Cooling my racks with "free-cooling"

[Extralarstig]

Hi everybody,

i've been mining for a while now and because of the size decided to work with a hot and cold isle. I thought about creating a high pressure side on the cold isle and use a big centrifugal fan that pulls the air through the filter case to the cold side. The centrifugal is chosen because it delivers way more pressure compared to axial fans.

Now if i start my system, without my fan, temperatures reach 70 degrees on my S9 modules (I have a hatch through which they can pull the air themselves on colder days). But when I test my system with the big ass fan, temps rise to a whopping 90 degrees! This even though the fan delivers way more air then the S9 units combined. Is this maybe a turbulence problem?

I'm a bit in the dark here...

I think i should try sucking the air on the hot isle.. But i'm still wondering why this does not work... Any thermodynamic geniusses here?

regards,
Lars

[BitMaxz]

Why you still need a fan? 70 degrees is a normal temp and I think you don't need to add more fan to cool more your miner 70 degrees is enough temp for each miner.

I think your problem is air circulation in your room, you must exhaust all hot air out in your room to cool down your miner.

Try to exhaust and use a duct host each miner to push your hot air outside on the room, it can help to cool down the miner.

[Extralarstig]

Thanks for your response!

I run 70 degrees on a cold day, so the fan is only there for when it hits 25 degrees outside.

The blow out isle for the miners is 50cm and then goes directly outside through big rosters. By the way, the cold and warm isles are airtight sealed from each other. I have used duct hoses and had an 2 degree impact.

So the main question remains; why does the forced air have a negative impact on the system in general?

[fanatic26]

forced air on the intake side is useless, the miners only flow so much. You need to 100% focus on removing hot air and letting the miners pull the ambient air in for themselves.

[dutchlincoln]

forced air on the intake side is useless, the miners only flow so much. You need to 100% focus on removing hot air and letting the miners pull the ambient air in for themselves.

Not completely true;
Take a look at my "small home farm" topic setup.

My experience is that when hot and cold side are really isolated, you can use "push-in" air. It equalised the temps of the miners within a few degrees from each other.
What you really need to do, is check the CFM of the used fan, and compare it with the 300cfm for each s9.
If you move less, they are sufficating, and its easy: the strongest wins and gets the most air, and won't frie. The less powerful one heats up. Temps will be further apart from eachother.

If i take a look right now at my miners in Awesome miner program, they are all within 4 degrees celcius from eachother. I have one hotter, and one colder one, wich is specifically miner related. All others are as good as equal.
My compartiments are truly separated.

I wll use a bigger fan this weekend to see if temps get further down, and this way i hope to shutdown my suction fan and use push-in air only.

[Razon]

You need to work on removing the hot air out of the warm side to prevent any heat blowback heating the miners

The reason your machines heat up is because you CAN'T blow a fan into another fan, it just impedes the initial fans from spinning killing your airflow. (Think of when you blow a fan into a computer, the video card fan eventually dies)

Work on heat control, circulate air, remove hot air.

[Ameador1]

I agree with dutchlincoln. Blowing/Creating air flow via pressure on the miners on the intake side should make the miner's fans spin easier as the cold side in your scenario would by moving air with the miner's fans - not against them. If the theory was correct that blowing a fan in the same flow direction as another fan would kill it, then the exhaust fans on the miners themselves would fail due to that fact that the intake fans are blowing on them. No, the aid each other - not hinder.

You just need the flow to all be going in the same direction - like you are doing. Flow from outside, through filter, into cold space, through miners, into hot side, out to outside.

Any chance that the warm air from outside is making its way back around to your large intake "big ass fan"? I have heard of this kind of loop being created and causing temp increases.

Also, like dutch said, make sure your big fan is able to actually move enough CFM's to at least - but preferably more than, exceed the CFM flow of all of your miners x 300CFM. I generally don't trust the spec'ed numbers on them (the fans) as they are only the best case scenario you know? Your fan will have indirect resistance as the air has to go through the miners. In other words - if the fan is actually outperforming the flow of the miners, you will generate a higher-pressure space on the cold side. That pressure buildup will cause resistance to the fan via back pressure on the fan and reduce its CFM potential - but it will eventually balance. The net effect would be that the miners would be cooled better, but with the fan experiencing more resistance than blowing into a non-pressurized space. This will strain the fan. If it is a small pressure increase the fan will be ok. If it is moving a lot more air and creating a relatively higher pressurized space, it will cool the miners well but could kill the fan early due to the additional stress on it fighting the increased air pressure. Just depends on how much pressure it can really build and thus fight against. This is not your problem though.

Pulling the air through the filter could be reducing the amount of air it is actually moving from outside to the inside by quite a lot. If the fan cannot keep up with the flow of the miners - that's a problem that can cause heating up and/or even overheating.

I am stepping outside of my REAL knowledge zone here - but I think that you want at least 1 atmosphere of pressure on your cold room (or slightly higher) and no more than 1 atmosphere on the hot side (or slightly less). But you DO NOT want less pressure on the cold side than on the hot side. There are testers you can get, or get an HVAC person to check the pressures for you. I would be willing to bet that your big fan (especially after going through a filter), just isn't keeping up with the miners - which is causing a vacuum on the cold side - which will actually cause hot air to start pulling back into the miners from the hot side and/or just not moving the hot air from themselves fast enough, allowing them to heat up.

This can turn into a heating loop that can overheat them. If the vacuum is strong enough on the cold side, they can definitely start pulling hot air back into themselves from the hot side. If the vacuum is very minor, they are probably just not able to get the hot air out fast enough. In any case, you see their temps go up - and potentially a lot - to damage levels.

I have 2 - 3200CFM fans running 11 miners. A mixed batch, but the heavies are the S9's. I have these on the hot side of a sealed hot/cold setup blowing the air outside. This pulls the air through the miners in the proper flow direction. I have 4 - 16x25 HVAC filters on a wall of the cold side that the air is coming into the cold side through. So, 11 x 300CFM = 3300CFM that the miners are moving. But I have 6400CFM (by spec) of fans blowing air out the hot side. Even with this, when I remove the filters - the temps on my warmest miners drop by about 8 degrees! The filters make a big difference - and/or the fan's specs aren't realistic. Oh, and there are vent covers over the fans that close when the fans are not running, but they also impact the fans CFM potential. I am getting ready to replace the filters with lower MERV filters to help allow the air flow to be better. The miners are ok as they are, but I'd like to take some of the resistance off of all the fans involved - this should help power use as well as lifespan, plus keep the miners cooler and more efficient.

Hope this helps!