RESEARCH STRATEGY FOR ESTIMATING ENERGY SAVINGS
FROM NON-RESIDENTIAL LIGHTING PROJECTS
10/9/2015
1. INTRODUCTION
The aim of this Research Strategy is to identify a simplified method for reliably estimating the
energy savings from lighting projects in non-residential buildings. A secondary aim is to
estimate peak demand savings from these projects as the data collected from this research
allows. A lighting project encompasses all energy efficiency-related upgrades or modifications
to a lighting System,1 including the lighting fixtures, ballasts, lamps, and control devices. This
Research Strategy supports the RTF’s existing Provisional Standard Protocol for Non-Res
Lighting Retrofits (hereafter “RTF Retrofit Protocol”) adopted at the December 2014 RTF
meeting, in addition to a provisional standard protocol for new construction and major
renovation lighting projects that is currently under development.2 Before reading this
document, the reader should be familiar with the key terms and savings methods described in
the RTF Retrofit Protocol.3
Energy savings from a lighting project are commonly computed as a function of the following
parameters:
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connected fixture wattage;4
equivalent full load hours of use (EFLH, or simply HOU in the RTF Retrofit Protocol);
controls savings factor (CSF);5 and
HVAC interaction factor (IF).6
For connected fixture wattage and HVAC IFs, the RTF has approved existing lookup tables of
values as sufficiently reliable for the determination of these parameters. For HOU and CSF, the
RTF has yet to approve a simplified, reliable method of determination.
1
A lighting System is defined as a set of fixtures within the same building space with a common control
mechanism (e.g. fixtures on the same manual switch).
2 Currently under the working title “Provisional Standard Protocol for Non-Residential Lighting Code
Compliance”.
3 Key terms that are defined in the Retrofit Protocol are italicized throughout this document.
4 Total connected wattage, including the effects of ballasts and drivers.
5 Annualized reduction factor resulting from lighting controls, calculated as 1 – (EFLH
efficient/EFLHbase).
6 Represents the net savings from a lighting conservation measure due to HVAC interactions.
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The RTF Retrofit Protocol describes a candidate Simplified Estimation Method for HOU and CSF
that does not require on-site logging or metering of lighting Systems.7 Instead, the Simplified
Method estimates HOU for a given space by applying an adjustment factor to the reported
Hours of Occupancy (HOO) obtained through a particular structured interview.
To estimate HOU for lighting system improvements that only affect connected wattage, the RTF
plans to estimate HOU/HOO Adjustment Factors as a function of control type and space type
(e.g. occupancy sensors in open offices). To estimate changes in HOU for improvements that
involve changes to controls, the RTF plans to estimate Control Savings Factors that are specific
to base-case control type, efficient-case control type, and space type (e.g., changing from
occupancy sensor to occupancy plus daylight sensor in open offices).
RTF Research Strategies generally do not specify required research methods. However, since
the RTF Retrofit Protocol is built around the idea of estimating HOU from reported HOO, both
the research objectives and the strawman approach (below) include references that are specific
to the HOU/HOO approach. While the RTF does not require that future researchers follow the
same approach, the RTF does strongly recommend that research planners consider the value of
consistency with current RTF products and existing research in weighing alternative study
designs.
2. RESEARCH OBJECTIVES
The primary objectives intended to achieve the overall aim of this Research Strategy are:
1. Compare HOU data obtained through metered light output and/or power output to
responses from the RTF’s structured HOO interview guide.8 Determine if a set of
adjustment factors can be derived such that an adjusted HOO interview response can
be used to reliably estimate actual HOU. Such a simplified method would be suitable
only if adjustment factors could be determined for a variety of common space use
types9 and lighting control types.
2. Compare controls-induced reductions in HOU from metered light output and/or
power output data to a default table of CSF values.10 Determine if a set of CSF values
can be derived such that they can be used to reliably estimate changes in HOU due to
a change in lighting controls. Similar to the first objective, such a simplified method
would be suitable only if CSFs could be determined across a variety of common space
use types and changes in lighting control types. In addition, to the extent that CSFs are
desired by the region for both retrofit and new construction projects, data will need to
be collected on changes in controls that are relevant to both cohorts. For example, if
current building codes are used as the new construction baseline, CSFs must be
7
Non-automated logging or metering. Sites or fixtures with automated metering would likely require a
different protocol.
8 The RTF non-res lighting interview guide is available for download here.
9 Space Use Types (SUTs) are defined in the RTF Retrofit Protocol
10 Default table of CSF values specified in the RTF Retrofit Protocol.
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determined relative to the controls already prescribed by code. More details are
provided on this in Section 3.2.
Research related to baseline Lighting Power Densities (LPDs) is not an objective of this Strategy.
For lighting retrofits, the Simplified Method obtains project-specific baseline LPDs from the
lighting project survey. For new construction, baseline LPDs will likely be based on known
building codes and/or existing regional studies looking at code compliance and current practice
baselines11.
3. DATA COLLECTION AND ANALYSIS
This section provides a strawman data collection and analysis approach as a means of sketching
out one potential path. The RTF recognizes that there may be alternative approaches. Since the
research objectives may be addressed individually, each is treated within its own subsection
below.
3.1. Objective 1: Determining a Simplified Method for HOU
To meet the objective of determining a simplified method for HOU, the RTF recommends the
following data collection approach:
1. Collect data on the existing- and efficient-case lighting Systems for each space in the
project. This includes data on the fixture type, fixture quantity, lamp nominal wattage,
ballast factor (if applicable), lamps per fixture, lighting control type, and space use type
(as defined by the RTF Retrofit Protocol).
2. Conduct a structured interview with building personnel using the RTF interview guide
to elicit HOO for each space in the lighting project. In the RTF Retrofit Protocol, HOO is
defined as “the number of hours spanned by the time period(s) that typically include
activity in a building space”. The HOO Interview Guide provides detailed instructions
that seek to standardize this definition.
3. Collect metered light output and/or power output data12 for each lighting System in
the project. For this research objective, the metering can be performed pre-lighting
project or post-project (both are not required). However, it is critical that the metered
spaces are the same spaces where the structured HOO interview is administered.
Using the data collected from the steps outlined above, the RTF recommends the following
analysis approach for this objective:
1. For each lighting System in a project, compute the ratio of annualized HOU to
annualized HOO (henceforth, the “Ratio”). See RTF Retrofit Protocol for details.
11
For example, BPA is researching the current practice for commercial lighting controls as part of their
Momentum Savings work.
12 Metered light output (via lighting loggers) would be sufficient for non-dimming fixtures, where power
output (or current output with spot measurements of power) would be needed for those with dimming.
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2. Compare Ratios across common characteristics – such as building type, space type,
and control type – to observe patterns and/or central tendencies and to determine
the appropriate level of granularity for the HOU/HOO Ratios used in the Protocol.13
3. Estimate energy savings for all projects using the Ratio-adjusted HOO and compare
these values to savings computed using actual, metered HOU. Use this comparison to
evaluate whether the Simplified Method meets the quality standards described in the
RTF Guidelines.14
3.2. Objective 2: Determining a Simplified Method for CSFs
To meet the objective of determining a simplified method for CSF, the RTF recommends the
following data collection approach:
1. Collect data on the base- and efficient-case lighting Systems for each building space in
the project. This is the same first step that is required for Objective 1. Resource
efficiencies can be gained by studying both research objectives in a single study.
2. For lighting Systems where there is a change in controls, collect metered light output
and/or power output data for both the base-case and efficient-case controls of each
System. For lighting retrofits, the RTF has stated that metering of the efficient case
alone would not be sufficient to determine savings from a change in controls. The RTF
staff believe there are at least two options for reliably collecting base- and efficient-case
data: Classical pre-/post-metering (i.e. metering a single System over two different time
periods), and Matched-pair metering (i.e. metering two very similar Systems, one with
efficient-case controls and one with baseline controls, over a single time period).
To estimate CSFs for new construction, researchers may need to collect data at retrofit
lighting projects whose efficient-case controls reflect what is required by current
building codes. Alternatively, researchers may be able to collect baseline data in new
construction projects by temporarily altering control functions to cause efficient-case
controls to operate with baseline functionality.
Using the data collected from the steps outlined above, the RTF recommends the following
analysis approach for this objective:
1. For each lighting System with a change in controls, compute the actual CSF from the
base case and efficient case meter data. CSF is computed as 1 – (EFLHefficient/EFLHbase).
Since the base case for new construction can rarely be directly observed (except cases
where efficient case controls can be disabled to a code compliant level), new
construction CSFs may need to be computed as the difference in code level CSFs (the
base case) and “beyond code” CSFs (the efficient case). These CSFs would need to come
from retrofit projects where savings may be achieved by installing either code compliant
controls or beyond code controls. The new construction CSFs can then be computed as
13
It is uncertain how similar or dissimilar Ratios will be across these characteristics. For example, will two
Ratios with the same control type but different space types be similar in value? What about two Ratios
from similar space types with different control types? Care must be taken in this step to determine how
narrowly or broadly the Ratios can be applied.
14 The complete operative version of the RTF’s Guidelines can be downloaded here.
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the difference between the code compliant control (e.g. a classroom with an occupancy
sensor) and a beyond code control (e.g. a classroom with an occupancy sensor with
daylighting and continuous dimming).
2. Compare CSFs across common characteristics – such as building type, space type, and
control type – to observe patterns and/or central tendencies. Develop a proposed
table of estimated average CSFs. It is uncertain how narrowly or broadly defined the
CSFs will be. For example, will CSFs be similar for the same control type across multiple
space types, or will CSFs apply only to a unique control and space type?
3. Compute energy savings for all projects using the estimated average CSFs and
compare these values to savings computed using actual meter data. Determine if the
difference in the savings estimates across all projects is within the quality standards of
reliability in the RTF Guidelines.
3.3. Estimated Sample Size
The current research plan15 associated with the RTF Retrofit Protocol estimates a total sample
size for the proposed research if it were undertaken as a single effort. This would theoretically
maximize regional resource efficiency, but it would also require base and efficient case
metering for each System. For practical reasons, multiple studies may be used to address one or
both of the research objectives. As a single effort, the RTF estimates that a sample size of
approximately 280 lighting Systems will be needed (assuming 20% precision at the 90%
confidence interval). It is assumed that each project site will have multiple lighting Systems, so
that the number of total sites requiring field visits would be significantly less than the number
of Systems. The RTF Retrofit Protocol provides a more detailed breakdown of sample targets by
specific building, space, and control type.
15
Research plan available for download at the RTF website here.
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