Meeting Energy Efficiency Standards for External Power Supplies

I previously wrote about the Energy Independence and Security Act of 2007 (EISA 2007). Its Section 301 establishes efficiency standards for external power supplies (EPS), such as power adapters. The U.S. Department of Energy (DOE) has recently published a Final Rule on "Energy Conservation Program: Certification, Compliance, and Enforcement Requirements for Certain Consumer Products and Commercial and Industrial Equipment." In this document under section 430.24 (bb), is the requirement for determining the number of EPS units to be tested to claim compliance with EISA 2007. In short, the DOE document requires 97.5% confidence level to reflect variations in materials, the manufacturing process, and testing tolerances.

The Section 24(bb) of Title 10 of the Code of Federal Regulations (10 CFR) Part 430 states:
For each basic model of external power supply selected for testing, a sample of sufficient size shall be selected at random and tested to ensure that—

(1) Any represented value of the estimated energy consumption of a basic model for which consumers would favor lower values shall be no less than the higher of: (i) The mean of the sample, or (ii) The upper 97.5 percent confidence limit of the true mean divided by 1.05;

and

(2) Any represented value of the estimated energy consumption of a basic model for which consumers would favor higher values shall be no greater than the lower of: (i) The mean of the sample, or (ii) The lower 97.5 percent confidence limit of the true mean divided by 0.95.

To demonstrate compliance with EISA 2007 standards for Class A EPSs (in effect since July 1, 2008), manufacturers must test representative sample of units according to the DOE test procedure, and certify their compliance by submitting a compliance statement and the first certification report to DOE by July 6, 2010.

To translate their language to plain English, when they say the "represented value of energy consumption for which consumers would favor higher values" they refer to the efficiency. Conversely, the "represented value for which consumers would favor lower values" is input watts. (Our lawmakers of course presume they know what we, the consumers would favor. Would you favor a charger with 51% efficiency over a charger with 49% if the latter one costs twice less?)

To determine the number of the samples to be tested to confirm the compliance with 97.5% confidence level, the manufacturers would have to revisit the statistical analysis theory. To be able to sell the affected external power supplies in US, they have to do the testing, the math, and to submit the required docs to DOE by 07/06/10.