Why Energy Consumption Matters

Gilbert Held
September 2001

Serious energy problems are facing residents of California and other western states. Commencing with utility companies reducing voltage by a few percent during the summer of 2000 that resulted in brownouts, the electrical situation rapidly deteriorated to rolling blackouts during the beginning of the year 2001. With the summer of 2001 upon us, it is apparent that both business and residential electrical consumers will continue to face a challenging situation. What may not be as apparent is that, as the cost of energy increases, so does the need to examine the operational energy cost of computer equipment during the equipment acquisition cycle. In this article, I will review the manner by which energy is billed and explain why a small change in the cost per kilowatt hour (kwh) can significantly affect the operating cost of data center equipment. I will examine the energy consumption of several general types of equipment and note how a small difference in the consumption level can affect the lifetime cost of equipment.

Overview

Consider the three key components that define an electrical circuit. Those components are the current flowing through a circuit, the voltage potential used to drive the current through the circuit, and the resistance to the flow of electrons in the circuit. The relationship between current (I), voltage (V), and resistance (R) is given by Ohm's Law where:

I = V/R or V = R x I

The resistance unit is the ohm, while current and voltage are expressed in terms of amperes and volts. As current flows through a circuit, heat is generated based upon the current flow and resistance. This heat represents the power expended due to resistance and is expressed as:

P = IV = I2R = V2R

where P is expressed in watts.