Table of Contents
Summary.................................................................................................................................... 3
Introduction ............................................................................................................................... 4
Motivation for Scoring .............................................................................................................. 4
Scoring Approach .................................................................................................................... 7
Score Applications.................................................................................................................. 12
Conclusions ............................................................................................................................. 14
References .............................................................................................................................. 152

Arc Performance Scores Core Concepts Guide
Pyke, C.R. (2021) Arc Performance Score – Core Concepts. Arc Skoru, LLC, Washington,
DC. 15 pages.

Summary
Arc is a technology platform to measure, analyze, and score the operational
performance of spaces, buildings, and places around the world. The Arc Performance
Score serves as the foundation for multiple Leadership in Energy and Environmental
Design (LEED) rating systems, including LEED v4.1 for Operations and Maintenance. The
Arc Performance Score is a weighted composite of five performance categories,
including energy, water, waste, transportation, and human experience. Category
scores are based on measured performance, including metrics for greenhouse gas
emissions, source energy consumption, potable water use, occupant satisfaction, andother factors. Metrics are normalized and compared to a global Reference Set
composed of 3,103 projects. An Arc Performance Score of 100 indicates that a projectis superior to all projects in the Reference Set, while a score of 0 indicates that it
underperforms all projects in the Reference Set. A minimum score of 40 is needed topursue LEED certification. Arc performance data provide an unprecedented view ofthe operational performance of LEED-certified projects. The data show that LEED
Platinum projects have an average greenhouse gas emissions intensity of 1.14 metrictonnes per occupant per year -- 63% better than the average for LEED Certified
projects. This reduction in emissions intensity is accompanied by a 19% improvement inaverage occupant satisfaction. Arc’s combination of benchmark-based scores andperformance indicators provide a powerful new market transformation tool.

3

Introduction
Arc is a technology platform to score the operational performance of spaces, buildings,
and places around the world. Arc is part of the U.S. Green Building Council’s family ofmarket transformation tools. Arc Performance Scores serve as the foundation for
multiple Leadership in Energy and Environmental Design (LEED) rating systems, including
LEED v4.1 for Operations and Maintenance, LEED v4.1 for Existing Interiors, LEED
Recertification, and LEED for Cities & Communities. Through October 2020, 3.9 billion
square feet have been activated on the Arc platform. These projects are located in 127
countries, and they have more than 7 million occupants. The projects report emitting
115 million metric tonnes of greenhouse gases over the last 12 months. During 2020,
approximately 19,000 individual users access the system to add, manage, or view
performance data each 90-days. Going forward, Arc represents a core technology tosupport the use of operational performance in green building practice.
This paper explains Arc’s approach to scoring the operational performance for spaces
and buildings. The paper is divided into three sections: motivation for scoring, scoring
approach, and scoring applications.

Motivation for Scoring
Arc emphasizes scoring as a tool to understand and communicate the operational
performance of spaces and buildings. Arc’s focus on scoring is motivated by threegoals: simplification, differentiation and flexibility.

Simplification
Arc is based on the idea that the future of green building is rooted in measuring theoperational performance of buildings, portfolios and communities. The idea is thatmeasured, real-world performance will complement and, in some cases, replace
documentation as the basis for recognizing high-performing green buildings. Ultimately,
this is driven by the desire to ensure that green buildings consistently deliver real-world
results.
In fact, we seek to define “green buildings” as facilities that deliver superior conditions
for people and benefits to the environment. Arc helps advance this definition withmetrics and scores encompassing human experience and multiple aspects ofenvironmental performance. However, there is no single, direct measurement of thisconcept. Operationalizing this idea requires a level of aggregation and interpretation.
Human experience in and around buildings reflects many performance dimensions,4

including thermal comfort, daylight, odors, noises, vibrations, chemical exposures andmuch more. Similarly, we have many ways to measure environmental performance,
including total energy use, peak demand, energy use intensity and more. Scoring
provides a way to aggregate and simplify this kind of multifaceted data into somethingthat can be readily understood and communicated understand, such as a 0-to-100
score.
There is both an art and a science to scoring. The art of scoring comes first. This may besurprising, since on the surface, scoring looks like math. However, scoring starts withspecific goals and values. In the case of Arc, the goal is to use operational
performance data to assess the degree to which spaces and buildings provide superiorconditions for people while protecting the environment. Evaluating these concepts
involves assigning weights to categories of project performance, such as energy
efficiency, accessibility, or water conservation. By design, these categories are discrete
concepts, such as greenhouse gas emissions, toxic exposure, or stormwater runoff. A
scoring framework can aggregate performance across these factors. The relative
importance of each issue can be analyzed in various ways, but weights for different
categories are ultimately an expression of values, not science.
Once values have been expressed, we get to the science of scoring. The science
involves selecting the most concise set of practical, measurable metrics to represent
each area of performance. Further, it involves making a myriad of increasingly granulardecisions regarding how metrics are defined, measured, analyzed and interpreted. For
example, we need to decide whether we measure occupant satisfaction on a 0 to 5 ora 1 to 10 scale, or, alternatively, if we measure CO2 concentration every year, month,day, hour, minute or second. Fortunately, we can analyze alternative strategies andlook for strategies that best represent different dimensions of performance.
Ultimately, scoring mixes structural choices, such as the number of categories and theirrelative weights, with a myriad of small choices, e.g., the interpretation of individual
metrics, to aggregate information. Scores do not create data. Rather, they interpretand simplify data to answer a specific question. In Arc’s case, this means reducing fivecategories and more than a dozen measured variables into a simple 0-to-100 score thatcan be used to communicate performance.

5Differentiation
The next critical issue is whether the score meaningfully distinguishes spaces andbuildings. In the case of Arc, we are trying to differentiate spaces, buildings and placesby the degree to which they actually provide superior conditions for people, while
protecting the environment. This means that the value of an Arc Performance Score isreflected by the degree to which a high score (100) is meaningfully different from a lowscore (0).
The Performance Score ensures that a high-scoring space or building has low
greenhouse gas emissions relative to similar projects with higher emissions. A project witha high overall Performance Score must also use less water, generate less waste andprovide a more satisfying indoor environment than its peers. It is equally true that a lowscoring building has higher emissions and is relatively lower performing with respect towater, waste and human experience. These conditions are enforced by the structure of
the Performance Score and the underlying interpretation of individual metrics.

Flexibility
The last essential element of scoring is flexibility. This might be a little less obvious. Arc
provides a hierarchical structure linking multiple measures of operational performanceto performance categories and ultimately to an aggregated score. One benefit of thisstructure is the ability to change individual metrics without reinventing the scoring
system or disrupting the function of other performance categories.
For example, Arc has tools to assess transportation behavior. Today, the primaryassessment tool is an occupant survey, and the metric is commuting-related
greenhouse gas emissions. In the future it might be possible to assess transportation
information based on a mobile app and potentially add a metric for time spentcommuting. Arc’s structure allows us to swap the assessment method and add an
additional metric, while still expressing the transportation score in terms of 0 to 100. This
allows for a “plug-and-play” relationship between individual performance metrics andtheir performance categories, while preserving the overall scoring structure. The
structure provides the flexibility for the basis for scoring to evolve over time.

6

Scoring Approach
The overall Arc Performance Score answers one specific question: How does a projectcompare to green buildings around the world green? The Arc Performance Score isbased on a three-level structure using five categories. It uses three types of informationin addition to measured performance data for each category:
1. Normalizations for floor area, occupancy, schedule, and outdoor air
temperature.
2. Key parameters, critically including the greenhouse gas emissions factor of gridsupplied electricity.
3. A Reference Set of green building projects around the world

Score Structure
The overall Arc Performance Score is a 0-to-100 metric. It is not limited to whole numbers
and fractional scores are allowed:
Arc Performance Score [0-100] =⅀(Category Weight * Category Score)
Category Score [0-100] =⅀(Metric Weight * Metric Score)
Metrics Score [0-100] = f(reference set, normalizations, parameters)
Performance categories include energy (33%), water (15%), waste (8%), transportation(14%), and human experience (20%). These weights are based on priorities establishedin the LEED v4.1 rating system, and, consequently, these reflect the expressed values of
the LEED Steering Committee and USGBC membership (USGBC 2015). The result is acomposite 0-100 value for any project, each category, and each metric. Minimum
data requirements to generate an Arc Performance Score for use with LEED include:
●
●
●
●
●

≥12 consecutive months of whole project energy consumption data
≥12 consecutive months of whole project water use data
≥1 survey for whole building waste generation and diversion from landfill
per year≥1 survey of occupant commuting per year
≥1 occupant satisfaction survey and measured carbon dioxide (CO2) andvolatile organic compound (VOC) concentrations

7

Measured data and normalizations used for each category are described in moredetail in the following section.
Arc applies two different strategies to interpret measured performance and generate
metric scores.
1. Reference Set Scoring: Energy, water, and waste performance are evaluated bycomparing a project to a “Reference Set”. This is a collection of projects
assembled to represent the range of energy, water, and waste performanceobserved for green buildings around the world.
2. Absolute Scoring: Transportation and Human Experience are evaluated basedon scoring functions. Transportation is based on transportation-related emissions
for average US commutes. Human Experience scores are based onmathematical interpretations of occupant satisfaction and measuring CO2 andVOC concentrations. These relationships are not based on the Reference Set.
Reference Set Scoring
Energy, water, and waste are scored based on intensities and comparisons to the Arc
Reference Set. Metrics scored based the Reference Set include:●●●

Energy○ Source energy○ GHG emissions
Water○ Potable water consumption
Waste○ Waste generation○ Waste diversion

Reference Set-based scoring for energy, water, and waste has several fundamental
characteristics (Othman 2013). Scoring relationships in Arc are:●●●Continuous – small changes in inputs produce small changes in output scores.
Multi-dimensional – buildings being scored can be described by many attributes(size, occupancy, etc.)
Monotone – Scores either always go up or always go down with an isolatedchange to each attribute.

8●Interpolating – Scores are generated based on a set of reference buildings. For
each reference building, the score produced by the spline is exactly the scorerequested in its input.

Taken together, the scoring process effectively provides a weighted average based on
the “similarity” of a new project to projects in the Arc Reference Set (Reference Set),
where similarity is based on floor area, occupancy, schedule, and outdoor air
temperature. The Reference Set is not divided by property type. This represented aconscious decision to focus on continuous variables and avoid classification issues
associated with complex, highly variable combinations of use types common amonggreen buildings (Todd et al. 2013, Heidarinejad et al. 2014).
The Reference Set was assembled from available LEED project data with a specificemphasis on representation of building types and buildings representing extreme
parameters (e.g., floor area, occupant density, energy intensity, etc.). The Reference
Set includes a total of 3,103 projects. The fraction of projects with complete scorable
data for each category varies. The Reference Set is static, and new projects using Arc
are not currently being added to the Reference Set.
The inputs to each Reference Set-based score are presented in Table 1. These yield acategory score between 0-and-100 based on the weighted rank in the Reference Set.
The relationship between metrics and scores varies function of occupancy, schedule,
floor area, and temperature. However, it is possible to describe several generalcharacteristics of these scores:●●●

Energy Score: The maximum score of 100 requires measured performancenear net zero energy and net zero carbon.
Water Score: The maximum score of 100 requires very low use of potablewater per occupant, e.g., <0.5 gallon per square foot per day.
Waste Score: The maximum score of 100 requires very low waste
generation and high waste diversion, e.g., <1 lbs per person per day with>95% diversion from landfill.

Arc provides tools to model Performance Scores for any combination of parametersand performance across all five categories.

9

Table 1. Energy, water, and waste are scored with respect to the Reference Set. Scores
are based on the data, normalization, and parameters below.
Energy Score

Water Score

Waste Score

Sub-Scores

Source energy intensity
GHG emissions intensity

Potablewater/occupant
Potable water/floor
area

Waste generation
Waste diversion

Measurements

Liquid fuels, electricity,
steam (min. monthly)

Whole project
potable water
consumption (min.
monthly)

Waste generation
intensity
Undiverted waste
intensity (1 survey/year)

Normalizations

Floor area,
occupancy, schedule,
outdoor air
temperature

Floor area,
occupancy

Occupancy

Parameters

Electricity emissions
factor, site-to-source
multiplier

None

None

Absolute Scoring
Arc uses a different scoring strategy for transportation and human experience. For thesecategories, Arc applies absolute mathematical functions (USGBC 2018). Categories
and metrics include:●●

Transportation○ Average one-way GHG emissions per commute
Human Experience○ Occupant satisfaction○ Indoor air quality: carbon dioxide (CO2) and volatile organic compounds(VOC)

The Transportation scoring function is based on the distribution of US commuting. The
distribution of commute-related emissions is roughly uniformly distributed between morethan 20 pounds per one-way commute to less than 1 pound. Arc scores this relationshipon a scale of 0 to 100.

10

Human Experience is scored based on the combination of two components: (1)perceived occupant satisfaction and (2) measured indoor air quality. Occupantsatisfaction is based on an occupant survey. This requires a specified minimum response
rate, and the score reflects both the mean and variance in occupant satisfaction. CO2
and Total Volatile Organic Compound (TVOC) concentration are used as a proxy forindoor air quality with literature-based thresholds to establish scoring breakpoints. CO2scores are highest below 600 ppm CO2 , and they decline rapidly after 1,000 ppm CO2.
TVOC scores are highest below 200 µg/m3 decline quickly after 500 µg/m3(USGBC 2018).
Table 2. Transportation and human experience are scored based on mathematical
functions. Scores are based on the data, normalization, and parameters below.
Transportation

Human Experience

Sub-Scores

Commuting emissions per
occupant

Occupant satisfaction
Indoor air quality

Measurements

Travel routes
Travel distance
Travel mode(min. 1 survey/year)

Occupant satisfaction and variance
CO2 concentration (95% of time)
TVOC concentration (95% of time)(min. 1 survey/year)

Normalizations

Regular occupants, visitors

Floor area, occupancy

Parameters

Electricity emissions factor, site-tosource multiplier

None

11

Score Applications
LEED Rating Systems
The Arc Performance Score is an input to several LEED rating systems, including LEED
v4.1 O+M, LEED v4.1 for Existing Interiors, and LEED Zero. The Arc Performance Score
serves as both a prerequisite and, effectively, a credit. For example, the LEED v4.1 for
O+M Energy & Atmosphere prerequisite requires projects to generate a valid Arc
Performance Score, and it references the Energy sub-scores for GHG emissions andsource energy. Projects must demonstrate a minimum sub-score of 40 for both GHG
emissions and source energy to earn an initial (minimum) 13 points toward LEED
certification. Higher levels of performance earn more points up to a category maximumof 33 points. LEED v4.1 for O+M uses a similar approach for water and waste, again, with
the Arc Performance Score serving as both a prerequisite and credit.

LEED Evaluation
The Arc Performance Score and, critically, its underlying metrics, provides opportunities
to characterize relationships between key performance indicators and LEED
certification levels. The data in Table 3 reflect performance for approximately 10,000
individual projects with a combined floor area of 2.7 billion square feet. The present
presents a cross-tabulation of a selected set of metrics by LEED certification level.

12Table 3. Relationship between Arc performance metrics and LEED v4 and v4.1 O+M
certification levels (Source: Arc, data accessed December 2019).
LEED
Certified

LEED
Silver

LEED
Gold

LEED
PlatinummTCO2e/occupant/
year

3.05

2.65

2.11

1.14

Change inemissions/occupant

0%

-13%

-31%

-63%

mTCO2e/per
commute/year

3.89

2.99

2.58

1.64

Change inemissions/commute

0%

-23%

-34%

-58%

Median occupantsatisfaction

7.1

7.3

7.5

8.4

Change occupantsatisfaction

0%

+4%

+7%

+19%

ENERGY STAR
The Arc Performance Score is often compared to the US Environmental Protection
Agency’s ENERGY STAR program for commercial buildings (ENERGY STAR 2018). Bothsystems provide 0-to-100 measures of operational building performance. However, thetools have different purposes, and they are best understood as distinct andcomplementary performance indicators.
ENERGY STAR the score is generated from a statistical representation of the US building
stock based on the Commercial Building Energy Consumption Survey (CBECS).
Consequently, ENERGY STAR scores can be interpreted as the rank of a building relative
to a portion of the US stock. In contrast, an Arc Performance Score represents theweighted rank of a project relative to the Arc Reference Set. The Arc Reference Set
was selected to represent the range of green building performance, not the US building
stock. The relationship between the Arc Reference Set and the CBECs representation of
the US building stock has not been fully analyzed.

13

The differences in objectives, formulation (e.g., normalizations), and, critically,
comparison sets mean that Arc Scores are only partially correlated with ENERGY STAR
scores. A linear regression between the Arc Carbon Score and ENERGY STAR has a r 2 of
0.34, and the Arc Source Energy Source has a r2 of 0.40. These are statistically significant,positive relationships. However, there is significant variance between Arc Performance
Scores and ENERGY STAR scores, and there is not a necessary relationship between
them (i.e., there is no a priori expectation for correlation).

Conclusions
Arc Performance Score is a practical tool to understand and communicate theoperational performance of space and buildings around the world. The Arc
Performance Score prioritizes simplicity and global applicability. Its five performance
categories also reflect USGBC’s long-standing commitment to an integrative, multicriteria definition for green buildings. Any project, anywhere in the world can generate
an Arc Performance Score and compare itself to a sample of green buildings. This
design allows for broad applicability, but it also has notable limitations.
The Arc Performance Score may not be sensitive enough to recognize globally small
differences between buildings in a local area or over time. This means that significant
improvements at a single facility may not be sufficient to generate changes in
performance relative to Arc’s global Reference Set. Further, the Arc Performance Score
is only one possible interpretation of the underlying data. There are other valid anduseful interpretations that could be used as the basis for scoring. For example, the samedata could be used to evaluate compliance with local energy efficiency regulation or
to inform a waste management program. It is important to recognize that the ability toanswer these important questions is an underlying capability of the Arc platform and abenefit of using the Arc Performance Score as an entry point operational performancemeasurement and scoring.
The Arc Performance Score will continue to evolve as we encourage every green
building to measure and improve real world performance. This will include incremental
improvements, such annual updates to emissions factors, and, from time-to-time, theaddition or removal of metrics or entire categories. These changes will be guided by
Arc’s commitment to recognizing leadership and long-term support for LEED as a global
market transformation tool.

14

References
El Sorady, D.A. and S.M. Rizk. (2020) LEED v4.1 operations and maintenance forexisting building and compliance assessment: Bayt Al-Suhaymi, Historic Cairo.
Alexandria Engineering Journal 59(1):519-531
ENERGY STAR (2018) Technical Reference: ENERGY STAR Score, 14 pages, URL:
https://portfoliomanager.energystar.gov/pdf/reference/ENERGY%20STAR%20Score.pdf
Heidarinejad, M., Dahlhausen, M., McMahon, S., Pyke, C.R., and J. Srebric. (2014).
Cluster analysis of simulated energy use for LEED certified US office buildings. Energy
and Buildings 85:86-97
Orthman, A. (2013) Scoring with Monotone Splines, 5 pages. Unpublished.
Todd, J.A., Pyke, C.R., and R. Tufts. (2013) Implications of trends in LEED usage forrating system design and market transformation. Building Research & Information
41(4):384-400
U.S. Green Building Council (2018) LEED v4.1 O+M Beta Guide. Washington, DC.
81 pages URL: https://www.usgbc.org/resources/leed-v41-om-beta-guide
U.S. Green Building Council (2015) Foundations of LEED. Washington, DC. 44
pages. URL: https://www.usgbc.org/sites/default/files/foundations-of-LEED.pdf

15