## Input for Design Calculations and Component Autosizing[LINK]

In order for EnergyPlus to successfully calculate zone design heating and cooling loads and air flow rates and for the program to use these results to automatically size the HVAC components a number of input objects must be present and certain object input fields must be entered.

• The input file should contain a SimulationControl object. The 1st field Do Zone Sizing Calculation should be entered as Yes. This will cause a zone sizing simulation to be done using all the sizing periods in the input file as weather. If there are no air or water loops in the HVAC input fields 2 and 3 can be set to No. If there are one or more air loops (i.e., there is at least one AirLoopHVAC object in the input file) then the 2nd field Do System Sizing Calculation should be entered as Yes. If there are one or more water loops (Plant Loop objects) then the 3rd field Do Plant Sizing Calculation should be set to Yes. Finally either the 4th field (Run Simulation for Sizing Periods) or the 5th field (Run Simulation for Weather File Run Periods) should be set to Yes in order to autosize the components and do a real simulation using the autosized components. The component autosizing calculations are done on the first pass through the HVAC system in the real simulation.
• There must be at least 2 (up to any number) SizingPeriod objects present. Normally one will be for summer conditions and one for winter. The summer day should normally have the field Day Type set to SummerDesignDay. The winter design day should normally have Day Type set to WinterDesignDay.
• To apply a global sizing factor include the Sizing:Parameters object.
• For each controlled zone in the input file there should be a corresponding Sizing:Zone](page-011.html#zone) object. Similarly for each AirLoopHVAC there should be a [Sizing:System object. And for each Plant or Condenser Loop there should be a Sizing:Plant object. Note however that if a controlled zone has no corresponding Zone Sizing object the data from the first Zone Sizing object will be used. Thus if all the zone sizing information is the same only one Zone Sizing object need be entered.
• Only controlled zones are included in the zone and system sizing calculations. Thus for a design air flow rate to be calculated for a zone, it must contain a thermostat even though it might not need or have a thermostat in the full simulation. An illustration would be a three zone building with a packaged single zone system and a thermostat in one of the zones. In order for the two slave zones to be included in the design air flow calculations they must be treated as if they have a thermostat: there must be a ZoneControl:Thermostat for each of the slave zones.
• Some attention should be paid to schedules. In a weekly schedule object the 9th and 10th day schedules are for summer and winter design days respectively. This means that if a SizingPeriod object has field Day Type set to SummerDesignDay the day schedule for summer sizing periods will be in effect. Similarly if a SizingPeriod object has field Day Type set to WinterDesignDay the day schedule for winter sizing periods will be in effect. Some possible applications of this capability are:

internal loads (lights, equipment, occupancy) to maximum all day for cooling and to zero all day for heating;
#. setting heating and cooling thermostat set points to constant values (no set up or set back);
#. setting heating and cooling equipment to be always on.

None of these applications are necessarily recommended but these and other uses of the special summer/winter design day schedules may prove useful for specific situations.

• Other than zone thermostat setpoints, the sizing calculations generally know nothing about the system control inputs such as setpoints and availability schedules. The user must coordinate sizing inputs with the actual simulation control inputs.
• The sizing calculations only recognize the presence of central heating and cooling coils, preheat and precool coils and reheat coils. These are assumed to deliver the various supply temperatures specified in the Sizing:System and Sizing:Zone objects. The impact of ther components such as heat recovery, dehumidifiers, fans, and pumps are not accounted for in the sizing calculations.

For autosizing to occur at the component level the user must enter the special value autosize in the numeric fields for which autosizing is available. Those fields can be found by looking at the Energy+.idd data dictionary file or under individual object details in this document. Fields that can be autosized are denoted with the comment \autosizable. The components and fields that are autosizable are listed in the following table. Note that spaces may be inserted in object names to facilitate readability.

Table: Details of Autosizable Objects/Fields

There are 3 places in the input where the user can impose sizing factors.

In Sizing Parameters (object: Sizing:Parameters), the user can specify an over-all sizing factor. This factor is applied to all the zone design loads and air flow rates resulting from the zone sizing calculations.

In Zone Sizing (object: Sizing:Zone), the user can specify a sizing factor for a specific zone. The factor is applied to the calculated zone design loads and air flow rates for the zone named in the Sizing:Zone object. This sizing factor overrides the global sizing factor. That is, a zone sizing factor, if specified, replaces the global sizing factor for the named zone.

For some plant components (basically all central chillers, boilers and cooling towers) the user can specify a sizing factor that modifies the autosized component capacity and flow rates. These factors are applied after the application of global or zone sizing factors. They are primarily used to split the design load between multiple components. These sizing factors can change the autosizing of the associated loops and pumps. The following rules are followed the effect of plant component sizing factors on loops and pumps.

For supply side branches, the sizing factors of all components in series on the branch are summed and the result becomes the branch sizing factor. If there is a branch pump its autosized design flow rate is multiplied by the branch sizing factor.

For each loop, if the average of the branch sizing factors is less than 1, the loop sizing factor is set equal to the sum of the branch sizing factors. If the average is greater than 1, the loop sizing factor is set equal to the maximum of the branch sizing factors. The loop sizing factor is applied to the loop design flow rate (if autosized) and to the loop pump flow rate (if autosized).

### Mixing User-Specified and Autosized Inputs[LINK]

Mixed user-specified and autosized inputs can be successfully used if the following points and suggestions are followed.

Each component is autosized independently. Thus user input for a flow rate in one component will have no effect on other components’ autosized flow rates. For instance, specifying the chilled water loop pump’s rated flow rate will have no effect on the autosizing of the chiller’s design evaporator flow rate or on the plant loop’s autosized maximum loop flow rate.

Within a component it is best to autosize all inputs are enter specified values for all inputs. For example, in a chiller, if only the nominal capaciity is user-specified, the autosized chilled water flow rate may not be consistent with the specified capacity.

Sizing information flows only from the sizing objects to the components. The sizing calculations have no knowledge of user-specified values in a component. The only exception to this rule is that plant loop sizing will collect all component design water flow rates whether autosized or user-specified.

If the user wants to specify a zone or system air flow rate it should be done using the Sizing:Zone and Sizing:System objects rather than done in the individual components.

The plant loop flow rates are sized from the total design demand of the components connected to each loop. The components demanding water need not be autosized for the plant loop autosizing to work successfully. So the user could specify all the air side components and autosize all the plant loops and plant components. Or specify the chilled water loop flow rate, chilled water pump inputs and chiller inputs and let the condenser loop and tower autosize.

The results of the component autosizing calculations are reported on the eplusout.eio file. For each component field that has been autosized the object type, object name, field description with unit, and value are printed out as comma separated data on a line beginning with Component Sizing. Examples of this are shown in the Output Details and Examples document.

The complete list of objects that have autosized fields is shown in the following table. Note that spaces may be inserted in object names to facilitate readability.

Table: Complete list of Objects with autosized Fields

Object Name|Object Name ———–|———– AirConditioner:VariableRefrigerantFlow|AirLoopHVAC AirLoopHVAC:Unitary:Furnace:HeatCool|AirLoopHVAC:Unitary:Furnace:HeatOnly AirLoopHVAC:UnitaryHeatCool|AirLoopHVAC:UnitaryHeatCool:VAVChangeoverBypass AirLoopHVAC:UnitaryHeatOnly|AirLoopHVAC:UnitaryHeatPump:AirToAir AirLoopHVAC:UnitaryHeatPump:AirToAir:MultiSpeed|AirLoopHVAC:UnitaryHeatPump:WaterToAir AirLoopHVAC:UnitarySystem|AirTerminal:DualDuct:ConstantVolume AirTerminal:DualDuct:VAV|AirTerminal:DualDuct:VAV:OutdoorAir AirTerminal:SingleDuct:ConstantVolume:CooledBeam|AirTerminal:SingleDuct:ConstantVolume:FourPipeInduction AirTerminal:SingleDuct:ConstantVolume:Reheat|AirTerminal:SingleDuct:ParallelPIU:Reheat AirTerminal:SingleDuct:SeriesPIU:Reheat|AirTerminal:SingleDuct:Uncontrolled AirTerminal:SingleDuct:VAV:HeatAndCool:NoReheat|AirTerminal:SingleDuct:VAV:HeatAndCool:Reheat AirTerminal:SingleDuct:VAV:NoReheat|AirTerminal:SingleDuct:VAV:Reheat AirTerminal:SingleDuct:VAV:Reheat:VariableSpeedFan|Boiler:HotWater Boiler:Steam|Branch Chiller:Absorption|Chiller:Absorption:Indirect Chiller:CombustionTurbine|Chiller:ConstantCOP Chiller:Electric|Chiller:Electric:EIR Chiller:Electric:ReformulatedEIR|Chiller:EngineDriven ChillerHeater:Absorption:DirectFired|ChillerHeater:Absorption:DoubleEffect ChillerHeaterPerformance:Electric:EIR|Coil:Cooling:DX:MultiSpeed Coil:Cooling:DX:SingleSpeed|Coil:Cooling:DX:SingleSpeed:ThermalStorage Coil:Cooling:DX:TwoSpeed|Coil:Cooling:DX:VariableRefrigerantFlow Coil:Cooling:DX:VariableSpeed|Coil:Cooling:Water Coil:Cooling:Water:DetailedGeometry|Coil:Cooling:WaterToAirHeatPump:EquationFit Coil:Cooling:WaterToAirHeatPump:VariableSpeedEquationFit|Coil:Heating:DX:MultiSpeed Coil:Heating:DX:SingleSpeed|Coil:Heating:DX:VariableRefrigerantFlow Coil:Heating:DX:VariableSpeed|Coil:Heating:Electric Coil:Heating:Electric:MultiStage|Coil:Heating:Gas Coil:Heating:Gas:MultiStage|Coil:Heating:Steam Coil:Heating:Water|Coil:Heating:WaterToAirHeatPump:EquationFit Coil:Heating:WaterToAirHeatPump:VariableSpeedEquationFit|CoilPerformance:DX:Cooling CondenserLoop|Controller:OutdoorAir Controller:WaterCoil|CoolingTower:SingleSpeed CoolingTower:TwoSpeed|CoolingTower:VariableSpeed CoolingTower:VariableSpeed:Merkel|EvaporativeCooler:Indirect:ResearchSpecial EvaporativeFluidCooler:SingleSpeed|EvaporativeFluidCooler:TwoSpeed Fan:ComponentModel|Fan:ConstantVolume Fan:OnOff|FanPerformance:NightVentilation Fan:VariableVolume|FluidCooler:SingleSpeed FluidCooler:TwoSpeed|HeaderedPumps:ConstantSpeed HeaderedPumps:VariableSpeed|HeatExchanger:AirToAir:SensibleAndLatent HeatExchanger:FluidToFluid|Humidifier:Steam:Electric HVACTemplate:Plant:Boiler|HVACTemplate:Plant:Chiller HVACTemplate:Plant:Tower|HVACTemplate:System:ConstantVolume HVACTemplate:System:DedicatedOutdoorAir|HVACTemplate:System:DualDuct HVACTemplate:System:PackagedVAV|HVACTemplate:System:Unitary HVACTemplate:System:UnitaryHeatPump:AirToAir|HVACTemplate:System:UnitarySystem HVACTemplate:System:VAV|HVACTemplate:System:VRF HVACTemplate:Zone:BaseboardHeat|HVACTemplate:Zone:ConstantVolume HVACTemplate:Zone:DualDuct|HVACTemplate:Zone:FanCoil HVACTemplate:Zone:IdealLoadsAirSystem|HVACTemplate:Zone:PTAC HVACTemplate:Zone:PTHP|HVACTemplate:Zone:Unitary HVACTemplate:Zone:VAV|HVACTemplate:Zone:VAV:FanPowered HVACTemplate:Zone:VAV:HeatAndCool|HVACTemplate:Zone:VRF HVACTemplate:Zone:WaterToAirHeatPump|PlantComponent:TemperatureSource PlantEquipmentOperation:ComponentSetpoint|PlantLoop Pump:ConstantSpeed|Pump:VariableSpeed Pump:VariableSpeed:Condensate|Sizing:System SolarCollector:FlatPlate:PhotovoltaicThermal|ThermalStorage:ChilledWater:Mixed ThermalStorage:ChilledWater:Stratified|UnitarySystemPerformance:HeatPump:Multispeed WaterHeater:Mixed|WaterHeater:Stratified ZoneHVAC:Baseboard:Convective:Electric|ZoneHVAC:Baseboard:Convective:Water ZoneHVAC:Baseboard:RadiantConvective:Electric|ZoneHVAC:Baseboard:RadiantConvective:Steam ZoneHVAC:Baseboard:RadiantConvective:Water|ZoneHVAC:EnergyRecoveryVentilator ZoneHVAC:EvaporativeCoolerUnit|ZoneHVAC:FourPipeFanCoil ZoneHVAC:HighTemperatureRadiant|ZoneHVAC:IdealLoadsAirSystem ZoneHVAC:LowTemperatureRadiant:Electric|ZoneHVAC:LowTemperatureRadiant:VariableFlow ZoneHVAC:OutdoorAirUnit|ZoneHVAC:PackagedTerminalAirConditioner ZoneHVAC:PackagedTerminalHeatPump|ZoneHVAC:TerminalUnit:VariableRefrigerantFlow ZoneHVAC:UnitHeater|ZoneHVAC:UnitVentilator ZoneHVAC:VentilatedSlab|ZoneHVAC:WaterToAirHeatPump ZoneHVAC:WindowAirConditioner|

### User or External Zone Design Flow Rate Inputs[LINK]

In EnergyPlus the autosizing calculations start with a calculation of the zone design air flow rates using zone by zone design day simulations. The resulting zone design air flow rates and daily air flow sequences are used in the subsequent HVAC and central plant air and fluid flow design calculations and in the component autosizing calculations. The user can override or change the calculated zone design air flow rates in several ways.

1. The user can enter a value for Sizing Factor in the Sizing:Parameters object (see description below).
2. The user can specify a zone level Zone Sizing Factor in each Sizing:Zone object.
3. For each zone the user can input a Cooling Design Air Flow Rate and/or a Heating Design Air Flow Rate (and specify Cooling Design Air Flow Method = Flow/Zone and Heating Design Air Flow Method = Flow/Zone). These user inputs override the calculated values. The program divides the user input cooling or heating design air flow rate by the calculated values and uses the result as a zone sizing factor to multiply all the elements in the design heating and cooling air flow and load sequences. From this point the design calculations proceed as usual.

### User or External System Design Flow Rate Inputs[LINK]

Using the results of the zone design air flow rate calculation (including any user input or altered flow rates) EnergyPlus proceeds to calculate central air system flow rates and cooling and heating loads. The results of this calculation can be overridden in the following way.

For each system (AirLoopHVAC](page-028.html#airloophvac)), in the corresponding [Sizing:System object, specify Cooling Design Air Flow Method to be Flow/System and input a value for Cooling Design Air Flow Rate. **Similarly for heating specify Heating Design Air Flow Method to be Flow/System and input a value for Heating Design Air Flow Rate.

This object allows for the outdoor air requirements to be defined in a common location for use by other objects. This object may be referenced by name from other objects (e.g., VAV terminal units) as required to identify an outdoor air quantity for use by that object. Note that a zone name Is not included as an input to this zone outdoor air definition and the number of people in a zone, zone floor area, and zone volume can only be determined after this object has been referenced by another. A single zone outdoor air definition may be referenced by multiple objects to specify that the same outdoor air requirements are used by those objects or multiple zone outdoor air objects may be defined and referenced by other objects as needed. If multiple zone outdoor air definitions are used, each outdoor air definition must have a unique name.

Unique identifying name. Any reference to this name by other objects will denote that the following outdoor air requirements will be used.

The input must be either Flow/Person, Flow/Area, Flow/Zone, AirChanges/Hour, Sum, or Maximum. Flow/Person means the program will use the input from the field Outdoor Air Flow per Person and the actual zone occupancy to calculate a zone outdoor air flow rate. Flow/Area means that the program will use the input from the field Outdoor Air Flow per Zone Floor Area and the actual zone floor area as the zone outdoor air flow rate. Flow/Zone means that the program will use the input of the field Outdoor Air Flow per Zone as the zone outdoor air flow rate. AirChanges/Hour means that the program will use the input from the field Air Changes per Hour and the actual zone volume (divided by 3600 seconds per hour) as the zone outdoor air flow rate. Sum means that the flows calculated from the fields Outdoor Air Flow per Person, Outdoor Air Flow per Area, Outdoor Air Flow per Zone, and Air Changes per Hour (using the associated conversions to m3/s for each field) will be added to obtain the zone outdoor air flow rate. Maximum means that the maximum flow derived from Outdoor Air Flow per Person, Outdoor Air Flow per Area, Outdoor Air Flow per Zone, and Air Changes per Hour (using the associated conversions to m3/s for each field) will be used as the zone outdoor air flow rate. The default is Flow/Person.

### Field: Outdoor Air Flow per Person[LINK]

The design outdoor air volume flow rate per person for this zone in cubic meters per second per person. The default is 0.00944 (20 cfm per person). An outdoor air flow rate is calculated based on the total number of people for all People statements assigned to the zone. Occupancy schedule values are not applied during sizing calculations and are applied during the remainder of the simulation. This input is used if Outdoor Air Method is one of Outdoor Air Flow per Person, Sum, or Maximum.

### Field: Outdoor Air Flow per Zone Floor Area[LINK]

The design outdoor air volume flow rate per square meter of floor area (units are m3/s-m2). This input is used if Outdoor Air Method is Flow/Area, Sum or Maximum. The default value for this field is 0.

### Field: Outdoor Air Flow per Zone[LINK]

The design outdoor air flow rate for this zone in cubic meters per second. This input field is used if Outdoor Air Method is Flow/Zone, Sum or Maximum. The default value for this field is 0.

### Field: Outdoor Air Flow Changes per Hour[LINK]

The design outdoor air volume flow rate in air changes per hour. This factor is used along with the Zone Volume and converted to cubic meters per second. This input field is used if Outdoor Air Method is AirChanges/Hour, Sum or Maximum. The default value for this field is 0.

### Field: Outdoor Air Flow Rate Fraction Schedule Name[LINK]

This field is the name of schedule that defines how outdoor air requirements change over time. The field is optional. If used, then the schedule values are multiplied by the outdoor air flow rate defined by the previous fields. The schedule values must be between 0 and 1, inclusive.

An IDF example:

DesignSpecification:OutdoorAir
Sum,                   !- Outdoor Air Method
0.00944,               !- Outdoor Air Flow per Person {m3/s}
0.00305,               !- Outdoor Air Flow per Zone Floor Area {m3/s-m2}
,                      !- Outdoor Air Flow per Zone {m3/s}
,                      !- Outdoor Air Flow Air Changes per Hour
OARequirements Sched;  !- Outdoor Air Flow Rate Fraction Schedule Name

Schedule:Compact,
OARequirements Sched,    !- Name
Any Number,              !- Schedule Type Limits Name
Through: 12/31,          !- Field 1
For: Weekdays SummerDesignDay WinterDesignDay,  !- Field 2
Until: 24:00, 1.0,       !- Field 4
For: AllOtherDays,       !- Field 5
Until: 24:00, 0.5;       !- Field 7

This object is used to describe the air distribution effectiveness and fraction of secondary recirculation air (return air not directly mixed with outdoor air) of a zone. It is referenced by the Sizing:Zone and Controller:MechanicalVentilation objects.

The unique user assigned name for an instance of this object. Any other object referencing this object will use this name.

### Field: Zone Air Distribution Effectiveness in Cooling Mode[LINK]

The positive numeric input for this field is the zone air distribution effectiveness when the zone is in cooling mode. Default value of this field is 1.0. ASHRAE Standard 62.1-2010 provides typical values.

### Field: Zone Air Distribution Effectiveness in Heating Mode[LINK]

The positive numeric input for this field is the zone air distribution effectiveness when the zone is in heating mode. Default value of this field is 1.0. ASHRAE Standard 62.1-2010 provides typical values as follows:

### Field: Zone Air Distribution Effectiveness Schedule Name[LINK]

This optional field input points to a schedule with values of zone air distribution effectiveness. It provides a more flexible way of specifying zone air distribution effectiveness if it changes with time and/or system operating status and controls. If the schedule is specified, the zone air distribution effectiveness in cooling mode and heating mode will be ignored.

### Field: Zone Secondary Recirculation Fraction[LINK]

The non-negative numeric input for this field is the fraction of a zone’s recirculation air that does not directly mix with the outdoor air. The zone secondary recirculation fraction Er is determined by the designer based on system configuration. For plenum return systems with secondary recirculation (e.g., fan-powered VAV with plenum return) Er is usually less than 1.0, although values may range from 0.1 to 1.2 depending upon the location of the ventilation zone relative to other zones and the air handler. For ducted return systems with secondary recirculation (e.g., fan-powered VAV with ducted return), Er is typically 0.0, while for those with system-level recirculation (e.g, dual-fan dual-duct systems with ducted return) Er is typically 1.0. For other system types, Er is typically 0.75. Minimum is 0.0, and default is 0.0 for single-path systems (also to maintain backward compatibility). For parallel fan-powered VAV systems, the secondary ventilation path only functions (Er > 0.0) when the fans in the VAV boxes operate, which is during heating. The local ventilation path and the benefits of secondary recirculation disappear during cooling, when the local parallel fans are off (Er = 0.0).

An example of this in an IDF context is shown:

DesignSpecification:ZoneAirDistribution,
1,                       !- Zone Air Distribution Effectiveness in Cooling Mode {dimensionless}
1,                       !- Zone Air Distribution Effectiveness in Heating Mode {dimensionless}
;                        !- Zone Air Distribution Effectiveness Schedule Name

This object allows the user to specify global heating and cooling sizing ratios. These ratios will be applied at the zone level to all of the zone heating and cooling loads and air flow rates. These new loads and air flow rates are then used to calculate the system level flow rates and capacities and are used in all component sizing calculations.

The user can also specify the width (in load timesteps) of a moving average window which can be used to smooth the calculated zone design flow sequences. The use of this parameter is described below.

The global heating sizing ratio applied to all of the zone design heating loads and air flow rates.

The global cooling sizing ratio applied to all of the zone design cooling loads and air flow rates

### Field: Timesteps in Averaging Window[LINK]

The number of load timesteps in the zone design flow sequence averaging window. The default is 1, in which case the calculated zone design flow rates are averaged over the load timestep.

The zone design air flow rate calculation is performed assuming a potentially infinite supply of heating or cooling air at a fixed temperature. Thus the calculated design air flow rate will always be able to meet any load or change in load no matter how large or abrupt. In reality air flow rates are limited by duct sizes and fan capacities. The idealized zone design flow calculation may result in unrealistically large flow rates, especially if the user is performing the sizing calculations using thermostat schedules with night setup or setback. The calculated zone design flow rates are always averaged over the load timestep. The user may want to perform a broader average to mitigate the effect of thermostat setup and setback and prevent the warm up or cool down flow rates from dominating the design flow rate calculation.. Specifying the width of the averaging window allows the user to do this.

For example, if the load calculation timestep is 15 minutes and the user specifies the Timesteps in Averaging Window to be 4, the zone design air flows will be averaged over a time period of 1 hour. Specifying 8 would result in averaging over a 2 hour period.

The sizing factors and the averaging window size are reported out on the eplusout.eio file. An example is:

! <Load Timesteps in Zone Design Calculation Averaging Window>, Value
Timesteps in Averaging Window,    1
! <Heating Sizing Factor Information>, Sizing Factor ID, Value
Heating Sizing Factor, Global,   1.3000
Heating Sizing Factor, Zone SPACE1-1,   1.3000
Heating Sizing Factor, Zone SPACE2-1,   1.3000
Heating Sizing Factor, Zone SPACE3-1,   1.3000
Heating Sizing Factor, Zone SPACE4-1,   1.3000
Heating Sizing Factor, Zone SPACE5-1,   1.3000
! <Cooling Sizing Factor Information>, Sizing Factor ID, Value
Cooling Sizing Factor, Global,   1.3000
Cooling Sizing Factor, Zone SPACE1-1,   1.3000
Cooling Sizing Factor, Zone SPACE2-1,   1.3000
Cooling Sizing Factor, Zone SPACE3-1,   1.3000
Cooling Sizing Factor, Zone SPACE4-1,   1.3000
Cooling Sizing Factor, Zone SPACE5-1,   1.3000

As described early in the document (see: EnergyPlus Output Processing), the user may select the “style” for the sizing result files (epluszsz., eplusssz.). This object applies to all sizing output files.

OutputControl:Sizing:Style,
\memo default style for the Sizing output files is comma -- this works well for
\memo importing into spreadsheet programs such as Excel(tm) but not so well for word
\memo processing progams -- there tab may be a better choice.  fixed puts spaces between
\memo the "columns"
\unique-object
A1; \field Column Separator
\required-field
\type choice
\key Comma
\key Tab
\key Fixed

For this field, the desired separator for columns is entered. “Comma” creates comma separated fields/columns in the outputs (eplus.csv files are created). “Tab” creates tab separated fields/columns in the outputs (eplus.tab files are created). “Fixed” creates space separated fields/columns in the outputs (eplus.txt files are created) but these are not necessarily lined up for easy printing.

Note that both tab and comma separated files easily import into Excel™ or other spreadsheet programs. The tab delimited files can also be viewed by text editors, word processing programs and easily converted to “tables” within those programs.

The Sizing:Zone object provides the data needed to perform a zone design air flow calculation for a single zone. This calculation assumes a variable amount of supply air at a fixed temperature and humidity. The information needed consists of the zone inlet supply air conditions: temperature and humidity ratio for heating and cooling. The calculation is done for every design day included in the input. The maximum cooling load and air flow and the maximum heating load and air flow are then saved for the system level design calculations and for the component automatic sizing calculations.

The Sizing:Zone object is also the place where the user can specify the design outdoor air flow rate by referencing the name of a design specification outdoor air object. This can be specified in a number of ways (ref. DesignSpecification:OutdoorAir).This data is saved for use in the system sizing calculation or for sizing zone components that use outdoor air.

The user can also place limits on the heating and design cooling air flow rates. See Heating Design Air Flow Method and Cooling Design Air Flow Method below and the explanations of the various heating and cooling flow input fields.

The name of the Zone corresponding to this Sizing:Zone object. This is the zone for which the design air flow calculation will be made using the input data of this Sizing:Zone Object.

### Field: Zone Cooling Design Supply Air Temperature Input Method[LINK]

The input must be either SupplyAirTemperature or TemperatureDifference. SupplyAirTemperature means that the user inputs from the fields of Zone Cooling Design Supply Air Temperature will be used to determine the zone cooling design air flow rates. TemperatureDifference means that the user inputs from the fields of Zone Cooling Design Supply Air Temperature Difference will be used to determine the zone cooling design air flow rates.

### Field: Zone Cooling Design Supply Air Temperature[LINK]

The supply air temperature in degrees Celsius for the zone cooling design air flow rate calculation. Air is supplied to the zone at this temperature during the cooling design day simulation, The zone load is met by varying the zone air flow rate. The maximum zone flow rate is saved as the zone cooling design air flow rate. This field is only used when Zone Cooling Design Supply Air Temperature Input Method = SupplyAirTemperature.

### Field: Zone Cooling Design Supply Air Temperature Difference[LINK]

The temperature difference between cooling design supply air temperature and room air temperature in degrees Celsius for the zone cooling design air flow rate calculation. Air is supplied to the zone at this temperature during the cooling design day simulation. The zone load is met by varying the zone air flow rate. The maximum zone flow rate is saved as the zone cooling design air flow rate. This field is only used when Zone Cooling Design Supply Air Temperature Input Method = TemperatureDifference.

### Field: Zone Heating Design Supply Air Temperature Input Method[LINK]

The input must be either SupplyAirTemperature or TemperatureDifference. SupplyAirTemperature means that the user inputs from the fields of Zone Heating Design Supply Air Temperature will be used to determine the zone heating design air flow rates. TemperatureDifference means that the user inputs from the fields of Zone Heating Design Supply Air Temperature Difference will be used to determine the zone heating design air flow rates.

### Field: Zone Heating Design Supply Air Temperature[LINK]

The supply air temperature in degrees Celsius for the zone heating design air flow rate calculation. Air is supplied to the zone at this temperature during the heating design day simulation, The zone load is met by varying the zone air flow rate. The maximum zone flow rate is saved as the zone heating design air flow rate. This field is only used when Zone Heating Design Supply Air Temperature Input Method = SupplyAirTemperature.

### Field: Zone Heating Design Supply Air Temperature Difference[LINK]

The temperature difference between heating design supply air temperature and room air temperature in degrees Celsius for the zone heating design air flow rate calculation. Air is supplied to the zone at this temperature during the heating design day simulation. The zone load is met by varying the zone air flow rate. The maximum zone flow rate is saved as the zone heating design air flow rate. This field is only used when Zone Heating Design Supply Air Temperature Input Method = TemperatureDifference.

### Field: Zone Cooling Design Supply Air Humidity Ratio[LINK]

The humidity ratio in kilograms of water per kilogram of dry air of the supply air in the zone cooling design air flow rate calculation.

### Field: Zone Heating Design Supply Air Humidity Ratio[LINK]

The humidity ratio in kilograms of water per kilogram of dry air of the supply air in the zone heating design air flow rate calculation.

### Field: Design Specification Outdoor Air Object Name[LINK]

This alpha field specifies the name of a DesignSpecification:OutdoorAir object which specifies the design outdoor air flow rate for the zone.

### Field: Zone Heating Sizing Factor[LINK]

This input is a zone level heating sizing ratio. The zone design heating air flow rates and loads will be multiplied by the number input in this field. This input overrides the building level sizing factor input in the Sizing:Parameters object. And, of course, if this field is blank or zero, the global heating sizing factor from the Sizing:Parameters object is used.

### Field: Zone Cooling Sizing Factor[LINK]

This input is a zone level cooling sizing ratio. The zone design cooling air flow rates and loads will be multiplied by the number input in this field. This input overrides the building level sizing factor input in the Sizing:Parameters object. And, of course, if this field is blank or zero, the global cooling sizing factor from the Sizing:Parameters object is used.

### Field: Cooling Design Air Flow Method[LINK]

The input must be either Flow/Zone](page-011.html#zone), DesignDay, or DesignDayWithLimit. Flow/Zone means that the program will use the input of the field Cooling Design Air Flow Rate as the zone design cooling air flow rate. DesignDay means the program will calculate the zone design cooling air flow rate using the [Sizing:[Zone](#zone) input data and a design day simulation without imposing any limits other than those set by the minimum outside air requirements. DesignDayWithLimit means that the maximum from Cooling Minimum Air Flow per Zone Floor Area and Cooling Minimum Air Flow will set a lower limit on the **design maximum cooling air flow rate. The default method is DesignDay: i.e., the program uses the calculated design values subject to ventilation requirements.

### Field: Cooling Design Air Flow Rate[LINK]

The design zone cooling air flow rate in cubic meters per second. This input is used if Cooling Design Air Flow Method is specified as Flow/Zone. This value will be multiplied by the global or zone sizing factor and by zone multipliers.

### Field: Cooling Minimum Air Flow per Zone Floor Area[LINK]

The minimum zone cooling volumetric flow rate per square meter (units are m3/s-m2). This field is used when Cooling Design Air Flow Method is specified as DesignDayWithLimit. In this case it sets a lower bound on the zone design cooling air flow rate. In all cases the maximum flow derived from Cooling Minimum Air Flow per Zone Floor Area, Cooling Minimum Air Flow, and Cooling Minimum Air Flow Fraction is used to set a minimum supply air flow rate for the zone for VAV systems. The default is .000762, corresponding to .15 cfm/ft2. The applicable sizing factor is not applied to this value.

### Field: Cooling Minimum Air Flow[LINK]

The minimum zone cooling volumetric flow rate in m3/s. This field is used when Cooling Design Air Flow Method is specified as DesignDayWithLimit. In this case it sets a lower bound on the zone design cooling air flow rate. In all cases the maximum flow derived from Cooling Minimum Air Flow per Zone Floor Area, Cooling Minimum Air Flow, and Cooling Minimum Air Flow Fraction is used to set a minimum supply air flow rate for the zone for VAV systems. The default is zero. The applicable sizing factor is not applied to this value.

### Field: Cooling Minimum Air Flow Fraction[LINK]

The minimum zone design cooling volumetric flow rate expressed as a fraction of the zone design cooling volumetric flow rate. . In all cases the maximum flow derived from Cooling Minimum Air Flow per Zone Floor Area, Cooling Minimum Air Flow, and Cooling Minimum Air Flow Fraction is used to set a minimum supply air flow rate for the zone for VAV systems. The default is zero. This input is currently used in sizing the fan minimum flow rate. It does not currently affect other component autosizing.

### Field: Heating Design Air Flow Method[LINK]

The input must be either Flow/Zone](page-011.html#zone), DesignDay, or DesignDayWithLimit. Flow/Zone means that the program will use the input of the field Heating Design Air Flow Rate as the zone design heating air flow rate. DesignDay means the program will calculate the zone design heating air flow rate using the [Sizing:[Zone](#zone) input data and a design day simulation without imposing any limits other than those set by the minimum outside air requirements. DesignDayWithLimit means that the maximum from Heating Maximum Air Flow per Zone Floor Area and Heating Maximum Air Flow will set a lower limit on the **design maximum heating air flow rate. The default method is DesignDay: i.e., the program uses the calculated design values subject to ventilation requirements.

### Field: Heating Design Air Flow Rate[LINK]

The design zone heating air flow rate in cubic meters per second. This input is used if Heating Design Air Flow Method is specified as Flow/Zone. This value will be multiplied by the global or zone sizing factor and by zone multipliers.

### Field: Heating Maximum Air Flow per Zone Floor Area[LINK]

The maximum zone heating volumetric flow rate per square meter (units are m3/s-m2). This field is used when Heating Design Air Flow Method is specified as DesignDayWithLimit. In this case it sets an upper bound on the zone design heating air flow rate. For this and the next two input fields, the maximum flow derived from Heating Maximum Air Flow per Zone Floor Area, Heating Maximum Air Flow, and Heating Maximum Air Flow Fraction is used to set a maximum heating supply air flow rate for the zone for VAV systems. The default is .002032, corresponding to .40 cfm/ft2. If the maximum heating design flow rate calculated using these input fields is greater than the design heating flow rate calculated during sizing, these input fields have no impact on sizing. It may be more appropriate to select only one of these three fields to calculate the maximum heating design flow rate (i.e., if one ore more of these three fields is 0, it will not be used in calculating the maximum heating design flow rate).

### Field: Heating Maximum Air Flow[LINK]

The maximum zone heating volumetric flow rate in m3/s. This field is used when Heating Design Air Flow Method is specified as DesignDayWithLimit. In this case it sets an upper bound on the zone design heating air flow rate. For this field and the two input fields just prior to and after this field,,the maximum flow derived from Heating Maximum Air Flow per Zone Floor Area, Heating Maximum Air Flow, and Heating Maximum Air Flow Fraction is used to set a maximum heating supply air flow rate for the zone for VAV systems. The default is .1415762, corresponding to 300 cfm. If the maximum heating design flow rate calculated using these input fields is greater than the design heating flow rate calculated during sizing, these input fields have no impact on sizing. It may be more appropriate to select only one of these three fields to calculate the maximum heating design flow rate (i.e., if one ore more of these three fields is 0, it will not be used in calculating the maximum heating design flow rate).

### Field: Heating Maximum Air Flow Fraction[LINK]

The maximum zone design heating volumetric flow rate expressed as a fraction of the zone design cooling volumetric flow rate. For this and the previous two input fields, the maximum flow derived from Heating Maximum Air Flow per Zone Floor Area, Heating Maximum Air Flow, and Heating Maximum Air Flow Fraction is used to set a maximum heating supply air flow rate for the zone for VAV systems. The default is 0.3. If the maximum heating design flow rate calculated using these input fields is greater than the design heating flow rate calculated during sizing, these input fields have no impact on sizing. It may be more appropriate to select only one of these three fields to calculate the maximum heating design flow rate (i.e., if one ore more of these three fields is 0, it will not be used in calculating the maximum heating design flow rate).

### Field: Design Specification Zone Air Distribution Object Name[LINK]

The name of the DesignSpecification:ZoneAirDistribution object, defining the air distribution effectiveness and secondary recirculation air fraction, that applies to the zone or zone list. This object may be used for the same zone in the Controller:MechanicalVentilation](page-051.html#controllermechanicalventilation) object if no such [DesignSpecification:ZoneAirDistribution object is specified.

An IDF example:

Sizing:Zone,
SPACE5-1,                !- Name of a zone
14.,                     !- Zone cooling design supply air temperature {C}
50.,                     !- Zone heating design supply air temperature {C}
0.009,                   !- Zone cooling design supply air humidity ratio {kg-H2O/kg-air}
0.004,                   !- Zone heating design supply air humidity ratio {kg-H2O/kg-air}
DSOA1,                   !- Design Specification Outdoor Air Object Name
0.0,                     !- zone heating sizing factor
0.0,                     !- zone cooling sizing factor
designdaywithlimit,      !- Cooling Design Air Flow Method
,                        !- cooling design air flow rate {m3/s}
,                        !- Cooling Minimum Air Flow per zone area {m3/s-m2}
,                        !- Cooling Minimum Air Flow {m3/s}
,                        !- fraction of the cooling design air flow rate
designday,               !- Heating Design Air Flow Method
,                        !- heating design air flow rate {m3/s}
,                        !- heating max air flow per zone area {m3/s-m2}
,                        !- heating max air flow {m3/s}
,                        !- fraction of the cooling design air flow rate
DSZADO1;                 !- Design Specification Zone Air Distribution Object Name

DesignSpecification:OutdoorAir,
DSOA1,                   !- Name
SUM,                     !- Outdoor Air Method
0.00236,                 !- Outdoor Air Flow per Person
0.000305,                !- Outdoor Air Flow per Zone Floor Area
0.0,                     !- Outdoor Air Flow per Zone
0.0,                     !- Outdoor Air Flow Air Changes per Hour
;                        !- Outdoor Air Flow Rate Fraction Schedule Name

DesignSpecification:ZoneAirDistribution,
1.0,                     !- Zone Air Distribution Effectiveness in Cooling Mode
1.0,                     !- Zone Air Distribution Effectiveness in Heating Mode
,                        !- Zone Air Distribution Effectiveness Schedule Name
0.3;                     !- Zone Secondary Recirculation Fraction

The zone design air flow rates and loads are output onto the local file “epluszsz.” where is the extension from the sizing style object (default is csv – a comma separated file epluszsz.csv). The columns are clearly labeled. It will easily import into Excel or other spreadsheet program that accepts delimited files. All of these values are design air flow rates and loads calculated by the program. No sizing factors have been applied.

The calculated zone design air flow rates and the user input or altered zone design air flow rates are also reported on the eplusout.eio file. The values are printed out for each zone as comma separated records beginning with Zone Sizing. Items output on the eio file are: zone name, load type (heating or cooling), design load, calculated design air flow rate, user design air flow rate, design day name, time of peak, outside temperature at peak, outside humidity ratio at peak.

The Sizing:System object contains the input 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 every design day in the input file and the resulting maximum heating and cooling air flow rates and capacities are saved for use 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.

The name of the AirLoopHVAC](page-028.html#airloophvac) corresponding to this [Sizing:System object. This is the air system for which the design calculation will be made using the input data of this Sizing:System Object.

The user specified type of load on which to size the central system. The choices are Sensible, Latent, Total and VentilationRequirement. Only Sensible and VentilationRequirement are operational. Sensible means that the central system supply air flow rate will be determined by combining the zone design air flow rates, which have been calculated to meet the zone sensible loads from the design days. VentilationRequirement means that the central system supply air flow rate will be determined by the system ventilation requirement.

### Field: Design Outdoor Air Flow Rate[LINK]

The design outdoor air flow rate in cubic meters per second. 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 outdoor air flow rate will be taken from the sum of the zone outdoor air flow rates or calculated based on the System Outdoor Air Method selection (field below).

### Field: Minimum System Air Flow Ratio[LINK]

The design minimum central air flow ratio. This ratio is the minimum system air flow rate divided by the maximum system air flow rate. The value must be between 0 and 1. For constant volume systems the ratio should be set to 1. Note that this ratio should be set to reflect what the user expects the system flow rate to be when maximum heating demand occurs. This ratio 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.

The design air temperature exiting the preheat coil (if any) in degrees Celsius.

### Field: Preheat Design Humidity Ratio[LINK]

The design humidity ratio exiting the preheat coil (if any) in kilograms of water per kilogram of dry air. (kgWater/kgDryAir)

The design air temperature exiting the precooling coil (if any) in degrees Celsius.

### Field: Precool Design Humidity Ratio[LINK]

The design humidity ratio exiting the precooling coil (if any) in kilograms of water per kilogram of dry air. (kgWater/kgDryAir)

### Field: Central Cooling Design Supply Air Temperature[LINK]

The design supply air temperature for cooling in degrees Celsius. This should be the temperature of the air exiting the central cooling coil.

### Field: Central Heating Design Supply Air Temperature[LINK]

The design supply air temperature for heating in degrees Celsius. 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.

If the input is coincident the central system air flow rate will be sized on the sum of the coincident zone air flow rates. If the input is noncoincident the central system air flow rate will be sized on the sum of the noncoincident zone air flow rates. The default is noncoincident.

### Field: 100% Outdoor Air in Cooling[LINK]

Entering Yes means the system will be sized for cooling using 100% outdoor air. Entering No means the system will be sized for cooling using minimum outside air (the default).

### Field: 100% Outdoor Air in Heating[LINK]

Entering Yes means the system will be sized for heating using 100% outdoor air. Entering No means the system will be sized for heating using minimum outside air (the default).

### Field: Central Cooling Design Supply Air Humidity Ratio[LINK]

The design humidity ratio in kilograms of water per kilogram of dry air at the exit of the central cooling coil. (kgWater/kgDryAir) The default is .008.

### Field: Central Heating Design Supply Air Humidity Ratio[LINK]

The design humidity ratio in kilograms of water per kilogram of dry air at the exit of the central heating coil. (kgWater/kgDryAir) The default is .008.

### Field: Cooling Design Air Flow Method[LINK]

The input must be either DesignDay or Flow/System. DesignDay means the program will calculate the system design cooling air flow rate using the System Sizing input data and a design day simulation. Flow/System means that the program will use the input of the field Cooling Design Air Flow Rate as the system design cooling air flow rate. The default method is DesignDay: i.e., the program uses the calculated design values.

### Field: Cooling Design Air Flow Rate[LINK]

The design system cooling air flow rate in cubic meters per second. This input is an alternative to using the program calculated value. This input is used if Cooling Design Air Flow Method is 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.

### Field: Heating Design Air Flow Method[LINK]

The input must be either DesignDay or Flow/System. DesignDay means the program will calculate the system design heating air flow rate using the System Sizing input data and a design day simulation. Flow/System means that the program will use the input of the field Heating Design Air Flow Rate as the system design heating air flow rate. . The default method is DesignDay: i.e., the program uses the calculated design values.

### Field: Heating Design Air Flow Rate[LINK]

The design system heating air flow rate in cubic meters per second. This input is an alternative to using the program calculated value. This input is used if Heating Design Air Flow Method is 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.

### Field: System Outdoor Air Method[LINK]

The method used to calculate the system minimum outdoor air flow. The two choices are ZoneSum and VentilationRateProcedure (VRP). ZoneSum sums the outdoor air flows across all zones served by the system. VRP uses the multi-zone equations defined in 62.1-2007 to calculate the system outdoor air flow. VRP considers zone air distribution effectiveness and zone diversification of outdoor air fractions.

### Field: Zone Maximum Outdoor Air Fraction[LINK]

This positive numeric input is the zone maximum outdoor air fraction. For an air loop, when a zone requires outdoor air higher than the user specified Zone Maximum Outdoor Air Fraction, the zone supply air flow will be increased to cap the outdoor air fraction at the maximum value. This allows the system level outdoor air flow to be reduced while the total supply air flow increases. Valid values are from 0 to 1.0. Default is 1.0 which indicates zones can have 100% outdoor air maintaining backward compatibility. This inputs work for constant volume air systems, single and dual duct VAV systems.

An IDF example:

Sizing:System,
VAV Sys 1,               !- name of an AirLoopHVAC object
sensible,                !- type of load to size on
autosize,                !- Design (minimum) outside air volumetric flow rate {m3/s}
0.3,                     !- minimum system air flow ratio
4.5,                     !- Preheat design temperature {C}
.008,                    !- Preheat design humidity ratio {kgWater/kgDryAir}
11.0,                    !- Precool design temperature {C}
.008,                    !- Precool design humidity ratio {kgWater/kgDryAir}
12.8,                    !- Central cooling design supply air temperature {C}
16.7,                    !- Central heating design supply air temperature {C}
noncoincident,           !- Sizing Option
no,                      !- Cooling 100% Outside Air
no,                      !- Heating 100% Outside Air
0.008,                   !- Central cooling design supply air humidity ratio {kgWater/kgDryAir}
0.008,                   !- Central heating design supply air humidity ratio {kgWater/kgDryAir}
designday,               !- Cooling Design Air Flow Method
0,                       !- cooling design air flow rate {m3/s}
designday,               !- Heating Design Air Flow Method
0,                       !- heating design air flow rate {m3/s}
ZoneSum,                 !- System Outdoor Air Method
0.5;                     !- Zone Maximum Outdoor Air Fraction

The system design air flow rates and heating and cooling capacities are output onto the local file “eplusssz.” where is the extension from the sizing style object (default is csv – a comma separated file eplusssz.csv). The columns are clearly labeled. It will easily import into Excel or other spreadsheet program that accepts delimited files. The results are calculated values and do not include any user input system flow rates.

The calculated system design air flow rates and the user input system design air flow rates are also reported on the eplusout.eio file. The values are printed out for each system as comma separated records beginning with System Sizing. An example is:

! <System Sizing Information>, System Name, Field Description, Value
System Sizing, VAV SYS 1, Calculated Cooling Design Air Flow Rate [m3/s],   1.3194
System Sizing, VAV SYS 1, User Cooling Design Air Flow Rate [m3/s],   1.5000
System Sizing, VAV SYS 1, Calculated Heating Design Air Flow Rate [m3/s],  0.90363
System Sizing, VAV SYS 1, User Heating Design Air Flow Rate [m3/s],   1.0000

The Sizing:Plant object contains the input needed for the program to calculate plant loop flow rates and equipment capacities when autosizing. This information is initially used by components that use water for heating or cooling such as hot or chilled water coils to calculate their maximum water flow rates. These flow rates are then summed for use in calculating the Plant Loop flow rates.

The program will size any number of chilled water, hot water, condenser water and other plant loops. There should be one Sizing:Plant object for each plant loop that is to be autosized.

### Field: Plant or Condenser Loop Name[LINK]

The name of a Plant Loop or Condenser Loop object corresponding to this Sizing:Plant object. This is the plant loop for which this data will be used for calculating the loop flow rate.

The possible inputs are Heating, Steam, Cooling, or Condenser.

### Field: Design Loop Exit Temperature[LINK]

The water temperature in degrees Celsius at the exit of the supply side of the plant loop, Thus this is the temperature of the water supplied to the inlet of chilled or hot water coils and other equipment that places loads on a plant loop.

### Field: Loop Design Temperature Difference[LINK]

The design temperature rise (for cooling or condenser loops) or fall (for heating loops) in degrees Celsius across the demand side of a plant loop. This temperature difference is used by component models to determine flow rates required to meet design capacities. Larger values lead to smaller design flow rates.

An IDF example:

Sizing:Plant,
Chilled Water Loop, ! name of loop
Cooling,            ! type of loop
7.22,               ! chilled water supply temperature
6.67;               ! chilled water delta T