Understanding Watts, Amps, KVA and Power Usage Effectiveness (PUE)

Watts, amperes, volts and kilovolts don’t often come up in general conversation, but these “power terms” are part of the day-to-day vocabulary in data center operations. Read on to learn some basic power terms and understand the importance of power usage effectiveness (PUE) in data center efficiency initiatives.

Power Terms Defined

Knowledge is power, right? So let’s jump into terms used in data center network architecture planning – one aspect of the complex world of electrical technology. For a deeper dive, check out the U.S. Department of Energy’s how-it-works report, All About Circuits and Electrical Classroom.

• Power supply chain – a system that delivers electrical power to run a data center. The chain typically spans power generation, distribution, management and backup systems.
• Watt (W) – a unit of power that measures the amount of electricity a device consumes.
• Ampere or amp (A) – electrical current.
• Volt or voltage (V) – a measurement of the electric pressure at which electricity flows through a system.
• Apparent power – the total power in an AC circuit (real power and reactive power), measured in volt-amperes (VA).
• Kilovolt-amperes (kVA) – a measurement of apparent power in a system. One kVA is 1,000 volt amps.
• Current – the flow of electrical charge per unit of time, measured in amperes. Direct current (DC) flows in one direction. Alternating current (AC) reverses direction periodically.
• Real (or true) power – the amount of actual power, measured in watts, that can be drawn from a circuit. Real power is the workhorse that produces an outcome such as light or heat.
• Reactive power – moves back and forth in a circuit between the source and reactive components but doesn’t do any work but is essential for maintaining voltage levels within power systems.
• Gigawatt (GW) – a unit of power equal to one billion watts.

We’ll use some of these terms in examples below; but first, an introduction to PUE.

Power Usage Effectiveness

Given the expected growth in power demand, a spotlight is on efficiency. PUE is an industry-accepted standard to quantify the energy efficiency of a data center. A PUE rating compares total power used to the power used by IT equipment. A lower number indicates better use of watts, meaning less wasted energy.

A PUE rating, however, is influenced by climate, cooling systems, the layout of the data center, the power supply chain, IT equipment, equipment underutilization (overprovisioning) and other variables.

An organization called PUE Calculator is a good resource for more information on data center energy efficiency. If you follow the link we’ve provided, you will see that they describe PUE ratings this way:

• Very Efficient (1.0-1.2) – World-class efficiency, typically seen in highly optimized facilities
• Efficient (1.2-1.5) – Good efficiency, achievable with modern best practices
• Average (1.5-2.0) – Room for improvement, typical of many existing facilities
• Inefficient (2.0+) – Significant improvement needed, indicates outdated infrastructure³

According to the U.S. Department of Energy, an average data center has a PUE of 1.6. A PUE of 1.0 represents the ideal – where every watt of energy supports computing, with none lost to cooling, lighting or overhead.⁴ Realistically, PUE will be above 1.0 because data centers are operating with certain variables, like climate, that can’t be controlled.

Power Factor, Real Power (Watts) and Apparent Power (kVA)

The power factor is used to measure and express an energy inefficiency. It’s a ratio of real power and apparent power. The typical measurement range of power factor is 0 (low) to 1 (ideal efficiency level). In the case of a 1.0 power factor, the real power equals the apparent power. In the case of a 0.5 power factor, real power is approximately half that of the apparent power. Systems that have higher power factors result in less electrical loss, and they can help improve PUE.

Let’s look at two examples. The first is a type of inefficiency that relates to the difference between real (or true) power and apparent power during electrical transmission. When the voltage and current of a circuit coincide, the real power is equal to the apparent power. However, as waves of current and voltage coincide less, less real power is transferred, even though the circuit is still carrying current.

The second example concerns an uninterrupted power supply (UPS) and UPS efficiency. UPS units typically list the average power factor and real-time load capacity of the UPS, in addition to the kVA. Assume a 500 kVA UPS unit (apparent power) with a 0.9 power factor. The resulting real power is 450 kilowatts.

Best Practices for Optimizing UPS Efficiency and PUE

Regulations and energy efficiency goals motivate data center operators to identify energy inefficiencies that waste heat or waste current. Actions that can improve PUE include:

• Update cooling strategies by evaluating airflow, cold aisle containment (isolating cold air supply from hot air exhaust), liquid cooling technologies and other relevant power supply chain components.
• Install energy-efficient power supplies and automated lighting.
• Use autoscaling technology, which is offered by the major cloud providers, to automatically adjust the use of cloud resources.
• Monitor and track PUE to set a baseline for improvement.
• Keep PUE in mind throughout data center lifecycle planning and design.

Know More

Visit CoreSite’s Knowledge Base to learn more about the ways in which data centers are meeting clients’ constantly increasing power and other infrastructure requirements.

The Knowledge Base includes informative videos, infographics, articles and more. This digital content hub highlights the pivotal role data centers play in transmitting, processing and storing vast amounts of data across both wireless and wireline networks – acting as the invisible engine that helps keep the modern world running smoothly.

Ready to discuss how CoreSite colocation data centers can help you achieve digital transformation objectives and execute a winning distributed computing strategy?  Contact us!

References
1. BCG, Breaking Barriers to Data Center Growth (source)
2. U.S. Department of Energy, How Much Power Is 1 Gigawatt? (source)
3. PUE Calculator, What Is PUE? Complete Guide to Power Usage Effectiveness (2024) (source)
4. Airedale, Power Usage Effectiveness: What It Means and Why It Matters (source)