MMeeaassuurree IInnffoorrmmaattiioonn …h-m-g.com/T24/Daylight/DaylightingCASE01_MSv10.pdfFigure 1:...

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M M e e a a s s u u r r e e I I n n f f o o r r m m a a t t i i o o n n T T e e m m p p l l a a t t e e D D a a y y l l i i g g h h t t i i n n g g 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

Transcript of MMeeaassuurree IInnffoorrmmaattiioonn …h-m-g.com/T24/Daylight/DaylightingCASE01_MSv10.pdfFigure 1:...

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.

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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

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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”

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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