Add More States

The energy relevant behavior of the cooker of the previous example can be modeled in greater detail by adding more states to the petri net of the cooker. Instead of modeling a single cooking phase two phases are implemented. The first one is the heating phase which uses the maximum power of the cooker to reach the boiling temperature. The second phase uses less power and only holds the target temperature. Additionally, a cleaning phase is added after the discharge phase.

idle_state = process_step.process_state_handler.create_idle_process_state(
    process_state_name="Idle"
)
fill_raw_materials_state = (
    process_step.process_state_handler.create_batch_input_stream_requesting_state(
        process_state_name="Fill raw materials"
    )
)

heating_state = process_step.process_state_handler.create_intermediate_process_state_energy_based_on_stream_mass(
    process_state_name="Heating"
)

hold_temperature_state = process_step.process_state_handler.create_intermediate_process_state_energy_based_on_stream_mass(
    process_state_name="Hold Temperature"
)

discharge_goods_state = (
    process_step.process_state_handler.create_batch_output_stream_providing_state(
        process_state_name="Discharge"
    )
)

cleaning_state = process_step.process_state_handler.create_intermediate_process_state_energy_based_on_stream_mass(
    process_state_name="Cleaning"
)

Each of the new intermediate states is connected with an additional process state switch delay. To determine the length of the heating phase it is assumed that the cooker has a maximum power of 2000 Watt. The water must be heated from 20 °C to 100°C assuming a heat capacity o c_P=4.2 KJ/(Kg*K)

\[ E_{heating, state} = m_{potato,water}*c_{p,water}*(T_{target}-T_{start}) =650 g *4.2kj/kg *(100°C-20°C)=0.06kWh \]

\[ t_{heating,state}=E_{heating, state}/P_{max}=0.06kWh/2000W=1.82 minutes \]

The Assuming that the total cooking time does not change

\[ t_{hold_temperature,state}=t_{cooking, state}-t_{heating, state}=24 minutes -1.82 minutes= 22.18 minutes \]

activate_not_cooking = process_step.process_state_handler.process_state_switch_selector_handler.process_state_switch_handler.create_process_state_switch_at_next_discrete_event(
    start_process_state=cleaning_state,
    end_process_state=idle_state,
)
process_step.process_state_handler.process_state_switch_selector_handler.create_single_choice_selector(
    process_state_switch=activate_not_cooking
)

activate_filling = process_step.process_state_handler.process_state_switch_selector_handler.process_state_switch_handler.create_process_state_switch_at_input_stream(
    start_process_state=idle_state,
    end_process_state=fill_raw_materials_state,
)

process_step.process_state_handler.process_state_switch_selector_handler.create_single_choice_selector(
    process_state_switch=activate_filling
)

activate_heating = process_step.process_state_handler.process_state_switch_selector_handler.process_state_switch_handler.create_process_state_switch_delay(
    start_process_state=fill_raw_materials_state,
    end_process_state=heating_state,
    delay=datetime.timedelta(minutes=1.82),
)

process_step.process_state_handler.process_state_switch_selector_handler.create_single_choice_selector(
    process_state_switch=activate_heating
)
activate_hold_temperature = process_step.process_state_handler.process_state_switch_selector_handler.process_state_switch_handler.create_process_state_switch_delay(
    start_process_state=heating_state,
    end_process_state=hold_temperature_state,
    delay=datetime.timedelta(minutes=22.18),
)

process_step.process_state_handler.process_state_switch_selector_handler.create_single_choice_selector(
    process_state_switch=activate_hold_temperature
)


activate_discharging = process_step.process_state_handler.process_state_switch_selector_handler.process_state_switch_handler.create_process_state_switch_at_output_stream(
    start_process_state=hold_temperature_state,
    end_process_state=discharge_goods_state,
)
process_step.process_state_handler.process_state_switch_selector_handler.create_single_choice_selector(
    process_state_switch=activate_discharging
)
activate_hold_temperature = process_step.process_state_handler.process_state_switch_selector_handler.process_state_switch_handler.create_process_state_switch_delay(
    start_process_state=discharge_goods_state,
    end_process_state=cleaning_state,
    delay=datetime.timedelta(minutes=3),
)

process_step.process_state_handler.process_state_switch_selector_handler.create_single_choice_selector(
    process_state_switch=activate_hold_temperature
)

Now the the energy data must be updated to model the different energy usage in both states. Therefore the energy demand must be converted to MJ/t for each state. It is assumed that the total energy demand does not change. There fore the heat demand for hold temperature phase is:

\[ E_{hold_temperature, state} = E_{total}-E_{heating, state}= 0.15 kWH -0.06kWh= 0.09kWH \]

The energy demand for both phase is converted into mass specific energy using the following conversion: $\( SEC_{heating, state}=E_{heating, state}/m_{potato,water}=0.06kWh/650 g=332.31 MJ/t \)$

\[ SEC_{hold_temperature, state}=E_{hold_temperature, state}/m_{potato,water}=0.09kWh/650 g=498.46 MJ/t \]

In this case it is assumed that no energy is used during the cleaning.

electricity_load = LoadType(name="Electricity")
heating_state.create_process_state_energy_data_based_on_stream_mass(
    specific_energy_demand=332.31,
    load_type=electricity_load,
    stream=raw_materials_to_cooking_stream,
)
hold_temperature_state.create_process_state_energy_data_based_on_stream_mass(
    specific_energy_demand=498.46,
    load_type=electricity_load,
    stream=raw_materials_to_cooking_stream,
)

The next example shows how to implement multiple cookers that produced in parallel.