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Energy Efficiency - Data Centers

On Wed, Dec 18, 2019 at 10:48 AM Thomas Bellman <bellman at nsc.liu.se> wrote:

> On 2019-12-18 15:57, Rod Beck wrote:
> > This led me to wonder what is the inefficiency of these servers in data>
> centers. Every time I am in a data center I am impressed by how much> heat
> comes off these semiconductor chips. Looks to me may be 60% of the>
> electricity ends up as heat.
> What are you expecting the remaining 40% of the electricity ends up as?
> There is another efficiency number that many datacenters look at, which
> is PUE, Power Usage Effectiveness.  That is a measure of the total energy
> used by the DC compared to the energy used for "IT load".  The differece
> being in cooling/ventilation, UPS:es, lighting, and similar stuff.
> However, there are several deficiencies with this metric, for example:
>  - IT load is just watts (or joules) pushed into your servers, and does
>    not account for if you are using old, inefficient Cray 1 machines or
>    modern AMD EPYC / Intel Skylake PCs.
>  - Replace fans in servers with larger, more efficient fans in the rack
>    doors, and the IT load decreases while the DC "losses" increase,
>    leading to higher (worse) PUE, even though you might have lowered your
>    total energy usage.
>  - Get your cooling water as district cooling instead of running your own
>    chillers, and you are no longer using electricity for the chillers,
>    improving your PUE.  There are still chillers run, using energy, but
>    that energy does not show up on your DC's electricity bill...
> This doesn't mean that the PUE value is *entirely* worthless.  It did
> help in putting efficiency into focus.  There used to be datacenters
> that had PUE numbers close to, or even over, 2.0, due to having horribly
> inefficient cooling systems, UPS:es and so on.  But once you get down
> to the 1.2-1.3 range or below, you really need to look at the details
> of *how* the DC achieved the PUE number; a single number doesn't capture
> the nuances.

Google has some information on PUE at
https://www.google.com/about/datacenters/efficiency/ -- the tl;dr is that
we have a datacenter PUE of 1.06, and a campus (including power substation)
PUE of 1.11.  By comparison, most large datacenters average around 1.67.

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