Guide for Module Developers — EnergyPlus 8.4

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Branches, Connectors, and Nodes[LINK]

In EnergyPlus, the HVAC system and plant form a network (technically, a graph). The individual pieces of equipment – the fans, coils, chillers, etc. – are connected together by air ducts and fluid pipes. In EnergyPlus nomenclature, the air and fluid circuits are called loops. Specifying how an individual system and plant are connected is done in the EnergyPlus input (IDF) file. The overall structure of the network is defined with Branch and Connector objects. The detail is filled with components and their inlet and outlet nodes. A Branch consists of one or more components arranged sequentially along a pipe or duct. A Connector specifies how three or more branches are connected through a Splitter or Mixer. Nodes connect components along a branch: the outlet node of one component is the inlet node of the next downstream component. The nodes represent conditions at a point on a loop. Each component has one or more inlet and outlet nodes, depending on how many loops it interacts with. A fan, for instance, has one inlet node and one outlet node, since it interacts with a single air loop. A water coil will have 2 inlet and 2 outlet nodes, since it interacts with an air and a fluid loop. Figure 1 shows a diagram of an EnergyPlus HVAC input.

Figure 1. HVAC Input Diagram

As an illustration of how such a network is built up on the IDF, here is the section of the IDF that describes the supply fan, splitter, and heating and cooling coil section of the dual duct air system.

BranchList,

Dual Duct Air Loop Branches, !- Name

Air Loop Main Branch, !- Branch 1 Name

Heating Coil Air Sys Branch, !- Branch 2 Name

Cooling Coil Air Sys Branch; !- Branch 3 Name

ConnectorList,

Dual Duct Connectors, !- Name

Connector:Splitter, !- Connector 1 Object Type

DualDuctAirSplitter; !- Connector 1 Name

NodeList,

Zone Equipment Inlet Node List, !- Name

Main Hot Air Inlet, !- Node 1 Name

Main Cold Air Inlet; !- Node 2 Name

NodeList,

Air Loop Outlet Node List, !- Name

Heating Coil Outlet Node,!- Node 1 Name

Cooling Coil Outlet Node;!- Node 2 Name

Branch,

Air Loop Main Branch, !- Name

autosize, !- Maximum Flow Rate {m3/s}

Fan:ConstantVolume, !- Component 1 Object Type

Supply Fan 1, !- Component 1 Name

Supply Fan Inlet Node, !- Component 1 Inlet Node Name

Supply Fan Outlet Node, !- Component 1 Outlet Node Name

PASSIVE; !- Component 1 Branch Control Type

Branch,

Heating Coil Air Sys Branch, !- Name

autosize, !- Maximum Flow Rate {m3/s}

Coil:Heating:Water, !- Component 1 Object Type

Main Heating Coil, !- Component 1 Name

Heating Coil Inlet Node, !- Component 1 Inlet Node Name

Heating Coil Outlet Node,!- Component 1 Outlet Node Name

ACTIVE; !- Component 1 Branch Control Type

Branch,

Cooling Coil Air Sys Branch, !- Name

autosize, !- Maximum Flow Rate {m3/s}

Coil:Cooling:Water, !- Component 1 Object Type

Simple Cooling Coil, !- Component 1 Name

Cooling Coil Inlet Node, !- Component 1 Inlet Node Name

Cooling Coil Outlet Node,!- Component 1 Outlet Node Name

ACTIVE; !- Component 1 Branch Control Type

Connector:Splitter,

DualDuctAirSplitter, !- Name

Air Loop Main Branch, !- Inlet Branch Name

Heating Coil Air Sys Branch, !- Outlet Branch 1 Name

Cooling Coil Air Sys Branch; !- Outlet Branch 2 Name

Fan:ConstantVolume,

Supply Fan 1, !- Name

FanAndCoilAvailSched, !- Availability Schedule Name

0.7, !- Fan Efficiency

600.0, !- Pressure Rise {Pa}

autosize, !- Maximum Flow Rate {m3/s}

0.9, !- Motor Efficiency

1.0, !- Motor In Airstream Fraction

Supply Fan Inlet Node, !- Fan Inlet Node Name

Supply Fan Outlet Node; !- Fan Outlet Node Name

Coil:Cooling:Water,

Simple Cooling Coil, !- Name

CoolingCoilAvailSched, !- Availability Schedule Name

autosize, !- Design Water Flow Rate {m3/s}

autosize, !- Design Air Flow Rate {m3/s}

autosize, !- Design Inlet Water Temperature {C}

autosize, !- Design Inlet Air Temperature {C}

autosize, !- Design Outlet Air Temperature {C}

autosize, !- Design Inlet Air Humidity Ratio {kg-H2O/kg-air}

autosize, !- Design Outlet Air Humidity Ratio {kg-H2O/kg-air}

Cooling Coil Water Inlet Node, !- Water Inlet Node Name

Cooling Coil Water Outlet Node, !- Water Outlet Node Name

Cooling Coil Inlet Node, !- Air Inlet Node Name

Cooling Coil Outlet Node,!- Air Outlet Node Name

SimpleAnalysis, !- Type of Analysis

CrossFlow; !- Heat Exchanger Configuration

AirLoopHVAC:ZoneSplitter,

ZoneColdAirSupplySplitter, !- Name

Main Cold Air Inlet, !- Inlet Node Name

Zone 1 Dual Duct Cold Inlet, !- Outlet 1 Node Name

Zone 2 Dual Duct Cold Inlet, !- Outlet 2 Node Name

Zone 3 Dual Duct Cold Inlet; !- Outlet 3 Node Name

AirLoopHVAC:ZoneSplitter,

ZoneHotAirSupplySplitter,!- Name

Main Hot Air Inlet, !- Inlet Node Name

Zone 1 Dual Duct Hot Inlet, !- Outlet 1 Node Name

Zone 2 Dual Duct Hot Inlet, !- Outlet 2 Node Name

Zone 3 Dual Duct Hot Inlet; !- Outlet 3 Node Name

AirLoopHVAC:ZoneMixer,

ZoneReturnAirMixer, !- Name

Return Air Mixer Outlet, !- Outlet Node Name

Zone 1 Outlet Node, !- Inlet 1 Node Name

Zone 2 Outlet Node, !- Inlet 2 Node Name

Zone 3 Outlet Node; !- Inlet 3 Node Name

Coil:Heating:Water,

Main Heating Coil, !- Name

FanAndCoilAvailSched, !- Availability Schedule Name

autosize, !- U-Factor Times Area Value {W/K}

autosize, !- Maximum Water Flow Rate {m3/s}

Heating Coil Water Inlet,!- Water Inlet Node Name

Heating Coil Water Outlet, !- Water Outlet Node Name

Heating Coil Inlet Node, !- Air Inlet Node Name

Heating Coil Outlet Node,!- Air Outlet Node Name

UFactorTimesAreaAndDesignWaterFlowRate, !- Performance Input Method

autosize, !- Nominal Capacity {W}

82.2, !- Design Inlet Water Temperature {C}

16.6, !- Design Inlet Air Temperature {C}

71.1, !- Design Outlet Water Temperature {C}

32.2; !- Design Outlet Air Temperature {C}

Controller:WaterCoil,

Main Cooling Coil Controller, !- Name

Temperature, !- Control Variable

Reverse, !- Action

FLOW, !- Actuator Variable

Cooling Coil Outlet Node,!- Sensor Node Name

Cooling Coil Water Inlet Node, !- Actuator Node Name

0.001, !- Controller Convergence Tolerance {deltaC}

autosize, !- Maximum Actuated Flow {m3/s}

0.0; !- Minimum Actuated Flow {m3/s}

Controller:WaterCoil,

Main Heating Coil Controller, !- Name

Temperature, !- Control Variable

Normal, !- Action

FLOW, !- Actuator Variable

Heating Coil Outlet Node,!- Sensor Node Name

Heating Coil Water Inlet,!- Actuator Node Name

0.01, !- Controller Convergence Tolerance {deltaC}

autosize, !- Maximum Actuated Flow {m3/s}

0.0; !- Minimum Actuated Flow {m3/s}

Obviously, the creation of such a system/plant network description is best handled by a graphical user interface (GUI). However, for testing purposes a developer may have to create the input for a component by hand and insert it into an existing IDF. Then the developer must be careful to choose unique names for the branches and nodes and make sure the entire network makes physical sense.