[Beowulf] bring back 2012?

Stu Midgley sdm900 at gmail.com
Mon Aug 22 08:22:06 PDT 2016

> While the risk of an explosion is a certainly a theoretical possibility,
> In practice, the risk of this is virtually non-existent for a variety of
> reasons.
> With water, the processors and other heat-generating components would fail
> from the heat before the boiling point of water is reached, so there would
> be little to no generation of water vapor that could lead to an explosion.
> Also, any heating/cooling system with water would be designed to included
> an expansion tank to account for the thermal expansion and contraction of
> water. There are millions, if not billions, of homes and businesses in
> existence with hot water heating systems, yet, I've never heard of any of
> them ever exploding.
> With Novec and other two-phase systems, the gas phase is compressible,
> meaning it can store energy like a spring, preventing or minimizing the
> case risk of an overpressure situation rupturing the vessel. All that is
> required for this to be used safely is an adequate volume for the gas, so
> that is has excess 'capacity' to be compressed. This simple design is what
> allows 20-pound propane tanks to be used all over America (and probably
> other countries) to fuel gas grills and be left out in direct sunlight all
> summer long, and be stored directly under the heat-producing burners.  If
> those tanks were filled to the top, they would explode in those conditions,
> but but leaving about 1/3 of the tank empty, the risk has been virtually
> eliminated. This was actually a top we spent a lot of time discussing in my
> Chemical Engineering Safety class in college.
> This also applies to the tanks storing liquid nitrogen, liquid oxygen, and
> other gases/liquid stored well below their boiling point. Tanks of these
> substances can be found throughout the world in industrial and laboratory
> environments, yet explosions caused by them are quite rare. When they
> explode, it's usually because someone who didn't know what they were doing
> overfilled the tank, or the ambient temperature exceeded the designed
> safety margins through some other catastrophic event. (structure file,
> etc).
> Finally, all systems where this is a risk would have plenty of safety
> features to prevent this. My gas water heater at home has a simple
> temperature/pressure switch to safely discharge excess pressure/temperature
> event. These are cheap, readily available items that you can buy at any
> local hardware store. I also have a steam heat system in my house. In the
> early days of steam heat, it was not unheard for a steam boiler to explode
> with devastating results, but just to some simple design elements (Hartford
> Loop) and basic mechanisms (low water cut-off valve, pressure relief
> valves) have virtually eliminated this risk.
> Before I got in to HPC as a profession, I was a process control systems
> engineer. My companies specialty was control systems for boilers for power
> generation. The pressures of these systems were much higher than what we're
> talking about here. Our systems had plenty of pressure sensors, release
> valves and failsafes. Incorporating any of these safety elements into a
> cooling system like this is trivial, and I'm sure the vendors who sell such
> solutions have already done that where appropriate

But if you have 40kW of gear still running, your not storing the liquid in
the sealed container well below boiling point - its actually the opposite
you are running at or just above the boiling point.  Even if you take the
approach "our systems will shot down if we loose the external cooling
circuit)... that still takes time to recognise and shutdown... mean while
your systems are pumping heat into the tank.

Again, with the boiler example, this isn't the sort of behaviour you want
in a computer room.  You don't want this stuff venting... and also, try and
get a permit to operate such a system in an existing or new facility.

With a non-phase change solution, this isn't an issue.

> Novec is a common fluid used in fire suppression systems in computer
> rooms... so you shouldn't have too much of an issue with the flammability
> of the fluid, but it is an entirely different issue to get them to warrant
> the solution.
> If it's already used in fire suppressions systems, where it's going to
> deliberately be sprayed into the atmosphere, I don't see how a system where
> it's designed to be completely contained would more of a safety issue, but
> this could be a local practice issue (USA vs. Australia laws, etc.) In the
> event of an emergency venting, as stated above, the vents are hooked up to
> exhaust piping so that that gases released are piped away to a location to
> where it can be safely released to the environment, so a venting event
> would pose no risk to the occupants of the data center. This is done all
> the time at chemical plants. In fact, venting like this happens quite
> regularly in those environments, but I honestly don't even see this type of
> venting being needed in a system like this.

If you look at the US laws around this (I've only been through the Houston
documentation - but I assume all states are roughly the same) their is a
massive different between holding a few hundred litres of fluids (which is
what is in a fire supression system) and say 30000L, which is what you'll
have in 30 tanks.

> Perhaps the final nail in the coffin of the Novec solutions... it has been
> on many different booths at SC for many years... now go and try to find a
> vendor that will actually sell you a solution...
> I guess you never stopped by the Icetope booth at SC, then. They've had
> solutions on the market for several years now, and have had booths at SC
> for several years now, too.
> http://www.iceotope.com/

I've seen them, I hadn't realised they were using Novec.  Even a 5min look
through their website doesn't make that clear.

Which brings us to another topic... and that's price.  The icetope stuff
looks very very custom... and thus very very expensive.  I can purchase
gigabyte or supermicro equipment already for the fluid we are using (they
modify the power supplies, leave the thermal paste off components etc)...
no modifications at our site necessary - and relatively cheap (is any HPC
gear cheap?)

Dr Stuart Midgley
sdm900 at sdm900.com
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