2.3 Software Modeling Requirements for Zones

2.3.1    Required Zone Modeling Capabilities

For California 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.

2.3.2    Modeling Requirements for Unconditioned Spaces

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 or in separate zones. When located in the same thermal zone, the indirectly and directly conditioned spaces assumed to have the space temperature schedule. When indirectly conditioned space is assigned to its own thermal zone, the zone cannot have heating/cooling system, but can have a ventilation or exhaust system.

2.3.3    Space Use Classification Considerations

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:

Schedule Group: There are many different schedule groups defined in Appendix 5.4B for California compliance. Each schedule group defines building specific hourly profiles for thermostat setpoints, HVAC system availability, occupancy, lighting, and so forth.

Space Functions: Each building space is assigned one space function. Design internal loads and other space function input assumptions, including the assigned schedule group described above, are defined in Appendix 5.4A. The schedule group and the schedule values for each space function are prescribed for compliance analysis.

These space functions are common to many different building types and, therefore, the user can assign any of the available schedule groups defined in Appendix 5.4B. 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, default assumptions are defined in the Appendix 5.4B.

Thermal Zones: Spaces can be combined into thermal zones. In this situation, peak internal loads and other design inputs for the thermal zone are determined by weight-averaging the space function design inputs by floor area. When spaces are combined into thermal zones, the thermal zone schedules (occupancy, HVAC schedule, lighting schedule, space setpoint schedule), are based on the schedule group of the predominant space function on the building floor (by floor area) included in the thermal zone.

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. For systems that serve more than one thermal zone, the HVAC schedule group and availability schedule are determined by the most predominant schedule group (by floor area) represented in the thermal zones served.

The schedule group in the standard design is defined for each building story according to the predominant space function type and the schedule group assignment in Appendix 5.4A. Residential spaces and covered process spaces shall be served by dedicated systems, separate from nonresidential spaces.