M e m o r a n d u m
FROM:
Michael Baker, SBW
TO:
Gillian Charles
DATE:
December 2, 2010
RE:
Deemed Measure Detail Review and Update Recommendations: Residential
Showerheads
CC:
Tom Eckman, Charlie Grist and Adam Hadley
This memo documents the results of SBW’s detailed review of the deemed measure category Residential
Showerheads. This measure category covers the installation of showerheads with nominal flow rate of
2.0, 1.75, or 1.5 gpm. Savings are computed against the current federal standard of 2.5 gpm (nominal)
for all types of residences. The delivery method can be retail purchase, direct install, or mail-by-request.
Gas savings are provided for homes with gas water heating. However, our review only covers the electric
savings (homes with electric water heating, and the electric savings due to reductions in water and
wastewater treatment). Savings are also delineated according to whether the showerhead is installed in
a primary or secondary shower. The review focused on the derivation of Unit Energy Savings (UES).
Summary Recommendation. This measure category should be re-classified as under review. Once the
recommended updates to the UES values have been implemented, it can be returned to the
classification deemed. Separate UES values should be estimated for showerheads multi-family
residences, but this should be possible based on existing sources. Additional data is needed to confirm
the installation rate for the retail delivery method. Also additional research, which accounts for
differences in spray force and coverage, should be considered to more definitively determine whether
shower duration is affected by the installation of efficient showerheads.
Limitation of Review. None.
Additions to Workbook Documentation.

A sheet called “Summary” has been added to the workbook. This sheet describes how measures
are identified, lists important constants and their sources, describes the savings estimation
2820 Northup Way, Suite 230
Bellevue, WA 98004
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
algorithm and the associated baseline and efficient case parameters and their sources for each
measure and UES component.
The following modifications were made to improve the documentation of sources within the
workbook:
o
On sheet ‘Current Input Assumptions’, added source figure for the rated baseline
showerhead flow rate (2.5 gpm).
o
On sheet ‘Residential Analysis’, added source figures for the RTF decision to use 2.2 gpm for
the in-situ baseline showerhead flow rate.
o
On sheet ‘Current Input Assumptions’, added source figure that was used to determine the
in-situ efficient case flow rate percentage. (90% of the rated showerhead flow rate)
o
On sheet ‘Residential Analysis’, added source figure that was used to estimate the number
of persons per showerhead.
o
On sheet ‘Current Input Assumptions’, added source figure that was used to estimate the
shower duration (minutes per shower).
o
On sheet ‘Residential Analysis’, added source figures that were used to estimate the range
of values for number of showers per person per day.
o
On sheet ‘Residential Analysis’, added source figure that RTF used to inform them of a
decision to use 75 degrees Fahrenheit as the difference between water heater inlet and
outlet temperatures.
o
On sheet ‘Current Input Assumptions’, added source figures that were used to estimate pre
and post-retrofit hot water mix percentages.
o
On sheet ‘Current Input Assumptions’, added source figures that were used to estimate
electric and gas water heater efficiencies.
Workbook Calculation Errors. No calculation errors were found.
Recommendations for Updates. The RTF should consider the following findings and recommendations
for additional updates:
1) Workbook Structure and Formulas
a) Total savings for each measure are the sum of two UES components. The lines of ProCost input
found on the sheet ShowerHead should be sorted so that the UES components for each
measure are on adjacent rows.
b) Consider removing ambiguous values used on sheet ‘Current Input Assumptions’. There are
values presented in the ‘Actual Flow Rate as a Percentage of Rated Flow Rate’ section (Range
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A28:H37) that suggest a different method for estimating savings compared to the method used
on the ‘Residential Analysis’ sheet. The ‘Residential Analysis’ sheet values are ultimately used for
the measure savings. The ambiguous/confusing values are:
i)
In-situ “baseline” flow rate of 2.25 gpm. This in-situ flow rate is not used for the baseline insitu flow rate in the savings analysis; 2.20 gpm is used as the baseline in-situ flow rate,
developed from reference to a 2008 impact evaluation (Seattle City Light, 2008). The layout
suggests that an in-situ flow rate percentage of 90% was going to be used on the rated
baseline flow rate of 2.5 gpm to give a baseline in-situ flow rate of 2.25 gpm, but this option
was abandoned over the 2.2 gpm baseline in-situ flow rate. This cell should be grayed out or
a comment should be included to note this discrepancy.
ii) % of Rated Flow Rate value of 90% for the baseline in-situ flow rate. This value is not used to
determine the baseline in-situ flow rate; a directly referenced value of 2.2 gpm is used for
the baseline in-situ flow rate (See the bullet above). This cell should be grayed out or a
comment should be included to note this discrepancy.
iii) The hot water temperatures (Range G32:G35) that are calculated under the “Hot Water
Percentage” area are not used in the savings analysis; only the hot water percentages
(Range F32:F35) are used to calculate savings. A difference of 75 degrees Fahrenheit
between the water heater inlet and outlet temperature is used along with the hot water
percentages to determine savings. The hot water temperatures should be removed or at
least moved to another area on the worksheet to reduce the chance of confusion in the
savings methodology.
iv) A comment (Cell H37) does not follow current values used in analysis. This comment should
be removed, or updated to represent the current analysis.
2) Documentation
a) No changes recommended.
3) Measure Definition
a) Consider timing and details of WaterSense Specification and whether this should in the future
become part measure definition.
4) UES Savings Estimation Method
a) Savings should be estimated separately for single and multi-family residences.
5) Input Parameters
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a) Review a U.S. EPA combined study1 that shows the possible range of values for number of
showers per person per day to see if there is sufficient basis for any changes to the assumed
value of 0.55.
b) Shower Duration Factor: Currently, the efficient case shower duration is increased from the
baseline shower duration due to a baseline shower duration % factor. This factor compensates
for the current assumption that lower flow rates correspond to longer shower durations.
Consider removing this factor and keep baseline and efficient case shower durations equivalent.
Although the workbook comments on the lack of empirical evidence to support this claim of
increased shower duration due to a lower flow rate, the studies reviewed do not support this
claim, and in fact, the data shows the contrary – shower duration decreased after installing a
lower flow showerhead. While the change in shower duration was only found to be statistically
significant in one of the three studies, the current data suggests that, if anything, a switch to
lower flow showerheads will not increase shower duration. Additional study may be warranted
as none of the studies yet account for difference in spray force and coverage among the
baseline and efficient showerheads Installation Rates: Consider updating the installation rates
for the different delivery types. The main rate used in the workbook analysis is a 90 percent
installation rate for direct-install, from a 2007 SPU Showerhead/aerator pilot program. This
value is then reduced for retail and mail-by-request installation rates, based on the assumption
that there is a correlation between lower flow rate and lower satisfaction. A recent PSE survey
study revealed that 76 percent of showerheads mailed to customers (mail-by-request) were still
installed 4 months after delivery, compared to the 60 percent installation rate currently being
used in the workbook analysis. While the 90 percent installation rate for the direct-install
program is still appropriate, update the mail-by-request program installation rates with the PSE
result of .76. Additional study is needed to determine the installation rates for the retail
delivery method.
c) The PSE survey study also determines the placement rates of low flow showerheads being
installed in the primary and secondary showers, so installation rates could be separately
determined for the primary and secondary showers. Consider further updates to program
installation rates by adding a weighting factor to the installation rates based on delivery type
and shower type (primary, secondary, etc.).
1
“Water and Energy Savings from High Efficiency Fixtures and Appliances in Single Family Homes: Volume
1”; Combined Retrofit Report; U.S. EPA 2005
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