<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div bgcolor="#FFFFFF" text="#000000"><span class=""><br></span>
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. <br>
<br>
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. <br>
<br>
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. <br>
<br>
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). <br>
<br>
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. <br>
<br>
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</div></blockquote><div><br></div><div><br></div><div><br></div><div>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.</div><div><br></div><div>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.</div><div><br></div><div>With a non-phase change solution, this isn't an issue.</div><div><br></div><div><br></div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div bgcolor="#FFFFFF" text="#000000"><span class=""><br>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_extra"><br>
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.</div>
</div>
</blockquote></span>
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. <br></div></blockquote><div><br></div><div><br></div><div>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.</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div bgcolor="#FFFFFF" text="#000000"><span class="">
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_extra"><br>
</div>
<div class="gmail_extra">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...</div>
</div>
</blockquote>
<br></span>
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. <br>
<br>
<a href="http://www.iceotope.com/" target="_blank">http://www.iceotope.com/</a><span class=""><br>
<br>
</span></div>
</blockquote></div><div class="gmail_extra"><br></div><div class="gmail_extra"><br></div>I've seen them, I hadn't realised they were using Novec. Even a 5min look through their website doesn't make that clear.</div><div class="gmail_extra"><br></div><div class="gmail_extra"><br></div><div class="gmail_extra">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?)<br><br clear="all"><div><br></div>-- <br><div class="gmail_signature" data-smartmail="gmail_signature">Dr Stuart Midgley<br><a href="mailto:sdm900@sdm900.com" target="_blank">sdm900@sdm900.com</a></div>
</div></div>