2.5 Conditioned Zones

The software requires the user to enter the characteristics of one or more conditioned zones. Subdividing single-family dwelling units into conditioned zones for input convenience or increased accuracy is optional.

2.5.1 Zone Type

The zone is defined as conditioned, living, or sleeping. Other zone types include garage, attic, and crawl space.

When the zone type is living or sleeping, this is reported as a special feature on the CF1R.

With the heating zonal control credit, the sleeping and living areas are modeled separately for heating, each with its own separate thermostat schedule and internal gain assumptions. Zonal control cannot be modeled with heat pump heating. The total nonclosable opening area between zones cannot exceed 40 ft². Other eligibility criteria for this measure are presented in the Residential Compliance Manual, Chapter 4.

The user selects zonal control as a building level input with separate living and sleeping zones.

2.5.2 Conditioned Floor Area

The total conditioned floor area (CFA) is the raised floor as well as the slab-on-grade floor area of the conditioned spaces measured from the exterior surface of exterior walls. Stairs are included in conditioned floor area as the area beneath the stairs and the tread of the stairs.

The compliance software requires the user to enter the total conditioned floor area of each conditioned zone.

The standard design building has the same conditioned floor area and same conditioned zones as the proposed design.

2.5.3 Number of Stories

The average ceiling height of the proposed design is the conditioned volume of the building envelope. The volume (in cubic feet) is determined from the total conditioned floor area and the average ceiling height.

Free ventilation area is the window area adjusted to account for bug screens, window framing and dividers, and other factors.

Free ventilation area for the proposed design is calculated as 5 percent of the fenestration area (rough opening), assuming all windows are operable.

The standard design value for free ventilation area is the same as the proposed design.

The default assumption for the proposed design is 2 feet for one-story buildings or one-story dwelling units and 8 feet for two or more stories (as derived from number of stories and other zone details).

The standard design modeling assumption for the elevation difference between the inlet and the outlet is 2 feet for one-story dwelling units and 8 feet for two or more stories.

The elevation of the top and bottom of each zone is required to set up the airflow network.

The user enters the height of the top surface the lowest floor of the zone relative to the ground outside as the “bottom” of the zone. The user also enters the ceiling height (the floor-to-floor height [ceiling height plus the thickness of the intermediate floor structure] is calculated by the software).

Underground zones are indicated with the number of feet below grade (for example, -8).

The standard design has the same vertical zone dimensions as the proposed design.

The software requires the user to specify a previously defined HVAC system to provide heating and cooling for the zone and an indoor air quality (IAQ) ventilation system. The user may also specify a ventilation cooling system that applies to this and other conditioned zones.

The software assigns standard design HVAC, IAQ ventilation, and ventilation cooling systems based on Section 150.1(c) and Table 150.1-A or 150.1-B for the applicable climate zone.

Natural ventilation (from windows) is available during cooling mode when needed and available, as shown in Table 22. The amount of natural ventilation used by computer software for natural cooling is the lesser of the maximum potential amount available and the amount needed to drive the interior zone temperature down to the natural cooling setpoint. When natural cooling is not needed or is unavailable, no natural ventilation is used.

Computer software shall assume that natural cooling is needed when the building is in “cooling mode,” when the outside temperature is below the estimated zone temperature, and when the estimated zone temperature is above the natural cooling setpoint temperature. Only the amount of ventilation required to reduce the zone temperature to the natural ventilation setpoint temperature is used, and the natural ventilation setpoint temperature is constrained by the compliance software to be greater than the heating setpoint temperature.

2.5.4 Conditioned Zone Assumptions

Internal mass objects are completely inside a zone so that they do not participate directly in heat flows to other zones or outside. They are connected to the zone radiantly and convectively and participate in the zone energy balance by passively storing and releasing heat as conditions change.

Table 23 shows the standard interior conditioned zone thermal mass objects and the calculation of the simulation inputs that represent them.

Table 22: Hourly Thermostat Setpoints

Hour	Cooling	Venting	Heat Pump Heating	Standard Gas Heating	Zonal Control Gas Heating
Hour	Cooling	Venting	Heat Pump Heating	Single-Zone	Living	Sleeping
1	78	Off	68	65	65	65
2	78	Off	68	65	65	65
3	78	Off	68	65	65	65
4	78	Off	68	65	65	65
5	78	Off	68	65	65	65
6	78	68*	68	65	65	65
7	78	68	68	65	65	65
8	83	68	68	68	68	68
9	83	68	68	68	68	68
10	83	68	68	68	68	65
11	83	68	68	68	68	65
12	83	68	68	68	68	65
13	83	68	68	68	68	65
14	82	68	68	68	68	65
15	81	68	68	68	68	65
16	80	68	68	68	68	65
17	79	68	68	68	68	68
18	78	68	68	68	68	68
19	78	68	68	68	68	68
20	78	68	68	68	68	68
21	78	68	68	68	68	68
22	78	68	68	68	68	68
23	78	68	68	68	68	68
24	78	Off	68	65	65	65

The proposed design has standard conditioned zone thermal mass objects (such as gysum board in walls, cabinets, sinks, and tubs) that are not user-editable and are not a compliance variable. If the proposed design includes specific interior thermal mass elements that are significantly different from what is included in typical wood-frame production housing, such as masonry partition walls, the user may include them. See also 2.5.6.4.

Table 23: Conditioned Zone Thermal Mass Objects

Item	Description	Simulation Object
Interior walls	The area of one side of the walls completely inside the conditioned zone is calculated as the conditioned floor area of the zone minus ½ of the area of interior walls adjacent to other conditioned zones. The interior wall is modeled as a construction with 25 percent 2x4 wood framing and sheetrock on both sides.	Wall exposed to the zone on both sides
Interior floors	The area of floors completely inside the conditioned zone is calculated as the difference between the CFA of the zone and the sum of the areas of zone exterior floors and interior floors over other zones. Interior floors are modeled as a surface inside the zone with a construction of carpet, wood decking, 2x12 framing at 16 in. on-center with miscellaneous bridging, electrical, and plumbing, and a sheetrock ceiling below.	Floor/ceiling surface exposed to the zone on both sides
Furniture and heavy contents	Contents of the conditioned zone with significant heat storage capacity and delayed thermal response, for example heavy furniture, bottled drinks, canned goods, contents of dressers, enclosed cabinets. These are represented by a 2 in. thick slab of wood twice as large as the conditioned floor area, exposed to the room on both sides.	Horizontal wood slab exposed to the zone on both sides
Light and thin contents	Contents of the conditioned zone that have a large surface area compared to weight, for example, clothing on hangers, curtains, pots and pans. These are assumed to be 2 BTU per square foot of conditioned floor area.	Air heat capacity (C_air) = CFA * 2

Thermostat settings are shown in Table 22. The values for cooling, venting, and standard heating apply to the standard design run and are the default for the proposed design run. See the explanation later in this section regarding the values for zonal control.

Systems with no setback required by Section 110.2(c) (gravity gas wall heaters, gravity floor heaters, gravity room heaters, noncentral electric heaters, fireplaces or decorative gas appliances, wood stoves, room air-conditioners, and room air-conditioner heat pumps) are assumed to have a constant heating set point of 68 degrees. The cooling set point from Table 22 is assumed in both the proposed design and standard design.

The proposed design assumes a mandatory setback thermostat meeting the requirements of Section 110.2(c). Systems exempt from the requirement for a setback thermostat are assumed to have no setback capabilities.

The standard design has setback thermostat conditions based on the mandatory requirement for a setback thermostat. For equipment exempt from the setback thermostat requirement, the standard design has no setback thermostat capabilities.

When the building is in the heating mode, the heating setpoints for each hour are set to the “heating” values in Table 22, the cooling setpoint is a constant 78°F, and the ventilation setpoint is set to a constant 77°F. When the building is in the cooling mode, the heating setpoint is a constant 60°F, and the cooling and venting setpoints are set to the values in Table 22.

The mode depends upon the outdoor temperature averaged over hours 1 through 24 of eight days prior to the current day through two days prior to the current day. (For example, if the current day is June 21, the mode is based on the average temperature for June 13 through 20.) When this running average temperature is equal to or less than 60°F, the building is in a heating mode. When the running average is greater than 60°F, the building is in a cooling mode.

2.5.5 Internal Gains

Internal gains assumptions are included in Appendix E and consistent with the CASE report on plug loads and lighting (Rubin 2019, see Appendix F).

2.5.6 Exterior Surfaces

The user enters exterior surfaces to define the envelope of the proposed design. The areas, construction assemblies, orientations, and tilts modeled are consistent with the actual building design and shall equal the overall roof/ceiling area with conditioned space on the inside and unconditioned space on the other side.

Ceilings below attics are horizontal surfaces between conditioned zones and attics. The area of the attic floor is determined by the total area of ceilings below attics defined in conditioned zones.

The software allows the user to define ceilings below attic, enter the area, and select a construction assembly for each.

The standard design for new construction has the same ceiling below attic area as the proposed design. The standard design is a high-performance attic with a ceiling constructed with 2x4 framed trusses and insulated with the R-values specified in Section 150.1(c) and Table 150.1-A or 150.1-B for the applicable climate zone, assuming Option B. The roof surface is a 10 lbs/ft² tile roof with an air space when the proposed roof is steep slope or a lightweight roof when the proposed roof is low slope.

Single-family dwelling units: Below-roof-deck insulation has R-0 in Climate Zones 1-3 and 5-7 and R-19 in Climate Zones 4 and 8-16. Insulation on the ceiling has R-38 in Climate Zones 1, 2, 4, and 8-16 and R-30 insulation in Climate Zones 3 and 5-7. Climate Zones 2, 3, and 5-7 have a radiant barrier, and Climate Zones 1, 4, and 8-16 have no radiant barrier.

Multifamily dwelling units: Below-roof-deck insulation has R-0 in Climate Zones 1-3 and 5-7, R-13 in Climate Zones 10 and 16, and R-19 in Climate Zones 4, 8, 9 and 11-15. Insulation on the ceiling has R-38 in Climate Zones 1, 2, 4, and 8-16, and R-30 insulation on the ceiling in Climate Zones 3 and 5-7. Climate Zones 2, 3, and 5-7 have a radiant barrier, and Climate Zones 1, 4, and 8-16 have no radiant barrier.

Ceiling below attic area and constructions are reported on the CF1R. Metal-framed and SIP assemblies are reported as a special feature on the CF1R.

Nonattic ceilings, also known as cathedral ceilings, are surfaces with roofing on the outside and finished ceiling on the inside but without an attic space.

The software allows the user to define cathedral ceilings, enter the area, and select a construction assembly for each. The user also enters the roof characteristics of the surface.

The standard design has the same area as the proposed design cathedral ceiling modeled as ceiling below attic with the features of Option B from Section 150.1(c) and Table 150.1-A or 150.1-B for the applicable climate zone.

The standard design building has an area of ceiling below attic equal to the nonattic ceiling/roof areas of the proposed design. The standard design roof and ceiling surfaces are modeled with the same construction assembly and characteristics, aged reflectance and emittance as Section 150.1(c), Table 150.1-A or 150.1-B for the applicable climate zone.

Non-attic ceiling/roof area and constructions are reported on the CF1R. Metal frame and SIP assemblies are reported as a special feature on the CF1R.

The software allows the user to define walls, enter the gross area, and select a construction assembly for each. The user also enters the plan orientation (front, left, back, or right) or plan azimuth (value relative to the front, which is represented as zero degrees) and tilt of the wall.

The wall areas modeled are consistent with the actual building design, and the total wall area is equal to the gross wall area with conditioned space on the inside and unconditioned space or exterior conditions on the other side. Underground mass walls are defined with inside and outside insulation and the number of feet below grade. Walls adjacent to unconditioned spaces with no solar gains (such as knee walls or garage walls) are entered as an interior wall with the zone on the other side specified as attic, garage, or another zone, and the compliance manager treats that wall as a demising wall. An attached unconditioned space is modeled as an unconditioned zone.

The standard design building has high-performance walls modeled with the same area of framed walls as is in the proposed design separating conditioned space and the exterior, with a U-factor equivalent to that as specified in Section 150.1(c)1B and Table 150.1-A or 150.1-B for the applicable climate zone.

Single-family dwellings: Above-grade framed walls in Climate Zones 1-5 and 8-16 have 2 x 6 16-in. on center wood framing with R-21 insulation between framing and R-5 continuous insulation (0.048 U-factor). Climate Zones 6-7 above-grade walls have 2 x 4 16-in. on center wood framing with R-15 insulation between framing and R-4 continuous insulation (0.065 U-factor). Walls adjacent to unconditioned space, such as garage walls, are treated the same as exterior walls, except there is no continuous insulation.

Multifamily dwellings: Above-grade framed walls in Climate Zones 1-5 and 8-16 have 2 x 6 16-in. on center wood framing with R-21 insulation between framing and R-4 continuous insulation (0.051 U-factor). Climate Zones 6-7 above-grade framed walls have 2 x 4 16-in. on center wood framing with R-15 insulation between framing and R-4 continuous insulation (0.065 U-factor). Walls adjacent to unconditioned space, such as garage walls, are treated the same as exterior walls, except there is no continuous insulation.

Standard design mass wall requirements are the same for single and multifamily buildings. Above-grade mass walls are 6-inch concrete with R-13 interior insulation in 3.5-inch wood furring in Climate Zones 1-15 and R-17 in Climate Zone 16. Below-grade mass walls in Climate Zones 1-15 have R-13, and Climate Zone 16 has R-15 interior insulation in 3.5-inch wood furring. When the proposed design is a wall type such as SIP, straw bale, or other construction type not specifically mentioned above, the standard design wall is a wood-framed wall meeting the requirements of Section 150.1(c) Table 150.1-A or 150.1-B.

The total gross exterior wall area in the standard design is equal to the total gross exterior wall area of the proposed design for each wall type. The gross exterior wall area of framed walls in the standard design (excluding demising walls) is equally divided among the four main compass points -- north, east, south, and west. The gross exterior wall area of mass walls in the standard design (excluding demising walls and below grade walls) is equally divided among these four main compass points. Window and door areas are subtracted from the gross wall area to determine the net wall area in each orientation.

Exterior wall area and construction details are reported on the CF1R. Metal-framed and SIP assemblies are reported as a special feature on the CF1R.

Constructions for standard exterior mass are supported but not implemented beyond the assumptions for typical mass.

The performance approach assumes that both the proposed design and standard design building have a minimum mass as a function of the conditioned area of slab floor and nonslab floor. (See Section 2.5.4.1.)

Mass such as concrete slab floors, masonry walls, double gypsum board, and other special mass elements can be modeled. When the proposed design has more than the typical assumptions for mass in a building, then each element of heavy mass is modeled in the proposed design, otherwise; the proposed design is modeled with the same thermal mass as the standard design.

The proposed design may be modeled with the default 20 percent exposed mass/80 percent covered mass or with actual mass areas modeled as separate covered and exposed mass surfaces. Exposed mass surfaces covered with flooring material that is in direct contact with the slab can be modeled as exposed mass. Examples of such materials are tile, stone, vinyl, linoleum, and hard-wood.

The conditioned slab floor in the standard design is assumed to be 20 percent exposed slab and 80 percent slab covered by carpet or casework. Interior mass assumptions as described in Section 2.5.4.1 are also assumed. No other mass elements are modeled in the standard design. The standard design mass is modeled with the following characteristics:

• The conditioned slab floor area (slab area) shall have a thickness of 3.5 inches, a volumetric heat capacity of 28 Btu/ft³-°F, and a conductivity of 0.98 Btu-in/hr-ft²-°F. The exposed portion shall have a surface conductance of 1.3 Btu/h-ft²-°F (no thermal resistance on the surface), and the covered portion shall have a surface conductance of 0.50 Btu/h-ft²-°F, typical of a carpet and pad.

• The “exposed” portion of the conditioned nonslab floor area shall have a thickness of 2.0 inches, a volumetric heat capacity of 28 Btu/ft³-°F, a conductivity of 0.98 Btu-in/hr- ft²-ºF; and a surface conductance of 1.3 Btu/h- ft²-°F (no added thermal resistance on the surface). These thermal mass properties apply to the “exposed” portion of nonslab floors for both the proposed design and standard design. The covered portion of nonslab floors is assumed to have no thermal mass.

Exposed mass greater than 20 percent exposed slab on grade, and any other mass modeled by the user is reported as a special feature on the CF1R.

Doors are defined as an opening in a building envelope. If the rough opening of a door includes fenestration equal to 25 percent or more of glass or fenestration, it is fenestration. (See Section 2.5.6.6.) Doors with less than 25 percent fenestration are an opaque door.

The compliance software shall allow users to enter doors specifying the U-factor, area, and orientation. Doors to the exterior or to unconditioned zones are modeled as part of the conditioned zone. For doors with less than 25 percent glass area, the U-factor shall come from JA4, Table 4.5.1 (default U-factor 0.20) or from NFRC certification data for the entire door. For unrated doors, the glass area of the door, calculated as the sum of all glass surfaces plus 2 inches on all sides of the glass (to account for a frame), is modeled under the rules for fenestrations; the opaque area of the door is considered the total door area minus this calculated glass area. Doors with 25 percent or more glass area are modeled under the rules for fenestrations using the total area of the door.

When modeling a garage zone, large garage doors (metal roll-up or wood) are modeled with a 1.0 U-factor.

The standard design has the same door area for each dwelling unit as the proposed design. The standard design door area is distributed equally among the four main compass points--north, east, south and west. The U-factor for the standard design is taken from Section 150.1(c) and Table 150.1-A or 150.1-B. All swinging opaque doors are assumed to have a U-factor of 0.20. The net opaque wall area is reduced by the door area in the standard design.

Fenestration is modeled with a U-factor and solar heat gain coefficient (SHGC). Acceptable sources of these values are National Fenestration Rating Council (NFRC), default tables from Section 110.6 of the standards, and Reference Appendix NA6.

In limited cases for certain site-built fenestration that is field fabricated, the performance factors (U-factor, SHGC) may come from Nonresidential Reference Appendix NA6 as described in Exception 4 to Section 150.1(c)3A.

There is no detailed model of chromogenic fenestration available at this time. As allowed by Exception 3 to Section 150.1(c)3A, the lower-rated labeled U-factor and SHGC may be used only when installed with automatic controls as noted in the exception. Chromogenic fenestration cannot be averaged with nonchromogenic fenestration.

The compliance software allows users to enter individual skylights and fenestration types, the U-factor, SHGC, area, orientation, and tilt.

Performance datum (U-factors and SHGC) are from NFRC values or from the Energy Commission default tables from Section 110.6 of the standards. In spaces other than sunspaces, solar gains from windows or skylights use the California simulation engine (CSE) default solar gain targeting.

Skylights are a fenestration with a slope of 60 degrees or more. Skylights are modeled as part of a roof.

If the proposed design fenestration area is less than 20 percent of the conditioned floor area, the standard design fenestration area is set equal to the proposed design fenestration area. Otherwise, the standard design fenestration area is set equal to 20 percent of the conditioned floor area. The standard design fenestration area is distributed equally among the four main compass points—north, east, south and west.

The net wall area on each orientation is reduced by the fenestration area and door area on each façade. The U-factor and SHGC performance factors for the standard design are taken from Section 150.1(c) and Table 150.1-A or 150.1-B, which is 0.30 U-factor in all climate zones. SHGC is 0.23 in Climate Zones 2, 4, and 6-15. Where there is no prescriptive requirement (Climate Zones 1, 3, 5, and 16), the SHGC is set to 0.35.

Fenestration area, U-factor, SHGC, orientation, and tilt are reported on the CF1R.

Software users enter a set of basic parameters for a description of an overhang and sidefin for each individual fenestration or window area entry. The basic parameters include fenestration height, overhang/sidefin length, and overhang/sidefin height. Compliance software user entries for overhangs may also include fenestration width, overhang left extension, and overhang right extension. Compliance software user entries for sidefins may also include fin left extension and fin right extension for both left and right fins. Walls at right angles to windows may be modeled as sidefins.

For both the proposed and standard design, all windows are assumed to have draperies, and skylights are assumed to have no interior shading. Window medium drapes are closed at night and half open in the daytime hours. Interior shading is not a compliance variable and is not user-editable.

For both the proposed and standard design, all windows are assumed to have bug screens, and skylights are assumed to have no exterior shading. Exterior shading is modeled as an additional glazing system layer using the ASHWAT calculation.

The compliance software shall require the user to accept the default exterior shading devices, which are bug screens for windows and none for skylights. Credit for shading devices that are allowable for prescriptive compliance are not allowable in performance compliance.

The standard design shall assume bug screens. The standard design does not have skylights.

The software allows users to enter areas and exterior perimeter of slabs that are heated or unheated, covered or exposed, and with or without slab-edge insulation. Perimeter is the length of wall between conditioned space and the exterior, but it does not include edges that cannot be insulated, such as between the house and the garage. The default condition for the proposed design is that 80 percent of each slab area is carpeted or covered by walls and cabinets, and 20 percent is exposed. Inputs other than the default condition require that carpet and exposed slab conditions are documented on the construction plans.

When the proposed heating distribution is radiant floor heating (heated slab), the software user will identify that the slab is heated and model the proposed slab edge insulation. The mandatory minimum requirement is R-5 insulation in Climate Zones 1-15 and R-10 in Climate Zone 16 (Section 110.8[g], Table 110.8-A).

The standard design perimeter lengths and slab on grade areas are the same as the proposed design. Eighty percent of standard design slab area is carpeted, and 20 percent is exposed. For the standard design, an unheated slab edge has no insulation with the exception of Climate Zone 16, which assumes R-7 to a depth of 16 inches. The standard design for a heated slab is a heated slab with the mandatory slab edge insulation of R-5 in Climate Zones 1-15 and R-10 in Climate Zone 16.

Slab areas, perimeter lengths, and inputs of other than the default condition are reported on the CF1R.

The software allows users to enter areas and depth below grade of slab floors occurring below grade. Unlike slab-on-grade floors, there is no perimeter length associated with underground floors.

The standard design underground floor areas are the same as the proposed design.

The software allows the user to input floor areas and constructions for raised floors over a crawl space, over exterior (garage or unconditioned), over a controlled ventilation crawl space, and concrete raised floors. The proposed floor area and constructions are consistent with the actual building design.

The standard design has the same area and type of construction as the proposed design. The thermal characteristics meet Section 150.1(c) and Table 150.1-A or 150.1-B. For floor areas that are framed construction, the standard design floor has R-19 in 2x6 wood framing, 16-in. on center (0.037 U-factor). For floor areas that are concrete raised floors, the standard design floor is 6 inches of normal weight concrete with R-8 continuous insulation in Climate Zones 1, 2, 11, 13, 14, 16; Climate Zones 12 and 15 have R-4; Climate Zones 3-10 have R-0.