Sizing
The Sizing tab contains information for system level sizing properties.
Sizing Method
The system can be sized based on the system block or system peak.
Block: A block system is based on the maximum simultaneous cooling load of all the rooms and includes the sensible and latent loads due to lights, infiltration, people, miscellaneous, solar, external conduction loads, and ventilation (outside) air (if the ventilation is delivered directly to the room).
Peak: A peak system is based on the sum of the individual room peak cooling loads that may or may not occur at the same time. Peak includes the sensible and latent loads due to lights, infiltration, people, miscellaneous, solar, external conduction loads, and ventilation (outside) air (if the ventilation is delivered directly to the room).
Load Sizing
Sizing can be based on either total load, sensible load, or the ventilation requirement.
Total: The system air flow rate is sized based on the combined sensible and latent load. This is common for most system types.
Sensible: The system air flow rate is sized based on the sensible load only and not the latent component. This is common when there is another piece of equipment used to condition the humidity loads.
Ventilation requirement: The system air flow rate is sized based on the system ventilation requirement. This is common for AHU coils associated with induction and chilled beam system types.
Ventilation Method
Zone Sum – Sum of Outdoor Air: The Sum of Outdoor air totals the ventilation requirements for all of the zones on the system to calculate the ventilation requirement for the system.
VRP – ASHRAE 62.1: The ventilation rate procedure uses the multizone calculations found in ASHRAE 62.1 to calculate the ventilation requirement for the system. If the ventilation at the building level is set to 62.1, make sure to set this ventilation method to 62.1 as well.
Airflow
The airflow section contains information for system level airflow sizing.
Supply Design Cooling Airflow
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Default: Autosize
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Min Max: 0–infinity
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Units: m3/sec, cfm, cfm/sq•ft (Floor), (m3/s)/sq•m (Floor), % Clg Airflow, cfm/ton, m3/hr•sq•m (Floor), cm3/sec, (m3/s)/kW, m3/hr•kW, m3/s•W, cm3/sec, m3/hr
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The Supply Design Cooling Airflow can be autosized by checking the Auto Size box. If the Auto Size box is unchecked, the design airflow for the system can be entered.
Supply Design Heating Airflow
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Default: Autosize
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Min Max: 0–infinity
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Units: cm3/sec, m3/hr, (m3/s)/kW, m3/hr•kW, cm3/sec, m3/hr•sq m (Floor), m3/sec, cfm, cfm/sq•ft (Floor), (m3/s)/sq•m (Floor), % Clg Airflow, m3/s•W, cfm/ton, % Htg Airflow
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The Supply Design Heating Airflow can be autosized by checking the Auto Size box. If the Auto Size box is unchecked, the design airflow for the system can be entered.
Design Outdoor Airflow
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Default: Autosize
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Min Max: 0–infinity
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Units: cfm
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The Design Outdoor Airflow can be autosized by checking the Auto Size box. If the system outdoor airflow is autosized, the program will use the sum of the outdoor air flow for each of the zones. If the Auto Size box is unchecked, the design airflow can be entered as the total design outdoor airflow at the system level.
Maximum Outdoor Air
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Default: 0
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Typical Range: 0–1
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Min Max: 0–infinity
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Units: dimensionless
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The zone maximum outdoor air fraction represents the maximum fraction of the total supply air that should be ventilation. If the ventilation requirement is higher than the maximum outdoor air fraction, the return airflow will be increased so both the ventilation cfm requirement and the maximum outdoor air fraction are met. This also takes into account unused outdoor air in the return air stream.
Cooling/Heating Design Setpoints
These cooling and heating setpoint temperatures are required by the program and cannot be autosized. This is the temperature of the air as it leaves the cooling or heating coil.
Supply Air Dry Bulb Cooling
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Default: 55°F
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Typical Range: 45 to 80°F; 7 to 26°C
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Min Max: - infinity to infinity
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Units: °F; °C
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Supply Air Dry Bulb Heating
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Default: 125°F
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Typical Range: 75 to 140°F; 24 to 60°C
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Min Max: - infinity to infinity
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Units: °F; °C
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Apply System Cooling SAT to Zone
This field can either be set to “yes” or “no”. When the field is set to “yes”, the cooling supply air temperature entered in the Supply Air Dry Bulb Cooling field on the Sizing properties tab of the system properties will override the Cooling Supply Air Dry Bulb field on the Zone Sizing tab of the system properties. Thus the same temperature will be used for the system cooling supply air temperature and the zone cooling supply air temperature. This is common when there is only one cooling coil in the system. For example, in a VAV Reheat system, there is only one main system level cooling coil and no cooling coil at the zone level.
When the field is set to “no”, the zone level cooling supply air temperature entered on the Cooling Supply Air Dry Bulb field on the Zone Sizing tab of the system properties will be used for the supply air temperature to the zone. Thus the cooling supply air temperature at the system level will be different than the cooling supply air temperature at the zone level. This is common when there is more than one cooling coil in the system. For example, in a four pipe induction system, there is a main preconditioning cooling coil at the system level and a second cooling coil in the zone level induction unit. The main coil cools the air to a certain temperature at the system level and the induction unit cools the air further at the zone level.
Apply System Heating SAT to Zone
This field can either be set to “yes” or “no”. When the field is set to “yes”, the heating supply air temperature entered in the Supply Air Dry Bulb Heating field on the Sizing properties tab of the system properties will override the Heating Supply Air Dry Bulb field on the Zone Sizing tab of the system properties. Thus the same temperature will be used for the system heating supply air temperature and the zone heating supply air temperature. This is common when there is only one heating coil in the system. For example, in a Single Zone VAV system, there is only one heating coil so there will be only one heating supply air temperature.
When the field is set to “no”, the zone level heating supply air temperature entered on the Heating Supply Air Dry Bulb field on the Zone Sizing tab of the system properties will be used for the supply air temperature to the zone. Thus the heating supply air temperature at the system level will be different than the heating supply air temperature at the zone level. This is common when there is more than one heating coil in the system. For example, in a VAV reheat system, there is a preheat coil at the system level and a zone level reheat coil in the terminal box. The preheat coil will heat the supply air up to a certain temperature at the system level and the reheat coil will further heat the air to a higher temperature at the zone level.
Cooling/Heating Design Capacity
The capacity represents the capacity of the system in both cooling and heating mode. The cooling and heating design capacity can either be autosized by the program or entered as a specific value.
Cooling Design Capacity
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Default: Autosize
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Min Max: 0–infinity
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Units: % Clg Capacity, W, kW, W/sq m, W/sq ft, tons, MW, Btuh, Mbh
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Heating Design Capacity
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Default: Autosize
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Min Max: 0–infinity
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Units: % Htg Capacity, tons, MW, Btuh, MBh, W, W/sq m, W/sq ft, kW
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