A thermal zone is a space or collection of spaces having similar space-conditioning requirements, has the same heating and cooling set point, and is the basic thermal unit (or zone) used in modeling the building. A thermal zone will include one or more spaces. Thermal zones may be grouped together, but systems serving combined zones shall be subject to efficiency and control requirements of the combined zones. Nonresidential buildings with identical floors served by like systems may be modeled with floor multipliers.
The general information is used to identify the various thermal zones included in the building project. This information will include whether the thermal zone is directly or indirectly conditioned and the floor area of the thermal zone. The HVAC system used to service the specific thermal zone is also identified.
Thermal Zone Name
Applicability: All projects.
Definition: A unique identifier for the thermal zone made up of 50 or fewer alphanumeric characters.
Units: Alphanumeric string.
Input Restrictions: None.
Standard Design: Not applicable.
Thermal Zone Description
Applicability: All projects.
Definition: A brief description of the thermal zone that identifies the spaces which make up the thermal zone or other descriptive information. The description should tie the thermal zone to the building plans.
Units: Alphanumeric string.
Input Restrictions: None.
Standard Design: Not applicable.
Thermal Zone Type
Applicability: All projects.
Definition: Designation of the thermal zone as a directly conditioned, unconditioned, or plenum (that is, unoccupied but partially conditioned as a consequence of its role as a path for returning air) space.
Units: List: directly conditioned, unconditioned or plenum.
Input Restrictions: The default thermal zone type is “directly conditioned.”
Standard Design: The descriptor is identical for the proposed design and standard design.
System Name
Applicability: All projects.
Definition: The name of the HVAC system that serves this thermal zone. This building descriptor links the thermal zone to a system (child points to parent). Compliance software can make this link in other ways.
Units: Text, unique.
Input Restrictions: None.
Standard Design: The standard design may have a different system mapping if the standard design has a different HVAC type than the proposed design.
Floor Area
Applicability: All projects.
Definition: The gross floor area of a thermal zone; including walls and minor spaces for mechanical or electrical services such as chases that are not assigned to other thermal zones.
Units: Square feet (ft²).
Input Restrictions: The floor area of the thermal zone is derived from the floor area of the individual spaces that make up the thermal zone.
Standard Design: Same as proposed design.
Inputs for interior lighting are specified at the space level (See specification below). In those instances, when thermal zones contain just one space, the inputs here will be identical to the inputs for the single space that is contained within the thermal zone.
For those instances when a thermal zone contains more than one space, the compliance software shall either
•Model the lighting separate for each space and sum energy consumption and heat gain for each time step of the analysis, or
•Incorporate some procedure to sum inputs or calculate weighted averages such that the lighting power used at the thermal zone level is equal to the combination of lighting power for each of the spaces contained in the thermal zone.
In some cases, combining lighting power at the space level into lighting power for the thermal zone may be challenging and would have to be done at the level of each time step in the simulation. These cases include:
•A thermal zone that contains some spaces that have daylighting and others that do not.
•A thermal zone that contains spaces with different schedules of operation.
•A thermal zone that contains some spaces that have a schedule adjusted in some way for lighting controls and other spaces that do not.
•Combinations of the above.
Inputs for receptacle and process loads are specified at the space level (See specification below.) In those instances, when thermal zones contain just one space, the inputs here will be identical to the inputs for the single space that is contained within the thermal zone.
For those instances when a thermal zone contains more than one space, the compliance software shall either
•Model the receptacle and process loads separate for each space and sum energy consumption and heat gain for each time step of the analysis, or
•Incorporate some procedure to sum inputs or calculate weighted averages such that the receptacle and process loads used at the thermal zone level are equal to the combination of receptacle and process loads for each of the spaces contained in the thermal zone.
When the spaces contained in a thermal zone have different schedules, combining receptacle and process loads from the space level may be challenging and would have to be done at the level of each time step in the simulation. See discussion above on lighting.
Inputs for occupant loads are specified at the space level (See specification below). In those instances, when thermal zones contain just one space, the inputs here will be identical to the inputs for the single space that is contained within the thermal zone.
For those instances when a thermal zone contains more than one space, the compliance software shall either
•Model the occupant loads separate for each space and the heat gain for each time step of the analysis, or
•Incorporate some procedure to sum inputs or calculate weighted averages such that the occupant loads used at the thermal zone level are equal to the combination of occupant loads for each of the spaces contained in the thermal zone.
When the spaces contained in a thermal zone have different occupant schedules, rolling up occupant loads from the space level may be challenging and would have to be done at the level of each time step in the simulation. Spaces with differences in full-load equivalent operating hours of more than 40 hours per week shall not be combined in a single zone. See discussion above on lighting.