HVAC Control Systems for Manufacturing

PROGRAM HVAC_TEMPERATURE_CONTROL_WITH_PID
VAR
    // Inputs
    room_temp : REAL;          // Current temperature °C
    temp_setpoint : REAL := 22.0;  // Desired temperature
    outdoor_temp : REAL;
    occupancy : BOOL;

    // Outputs
    heating_valve : REAL;      // 0-100% valve position
    cooling_valve : REAL;
    fan_speed : REAL;          // 0-100%

    // PID Variables
    error : REAL;
    integral : REAL := 0.0;
    last_error : REAL := 0.0;
    derivative : REAL;

    // PID Gains
    Kp : REAL := 5.0;
    Ki : REAL := 0.5;
    Kd : REAL := 1.0;

    // Control Output
    pid_output : REAL;


    // Production Tracking
    Production_Count : INT := 0;
    Target_Production : INT := 1000;
    Production_Rate : REAL;  // Units per hour
    Shift_Start_Time : DATE_AND_TIME;

    // Predictive Maintenance
    Vibration_Level : REAL;  // mm/s RMS
    Bearing_Temperature : REAL;
    Runtime_Hours : REAL;
    Maintenance_Due : BOOL;
    Next_PM_Date : DATE;

    // Energy Monitoring
    Power_Consumption : REAL;  // kW
    Energy_Total_Daily : REAL; // kWh
    Energy_Per_Unit : REAL;    // kWh per part
    Peak_Demand_Alarm : BOOL;

    // Material Tracking
    Material_Batch_ID : STRING[20];
    Material_Quantity : REAL;
    Scrap_Count : INT;
    Scrap_Percentage : REAL;

    // Machine Status
    Machine_State : STRING[20];
    Idle_Time : TIME;
    Run_Time : TIME;
    Utilization_Percent : REAL;
END_VAR

// ==========================================
// BASE APPLICATION LOGIC
// ==========================================

// Calculate PID error
error := temp_setpoint - room_temp;

// Integral term with anti-windup
integral := integral + (error * 0.1);
integral := LIMIT(-50.0, integral, 50.0);

// Derivative term
derivative := (error - last_error) / 0.1;
last_error := error;

// PID calculation
pid_output := (Kp * error) + (Ki * integral) + (Kd * derivative);

// Map PID output to heating/cooling
IF pid_output > 0.0 THEN
    heating_valve := LIMIT(0.0, pid_output, 100.0);
    cooling_valve := 0.0;
ELSE
    heating_valve := 0.0;
    cooling_valve := LIMIT(0.0, ABS(pid_output), 100.0);
END_IF;

// Fan speed based on demand and occupancy
IF occupancy THEN
    fan_speed := LIMIT(30.0, ABS(pid_output) * 1.5, 100.0);
ELSE
    fan_speed := 20.0;  // Minimum circulation
END_IF;

// ==========================================
// MANUFACTURING SPECIFIC LOGIC
// ==========================================

    // Production Rate Calculation
    Production_Rate := Production_Count / Runtime_Hours;

    // Utilization Tracking
    Utilization_Percent := (Run_Time / (Run_Time + Idle_Time)) * 100.0;

    // Predictive Maintenance Alert
    IF (Vibration_Level > Normal_Vibration * 2.0) OR
       (Bearing_Temperature > Normal_Temp + 20.0) OR
       (Runtime_Hours >= PM_Interval_Hours) THEN
        Maintenance_Due := TRUE;
        Machine_State := 'MAINTENANCE_REQUIRED';
    END_IF;

    // Energy Efficiency Monitoring
    Energy_Per_Unit := Energy_Total_Daily / Production_Count;

    IF Power_Consumption > Peak_Demand_Limit THEN
        Peak_Demand_Alarm := TRUE;
        // Implement load shedding if needed
    END_IF;

    // Scrap Rate Tracking
    Scrap_Percentage := (Scrap_Count / Production_Count) * 100.0;

    IF Scrap_Percentage > Target_Scrap_Percent THEN
        Quality_Alert := TRUE;
    END_IF;

// ==========================================
// MANUFACTURING SAFETY INTERLOCKS
// ==========================================

    // Production Enable
    Production_Allowed := NOT Maintenance_Due
                          AND (Material_Quantity > Min_Material)
                          AND NOT Emergency_Stop
                          AND NOT Peak_Demand_Alarm;