Data centers consume huge amounts of electricity, much of it wasted. Data centers convert electricity to heat, so all energy used for computing is paired with a similar load for heat removal. Rethinking data centers is a good way to make a strong impact on energy usage in a hurry.
All computers use direct current (DC) to actually run. So does most consumer electronics. That little brick, or wall wart on the power cord transforms power from the alternating current (AC) of the power grid to DC to be used by the computer. In most desktop computers and servers, that “brick” is internal to the computer. Improving this process is straight-forward, and does not require any fundamental re-engineering of the computers.
Recently I was reading that the EPA is proposing higher efficiency standards for power conversion efficiency in computer systems. Most systems today still have not met the current version of these standards, called EnergyStar. What caught my eye was how much power is wasted even in today’s EnergyStar compliant systems. The numbers are so large that they make the case for re-thinking power systems for data centers far stronger than I had thought.
EnergyStar standards require power supplies are that no more than 80% efficient or better. This means that to be compliant, no more than 20% of the A/C power coming to your data center computer be converted to heat and lost before it even gets to the computing circuitry. This lost power is converted to heat before it ever gets to support actual computing.
This increases the arguments for Direct Current (DC) data centers. DC Data Centers convert Alternating Current (AC) power to DC before it is distributed to the servers. Telecommunications has longed used DC distribution for its big racks. There are several processes that can be improved by re-thinking power distribution in data centers around the principle of DC distribution.
All of that power lost by conversion is today heat lost in the data center. That heat must then be removed to keep the computing equipment sufficiently cool. Air conditioning is one of the most significant costs of a operating a data center. Many estimate that it takes up to 1.7 times as much energy to remove heat from conditioned space as the initial energy that generated the heat.
By simple moving the AC/DC conversion outside of the conditioned space of the data center, 20%-40% of the heat is moved out of the data center where it will not need to be air conditioned away.
Many reputable companies sell data center batteries to support uninterrupted power. These usually have AC converted to DC to charge batteries, with the same losses as above. The servers run off batteries. The batteries supply DC, which is converted to AC (5-15% loss of power as heat) to support the AC servers. The power supplies in the servers then convert the AC to DC (as above, with loss of power and generation of heat).
When people discuss the efficiency of this process, they usually describe the efficiency of the battery storage as the limiting factor. What the process above shows, however, that as much as half of the power stored may be lost as heat though the double conversion before it ever gets used for computing.
In a DC data center, the batteries still supply DC power, but all of it goes directly to the servers. Not only does this generate less heat, but it can as much as double the effective efficiency and life of the batteries by removing the double conversion for the last yard of distribution.
This increase of efficiency comes with today’s technologies, without waiting on the perfection of any novel or exotic battery technology.
It is hard to use the waste heat from Air Conditioning. A large AC/DC transformer, however, concentrates the energy lost as heat into one place. It is easy to harvest heat from a single very hot location. I have even seen proposals for fueling a steam distillation chiller off waste heat from a transformer to provide supplemental air conditioning for a data center. You could run domestic hot water heating off the external transformer. I suppose you could even hook a Stirling engine to the transformer and light the building using the waste heat.
We do not have to wait for exotic technologies, although they will come. We need to re-think processes with an awareness of power at each step. Transactive pricing for energy will encourage us to do just that.