Learning to implement Function Blocks for HVAC Control using INVT's INVT Workshop / AutoStudio 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.
INVT has established itself as Moderate in HVAC, water treatment, textiles, basic process equipment, and OEM machines paired with INVT drives, making it a strategic choice for HVAC Control applications. With <1% global global market share and 5 popular PLC families including the IVC1 and IVC2, INVT provides the robust platform needed for intermediate complexity projects like HVAC Control.
The Function Blocks approach is particularly well-suited for HVAC Control because process control, continuous operations, modular programming, and signal flow visualization. This combination allows you to leverage visual representation of signal flow 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 INVT Workshop / AutoStudio, 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 INVT Function Blocks programming.
INVT INVT Workshop / AutoStudio for HVAC Control
INVT Workshop and AutoStudio are the two programming tools for the IVC-series PLCs (IVC1, IVC2, IVC3) and the AX-series (AX70 etc.) respectively. The core IDE feel is FX-style — ladder, IL, and SFC editors with soft-element tables and offline simulator support — and the instruction set borrows from Mitsubishi FX conventions. INVT's heritage is in drives (variable-frequency and servo) rather than PLCs, and the engineering tools reflect that bias: drive-PLC integration is unusually clean, with a u...
Platform Strengths for HVAC Control:
- Excellent price-performance for combined PLC + drive systems
- Free programming software with simulator
- Compact CPUs with built-in pulse outputs and PID
- Strong drives heritage — tight VFD/servo integration
Unique ${brand.software} Features:
- Free Workshop / AutoStudio IDE with offline simulator
- FX-style instruction set easing migration
- Tight integration with INVT VFDs and servo drives
- Unified scope / trace across PLC and drive parameters
Key Capabilities:
The INVT Workshop / AutoStudio environment excels at HVAC Control applications through its excellent price-performance for combined plc + drive systems. 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
INVT's controller families for HVAC Control include:
- IVC1: Suitable for intermediate HVAC Control applications
- IVC2: Suitable for intermediate HVAC Control applications
- IVC3: Suitable for intermediate HVAC Control applications
- AX series: Suitable for intermediate HVAC Control applications
Hardware Selection Guidance:
IVC1 covers entry compact applications, IVC2 / IVC3 are mid-range with extended I/O and Ethernet (IVC3-Ethernet variants), AX70 represents INVT's higher-tier compact-modular line with motion features. Choice usually mirrors the drive size — small VFDs pair with IVC1; AX70 fits where servo motion and EtherCAT-like buses are required....
Industry Recognition:
Moderate in HVAC, water treatment, textiles, basic process equipment, and OEM machines paired with INVT drives. Limited Tier 1 presence; common in Chinese aftermarket fixturing where INVT VFDs are already specified....
Investment Considerations:
With $ pricing, INVT positions itself in the value 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 Function Blocks for HVAC Control
Function Block Diagram (FBD) is a graphical programming language where functions and function blocks are represented as boxes connected by signal lines. Data flows from left to right through the network.
Execution Model:
Blocks execute based on data dependencies - a block executes only when all its inputs are available. Networks execute top to bottom when dependencies allow.
Core Advantages for HVAC Control:
- Visual representation of signal flow: Critical for HVAC Control when handling intermediate control logic
- Good for modular programming: Critical for HVAC Control when handling intermediate control logic
- Reusable components: Critical for HVAC Control when handling intermediate control logic
- Excellent for process control: Critical for HVAC Control when handling intermediate control logic
- Good for continuous operations: Critical for HVAC Control when handling intermediate control logic
Why Function Blocks 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 Function Blocks:
StandardBlocks:
- logic: AND, OR, XOR, NOT - Boolean logic operations
- comparison: EQ, NE, LT, GT, LE, GE - Compare values
- math: ADD, SUB, MUL, DIV, MOD - Arithmetic operations
TimersCounters:
- ton: Timer On-Delay - Output turns ON after preset time
- tof: Timer Off-Delay - Output turns OFF after preset time
- tp: Pulse Timer - Output pulses for preset time
Connections:
- wires: Connect output pins to input pins to pass data
- branches: One output can connect to multiple inputs
- feedback: Outputs can feed back to inputs for state machines
Best Practices for Function Blocks:
- Arrange blocks for clear left-to-right data flow
- Use consistent spacing and alignment for readability
- Label all inputs and outputs with meaningful names
- Create custom FBs for frequently repeated logic patterns
- Minimize wire crossings by careful block placement
Common Mistakes to Avoid:
- Creating feedback loops without proper initialization
- Connecting incompatible data types
- Not considering execution order dependencies
- Overcrowding networks making them hard to read
Typical Applications:
1. HVAC control: Directly applicable to HVAC Control
2. Temperature control: Related control patterns
3. Flow control: Related control patterns
4. Batch processing: Related control patterns
Understanding these fundamentals prepares you to implement effective Function Blocks solutions for HVAC Control using INVT INVT Workshop / AutoStudio.
Implementing HVAC Control with Function Blocks
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 INVT INVT Workshop / AutoStudio and Function Blocks 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 INVT Workshop / AutoStudio, document all zones with temperature requirements and occupancy schedules.
Step 2: Create I/O list with all sensors, actuators, and their signal types
In INVT Workshop / AutoStudio, create i/o list with all sensors, actuators, and their signal types.
Step 3: Define setpoints, operating limits, and alarm thresholds
In INVT Workshop / AutoStudio, define setpoints, operating limits, and alarm thresholds.
Step 4: Implement zone temperature control loops with anti-windup
In INVT Workshop / AutoStudio, implement zone temperature control loops with anti-windup.
Step 5: Program equipment sequencing with proper lead-lag rotation
In INVT Workshop / AutoStudio, program equipment sequencing with proper lead-lag rotation.
Step 6: Add economizer logic with lockouts for high humidity conditions
In INVT Workshop / AutoStudio, add economizer logic with lockouts for high humidity conditions.
INVT Function Design:
P-label subroutines plus a small library of INVT-supplied drive-control FBs that wrap the proprietary Modbus parameter map. Reuse beyond the supplied library is open-coded.
Common Challenges and Solutions:
1. Tuning PID loops for slow thermal processes without causing oscillation
- Solution: Function Blocks addresses this through Visual representation of signal flow.
2. Preventing simultaneous heating and cooling which wastes energy
- Solution: Function Blocks addresses this through Good for modular programming.
3. Managing zone interactions in open-plan spaces
- Solution: Function Blocks addresses this through Reusable components.
4. Balancing fresh air requirements with energy efficiency
- Solution: Function Blocks addresses this through Excellent for process control.
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 IVC1 capabilities
- Response Time: Meeting Building Automation requirements for HVAC Control
INVT Diagnostic Tools:
Workshop online monitoring with rung-state highlighting,Combined PLC + drive scope / trace tool,Soft-element watch table,Drive-parameter live-monitor view,Modbus RTU / TCP communication analyzer,Built-in offline simulator,Distributor loaner CPU/drive pairs for triage,INVT community forum (Chinese-dominant) for protocol-specific issues
INVT's INVT Workshop / AutoStudio provides tools for performance monitoring and optimization, essential for achieving the 2-4 weeks development timeline while maintaining code quality.
INVT Function Blocks Example for HVAC Control
Complete working example demonstrating Function Blocks implementation for HVAC Control using INVT INVT Workshop / AutoStudio. Follows INVT naming conventions. Tested on IVC1 hardware.
(* INVT INVT Workshop / AutoStudio - HVAC Control Control *)
(* Reusable Function Blocks Implementation *)
(* P-label subroutines plus a small library of INVT-supplied dr *)
FUNCTION_BLOCK FB_HVAC_CONTROL_Controller
VAR_INPUT
bEnable : BOOL; (* Enable control *)
bReset : BOOL; (* Fault reset *)
rProcessValue : REAL; (* Temperature sensors (RTD, thermistors, thermocouples) for zone and supply/return monitoring *)
rSetpoint : REAL := 100.0; (* Target value *)
bEmergencyStop : BOOL; (* Safety input *)
END_VAR
VAR_OUTPUT
rControlOutput : REAL; (* Variable frequency drives (VFDs) for fan and pump speed control *)
bRunning : BOOL; (* Process active *)
bComplete : BOOL; (* Cycle complete *)
bFault : BOOL; (* Fault status *)
nFaultCode : INT; (* Diagnostic code *)
END_VAR
VAR
(* Internal Function Blocks *)
fbSafety : FB_SafetyMonitor; (* Safety logic *)
fbRamp : FB_RampGenerator; (* Soft start/stop *)
fbPID : FB_PIDController; (* Process control *)
fbDiag : FB_Diagnostics; (* M-flag banks plus drive-fault flags read via Modbus parameter mapping; combined alarm rollup to HMI tag. *)
(* Internal State *)
eInternalState : E_ControlState;
tonWatchdog : TON;
END_VAR
(* Safety Monitor - Freeze protection for coils with low-limit thermostats and valve positioning *)
fbSafety(
Enable := bEnable,
EmergencyStop := bEmergencyStop,
ProcessValue := rProcessValue,
HighLimit := rSetpoint * 1.2,
LowLimit := rSetpoint * 0.1
);
(* Main Control Logic *)
IF fbSafety.SafeToRun THEN
(* Ramp Generator - Prevents startup surge *)
fbRamp(
Enable := bEnable,
TargetValue := rSetpoint,
RampRate := 20.0, (* Building Automation rate *)
CurrentValue => rSetpoint
);
(* PID Controller - [object Object] *)
fbPID(
Enable := fbRamp.InPosition,
ProcessValue := rProcessValue,
Setpoint := fbRamp.CurrentValue,
Kp := 1.0,
Ki := 0.1,
Kd := 0.05,
OutputMin := 0.0,
OutputMax := 100.0
);
rControlOutput := fbPID.Output;
bRunning := TRUE;
bFault := FALSE;
nFaultCode := 0;
ELSE
(* Safe State - High-limit safety shutoffs for heating equipment *)
rControlOutput := 0.0;
bRunning := FALSE;
bFault := NOT bEnable; (* Only fault if not intentional stop *)
nFaultCode := fbSafety.FaultCode;
END_IF;
(* Diagnostics - Offloaded to HMI / SCADA via Modbus; some scope traces savable from Workshop for one-off captures. *)
fbDiag(
ProcessRunning := bRunning,
FaultActive := bFault,
ProcessValue := rProcessValue,
ControlOutput := rControlOutput
);
(* Watchdog - Detects frozen control *)
tonWatchdog(IN := bRunning AND NOT fbPID.OutputChanging, PT := T#10S);
IF tonWatchdog.Q THEN
bFault := TRUE;
nFaultCode := 99; (* Watchdog fault *)
END_IF;
(* Reset Logic *)
IF bReset AND NOT bEmergencyStop THEN
bFault := FALSE;
nFaultCode := 0;
fbDiag.ClearAlarms();
END_IF;
END_FUNCTION_BLOCKCode Explanation:
- 1.Encapsulated function block follows P-label subroutines plus a small library - reusable across Building Automation projects
- 2.FB_SafetyMonitor provides Freeze protection for coils with low-limit thermostats and valve positioning including high/low limits
- 3.FB_RampGenerator prevents startup issues common in HVAC Control systems
- 4.FB_PIDController tuned for Building Automation: Kp=1.0, Ki=0.1
- 5.Watchdog timer detects frozen control - critical for intermediate HVAC Control reliability
- 6.Diagnostic function block enables Offloaded to HMI / SCADA via Modbus; some scope traces savable from Workshop for one-off captures. and M-flag banks plus drive-fault flags read via Modbus parameter mapping; combined alarm rollup to HMI tag.
Best Practices
- ✓Follow INVT naming conventions: Raw FX-style addressing dominates. Symbolic naming is supported but rarely used
- ✓INVT function design: P-label subroutines plus a small library of INVT-supplied drive-control FBs that
- ✓Data organization: No structured DB; D / HD register banks with engineer-documented range conventio
- ✓Function Blocks: Arrange blocks for clear left-to-right data flow
- ✓Function Blocks: Use consistent spacing and alignment for readability
- ✓Function Blocks: Label all inputs and outputs with meaningful names
- ✓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 INVT Workshop / AutoStudio: Use the combined scope to confirm whether a fault is in PLC logic or i
- ✓Safety: Freeze protection for coils with low-limit thermostats and valve positioning
- ✓Use INVT Workshop / AutoStudio simulation tools to test HVAC Control logic before deployment
Common Pitfalls to Avoid
- ⚠Function Blocks: Creating feedback loops without proper initialization
- ⚠Function Blocks: Connecting incompatible data types
- ⚠Function Blocks: Not considering execution order dependencies
- ⚠INVT common error: Drive-parameter mapping desync after firmware update on attached VFD
- ⚠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 Function Blocks programs unmaintainable over time
Related Certifications
Mastering Function Blocks for HVAC Control applications using INVT INVT Workshop / AutoStudio 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.
INVT's <1% global market share and moderate in hvac, water treatment, textiles, basic process equipment, and oem machines paired with invt drives 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 Function Blocks best practices to INVT-specific optimizations—you can deliver reliable HVAC Control systems that meet Building Automation requirements.
Next Steps for Professional Development:
1. Certification: Pursue INVT distributor training to validate your INVT expertise
2. Advanced Training: Consider Drive-PLC integration certificates for specialized Building Automation applications
3. Hands-on Practice: Build HVAC Control projects using IVC1 hardware
4. Stay Current: Follow INVT Workshop / AutoStudio updates and new Function Blocks features
Function Blocks Foundation:
Function Block Diagram (FBD) is a graphical programming language where functions and function blocks are represented as boxes connected by signal line...
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 Temperature control, Hospital environmental systems, and INVT platform-specific features for HVAC Control optimization.