SUMMARY OF EUL-RUL ANALYSIS FOR THE
APRIL 2008 UPDATE TO DEER
Prepared by KEMA Inc.
The purposes of the DEER Update effective useful life (EUL) analysis were to:
 Review EULs in the DEER05 database to ensure that proper values were included
 Develop EULs for new measures not included in DEER05
 Review and, if necessary, revise EULs for past DEER measures
 Develop estimates of remaining useful life (RUL) for early replacement measures
Lifetimes were collected from a variety of sources, including:
 6th and 9th year retention reports from California IOUs
 Other retention/EUL studies from non-California utilities and independent analysts
 Appliance Magazine
 Lawrence Berkeley National Laboratory
 Energy Star
 Food Service Technology Center
 Utility work papers
The sources reviewed are listed in the accompanying spreadsheet along with preliminary
recommended EUL values for the current DEER update.
The number of EUL sources available for the different measures varied widely. We found no
applicable sources for fifteen percent of measures under study, one EUL source for 13 percent
of the measures, two sources for 10 percent of the measures, and three or more sources for 61
percent of the measures. In addition, many EUL sources in the industry are tautological,
referring back to other sources. There are very few statistically robust “cradle to grave” studies
of effective useful measure life. Measure EUL results obtained in this research, if any, were
assessed in combination with:
 The reliability of the DEER05 EUL
 The reliability of the retention studies assessed in this current study
 EULs of similar measures
 Market trends
 Expert judgment
The general approach for selecting EULs for this current DEER Update was to review the
various data sources and their underlying strengths and weaknesses and provide EUL
recommendations that were determined to be most appropriate, based on the information that
was available. Factors that contributed to selection of an EUL for a given measure included:
the technical strength of the study supporting an EUL, the appropriateness of the study for the
measure and market under consideration, the number of studies recommending the same EUL
(or similar EULs), and the reasonableness of the source EUL in light of EULs for similar
measures. In some cases, EULs were extracted directly from source data, and in other cases,
-1-
KEMA
EULs from different sources were averaged. This second approach was used when there were
a range of EUL estimates from different sources, and a preferred source could not be identified.
For a number of measures, there was very limited information on EULs. For these measures, it
was necessary utilize EULs from similar types of measures and to utilize judgment-based EUL
estimates.
RULs
RULs (remaining useful lifetimes) are relevant for early replacement measures that are
designed to retire equipment before the end of their useful live. Early replacement measures
capture additional energy savings that result from the replacement of older, less efficient
equipment with newer, higher efficiency equipment.
Normally, energy savings for “replace on burnout” measures are calculated as the difference in
energy use between the high-efficiency equipment and standard-efficiency equipment that
would have been purchased without program intervention. For early replacement measures,
energy savings are calculated in two parts: for the RUL of the old equipment, savings are
calculated as the difference between the energy use of high efficiency equipment and the old
equipment that is being replaced, and for the remaining measure live, savings are calculated as
the difference in energy use for the high-efficiency equipment and the standard-efficiency
equipment.
For RULs we have proposed using 1/3 of the estimated EUL for a measure. This approach
provides a reasonable RUL estimate without the requiring any a priori knowledge about the age
of the equipment being replaced.
It has also been proposed that RULs could be estimated as a function of the age of the
equipment and the measure EUL. One simple equation is:
RUL = EUL – replaced equipment age.
Alternate equations involve the use of survival functions. However, these equations all require
knowledge about the age of the equipment being replaced, which is not available for program
planning, but could be available for program reporting.
One could use a combination approach to deal with situations where equipment age is known
and where it is unknown:
 If replaced equipment age is known, use equation involving EUL and equipment age
 If replaced equipment is unknown, use 1/3 of the EUL
The primary drawback to the combined approach is that it can be gamed to get higher lifetime
measure savings. If the equipment age is less than 2/3 of the EUL, then one might want to use
the equation approach. If the equipment age is greater than 2/3 of the EUL, then one could
claim not to know the equipment age and thus use 1/3 of the EUL for the RUL.
Given our limited current understanding about appropriate RULs to use for energy savings
calculations, we believe that simple use of 1/3 the EUL to be appropriate for the current DEER
update. We recommend that RULs receive additional study as part of ongoing program
evaluation studies.
-2-
KEMA