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An EPRI White Paper

DC Power Production, Delivery and Utilization

as much as needed is a better solution. It goes a little faster after you open the door, to lower the temperature, then a little slower after it has been closed a while.

By varying the speed, a lot of good things happen. For one, you don’t have all the energy losses from acceleration and deceleration.Also, you don’t need as big a compressor, since it doesn’t have to deliver all the energy in such a short period. You can also replace the old-style AC induction motor.

  • Alex Lidow, CEO, International Rectifier Corp.8

Since a variable frequency drive converts 60 Hz power to DC and then converts the DC to variable frequency AC that is fed to the motor, a DC supply can be readily accommodated, fur- ther increasing energy efficiency.

Greater adoption of energy-efficient variable speed motors, now underway for heating, ventilating and air conditioning systems and other applications, represents a greater opportu- nity for deploying DC power. In addition, several manufactur- ers now offer DC variable frequency drives for solar-powered water and irrigation pumps.9

Figure 7. Examples of small motor drive units (5–50 hp)

Example Application: Data Centers and IT Loads

One of the nearest-term applications for DC power delivery systems is data centers, or “server farms.” These facilities are strong candidates for DC power delivery due to: 1) the avail- ability of products that could enable near-term implementa- tion; and 2) an economic imperative to increase energy effi- ciency and power reliability.

Seeking relief from skyrocketing power density— and costs

A data center may consist of thousands of racks housing mul- tiple servers and computing devices. The density of these serv- ers keeps increasing, wasting power and generating heat with multiple AC to DC conversions. According to the Consortium for Energy Efficient Thermal Management (CEETHERM), an academic/industry partnership:

A server farm or data center consists of thousands of racks with multiple computing units.The heat dissipation from a single rack containing such units exceeds 10 kW.

Today’s typical data center has 1000 racks, occupies 30,000 square feet and requires 10 MW of power for comput- ing infrastructure.A 100,000 square foot data center of the future will require 50 MW of power for the computing infrastructure.The cooling for such a data center will consume an additional 25 MW of power. Such a data center could cost approximately $46 million each year (at the rate of 10¢ per kWh) just to power the services, and $22 million a year to power the cooling. Energy efficiency is the key to containing these costs.

  • C. Patel, ITHERM 2002, CEETHERM

June 2006

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