted this is mandatory when we build data centers, apartment complexes or substations (and the like!).

 

[LittleInch]

I would be a bit wary about cutting holes in the floor myself and me and 3D Dave agree that you should try two fans blowing in and two fans exhausting.

I doubt this would be effective though without changing the internal air flow withing the closet.

Time for action now I think.

 

[MintJulep]

What does it sound like if you take off the grills?

 

[dvd]

That is a good point, however supplying cooled air from my HVAC unit would cost an absolute fortune as there would be no zoning setup. The house is quite large, I have two separate HVAC systems and running the downstairs system costs ~80c per hour.

So you do not run your HVAC system? Because one way or another the load is removed by an HVAC system if it is running.

 

[kaspor]

Ok so I have found the issue. After replacing the fans with the Noctua fans, it runs very quiet now whilst still cooling the space down (no need for holes etc.). I still haven't had a hot day yet, so waiting for that. But I seem to be able to get ambient temps inside the closet to within 2deg above outside ambient which is good enough for me. Plus they're so quiet and very low power, I can pretty much run them all day if I wanted to.

For anyone having the same problem, here are my tips (hopefully they save you some hair, as I have ripped most of mine out):

1. Don't over cook the air flow. This is what I was doing with those original wall fans. They were unnecessarily over powered, the amount air being drawn through the closet was excessive for my heat load. I think someone mentioned that in this thread, so thank you.

2. Use extra low voltage DC fans where possible (like the Noctua's), these are much, much more quiet than the mains powered wall fans.

3. Slow down the fans if possible. Slower fans = less noise, although you compromise on performance. Noctua's come with what they call a low noise amplifier, looks like it's just a voltage divider to be honest. You can run the non-PWM fans at 2 different speeds lower than full speed with these things. This was enough for me, otherwise you can get the PWM style fans and then get yourself a PWM controller and play around with speed vs performance vs noise.

4. Make sure you have clear pathways for inlet/outlet air flow. You'd be surprised how much extra noise is generated when there's an obstruction.

5. Use soundscreen insulwool (or batts) around the fans if possible. This reduces electro-mechanical noise significantly.

Thanks all for the contributions.

 

[LittleInch]

Great. Thanks for letting us know what worked.

So all 4 fans still just extracting?

 

[kaspor]

Great. Thanks for letting us know what worked.

So all 4 fans still just extracting?

Yep 4 fans extracting. They pretty much run most of the day where as the original ones would run for about 20 mins every hour (both setups were/are under thermostat control). But I don’t mind, these things are so quiet I’m happy to let them run 24/7 if need be.

 

[HVAC-Novice]

I think your goal is too ambitious. With only 2°C dT, this is as good as it gets. to get to less than dT of 2°C, you would have to get closer to infinite flow. If you keep your houses at 28°C, you just have to live with warm electronics. Normally the air used to cool is 10+ °C colder than what you want to achieve. You just run against what is possible.
In heat exchangers it is called "approach". You approached what is really possible.

You can't cool to 20°C with 28°C air.

Look at the rating of the hardware. If it is good hardware, it is rated to much more than 30°C ambient.

 

[MintJulep]

Ok so I tried those more expensive fans, what total rubbish. Louder than the ones I have.

What changed between when you wrote that to now?

 

[LittleInch]

He was referring to the fans listed in post number 30, basically the same sort of 240V mains fans designed for bathrooms.

 

[kaspor]

What changed between when you wrote that to now?

I tried 3 types of fans. The original were mains 240v fans. Then I tried another more expensive set of 240v fans. They were both as loud as each other which signified to me that mains 240v fans were too loud for this application (due to motor noise) The 12vdc ones were much quieter which were the 3rd set.