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Ok, so having a debate with somebody and hopefully somebody on here can answer this question with an explanation. The shrouds I am refering to are https://www.ebay.com/itm/AntMiner-S1-S3-S5-S7-S9-L3-120mm-Fan-Duct-Cooling-Shroud-to-4-Inch-Vent-Sampler/132534314729?hash=item1edba926e9:g:tjsAAOSw4qxapTmo (Thats the 4in version, 6in same thing but 6 inches in diameter.)

I believe I had read on a thread here sometime that 6in ran cooler than 4in, I cant find it, if somebody does and can post it would be appreciated.

Ok so the debate is, will 6in intake and exhaust make the miner run cooler than a 4in. One person says yes, bigger size more airflow. One person says no, the airflow will be the same since the limiting factor is the inside of the miner. Since the inside is the "choke point" 4 or 6 inches wont make a difference. Peoples opinions on this?

Person 2 is citing Bernoulli's principle as proof that 4 or 6 wont make a difference.

It is not the shrouds that need consideration - it is the ducting they are used with. By themselves, yes a 120mm to 6" shroud will have marginally less reduction of airflow vs a 4" but I wouldn't worry about it. Connect ducting and it's a whole 'nother ballgame -- 6" or larger is a MUST.

My opinion is you shouldnt be shrouding and ducting these machines, they were never meant to be setup like that.

If you have to, there have been many people on here that can confirm 6 inch ducts lead to much lower temps than 4 inch.

Yes ducting is used with these, so 4" shrouds have 4" ducting, 6" would have 6". The question remains why 6" would cool a machine more if indeed the limiting factor is the machine itself. Can somebody explain with a reason please?

I thought so as well, but couldn't find the relevant thread or posts. Can you link me?

Here's my post, and yeah it made a big difference between 4" and 6" on my S9. Person 2 needs to stop Googling :)

https://bitcointalk.org/index.php?topic=2796117.0

The reason is that miners - and any other machine that uses high volume fans for cooling such as, chillers, compressors, etc are designed with the expectation that the device has free air flow in and out. ANY added restrictions will result in higher temperatures. There is near zero margin to allow for also having to push the air through ducts.

Ductwork adds resistance to the airflow. Bigger diameter = less resistance but added resistance is still present and is NOT a good thing. If you insist on using ducts you MUST use an in-line booster fan rated to pull at least the miner airflow to cancel out the added resistance to airflow.

So the argument to this is, there is no free airflow because of the hash boards inside which are in person 2's opinion the "choke point" or "area of greatest resistance" Since the diameter is the smallest at that point 4" or 6" doesn't make a difference afterwards. Person 1 says even if that is the area of greatest resistance or choke point  the 3 fans (2 in the antminer, 1 exhaust fan in the box the duct is connected to) will benefit from 6" ducting.

Love your post. Your officially an idiot according to person 2 because you have no proof and your just trying to "sell product".

You are mistaking free flow in/out of the miner (the 'room' side of the fans) with what happens inside of the miner.

Yes the inside of the miner has high resistance to airflow. The design has been engineered so the fans overcome that internal resistance enough to force enough air through to keep the miners cool. The design has NOT been engineered to handle the added resistance caused by ductwork -- that is why booster fans are required to counteract the added resistance.

Allowing extra capacity for pusing the flow through ductwork would require spec'ing the miner fans to run at even higher SP/CFM and that just raises mfg cost (and the noise level). Bitmain, Canaan, and the other manufacturers chose to not do that. Welcome to the world of system design engineering.

LOL, I'm not even selling it. Honestly I wish my friend would have just posted the file vs. selling, but hey, it's his choice.

Tell you what, do you have an S9? Pretty sure I've got some different size duct adapters laying around. I'll send them to you, you and Einstein test them yourselves then send them back.

Man I would love this. I got s9's t9's a3's b3's and T1's. Ill PM you now.

u dont need to buy the fan shrouds. I made them a while back but found that they werent needed. if u want the best cooling u have to first tell folks if u have a drop ceiling or are you trying to run duct to some cobbled together window setup. if its the former u will want to mount the miners on legs so they are vertical not horizontal. you can then run ducts up to the drop ceiling panels and cut holes slightly smaller than the duct tubing so it stays snugly in place. 6in or larger and stretch it out completely so there are no rippled and pull it over the exhaust fan of the miner. if its the later then regular ol duct work isnt somethin i would recommend unless you have something on the other end also pulling the air through the tubing. I havent ever been able to get any benefit from running duct work to a window or whatever. the only temp lowering solution i have found to work is running it into a drop ceiling. just running duct tubing horizontally will do more harm than good usually.

All my s9's are vertical with duct running up into the ceiling btw...this isnt me speculating. I also have a huge ass exhaust system pumpin the air from the miners into the building chiller but it has been done in none commercial environments too.

The system I have now is 19 miners with most of them hooked up to 4in ducting. They are all on racks. The ducts lead to a box which has a massive fan inside venting the heat outside. I might post some photos later. Its mess still and im looking to move to a commercial spot as I have another 20 miners I cant hook up due to not enough electric.

One thing to keep in mind if you do comparison tests to make Copernicus happy is that the shroud, the duct, and the junctions all need to be large enough to accommodate the airflow. So if you put a 6" duct on, but neck it down at the junction you won't be gaining anything.

Just FYI.

@userghost, good bad, whatever it'd be good if you could post your results for others.

Also I've PM'd you with no response, can you go ahead and ship me back the ducts?