M e m o r a n d u m
FROM:
Michael Baker, SBW
TO:
RTF Staff
DATE:
February 11, 2013
RE:
Phase I Review and Update Recommendations: Floating Head Pressure Controls on
Single Compressor Systems
This memo documents the results of Cadmus’s detailed review of the UES (Unit Energy Savings) measure
Floating Head Pressure Controls on Single Compressor Systems. This measure has been classified by the
RTF as Proven. This measure includes savings resulting from adding an adjustable condenser head
pressure control valve to refrigeration systems with single compressors. The head pressure control
(flood back) valve must be set to 70°F or lower. The compressor must be 1 HP or larger. The review
focused on the derivation of Unit Energy Savings (UES).
Summary Recommendation. The status of this measure should be changed to Out-of-Compliance.
The following recommendations lead to a change in status to Out-of-Compliance.
1. The eQuest simulation models used to derive energy savings by motor size, climate zone, and
case temperature need to be made public for review.
2. The Suction Temperature Setpoints used to derive savings need a citable source.
3. The models need to be calibrated to baseline and efficient-case data.
4. The eQuest model output for 7.5 HP compressors for medium temperature unitary condensers
should be re-examined to correct a discrepancy in baseline and proposed energy use relative to
other compressor sizes.
5. The geographic area of climate zones should be clarified and the distribution of stores by
climate zone should be re-examined.
The following recommendations lead to a change in status to Under Review.
1. Workbook needs to be updated to use latest ProCost template, which includes Measure Cost
and EUL summary worksheets.
2. The sensitivity analysis and tornado diagrams should be removed from the workbook.
3. The analysis should have used a 3 HP compressor motor to calculate the climate-weighted UES
for medium temperature unitary condensers, rather than a 5 HP compressor.
2820 Northup Way, Suite 230
Bellevue, WA 98004
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Limitation of Review.
None.
Alterations to Workbook and Documentation.
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
Since the measure definition stated compressors must be 1 HP or larger, in the worksheet
“CondUnit Weighted Savings”, references to 0.5 HP compressors were removed.
Corrected misspellings and grammatical errors.
The worksheet “Measure_InputOutput” contained numerous rows for compressor motor size
iterations that were not used in final UES estimates. Unused rows were removed.
On the worksheets “CondUnit Sensitivity Analysis” and “Remote Sensitivity Anal,” the maximum
compressor oversizing is listed as 120%, while the typical value is listed as 130%. Values were
reversed so they were in appropriate cells.
Workbook Calculation Errors.
a) No calculation errors were found.
Recommendations for Updates.
The RTF should implement the following recommendations.
1) Workbook Structure and Formulas
b) Update workbook with latest ProCost template to include Measure Cost and Effective Useful
Life (EUL) summary worksheets. This deficiency causes the measure status to change to
Under Review.
c) On worksheet “CondUnit Sensitivity Analysis” an analyst notes “some errors were found in
the modeling method used in the sensitivity analysis which is why the ‘typical’ values from
tornado diagrams do not match final savings values.” As an example, the medium
temperature unitary condenser tornado diagram used 3 HP as the typical compressor motor
size, although the analysis used a 5 HP compressor. The typical energy savings in each
tornado diagram is significantly different from the final UES value (for example, 315 kWh in
the medium temperature unitary tornado diagram versus the final UES of 757 kWh). Since
these types of analysis are not valid UES analysis mythologies, these worksheets should be
removed from the workbook. This deficiency causes the measure status to change to Under
Review.
2) Documentation
a) The review team did not have access to the eQuest simulation models used to derive energy
savings by Compressor Size, climate zone, and case temperature. The review team also did
not have access to the GrocerSmart database that identified the frequency of Compressor
Size by case temperature and distribution of stores by climate zones. The workbook also
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does not list the source and geographic range of climate zones use to determine Climate
Weighting Factors. Those do not match the climate zone maps with which the review team
typically works, such as ones produced by the RTF1 or Pacific Northwest National
Laboratory2. Therefore, the review team could not confirm the accuracy of this data due to
lack of documentation. This deficiency causes the measure status to change to Out-ofCompliance.
b) The analysis cites the following Suction Temperature Setpoints. However, the source of
these set points is not cited. This deficiency causes the measure status to change to Out-ofCompliance.
a. Condensing Unit MT: 12°F
b. Condensing Unit LT: -23°F
c. Remote Condenser MT: 17°F
d. Remote Condenser LT: -20°F
3) Measure Definition
a) No changes recommended.
4) UES Savings Estimation Method
a) The analyst calculated the motor-weighted energy savings for medium temperature unitary
condenser at 803 kWh per year. The analyst then used eQuest runs with a 5 HP compressor
to calculate the climate-weighted UES value for this measure. As shown in Table 1 below,
the closest value to the motor-weighted savings was the 3 HP compressor, not the 5 HP
compressor. Based on the results, the 5 HP compressor savings may have been selected as
the more conservative value since they are less than those for the 3 HP compressor.
However, this is not indicated in the documentation, which only stated the 5 HP motor
“most closely matched the weighted motor savings.” The review team recommends the
compressor size used to calculate the climate-weighted UES for medium temperature
unitary condensers be changed to 3 HP. This deficiency causes the measure status to change
to Under Review.
Table 1. Variance from Weighted Energy Savings by Compressor Size
Compressor
HP
1
2
3
5
7.5
10
Baseline
Energy Use
(kWh)
85,607
119,886
132,159
143,527
121,550
167,471
Proposed
Energy Use
(kWh)
85,095
118,024
129,679
139,725
114,943
160,136
Energy
Savings (kWh)
512
931
826
760
881
733
Variance from
Weighted Energy
Savings
-36%
16%
3%
-5%
10%
-9%
1
http://www.nwcouncil.org/energy/rtf/zones/regional_hot.pdf
2
http://apps1.eere.energy.gov/buildings/publications/pdfs/building_america/ba_climateguide_7_1.pdf
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b) The review team noted the analyst derived UES values from the difference in total store
energy use between the eQuest baseline and proposed models with a single compressor per
store, an unlikely scenario for an actual grocery store. The simulation model required
artificial constraints on case size and refrigeration energy for appropriate scaling. The
resulting modeled annual store energy use is less than the average monthly utility bill for an
actual grocery store. The guidelines require that simulation models be calibrated to pre and
post-installation data. This deficiency causes the measure status to change to Out-ofCompliance.
5) Input Parameters
a) The review team identified a discrepancy in the eQuest output for 7.5 HP compressors for
medium temperature unitary condensers. Compressor Size was the primary eQuest model
input that varied between iterations. As compressor HP increases, annual energy use should
increase, as shown in Table 1. The review team noted the 7.5 HP compressor baseline and
proposed energy use decreased over the outputs for the 5 HP compressor. This variance
indicated a potential deficiency in the simulation model assumptions for the 7.5 HP
compressor. The review team recommends investigating the model input parameters to
determine whether the annual energy use should be higher. This deficiency causes of the
measure status to change to Out-of-Compliance.
b) The Climate Weighting relied on GrocerSmart database counts of stores in the Pacific
Northwest by region and climate zone. The Seattle UES value is the largest, and also has the
highest proportion of the overall store population (and therefore the highest weighting). As
noted earlier, the climate zone definitions do not match any with which the review team is
familiar. Therefore, it is not clear what total geographic area each climate zone represents.
The GrocerSmart data indicated 2,938 stores were located in the Seattle region (Zone 22)
and 999 were located in the Portland region (Zone 20), a ratio of 2.9 to 1. The review team
reviewed demographic information and determined the Puget Sound region (Seattle,
Tacoma, Olympia, and adjacent urban areas) has a population of 4,269,349 people1, while
the Portland metropolitan area (Portland, Vancouver, Hillsboro, and adjacent urban areas)
has a population of 2,262,605 people2, a ratio of 1.9 to 1. Without knowledge of the specific
geographic regions encompassing each climate zone, the review team considered it unlikely
that a region with only twice the population would have nearly three times the number of
stores as another region. The review team could not confirm the accuracy of this data. This
deficiency causes the measure status to change to Out-of-Compliance.
Additional Considerations.
None.
1
http://www.census.gov/popest/data/metro/totals/2011/tables/CBSA-EST2011-02.csv
2
http://www.census.gov/popest/data/metro/totals/2011/tables/CBSA-EST2011-01.csv
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