A thermal zone is a space or collection of spaces having similar space-conditioning requirements, the same heating and cooling setpoint, 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. High-rise residential and non-residential buildings with identical floors served by like systems may be modeled with floor multipliers.
Thermal Zone Name
Applicability
All projects
Definition
A unique identifier for the thermal zone made up of 50 or fewer alphanumeric characters.
Units
Text
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
Text
Input Restrictions
None
Standard Design
Not applicable
Thermal Zone Type
Applicability
All projects
Definition
Designation of the thermal zone as directly conditioned space, indirectly conditioned space (i.e., conditioned only by passive heating or cooling from an adjacent thermal zone), or plenum (i.e., unoccupied but partially conditioned as a consequence of its role as a path for returning air).
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. The purpose of this building descriptor is to link the thermal zone to a system (child points to parent). 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 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 it must 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 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 it must 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 software shall either model the occupant loads separate for each space and the heat gain for each time step of the analysis or it must 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.
Natural ventilation may be modeled for a thermal zone in the proposed design when there are automatic controls that maintain natural ventilation openings open whenever the space is occupied. If zone temperature setpoints are maintained using only natural ventilation, the heating, cooling and ventilation systems may be shut off.
If the proposed design results in excessive unmet load hours in cooling for any naturally ventilated zone, then the user must define and specify a capacity for a Supplementary DX Cooling Unit (Section 6.1.5.2) to serve each zone (with excessive UMLH). If the proposed design results in excessive unmet load hours in heating for any naturally ventilated zone, the user must define a Supplementary DX Cooling Unit with gas furnace heating to serve each zone with excessive UMLH in heating.
The standard design model shall not include natural ventilation.
Natural Ventilation Method
Applicability
All thermal zones with natural ventilation
Definition
The method used to model natural ventilation. The choices will depend on the capabilities of the energy simulation program.
Units
List: choices depend on the capabilities of the energy simulation program.
Input Restrictions
When the building is conditioned solely by natural ventilation, theproposed design must have automatic controls that maintain natural ventilation whenever the space is occupied. When the building has mechanical ventilation and cooling in conjunction with natural ventilation (operable windows), natural ventilation may only be allowed in the model if the building has interlocks on operable windows or other means of automatic controls (automatic window controls).
Natural ventilation that is used for spaces as a means of ventilation only (no space conditioning) may only be specified in the compliance model if there are controls to ensure that the required minimum ventilation is maintained during occupied hours. Operable windows that are opened and closed manually do not qualify for this modeling option.
Standard Design
The standard design is not modeled with natural ventilation.
Air Flow Rate
Applicability
All projects with natural ventilation that use a method that require the specification of an air flow rate
Definition
The rate of air flow through the thermal zone when the natural ventilation system is operating
Units
Air changes per hour or cfm
Input Restrictions
Documentation shall be provided supporting the air flow rate for the proposed design. The air flow rate shall meet mandatory ventilation requirements of the Standard.
Standard Design
The standard design is not modeled with natural ventilation.
Minimum Indoor Temperature
Applicability
All projects with natural ventilation or mixed mode ventilation with automatic controls
Definition
The minimum indoor temperature below which natural ventilation is disabled
Units
Degrees F
Input Restrictions
Fixed at 71°F for mixed mode ventilation and 70°F for natural ventilation
Standard Design
Not applicable
Maximum Indoor Temperature
Applicability
All projects with natural ventilation or mixed mode ventilation with automatic controls
Definition
The maximum indoor temperature below which natural ventilation is disabled
Units
Degrees F
Input Restrictions
Fixed at 74°F for mixed mode ventilation and 76°F for natural ventilation
Standard Design
Not applicable.
Minimum Outdoor Temperature
Applicability
All projects with natural ventilation or mixed mode ventilation with automatic controls
Definition
The minimum outdoor temperature below which natural ventilation is disabled
Units
Degrees F
Input Restrictions
Fixed at 55°F
Standard Design
Not applicable
Maximum Outdoor Temperature
Applicability
All projects with natural ventilation or mixed mode ventilation with automatic controls
Definition
The maximum outdoor temperature above which natural ventilation is disabled
Units
Degrees F
Input Restrictions
Fixed at 75°F
Standard Design
Not applicable
This set of building descriptors characterize the thermal mass that is not explicitly captured by the definition of exterior surfaces and interior partitions.
Thermal Response Characteristics
Applicability
All projects
Definition
This building descriptor only addresses the building contents. The thermal mass associated with floors, interior walls, and other building envelope components is derived from the thermal properties and materials that make up these components. However, if interior partitions are not explicitly entered (see below) their effect may be captured with this input.
The thermal capacitance of the building contents are typically specified in terms of the composite weight of the building contents in lb/ft² or absolute lb. In this instance, the software assumes an average specific heat for the contents. This input can also be specified as the mass of the contents multiplied times the specific heat of the contents. The latter method would be a summation, since each item may have a different specific heat.
Units
lb/ft² or lb
Input Restrictions
As designed
Standard Design
The interior thermal mass in the standard design shall be the same as the proposed design.
Furniture and Contents
Applicability
All projects
Definition
A specification of the mass and heat capacity of furniture and other elements in the interior of the building. This includes information about the coverage and weight of furniture in the space as well as how much of the floor is covered by furniture. The latter affects how much of the solar gains that enters the space is directed to the floor with delayed heat gain and how much becomes a more instantaneous load.
Units
Data structure
Input Restrictions
As designed
Standard Design
The interior thermal mass and modeling assumptions in the standard design shall be the same as the proposed design.