For California compliance, software shall accept input for and be capable of modeling a minimum of fifty (50) thermal zones, each with its own control. Software shall also be capable of reporting the number of control points at the building level. When the number of control points is not greater than twenty (20) the compliance software shall have one HVAC zone per control point. Compliance software may use zone multipliers for identical zones. When the number of zones exceeds twenty (20), then (and only then) thermal zones may be combined subject to a variety of rules and restrictions.
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 its impact on the permitted space may be approximated by modeling the space as outdoor space and turning off solar gains to the demising wall that separates the permitted space from the adjacent unconditioned 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 zone as conditioned spaces. Conditioned spaces and indirectly conditioned spaces may be located in the same zone; when this occurs, the indirectly conditioned spaces will assume the space temperature schedule of the conditioned space.
Thermal zones shall contain no more than ten different space functions, which shall only be combined if the spaces have similar space conditioning requirements. If the complete building method is used, each thermal zone must be assigned to one and only one complete building type. For California compliance, space function inputs, as how they translate to thermal zone and HVAC system analysis assumptions are defined by the following rules:
Schedule Group: 13 different schedule groups are defined in Appendix 5.4B for California compliance. Each schedule group defines building specific hourly profiles for thermostat setpoints, HVAC system availability, occupancy, lighting, etc.
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, with the exception of the following space functions:
•Corridors, Restrooms, Stairs, and Support Areas
•Electrical, Mechanical, Telephone Rooms
•Lobby, Main Entry
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 mitigates 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. However, if the peak lighting, receptacle, and process load of the individual space functions differs by more than 2 Watts/sf or a factor of 2, the space functions cannot be combined into a single thermal zone. If spaces combined into thermal zones meet these criteria, the thermal zone schedules are based on the schedule group of the predominant space function (by floor area) included in the thermal zone.
HVAC Systems: In many cases, more than one conditioned thermal zone is served by a single 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 is determined by the most predominant schedule group (by floor area) represented in the thermal zones served.
If peak lighting, receptacle, or process loads of the individual thermal zones differs by more than 2 Watts/sf or a factor of 2, the compliance software will identify this HVAC system and the range of peak thermal zone internal loads for the given system in the final compliance report; however, compliance analysis will still be performed.
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.
In the rare case that the predominant schedule group for the thermal zones/HVAC system cannot be determined by floor area (i.e. two or more different schedule groups are represented by equal floor areas), the schedule group corresponding to the combined space functions or thermal zones with the highest combined peak lighting and receptacle load shall be used at each respective step described above.