ASHRAE Journal - December 2019 - 13

TECHNICAL FEATURE

or RCx. As a result, one
of ComEd's independent
energy-efﬁciency consultants, undertook a substantial primary data collection effort, ultimately
visiting 28 separate buildings and investigating 167
individual measures.
The primary objectives of
this study were to:
* Quantify the persistence of RCx measures.
* Identify operational
factors and energy management characteristics
that inﬂuence the persistence of savings.
* Determine how to
improve program activities
to promote persistence or
determine whether RCx
follow-up is needed after
some amount of elapsed
time.

TABLE 1 Prior literature measuring persistence of RCx and commissioning.

Measured
Persistence

Evaluated or
Published
Assumptions

PRIMARY
AUTHOR

NUMBER OF
BUILDINGS

BY MEASURE
OR BUILDING

STUDY TYPE

TIME AFTER
CX (YEARS)

RESULTS: PERSISTENCE

Bourassa

Building

Survey and On-Site

1 to 2

81%

Eardley

Measure

On-Site

Not Stated

36% (Measure Count)

Potter

Measure

Survey and On-Site

2 to 8

69% (Measure Count)

Mills

362

Building

Energy Usage

88% (Measure Count)

Peterson

Measure

On-Site

Electricity: 89%; Gas: 0%

Roberts

Measure Survey (Some On-Site)

1 to 3

Estimated Average EUL - 8 Years

Selch

Measure

Usage Analysis,
Reconducting RCx

Electricity: 83%; Gas: 100%

Toole

Building

Usage Analysis, OnSite, Some Simulation

Overall: 83%

Cadmus-1
(2012)

Evaluation

Assumed EUL - 7 Years

Cadmus-2
(2010)

Evaluation

Assumed EUL - 5 Years

DEER

Established
Assumptions

EUL (Years) - Economizer: 5, RTU
Control: 5, Lighting Control: 8,
Supermarket: 10, Ventilation: 10,
Resets: 10

SBW

Field Study and
Evaluation

1 to 3

Varies by Utility - 3 to 20 Years

Tetra Tech

Evaluation

Assumed EUL - 7 Years

Prior Research
In reviewing literature from the past twenty years,
we found eight studies that had published quantitative
results on the persistence of either commissioning or
RCx (Table 1).
Of those eight, only three had quantiﬁed RCx persistence on a signiﬁcant sample of buildings. And all the
studies varied in type, time frame, and approach, preventing us from doing a substantial meta-study. In taking a simple average of persistence across all the studies,
which ranged from one to eight years of post-RCx data,
we ﬁnd an average persistence of 76%. Little of the data,
however, comes from longer time-frame studies; most
are two to three years post-RCx.
Five studies in our literature were based on program
evaluations and did not include any primary site data
collection (Table 1, Evaluated or Published Assumptions).
These ﬁve publications included estimated useful life (EUL)
data on nine different utility RCx program assumptions.
Two studies departed signiﬁcantly from that overall average of 76%. Peterson (2005) investigated three

buildings about four years after RCx. The study found a
typical rate of persistence with electric measures (83%),
but the few gas measures that they studied had all been
disabled or changed, resulting in a rated persistence of
0% for gas. Eardley (2007) also found lower than typical
persistence. That study only investigated two buildings
but found that roughly two-thirds of the measures in
those buildings had been disabled or had their effectiveness signiﬁcantly reduced. These studies are included
in the averages above but represent less than 10% of the
buildings studied in the eight publications.
The study by Roberts (2010) also stands out from the
others based on the amount and granularity of data collected. It not only collected data on 32 buildings, it did so
on a measure-by-measure basis. The majority of typical
RCx measures (schedules, resets, setpoints, valves/dampers, etc.) were investigated, and most showed high persistence. Eighty percent of the measures persisted after three
years while 20% did not. Speciﬁc measures that degraded
more than others include HVAC scheduling (60% of measures persisted), temperature setpoints (38%), boiler controls (33%), and lighting occupancy sensors (0%). We also
D E C E M B E R 2 0 19

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ASHRAE Journal - December 2019

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