Stencil: Zone HVAC Stencil: Ideal Loads System
Type: Unitary Zone Equipment
Sub Type: Ideal Loads Air System
EnergyPlus Object - ZoneHVAC:IdealLoadsAirSystem
The simplest piece of zone equipment is the ZoneHVAC:IdealLoadsAirSystem component. ZoneHVAC:IdealLoadsAirSystem is used in situations where the user wishes to study the performance of a building without modeling a full HVAC system. In such a case, the Ideal Loads Air System is usually the sole conditioning component: the user does not need to specify air loops, water loops, etc. All that is needed for the ideal system are zone controls, zone equipment configurations, and the ideal loads system component.
This component can be operated with infinite or finite heating and cooling capacity. For either mode – infinite or limited capacity – the user can also specify on/off schedules for heating and cooling and outdoor air controls. There are also optional controls for dehumidification, humidification, economizer, and heat recovery. This component may be used in combination with other HVAC equipment serving the same zone.
This component can be thought of as an ideal unit that mixes air at the zone exhaust condition with the specified amount of outdoor air and then adds or removes heat and moisture at 100% efficiency in order to produce a supply air stream at the specified conditions. The energy required to condition the supply air is metered and reported as DistrictHeating and DistrictCooling.
Notes: The ideal loads system uses the zone return node or an optional zone exhaust node to extract air from the zone. Every zone served by an HVAC component must have a return air node, even though this node may not be connected to anything.
The ideal loads system was significantly expanded in version 7.0 (October 2011). As part of this upgrade, any change in the moisture content of the supply air stream results in a latent cooling (dehumidification) or latent heating (humidification) load which is metered as DistrictCooling and DistrictHeating energy consumption. Prior to version 7.0, when the ideal loads system was in heating mode, only the energy for sensible heating was metered. This results in significant changes in reported energy use compared to earlier versions, especially when using the ConstantSupplyHumidityRatio option for Humidification Control Type.
Older idf files which are transitioned to version 7.0 will automatically be set to use the ConstantSupplyHumidityRatio option for both dehumidification and humidification controls, because this is equivalent to the controls used in the older version of this system. However, the user should review all of the humidity control options and select the one which best reflects the goal of the simulation.
The table shows the properties that are displayed when the component is selected while in diagram mode. The second column shows the selection options available that are dictated by EnergyPlus or it shows the source for the library entries that are displayed in the drop down list.
| Property Name | Value Sources/Options |
|
Name |
Simergy provides unique name (editable) |
|
Availability Schedule Name |
|
|
Maximum Heating Supply Air Temperature |
32C-Min; 212C-Max; 122C-default |
|
Minimum Cooling Supply Air Temperature |
-148C-Min; 122C-Max; 5.4C-default |
|
Maximum Heating Supply Air Humidity Ratio |
0-Min; 0.02-default |
|
Minimum Cooling Supply Air Humidity Ratio |
0-Min; 0.01-default |
|
Heating Limit |
Limit Flow Rate and Capacity Limit Capacity Limit Flow Rate No Limit (default) |
|
Maximum Heating Air Flow Rate |
0-Min; Autosize |
|
Maximum Sensible Heating Capacity |
0-Min; Autosize |
|
Cooling Limit |
Limit Flow Rate and Capacity Limit CapacityLimit Flow Rate No Limit (default) |
|
Maximum Cooling Air Flow Rate |
0-Min; Autosize |
|
Maximum Sensible Cooling Capacity |
0-Min; Autosize |
|
Heating Availability Schedule Name |
|
|
Cooling Availability Schedule Name |
|
|
Dehumidification Control Type |
Constant Supply Humidity Ratio None Humidistat Constant Sensible Heat Ratio |
|
Cooling Sensible Heat Ratio |
0-Min; 1-Max; 0.7-default |
|
Humidification Control Type |
Constant Supply Humidity Ratio None Humidistat |
|
Design Specification Outdoor Air Object Name |
|
|
Demand Controlled Ventilation Type |
CO2 Setpoint Occupancy Schedule None |
|
Outdoor Air Economizer Type |
Differential Enthlapy Differential Dry Bulb None |
|
Heat Recovery Type |
Enthalpy Sensible None |
|
Sensible Heat Recovery Effectiveness |
0-Min; 1-Max; 0.7-default |
|
Latent Heat Recovery Effectiveness |
0-Min; 1-Max; 0.65-default |
Simergy automatically defines a unique name for each component. This can be changed by the user if desired.
Schedule that this component will operate or is available to operate.
The maximum air temperature (degrees C) of the air used for heating the zone. The default is 50C (122F).
The minimum air temperature (degrees C) of the air used for cooling the zone. The default is 13C (55.4F).
The maximum humidity ratio (kg of water per kg of dry air) of the hot supply air. The default is 0.0156 kg-H2O/kg-air which corresponds to a 20%RH at 50C (122F) dry bulb.
The minimum humidity ratio (kg of water per kg of dry air) of the cool supply air. The default is 0.0077 kg-H2O/kg-air which corresponds to a 10C (50F) dew point.
The input must be either LimitFlowRate, LimitCapacity, LimitFlowRateAndCapacity or NoLimit. LimitFlowRate means that the heating supply air flow rate will be limited to the value specified in the next input field. LimitCapacity means that the sensible heating capacity will be limited to the value specified in the Maximum Sensible Heating Capacity field. LimitFlowRateAndCapacity means that both flow rate and capacity will be limited. NoLimit (the default) means that there will not be any limit on the heating supply air flow rate or capacity and the subsequent two fields will be ignored.
The maximum heating supply air flow rate in cubic meters per second if heating limit is set to LimitFlowRate or LimitFlowRateAndCapacity . This field may be autosized. This field is ignored if heating limit is set to NoLimit or LimitCapacity. If blank, there is no limit.
The maximum allowed sensible heating capacity in Watts if Heating Limit is set to LimitCapacity or LimitFlowRateAndCapacity. This field may be autosized. If blank, there is no limit. If Heating Limit is set to NoLimit or LimitFlowRate, this field is ignored.
The input must be either LimitFlowRate, LimitCapacity, LimitFlowRateAndCapacity or NoLimit. LimitFlowrate means that the cooling supply air flow rate will be limited to the value specified in the next input field. LimitCapacity means that the total cooling capacity will be limited to the value specified in the Maximum Total Cooling Capacity field. LimitFlowRateAndCapacity means that both flow rate and capacity will be limited. NoLimit (the default) means that there will not be any limit on the cooling supply air flow rate or capacity and the subsequent two fields will be ignored.
The maximum cooling supply air flow rate in cubic meters per second if Cooling Limit is set to LimitFlowRate or LimitFlowRateAndCapacity. This field may be autosized. This field is ignored if cooling limit is set to NoLimit or LimitCapacity. If blank, there is no limit. If Cooling Limit is set to NoLimit, this field is ignored. This field is required if Outdoor Air Control Type is TemperatureEconomizer in order to establish an upper limit on outdoor air flow when the economizer is active.
The maximum allowed total (sensible plus latent) cooling capacity in Watts if Cooling Limit is set to LimitCapacity or LimitFlowRateAndCapacity. This field may be autosized. If blank, there is no limit. If Cooling Limit is set to NoLimit or LimitFlowRate, this field is ignored.
The name of a schedule (ref: Schedule) that denotes whether heating is available. A schedule value greater than 0 (usually 1 is used) indicates that heating and humidification are available. A value less than or equal to 0 (usually 0 is used) denotes that heating and humidification are not available. If blank, heating and humidification are always available.
The name of a schedule (ref: Schedule) that denotes whether cooling is available. A schedule value greater than 0 (usually 1 is used) indicates that cooling and dehumidification are available. A value less than or equal to 0 (usually 0 is used) denotes that cooling and dehumidification is not available. If blank, cooling and dehumidification are always available.
Select from ConstantSensibleHeatRatio, Humidistat, None, or ConstantSupplyHumidityRatio. ConstantSensibleHeatRatio (the default) means that the ideal loads system will be controlled to meet the sensible cooling load, and the latent cooling rate will be computed using a constant sensible heat ratio (SHR) (see next field). Humidistat means that there is a ZoneControl:Humidistat for this zone and the ideal loads system will attempt to meet the humidistat request (i.e. will dehumidify according to the Dehumidifying Relative Humidity Schedule in the ZoneControl:Humidistat object). None means that there is no dehumidification. ConstantSupplyHumidityRatio means that during cooling the supply air will always be at the Minimum Cooling Supply Humidity Ratio. For ConstantSensibleHeatRatio and Humidistat, if the mixed air humidity ratio is less than the target humidity ratio, then the mixed air humidity ratio will be used. For all options, the supply air humidity ratio will never be allowed to exceed saturation at the supply dry bulb temperature.
The selected dehumidification control type is always applied when the unit is in cooling mode. If the unit is in deadband mode (not actively heating the supply air) control type Humidistat will be active. If the unit is in heating mode, control type Humidistat will be active if the Humidification Control Type field below is set to Humidistat or None.
This allows the ideal loads system to heat and dehumidify at the same time.
When the Dehumidification Control Type is set to ConstantSensibleHeatRatio the ideal loads system will be controlled to meet the sensible cooling load, and the latent cooling rate will be computed using the value of Cooling Sensible Heat Ratio (SHR), where SHR = Sensible Cooling divided by Total Cooling (sensible plus latent). The default is 0.7. If Dehumidification Control Type is set to something other than ConstantSensibleHeatRatio then this field will be ignored.
Select from None, Humidistat, or ConstantSupplyHumidityRatio. None means that there is no humidification. Humidistat means that there is a ZoneControl:Humidistat for this zone and the ideal loads system will attempt to meet the humidistat request (i.e., humidify according to the Humidifying Relative Humidity Setpoint Schedule in the ZoneControl:Humidistat object). ConstantSupplyHumidityRatio means that during heating the supply air will always be at the Maximum Heating Supply Humidity Ratio. The default is None. For Humidistat, if the mixed air humidity ratio is greater than the target humidity ratio, then the mixed air humidity ratio will be used. For all options, the supply air humidity ratio will never be allowed to exceed saturation at the supply dry bulb temperature.
The selected humidification control type is always applied when the unit is in heating mode. If the unit is in deadband mode (not actively heating the supply air) control type Humidistat will be active. If the unit is in cooling mode, control type Humidistat will be active if the Dehumidification Control Type field above is set to Humidistat or None.
This allows the ideal loads system to cool and humidify at the same time.
This alpha field specifies the name of a DesignSpecification:OutdoorAir object which specifies the outdoor air requirements and schedule for this system. The outdoor air flow rate may also be affected by the next two fields, Demand Controlled Ventilation Type and Outdoor Air Economizer Type. If this field is blank, this system will have no outdoor air, and all outdoor air control and heat recovery options will be ignored..
This alpha field specifies the node name of the outdoor air inlet node. This node name is also specified in an OutdoorAir:Node or OutdoorAir:NodeList object. If this field is blank, a node name will be created internally.
This field, along with the Design Specification Outdoor Air Object (if used) specifies how the minimum outdoor air flow rate is calculated. The choices are: None, OccupancySchedule or CO2Setpoint. The default is None.
n None means that the design occupancy level will be used when computing the minimum outdoor air flow rate based on the inputs in the Design Specification Outdoor Air Object (see previous field).
n OccupancySchedule means that the current occupancy level will be used when computing the minimum outdoor air flow rate based on the inputs in the Design Specification Outdoor Air Object (see previous field).
n CO2Setpoint means that the design occupancy level will be used when computing the minimum outdoor air flow rate based on the inputs in the Design Specification Outdoor Air Object (see previous field). In addition, the minimum outdoor air flow rate may be increased if necessary to maintain the level of indoor air carbon dioxide at or below the setpoint defined in a ZoneControl:ContaminantController object.
This field specifies if there is an outdoor air economizer. The choices are: NoEconomizer, DifferentialDryBulb, or DifferentialEnthalpy. The default is NoEconomizer. DifferentialDryBulb and DifferentialEnthalpy mean that the economizer will increase the outdoor air flow rate above the minimum outdoor air flow (see the previous two fields) when there is a cooling load and the outdoor air temperature or enthalpy is below the zone exhaust air temperature or enthalpy. The DifferentialDryBulb and DifferentialEnthalpy options require that the Maximum Cooling Air Flow Rate be specified which will be used as the limit for maximum outdoor air flow rate.
Select from None, Sensible, or Enthalpy. None means that there is no heat recovery. Sensible means that there is sensible heat recovery whenever the zone exhaust air temperature is more favorable than the outdoor air temperature. Enthalpy means that there is latent and sensible heat recovery whenever the zone exhaust air enthalpy is more favorable than the outdoor air enthalpy.
The sensible heat recovery effectiveness, where effectiveness is defined as the change in supply temperature divided by the difference in entering supply and relief air temperatures. The default is 0.70.
The latent heat recovery effectiveness, where effectiveness is defined as the change in supply humidity ratio divided by the difference in entering supply and relief air humidity ratios. The default is 0.65.
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