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To model a default HVAC system, simply set the HVAC input of the System element to "Undefined". NR T24
Performance will automatically define a packaged, single-zone system for both the standard and proposed
designs.
For projects where a built-up system is the appropriate system type, you may use an alternative method to
force the program to model the system type you select. In the Central System Library, Heating Tab, select
the System Type from the drop-down list. Set all heating and cooling entries to zero. You may model the
actual fan characteristics (if known) or model a fan power index equal to 0.365 Watts/cfm, which will be used
for both the standard and proposed systems. Be sure to model sufficient supply air to meet the minimum
ventilation requirements. NR T24 Performance will automatically define the type of system specified for both
the standard and proposed designs.
Default Chiller
To model a default Chiller, simply set the Chiller input of the Plant element to "Undefined". NR T24
Performance will automatically define a chiller for both the standard and proposed designs.
Default Central Cooling Tower
To model a default Cooling Tower, simply set the Cooling Tower input of the Plant element to "Undefined".
NR T24 Performance will automatically define a cooling tower for both the standard and proposed designs.
Default Zonal Systems
When modeling a default built-up mechanical system with VAV boxes, reheating, or recooling, you must
create default zonal conditions as well.
1. In the Zonal System Library, create, for example, a default VAV box (e.g., Std 30% VAV Box/Reheat).
Set the Minimum Airflow Ratio to the appropriate value (e.g., 0.30), and indicate the presence or absence
of a Reheat Coil depending on the default condition.
2. Save the Zonal system, and select it in the Zone element under the Mechanical tab, Zonal System Data.
Default Boiler
To model a default Boiler, simply set the Heating Boiler input of the Plant element, Heating Hot Water Tab to
"Undefined". NR T24 Performance will automatically define a boiler for both the standard and proposed
designs.
Zonal Systems
Zonal systems include different kinds of VAV (variable air volume) or variable refrigerant volume boxes.
Zonal systems are defined in the Zonal System Library and are input in the Zone element(s) under the
Mechanical tab.
Each zone may have up to 99 identical terminal units such as VAV boxes. Table D-4 lists which mechanical
system types may include specific zonal components.
Chillers and Cooling Towers
Chillers and cooling towers are components of more complex systems, such as built-up VAV systems. They
are generally found in larger nonresidential and high-rise residential construction. Chillers and cooling towers
are defined in the Plant Library and are incorporated into the overall building description using the Chilled
Water tab in the Plant element.
190 • Building Tree
User's Manual EnergyPro Version 5