Last year I spoke to Ron Croce COO of Validus DC Systems about their unique approach to Data Center power provision. He and I both share strong backgrounds in power engineering and the certain knowledge that the way that data centers are powered today is fundamentally flawed.
Today’s data centers take power from the grid distribution at 20 KV or more and transform down to working AC voltages. To provide power protection, power needs to be stored to provide holdup capability in case of interruption of the electrical supply (time for the generator sets to kick in). In most modern data centers this power storage is done in lead acid batteries (although it is also possible to utilize flywheel technologies as an alternative).
So AC power feeds are rectified into DC to power strings of lead acid batteries. The DC power from the batteries is then used to drive rotary Uninterupptable Power Supplies (UPS) that regenerate AC ready for supply to the computer and ancillary equipment in the Data Center.
The regenerated AC power is then fed into the raised floor area via PDUs. The PDUs route the AC power into cabinets housing servers. The servers take in the AC power and convert it into DC power to supply the electronic components.
AC -> DC -> AC -> DC
This is complex, expensive and frankly stupid. We start with AC, convert to DC, convert back to AC and finally convert back to DC. Nuts, completely and utterly nuts. Each conversion adds complexity, additional areas for failure and misconfiguration as well as losing energy in each power conversion stage and that costs real money. Depending on the UPS load factors this conversion loss can be as much as 15% of the total supplied energy. In an AC powered data center, UPSs must not be configured to run at full load as they are always wired in an N+1 of N+N configuration to allow a single unit to fail and the remaining units are able to carry the load transfered from the failed unit. As a result UPS are inherently innefficient.
Telecommunications companies have always used DC power, because telecoms equipment was designed for telephone exchanges and telephone exchanges always had strings of batteries delivering 48V DC. Personal computer equipment and mini computers were always designed to operate in an office environment and that meant 110V or 240V AC, the same stuff that is supplied out of the power receptacles on the wall. When computers transfered into the data center, they took their power demands with them. All just history and custom and practice.
At BT we designed our power distribution for the 21st Century Data Center to be DC, leveraging the 48V capability we already had and developing modular power management systems that could be rapidly and inexpensively deployed. At BT we located the DC rectifiers in the data center as we did the lead acid batteries. So AC came in from the street and was delivered direct to the raised floor area without power protection. On the floor the conversion to DC occurred and the stay up power was delivered by the local lead acid batteries. Smart, cheap and modular.
Putting rectifiers and batteries on the raised floor has it’s own challenges and whilst it may be low cost and effective it is not the only solution to delivering DC power. Here’s the problem Ohms law states that V=IR, that is that to maintain a steady voltage across a circuit carrying high currents, the resistance of the circuit must be very low. So if we want to put 48V DC into the data center from outside the raised floor area we need huge conductors that simultaneously cost a fortune and occupy a lot of space.
An alternative is to pipe in high voltage DC such as 575V and use much smaller and cheaper conductors. The problem here is one of crispy bacon – Data Center operators coming into contact with high voltage DC will literally fry, an unacceptable health and safety risk. Operators are always working at the cabinet level and plugging and unplugging power cords. 110V, 240V AC and 48V DC are safe, an inadvertent contact with electricity at this level is unpleasant but not lethal. Higher voltages are killers.
Validus DC systems have a solution that neatly skirts around the problem, high voltage DC is delivered to distribution points inside the raised floor area. Lead acid batteries are located outside as are the high voltage rectifiers.
Here is what Validus say about the product:
- -575 VDC system architecture replaces legacy AC system components such as UPS, PDUs, static transfer switches, and related switchgear
- Reduce energy consumption by up to 40%
- Lowest total cost of ownership compared with AC systems
- Dramatically reduce square footage requirements and installation costs of infrastructure equipment
- Reduce operating and equipment maintenance costs
- Improve system reliability
- Enable the use of standard DC powered IT equipment
This is an excellent solution that can be implemented both in new builds and also as a retrofit to existing data centers. Energy savings of up to 40% can be achieved as can significant reductions in capital spend. Reliability is enhanced because there are fewer components that are under less electrical and mechanical stress. To top it all the high voltage DC skills that are needed to support this are already available as this is the standards that are use for building DC lead acid battery strings.