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MMeeaassuurree IInnffoorrmmaattiioonn TTeemmppllaattee –– DDaayylliigghhttiinngg
2011 California Building Energy Efficiency Standards
[Proposer and date]
CONTENTS
1. Purpose ........................................................................................................................ 5
2. Overview ....................................................................................................................... 6
3. Argument for Watt Calculation Method ................................................................... 12
4. Methodology............................................................................................................... 14
4.1 Proposal 1: Watt Calculation Method ......................................................................................14
4.1.1 Development of a Basic Concept for the Watt Calculation Method .................................14
4.1.2 Dataset Development .........................................................................................................16
4.1.3 Sidelighting Watt Calculation Method Development ........................................................19
4.1.4 Toplighting Watt Calculation Method Development ........................................................19
4.1.5 Development of a Method to Apply Calculation Result to Daylit Spaces ........................20
4.1.6 Assessing Watt Calculation Method‟s Energy Impact ......................................................20
4.2 Proposal 2: Photocontrols Requirement Trigger ......................................................................21
4.2.1 Photocontrols Cost Survey .................................................................................................21
4.2.2 Analysis..............................................................................................................................21
4.3 Proposal 3: Minimum Skylight Area Requirement ..................................................................22
4.3.1 Rooftop Survey ..................................................................................................................22
4.3.2 Analysis..............................................................................................................................23
4.4 Proposal 4: Ceiling Height Trigger for Skylight Area Requirement ........................................23
4.4.1 Cost Survey for Light Wells and New Skylights for Dropped Ceilings ............................23
4.4.2 Update 2008 Title 24 Life Cycle Cost Analysis for Skylights with Light Wells ..............23
4.5 Stakeholder Outreach Process ..................................................................................................24
5. Analysis and Results ................................................................................................. 25
5.1 Proposal 1: Watt Calculation Method ......................................................................................25
5.1.1 Using the Daylight Autonomy Metric to Develop Prescriptive Code Requirements ........25
5.1.2 Formula Format .................................................................................................................26
Measure Information Template - Daylighting Page 2
2013 California Building Energy Efficiency Standards [March 2011]
5.1.3 Façade-Template Approach for Spaces with Multiple Façade Orientations .....................30
5.1.4 Façade-Template Approach for Spaces with Toplighting and Sidelighting ......................32
5.1.5 Sidelighting Watt Calculation Method Development ........................................................34
5.1.6 Toplighting Watt Calculation Method Development ........................................................42
5.1.7 Method to Apply Calculation Result to Daylit Spaces ......................................................48
5.1.8 Assessing Energy Impact of Watt Calculation‟s Method ..................................................51
5.2 Proposal 2: Photocontrols Requirement Trigger ......................................................................51
5.2.1 Photocontrol System Cost ..................................................................................................57
5.2.2 Energy Savings ..................................................................................................................61
5.2.3 Cost Effectiveness Analysis ...............................................................................................62
5.2.4 Recommendations ..............................................................................................................64
5.3 Proposal 3: Minimum Skylight Area Requirement ..................................................................64
5.3.1 Rooftop Survey ..................................................................................................................64
5.3.2 Analysis and Recommendation..........................................................................................66
5.4 Proposal 4: Ceiling Height Trigger for Skylight Area Requirement ........................................66
5.4.1 Cost Survey Results ...........................................................................................................66
5.4.2 Energy Savings ..................................................................................................................67
5.4.3 Cost Effectiveness Analysis ...............................................................................................67
5.4.4 Tubular Daylighting Devices (TDDs) ...............................................................................70
5.4.5 Recommendations ..............................................................................................................71
6. Recommended Language for the Standards Document, ACM Manuals, and the Reference Appendices ....................................................................................................... 72
7. Bibliography and Other Research ............................................................................ 73
8. Appendices A ............................................................................................................. 74
FIGURES
Figure 1: Decision Tree - Current Daylighting Code ........................................................................... 12
Figure 2: Decision Tree - Alternate Calculation Method ..................................................................... 13
Figure 3: Current method of determining Daylit Areas from Title 24 - 2008 ...................................... 15
Figure 4: DA Plot for a space - contour lines mark Daylit Autonomy % time ..................................... 16
Measure Information Template - Daylighting Page 3
2013 California Building Energy Efficiency Standards [March 2011]
Figure 5: Template Space 60ft x 40ft with 60” furniture ...................................................................... 17
Figure 6: 30”, 45” and 60” Furniture Layouts ...................................................................................... 18
Figure 7: Number of buildings surveyed .............................................................................................. 22
Figure 8: DA plot for space A with sidelighting - green lines show primary daylit area ..................... 27
Figure 9: DA plot for space B with sidelighting - green lines show primary daylit area ..................... 28
Figure 10: DA plot for space C with toplighting - green lines show primary daylit area .................... 29
Figure 11: DA plot for space D with toplighting - green lines show primary daylit area .................... 29
Figure 12: DA plot for space E with sidelighting from two adjacent walls ......................................... 30
Figure 13: Individual and Combined Facades ...................................................................................... 31
Figure 14: Table with sDA300,50% values for Cases A - C ..................................................................... 32
Figure 15: Sidelighting and Toplighting Overlap Study Cases 1-4 ...................................................... 33
Figure 16: Table with sDA300,50% values for Cases 1 - 4 ...................................................................... 33
Figure 17. Daylight Autonomy depending on effective aperture for different window location
coefficient values ............................................................................................................................ 37
Figure 18. Daylight Autonomy depending on location coefficient for different effective aperture
values .............................................................................................................................................. 38
Figure 19. Sidelighting Formula Coefficients ...................................................................................... 41
Figure 20: DA as a function of distance from daylit source ................................................................. 43
Figure 21: Stack of median height at a median distance from skylight ................................................ 46
Figure 22: Daylit areas for different skylight sizes and ceiling heights ............................................... 48
Figure 23: Steps to Apply Calculation Results to Sidelit Spaces ......................................................... 49
Figure 24: Steps to Apply Calculation Results to Sidelit Spaces ......................................................... 50
Figure 25: Plan diagram of hypothetical sidelit space .......................................................................... 58
Figure 26: Plan diagram of hypothetical toplit space ........................................................................... 58
Figure 27: Photocontrols price summary .............................................................................................. 59
Figure 28: RS Means CostWorks Hourly Labor Rates for Electrical Contractors ............................... 60
Figure 29: RS Means CostWorks Variance in labor cost by region ..................................................... 60
Figure 30: Total Costs for Switching System, Sacramento, CA........................................................... 61
Figure 31: Total Costs for Dimming System, Sacramento, CA ........................................................... 61
Figure 32: Cost Effectiveness Analysis for automatic daylighting controls based on controlled watts 63
Figure 33: Cost Effectiveness Analysis for automatic daylighting controls based on daylit area ........ 64
Figure 34: Screen capture of Bing maps showing polygon tool to estimate total roof area. ................ 65
Measure Information Template - Daylighting Page 4
2013 California Building Energy Efficiency Standards [March 2011]
Figure 35: Screen capture of Bing maps showing polygon tool to estimate rooftop obstructions. ...... 65
Figure 36: Summary of Rooftop Survey Findings ................................................................................ 66
Figure 37: Installation costs of skylights, with and without light wells ............................................... 67
Figure 38: Model building scenarios for cost effectiveness analysis ................................................... 67
Figure 39: BCR for skylighting in retail buildings with 1.6 W/sf LPD, 12‟ ceilings and 4‟ lightwells 68
Figure 40: BCR for skylighting in retail buildings with 1.6 W/sf LPD, 10‟ ceilings and 4‟ lightwells 69
Figure 41: BCR for skylighting in office buildings with 1.1 W/sf LPD, 10‟ ceilings and 4‟ lightwells
........................................................................................................................................................ 70
Figure 42: Detailed Rooftop Survey Results (part 1 of 3) .................................................................... 74
Figure 43: Detailed Rooftop Survey Results (part 2 of 3) .................................................................... 75
Figure 44: Detailed Rooftop Survey Results (part 3 of 3) .................................................................... 76
Measure Information Template - Daylighting Page 5
2013 California Building Energy Efficiency Standards [March 2011]
1. Purpose
This document describes the code change proposals for 2013 Title 24 - Part 6 Building Energy
Efficiency Standards, for the topic of Daylighting.
Measure Information Template - Daylighting Page 6
2013 California Building Energy Efficiency Standards [March 2011]
2. Overview
Complete the following table, providing responses for each category of information.
a. Measure
Title
Proposed changed to the daylighting requirements in Title 24-Part6
b.
Description
Four code changes are being proposed, that increase stringency of daylight code
requirements, resulting in greater energy savings, and simplify the daylighting code
implementation process, removing key barriers to code compliance for greater and
more widespread use.
Proposal 1 - Watt Calculation Method: This code change proposes a new simpler
procedure for determining requirements for controlling electric lighting in daylit
spaces in the mandatory requirements for lighting system and equipment - Section
131(c). This proposal would also modifies the calculation of reduction of wattage
through controls in the prescriptive requirements for indoor lighting Section 146(a)2.
Proposal 2 - Photocontrols requirement trigger: This proposal would modify the
mandatory requirement photocontrols in sidelit and toplit spaces by changing the
exception under 131(c)2A and 131(c)2B.
Proposal 3 - Minimum skylight area requirement: This proposal would modify the
prescriptive requirements for building envelopes - Section 143(c) by increasing the
minimum skylight area requirement.
Proposal 4 - Ceiling height trigger for skylight area requirement: This proposal
would modify the prescriptive requirements for building envelopes - Section 143(c)
by increasing the minimum skylight area requirement
The proposed code change apply to all non-residential, high-rise residential and
hotel/motel occupancies.
c. Type of
Change
Modeling - The change proposed in proposal 1 would modify the calculation
procedures used in complying with mandatory requirements for photocontrols in
sidelit and top light spaces. Also the definitions under Section 131(c)1 would be
modified.
Mandatory Measure - The change proposed in proposal 2 would modify the
mandatory measure by changing the exception under 131(c)2A and 131(c)2B.
Prescriptive Requirement - The change proposed in proposal 3 and proposal 4
would modify the prescriptive requirement in Section 143(c) by increasing the
minimum skylight area requirement, and reducing the ceiling height trigger. Also
proposal 1 would modify the calculation of reduction of wattage through controls in
Section 146(a)2.
The documents that would need to be modified in order to implement the proposed
change are the Standards, ACM, Manuals and compliance forms.
None of the proposed changes would add a compliance option or a new requirement.
Measure Information Template - Daylighting Page 7
2013 California Building Energy Efficiency Standards [March 2011]
d. Energy
Benefits
Describe the benefits of the change/measure proposed for 2011 Standards relative to
2008 Standards; if no current Standards are available, use current practice as the
baseline. The proposer must identify:
1. Site energy: Electrical energy savings in kWh/yr, for a prototype building. For
natural gas savings, identify savings in therms for a prototype buildings.
1. Electrical demand savings in kW for a prototype building
2. TDV energy savings for electricity and natural gas
The proposer must show all assumption and calculations used to derive the energy
and demand savings for prototype buildings including but not limited to hours of
operations, energy and demand savings per unit of equipment, and square footage of
the prototype buildings; these assumptions must be consistent with the procedures
described under the Methodology section below. Describe how Time Dependent
Valuation (TDV) would affect benefits attributed to the measure. Reference the
“Analysis and Results” section below for detailed calculations. If the proposed
measure impacts more than one building prototype fill out this form for each
prototype. Use the table below to document the energy savings resulting from the
proposed measure;
Electricity
Savings
(kwh/yr)
Demand
Savings
(kw)
Natural Gas
Savings
(Therms/yr)
TDV
Electricity
Savings
TDV Gas
Savings
Per Unit Measure1
Per Prototype
Building2
Savings per
square foot3
1. Specify the type of unit such as per lamp, per luminaire, per chiller, etc.
2. For description of prototype buildings refer to Methodology section below.
3. Applies to nonresidential buildings only.
4. Note: If the measure is climate zone dependent, a separate Table must be filled
out for each climate zone impacted by this measure.
e. Non-
Energy
Benefits
Identify non-energy benefits, such as comfort, reduced maintenance costs, improved
indoor air quality, health and safety benefits, productivity, and/or increased property
valuation.
Measure Information Template - Daylighting Page 8
2013 California Building Energy Efficiency Standards [March 2011]
f. Environmental Impact
Does the change/measure have any potential adverse environmental impacts? Is water consumption
increased? Is there impact on water quality and contaminants? Are there environmental or energy
impacts associated with material extraction, manufacture, packaging, shipping to the job site,
installation at the job site, or other activities associated with implementing the measure in buildings?
Use the following tables to identify the environmental impact per unit of measure and prototype
buildings and state your assumptions; NOTE if the impacts are climate zone dependent, a separate
Table must be filled out for each climate zone impacted by the measure:
Material Increase (I), Decrease (D), or No Change (NC): (All units are lbs/year)
Mercury Lead Copper Steel Plastic Others
(Indentify)
Per Unit
Measure1
Per Prototype
Building2
1. Specify the type of unit such as per lamp, per luminaire, per chiller, etc.
2. For description of prototype buildings refer to Methodology section below.
Water Consumption:
On-Site (Not at the Powerplant)
Water Savings (or Increase)
(Gallons/Year)
Per Unit Measure1
Per Prototype
Building2
1. Specify the type of unit such as per lamp, per luminaire, per chiller, etc.
2. For description of prototype buildings refer to Methodology section below.
3. Water Quality Impacts:
4. Comment on the potential increase (I), decrease (D), or no change (NC) in contamination
compared to the basecase assumption, including but not limited to: mineralization (calcium, boron,
and salts), algae or bacterial buildup, and corrosives as a result of PH change.
5. 6. Mineralizatio
n
7. (calcium,
boron, and salts
8. Algae or
Bacterial Buildup
9. Corrosive
s as a Result of PH
Change
10. Others
11. Impact (I, D,
or NC)
12. 13. 14. 15.
16. Comment on
reasons for your impact
assessment
17.
18.
19.
20. 21. 22. 23.
24.
25.
26.
27.
Measure Information Template - Daylighting Page 9
2013 California Building Energy Efficiency Standards [March 2011]
g.
Technology
Measures
If the measure requires or encourages a particular technology, address the following,
otherwise skip this section.
Measure Availability:
Identify the principal manufacturers/suppliers who make the measure (product,
technology, design strategy or installation technique), and their methods of
distribution. Is the measure readily available from multiple providers? Comment on
the current ability of the market to supply the measure in response to the possible
Standards change and the potential for the market to ramp up to meet demand
associated with the possible Standards change. If the measure needs further
development and refinement in response to possible Standards changes, comment on
if the measure will be available from several manufacturers by the effective date of
the Standards. Identify competing products.
Useful Life, Persistence, and Maintenance:
Describe the life, frequency of replacement, and maintenance procedures related to
the measure. How long will energy savings related to the measure persist? Is
persistence related to performance verification, proper maintenance and/or
commissioning? If there are issues related to persistence, how can they be addressed?
(See Performance Verification below.)
h.
Performance
Verification
of the
Proposed
Measure
In this section, identify the type of performance verification or commissioning that is
needed in order to assure optimum performance of the measure. For residential
buildings, field verification and diagnostic testing are required for many measures.
For nonresidential buildings, the parallel is acceptance testing. Here are some
questions to ask: Does the technology or design strategy need performance
verification or commissioning to ensure that it is properly installed and/or performing
as designed? How are energy performance, useful life and persistence of savings
affected by performance verification or commissioning? What specific performance
verification measures or requirements are needed to assure that the measure is
properly installed and performing as designed?
Measure Information Template - Daylighting Page 10
2013 California Building Energy Efficiency Standards [March 2011]
i. Cost Effectiveness
Show the proposed change is cost effective using life cycle costing (LCC) methodology for the
prototype building(s) where the measure is installed. Use the Energy Commission Life Cycle Costing
Methodology posted on the 2011 Standards website and state the additional first and maintenance
costs, the measure life, energy cost savings, and other parameters required for LCC analysis. Use the
following table to show the assumptions used to derive the LCC analysis:
a b c d e f g
Measure
Name
Measu
re Life
(Years
)
Additional
Costs1– Current
Measure Costs
(Relative to
Basecase)
($)
Additional Cost2–
Post-Adoption
Measure Costs
(Relative to
Basecase)
($)
PV of Additional3
Maintenance
Costs (Savings)
(Relative to
Basecase)
(PV$)
PV of4
Energy
Cost
Savings
– Per
Proto
Buildin
g (PV$)
LCC Per Prototype
Building
($)
Per
Unit
Per
Proto
Buildin
g
Per
Unit
Per
Proto
Buildin
g
Per
Unit
Per
Proto
Buildin
g
(c+e)-f
Based
on
Current
Costs
(d+e)-f
Based
on Post-
Adoptio
n Costs
1. Current Measure Costs - as is currently available on the market, and
2. Post Adoption Measure Costs - assuming full market penetration of the measure as a result of the new
Standards, resulting in mass production of the product and possible reduction in unit costs of the product
once market is stabilized. Provide estimate of current market share and rationale for cost prediction.
Cite references behind estimates.
3. Maintenance Costs - the initial cost of both the basecase and proposed measure must include the PV of
maintenance costs (savings) that are expected to occur over the assumed life of the measure. The present
value (PV) of maintenance costs (savings) must be calculated using the discount rate (d) described in the
2011 LCC Methodology. The present value of maintenance costs that occurs in the nth year is calculated
as follows (where d is the discount rate):
n
d1
1Cost Maint Cost Maint PV
4. Energy Cost Savings - the PV of the energy savings are calculated using the method described in the
2011 LCC Methodology report.
For measures that are climate sensitive, this analysis will need to be conducted by climate zones
impacted by the measure. Residential measures are evaluated over a 30 year period of analysis.
Nonresidential envelope measures are evaluated over a 30 year period of analysis and all other
nonresidential measures are evaluated over 15 year period of analysis.
If the change is a mandatory measure or prescriptive requirement, then it is necessary to demonstrate
cost effectiveness. See the “Methodology” and “Analysis and Results” sections below, and present the
detailed analysis there.
Measure Information Template - Daylighting Page 11
2013 California Building Energy Efficiency Standards [March 2011]
j. Analysis
Tools
List and describe the tools needed to quantify energy savings and peak electricity
demand reductions resulting from the proposed measure. Can these benefits be
quantified using the Standards reference methods (such as Calres for residential and
EnergyPlus for nonresidential buildings)? What enhancements to the reference
methods are needed, if any? If a measure is proposed as mandatory, then analysis
tools are not relevant, since that measure would not be subject to whole building
performance trade-offs.
k.
Relationship
to Other
Measures
Identify any other measures that are impacted by this change. Explain the nature of
the relationship.
Measure Information Template - Daylighting Page 12
2013 California Building Energy Efficiency Standards [March 2011]
3. Argument for Watt Calculation Method
A repeated concern voiced by stakeholders has been that the current method to show compliance with
the daylighting portion of the code is perceived to be too complicated. This includes mandatory
measures in Sections 131(c)2B, and 131(c)2C as well as the prescriptive measures in Section
146(a)2E. This was echoed by others from whom we have obtained input, such as energy consultants
(members of CABEC), architects and educators responsible for teaching the code. This is a possible
reason for low compliance, as evidenced in a survey of CALBO members conducted by the codes and
standards team (see Section xx).
To determine the cause of this perception, we reviewed the decision process required for the current
calculation method. This is shown as a decision tree diagram in Figure 1.
Figure 1: Decision Tree - Current Daylighting Code
The process required to make the decisions for compliance involves:
(a) A graphical process of drawing and then calculating total daylit areas on a plan. The
calculation involves accounting for overlapping daylit areas, and truncation due to permanent
partitions
(b) Calculation of effective aperture, a function of the total daylit area
(c) Superimposing electric lighting layout over the daylit area polygons, which necessitates
knowledge of electric lighting layout.
Measure Information Template - Daylighting Page 13
2013 California Building Energy Efficiency Standards [March 2011]
This process can take a considerable amount of time and effort to ensure accuracy. Furthermore, it
also requires that the building code official checking for compliance, also spend a considerable
amount of time to make sure that all calculations were correctly done and all process correctly
implemented.
An alternate method of compliance that computes the answer (how many electric lights need to be
controlled?) without the use of either a graphical drawing method or superimposing electric lighting
layout, addresses this problem of complexity. Figure 2 provides a decision tree for a proposed
calculation method that uses simple take-offs from buildings plans to compute min. percent watts
controlled.
Figure 2: Decision Tree - Alternate Calculation Method
Central to this approach is a calculation procedure or formula. Exceptions, such as effective aperture
calculations can be built into the formula, and thus removed from the decision tree. The proposal for a
„Watt Calculation Method‟ discussed in this report derives such a formula for sidelighting and
toplighting, using detailed data on illuminance from Radiance developed for the PIER Daylight
Metrics project.
In addition to simplifying the compliance approach, the method also applies a level of refinement to
the graphical calculation procedure, going beyond the simple rule of thumb of one window head
height used in the current method. Due to this, the Watt Calculation Method can require more savings
when available, ie. from buildings that are designed to have ample daylighting, and limit savings
when daylighting is not present. While the one head height rule is a robust, and well researched
principle, it is not possible to implement more or less aggressive code requirements based on
individual building design with a code requirement based on this principle.
The proposed approach requires that luminaires closest to the daylighting sources get circuited in a
logical manner for successful implementation of photocontrol zones. The procedure to determine
luminaires closest to the daylighting sources leverages the one head height principal.
Measure Information Template - Daylighting Page 14
2013 California Building Energy Efficiency Standards [March 2011]
4. Methodology
This section describes the methodology that we followed to determine the code change proposals,
collect costs and calculate energy savings and cost effectiveness.
The methodology section is sub-divided into four sections, one for each code change proposal as
described below:
1. Watt Calculation Method. A proposal to modify the calculation procedures used to determine
the mandatory requirements for photocontrols in sidelit and top light spaces.
2. Photocontrols Requirement Trigger: A proposal to change the threshold for requiring
photocontrols in sidelit and toplit spaces.
3. Minimum Skylight Area Requirement: A proposal to increase the minimum skylight area
required for large enclosed spaces.
4. Ceiling Height Trigger for Skylight Area Requirement: A proposal to decrease the ceiling
height trigger for minimum skylight area requirement.
5. Stakeholder Outreach Process: A description of
This work was publicly vetted through our stakeholder outreach process, which through in-person
meetings, webinars, email correspondence and phone calls, requested and received feedback on the
direction of the proposed changes. The stakeholder meeting process is described at the end of the
Methodology section.
4.1 Proposal 1: Watt Calculation Method
This section describes the methodology used to develop a new method for determining the wattage
and number of electric lights need to be controlled by photosensors without the need to draw daylit
areas on the plans using the current (2008, graphical) method.
The key elements of the methodology are:
Development of a Basic Concept for the Watt Calculation Method
Dataset Development
Sidelighting Watt Calculation Method Development
Toplighting Watt Calculation Method Development
Assessing Watt Calculation Method‟s Energy Impact
Development of a Method to Apply Calculation Result to Daylit Spaces
4.1.1 Development of a Basic Concept for the Watt Calculation Method
The concept for a watt calculation method is that given a specific set of inputs that describe a façade
design and physical characteristics of a space, the percent of electric lights that must be controlled
using photocontrols, or percent watts controlled, can be calculated.
Measure Information Template - Daylighting Page 15
2013 California Building Energy Efficiency Standards [March 2011]
Photocontrols need only be applied to luminaires serving an area of a space that is „sufficiently served
by daylighting‟ over the course of a year. Two potential methods for determining the area sufficiently
served by daylighting were assessed.
The first method assumes that the current Title 24 method of determining daylit areas, shown
graphically in Figure 3, provides an accurate description of area „sufficiently served by daylighting‟.
An algebraic formula could then be derived that replaces the geometric method of drawing daylit
areas.
Figure 3: Current method of determining Daylit Areas from Title 24 - 2008
In the second methodwe used two-dimensional distribution plots of „annual daylight autonomy‟ in a
daylit space, using the Dynamic Radiance1 daylighting simulation software. Daylight autonomy is the
percent of time of a year that there is sufficient daylight available at any point in a space. When the
analysis is done for a grid of sensors across a space, it results in a two-dimensional distribution plot of
annual daylight autonomy (called an sDA plot - for spatial daylight autonomy). A threshold percent
time of 50% (sDA50%) was used to determine the area „sufficiently served by daylighting‟. In other
words, the area can be sufficiently served by daylighting for at least 50% of time (occupied hours) of
a year. Assumptions behind the use of these values and simulation runs are described in the Results
and Analysis section (Section 5).
Once a method to determine area „sufficiently served by daylighting‟ can be established, a formula
can then be derived that predicts this area from a set of façade design and space characteristics inputs.
1 MS Simbuild paper reference
Measure Information Template - Daylighting Page 16
2013 California Building Energy Efficiency Standards [March 2011]
The pros and cons of each method are discussed for both sidelighting and toplighting and summarized
in the Results and Analysis section.
Figure 4: DA Plot for a space - contour lines mark Daylit Autonomy % time
4.1.2 Dataset Development
A dataset was developed from which results for sDA50% could form the „training data‟ for a formula.
To enable creation of a sufficiently diverse dataset, we leveraged a process of creating “templates” of
various façade designs, used in the CEC PIER Office Daylighting study2. In this method a space 60ft
x 40ft in dimension, was modeled in Dynamic Radiance with sensors at 31inches from floor, on a 2ft
x 2ft grid across whole floor. The 60ft dimension had various façade design options, or „façade-
templates‟, used to generate a series of „template-spaces‟. These spaces were then run in Dynamic
Radiance for an annual daylighting simulation using a California climate zone weather file. Through a
sequence of automated steps, various parameters of each template-space were modified, such as
orientation, window VLT and interior furniture type, to generate a sufficiently large and diverse
dataset of results. Figure 5 shows an image of a template-space used in this analysis. Further details
about façade-templates and the daylighting simulation parameters and assumptions are available in
the PIER Office Daylighting study final report.
2 PIER Office Daylighting Study - insert citation
Measure Information Template - Daylighting Page 17
2013 California Building Energy Efficiency Standards [March 2011]
Figure 5: Template Space 60ft x 40ft with 60” furniture
Further details about façade-templates and the daylighting simulation parameters and assumptions are
available in the PIER Office Daylighting study final report3. Dynamic Radiance simulations provide a
highly accurate reverse ray-tracing method of daylighting simulation, that accounts for window
blinds/shades and their operation by occupants; an important factor that can affect quantity and
distribution of daylight in a space. It also enables modeling of furniture of different heights inside the
template-space. For this and other reasons, Dynamic Radiance is a preferred simulation method for
modeling daylighting as compared to other available software such as DOE2 or Energy Plus.
Assumptions for Furniture Heights
Furniture plays an important role in determining daylight distribution in a space, and thus cannot be
ignored in the development of template-spaces. To account for furniture in the template-spaces, we
developed a typical office furniture layout with three different furniture heights, namely 30”, 45” and
60”. Further details about the furniture layout are provided in the PIER Office Daylighting Report.
3 PIER Office Daylighting Report
Measure Information Template - Daylighting Page 18
2013 California Building Energy Efficiency Standards [March 2011]
Figure 6: 30”, 45” and 60” Furniture Layouts
The template-spaces with 30” high furniture are most like a classroom or lecture hall with only desks
at 30”, and few partitions that raise above that level. The 60” furniture are most like a typical office,
with high partitions separating cubicles.
Façade-Templates
A set of façade-templates were developed to represent a variety of façade types found typically in
most office buildings in California, as documented from a study of the CEUS database in the PIER
Office Daylighting study, and to provide a good range of parameters over which the proposed formula
was expected to perform. Using an automated process of developing space-templates from an initial
set of models, a total of 432 template-spaces were developed and run in Dynamic Radiance. The
parameters used to develop the template-spaces were:
Orientation: N, S, E, W
Window to Wall Ratio: 26% - 52%
Average VLT: 10% - 40% - 70%
Average Sill Height and Average Head Height combination of : 0ft/5ft - 2.5ft/7.5ft - 5ft/10ft
Average ceiling height: 8‟ - 10‟
Furniture: Yes/No
Furniture height: 30” - 45” - 60”
Measure Information Template - Daylighting Page 19
2013 California Building Energy Efficiency Standards [March 2011]
Data Processing
Output from Dynamic Radiance for a template-space is illuminance values for each hour of the year,
reported by every sensor in the space. Daylight Autonomy plots were generated for each template-
space simulation run. Bins were created for Daylight Autonomy from 10% to 100%, at 10%
increments and the number of sensors within each bin was reported from each simulation run. The
data were then processed to develop percent area at each Daylight Autonomy threshold ranging from
10% to 100%.
4.1.3 Sidelighting Watt Calculation Method Development
Sidelighting is the daylight admitted into a space through vertical fenestrations on walls. The
coverage of daylight from vertical fenestrations is dependent on many factors such as physical
properties of fenestrations, their placement on a façade, orientation and blinds operation. Penetration
of daylighting in a sidelit space is typically tempered by the presence of vertical obstructions in the
space, such as furniture.
To develop a sidelighting Watt Calculation Method formula, the following tasks were performed:
Formula type assessment: The format of the formula was determined and variables identified
as the key components of the formula. Through statistical methods, the formula format was
tested to determine interaction between variables.
Formula coefficient characterization: Two statistical methods were identified to determine
the format of the formula and the different formula coefficients:
• Linear least square regression method on multiple variables
• Least square regression on single variable
The linear least square regression method consists of developing the formula in a linear
equation with multiple variables which can be functions of chosen variables. Different
coefficients of the equation can then be calculated. These coefficients can be transformed to
get back to the initial formula based on the chosen variables.
The least square regression on single variable method involves using a regression analysis tool
to define the formula for each set of data. This does not require the initial equation to be
transformed into a linear equation, and thus has more predictive power. The different
coefficients for each data set are reconciled through statistical analysis as well as visual
assessment of graphed data.
4.1.4 Toplighting Watt Calculation Method Development
Toplighting is daylighting admitted into a space through skylights or other fenestration of roofs such
as rooftop monitors. As opposed to sidelighting, toplighting does not have the added complexity due
to orientation or blind operation, and the daylight coverage is mainly dependent on the physical
properties of the skylights and ceiling height. Skylights are typically arranged uniformly on roofs, and
vertical elements in the space such as furniture, stacks in warehouses or display shelving in retail
spaces generally reduce daylight levels in a more or less uniform manner. To develop a toplighting
watt calculation method, the following tasks were performed:
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Formula Type Assessment: The format of the formula was determined and variables
identified as the key components of the formula.
Formula coefficient characterization: Different formula coefficients were determine using
statistical methods based on the dataset.
4.1.5 Development of a Method to Apply Calculation Result to Daylit Spaces
The result of the Watt Calculation Method is the minimum percent of total space watts that must be
controlled using photocontrols. In order to apply this result, instructions need to be provided on which
luminaires in the space this requirement applies, and how they need to be zoned (circuited), in order
for the photocontrols to work effectively.
To develop instructions, we leveraged the one and two window head height approach, which is the
basis for the current 2008 Title 24 requirement, and the accepted rule of thumb for circuiting
photocontrolled luminaires. Similarly we use the 0.7*Ceiling Height approach to determine
luminaries to control for toplit spaces.
This method provides users the ability to determine additional wattage to claim for a power
adjustment factor, if they control more wattage than what the Watt Calculation Method requires.
4.1.6 Assessing Watt Calculation Method’s Energy Impact
The proposed calculation method was validated by implementing it on multiple example spaces that
deviate in façade design and form, from the space and facade-templates used in the dataset to develop
the Watt Calculation Method. The results from the Watt Calculation Method, and their potential
energy savings, were then compared to:
(a) Results of the percent watts controlled from simulation for the same space (Simulation)
(b) Results of equivalent percent watts controlled determined using the current Title 24 method
(Graphical Method).
To develop a sufficiently large set of examples that represent a variety of space geometries and
window layouts, we developed 12 different examples spaces. Then to each example space, the
following variations were applied to get a total of 384 separate examples:
Four (4) orientations
Two (2) Window-to-wall Ratios
Four (4) furniture heights
Additionally the Watt Calculation Method was applied to an example plan provided by one of our
stakeholders as an example of where the current 2008 Title 24 method could not be applied
effectively without a significant amount of time and effort. This example provides a demonstration of
how the process of code compliance will be simplified to a large extent with the Watt Calculation
Method.
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4.2 Proposal 2: Photocontrols Requirement Trigger
This section describes the methodology used to update the minimum daylit area trigger for
photocontrols for sidelit and toplit spaces in Sections 131(c)2B and 131(c)2C, to a more aggressive
requirement based on updated costs of photocontrols, and updated energy costs compared to the 2008
code change proposal.
The key elements of the methodology were as follows:
Photocontrols Cost Survey
Analysis
4.2.1 Photocontrols Cost Survey
HMG conducted a market assessment of the purchase price for photosensors and associated
equipment (e.g. controllers, dimmers, switches, power packs). In preparation for this data collection
effort, HMG created a database including a photosensor product list with 30 products from 10
manufacturers. For each manufacturer, HMG collected distributor contacts from across California. A
sample of these 184 distributors was contacted from six regions of the state (Sacramento, SF Bay
Area, LA, Riverside County/Fresno, San Diego and Other). Each distributor was asked to provide the
cost for photosensor and associated equipment needed for two sample projects:
1. 800 sf side lit open office area; 250 sf daylit area; 4 fixtures controlled
2. 1120 sf top lit warehouse space; 896 sf daylit area; 14 fixtures controlled
Cost data was broken down into two categories:
(c) Fixed Cost: cost of equipment and labor which is fixed for any size daylit space.
(d) Variable Cost: cost of equipment and labor, which vary by the size of the daylit space.
Finally, both costs were combined to determine the cost of photocontrols for different sizes of daylit
spaces.
4.2.2 Analysis
Cost data from photocontrols from the photocontrols cost survey was used to determine the cost of
photocontrols for a range of daylit space sizes. A threshold of daylight sufficiency was then used to
determine energy savings at each daylit space size. Daylight sufficiency was measured in terms of
daylight autonomy, or percent of time that daylight in the space is equal to or greater than 300 lux of
illuminance. This translates to percent hours that a simple on-off photocontrol can turn electric lights
off.
Once savings were calculated, benefit-to-cost ratios were generated for each daylit space size to
determine a new threshold where photocontrols should be required.
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4.3 Proposal 3: Minimum Skylight Area Requirement
This section describes the methodology used to derive a new minimum skylit area requirement for
Section 143(c).
The key elements of the methodology were as follows:
Rooftop Survey
Analysis
4.3.1 Rooftop Survey
HMG conducted a visual survey of building rooftops to determine the existence of typical rooftop
obstructions. HMG used data collected by the Western Cooling Energy Center (WCEC) and the Cool
Ducts CASE team to establish a sample of target buildings to survey. The original data provided by
the WCEC included address and lot characteristics, such as building size and end use, as well as
information on the presence and area of exposed ducts, for a sample of 500 commercial buildings
throughout Climate Zone 12. From this dataset, HMG developed a targeted sample of building types
likely to be required to have skylights. The targeted building types (as described in the survey data)
were general commercial, shopping centers, retail stores, grocery stores, and industrial. The survey
does not provide detailed information about the use of each building, but it is expected that these
targeted building types could correspond to one or more of the following space types defined in Title
24: auto repair, commercial and industrial storage, exercise center/gymnasium, general commercial
and industrial work, grocery sales, grocery store, mall, office, retail merchandise sales, or tenant lease
space.
For each of the five target building types, HMG surveyed 25% of the original sample (125 buildings),
targeting 70 buildings most likely to trigger skylighting requirements if built under current 2008 code
(i.e. single story, high ceilinged buildings over 8000 square feet, such as big-box retail, industrial
factory or warehouses). Final quantities of surveyed buildings are as follows:
Number
of
Buildings
General Commercial 36
Shopping Centers 5
Retail Sales 7
Grocery Stores 1
Industrial 21
Total 70
Figure 7: Number of buildings surveyed
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Each of the 70 buildings was visually surveyed for rooftop obstructions using satellite imagery from
Bing maps (www.bing.com/maps). Area (square footage) of rooftop obstructions, such as packaged
HVAC units was calculated using tools available in Bing maps. Area of exposed ducts was already
included in the original data set from WCEC. Because the objective of the survey was to determine
the amount of roof space available for skylights, existing skylights were not considered to be rooftop
obstructions.
4.3.2 Analysis
Following the rooftop survey, a metric of percent obstructed area was analyzed for the dataset, and
based on findings, a new minimum skylight area requirement was recommended.
4.4 Proposal 4: Ceiling Height Trigger for Skylight Area Requirement
This section describes the methodology used to update the minimum ceiling height trigger for skylit
area requirement in Section 143(c).
The key elements of the methodology were as follows:
Cost survey for light wells and new skylight products for dropped ceilings
Update 2008 Title 24 life cycle cost analysis for skylights with light wells
4.4.1 Cost Survey for Light Wells and New Skylights for Dropped Ceilings
A cost survey was conducted to collect costs from contractors for building light wells for dropped
ceilings. These costs were determined in the PG&E 2008 Title 24 Daylighting CASE study4 to be
close to $2,000 (labor and materials) for building a single light well on-site. The new survey was
intended to determine if the cost of building a light well has changed since the 2008 T-24 study. We
collected costs from two contractors with experience in on-site light well fabrication to collect this
data.
Since the previous study, New products are now available for spaces with dropped ceilings, that can
be used instead of traditional skylights with light wells. These products such as Tubular Daylighting
Devices (TDDs) and Hybrid TDDs come with pre-assembled, specular, tubular light wells that are
well suited for delivering daylight in buildings with dropped ceilings. The cost survey also collected
costs for these new products from two of the leading manufacturers.
4.4.2 Update 2008 Title 24 Life Cycle Cost Analysis for Skylights with Light Wells
Cost effectiveness analysis done for the 2008 Title 24 Daylighting CASE work was updated with
(a) New costs for photocontrols, from the survey described in Section 4.2.1
(b) New costs for electric and gas energy, and new scalar for life cycle cost analysis
4 Reference 2008 CASE Report on Daylighting
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(c) Updated costs for traditional light wells
(d) Updated costs for new skylight products for dropped ceilings
4.5 Stakeholder Outreach Process
All of the main approaches, assumptions and methods of analysis used in this proposal have been
presented for review at one of three public Daylighting Stakeholder Meetings.
At each meeting, the utilities' CASE team invited feedback on the proposed language and analysis
thus far, and sent out a summary of what was discussed at the meeting, along with a summary of
outstanding questions and issues.
A record of the Stakeholder Meeting presentations, summaries and other supporting documents can be
found at www.calcodes.com. Stakeholder meetings were held on the following dates and locations:
First daylighting stakeholder meeting: June 23rd
2010, California Lighting Technology Center,
Davis, CA
Second daylighting stakeholder meeting: December 15th
2010, Webinar event
Additional stakeholder webinar to review Watt Calculation Method: March 17th
2011,
Webinar event
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5. Analysis and Results
This section describes the analysis done for each of the four proposals described in the Methodology
section and the associated results.
5.1 Proposal 1: Watt Calculation Method
This section describes the analysis steps undertaken to develop the formula for the Watt Calculation
Method, and a method to apply the calculation results to daylit spaces. The key sub-sections of this
section are as follows:
Using the Daylight Autonomy Metric to Develop Prescriptive Code Requirements
Formula Format
Façade-Template Approach for Spaces with Multiple Façade Orientations
Sidelighting Watt Calculation Method Development
Toplighting Watt Calculation Method Development
Method to Apply Calculation Result to Daylit Spaces
Assessing Watt Calculation‟s Method Energy Impact
5.1.1 Using the Daylight Autonomy Metric to Develop Prescriptive Code Requirements
A key component in the analysis for development of a Watt Calculation Method was the use of annual
daylight autonomy as a metric to describe daylight availability over the space area, through Radiance
simulations. Daylight autonomy (DA) is the percent of time of year that there is sufficient daylight
available at any point in a space. Sufficient daylight is expressed as a base illuminance value in lux. A
common base value is 300 lux for normal task work in offices and classrooms. This metric, which is
being currently discussed by the IES Daylighting Metrics Sub-committee as a potential metric for
determining daylight sufficiency of a space, is a useful means of determining how much daylighting is
available at any given point (sensor) in a daylit space as a percentage of time. For example, a sensor
that reports 50% daylight autonomy for a 300 lux base, will achieve 300 lux for 50% of occupied
hours in a year. In a space with a grid of sensors, each sensor represents a small area. The area of the
space that has at least 50% DA or more, is the spatial daylight autonomy, or sDA300,50% represented by
a percent value. Since the base illuminance value is fixed at 300 lux for this study, spatial daylight
autonomy is denoted by sDA50%.
Equation 1
For this study the threshold illuminance value, and occupied hours to be 8:30am to 5:30pm for every
day of the year (adjusted for Daylight Savings Time). These assumptions were determined as
appropriate values for use by the IES Daylight Metrics Sub-committee for developing climate based
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Daylight Metrics, and have been reproduced here for this analysis. The PIER Daylight Metric project5
final report provides further details and reasoning behind these choices.
In this analysis, 50% daylight autonomy has been used as a threshold to define sufficient daylighting.
The basis for the 50% value is findings from the PIER Daylight Metrics study and the IES Daylight
Metrics Sub-committee recommendations show that spaces with sDA50% has a high correlation to
occupants reporting high levels of satisfaction on questions about daylight sufficiency.
Dynamic Radiance Approach
The daylight autonomy metric is calculated using illuminance values reported by each sensor. These
illuminance values are determined using daylighting simulation through a Radiance based method
using the RTCONTRIB program. This approach is referred to as Dynamic Radiance6 as it provides
annual daylighting simulation, with an added advantage of modeling dynamic blinds operation. As
part of the PIER Daylight Metrics report, Dynamic Radiance was validated against DaySim7, a
software program using Radiance validated with field-measurements, and showed a very good
correlation between the two.
Limitations of Using Daylight Autonomy as a Metric
While Daylight Autonomy is a useful metric, some fundamental limitations of the approach should be
noted. One key limitation is that since daylight autonomy is reported by sensors as a summation over
an entire year, there is no differentiation between time of day/year that a certain sensor “sees”
sufficient daylight. Hence a space with two facades with windows, one on the east and one on the
west, may admit daylight at different times of the day, a DA plot will show no difference between
sensors close to the east façade and those close to the west façade. It would hence be incorrect to
assume that sensors with the same daylight autonomy values may be circuited together. It is however,
reasonable to assume that daylight savings are possible near both east and west facades, and that if
circuited properly, energy savings on both facades can be achieved.
5.1.2 Formula Format
To determine a format for the formula used in the Watt Calculation Method, we first needed to select
a method to determine area „sufficiently served by daylighting‟ for sidelighting and toplighting. As
described in Section 4.1.1 we assessed the current Title 24 method of graphically determining daylit
areas, and compared that to sDA50%, for both sidelighting and toplighting.
A set of spaces from the PIER Daylight Metrics study were chosen to determine how closely the
current Title 24 method (called graphical method from here on), matched sDA50%. It should be noted
that this is not a true comparison of the current Title 24 method of code compliance, as lighting
5 PIER Dayligth Metric report
6 MS Sim Build Paper
7 DaySim reference
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layouts for these spaces were not known. Instead this was a means to determine if the daylit area, as
defined by the current method could be used (either as-is, or with some modification) as a close
representation of area „sufficiently served by daylighting‟.
For sidelighting, this comparison found that the graphical method of defining daylit areas was not
closely related to sDA50%. However for toplighting, the match was much closer. This is an expected
result, as daylight from sidelighting is affected by multiple factors as explained in Section 4.1.3, and
hence cannot be reliably predicted with just geometric description known i.e. window head heights
and width. Toplighting, on the other hand, as explained in Section 4.1.4, has fewer factors that affect
daylight, and hence a geometric description of the skylight layout, can predict reasonably well the
daylight in a toplit space.
Sidelighting
Figure 8 and Figure 9 are examples of daylight autonomy plots (DA plots) from one of the 61 spaces
in the PIER Daylight Metrics study with sidelighting. In Figure 8, daylight enters the room from
windows on two opposite side walls (left and right sides of the plot). In Figure 9, daylight enters the
room from windows on two opposite side walls (top and bottom sides of the plot). The solid green
line shows primary daylit area using the geometric method and the dotted green line denotes
secondary daylit area. The colors and contour lines denote different daylit autonomy levels. Dark red
signified 0% DA, while light yellow signifies 90% DA.
Figure 8: DA plot for space A with sidelighting - green lines show primary daylit area
In the space in Figure 8, the total primary daylit area estimated by the graphical method is 232 sf, or
28% of the space. The primary daylit areas cover an area with mostly very high daylit autonomy. The
sDA50% ie area covered by the 50% contour line, is 501 sf, or 60%. In this example the graphical
method underestimates area sufficiency served by daylight.
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Figure 9: DA plot for space B with sidelighting - green lines show primary daylit area
In the space in Figure 9, the total primary daylit areas by graphical method is 338 sf, or 35% of the
space. The primary daylit areas covers an area with high as well as low daylit autonomy. The sDA50%
ie area covered by the 50% contour line, is 171 sf, or 18%. In this example the graphical method
overestimates area sufficiency served by daylight.
Reviewing these results and comparing net primary daylit areas (accounting for overlapping daylit
areas) using the graphical method, and sDA50% for multiple spaces, we found that results from
graphical method did not follow any specific trend when compared to sDA50% results (consistently
over or under predicting), which means that the graphical method could not be easily altered or
modified to get a better fit, and therefore a better prediction.
We thus concluded that for the development of a sidelighting formula to predict daylight in a space, a
geometric description was not sufficient to describe an area „sufficiently served by daylighting‟.
Instead, sDA50% plots from Dynamic Radiance will be needed.
Toplighting
Figure 10 and Figure 11 are examples of DA plots from spaces with toplighting from the PIER
Daylight Metrics study.
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Figure 10: DA plot for space C with toplighting - green lines show primary daylit area
In Figure 10, the total skylight daylit areas by graphical method is 1554 sf, or 100% of the space. The
area covered by daylight autonomy of 50% or greater (sDA50%) is also 1554 sf, or 100%. In this
example as the space reaches daylight saturation, the graphical method accurately estimates area
sufficiency served by daylight.
Figure 11: DA plot for space D with toplighting - green lines show primary daylit area
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In Figure 11, the total skylight daylit areas by graphical method is 816 sf, or 98% of the space. The
area covered by daylight autonomy of 50% or greater (sDA50%) is 761 sf, or 91%. In this example
daylight does not gets saturated, but the graphical method still more or less accurately estimates area
sufficiency served by daylight.
From these and other examples of toplit spaces, we see that for the development of a toplighting
formula to predict daylight in a space, a geometric description was sufficient to describe the area
„sufficiently served by daylighting‟.
5.1.3 Façade-Template Approach for Spaces with Multiple Façade Orientations
A key assumption in the façade-template approach is that daylight from individual facades can be
summed up by space. This includes sidelighting and toplighting as well as adjacent facades that may
have daylight overlap.
In the current Title 24 graphical method, the user is expected to deduct overlapping daylit zones.
However, in multiples spaces from the 61 examples of real buildings from PIER Daylight Metrics
project, we see that when two primary daylit areas from adjacent facades overlap, there are higher
daylight autonomy levels in the overlapping area, as well as an increase in area covered by sDA50%.
Furthermore, the increase in area is more or less equivalent to the overlapping areas. The result is that
sDA50% for the space with overlapping daylighting from adjacent facades, is close to the same as that
calculated individually for each façade and added up per space.
Figure 12: DA plot for space E with sidelighting from two adjacent walls
Figure 12 shows a DA plot for one such space from the set of 61 real spaces, with windows on two
adjacent facades (left and top sides of the plot). The solid green line represents net primary daylit area
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and dotted green line, net secondary daylit areas. The overlap of daylit areas on the top left hand
corner of the plot creates additional sDA50% area in the overlapping secondary daylit areas region.
What we find here is, when two sources of daylight are brought close to each other (as with two
adjacent facades), sensors in the secondary daylit area, that had lower illuminance get additional
illuminance, causing them to go above the 300 lux threshold, and thus increase the count of sensors
with 50% daylight autonomy.
Case A: SOUTH Case B: EAST
Case C: SOUTH & EAST
Figure 13: Individual and Combined Facades
We conducted further investigations to confirm this phenomenon using the template-spaces, and
found that when two walls with windows are adjacent to each other, the sDA50% was about the same
as when the two facades were simulated separately, and results added together. Figure 13 shows two
simulation runs with individual facades facing South and East (Case A and B), and a third simulation
run with a template-space with a south and east façade (Case C).
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Figure 14: Table with sDA300,50% values for Cases A - C
Figure 14 shows a table with sDA50% for all three cases. Note here that while the image for Case B
shows a 60 ft East facing façade, the value for sDA50% for Case B in the table is adjusted for a 40ft
façade, to make an applicable comparison. What we find here is that the sum of individual facades
from Cases A and B (47%) is very close to, in fact slightly lower than, the result from Case C (51%).
5.1.4 Façade-Template Approach for Spaces with Toplighting and Sidelighting
This increase in sDA50% area for overlapping daylit areas was also found to be true when daylit areas
from toplighting and sidelighting overlap. We developed a model with one skylight and one south
facing window, and moved the skylight closer to the window until the skylight was completely within
the area served by the daylight from the window. The four cases and their DA plots are shown in
Figure 15, and their total sDA50% are shown in Figure 16. The sDA50% values are calculated by
totaling up sensors with 50%DA or more and dividing by the total number of sensors.
Case 1 Case 2
sDA50%
Case A, South Facing Façade (60ft façade) 28%
Case B, East Facing Façade (40ft façade) 19%
Case C, South (60ft) and East (40ft) Façade 51%
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Case 3 Case 4
Figure 15: Sidelighting and Toplighting Overlap Study Cases 1-4
Figure 16: Table with sDA300,50% values for Cases 1 - 4
The results tell us that when the skylight and window are far apart (same as calculating side and top
lighting results separately and summing up) as in case 1, the sDA50% value of 22% is either close, or
lower than the values for cases 2, 3 and 4, were the skylight is progressively brought closer to the
window. The result seems counter-intuitive as one would expect daylit areas to overlap in cases 3 and
4 and thus the sDA50% to decrease, compared to case 1.
sDA50%
CASE 1, Skylight 60 ft from window 22%
CASE 2, Skylight 40 ft from window 28%
CASE 3, Skylight 22.5 ft from window 25%
CASE 4, Skylight 12.5 ft from window 21%
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What we find here is, like in the case with two adjacent facades, when two sources of daylight
(skylight and window) are brought closer, sensors that had lower illuminance when they were far
apart, get additional illuminance, causing them to go above the 300 lux threshold, and thus increase
the count of sensors with 50% daylight autonomy. In other words, the overlapping daylit areas not
only increase illuminance in the overlapped area, but also increase useful daylit areas on the edges of
the daylit areas.
With this study, we can conclude that results for sDA50% can be calculated separately for toplighting
and sidelighting, as well as for two façades with windows, and summed up without the need to
subtract overlapping daylit areas.
5.1.5 Sidelighting Watt Calculation Method Development
As described in Section 5.1.2, daylight from sidelighting is affected by multiple factors, which are not
well captured by just the geometric description of a façade. To develop a sidelighting Watt
Calculation Method formula we first developed two metrics that were likely to have a direct
correlation with the daylight and its distribution in a sidelit space. These two metrics were „Effective
Aperture‟, and „Window Location Coefficient‟.
Effective Aperture (EA)
Effective Aperture (EA) is defined as in the „classic‟ definition of the term shown in Equation 2. EA
is calculated for each façade orientation as shown below:
Equation 2
Where:
Glazing Area = Total of area of all windows in a given orientation
Net Wall Area = Total area of wall in a given orientation, from finished floor level to ceiling height
where the ceiling meets the wall. (Note that this is different from Gross Wall Area which is the total
wall area including plenum)
Visible Transmittance = Area weighted average visible transmittance of all windows in a given
orientation.
This form of the equation (also known as the „classic‟ EA definition) differs from the current Title 24
form of the Effective Aperture definition in that the Title 24 definition uses daylit area in the
denominator instead of wall area. The change from classic EA was made in the Title 24 definition
because the desired metric was not the average amount of daylight entering the room, but the amount
of daylight entering the daylit area. In the Watt Calculation Method, the metric of interest is now the
amount of daylight entering the room, as the new formula calculates minimum percent wattage
controlled in the room. Here the percentage is relative to the total wattage installed.
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This choice of the „classic‟ EA definition helps elevate some of the confusion with the EA term, that
has been a source of confusion, and perceived complexity with the daylighting code.
Window Location Coefficient (WLC)
Window Location Coefficient is defined as a measure of the vertical placement of a window on a
wall. WLC is calculated for each façade orientation as shown below:
Equation 3
Where:
Average Sill Height = Area weighted average sill height of all windows in a given orientation
Average Window Height = Area weighted average height (sill to head) of all windows in a given
orientation
Ceiling Height = Average ceiling height at the point where the ceiling meets the wall
A thin window placed at the bottom of the wall with sill height = 0ft will have a low WLC, close to 0.
On the other hand, a thin window placed at the top of a wall with head height same a ceiling height
will have a high WLC, close to 2. WLC will be 1 for a window placed at the center of a wall.
The formula was derived keeping in mind that a window placed higher on a wall will provide better
daylight coverage than a window placed lower. Equation 3 was selected from a set of multiple
equations, each describing the vertical location of the window based on the window vertical
dimension, head height, sill height, and ceiling height including.
We analyzed each of them in terms of relation with daylight coverage from simulation data and
looked for the closest fit. Equation 3 was chosen not only because it had the best fit, but also because
it provides a finite range of 0 to 2 with WLC = 1 (or neutral) for a window placed in the center of a
wall.
Formula Type Assessment
The next step was to determine the shape of the formula. As described in Section 5.1.3, the formula
was developed using template-spaces with a single façade orientation with glazing, and the results
added together for more than one façade orientation. This is because our pilot runs showed that
overlapped daylighting from two adjacent facades result in more or less the same area with 50%
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Daylight Autonomy, as when daylight from the two facades are calculated separately and added
together. A formula was thus developed to be used for one façade orientation at a time, summing up
the result from multiple orientations for a space with more than one façade orientation.
Five variables were identified as components of the formula:
Effective Aperture: A measure of how much daylight is available from a façade. EA is a
value that ranges from 0% for a wall with no windows to 100% for a fully glazed façade with
100% VT glass.
Window Location Coefficient: A measure of the vertical placement of the windows on a
façade. WLC values range from 0 to 2.
Orientation: Orientation of the façade, as South or Non-South. South is defined as all angles
in 45 degrees of magnetic South.
Activity Type (Furniture Type): Furniture layout and partition heights (described in Section
4.1.2) were categorized in two simple categories which could be applied by space activity
type, namely 30” partition heights, and 60” partition heights. Table xx gives a lookup table for
Title 24 space activity type and furniture partition heights
Climate Zone: Title 24 California Climate Zones.
We postulated that the effect of furniture type, orientation and climate zones could be accounted for
by simple coefficients, modulating the core formula. The core formula itself would be the product of a
function of effective aperture and a function of the window location coefficient. The five variables
were all assumed to be independent, i.e. interactive effects between these variables would be minimal
or null. This assumption was later tested and found to be correct. Equation 4 below gives the basic
form of the formula. The formula predicts sDA50%, or area in the space, in sf, that will have daylight
autonomy of 50% or more.
Equation 4
Where:
C1orientation = Value looked up from a table for orientation, from Figure 19
C2activity type = Value looked up from a table for appropriate furniture height, from Figure 19
C3climate zone = Value looked up from a table for climate zone, from Figure 19
f1(EA) = A function of effective aperture, from Equation 5
f2(WLC) = A function of window location coefficient, from Equation 6
Façade Length = Total length of façade in a given orientation, in ft
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To test our assumptions about the shape of the formula, we analyzed our façade template dataset both
statistically and graphically.
If two variables are independent, plotting series of curves of one variable (say WLC) for different
values of the other (say EA), will either return parallel curves if they can be described by affine or
polynomial equation, or curves with different slopes if their descriptive function is linear. In addition
to validating these assumptions, the graphical analysis provided an understanding of the specific
formulation of effective aperture function and the window location coefficient function.
Figure 17. Daylight Autonomy depending on effective aperture for different window location
coefficient values
Figure 17 shows the curves for different window location coefficients as a function of effective
apertures. Here when the window location coefficient value is fixed, the percent sDA50% varies as an
affine function of effective aperture.
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Figure 18. Daylight Autonomy depending on location coefficient for different effective aperture
values
Similarly Figure 18 shows the curves for different effective apertures as a function of window
location coefficients. The curves follow a polynomial equation, based on a least square regression
analysis.
Based on this observation, the effective aperture function and the window location coefficient
function have the following shape:
Equation 5
Equation 6
where
f1(EA) = A function of effective aperture
f2(WLC) = A function of window location coefficient
a, b, c, d, e = Coefficients determined using our dataset, see Figure 18
The same formula format is applied to spaces with more than one façade orientation with windows.
As described in Section 5.1.3, two adjacent facades will result in more or less the same sDA50%, as
when daylight from the two facades are calculated separately and added together. Thus, for spaces
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with multiple façade orientations, sDA50% can be expressed as the sum of the sDA50% calculated for
each façade orientation separately.
Equation 7
Where:
C1orientation = Value looked up from a table for orientation, from Figure 19
C2activity type = Value looked up from a table for appropriate furniture height, from Figure 19
C3climate zone = Value looked up from a table for climate zone, from Figure 19
f1(EA) = A function of effective aperture, from Equation 5
f2(WLC) = A function of window location coefficient, from Equation 6
Façade Length = Total length of façade in a given orientation, in ft
Formula Coefficient Characterization
To determine the value of the C1orientation, C2activity type, and C3climate zone coefficients, as well as the
effective aperture and window location coefficient function coefficients (a,b,c,d and e) two separate
approaches were evaluated:
Linear least square regression method on multiple variables
Least square regression on single variable
In the first approach, the formula is developed into a linear equation with multiple variables.
It can be rewritten as
Where
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This linear equation has five variables namely , , , , and .
A linear regression analysis can determine each A, B, C, D, E, F coefficients from which each a, b, c,
d, e can be evaluated. The C1orientation, C2activity type and C3climate zone coefficients can be found by using
the data with exactly the same value for each parameter but varying one parameter at a time.
In the second approach, we performed regression analyses on the dataset to define a set of location
coefficient functions for different effective apertures for each orientation. Further regression analyses
were carried out on this pool of location coefficient functions to determine a set of effective aperture
functions. This exercise enabled us to define each location coefficient and effective aperture function
coefficients for each orientation.
We then defined orientation coefficients (C1) by setting one orientation as the origin and assessing the
others as the average of the ratio of the two orientation coefficients.
We developed the activity-type coefficients (C2) by dividing each data point with specific furniture
type by the same data point with no furniture (same effective aperture, location coefficient,
orientation, climate zone but different furniture type) calculated by the formula previously generated.
We took the average on these ratios. The same method was used to define the climate zone
coefficients.
When we applied both approaches to the data set, we found that the accuracy of both approaches was
very similar. The first approach turned out to be very sensitive to the dataset, and was delivering
different coefficients (a, b, c, d, e) for each orientation. The second approach had the advantage of
reducing the number of coefficients while maintaining accuracy. It also simplified the shape of the
formula. The second approach was adopted to evaluate the different coefficients.
Because the South orientation has very different daylight availability, we couldn‟t achieve a good fit
for all orientations using a single set of coefficients. We hence developed two sets of coefficients, one
fitting the North, East and West orientations, and another one fitting South.
The sidelighting coefficients for each orientation are summarized in Figure 19 below.
Coefficients South North, East, West
40 60
Classroom 0.8 0.8
Office, Retail 0.56 0.46
Climate Zone 01 0.81
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Climate Zone 02 0.99
Climate Zone 03 0.97
Climate Zone 04 1.02
Climate Zone 05 1.04
Climate Zone 06 1.00
Climate Zone 07 1.03
Climate Zone 08 1.03
Climate Zone 09 1.05
Climate Zone 10 1.06
Climate Zone 11 1.00
Climate Zone 12 1.00
Climate Zone 13 1.01
Climate Zone 14 1.13
Climate Zone 15 1.10
Climate Zone 16 1.03
Figure 19. Sidelighting Formula Coefficients
Calculating Lighting Wattage Controlled
The formula in Equation 4 and Equation 7 provide a method to calculate sDA50%, or area that has
daylight autonomy greater than 50%. The total lighting wattage that serves this area can thus be
controlled cost effectively. This lighting wattage controlled, can be calculated by a formula given in
Equation 8
Equation 8
Where
sDA50% = Spatial Daylight Autonomy 50%, as calculated from Equation 7, in sf
LPD = Installed Lighting Power Density, in W/sf
Once lighting wattage controlled is calculated it can be checked to determine if this is enough to pass
the cost effectiveness calculations derived in Section 5.2.2. It should be noted that this check, allows
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the Watt Calculation Method to eliminate two separate checks that currently form the basis of two
exceptions in the current Title 24 code - Effective Aperture exception and Minimum Daylit Area.
To convert this to a percentage, the lighting wattage controlled is divided by the total installed
wattage.
Equation 9
Where:
Lighting Wattage Controlled = Total electric lighting wattage that must be controlled, as calculated in
Equation 8, in Watts
Total Installed Lighting Power = Total installed lighting power, in Watts, which is usually space area
multiplied by Lighting Power Density, in W/sf
Equation 9 can be written in its expanded form as:
Equation 10
Where:
C1orientation = Value looked up from a table for orientation, from Figure 19
C2activity type = Value looked up from a table for appropriate furniture height, from Figure 19
C3climate zone = Value looked up from a table for climate zone, from Figure 19
f1(EA) = A function of effective aperture, from Equation 5
f2(WLC) = A function of window location coefficient, from Equation 6
Façade Length = Total length of façade in a given orientation, in ft
LPD = Installed Lighting Power Density, in W/sf
Total Installed Lighting Power = Total installed lighting power, in Watts, which is usually space area
multiplied by Lighting Power Density, in W/sf
5.1.6 Toplighting Watt Calculation Method Development
As described in Section 5.1.2, daylight from toplighting is fairly well described by a geometric
description of the space ceiling height and skylight dimensions provided by the Title 24 daylit area
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graphical calculation method. This informs the process of compliance proposed for toplighting
described in this section.
Difference between Daylight Coverage from Toplighting and Sidelighting
A key difference between how daylight from toplighting and sidelighting provide daylight coverage
in a space, is that daylight from a toplighting source (skylight) is mostly available in a fairly narrow
cone projected from the skylight. This cone has been determined in previous studies to be an angle of
35 degrees from the edge of the skylight, outward. This translates to a 0.7 * CH from the edge of the
skylight on a floor, which forms the current Title 24daylit area definition. Moreover, we find that
daylight availability outside this cone reduces very rapidly. In sidelighting we see a more gradual
decline in daylight availability as we progress further away from the window. This can be seen
graphically in the plot in Figure 20. It is because of this difference in daylight behavior, that there is
no „secondary‟ daylit zone for toplighting.
Figure 20: DA as a function of distance from daylit source
In Figure 20, the solid blue line represents daylight autonomy values from toplighting, and the blue
dotted line shows the point where 0.7 x CH cone intersects the daylit area plot. The solid red dotted
line represents the daylight autonomy values from sidelighting, and the red dotted line shows the point
where the one head height line intersects the daylit area plot. We see here that daylight availability
reduces rapidly for toplighting, after the 0.7 * CH line, it reduces more gradually for sidelighting,
after the one head height line.
It is also clear from Figure 20 that the 0.7 x CH is intersecting the DA plot at about 50% DA, which
reinforces its merit as a good predictor of area „sufficiently served by daylight‟.
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Concept of Skylit Area
The current Title 24 code refers to the area projected by the 35 degree cone on the floor, minus
overlaps with other daylit areas and truncated by permanent stacks and racks as „Skylight Daylit
Area‟. In this report we refer to the area projected by the 35 degree cone on the floor as „Skylit Area‟.
As our previous analysis has shown (section xx), this area is fairly equivalent to the area with at least
50% daylight autonomy, calculated using Dynamic Radiance outputs for toplit spaces. This area
hence represents area „sufficiently served by daylight‟ for toplit spaces, and is equivalent to the
sDA50% calculated in sidelighting calculations.
Skylit area is calculated for each skylight in a space using a formula that uses an effective skylight
area length (Lskylit area) and width (Wskylit area). This total skylit area for a space is calculated as:
Equation 11
Were:
Lskylit area = Effective length of skylit area for one skylight, calculated as shown in Equation 12
Wskylit area = Effective width of skylit area for one skylight, calculated as shown in Equation 13
Accounting for Overlapping Skylit Areas
Skylit areas from skylights that are closer than 0.7 * CH will overlap to some extent. To account for
this overlap effective skylit area length (Lskylit area) and width (Wskylit area) used in Equation 11 are
calculated using the following logic.
In this method, we collect input from the user for the average skylight length (L) and width (W) and
the minimum center to center distance between skylights in the length direction (L’) and width
direction (W’). Using these values to determine skylit areas, we ensure that the skylit area (Lskylit area x
Wskylit area) is always a conservative value hence never overestimated by the formula.
It is important to note that while overlapping skylit areas will extend the skylit area boundary
elsewhere, as we see in the case of overlapping daylight from adjacent facades in sidelighting, when
dealing with toplighting, overlapping area has to be accounted for, else the formula would grossly
overestimate the skylit area for a grid of skylights.
Equation 12 calculates effective length of the skylit area for one skylight.
Equation 12
Here:
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L = length of skylight
L' = minimum center to center distance between skylights in the length direction
Alength = 0.7 for spaces without stacks, 0.5 for spaces with stacks running along the width direction
The impact of accounting for stacks is discussed below.
Equation 13 calculates effective width of the skylit area for one skylight.
Equation 13
Here:
W = average width of skylights
W' = minimum center to center distance between skylights in the width direction
Awidth = 0.7 for spaces without stacks, 0.5 for spaces with stacks running along the length direction
The impact of accounting for stacks is discussed below.
Accounting for Stacks and Racks
Skylit areas will need to be adjusted for areas where there are likely to be stacks and racks (called
stacks here on for brevity). These spaces, typically warehouses, are design with stacks running in one
direction, and electric lighting and skylights in rows running in the same direction. The current Title
24 method asks the user to truncate the skylight daylit areas if the distance between the edge of a
skylight and a stack is greater than the 0.7 times the difference between the ceiling height (CH) and
the height of the stack (OH). This is a fairly cumbersome process that requires the knowledge of
stacks layout, which may not be available during compliance stage or envelope design stage. Besides,
most users may easily avoid this step of truncating daylit areas altogether, by indicating that stacks are
not „permanent‟.
A simpler way to account for this could be to use an assumption for the layout and height of stacks, to
determine how much the skylit area in one direction should be reduced. We make a reasonable
assumption that there is an equal 50%-50% chance that stacks are present at a distance greater than
the value ½ * (0.7*CH) i.e. median distance, and less than that value. A similarly assumption can also
be made for the stack height. There is an equal 50%-50% chance that stack heights can be greater than
the value ½ * CH i.e. median height, or less than that value.
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Figure 21: Stack of median height at a median distance from skylight
Based on this logic it would be reasonable to calculate skylit area in the direction perpendicular to the
direct of stacks, by 0.35*CH instead of 0.7*CH. However, it is likely that the daylight that bounces
off the shelves, will still be useful daylight with some losses due to shelf reflectance. To keep the
formula simple, we hence recommend that the skylit area in the direction perpendicular to the direct
of stacks, be calculated as 0.5*CH.
Thus for „warehouse‟ spaces which are extremely likely to have stacks, (either in their first occupancy
or later), and any other space that is indicated as having stacks/racks, the calculation of effective
length (Lskylit area) or width (Wskylit area) uses a multiplier value (A) of 0.5, using the following logic:
If racks/stacks run in the skylight length direction,
Value of Awidth in Equation 13 is set to 0.5
If racks/stacks run in the skylight width direction,
Value of Alength in Equation 12 is set to 0.5
Calculating Lighting Wattage Controlled
The formula in Equation 11, along with Equation 12 through Equation 13, provide a method to
calculate Skylit Area, which is equivalent to area that has daylight autonomy greater than 50%. The
total lighting wattage that serves this area can thus be controlled cost effectively. This lighting
wattage controlled, can be calculated by a formula given in Equation 14
Equation 14
Here:
Skylit Area = Area served by daylighting from toplighting, in sf
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LPD = Installed Lighting Power Density, in W/sf
Once lighting wattage controlled is calculated it can be checked to determine if this is enough to pass
the cost effectiveness calculations derived in Section 5.2.2. At this time, an effective aperture check
must also be done. Effective Aperture can be calculated as per the formula given in Equation 15
Equation 15
Here:
VT = Average Skylight Visible Transmittance
Well Efficiency = Ratio of amount of visible light leaving a skylight well to the amount of visible light
entering the skylight well
Total Skylit Area = Skylit areas for all skylights, calculated using Equation 11
To convert this to a percentage, the lighting wattage controlled is divided by the total installed
wattage.
Equation 16
Here:
Lighting Wattage Controlled = Total electric lighting wattage that must be controlled, as calculated in
Equation 14, in Watts
Total Installed Lighting Power = Total installed lighting power, in Watts, which is usually space area
multiplied by Lighting Power Density, in W/sf
Skylit Area Threshold Cost Effectiveness
As described in Section 5.2.1 on photocontrols cost effectiveness analysis, photocontrols were found
to be conservatively cost effective with 215 watts of electric lighting controlled. They were also cost
effective for a daylit area of 218 sf. Here daylit area is calculated using the current Title 24 method of
0.7 x ceiling height (CH) from each edge of the skylight. Figure 22 below shows skylit areas
calculated for a single 2ft x 2ft, 2ft x 4ft and 4ft x 4ft skylight, for a 10ft, 12ft and 15ft ceiling.
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Figure 22: Daylit areas for different skylight sizes and ceiling heights
We find that even the smallest skylight with the lowest ceiling is less than the threshold 220 sf for
cost effective photocontrols. Based on this, we conclude that even a single skylight will project a large
enough skylit area to cost effectively require photocontrols. This allows simple instructions to be
provided for code compliance for toplighting, which state that all spaces with skylights must control
luminaires that fall within 0.7 x CH from the skylights‟ edges.
The logic behind requiring photocontrols for all spaces with any number of skylights is that a skylight
without photocontrols presents a no-win situation. The skylight reduced the effective insulation of the
roof with penalties for heating and cooling, while not providing any lighting energy savings.
5.1.7 Method to Apply Calculation Result to Daylit Spaces
To apply calculation results to a daylit space, the following steps are required to be followed. Figure
23 provides a flow-chart of steps for sidelighting and Figure 24 for toplighting.
Skylight
width
Skylight
length
Ceiling
Height
Daylit
Area
2' x 2', 10ftCH 2 2 10 256
2' x 2', 12ftCH 2 2 12 353
2' x 2', 15ftCH 2 2 15 529
2' x 4', 10ftCH 2 4 10 288
2' x 4', 12ftCH 2 4 12 391
2' x 4', 15ftCH 2 4 15 575
2' x 2', 10ftCH 2 2 10 256
2' x 2', 12ftCH 2 2 12 353
2' x 2', 15ftCH 2 2 15 529
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Sidelighting
Figure 23: Steps to Apply Calculation Results to Sidelit Spaces
Step 1: Collect information from building floor plans. This following information is collected per
space:
1. Space Area
2. Ceiling Height
3. LPD
4. Activity Type
The following information is collected per façade:
1. Orientation
2. WWR
3. Average VLT
4. Average Sill Height
5. Average Head Height
6. Façade length
Step 2: Apply the Watt Calculation Method and calculate the minimum percent watts controlled.
Step 3: If the answer is 0%, claim exception, else goto Step 4
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Step 4: Determine Luminaires one head height and two head heights from each window. Circuit all
luminaires that are partially or completely within one head height separately from the rest of the
luminaires. Circuit all luminaires that are partially or completely within two head height separately
from the rest of the luminaires.
Step 5: Provide automatic photocontrols to control up to the minimum watts controlled requirement
for the space. Control luminaires closest to windows (one head height) first, progressively moving to
luminaires away from windows (two head heights).
Step 6: To claim a power adjustment factor credit, control luminaires up to two times the minimum
watts controlled as required from the Watt Calculation Method, but only within two head heights.
Toplighting
Figure 24: Steps to Apply Calculation Results to Sidelit Spaces
Step 1: Collect information from building floor plans. This following information is collected per
space:
1. Space Area
2. Ceiling Height
3. LPD
4. Activity Type
5. Average skylight length (L)
6. Average skylight width (W)
7. Minimum center to center skylight distance, in length direction (L‟)
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8. Minimum center to center skylight distance, in width direction (W‟)
Step 2: Calculate the Minimum Percent Watts Controlled
Step 3: Calculate Skylight Effective Aperture.
Step 4: If Skylight EA is less than threshold value, claim exception, else go to Step 5
Step 5: Determine Luminaires A * Ceiling Height from each side of skylight. Circuit these luminaires
separately from the rest of the luminaires in the space.
Step 6: Provide automatic photocontrols to control luminaires identified in Step 5, up to minimum
watts controlled requirement for the space.
5.1.8 Assessing Energy Impact of Watt Calculation’s Method
To validate the proposed Watt Calculation Method on a variety of spaces, and to assess the energy
savings compared to the current method, we developed a set of 12 different example spaces. As
explained in Section 4.1.6, variations in orientation, window-to-wall ratio, and furniture heights were
applied to generate 384 separate examples that were run in Dynamic Radiance.
Three values were calculated for each example.
(a) Percent watts controlled from simulation results.
(b) Percent watts controlled from applying the Watt Calculation Method
(c) Percent watts controlled from applying the current Title 24 graphical method
These values were then plotted over a curve representing Daylight Autonomy (percent time) on y-
axis, over area (percent space) on x-axis. The curve called a „Cumulative sDA Curve‟ shows how
much space area (read on the x-axis) is covered by a minimum threshold of daylight autonomy (read
on the y-axis). Figure 25 shows an example of a cumulative sDA Curve. The red arrow on the figure
shows percent area (31%) with at least 50% DA.
Additionally, the area below the curve represents the energy savings possible due to daylighting in the
entire space. The area under the curve, up to a percent area mark, say 31%, represents energy savings
possible in that 31% of the space.
For a space with uniform lighting power density, percent watts is equivalent to percent area. Thus the
percent watts values calculated in (a), (b) and (c) above, can be plotted as values of percent area on
the cumulative sDA curve, and their respective energy savings potential determined.
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Figure 25: Example of a Cumulative sDA Curve
The following five examples show a sample of the results from the 384 examples. A spreadsheet with
the results from all examples is provided as an appendix to this report. In all plots, the red line
represented (a) - Simulation results, the green line represents (b) - Watt Calculation Method, and
purple line represents (c) - Graphical method.
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Figure 26: Example A - Cumulative sDA Plot
Example A: 60 ft x 30 ft space, with 55% WWR, South Facing, with 30” furniture
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Figure 27: Example B - Cumulative sDA Plot
Example B: 60 ft x 40 ft space, with 55% WWR, Facing South and East, with 60” furniture
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Figure 28: Example C - Cumulative sDA Plot
Example C: 60 ft x 40 ft space, with 55% WWR, Facing East, North and South, with 30” furniture
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Figure 29: Example D - Cumulative sDA Plot
Example D: 60 ft x 60 ft space „L-shape plan‟, with 55% WWR, Facing West, with 60” furniture
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Figure 30: Example E - Cumulative sDA Plot
Example E: 60 ft x 40 ft space , with 55% WWR multiple head height windows, Facing East, with
60” furniture
5.2 Proposal 2: Photocontrols Requirement Trigger
This section describes the analysis steps used to update the minimum daylit area trigger for
photocontrols for sidelit and toplit spaces in Sections 131(c)2B and 131(c)2C, to a more aggressive
requirement based on updated costs of photocontrols, and updated energy costs from the 2008 code
change proposal. This section also discusses the results from the analysis and their code implications.
5.2.1 Photocontrol System Cost
As discussed in section 4.2.1, above, HMG collected cost data for daylighting control equipment from
product distributers throughout California, based on two hypothetical projects:
800 sf side lit open office area; 250 sf daylit area; 4 fixtures controlled
1120 sf top lit warehouse space; 896 sf daylit area; 14 fixtures controlled
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Diagrammatic plans of the two scenarios are illustrated below in Figure 31 and Figure 32. Yellow
shading in each diagram indicates areas where current code requires luminaires to be controlled by
separately for daylighting. For these cost assessments we assumed that luminaires in the daylit zone
will be automatically controlled by photocontrols.
Figure 31: Plan diagram of hypothetical sidelit space
Figure 32: Plan diagram of hypothetical toplit space
HMG received 40 price quotes of retail prices for 11 different photocontrol products and their
required auxiliary components (lens, relay, power pack etc.).
Costs were collected for three different types of photocontrol products:
Wireless Systems: a photosensor sends a wireless signal to a controller that turns off or dims
lights at the pre-determined setpoint(s).
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Area = 70' x 16' = 1120sf
14 x 2-lamp T-8 fixures = 896 watts
LPD = 0.8 W/sf
Daylit Area = 896 sf
3% Skylights = 4 x 2'x4' skylights
# of fixtures in skylit daylit area = 14
Watts Controlled = 896 watts
2-lamp T8 fixture (64watts)
2'x4' skylight
Toplit Daylit Area
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Wired Stand-Alone Products: a photosensor sends a wired signal (line- or low-voltage)
directly to the lighting to be turned off or dimmed.
Wired Systems: a photosensor sends a wired signal (usually low-voltage) to a controller at the
pre-determined setpoint(s); the controller then relays a control signal to the lighting to be
turned off or dimmed.
The specific capabilities of each product were taken into account, and any auxiliary equipment such
as power packs, controllers, or transformers was included in the cost data for each product. In
addition, some of the products would require more than one sensor or controller to meet the current
multi-level requirements for Automatic Daylight Control Devices in the current code, section
131(c)2D. The cost of the additional equipment was included. Results of the cost survey for the three
product types are summarized below in Figure 33.
Figure 33: Photocontrols price summary
Initial fixed costs for wireless photocontrol systems are more than wired stand-alone photocontrol
systems and wired complete systems (photosensor with controller). However, when the cost of
installation and commissioning is included (analysis outlined below), the wireless daylight systems
are the least expensive to install, but on balance, not considerably different from the cost of wired
photosensor control systems. The major drawback to wireless daylight systems are in buildings
where the wireless signal affects the performance of the building, some examples include:
government buildings where outside access to insecure wireless communication is a security concern
and hospitals where wireless signals could reduce equipment performance.
In addition to the fixed equipment costs, we estimated the variable cost of labor to install and
commission the system. We obtained estimates of electrical contractor labor hours from a variety of
industry stakeholders, ranging from manufacturers, to contractors, to consultants. Estimated
installation times ranged from 30 minutes per fixture for wireless systems to 2 hours per fixture for
wired systems. In addition to installation, the systems were assumed to require 15-30 minutes per
ballast for commissioning of dimming systems, or up to 15 minutes per ballast for switching systems
Max Price Average Price Min Price
Wireless Photocontrols System (n=3) $436.00 $320.94 $261.00
Wireless Photosensors $134.49 $115.16 $100.00
Wireless Reciever $336.00 $205.78 $131.33
Wired Stand-Alone System (n=4) $231.82 $129.89 $62.00
Wired Photosensors $181.82 $99.89 $62.00
Power Pack $50.00 $30.00 $0.00
Wired Phtocontrols System (n=4 $662.50 $381.22 $121.87
Wired Photosensors $236.00 $138.72 $84.50
Controller & Aux Equipment $550.00 $242.50 $0.00
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(larger systems are assumed to have a commissioning cap of $2000, based on daily fees for
manufacturer support services).
A more detailed summary of the basis for the labor time assumptions can be found in Appendix xx.
Using the labor estimates obtained from stakeholders, and data sourced from RS Means CostsWorks
for electrical contractor labor rates throughout the state (see Figure 34), we estimated the variable cost
for installation and commissioning daylight control systems (in Sacramento) to be $350.50
(switching) or $467.75 (dimming) for the sample office sidelit project (shown in Figure 31) and
$559.50 (switching) or $886.75 (dimming) for the sample warehouse top lit project (shown in Figure
32). See Figure 35, below, for a detailed summary of labor and commissioning cost estimates.
Figure 34: RS Means CostWorks Hourly Labor Rates for Electrical Contractors
Figure 35: RS Means CostWorks Variance in labor cost by region
The total costs, documented below in Figure 36 (switching system) and Figure 37 (dimming system)
include photocontrol equipment, installation labor and commissioning labor. The cost differential
between a std ballast and a dimmable ballast was not included based on a companion CASE proposal
requiring controllable ballasts. Labor costs from the Sacramento area were used to represent an
average labor cost for the state. Total costs for wireless and wired jobs were averaged to provide an
average total project cost for both dimming and switching systems for both hypothetical spaces.
Labor + O&P ($/hr)
from RS Means City
City Multipliers
RS Means (%)
Labor O+P by
city
$72.85 Sacramento 115.1 $83.85
Bay Area 151.6 $110.44
Los Angeles 122.1 $88.95
Riverside 110.2 $80.28
San Diego 103.7 $75.55
Other (avg) 106.5 $77.59
Wireless Wired Wireless Wired
0.5 hrs 2hrs 2hrs 0.5 hrs 2hrs 7hrs
Sacramento $41.93 $167.70 $167.70 $41.93 $167.70 $586.95
Bay Area $55.22 $220.88 $220.88 $55.22 $220.88 $773.08
Los Angeles $44.47 $177.90 $177.90 $44.47 $177.90 $622.65
Riverside $40.14 $160.56 $160.56 $40.14 $160.56 $561.96
San Diego $37.77 $151.09 $151.09 $37.77 $151.09 $528.82
Other (avg) $38.79 $155.17 $155.17 $38.79 $155.17 $543.10
Sidelighting
4 fixtures controlled
Toplighting
14 fixtures controlledInstallation Cost Comissioning
Cost
Installation Cost Comissioning
Cost
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Figure 36: Total Costs for Switching System, Sacramento, CA
Figure 37: Total Costs for Dimming System, Sacramento, CA
5.2.2 Energy Savings
In order to determine cost effectiveness, energy savings were calculated for the two hypothetical
projects described above using the following parameters:
15 year analysis period
LPD of 0.8 W/sf
2600 annual hours of operation
Energy costs of $0.10/kWh
Simple on-off photocontrols system applied to luminaries one head height from the windows,
and 0.7*Ceiling Height from the skylights
To estimated energy savings, we used a theoretical method that assumes various Daylight Autonomy
levels (ranging from 20% to 70% at 10% intervals) in the region identified as one head height from
the windows, and 0.7*Ceiling Height from the skylights. The actual levels of daylight illuminance
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and hours per year of sufficient daylight availability will depend on multiple factors identified in the
watt calculation method in Section 5.1, such as, window to wall ratio, window VLT, sill height, head
height, ceiling height, orientation etc. Simulation runs and analysis done in Sections 5.1.8 and 5.1.6
shows that 50% Daylight Autonomy in the one head height region, and the 0.7*Ceiling Height region
is achievable in most cases.
An example of a theoretical calculation using Daylight Autonomy is provided below:
At 20% Daylight Autonomy, the lights are assumed to be off for 20% of the year, or 520 hours. At 0.8
W/sf for the sidelighting case, this results in an annual energy saving of 104 kWh for the sidelighting
case and 372.7 kWh for the toplighting case, which translates to $156 for the sidelighting case, and
$559 for the toplighting case, over 15 yrs.
5.2.3 Cost Effectiveness Analysis
Using the system cost data and the energy savings presented above, HMG conducted a cost
effectiveness analysis to determine the viability of reducing the area thresholds for mandatory
daylighting controls.
In our cost effectiveness analysis, we used several layers of conservatism. First, the cost effectiveness
analysis assumes an on/off daylighting control, rather than the current multi-level requirement. A
basic on/off control requires a higher daylight illuminance level threshold to turn off the electric
lighting, than the code-required multi-level daylight control. Second, we used conservative energy
costs of $0.10/kWh for the full 15 year assessment. Finally, the cost effectiveness assessment was
based on 50% daylight autonomy (50% DA) at 30 footcandles in the photocontrolled area. In other
words, the analysis assumes that daylighting provides all necessary illumination (in this case, 30
footcandles) in the space within one window head height of the façade during 50% of the annual
occupied hours. As discussed above in Sections 5.1.8 and 5.1.6, the 50% daylight autonomy threshold
is a conservative assumption because our analysis of 61 daylit spaces shows that higher levels are
typically achieved.
Cost Effectiveness by Controlled Wattage
We determined the cost effectiveness of automatic photocontrols based on the estimate of energy
savings from the two example projects as shown above in Figure 31 and Figure 32. Savings for the
various daylight autonomy levels were determined and compared to the cost of providing
photocontrols for the two cases.
Overall cost effectiveness is illustrated below in Figure 38. The black line illustrates the cost of
photocontrols, which increases slightly with the size of the daylit area, whereas colored lines indicate
savings for various Daylight Autonomy levels. Cost effectiveness for each Daylight Autonomy level
can be determined by where the corresponding colored savings line crosses the black cost line. Using
the 50% DA basis, the minimum cost effective area was determined by finding the intersection of the
50% DA savings line (shown in orange) and the photocontrol cost line, which occurs at 215 Watts. In
other words, automatic photocontrols will be cost effective in any space with at least 215 Watts
controlled by photosensors and at least 50% daylight autonomy.
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Figure 38: Cost Effectiveness Analysis for automatic daylighting controls based on controlled
watts
Cost Effectiveness by Daylit Area
Similarly, cost effectiveness can be determined based on the existing “daylit area” standard in the
code. In this case, rather than using controlled wattage numbers from the two hypothetical scenarios
in Figure 31 and Figure 32, controlled wattage for the savings calculations was determined by
multiplying the daylit area for each space by the lighting power density (LPD). This provides a more
conservative estimate of the photocontrolled wattage, because the “daylit area” used to determine
which luminaires are controlled for daylighting is not always equal to the area served by luminaires.
For example, in the hypothetical sidelit space the daylit area of 250 square feet (determined by the
area within one window head height of the façade) multiplied by the LPD of 0.8 W/sf results in a
controlled power of 200W, whereas, as shown in Figure 31, the actual controlled wattage would be
256W (four fixtures at 64W each), which would result in higher savings than assumed in these
calculations.
Using this approach, energy cost savings line for 50% DA intersects with the initial cost line at 218
square feet, as shown below in Figure 39.
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Figure 39: Cost Effectiveness Analysis for automatic daylighting controls based on daylit area
5.2.4 Recommendations
As described in the analysis above, automatic daylight photocontrols are cost effective for any
photocontrolled lighting wattage over 215 Watts with at least 50% daylight autonomy. Based on the
Watt Calculation method, HMG recommends revising the code to require automatic daylighting
controls for any space where the daylight controlled wattage is 215 Watts or more.
If the Watt Calculation method is not incorporated into the 2013 Title 24 code, and the current “daylit
area” method is retained, HMG recommends reducing the daylit area threshold for required
automatic daylight controls from 2500 square feet to 220 square feet, since the analysis above shows
that automatic daylight photocontrols are cost effective for any daylit area of over 218 square feet
with at least 50% daylight autonomy.
.
5.3 Proposal 3: Minimum Skylight Area Requirement
This section describes the analysis used to derive a new minimum skylit area requirement for Section
143(c).
5.3.1 Rooftop Survey
As discussed in section 4.3.1, above, HMG surveyed a sample of 70 commercial and industrial
buildings in climate zone 12 for rooftop obstructions using satellite imagery from Bing maps. Using
tools available in Bing maps, the survey estimated the area of the roof, and the area of any
obstructions such as packaged HVAC units. Figure 40 and Figure 41, below, show examples of the
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survey process, illustrating the polygon tool used to estimate roof and obstruction area (in square feet)
using the polygon tool in Bing maps (polygons are shown with blue outline and green transparent
overlay).
Figure 40: Screen capture of Bing maps showing polygon tool to estimate total roof area.
Figure 41: Screen capture of Bing maps showing polygon tool to estimate rooftop obstructions.
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As summarized in Figure 42, below, of the 70 buildings surveyed, the maximum obstructed area was
11%. However, most buildings had much lower amounts of rooftop obstructions. The average was
2% roof obstruction, though 18 of the 70 buildings (26%) had no obstructions at all, and 50 of the 70
buildings (71%) had 2% or less obstructed area. These findings suggest that there is ample room for
skylights and an increase in the skylit area requirement would not create interference with other
rooftop systems in typical conditions.
Maximum Average Minimum
Percent Obstructed Area 11% 2% 0%
Figure 42: Summary of Rooftop Survey Findings
In addition to identifying rooftop obstructions, the survey recorded estimates of the skylit area for
buildings where skylights were present. Eleven of the 70 buildings surveyed had skylights. Of those
eleven, ten buildings were estimated to have more than 50% daylit area through skylights, including
five where 100% of the floor area seemed to be daylit using skylights. This finding shows that there
are situations where builders or building owners choose to voluntary include more skylighting that
required by code. Based on this evidence, an increase in the code requirement from the current
minimum skylight daylit area of 50% to a higher value should be achievable by most buildings. We
recommend that the minimum skylit area be increase to 75%, as it leaves a large margin of 25%, for
areas that may not be amenable to having skylights, for privacy, or any other reason.
Detailed results of the rooftop surveys can be found in Appendix A.
5.3.2 Analysis and Recommendation
Based on the findings discussed above, on average, only 2% of a building‟s roof area is taken up by
mechanical equipment or other obstructions. In addition, of the buildings surveyed that had existing
skylights, all but one exceeded the current minimum skylit area requirement of 50%. As a result of
these findings, HMG recommends increasing the minimum skylit are requirement from 50% to 75%.
5.4 Proposal 4: Ceiling Height Trigger for Skylight Area Requirement
5.4.1 Cost Survey Results
As described above, in section 4.4.1, HMG conducted a cost survey to determine the material and
labor costs associated with installing a skylight with a 4‟ deep light well in spaces with dropped or
finished ceilings. Based on input from a range of contractors, HMG found that costs have not
changed substantially from the previous code revision. Figure 43 outlines cost information gathered
from six contractors. Based on this data, the average cost of a 4‟ x 4‟ skylight with a light well was
determined to be $1,373, compared to $561 for the skylight without a light well. Using the difference
between the two average values, it was estimated that the average cost of a 4‟ deep light well is $812.
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Figure 43: Installation costs of skylights, with and without light wells
5.4.2 Energy Savings
In addition to cost data, HMG modeled energy savings from skylights for a three typical building
scenarios, described in Figure 44, to determine if a reduction in the ceiling height threshold was
possible. For all three scenarios, a 4‟ deep light well as assumed.
Building Type Ceiling Height Lighting Power Density (W/sf)
Retail 12‟ 1.6 W/sf
Retail 10‟ 1.6 W/sf
Office 10‟ 1.1 W/sf
Figure 44: Model building scenarios for cost effectiveness analysis
SkyCalc, a modeling program that determines impacts on lighting, cooling and heating energy use
from various skylighting strategies was used to estimate energy savings. The simplicity of the
SkyCalc tool made it possible to simulate a range of skylight to floor area ratios for multiple climate
zones throughout the state. Results of the energy savings simulations were then combined with the
cost data presented above to determine cost effectiveness, as described below.
5.4.3 Cost Effectiveness Analysis
Using the cost data and the energy savings presented above, HMG was able to determine the cost
effectiveness of skylights for the three model scenarios described in Figure 44.
Because SkyCalc produces only annual energy savings, it was necessary to use an average TDV value
to determine cost effectiveness. The average TDV value of $1.86/kWh used in the analysis represents
a conservative assumption because energy savings from skylighting tend to be highest at peak demand
times that have higher TDV values.
The cost effectiveness analysis assessed two different skylight types (single and double glazed), as
well as two different control scenarios (two levels plus off, and on/off only for 2/3 of the lamps). The
analysis also considered a range of quantity of skylights, determined by skylight to floor area ratios
(SFR) ranging from 0 to 12%. Cost effectiveness was determined for a broad range of climate zones.
4x4 Skylight
w/o light well
4x4 Skylight
w/ light well
Contact A $1,100Contact B $347 $741
Contact C $550 $1,100
Contact D $1,150 $2,550
Contact E $426
Contact F $332
Average $561 $1,373
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However, only results for climate zones 3 (San Francisco Bay Area coastal-northern California) and 7
(San Diego coastal southern California) are shown here, as illustrations.
The benefit:cost ratio (BCR) tables shown below illustrate where skylighting was found to be cost
effective for each model building type. Figure 45, below, shows the BCR for a range of scenarios for
retail buildings with 1.6 W/sf LPD, 12‟ ceilings and 4‟ lightwells. BCR of 1 or higher are considered
to be cost effective, and are highlighted below in grey. As shown, only a handful of conditions for
this scenario are cost effective.
Figure 45: BCR for skylighting in retail buildings with 1.6 W/sf LPD, 12’ ceilings and 4’
lightwells
Cost effectiveness is even less likely for lower ceiling heights, as shown in Figure 46 below,
illustrating a retail building with 10‟ ceilings. In this case, none of the scenarios shown were found to
be cost effective.
two level
plus off
on/off for 2/3
of lamps
two level
plus off
on/off for 2/3
of lamps
CZ 3 0% 0.00 0.00 0.00 0.00
1% 0.23 0.49 0.18 0.45
2% 0.70 0.87 0.64 0.82
3% 0.84 0.95 0.82 0.93
4% 0.86 0.91 0.87 0.93
5% 0.80 0.84 0.84 0.89
6% 0.74 0.76 0.80 0.83
8% 0.59 0.60 0.70 0.71
10% 0.46 0.45 0.60 0.60
12% 0.34 0.33 0.51 0.50
CZ 7 0% 0.00 0.00 0.00 0.00
1% 0.29 0.60 0.23 0.53
2% 0.88 1.05 0.76 0.95
3% 1.06 1.13 0.97 1.05
4% 1.04 1.08 0.97 1.02
5% 0.98 1.00 0.94 0.96
6% 0.90 0.90 0.86 0.88
8% 0.73 0.73 0.72 0.72
10% 0.58 0.57 0.59 0.58
12% 0.45 0.44 0.47 0.46
Climate
Zone SFR
Single Glazed Acrylic Double Glazed Acrylic
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Figure 46: BCR for skylighting in retail buildings with 1.6 W/sf LPD, 10’ ceilings and 4’
lightwells
Similarly, as shown below in Figure 47, traditional skylight products are even less cost effective for
spaces with lower LPDs such as offices.
two level
plus off
on/off for 2/3
of lamps
two level
plus off
on/off for 2/3
of lamps
CZ 3 0% 0.00 0.00 0.00 0.00
1% 0.19 0.39 0.15 0.35
2% 0.58 0.70 0.53 0.66
3% 0.69 0.77 0.68 0.76
4% 0.72 0.75 0.73 0.77
5% 0.68 0.70 0.72 0.75
6% 0.63 0.64 0.68 0.70
8% 0.52 0.52 0.61 0.62
10% 0.40 0.40 0.53 0.53
12% 0.30 0.29 0.45 0.45
CZ 7 0% 0.00 0.00 0.00 0.00
1% 0.24 0.47 0.18 0.41
2% 0.71 0.84 0.62 0.76
3% 0.87 0.92 0.81 0.86
4% 0.87 0.89 0.81 0.85
5% 0.83 0.83 0.79 0.80
6% 0.76 0.77 0.74 0.75
8% 0.64 0.63 0.63 0.62
10% 0.51 0.50 0.52 0.51
12% 0.40 0.39 0.42 0.41
Climate
Zone SFR
Single Glazed Acrylic Double Glazed Acrylic
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Figure 47: BCR for skylighting in office buildings with 1.1 W/sf LPD, 10’ ceilings and 4’
lightwells
Results shown in the above tables are similar to cost effectiveness conditions for other climate zones.
Based on these findings, traditional skylights with finished light wells are not considered cost
effective at this time.
5.4.4 Tubular Daylighting Devices (TDDs)
HMG also collected and analyzed cost data from two manufacturers of tubular daylighting devices
(TDDs) and hybrid TDD products that have integrated pre-assembled specular light wells. Because
of their highly specular light wells, and the used of diffusing lenses to distribute daylight more evenly
throughout the space, these TDD products are expected to be more effective at delivering daylight
than traditional skylight products with finished drywall light wells.
However, there is currently no independent methodology for determining annual daylighting potential
and energy savings for these products (manufacturers use proprietary product-specific simulation
methods to estimate daylight potential and energy savings). Without an accepted simulation
methodology that can accommodate a range of such products, we found that it was not possible to
account for the higher performance potential of TDDs. We looked at the cost effectiveness of these
products, by using the same energy savings as described above for „traditional‟ skylight with light
two level
plus off
on/off for 2/3
of lamps
two level
plus off
on/off for 2/3
of lamps
CZ 3 0% 0.00 0.00 0.00 0.00
1% 0.14 0.25 0.12 0.24
2% 0.32 0.37 0.32 0.38
3% 0.34 0.36 0.37 0.40
4% 0.31 0.32 0.36 0.38
5% 0.26 0.27 0.34 0.35
6% 0.21 0.21 0.31 0.31
8% 0.11 0.11 0.24 0.24
10% 0.02 0.02 0.18 0.18
12% (0.06) (0.06) 0.12 0.12
CZ 7 0% 0.00 0.00 0.00 0.00
1% 0.22 0.33 0.16 0.29
2% 0.42 0.46 0.39 0.44
3% 0.43 0.45 0.41 0.43
4% 0.40 0.40 0.38 0.39
5% 0.34 0.34 0.34 0.34
6% 0.29 0.29 0.29 0.29
8% 0.18 0.18 0.20 0.20
10% 0.09 0.09 0.12 0.11
12% 0.01 0.01 0.05 0.04
Climate
Zone SFR
Single Glazed Acrylic Double Glazed Acrylic
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well products, and the cost collected from the TDD and hybrid TDD manufacturers, and found that
without correctly accounting for the additional energy savings we did not achieve B/C ratios greater
than 1 for most climate zones.
Finally, it was determined that there is a need to develop a daylighting energy simulation method that
counts for the enhanced daylighting performance for the TTDs and hybrid TDDs. Without these, it
was not possible to determine their cost effectiveness appropriately.
5.4.5 Recommendations
Based on updated cost data, energy savings and TDV values, reducing the ceiling height threshold
was not found to be cost effective at this time, and is therefore not recommended.
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6. Recommended Language for the Standards Document,
ACM Manuals, and the Reference Appendices
Provide complete language change recommendations for the Standards, ACM Manuals, and
Reference Appendices. This section should have specific recommended language and contain enough
detail to develop the draft standard in the next phase of work. Use the language from the relevant
2008 document(s), and use underlining to indicate new language and strikethroughs to show deleted
language.
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7. Bibliography and Other Research
List and describe each of the research studies, reports, and personal communications that provide
background for this research. Identify all resources that have been pursued to further this measure.
Identify all “experts” that were involved in further developing the change, all research and analysis
reports and documents that were reviewed, and all industry standards that were consulted (e.g.,
ASTM, UL, ASHRAE test procedures, etc.). Include research that is underway that addresses the
measure/change. Indicate if data or information will be produced in time to be used in this update of
the Standards.
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8. Appendices A
Detailed results for each of the properties surveyed in the rooftop survey are presented below in
Figure 48, Figure 49 and Figure 50.
Figure 48: Detailed Rooftop Survey Results (part 1 of 3)
Survey #
Roof Area
(sf) Duct Area (sf)
Other
Obstruction
Area (sf)
Total
Obstruction
Area (sf) % Obstructed
Approximate
Skylit Area
1 78475 0 6225 6225 8% NA
2 7904 0 0 0 0% NA
3 46609 0 942 942 2% NA
4 17000 0 163 163 1% NA
5 5379 335 0 335 6% NA
6 26420 0 1360 1360 5% NA
7 29249 0 857 857 3% 60%
8 5932 0 503 503 8% NA
9 3893 0 380 380 10% NA
10 7588 0 0 0 0% NA
11 9054 0 0 0 0% NA
12 12459 0 700 700 6% NA
13 5475 0 119 119 2% NA
14 7463 0 400 400 5% NA
15 1591 0 48 48 3% NA
16 9774 0 0 0 0% NA
17 17887 0 140 140 1% NA
18 2053 0 34 34 2% NA
19 2150 0 30 30 1% NA
20 20274 120 80 200 1% NA
21 5040 0 50 50 1% NA
22 24014 0 337 337 1% NA
23 6422 0 50 50 1% NA
24 10198 0 24 24 0% NA
25 4600 0 50 50 1% NA
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Figure 49: Detailed Rooftop Survey Results (part 2 of 3)
Survey #
Roof Area
(sf) Duct Area (sf)
Other
Obstruction
Area (sf)
Total
Obstruction
Area (sf) % Obstructed
Approximate
Skylit Area
26 22403 0 65 65 0% NA
27 6099 0 86 86 1% NA
28 20630 0 48 48 0% NA
29 6024 0 0 0 0% NA
30 6705 0 100 100 1% NA
31 50267 0 250 250 0% NA
32 145125 0 0 0 0% NA
33 46087 0 520 520 1% NA
34 3352 0 100 100 3% NA
35 3960 0 0 0 0% NA
36 2353 0 40 40 2% NA
37 7441 0 490 490 7% NA
38 23935 0 1343 1343 6% NA
39 110089 100 1200 1300 1% NA
40 5818 0 160 160 3% NA
41 50052 0 220 220 0% NA
42 18727 0 365 365 2% NA
43 11073 0 600 600 5% NA
44 25238 0 525 525 2% NA
45 108178 0 2140 2140 2% 100%
46 5109 0 45 45 1% NA
47 6999 751 0 751 11% NA
48 39919 0 625 625 2% NA
49 31705 0 1279 1279 4% NA
50 38193 236 1518 1754 5% NA
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Figure 50: Detailed Rooftop Survey Results (part 3 of 3)
Survey #
Roof Area
(sf) Duct Area (sf)
Other
Obstruction
Area (sf)
Total
Obstruction
Area (sf) % Obstructed
Approximate
Skylit Area
51 17151 0 0 0 0% 100%
52 67176 0 0 0 0% NA
53 12419 0 216 216 2% NA
54 51472 0 340 340 1% 60%
55 49733 0 467 467 1% NA
56 24615 0 0 0 0% NA
57 20922 0 390 390 2% NA
58 26630 0 0 0 0% NA
59 20600 0 0 0 0% 40%
60 11734 0 40 40 0% 100%
61 14940 0 780 780 5% NA
62 40015 0 2080 2080 5% 100%
63 16628 0 100 100 1% NA
64 145421 0 2700 2700 2% NA
65 154807 0 1080 1080 1% 100%
66 12477 0 80 80 1% NA
67 20777 0 132 132 1% 80%
68 72392 0 520 520 1% 60%
69 68533 0 1300 1300 2% 60%
70 125181 0 3419 3419 3% NA