Air Handling Units (AHUs) are at the heart of many commercial HVAC systems, providing ventilation, heating, cooling, filtration, and air distribution throughout a building.
However, the performance of an AHU depends heavily on its control system. Modern AHU controls ensure that air is delivered at the correct temperature, humidity, and airflow rate while minimising energy consumption and maintaining occupant comfort.
Whether you're a building owner, facilities manager, consultant, contractor, or HVAC engineer, understanding AHU controls is essential for achieving efficient and reliable building performance.
Table of Contents
This guide explains everything you need to know about AHU controls, including:
- What AHU controls are
- How AHU controls work
- The key components within an AHU control system
- Common AHU control sequences
- Heating, cooling, fan, and damper control strategies
- Building Management System (BMS) integration
- Energy-saving opportunities
- Common AHU control problems
- Benefits of upgrading AHU controls
- Frequently asked questions
By the end of this guide, you'll have a clear understanding of how modern AHU control systems optimise performance, improve indoor air quality, and reduce operating costs.
Table of Contents
- What Are AHU Controls?
- Why Are AHU Controls Important?
- Components of an AHU Control System
- How AHU Controls Work
- Typical AHU Control Sequence
- Heating Coil Control
- Cooling Coil Control
- Fan Control Strategies
- Damper Control Strategies
- AHU Controls and Building Management Systems (BMS)
- Energy Efficiency Benefits of AHU Controls
- Common AHU Control Problems
- Should You Upgrade Your AHU Controls?
- Frequently Asked Questions
- Conclusion
1. What Are AHU Controls?
AHU controls are the collection of hardware and software responsible for managing the operation of an Air Handling Unit.
The control system monitors environmental conditions and adjusts various components to maintain the required indoor conditions.
Typical functions include:
- Temperature control
- Airflow control
- Humidity management
- Fresh air regulation
- Energy recovery optimisation
- Occupancy scheduling
- Alarm monitoring
- Equipment protection
Without an effective control strategy, even the most advanced Air Handling Unit will struggle to operate efficiently.
2. Why Are AHU Controls Important?
Modern buildings require HVAC systems to balance comfort, energy efficiency, and indoor air quality.
AHU controls help achieve these objectives by:
- Maintaining stable supply air temperatures
- Ensuring adequate fresh air ventilation
- Preventing overheating and overcooling
- Reducing energy consumption
- Protecting equipment from damage
- Supporting sustainability goals
- Improving occupant comfort
As energy costs continue to rise, intelligent AHU controls have become increasingly important for commercial building operators.
3. Components of an AHU Control System
An AHU control system consists of several key components working together.
Sensors
Sensors provide the information required for control decisions.
Common sensors include:
- Supply air temperature sensors
- Return air temperature sensors
- Outdoor air temperature sensors
- Humidity sensors
- Differential pressure sensors
- Air quality sensors
- CO₂ sensors
Controllers
The controller acts as the brain of the system.
Modern controllers continuously analyse sensor data and adjust outputs accordingly.
Actuators
Actuators control mechanical devices such as:
- Heating valves
- Cooling valves
- Dampers
- Variable speed drives
Variable Speed Drives (VSDs)
VSDs allow fan speeds to be adjusted dynamically based on demand.
User Interfaces
Modern systems often include:
- Touchscreen interfaces
- Web-based dashboards
- Mobile access
- Remote monitoring portals
4. How AHU Controls Work
AHU controls continuously monitor building conditions and compare them against desired setpoints.
For example:
If the supply air temperature falls below the required setpoint:
- The controller detects the temperature deviation.
- The heating valve opens.
- Hot water flow increases.
- The supply air temperature rises.
- The valve modulates to maintain the desired temperature.
This process occurs continuously throughout the day to ensure stable operation.
5. Typical AHU Control Sequence
A standard AHU sequence of operation may include:
Startup
- Dampers open
- Fans start
- Airflow is proven
- Safety checks are completed
Normal Operation
- Temperature control loops become active
- Heating and cooling outputs modulate
- Fresh air dampers adjust as required
- Fan speeds optimise based on demand
Shutdown
- Heating and cooling outputs close
- Fans stop after delay periods
- Dampers return to their safe position
6. Heating Coil Control
Heating coils are commonly used to raise supply air temperature.
Control strategies typically involve:
- PID temperature control
- Frost protection logic
- Low-temperature alarms
- Valve modulation
The heating valve continuously adjusts to maintain the desired supply air temperature while preventing energy waste.
7. Cooling Coil Control
Cooling coils remove heat from incoming air.
Common cooling control functions include:
- Chilled water valve modulation
- DX cooling control
- Mechanical cooling staging
- Free cooling optimisation
Effective cooling control helps maintain comfort while reducing energy consumption.
8. Fan Control Strategies
Fans are among the largest energy consumers within an AHU.
Modern systems use Variable Speed Drives (VSDs) to optimise fan performance.
Benefits include:
- Reduced energy usage
- Lower noise levels
- Improved airflow control
- Extended equipment life
Fan control strategies often use:
- Constant pressure control
- Constant airflow control
- Demand-controlled ventilation
9. Damper Control Strategies
Dampers regulate airflow through the AHU.
Typical damper functions include:
- Fresh air control
- Return air control
- Exhaust air control
- Free cooling operation
- Frost protection
Intelligent damper control can significantly improve overall HVAC efficiency.
10. AHU Controls and Building Management Systems (BMS)
Most commercial AHU control systems integrate with a Building Management System.
BMS integration allows facilities teams to:
- Monitor system performance remotely
- Adjust operating schedules
- Generate alarms
- View trends and reports
- Analyse energy consumption
- Optimise building performance
Common communication protocols include:
- Modbus
- BACnet
- KNX
- MQTT
- OPC UA
BMS integration provides greater visibility and control across the entire building.
11. Energy Efficiency Benefits of AHU Controls
One of the primary reasons organisations invest in advanced AHU controls is energy efficiency.
Key energy-saving strategies include:
- Demand-controlled ventilation
- Heat recovery optimisation
- Variable speed fan control
- Occupancy scheduling
- Supply air temperature reset
- Free cooling control
- Night setback operation
These strategies can significantly reduce HVAC operating costs while maintaining occupant comfort.
12. Common AHU Control Problems
Poor Temperature Control
Often caused by faulty sensors or incorrectly tuned control loops.
Excessive Energy Consumption
May result from poor scheduling, incorrect setpoints, or failed control components.
Fan Issues
Can be caused by VSD faults, airflow sensor problems, or incorrect commissioning.
Damper Failures
Actuator faults can lead to ventilation problems and reduced efficiency.
Communication Failures
Network issues can interrupt BMS communication and monitoring.
Regular maintenance and monitoring help identify these issues before they affect building operation.
13. Should You Upgrade Your AHU Controls?
Many older AHUs still contain mechanically sound equipment but operate using outdated control systems.
Upgrading the controls can deliver:
- Improved energy efficiency
- Better comfort levels
- Enhanced fault diagnostics
- Remote monitoring
- BMS integration
- Reduced maintenance costs
- Greater operational flexibility
In many cases, upgrading controls provides a faster return on investment than replacing the entire Air Handling Unit.
14. Frequently Asked Questions
What Does AHU Stand For?
AHU stands for Air Handling Unit.
What Is the Purpose of AHU Controls?
AHU controls manage heating, cooling, ventilation, airflow, and overall system performance.
Can AHU Controls Reduce Energy Costs?
Yes. Modern control strategies can significantly reduce HVAC energy consumption while maintaining comfort.
What Sensors Are Used in AHU Controls?
Common sensors include temperature, humidity, pressure, airflow, and CO₂ sensors.
Can AHUs Be Connected to a Building Management System?
Yes. Most modern AHU controls support BMS integration using industry-standard communication protocols.
How Often Should AHU Controls Be Maintained?
Control systems should be inspected regularly as part of routine HVAC maintenance to ensure optimal performance.
Conclusion
AHU controls play a critical role in maintaining comfortable, healthy, and energy-efficient buildings. By intelligently managing heating, cooling, ventilation, dampers, and fan operation, modern control systems help organisations reduce operating costs while improving indoor environmental quality.
Whether you're designing a new HVAC system, upgrading an existing AHU, or seeking to improve building performance, investing in the right control strategy is essential for long-term success.
Need Help with AHU Controls?
At iACS, we specialise in intelligent AHU control solutions for commercial and industrial applications. From standalone Air Handling Units to fully integrated Building Management Systems, our team helps customers achieve maximum performance, efficiency, and reliability.
Whether you're designing a new project, upgrading existing controls, or looking to improve building energy performance, our HVAC controls specialists are here to help.