A New Energy Star... in 2007

The Silent Front
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The requirements in the Energy Star draft for PSU efficiency are high, but certainly within reach now, as demonstrated by the first qualifying >80% efficient Seasonic PSU in the 80 Plus program we reported about recently. By the time the new spec becomes effective, >80% efficient PSU should be much more common than they are now. High efficiency in an EPS1U PSU may be a bit harder to achieve simply because of the small size, but allowing just a few dollars increase in almost any PSU category is probably enough for efficiency to be raised to >80%, even with current technology. With enough demand, high efficiency PSU components will also become less expensive as economies of scale slide up. (An Aside: Seasonic's Vincent Chang announced just before the meeting in Washington, D.C., his company's objective to achieve 80 Plus certification for all the PSU products they sell in the US before the end of the 2005.)

Aside from Seasonic's 80 Plus approved PSU, there has been a general effort in recent years by many PSU makers to improve efficiency. Some of this effort comes from the natural competition among about the PSU makers. Efficiency is a natural peformance criteria that can be be used to differentiate from competitiors. The increased efficiency incentive has also come from Intel's PSU guides, which are not mandatory standards, but specifications that almost every PSU and PC maker in the industry follows. This is part of the role that Intel has played since the early formative days of the PC industry: Set rules and guidelines for companies to follow in order to build products that work with each other.

Those who have followed the evolution of the ATX12V Power Supply Design Guide (now v2.01) authored by Intel's power division can identify that it was the release of v1.3 in April 2003 that added efficiency guidelines at typical and light loads, and saw the minimum efficiency increased from 68% to 70%. Details for Energy Star and standby efficiency were also added in that version.

From AXT12V v2.0 Guide: "Minimum PSU Efficiency Vs Load"
Loading Full Typical Light
Required Min 70% 70% 60%
Recommended Min 75% 80% 68%

Version 2.0 of the ATX12V guide released February 2003 underwent a few more significant changes. Aside from those related to higher power requirements for more power hungry systems, section 3.2.5. for Efficiency listed not only the required minimum efficiency, but for the first time, the recommended minimum efficiency. Those numbers are substantially higher. At a presentation in Europe late last fall, Intel unveiled the possible recommended numbers for this year: >80% efficiency at 50% load and >75% at 20% and 100% loads.

A interesting point is that the >80% PSU AC-to-DC conversion efficiency at 20, 50 and 100% load specified in the draft Energy Star spec is the same specification established for the 80 Plus program begin in the first quarter of 2004. Ecos Consulting, the highly specialized company that created the 80 Plus program, "only undertakes projects that make a positive environmental impact" and has been successful in helping utility companies encourage conservation among its customers rather than build more power generation capacity (which is more costly).

It turns out Intel's power department personnel, and the Ecos Consulting folks have been attending some of the same power conversion seminars and trade events, and began influencing each other some time ago. It's difficult to attribute particular ideas to any one specific group or individual; a confluence of factors lead to the same efficiency target being adopted for the draft Energy Star spec. It's even possble that Intel's ATX12V guide will recommend the same 80% across-all-loads efficiency by the time the new Energy Star spec becomes effective.

One thing is very clear: Computer PSUs have become noticeably more efficient over the three years that SPCR has been reviewing them.


This was a topic of discussion in one of the sessions at the recent IDF in San Francisco, the concept of choosing a PSU whose efficiency curve is well-matched to the system power load. Such matching can yield incremental improvements in average power consumption and ensure that the right amount of power supply capacity is paid for. Correct PSU sizing is very carefully practiced by tier one computer makers concerned with maximum cost effectiveness.

SPCR's own PSU testing has shown that power efficiency in PSUs varies not only with load but also from model to model. In a given line of PSU models, the maximum and average efficiency tends to be very similar; where the peak occurs depends mostly on power rating. Most PSUs reach peak efficiency between 50~75% loading, tail off a bit at maximum power and drop at least 10% at minimum load.

PSU efficiency data from SPCR review database.

A 250W PSU for a system that draws 200W maximum and idles at 50W means the PSU and system are well suited for each other, and the PSU usually runs at its most efficient. A 500W PSU in this system would never operate at maximum efficiency, and in idle, work at <10% below best efficiency. This is an example of incorrect, costly PSU sizing. It is practised most frequently by gaming enthsiasts who are encouraged to believe that greater power capacity is always better.


The current non-mention of Power Factor Correction in the Energy Star draft is something of an oddity. PFC is mandatory for any >75W device in most other industrialized nations, including Japan, China and the EU. Why not make it part of Energy Star at least? Active Power Factor Correction, in particular, has the potential to greatly reduce harmonics and other garbage in the AC lines. For industrial or commercial operators who pay for VA rather than Watts, there is real money to be saved. The utility bill is reduced, and the size of Uninterruptable Power Supply units can also be significantly reduced.

UPS units are rated and priced by VA. If a low 0.6 PF power supply draws 200W from the wall, it draws 333VA while doing so. This means that to ensure an adequate overhead UPS, you might choose a 350VA or 400VA unit. But with an Active PFC PSU, the same 200W draw will allow result in ~205VA or lower. This means a single 450VA UPS would handle two 200W computers. Multiply the savings in the utility bill, UPS backup costs, reduced AC rewiring needs (due to lower current demand) for a corporate building housing several thousand computers, and possibly reduced air conditioning bills due to lower IT heat, and suddenly the numbers get pretty enticing for bean counters, CTOs and even CEOs.

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