This chapter describes how the Energy Design Rating (EDR) is calculated, how the proposed design is modeled, and how the standard design is established.
The EDR is a score from zero to 100, where zero represents a building that has zero-net-energy consumption based on the time-dependent valuation (TDV) energy consumption, and 100 represents a building that is minimally compliant with the 2006 International Energy Conservation Code. The EDR score is a ratio of proposed design TDV budget to reference design TDV budget adjusted as described in Section 3.1. The EDR has three components:
1. Efficiency EDR
2. EDR of PV and demand flexibility
3. Total EDR is calculated by subtracting the PV/flexibility EDR from the efficiency EDR.
For a building to comply:
1. The EDR score of proposed efficiency must be equal or less than the EDR score of the standard efficiency.
2. Total proposed EDR score must be equal or less than the total standard design EDR score.
The building configuration is defined by the user through entries that include floor areas, wall areas, roof and ceiling areas, fenestration (which includes skylights), and door areas. The performance characteristics such as U-factors, R-values, solar heat gain coefficient (SHGC), solar reflectance. Information about the orientation and tilt is required for roofs, fenestration, and other elements. Details about any solar generation systems and battery storage is also defined. The user entries for all these building elements are consistent with the actual building design and configuration. If the compliance software models the specific geometry of the building by using a coordinate system or graphic entry technique, the data generated are consistent with the actual building design and configuration.
For low-rise homes, the standard design building, from which the energy budget is established, is in the same location and has the same floor area, volume, and configuration as the proposed design, except that the wall and window areas are distributed equally among the four main compass points (north, east, south, and west). For additions and alterations, the standard design shall have the same wall and fenestration areas and orientations as the proposed building. The details are described below.
The energy budget for the residential standard design is the energy that would be used by a building similar to the proposed design if the proposed building met the requirements of the prescriptive standards. The compliance software generates the standard design automatically, based on fixed and restricted inputs and assumptions. Custom energy budget generation shall not be accessible to program users for modification when the program is used for compliance or when the program generates compliance forms.
The basis of the standard design is prescriptive requirements from Section 150.1(c) of the standards, Table 150.1-A or 150.1-B. Prescriptive requirements vary by climate zone. Reference Joint Appendix JA2, Table 2-1, contains the 16 California climate zones and representative cities. The climate zone is based on the zip code, as documented in JA2.1.1.
The following sections present the details of how the proposed design and standard design are determined. For many modeling assumptions, the standard design is the same as the proposed design. When a building has special features, for which the Energy Commission has established alternate modeling assumptions, the standard design features will differ from the proposed design so the building receives appropriate credit for its efficiency. When measures require verification by a Home Energy Rating System (HERS) rater or are designated as a special feature, the specific requirement is listed on the CF1R.
The reference design is calculated using the same inputs, assumptions and algorithms as the standard design except for the following requirements:
a. Air handler power. The air handler power is 0.8 W/CFM.
b. Air infiltration rate. The air infiltration rate is 7.2 ACH50.
c. Cooling airflow. The air handler airflow is 300 CFM/ton.
d. Duct R-value. The duct R-value is R-8.
e. Duct leakage rate. The duct leakage rate is modeled as an HVAC distribution efficiency of 80 percent.
f. Quality insulation installation (QII). QII is modeled as “Yes.”
g. Wall construction. Climate Zones 2-15 have 2x4 R-13 walls. Climate Zones 1 and 16 have 2x6 R-19 walls.
h. Roof/ceiling construction. Climate Zones 2-15 have R-30 ceiling. Climate Zones 1 and 16 have R-38 ceiling. No climate zones include radiant barriers or cool roofs.
i. Raised floor construction. Climate Zones 2-15 have 2x10 R-19 floors. Climate Zones 1 and 16 have 2x10 R-30 floors.
j. Slab edge insulation. Climate Zones 1 and 16 include R-10 insulation 24 inches deep.
k. Window U-factors. Climate Zones 2-15 have 0.65 U-factor. Climate Zones 1 and 16 have 0.35 U-factor.
l. Window SHGC. All windows have 0.4 SHGC.
m. Window area. When the window area is below 18 percent of the floor area, the reference design has the same area as the proposed design. Above 18 percent, the reference design has 18 percent.
n. HVAC equipment efficiencies. HVAC equipment meets National Appliance Energy Conservation Act (NAECA) requirements in effect in 2006 such as 78 percent AFUE for gas central furnace, and 13 SEER for central air-conditioning.
o. Water heating efficiency. Water heating modeled as a 40-gallon storage water with a 0.594 energy factor (EF) if gas or a 0.9172 EF if electric.
p. Appliance and plug load energy use and internal gains. Energy use and internal gains for appliance and miscellaneous plug loads are modeled as specified the ANSI/RESNET/ICC 301-2014 Standard.
The PV requirements are applicable to newly constructed low-rise residential buildings. PV system details are from PVWatts, which is a web application developed by the National Renewable Energy Laboratory (see Appendix F).
The standard design PV system (based on CFI assumptions) is sized to generate just enough electricity to offset the annual kWh consumption for a mixed fuel building that meets all the 2019 prescriptive requirements.
This standard design PV system is shown on the energy use details screen where the standard design site (kilowatt-hours [kWh]) total is zero after the PV is subtracted (Figure 1).
For PV sizing calculations, the software assumes the California flexible installation (CFI) orientation, standard efficiency for modules and inverters, fixed tracking, standard shading, and roof tilt of 22.61 degrees (5:12 pitch).
The proposed PV system is sized to generate the amount of electricity to offset the annual kWh load of the proposed design.
For PV sizing calculations, the software uses user-defined values for:
1. Array orientation, including CFI or actual orientation.
2. Module type, including standard (for example, poly- or monocrystalline silicon modules), premium (e.g., high-efficiency monocrystalline silicon modules with antireflective coatings), or thin film (in other words, low efficiency such as 11 percent).
3. Inverter efficiency.
4. Array tilt in degrees or roof pitch.
5. Array tracking type including fixed, one-axis tracking, and two-axis tracking.
6. Actual shading of the modules.
The PV size is reported in kWdc.
2.1.5.1 Exceptions to the PV Requirements
1. No PV is required if the effective annual solar access is restricted to less than 80 contiguous square feet by shading from existing permanent natural or manmade barriers external to the dwelling, including but not limited to trees, hills, and adjacent structures.
2. In Climate Zone 15, the PV size shall be the smaller of a size that can be accommodated by the effective annual solar access roof areas, or a PV size required by Equation 1 but no less than 1.5 watt DC per square foot of conditioned floor area.
Figure 1: Energy Use Details
3. In all climate zones, for dwelling units with two habitable stories, the PV size shall be the smaller of a size that can be accommodated by the effective annual solar access roof areas, or a PV size required by Equation 1 but no less than 1.0 watt DC per square foot of conditioned floor area
4. In all climate zones, for low-rise residential buildings with three habitable stories and single-family homes with three or more habitable stories, the PV size shall be the smaller of a size that can be accommodated by the effective annual solar access roof areas, or a PV size required by Equation 1 but no less than 0.8 watt DC per square foot of conditioned floor area
5. For a dwelling unit plan that is approved by the planning department before January 1, 2020, with available solar ready zone between 80 and 200 square feet, the PV size is limited to the lesser of the size that can be accommodated by the minimum solar zone area specified in Section 110.10(b) or a size that is required by the Equation 1.
When the solar electric generation system meets one of the prescriptive exceptions, the standard design is modeled with an appropriately sized PV system.
2.1.5.2 Specifying Target Energy Design Rating
The software provides the option of specifying a PV size based on a user specified target EDR. When this option is selected, the software calculates the required PV size based on the following parameters:
a. The user defined target EDR
b. The size of the battery storage system and the battery control strategy
c. The proposed annual kWh budget of the building
2.1.5.3 Battery Storage
Detailed calculations for PV and battery storage are included in Appendices C and D.
The software provides credit for a battery storage system coupled with a PV array. If specified, the battery storage size must be 5 kWh or larger. For Part 6 compliance, PV has no impact on energy efficiency requirements or the efficiency EDR unless a battery storage system is included and the self-utilization credit is modeled.
Including a battery storage system allows downsizing the PV system to reach a specific EDR target.
Software includes a checkbox option to allow excess PV generation credit for above-code programs. This option, combined with a battery storage system, allows any PV size with full EDR credit.
2.1.5.4 Battery Controls
The three control options available are:
1. Basic (Default Control). A simple control strategy that provides a modest credit. The software assumes that the batteries are charged anytime PV generation (generation) is greater than the house load (load); conversely, the batteries are discharged when load exceeds generation. This control strategy does not allow the batteries to discharge into the grid.
2. Time of Use. To qualify for the TOU control, the battery storage system shall be installed in the default operation mode to allow charging from an on-site photovoltaic system. The battery storage system shall begin discharging during the highest priced TOU hours of the day, which varies by time of the year and the local utility. At a minimum, the system shall be capable of programming three seasonal TOU schedules, such as spring, summer, and winter.
3. Advanced DR Control. To qualify for the advanced demand response control, the battery storage system shall be programmed by default as basic control or TOU control, as described above. The battery storage control shall meet the demand responsive control requirements specified in Section 110.12(a). The battery storage system shall have the capability to change the charging and discharging periods in response to signals from the local utility or a third-party aggregator. Upon receiving a demand response signal from a grid operator, this option allows discharging directly into the grid.
Battery system storage details are reported as special features on the CF1R.
2.1.5.5 Self-Utilization Credit
The 2019 Standards do not allow a tradeoff between the efficiency EDR and the effect of PV on the total EDR unless battery storage is provided. When the PV system is coupled with at least a 5 kWh battery storage system, the software allows a portion of the PV plus storage EDR to be traded against the efficiency EDR. A modest self-utilization credit can be used for tradeoffs against building envelope and efficiencies of the equipment installed in the building. A checkbox in provided in the software to enable this credit.
The magnitude of the credit is equal to the 90 percent of the difference between the 2019 and 2016 Standards envelope improvements, including:
1. Below-deck batt roof insulation value of R-19 for the 2019 Standards and R-13 for the 2016 Standard.
2. Wall U-factor of 0.48 for the 2019 Standards, and U-factor of 0.51 for the 2016 Standards.
3. Window U-factor of 0.30 for the 2019 Standards, and window U-factor of 0.32 for the 2016 Standards.
4. In cooling climate zones, window SHGC of 0.23 for the 2019 Standards, and 0.25 for the 2019 Standards.
5. New QII requirement in the 2019 standards, and no QII requirements in the 2016 Standards.
Table 1 shows the self-utilization credits by building type and climate zone.
|
Climate Zone |
Single-Family |
Multifamily |
|
01 |
13% |
10% |
|
02 |
11% |
7% |
|
03 |
11% |
6% |
|
04 |
11% |
8% |
|
05 |
13% |
5% |
|
06 |
8% |
3% |
|
07 |
6% |
2% |
|
08 |
16% |
6% |
|
09 |
13% |
7% |
|
10 |
13% |
6% |
|
11 |
13% |
8% |
|
12 |
14% |
9% |
|
13 |
12% |
8% |
|
14 |
12% |
8% |
|
15 |
11% |
6% |
|
16 |
12% |
8% |
Source: California Energy Commission
2.1.5.6 CO2 Emissions
For every hour of the year, the software tracks all house loads including HVAC, water heating, indoor air quality (IAQ), plug loads, appliances, inside and exterior lighting, and PV generation. Based on these hourly calculations, the software calculates PV-generated kWh that serve the house loads (which reduces the kWh purchased from the grid) and the hourly exports back to the grid. Next, the software applies emission rates that represent the CO2 generation characteristics of the grid to the hourly kWh balances to calculate the CO2 generation impact for each hour of the year. Finally, the software adds all the hourly results to yield the annual CO2 emissions in metric tons per year.
The software reports CO2 generation for:
1. Total CO2 generation, and
2. CO2 generation excluding exports to the grid (self-use only).
2.1.5.7 Community Solar
A community-shared solar electric generation system, or other renewable electric generation system, and community shared battery storage system, which provides dedicated power, utility energy reduction credits, or payments for energy bill reductions or a combination thereof to the permitted building may offset part or all of the solar electric generation system EDR required to comply with the standards. The Energy Commission must approve the community solar system before it can be used for compliance (see Title 24, Part 1, Section 10-115).
The software has a pulldown menu of all Energy Commission approved community shared solar programs, and allows user to select a full or partial offset of the site PV requirements.