For California compliance, compliance software shall accept input for and be capable of modeling a minimum of 50 thermal zones, each with a control. Compliance software may use zone multipliers for identical zones.
Unconditioned space is enclosed space that is neither directly nor indirectly conditioned. Examples include stairways, warehouses, unoccupied adjacent tenant spaces, attached sunspaces, attics, and crawl spaces.
Unconditioned spaces shall be modeled if they are part of the permitted space. All applicable envelope information shall be specified in a similar manner to conditioned space.
If unconditioned space is not a part of the permitted space, the space may be either explicitly modeled or the impact thereof on the permitted space may be approximated by modeling the space as outdoor space. For unconditioned spaces that are explicitly modeled, all internal gains and operational loads (occupants, water heating, receptacle, lighting, and process loads) shall be modeled as specified in Appendix 5.4A.
Return air plenums are considered indirectly conditioned spaces and shall be modeled as part of the adjacent conditioned space with equipment, lighting, and occupant loads at zero.
Indirectly conditioned spaces can either be occupied or unoccupied. For spaces that are unoccupied, such as plenums, attics, or crawlspaces, lighting, receptacle, and occupant loads shall be zero. For spaces that can be occupied, such as stairwells or storage rooms, modeling assumptions shall be taken from Appendix 5.4A.
Unconditioned spaces may not be located in the same thermal zone as conditioned spaces. Conditioned spaces and indirectly conditioned spaces may be located in the same thermal zone or in separate zones. When located in the same thermal zone, the indirectly and directly conditioned spaces are assumed to have the space temperature schedule. When indirectly conditioned space is assigned to a thermal zone, the zone cannot have heating/cooling system, but can have a ventilation or exhaust system.
Thermal zones shall be combined only if the spaces have similar space conditioning requirements and operating schedules. Space function inputs, as how they translate to thermal zone and HVAC system analysis assumptions, are defined by the following rules:
Spaces: Building spaces are sections of a building sharing the same space function (for example, office, retail, lab) and serve as the structure for modeling the envelope, ventilation, exhaust, lighting, daylighting, and occupancy and process loads of the building. Spaces can only have one space function, can only be assigned to one thermal zone, and can’t span multiple building stories.
Space Functions: Each building space is assigned one space function. Design internal loads and other space function input assumptions, are defined in Appendix 5.4A. Appendix 5.4A also defines the schedule group associated with each space function. The schedule group and the schedule values for each space function are prescribed for compliance analysis.
Some space functions are common to many schedule groups. These space functions are defined in Appendix 5.4A as having schedule groups that are editable. This addresses the issue of conflicting schedule profiles if these common functions are combined into a single thermal zone or served by the same HVAC system as surrounding zones. In the event the user does not assign a schedule group to these common space types, a default assumption is defined in the Appendix 5.4A.
Thermal Zones: Spaces can be combined into thermal zones. In this situation, peak internal loads and other design inputs for the thermal zone are modeled separately or weight-averaged based on floor area. The thermal zone schedules (occupancy, HVAC schedule, lighting schedule, space setpoint schedule), are based on the predominant schedule group described below. Thermal zones cannot combine spaces that are associated with different building stories.
Schedule Group: There are many different schedule groups defined in Appendix 5.4B for California compliance. Each schedule group defines hourly profiles for thermostat set points, HVAC system availability, occupancy, lighting, receptacles, service hot water, gas equipment, infiltration, refrigeration elevators, and escalators. The schedule group is based on the space function.
HVAC Systems: In many cases, more than one conditioned thermal zone is served by an HVAC system, which has scheduled availability (ON or OFF) to address the occupancy and internal load patterns of the thermal zones it serves.
Predominant Schedule Group: For a building thermal zone or building story that includes multiple schedule groups, the hourly profiles are determined by the compliance software according to the predominant schedule group for each thermal zone or building story. The predominant schedule group for the thermal zone or building story is determined by the schedule group, as defined above, associated with the largest floor area of the thermal zone or building story. Residential multifamily dwelling units, hotel/motel guestrooms, and common areas associated with these residential spaces, as well as enclosed parking garages and covered process spaces (laboratory, data, and commercial kitchen), shall always have their own prescribed schedule group, regardless of the predominant schedule group for the thermal zone.