See Generic Air Loop Tutorial
The air loop edit dialog incorporates two tabs, the first tab is General and incorporates loop characteristic and sizing data, the second tab covers Plant Equipment Operation allowing you to set up various equipment operation schemes for the loop.
This is the name of the loop. If the supplied loop name is found to already exist, the software will automatically append an integer to create a unique name.
The rest of the Air loop dialog provides the sizing inputs needed to perform a central forced air system design air flow, heating capacity, and cooling capacity calculation for a system serving one or more zones. The information needed consists of the outside environmental conditions and the design supply air temperatures, outdoor air flow rate, and minimum system air flow ratio.
The outside conditions come from the design days in the input. A system sizing calculation is performed for the design day defined in the input file and the resulting maximum heating and cooling air flow rates and capacities are used in the component sizing calculations.
Supply air conditions are specified by inputting a supply air temperature for cooling, a supply air temperature for heating, and a preheat temperature. The system sizing calculation sums the zone design air flow rates to obtain a system supply air flow rate. The design conditions and the outdoor air flow rate are used to calculate a design mixed air temperature. The temperature plus the design supply air temperatures allows the calculation of system design heating and cooling capacities.
Note: Detailed HVAC autosizing calculations are not to be confused with Heating and Cooling design calculations, which use separate simpler data entry from the HVAC tab. No Detailed HVAC data is used for Heating and Cooling design calculations, which are based on the EnergyPlus Ideal loads system.
The design outdoor air flow rate (in m3/s or ft3/min). Generally this should be the minimum outdoor air flow. It is used for both heating and cooling design calculations. The assumption for cooling is that any outdoor air economizer will be closed. If Autosize is input the Design outdoor air flow rate will be taken from the sum of the zone outdoor air flow rates based on the Sizing option below.
Note that the Design supply air flow rate is defined in the AHU dialog contained within the Air loop.
This ratio should be set to the expected system flow rate when maximum heating demand occurs. It is used in calculating the central system heating capacity. Thus if the system is VAV with the zone VAV dampers held at minimum flow when there is a zone heating demand, this ratio should be set to the minimum flow ratio. If the zone VAV dampers are reverse action and can open to full flow to meet heating demand, this ratio should be set to 1.
This ratio is only required when the Fan type of the attached AHU is 2-Variable volume. The value entered must be between 0 and 1.
The options are:
The user specified type of load on which to size the central system. The choices are:
Note: In cases where the air loop is being used to model a dedicated outdoor air system (DOAS), it is important to set the type of load to size on to 4‑Ventilation requirement. This is true even if the air is being pre-heated and/or pre-cooled to temper it before delivery.
This is the design outdoor air flow rate (in m3/s or ft3/min). Generally this should be the minimum outdoor air flow. It is used for both heating and cooling design calculations. The assumption for cooling is that any outdoor air economizer will be closed. If auto-sized, the outdoor air flow rate will be taken from the sum of the zone outdoor air flow rates.
This is the design air temperature exiting the preheat coil (°C or °F).
This is the design humidity ratio exiting the preheat coil (in kg/kg).
This is the design supply air temperature for heating (°C or °F). This can be either the reset temperature for a single duct system or the actual hot duct supply air temperature for dual duct systems. It should be the temperature at the exit of the main heating coil.
Entering 2-Yes means the system will be sized for heating using 100% outdoor air. Entering 1-No means the system will be sized for heating using minimum outside air (the default). For Air loops
When the Type of load to size on is set to 4‑Ventilation requirement, this dialog setting is disabled and set to 2-Yes.
This is the design humidity ratio at the exit of the central heating coil (in kg/kg) . The default is 0.008.
The input must be either:
The default method is 1-Design day, i.e., the program uses the calculated design values.
This is the design system heating air flow rate (m3/s or ft3/min). This input is an alternative to using the program calculated value. This input is used if Heating design air flow method is 2-Flow/System. This value will not be multiplied by any sizing factor or by zone multipliers. If using zone multipliers, this value must be large enough to serve the multiplied zones.
This is the design air temperature exiting the pre-cooling coil (°C or °F).
This is the design humidity ratio exiting the pre-cooling coil (kg/kg).
This is the design supply air temperature for cooling (in °C or °F). This should be the temperature of the air exiting the central cooling coil.
Entering 2-Yes means the system will be sized for cooling using 100% outdoor air. Entering 1-No means the system will be sized for cooling using minimum outside air (the default).
When the Type of load to size on is set to 4‑Ventilation requirement, this dialog setting is disabled and set to 2-Yes.
This is the design humidity ratio at the exit of the central cooling coil (in kg/kg). The default is 0.008.
The input must be either:
The default method is 1-Design Day, i.e. the program uses the calculated design values.
This is the design system cooling air flow rate (m3/s or ft3/min). This input is an alternative to using the program calculated value. This input is used if Cooling design air flow method is 2-Flow/System. This value will not be multiplied by any sizing factor or by zone multipliers. If using zone multipliers, this value must be large enough to serve the multiplied zones.
Schedule values greater than zero (usually 1 is used) indicate that the system is on. Schedule values less than or equal to zero (usually 0 is used) denote that the system is off. This schedule overrides the air loop fan schedules for determining whether the fans are on.