Python EMS (EnergyPlus Python Plugins)

Custom control/reporting logic that runs inside EnergyPlus each timestep. A plugin is a Python class attached to the model; it reads sensors (output variables), sets actuators (schedule values, setpoints, flows), and publishes custom output variables you can query like any other result.

Always prefer the named templates in create_python_plugin — they generate correct, validated plugin code. Write template="custom" code only when no template fits.

Workflow

1. Model loaded (any create/load tool). The model must have a file path — save first if needed.
2. Discover what you can control:

   list_ems_actuators(component_type="Schedule")
   

   Returns (component_type, control_type, actuator_key) triples from a hidden sizing-only run (a few seconds). Names come back UPPERCASE — matching inside plugins is case-insensitive. Requires design days in the model.
3. Create the plugin from a template:

   create_python_plugin(name="Night Setback", template="schedule_override",
                        schedule_name="Htg Setpoint Sched", default_value=15.6,
                        rules=[{"days": "weekdays", "start_hour": 5, "end_hour": 19, "value": 21.0}])
   

4. save_osm_model() — the script lives in the model's companion files/ dir and travels with it.
5. run_simulation(...), then verify the plugin loaded: extract_simulation_errors(run_id=<run_id>) should show no severe messages; the .err file logs PythonPlugin: Class X imported.
6. Read the plugin's outputs:

   query_timeseries(run_id=<run_id>, variable_name="PythonPlugin:OutputVariable",
                    key_value="Night Setback Applied Value")
   

Worked examples

Average building temperature (custom metric, no actuation):

create_python_plugin(name="Avg Building Temp", template="zone_metric_aggregate",
                     variable_name="Zone Mean Air Temperature",
                     aggregation="volume_weighted_average",
                     output_variable_name="Averaged Building Temperature", units="C")

Defaults to all zones; pass zone_names to restrict.

Schedule/setpoint override by time-of-day rules:

create_python_plugin(name="Night Setback", template="schedule_override",
                     schedule_name="Htg Setpoint Sched", default_value=15.6,
                     rules=[{"days": "weekdays", "start_hour": 5, "end_hour": 19, "value": 21.0},
                            {"days": "saturday", "start_hour": 6, "end_hour": 12, "value": 18.0}])

First matching rule wins, else default_value. Works on ScheduleConstant, ScheduleRuleset (actuated as Schedule:Year), and ScheduleCompact schedules.

Outdoor-air setpoint reset (overrides setpoint managers):

create_python_plugin(name="SAT Reset", template="node_setpoint_reset",
                     air_loop_name="Packaged Rooftop Air Conditioner",
                     oat_low=-20, oat_high=10,
                     setpoint_at_oat_low=15.0, setpoint_at_oat_high=12.8)

Pass node_name directly, or air_loop_name to use its supply outlet node.

Custom plugin (escape hatch): provide full source. Contract:

from pyenergyplus.plugin import EnergyPlusPlugin

class MyControl(EnergyPlusPlugin):
    def on_begin_timestep_before_predictor(self, state) -> int:
        if not self.api.exchange.api_data_fully_ready(state):
            return 0
        # get_*_handle returns -1 when not found — check it, issue_severe, return 1
        # return 0 = success; nonzero aborts the simulation
        return 0

Pass code=..., class_name="MyControl", and global_variables=[...] for any globals used via get_global_handle/set_global_value. Use list_ems_actuators first for valid actuator triples.

Rules of the plugin runtime

• Look up handles lazily, only after self.api.exchange.api_data_fully_ready(state) is True; cache them.
• Handle lookups return -1 (never raise). On -1: self.api.runtime.issue_severe(state, msg); return 1.
• Callback return 0 = success; nonzero is FATAL to the whole simulation.
• Globals must be declared (create_python_plugin does this) before get_global_handle finds them.
• A sensed variable needs an Output:Variable request to have a handle — the templates add it.
• self.api.exchange.hour(state) is 0-23; self.api.exchange.day_of_week(state) is 1=Sunday..7=Saturday.
• Plugins run inside EnergyPlus (embedded Python 3.12, stdlib by default). For third-party packages (numpy etc.): install_plugin_packages(["numpy"]) first — wheels-only, quota-capped, wired in automatically. pkg==version pins allowed; URLs/paths are not.
• To revise a plugin: edit_python_plugin(name=..., code=...) (validated; the class name must stay unchanged). delete_object on the instance removes it.
• trend_timesteps=N on create logs the plugin global as a PythonPlugin:TrendVariable for get_trend_average/min/max history access.

Common actuator triples

Component type	Control type	Key
Schedule:Constant / Schedule:Year / Schedule:Compact	Schedule Value	schedule name
System Node Setpoint	Temperature Setpoint	node name
Zone Temperature Control	Heating (or Cooling) Setpoint	zone name
Weather Data	Outdoor Dry Bulb	Environment

Confirm with list_ems_actuators — availability is model-dependent.