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From: "Bob Bradlee" <Bob@BRADLEE.ORG> To: "Paul Vixie" <Paul_Vixie@isc.org> Date: Tue, 25 Mar 2008 11:16:17 -0400 X-Mailer: PMMail 2000 Professional (2.20.2717) For Windows 2000 (5.1.2600;2) Subject: Re: rack power question

On 25 Mar 2008 06:17:15 +0000, Paul Vixie wrote:

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this has been, to me, one of the most fascinating nanog threads in years.

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at the moment my own datacenter problem is filtration. isc lives in a place where outside air is quite cool enough for server inlet seven or more months out of the year. we've also got quite high ceilings. a 2HP roof fan will ....

Point taken, and I agree ...

May I suggest we, make that the collective we, take all that extra floor space that we don't have power for anywaydue to all the new blades servers that need the cooling and put it to good use as a dust or (not so clean) clean room to lower your cooling and cleaning costs.

I worked on a project many years ago where "they" had built a big dust collection room as an air scrubber for the computer room and some labs.

Outside air and inside return air was brought in and mixed to an optimun temp for the season at one end of a very long, very tall, very large, not so clean, room sized dust collector they called the "clean room". On the far wall was an array of low cost filters that fed the HVAC cold air return path.

Because the room was very large with a small inlet and a huge filtered outlet wall. The air in the room stayed at a low pressure and was slowly exhausted from the area at a very slow surface velocity. The vast majority of the dust and just about all of the grit just fell out of the air onto the floor where it could be cleaned up with a big shopvac or a snow shovel if I had my way :-).

Because most of the particulate matter hit the floor before it got to the filters, the filter wall lasted many months vs the previous few weeks between cleaning before the dust room was built. The "normal" filters in the HVAC system had quality HEPA filters and rarely needed to be changed because the air was being so well precleaned in the (not so) clean room long before it ever got to the HVAC system.

I was told me that what I was looking at was the second version, about twice the cubic feet as the origional halway they first used. The filters now lasted almost twice as long and they were moving much more air.

The dust room I saw was very tall, I think 10 or 12 foot to the roof, it was also very long over 30+ feet as I remember, but was limited to about 8 or 10 feet wide (for other reasons). The filters used on the back wall were designed to be used in the back wall of an auto paint booth and were low cost and could be washed. Now that I think about it I expect the width was determined by the size of the filter rack. I was told that before remodeling, version one started as a long wide hallway that was off sealed off and used as a big cold air return, using the old double doors on one end as the "filter rack". I worked so well that when they remodeled, the hall was widened and was opened up so that the cubic area of the low pressure area could be maximized.

What made it work was, the fact that small inlet vs a large outlet creates low pressure in a large area. A long run of slow moving air in low pressure will drop its dust and grit along the way, long before it gets a chance to plugged up the filters. Think of it as a room size shopvac or a big Dysen vacuum cleaner. :)

I was told by the operator it worked better than he thought it would, and if he was to build it again he would have wasted more floor space and made it wider but could not justify the Sqfoot cost at that time. If he was designing from scrach at todays energy costs, it would feed the whole building not just the computer room and labs.

He pointed out that while increased room height increased the cubic feet and reduced pressure allowing more particulate to fall per SQfoot, increasing the floor area was the same as increasing the effective filter area while also reducing the static pressure in the room, win win.

Bottom line, the bigger the better, make a dust room big enough you might not need filters :-).

Got a back room, you can seal up, or some unimproved space you can convert into a home built open air scrubber ?

I have seen it work ..... and it has been working for many years .... Sorry I just can't tell you where, or I would have to kill you :-)

Bob Bradlee 614-xxx-xxxx

PS. As I can not post to this list from this address, feel free to reply on list if you think others might like to chime in.