Any approved computer program may be used to comply with the Energy Standards using the performance method. The following steps are an outline of the typical computer program procedure:
1. Collect all necessary data on each component.
a. For the building envelope, the area of each fenestration, wall, door, roof, ceiling and floor is needed. For each component, the applicable energy characteristics needs to be defined including U-factor, solar heat gain coefficients (SHGC), solar reflectance, and thermal mass values.
b. For HVAC systems, the type and efficiency of space conditioning equipment are required. For hydronic space heating, the specific water heater type and efficiency are required. For fan-forced conditioning systems, the location and amount of insulation of the duct system are needed.
c. For domestic hot water systems, the water heater type, quantity, efficiency, and area served will be required, along with the water-heating distribution system. Additional information will be required for features such as solar thermal systems and drain water heat recovery devices. More information is in Chapter 5.
d. For PV systems, the proposed size, and installation location information such as roof slope and orientation of the PV system are needed. Battery storage capacity and control information must be described if battery storage is proposed. Refer to Chapter 7 for more information.
Other efficiency measures and options can be used to improve building efficiency.
2. Enter the building envelope basic data such as square footage, number of stories, occupancy type, and climate zone. Define each opaque surface with the related orientation, area, and thermal performance properties. Add the fenestration associated with each opaque surface, including any fixed shading such as overhangs and side fins. Enter the data of the equipment and distribution systems for the space conditioning and water-heating systems. The input values and assumptions must correspond to the information on the final approved plan set and inputs must be equal to or more energy efficient than required mandatory measures.
3. Launch a computer simulation to calculate the efficiency EDR and total EDR of the standard design and the proposed design.
For additions and alterations, compliance is based on the TDV energy, and not the EDR criteria for newly constructed buildings. In existing buildings, where the values of installed features are unknown, default values may be used based on the year of the construction. Refer to Table 8-1, Default Assumption for Year Built, at the end of this chapter.
The building energy efficiency complies if all mandatory measures are met and the total TDV energy use of the proposed design is the same as or less than the standard design TDV energy budget.
When creating a computer input file, use the space provided for the project title information to concisely describe the building being modeled. User-designated names should be clear and internally consistent with other orientations and/or buildings being analyzed. Title names and explanatory comments should assist in the compliance and enforcement processes.
Approved compliance software programs automatically calculate the standard efficiency based on data entered for the proposed building.
The computer program defines the standard building by modifying the geometry of the proposed building and inserting the features of Table 150.1-A (single family) or Table 150.1-B (multifamily) of the Energy Standards. Details are in the 2019 Residential ACM Reference Manual.
Note the details of how the standard efficiency is determined. Deviations from the prescriptive requirements will be reflected in the compliance margin. For example, if the prescriptive requirements from Table 150.1-A or B include roof deck insulation in Option B for the applicable climate zone, and the proposed building is modeled without roof deck insulation, it will significantly affect the attic temperature and result in a compliance penalty. (In prescriptive compliance, a roof with no roof deck insulation would require ducts inside the conditioned space.) In 2019, the standard efficiency includes QII and solar generated electricity. Compliance will be much more difficult to achieve if either of these is not included in the proposed efficiency.
The standard design assumes the same total conditioned floor area and volume as the proposed design and the same gross exterior wall area as the proposed design except that the wall area in each of the four cardinal orientations is divided equally. The standard design uses the same roof/ceiling area, raised floor area, slab-on-grade area, and perimeter as the proposed design but uses the standard insulation R-values required in Table 150.1-A or B of the Energy Standards.
The standard design includes all features of the prescriptive compliance tables, including QII, walls with the prescriptive U-factor, roofs with below deck insulation in many climate zones or radiant barrier in other climate zones, and a solar PV system.
Total fenestration area in the standard is equal to the proposed if the fenestration area in the proposed design is less than or equal to 20 percent of the floor area, Otherwise, the fenestration area is equal to 20 percent of the floor area. Fenestration area in the standard is evenly distributed among the four cardinal orientations. SHGC and U-factors are the same as those listed in the prescriptive tables with no overhangs.
The standard design includes minimum efficiency heating and cooling equipment, as well as the minimum duct R-value required for Option B from Table 150.1-A or 150.1-B of the Energy Standards. Ducts are assumed to be sealed as required by §150.0(m). The standard design also assumes correct refrigerant charge as required by §150.1(c)7A.
For water-heating systems that serve dwelling units, the standard design is an instantaneous gas storage water heater with an energy factor equal to the federal minimum standard. The distribution system meets all mandatory requirements specified in §150.0.
For multifamily buildings, when central water heating is proposed, the standard design is based on §150.1(c)8B, which includes details about the recirculation system and a minimum solar fraction that varies by climate zone. See the ACM Reference Manual for more information.
8.3.2.1 Standard Reports
For consistency and ease of enforcement, the manner in which building features are reported by compliance software programs is standardized. Energy Commission-approved compliance software programs produces compliance reports in a standard format. The principal report is the certificate of compliance (CF1R-PRF-01-E).
The CF1R-PRF-01 includes two sections, one for special features and modeling assumptions, and a second requires field verification and/or diagnostic testing by approved HERS Raters. These sections provide a general overview during compliance verification by the local enforcement agency and the HERS Rater. Items in the special features and modeling assumptions section indicate that if such features or assumptions used for compliance are not installed, the building would be noncompliant, and they call for special care by the local enforcement agency. Items in the HERS required verification section rely on diagnostic testing and independent verification by an approved HERS Rater to ensure proper field installation. Diagnostic testing and verification by HERS Raters is in addition to local enforcement agency inspections.
Some modeling techniques and compliance assumptions applied to the proposed design are fixed or restricted. At other times, professional judgment may be acceptable or necessary.
Enforcement agencies can reject a particular input if the permit applicant cannot substantiate the value with supporting documentation or cannot demonstrate that appropriate professional judgment was applied.
Two questions can resolve whether professional judgment was applied correctly:
•Is a simplified input or assumption appropriate and conservative? If simplification increases the predicted energy use of the proposed building or reduces the compliance margin when compared to a more explicit and detailed modeling assumption, the simplification is acceptable. Simplification must reflect a worse case than a more detailed model and result in the same or lower compliance margin.
•Is the approach or assumption consistent with what is used by the compliance software to generate the standard design?
Any unusual modeling approach, assumption, or input value should be documented with published data and conform to standard engineering practice.
Call the Energy Hotline or contact the compliance software vendor for help in evaluating the appropriateness of input assumptions.
Example 8-1
Question
Three different-sized windows in the same wall of a new home are designed without exterior shading. They have the same National Fenestration Rating Council (NFRC) rated U-factors and SHGC values. Is it acceptable professional judgment to simplify the computer model by adding the areas of the windows and inputting them as a single fenestration area?
Answer
No.
Although the compliance software will produce the same results whether the
windows are modeled individually or together as one area, plan checking or
finding errors when windows are combined is much more difficult. If the software
has a multiplier, identical window sizes with identical shading features can be combined.
Otherwise each window is modeled individually.