Learning to implement Structured Text for HVAC Control using Inovance's InoProShop / AutoShop is an essential skill for PLC programmers working in Building Automation. This comprehensive guide walks you through the fundamentals, providing clear explanations and practical examples that you can apply immediately to real-world projects.
Inovance has established itself as High in China across textiles, packaging, lithium battery, EV manufacturing, elevators, robotics; growing in SE Asia and MEA, making it a strategic choice for HVAC Control applications. With ~2% global, top-3 in China global market share and 7 popular PLC families including the AM600 and AM610, Inovance provides the robust platform needed for intermediate complexity projects like HVAC Control.
The Structured Text approach is particularly well-suited for HVAC Control because complex calculations, data manipulation, advanced control algorithms, and when code reusability is important. This combination allows you to leverage powerful for complex logic while managing the typical challenges of HVAC Control, including energy optimization and zone control coordination.
Throughout this guide, you'll discover step-by-step implementation strategies, working code examples tested on InoProShop / AutoShop, and industry best practices specific to Building Automation. Whether you're programming your first HVAC Control system or transitioning from another PLC platform, this guide provides the practical knowledge you need to succeed with Inovance Structured Text programming.
Inovance InoProShop / AutoShop for HVAC Control
Inovance ships InoProShop as its primary programming IDE for the AM600 / AM610 / H5U medium-PLC families and AutoShop for the Easy-series compact PLCs. InoProShop is built on the CODESYS 3.5 platform, which means engineers transferring from Beckhoff TwinCAT, WAGO e!Cockpit, or Schneider EcoStruxure Machine Expert will recognise the project tree, IEC 61131-3 editors, and visualisation tools immediately. AutoShop is a more traditional ladder-and-IL editor closer to compact-PLC tradition. Inovance'...
Platform Strengths for HVAC Control:
- CODESYS-based InoProShop for IEC 61131-3 compliance
- Tight integration with Inovance servo drives and inverters
- Strong motion, robotics, and elevator-control product lines
- EtherCAT support across mid-tier and high-end CPUs
Unique ${brand.software} Features:
- InoProShop built on CODESYS 3.5 — full IEC 61131-3 compliance
- Native EtherCAT motion across mid-tier and high-end CPUs
- Tight integration with Inovance servo drives, inverters, and HMIs
- AutoShop for compact AC800 / Easy-series CPUs (lighter IDE)
Key Capabilities:
The InoProShop / AutoShop environment excels at HVAC Control applications through its codesys-based inoproshop for iec 61131-3 compliance. This is particularly valuable when working with the 5 sensor types typically found in HVAC Control systems, including Temperature sensors (RTD, Thermocouple), Humidity sensors, Pressure sensors.
Control Equipment for HVAC Control:
- Air handling units (AHUs) with supply and return fans
- Variable air volume (VAV) boxes with reheat
- Chillers and cooling towers for central cooling
- Boilers and heat exchangers for heating
Inovance's controller families for HVAC Control include:
- AM600: Suitable for intermediate HVAC Control applications
- AM610: Suitable for intermediate HVAC Control applications
- H5U: Suitable for intermediate HVAC Control applications
- AC800: Suitable for intermediate HVAC Control applications
Hardware Selection Guidance:
Inovance CPU choice ranges from Easy320 / Easy510 (compact, AutoShop-programmed, FX-style memory model) through AC800 (mid-range compact) to AM600 / AM610 / H5U (medium PLC with EtherCAT, OPC UA, redundant networking on H5U). AM600 is the volume product for OEM machinery; H5U is the choice for higher-axis-count motion applications and lithium-battery / EV manufacturing lines where EtherCAT and tig...
Industry Recognition:
High in China across textiles, packaging, lithium battery, EV manufacturing, elevators, robotics; growing in SE Asia and MEA. High in Chinese EV manufacturing — Inovance is a major automation supplier to BYD, NIO, and Tier 2/3 EV-component plants. AM600 + H5U with EtherCAT motion controls battery-cell assembly, module welding, pack assembly, and end-of-line test stations. Less common in Western Tier 1 automotive but appear...
Investment Considerations:
With $$ pricing, Inovance positions itself in the mid-range segment. For HVAC Control projects requiring intermediate skill levels and 2-4 weeks development time, the total investment includes hardware, software licensing, training, and ongoing support.
Understanding Structured Text for HVAC Control
Structured Text (ST) is a high-level, text-based programming language defined in IEC 61131-3. It resembles Pascal and provides powerful constructs for complex algorithms, calculations, and data manipulation.
Execution Model:
Code executes sequentially from top to bottom within each program unit. Variables maintain state between scan cycles unless explicitly reset.
Core Advantages for HVAC Control:
- Powerful for complex logic: Critical for HVAC Control when handling intermediate control logic
- Excellent code reusability: Critical for HVAC Control when handling intermediate control logic
- Compact code representation: Critical for HVAC Control when handling intermediate control logic
- Good for algorithms and calculations: Critical for HVAC Control when handling intermediate control logic
- Familiar to software developers: Critical for HVAC Control when handling intermediate control logic
Why Structured Text Fits HVAC Control:
HVAC Control systems in Building Automation typically involve:
- Sensors: Temperature sensors (RTD, thermistors, thermocouples) for zone and supply/return monitoring, Humidity sensors (capacitive or resistive) for moisture control, CO2 sensors for demand-controlled ventilation
- Actuators: Variable frequency drives (VFDs) for fan and pump speed control, Modulating control valves (2-way and 3-way) for heating/cooling coils, Damper actuators (0-10V or 4-20mA) for air flow control
- Complexity: Intermediate with challenges including Tuning PID loops for slow thermal processes without causing oscillation
Control Strategies for HVAC Control:
- zoneTemperature: Cascaded PID control where zone temperature error calculates supply air temperature setpoint, which then modulates cooling/heating valves or VAV damper position
- supplyAirTemperature: PID control of cooling coil valve, heating coil valve, or economizer dampers to maintain supply air temperature setpoint
- staticPressure: PID control of supply fan VFD speed to maintain duct static pressure setpoint for proper VAV box operation
Programming Fundamentals in Structured Text:
Variables:
- declaration: VAR / VAR_INPUT / VAR_OUTPUT / VAR_IN_OUT / VAR_GLOBAL sections
- initialization: Variables can be initialized at declaration: Counter : INT := 0;
- constants: VAR CONSTANT section for read-only values
Operators:
- arithmetic: + - * / MOD (modulo)
- comparison: = <> < > <= >=
- logical: AND OR XOR NOT
ControlStructures:
- if: IF condition THEN statements; ELSIF condition THEN statements; ELSE statements; END_IF;
- case: CASE selector OF value1: statements; value2: statements; ELSE statements; END_CASE;
- for: FOR index := start TO end BY step DO statements; END_FOR;
Best Practices for Structured Text:
- Use meaningful variable names with consistent naming conventions
- Initialize all variables at declaration to prevent undefined behavior
- Use enumerated types for state machines instead of magic numbers
- Break complex expressions into intermediate variables for readability
- Use functions for reusable calculations and function blocks for stateful operations
Common Mistakes to Avoid:
- Using = instead of := for assignment (= is comparison)
- Forgetting semicolons at end of statements
- Integer division truncation - use REAL for decimal results
- Infinite loops from incorrect WHILE/REPEAT conditions
Typical Applications:
1. PID control: Directly applicable to HVAC Control
2. Recipe management: Related control patterns
3. Statistical calculations: Related control patterns
4. Data logging: Related control patterns
Understanding these fundamentals prepares you to implement effective Structured Text solutions for HVAC Control using Inovance InoProShop / AutoShop.
Implementing HVAC Control with Structured Text
HVAC (Heating, Ventilation, and Air Conditioning) control systems use PLCs to regulate temperature, humidity, and air quality in buildings and industrial facilities. These systems balance comfort, energy efficiency, and equipment longevity through sophisticated control algorithms.
This walkthrough demonstrates practical implementation using Inovance InoProShop / AutoShop and Structured Text programming.
System Requirements:
A typical HVAC Control implementation includes:
Input Devices (Sensors):
1. Temperature sensors (RTD, thermistors, thermocouples) for zone and supply/return monitoring: Critical for monitoring system state
2. Humidity sensors (capacitive or resistive) for moisture control: Critical for monitoring system state
3. CO2 sensors for demand-controlled ventilation: Critical for monitoring system state
4. Pressure sensors for duct static pressure and building pressurization: Critical for monitoring system state
5. Occupancy sensors (PIR, ultrasonic) for demand-based operation: Critical for monitoring system state
Output Devices (Actuators):
1. Variable frequency drives (VFDs) for fan and pump speed control: Primary control output
2. Modulating control valves (2-way and 3-way) for heating/cooling coils: Supporting control function
3. Damper actuators (0-10V or 4-20mA) for air flow control: Supporting control function
4. Compressor contactors and staging relays: Supporting control function
5. Humidifier and dehumidifier control outputs: Supporting control function
Control Equipment:
- Air handling units (AHUs) with supply and return fans
- Variable air volume (VAV) boxes with reheat
- Chillers and cooling towers for central cooling
- Boilers and heat exchangers for heating
Control Strategies for HVAC Control:
- zoneTemperature: Cascaded PID control where zone temperature error calculates supply air temperature setpoint, which then modulates cooling/heating valves or VAV damper position
- supplyAirTemperature: PID control of cooling coil valve, heating coil valve, or economizer dampers to maintain supply air temperature setpoint
- staticPressure: PID control of supply fan VFD speed to maintain duct static pressure setpoint for proper VAV box operation
Implementation Steps:
Step 1: Document all zones with temperature requirements and occupancy schedules
In InoProShop / AutoShop, document all zones with temperature requirements and occupancy schedules.
Step 2: Create I/O list with all sensors, actuators, and their signal types
In InoProShop / AutoShop, create i/o list with all sensors, actuators, and their signal types.
Step 3: Define setpoints, operating limits, and alarm thresholds
In InoProShop / AutoShop, define setpoints, operating limits, and alarm thresholds.
Step 4: Implement zone temperature control loops with anti-windup
In InoProShop / AutoShop, implement zone temperature control loops with anti-windup.
Step 5: Program equipment sequencing with proper lead-lag rotation
In InoProShop / AutoShop, program equipment sequencing with proper lead-lag rotation.
Step 6: Add economizer logic with lockouts for high humidity conditions
In InoProShop / AutoShop, add economizer logic with lockouts for high humidity conditions.
Inovance Function Design:
InoProShop strongly favours function-block reuse via the Library Manager — Inovance ships standard libraries for motion, drives, HMI, OPC UA, and industry-specific applications (lithium-battery, EV, elevator). AutoShop reuse is open-coded via P-label subroutines. OEM machine-builders increasingly default to InoProShop / AM600 to access the FB libraries.
Common Challenges and Solutions:
1. Tuning PID loops for slow thermal processes without causing oscillation
- Solution: Structured Text addresses this through Powerful for complex logic.
2. Preventing simultaneous heating and cooling which wastes energy
- Solution: Structured Text addresses this through Excellent code reusability.
3. Managing zone interactions in open-plan spaces
- Solution: Structured Text addresses this through Compact code representation.
4. Balancing fresh air requirements with energy efficiency
- Solution: Structured Text addresses this through Good for algorithms and calculations.
Safety Considerations:
- Freeze protection for coils with low-limit thermostats and valve positioning
- High-limit safety shutoffs for heating equipment
- Smoke detector integration for fan shutdown and damper closure
- Fire/smoke damper monitoring and control
- Emergency ventilation modes for hazardous conditions
Performance Metrics:
- Scan Time: Optimize for 5 inputs and 5 outputs
- Memory Usage: Efficient data structures for AM600 capabilities
- Response Time: Meeting Building Automation requirements for HVAC Control
Inovance Diagnostic Tools:
InoProShop online mode with full POU monitoring and breakpoint debug,EtherCAT diagnostics page with topology and slave status,Trace tool for analogue / motion signal capture,OPC UA server diagnostics page,Modbus communication trace utility,AutoShop online mode for legacy AC800 / Easy series,Inovance HMI integrated diagnostics for HMI-PLC binding faults,Servo-drive panel diagnostics with InoProShop drive-monitor view,EtherCAT slave-firmware update tool,Project compare tool for change tracking
Inovance's InoProShop / AutoShop provides tools for performance monitoring and optimization, essential for achieving the 2-4 weeks development timeline while maintaining code quality.
Inovance Structured Text Example for HVAC Control
Complete working example demonstrating Structured Text implementation for HVAC Control using Inovance InoProShop / AutoShop. Follows Inovance naming conventions. Tested on AM600 hardware.
(* Inovance InoProShop / AutoShop - HVAC Control Control *)
(* Structured Text Implementation for Building Automation *)
(* On InoProShop projects, conventions follow CODESYS / IEC norms — Pasca *)
PROGRAM PRG_HVAC_CONTROL_Control
VAR
(* State Machine Variables *)
eState : E_HVAC_CONTROL_States := IDLE;
bEnable : BOOL := FALSE;
bFaultActive : BOOL := FALSE;
(* Timers *)
tonDebounce : TON;
tonProcessTimeout : TON;
tonFeedbackCheck : TON;
(* Counters *)
ctuCycleCounter : CTU;
(* Process Variables *)
rTemperaturesensorsRTDThermocouple : REAL := 0.0;
rVariablefrequencydrivesVFDs : REAL := 0.0;
rSetpoint : REAL := 100.0;
END_VAR
VAR CONSTANT
(* Building Automation Process Parameters *)
C_DEBOUNCE_TIME : TIME := T#500MS;
C_PROCESS_TIMEOUT : TIME := T#30S;
C_BATCH_SIZE : INT := 50;
END_VAR
(* Input Conditioning *)
tonDebounce(IN := bStartButton, PT := C_DEBOUNCE_TIME);
bEnable := tonDebounce.Q AND NOT bEmergencyStop AND bSafetyOK;
(* Main State Machine - Pattern: InoProShop state machines typically use *)
CASE eState OF
IDLE:
rVariablefrequencydrivesVFDs := 0.0;
ctuCycleCounter(RESET := TRUE);
IF bEnable AND rTemperaturesensorsRTDThermocouple > 10.0 THEN
eState := STARTING;
END_IF;
STARTING:
(* Ramp up output - Gradual start *)
rVariablefrequencydrivesVFDs := MIN(rVariablefrequencydrivesVFDs + 5.0, rSetpoint);
IF rVariablefrequencydrivesVFDs >= rSetpoint THEN
eState := RUNNING;
END_IF;
RUNNING:
(* HVAC Control active - HVAC (Heating, Ventilation, and Air Conditioning) *)
tonProcessTimeout(IN := TRUE, PT := C_PROCESS_TIMEOUT);
ctuCycleCounter(CU := bCyclePulse, PV := C_BATCH_SIZE);
IF ctuCycleCounter.Q THEN
eState := COMPLETE;
ELSIF tonProcessTimeout.Q THEN
bFaultActive := TRUE;
eState := FAULT;
END_IF;
COMPLETE:
rVariablefrequencydrivesVFDs := 0.0;
(* Log production data - InoProShop on AM600 / H5U supports SD-card logging via library FBs, plus OPC UA streaming for cloud / on-premises historians. Inovance HMIs add CSV logging at HMI tier. AutoShop projects rely on HMI-tier logging exclusively. *)
eState := IDLE;
FAULT:
rVariablefrequencydrivesVFDs := 0.0;
(* InoProShop alarms are typically defined in the visualisation alarm-configuration page with severity, latching, and acknowledgement behaviour configured per alarm. The runtime maintains active and historical alarm lists. AutoShop projects fall back to M-flag banks with HMI-side alarm logging. *)
IF bFaultReset AND NOT bEmergencyStop THEN
bFaultActive := FALSE;
eState := IDLE;
END_IF;
END_CASE;
(* Safety Override - Always executes *)
IF bEmergencyStop OR NOT bSafetyOK THEN
rVariablefrequencydrivesVFDs := 0.0;
eState := FAULT;
bFaultActive := TRUE;
END_IF;
END_PROGRAMCode Explanation:
- 1.Enumerated state machine (InoProShop state machines typically use IEC SFC steps with action blocks per step, or a state-enum-and-CASE pattern in Structured Text. SFC dominates production-line sequencers; CASE patterns dominate axis-control state and recipe-routing logic. AutoShop projects fall back to FX-style SFC step memory (S0..S511) or D-register integer state.) for clear HVAC Control sequence control
- 2.Constants define Building Automation-specific parameters: cycle time 30s, batch size
- 3.Input conditioning with debounce timer prevents false triggers in industrial environment
- 4.STARTING state implements soft-start ramp - prevents mechanical shock
- 5.Process timeout detection identifies stuck conditions - critical for reliability
- 6.Safety override section executes regardless of state - Inovance best practice for intermediate systems
Best Practices
- ✓Follow Inovance naming conventions: On InoProShop projects, conventions follow CODESYS / IEC norms — PascalCase for
- ✓Inovance function design: InoProShop strongly favours function-block reuse via the Library Manager — Inova
- ✓Data organization: InoProShop uses GVLs and persistent variables for shared data. AutoShop uses D /
- ✓Structured Text: Use meaningful variable names with consistent naming conventions
- ✓Structured Text: Initialize all variables at declaration to prevent undefined behavior
- ✓Structured Text: Use enumerated types for state machines instead of magic numbers
- ✓HVAC Control: Use slow integral action for temperature loops to prevent hunting
- ✓HVAC Control: Implement anti-windup to prevent integral buildup during saturation
- ✓HVAC Control: Add rate limiting to outputs to prevent actuator wear
- ✓Debug with InoProShop / AutoShop: Use InoProShop's online mode to set breakpoints in POUs and step throu
- ✓Safety: Freeze protection for coils with low-limit thermostats and valve positioning
- ✓Use InoProShop / AutoShop simulation tools to test HVAC Control logic before deployment
Common Pitfalls to Avoid
- ⚠Structured Text: Using = instead of := for assignment (= is comparison)
- ⚠Structured Text: Forgetting semicolons at end of statements
- ⚠Structured Text: Integer division truncation - use REAL for decimal results
- ⚠Inovance common error: EtherCAT slave order mismatch after physical re-cabling — slave addressing break
- ⚠HVAC Control: Tuning PID loops for slow thermal processes without causing oscillation
- ⚠HVAC Control: Preventing simultaneous heating and cooling which wastes energy
- ⚠Neglecting to validate Temperature sensors (RTD, thermistors, thermocouples) for zone and supply/return monitoring leads to control errors
- ⚠Insufficient comments make Structured Text programs unmaintainable over time
Related Certifications
Mastering Structured Text for HVAC Control applications using Inovance InoProShop / AutoShop requires understanding both the platform's capabilities and the specific demands of Building Automation. This guide has provided comprehensive coverage of implementation strategies, working code examples, best practices, and common pitfalls to help you succeed with intermediate HVAC Control projects.
Inovance's ~2% global, top-3 in China market share and high in china across textiles, packaging, lithium battery, ev manufacturing, elevators, robotics; growing in se asia and mea demonstrate the platform's capability for demanding applications. The platform excels in Building Automation applications where HVAC Control reliability is critical.
By following the practices outlined in this guide—from proper program structure and Structured Text best practices to Inovance-specific optimizations—you can deliver reliable HVAC Control systems that meet Building Automation requirements.
Next Steps for Professional Development:
1. Certification: Pursue Inovance Certified Engineer to validate your Inovance expertise
2. Advanced Training: Consider InoProShop / AutoShop training certificates for specialized Building Automation applications
3. Hands-on Practice: Build HVAC Control projects using AM600 hardware
4. Stay Current: Follow InoProShop / AutoShop updates and new Structured Text features
Structured Text Foundation:
Structured Text (ST) is a high-level, text-based programming language defined in IEC 61131-3. It resembles Pascal and provides powerful constructs for...
The 2-4 weeks typical timeline for HVAC Control projects will decrease as you gain experience with these patterns and techniques. Remember: Use slow integral action for temperature loops to prevent hunting
For further learning, explore related topics including Recipe management, Hospital environmental systems, and Inovance platform-specific features for HVAC Control optimization.