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I know a couple of builders. All have told me (speaking generally, not about data centers in particular) that retrofitting was where it was going to be for the next few years, but that they would much rather build new than retrofit. I of course asked why, and the simple answer was “It’s just easier."


Having been in a few buildings that have been retrofitted for HVAC in New York, and seeing both good and bad examples of that kind of thing, it is easy to see, even as a layman, what the issues might be.


For a data center with good infrastructure, it is not quite as bad as all that, at least until you hit design limits that you have to work around. What about new? Are there issues there that are less than obvious?


Everything is New


As I started to consider the issues that surround building a new data center, I wondered about some things. One example I had in mind was the issue of the hybrid car. Clearly it uses for more energy and resources to to build something from the ground up. From the machines that dig and flatten the ground through the amount of energy / CO2 used to create and shape the raw materials to the shipping and the power used to bolt, staple, hammer and glue the whole thing together a brand new building has to be far more CO2 intensive than a retrofit.


I keep hear anecdotal references to all the spare or empty data centers laying about, and every time I ask why they are that way the answer is power density. Its an 'old’ data center  and can’t handle the power density of today’s equipment. I talked about this a bit in the first post.


New, modern data centers are being built all over the place that can handle the more modern densities we are considering here, and as I was touring one such facility recently I was struck by just how much concrete was being used. A quick bit of the Google told me that concrete was used over twice as much as the next material in a new building (and I assume the next one is iron, for things like rebar (reinforcing bars, usually iron) in the concrete.)


CO2 and Concrete


According to the Portland Cement Association, concrete is the second most used ‘thing’ in the world after water. Since it requires a great deal of heat to make the stuff we all love to drive on, it is the third largest source of greenhouse gases in the US. According to Scientific American, one ton of cement makes one ton of CO2, more or less.


That seemed low to me, since 1 kilowatt of electricity generation, for one hour ranges anywhere from basically no CO2 (Wind, Water, Solar, not counting construction costs) to 2.1 tons for Coal (burning to create that power). That’s per Kilowatt hour. That make one ton of concrete generate the same about of CO2 as one kilowatt of electricity generated with a 50/50 mix of Coal and Solar.


If a cubic foot of concrete weighs in at 145 pounds, there are 13.7 cubic feet of concrete per ton and therefore 1 ton of CO2 emitted to created those 13.7 cubic feet of concrete. There are 27 cubic feet in a cubic yard, and that is a common measure for use of concrete in building things, or 2 tons of CO2 per cubic yard, in round numbers.


I have been working these numbers to get to some idea of how much CO2 just went into making the concrete for the theoretical new data center. I picked concrete because it is the majority material in the new building.


How much concrete is in the floor?


When I was looking at a new data center, a few things struck me about it. First was how much bigger the building was than the actual data center. The loading dock, offices, halls, ramps, conference rooms, UPS room, and such easily doubled the size of the building over the core data center.


Second was just how thick the floor was. I know that this can be changed with various building strategies, such as the way the floor was pre-stressed, the type and design of rebar, and so on. But still, this was a six foot slab! That means for every three square feet of data center floor, there are two cubic yards of concrete. Just the floor. Not counting the walls or anything else. A 10,000 square foor data center floor (about what I think I need) is then 3334 cubic yards of concrete. The other 10,000 square feet don’t need that depth of floor (Other than the loading dock), and I could not see what was used, but probably no more than a foot on average I am guessing. Another 1100 cubic yards or so.


Concrete in Walls


Bear with me....


The walls were two stories high, and four inches thick, and surrounded the perimeter, and the DC.


For the perimeter that is 2 100 foot long walls, and 2 200 foot long walls, each 30 feet tall. 600 linear feet.


For the DC that is 4 100 four long walls, or 400 linear feet.


1000 linear feet of 4 inch thick, 30 foot tall concrete walls. That is the same as 1000 linear foot of 10 foot tall, foot deep walls in terms of concrete. 1000x10x1=10,000 cubic feet / 27 = 370 cubic yards.


So, my low estimate as a non-building engineer is that my theoretical 10,000 square foot data center, based off what I have seen of the way data centers are built, would have around 5000 cubic yards of concrete.


And part of that CO2 generated, depending on the type of concrete gets re-absorbed. Use a carbon negative material (See Caveats) and you could be carbon negative even after you counted everything else that went into making the building. Steel, glass, transportation, and all sorts of other things.


On the other hand, not a bit of that probably incurred on a retrofit. It was incurred back when the data center was built.


Whiny Caveats


This is tricky math, because of number of things.


  • Cement is not concrete. Concrete is what we make things like data centers and roads out of, but it is filled with sand and rocks and other aggregates. Cement just holds it together, and is somewhere between 7 and 15% of the total, depending on type and aggregates used.
  • There are ways to create alternate forms of cement and concrete coming online that are far less CO2 producing
  • There are similarly new types of concrete being developed that over their life space actually are carbon negative. They absorb more CO2 than was used to create them.
  • There is a concept/process being proposed for using waste heat to create the cement.
  • Just normal everyday created by current practices cement re-absorbs about 60% of the CO2 that was used to create it.
  • Cement / Concrete are not, it seems, huge CO2 producers per ton. It is just we use so many tons of it. This in some ways matches up to the idea about CO2 itself. CO2 is not nearly the greenhouse gas that methane (for example) is, it is just that we liberate so much of it in order to generate the annual 98 quadrillion Btu of energy we used in 2010.19,108,767,320 metric tons of CO2 in that year, just in the USA alone.
  • I am trying to figure out things for a data center build based off pure observation. I cross checked this against a calculator I found for a standard office building this same size, and that came up about 1000 cubic yards of concrete rather than 5000. With all the things that could change in the design that would affect the depth of the data center floor alone, it seems I’m in the ball park.


This Affects Others


Balanced against all of the above is that building a new DC is not only easier because it can be exactly how you want it to be, it gives a lot of people jobs building it. Retrofitting might be cheaper, and generate less CO2, but it also will only pay the trades that make and install the new HVAC, ducting, PDU’s, UPS’s, Gensets, and whatnot.


There is also that the new building will be not only more power dense, but because it is built now, under today’s building codes, it will be cleaner, safer, and use less power over its operating life. It would be built to the newest LEED and ASHRAE parameters, and it potentially would be built someplace where free cooling at least part of the year is an option.


Finally, what struck me about this exercise was this: the energy used (CO2 created) to build a building is but a tiny fraction of the power that goes to run the computers it will house. That may seem intuitively obvious to some, but I was surprised at the numbers.


Next: To explore a retrofit