Ratings for Standards, A Quarter Century at a Time

Appliance and equipment efficiency rating methods are laboratory tests based on models of how we think equipment operates in the field. Rating methods determine compliance with efficiency standards, and underlie incentive programs. Product efficiency claims in the US must be based on the federal standards, so manufacturers design to maximize test performance. “What you measure is what you get.” But, most rating methods date back decades. Technologies have changed, and many rating methods are obsolete. For example, the water heater rating method, developed to compare relative performance of tank water heaters, gives misleading results when used to compare tank to tankless units. The air conditioner rating method uses values for duct resistance and fan power that are much too low, discouraging air handler efficiency investments and distorting humidity control capability. The commercial boiler rating overstates applied efficiency of non-condensing boilers, and drastically underestimates the savings from condensing systems at part load. These shortcomings have profound real-world implications. Federal tax credits were based on incorrect assumptions about tankless water heater savings. Air conditioner rating methods discouraged differentiated regional products that could cost-effectively save energy (and inadequately policed some simulation-certified equipment). As important now, using federal ratings as the basis for efficiency programs may lead to reduced savings from equipment that tests better than it works in the field. We need a national commitment to expanded field studies of how buildings and equipment work and interact, and substantial collaborative work to revise our rating methods to be better models of performance and innovation. As part of the process overhaul, more stringent certification programs are required, and can improve quality as well as performance.