Watts what with personal computer power supplies? Part Two

By Peter Brownlee
Monday, 10 September, 2007

As we saw in the first part of this series, computer power supply units are now hot components, in more than one sense of the word. Peter Brownlee looks at the power and heat management issues arising from the new generation of PSUs and what you can do to maximise the energy efficiency of your computer systems.

In most commercial premises as much as 10 to 15% of the total energy bill is feeding the power supplies used in business computers of some kind. Intensively IT businesses such as financial organisations, call centres, ISPs and the like will have computer power as an even higher proportion of total energy costs, especially when air-conditioning and other cooling systems' power requirements are taken into account.

Industry groups are working to manage computer power use more efficiently and we may well see in the very near future much greater public and business awareness of the economic and environmental impact of computer power use.

Government environmental agencies in many countries are also developing and mandating new energy-efficient regulations to govern IT and related digital technologies.

According to 80 Plus, a US electricity utility funded incentive program focused on integrating more energy-efficient power supplies into desktop computers and servers, newly available 80% efficient power supplies are about a third more efficient than most existing PSUs because they reduce the power wasted in heat dispersed into the environment.

Typical current desktop computer power supplies waste some 30 to 45% of the electricity that passes through them, consuming about 125 to 150 kWh/year by themselves.

Desktop-derived servers generally run 24 hours a day, seven days a week, with no sleep modes or power management, so energy savings per unit can be significantly higher than desktop computers.

These supplies consume about 450 to 720 kWh/year (similar energy consumption of a side-by-side refrigerator), so each one represents a savings opportunity of about 300 kWh/year.

In offices, much of this usage occurs on or near the commercial peak, increasing demand charges and the need for additional electricity-generating capacity.

Systems with 80% efficient power supplies are of particular importance since the US Environmental Protection Agency revised its Energy Star certification requirements for hardware. Effective from 20 July 2007, the new guidelines require that computers incorporate 80% efficient power supplies in order to meet the new, more stringent Energy Star 4.0 criteria.

Significantly, 80% efficient power supplies can reduce the need for system maintenance by improving system reliability, reduced system maintenance costs, less noise from fans and other cooling devices, lower air-conditioning and related costs - all due to lower heat generation.

Another substantial benefit of the 80% efficient power supply specification set is its 0.9 active power factor correction (PFC), which means that 90% of the system's apparent power is actually transferred to available real power.

Power supplies that are not power factor corrected tend to cause variations in AC voltage that can distort the performance of - or damage - other equipment on the same circuit.

Active power factor correction in the power supply causes the RMS input current to drop by nearly 50%, and the peak AC input current by over 75% compared with non-power factor corrected power supplies.

Of course, the PSU does not exist in isolation but rather is part of a system in which other elements play crucial roles in determining power needs and performance.

Computer processor manufacturers are integrating the ability to manage power use directly into their latest processors. Enhanced Intel SpeedStep Technology (EIST) and AMD Cool 'n' Quiet Technology both include features that work with the basic input/output system and operating system to lower power consumption.

Business PCs with these types of processors use less power when software activity does not require the full capabilities of the processor. Along with being more environmentally friendly, reduced power consumption results in reduced heat production.

Less heat means lower fan speed requirements, thereby providing quieter, more efficient computers. This technology is also especially useful for notebook computers, as reduced power consumption leads to increased battery life.

PCs with configurable BIOS allow the user or IT manager to balance the thermal requirements and the acoustic levels of the computer to ensure that the computer performs optimally in any environment.

Configurable BIOS enables users to control the airflow in their computers by adjusting the fan speed to be maximised for environments where thermal concerns are a priority, or minimised for acoustically sensitive environments.

The Advanced Configuration and Power Interface Specification (ACPI specifications) sets the technology industry's standard for energy and power system states. The ACPI defines several system states:

  • S1: Standby state resulting in the processor being halted, but content is not lost. All other devices remain at the normal power state. This state offers the fastest wake-up time and the lowest power savings;
  • S3: Standby state known as suspend to RAM. All devices in the system are powered down, except for computer memory. Recovery is almost instant (about 2 to 3 seconds) and power consumption is very low (typically \<5 W);
  • S4: This state is referred to as hibernation. The computer's memory content is saved to the hard drive, then most power is removed from the system;
  • S5: This state is often referred to as soft off. The computer is off. This state offers the slowest wake-up time and the greatest power savings (typically \<2 W).

Many watt classifications of processors exist, but the most common available today are 95, 65 and 35 W processors. While 35 W processors achieve the maximum in power savings, 65 and 95 W devices provide mainstream power savings.

These types of processors keep power requirements to a minimum. At one time, increased performance often meant higher power consumption and more noise. With the development of power-efficient processors from AMD and Intel, performance is treated as 'on-demand', which helps reduce processor heat.

On-demand processor frequency and voltage switching help decrease power and fan speed - resulting in a cooler PC and a quieter work environment.

Replacing CRT displays with thin-film transistor or 'flat panel' screens can also provide substantial power savings. For example, a floor with 100 workstations would require energy consumption of 9000 W an hour if equipped with CRTs, versus only 1700 W/h when equipped with comparable 15-inch TFT monitors.

In addition to the benefits TFTs offer in these areas, their smaller size requires less desk and office space.

With the rising cost of energy, there's a lot at stake when it comes to technology's far-reaching influence on the environment.

As PC manufacturers recognise their relevance to exacting change by incorporating energy-saving systems into their products, businesses and users - as well as the general population - will benefit from these environmentally conscious products and the extensive savings they can provide.

Simply put, when a PC (or any other electronic device) can deliver maximum energy savings, along with enhanced system reliability and a longer equipment life cycle, the overall total cost of technology ownership is dramatically lowered.

Five steps to maximise energy efficiency

Choosing PCs (or individual components) that provide maximum energy savings, enhanced system reliability and longer life cycle can deliver significant savings.

  1. Select a system with an 80% efficient power supply or replace existing PSUs with 80 Plus units;
  2. Select a system that has power management technology and make sure this technology is enabled on all your systems;
  3. Select a system (or motherboard) with a BIOS that offers a wide range of configurable power management options or see if you can upgrade to revised BIOS that does this;
  4. Choose a system processor that provides the maximum level of power efficiency;
  5. Replace cathode ray tube monitors with liquid crystal displays.
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