Submodule 3: PID Applications in HVAC
Let's go!
Understanding PID through PV
From the previous submodules, you have learned that a controller uses real-time feedback to minimize the difference between the SP and the PV. Specifically, a PID controller continuously measures the error and calculates an output that adjusts system devices (such as valves, dampers, fans, etc.) to bring the PV closer to the SP. Together, proportional, integral, and derivative terms enable the controller to maintain system stability, improve accuracy, and respond effectively to disturbances or changing conditions.
Continue
Understanding PID through PV
For HVAC systems, focusing on the PV is crucial because it represents the actual environmental conditions that impact occupant comfort and energy efficiency. The controller's efficacy is judged by how well it drives the PV to remain consistently at or near the SP despite external variations. This understanding will help you interpret control responses and optimize tuning for better performance in HVAC applications.
Continue
Hint 1
PV Understanding Check
Hint 2
Drag and drop examples of PVs into the gray box. You will only complete the question once all the proper PV examples have been placed. If you are stuck, two Hint buttons will appear after 30 and 60 seconds, respectively, in the upper right corner.
Word Bank:
PV Examples:
Control Temperature (°C, °F)
Valve Position (%Open)
Pressure (psi, bar, Pa)
Liquid Flow (GPM, L/min)
Proportional Gain (unitless)
Outside Temperature (°C, °F)
Level (in a tank—%full, inches, cm)
Millivolt Signal (mV)
Incorrect/Incomplete!
Correct!
Continue
Check Answers
Back
Practical Application of PID Theory Through System Loop Identification
Having explored how PID controllers influence PV to maintain precise system control, it is essential to translate this theoretical understanding into practical skills. Recognizing how PID control manifests in real HVAC systems requires identifying individual control loops that work together to regulate environmental conditions.
Continue
Practical Application of PID Theory Through System Loop Identification
This section will demonstrate how to locate and interpret these control loops within system architectures, enabling effective monitoring, troubleshooting, and optimization baed on the impacts observed on the PV. By bridging theory with hands-on system identification, you gain the ability to apply PID concepts directly to real-world HVAC controls for improved performance and reliability.
Continue
General Principles of Finding Control Loops
Follow the flowchart and click on each general principle to learn more. Once you have completed the flowchart, please move on.
Determine Controlled Devices that Affect the Process Plant
Identify Sensors Measuring PV
Locate Controllers Comparing PVs to SPs
Recognize Independence or Interaction Among Loops
Map Signal Flow to Outline the Loop
Use Signal Labels and System Documentation
Continue
PID in Real-World Applications
Next, you will review several examples of HVAC equipment: a furnace with a residential thermostat, a variable air volume (VAV) box, and an air handling unit (AHU). For each system, identify the control loops and answer the questions by dragging and dropping the correct responses into the appropriate boxes. The Continue button will appear once all answers are correct. A Description button will be available in the upper-right corner to review the equipment details. If you get stuck on the PV identification questions, two Hint buttons will appear after 30 and 60 seconds, respectively, in the upper-right corner.
Continue
Furnace with Thermostat
A furnace with a thermostat heats a room by first detecting when the air has dropped below a user-set temperature. When this happens, the thermostat signals the furnace to turn on. Inside the furnace, fuel (like natural gas or oil) is burned in a combustion chamber, heating up a metal part called the heat exchanger. Cool air from the room is drawn in by a blower and passed over the hot heat exchanger, raising its temperature. The warmed air is then blown back through the home's ductwork and into the room. This cycle repeats, with the thermostat turning the furnace on and off as needed, to keep the room close to the desired temperature, while the furnace's exhaust gases are safely vented outside.
Continue
Description
Furnace with Thermostat
Hint 1
Hint 2
A standard home furnace represents the simplest form of a control loop.
What are the PV(s) for this system?
Room Temperature
Humidity
Outdoor Air Temperature
Fuel Flow
Position of Damper
Fan Speed
You have correctly identified the PV (room temperature); this confirms there is only one control loop in this furnace system.
Correct!
Continue
Check Answers
Incorrect!
Back
Description
Furnace with Thermostat
A standard home thermostat represents the simplest form of a closed control loop.
Which device supplies the PV in this furnace system?
Thermostat Dial
Furnace Burner
Supply Air Vent
Room Temperature Sensor
Outdoor Temperature Sensor
Blower Fan
The room temperature sensor supplies the PV and allows the thermostat to continuously monitor the space and regulate heating as needed.
Correct!
Continue
Check Answers
Incorrect!
Back
Description
Furnace with Thermostat
A standard home thermostat represents the simplest form of a closed control loop.
What happens if the PV is below the SP?
Nothing; the furnace remains off.
The thermostat lowers the SP to match the room temperature.
The furnace turns on until the SP is reached.
Only the blower turns on; the furnace remains off.
When the PV drops below the SP, the thermostat responds by signaling the furnace to turn on—raising the temperature back toward the user's desired level.
Correct!
Continue
Check Answers
Incorrect!
Back
Variable Air Volume (VAV) Box
A VAV box is a device used to control the amount of air that enters a room or zone. It operates by adjusting a damper to vary the airflow based on temperature requirements and occupant comfort. The VAV box receives cooled or heated supply air from the HVAC system, and a sensor measures the actual airflow delivered to the zone. The controller analyzes the error and moves the damper to either increase or decrease the flow. When heating is needed in the zone, a reheat coil within the VAV box can warm the supply air, keeping the space comfortable without sending extra airflow. These systems may have separate control loops for airflow and temperature, working together to provide energy-efficient climate control.
Continue
Description
Variable Air Volume (VAV) Box
Hint 1
Hint 2
A VAV box represents a more advanced form of a control loop.
What are the PV(s) for this system?
Position of Damper
Humidity
Fan Speed
Airflow
Reheat Temperature
Outdoor Air Temperature
You have correctly identified the PVs (reheat temperature and airflow); this confirms there are two control loops in this VAV system.
Correct!
Continue
Check Answers
Incorrect!
Back
Description
Variable Air Volume (VAV) Box
A VAV box represents a more advanced form of a closed control loop.
What is the function of the airflow control loop in a VAV system?
Adjusts the damper position.
Adjusts the supply air temperature.
Modules the reheat coil output.
Controls fan speed at the main HVAC unit.
Maintains constant zone humidity.
The airflow control loop continuously adjusts the damper position to keep actual airflow at the required SP.
Correct!
Continue
Check Answers
Incorrect!
Back
Description
Variable Air Volume (VAV) Box
A VAV box represents a more advanced form of a closed control loop.
If the zone temperature overshoots the SP after reheat activation, what is the most likely cause?
The damper is undersized and restricting airflow.
The reheat valve PID gain is too aggressive, causing overshoot.
The supply air temperature from the HVAC system is too cold.
The airflow loop has a sensor fault.
The proportional gain of the PID controller is set too high. This causes the reheat valve to react too strongly to temperature errors, resulting in the zone temperature rising past the SP after reheat is activated.
Correct!
Continue
Check Answers
Incorrect!
Back
Air Handling Unit (AHU)
An AHU is a central building device designed to clean, heat, cool, and move air for comfort and ventilation. It draws return air from inside rooms and often mixes it with fresh ventilation air from outside, helping to maintain good indoor air quality. That air first passes through filters that trap dust and other particles. Afterwards, the air moves over heating and cooling coils to adjust its temperature—this determines the supply air temperature, which is the temperature of the air as it leaves the unit and is delivered to rooms throughout the building. Fans then push this conditioned, temperature-controlled air through the building's ductwork. Dampers inside the AHU are used to control both the direction and amount of airflow, including regulation of relief air, which is sometimes vented to the outdoors to keep indoor air fresh. Sensors measure these PVs, and a controller compares them to their desired SPs and adjusts valves, coils, dampers, or fan speeds as needed to keep the indoor environment healthy and comfortable.
Continue
Description
Air Handling Unit (AHU)
Hint 1
Hint 2
An AHU represents a more complex form of a control loop.
What are the PV(s) for this system?
Supply Air Temperature
Ventilation Air
Humidity
Relief Air
Airflow
Fan Speed
You have correctly identified some of the PVs that appear in an AHU; this confirms there are multiple control loops in this AHU system.
Correct!
Continue
Check Answers
Incorrect!
Back
Description
Air Handling Unit (AHU)
An AHU represents a more complex form of a closed control loop.
What could happen if air filters inside the AHU become clogged?
Both heating and cooling coils stop working entirely.
The supply air temperature automatically increases.
Airflow through the AHU decreases.
Relief air is no longer needed in the system.
A clogged filter restricts airflow, making it harder for the system to condition and move air. Regularly replacing or cleaning filters helps the AHU keep indoor air quality high and the climate stable.
Correct!
Continue
Check Answers
Incorrect!
Back
Description
Air Handling Unit (AHU)
An AHU represents a more complex form of a closed control loop.
If discharge air temperature fluctuates widely around the SP, what might this suggest?
The air ducts are leaking air.
The supply fan is running too slowly.
The return air damper is stuck in an open position.
The PID loop is poorly tuned.
Someone changed the SP recently.
The temperature sensor is installed incorrectly.
Large, frequent swings in discharge air temperature often mean the controller is not responding smoothly, which can be fixed by improving the PID tuning to avoid strong or delayed reactions.
Correct!
Continue
Check Answers
Incorrect!
Back
Thank you!
You have reached the end of the slideshow. Please return to the homepage and follow the next steps.
Homepage
Determine Controlled Devices that Affect the Process Plant
Look into the mechanical or electrical devices influenced by controller outputs. Understand the operational range of responsiveness of these devices, ad device limitations often restrict control effectiveness. Also, be aware of any manual overrides or safety limits that may temporarily suspend automated control.
VAV Box
A VAV box is a device used to control the amount of air that enters a room or zone. It operates by adjusting a damper to vary the airflow based on temperature requirements and occupant comfort. The VAV box receives cooled or heated supply air from the HVAC system, and a sensor measures the actual airflow delivered to the zone. The controller analyzes the error and moves the damper to either increase or decrease the flow. When heating is needed in the zone, a reheat coil within the VAV box can warm the supply air, keeping the space comfortable without sending extra airflow. These systems may have separate control loops for airflow and temperature, working together to provide energy-efficient climate control.
Hint 1
Remember that PV is defined as the current measured value of the property being managed. What examples are properties that can be managed?
AHU
An AHU is a central building device designed to clean, heat, cool, and move air for comfort and ventilation. It draws return air from inside rooms and often mixes it with fresh ventilation air from outside, helping to maintain good indoor air quality. That air first passes through filters that trap dust and other particles. Afterwards, the air moves over heating and cooling coils to adjust its temperature—this determines the supply air temperature, which is the temperature of the air as it leaves the unit and is delivered to rooms throughout the building. Fans then push this conditioned, temperature-controlled air through the building's ductwork. Dampers inside the AHU are used to control both the direction and amount of airflow, including regulation of relief air, which is sometimes vented to the outdoors to keep indoor air fresh. Sensors measure these PVs, and a controller compares them to their desired SPs and adjusts valves, coils, dampers, or fan speeds as needed to keep the indoor environment healthy and comfortable.
AHU
An AHU is a central building device designed to clean, heat, cool, and move air for comfort and ventilation. It draws return air from inside rooms and often mixes it with fresh ventilation air from outside, helping to maintain good indoor air quality. That air first passes through filters that trap dust and other particles. Afterwards, the air moves over heating and cooling coils to adjust its temperature—this determines the supply air temperature, which is the temperature of the air as it leaves the unit and is delivered to rooms throughout the building. Fans then push this conditioned, temperature-controlled air through the building's ductwork. Dampers inside the AHU are used to control both the direction and amount of airflow, including regulation of relief air, which is sometimes vented to the outdoors to keep indoor air fresh. Sensors measure these PVs, and a controller compares them to their desired SPs and adjusts valves, coils, dampers, or fan speeds as needed to keep the indoor environment healthy and comfortable.
Hint 1
Based on the description of how a VAV box works, what are the properties that can be managed?
Hint 1
Based on the description of how an AHU box works, what are the properties that can be managed?
Hint 1
Based on the description of how a furnace with a thermostat works, what are the properties that can be managed?
Hint 2
There are five correct answers for this question!
Hint 2
There is only one correct answer for this question!
Identify Sensors Measuring PV
Focus on locating the physical sensors installed in the system. Consider their locations relative to the spaces or equipment they monitor, as this influences the accuracy and relevance of the measurement. Sensor type and quality affect the fidelity of control loops, so note whether sensors are analog or digital, and their calibration status.
Use Signal Labels and System Documentation
Cross-reference signal names and control sequences with wiring diagrams, control narratives, and software graphics. Familiarity with labeling conventions aids in quickly identifying loop components and understanding the intended function of each signal patch.
Hint 2
There are four correct answers!
Hint 2
There are two correct answers for this question!
AHU
An AHU is a central building device designed to clean, heat, cool, and move air for comfort and ventilation. It draws return air from inside rooms and often mixes it with fresh ventilation air from outside, helping to maintain good indoor air quality. That air first passes through filters that trap dust and other particles. Afterwards, the air moves over heating and cooling coils to adjust its temperature—this determines the supply air temperature, which is the temperature of the air as it leaves the unit and is delivered to rooms throughout the building. Fans then push this conditioned, temperature-controlled air through the building's ductwork. Dampers inside the AHU are used to control both the direction and amount of airflow, including regulation of relief air, which is sometimes vented to the outdoors to keep indoor air fresh. Sensors measure these PVs, and a controller compares them to their desired SPs and adjusts valves, coils, dampers, or fan speeds as needed to keep the indoor environment healthy and comfortable.
Furnace with Thermostat
A furnace with a thermostat heats a room by first detecting when the air has dropped below a user-set temperature. When this happens, the thermostat signals the furnace to turn on. Inside the furnace, fuel (like natural gas or oil) is burned in a combustion chamber, heating up a metal part called the heat exchanger. Cool air from the room is drawn in by a blower and passed over the hot heat exchanger, raising its temperature. The warmed air is then blown back through the home's ductwork and into the room. This cycle repeats, with the thermostat turning the furnace on and off as needed, to keep the room close to the desired temperature, while the furnace's exhaust gases are safely vented outside.
VAV Box
A VAV box is a device used to control the amount of air that enters a room or zone. It operates by adjusting a damper to vary the airflow based on temperature requirements and occupant comfort. The VAV box receives cooled or heated supply air from the HVAC system, and a sensor measures the actual airflow delivered to the zone. The controller analyzes the error and moves the damper to either increase or decrease the flow. When heating is needed in the zone, a reheat coil within the VAV box can warm the supply air, keeping the space comfortable without sending extra airflow. These systems may have separate control loops for airflow and temperature, working together to provide energy-efficient climate control.
VAV Box
A VAV box is a device used to control the amount of air that enters a room or zone. It operates by adjusting a damper to vary the airflow based on temperature requirements and occupant comfort. The VAV box receives cooled or heated supply air from the HVAC system, and a sensor measures the actual airflow delivered to the zone. The controller analyzes the error and moves the damper to either increase or decrease the flow. When heating is needed in the zone, a reheat coil within the VAV box can warm the supply air, keeping the space comfortable without sending extra airflow. These systems may have separate control loops for airflow and temperature, working together to provide energy-efficient climate control.
Locate Controllers Comparing PVs to SPs
Examine controller settings and logic to understand their role in control. Controllers may be part of centralized automation platforms or distributed throughout the system. Check if the controller's algorithm is PID-based or uses other control strategies, and verify how control decisions are made based on input signals.
Recognize Independence or Interaction Among Loops
Identify whether control loops operate independently, or if they have cascading or supervisory relationships. Multi-loop interactions can impact system dynamics, making it essential to understand these relationships for accurate diagnosis and tuning.
Map Signal Flow to Outline the Loop
Use system documentation and real-time monitoring tools to trace how signals move between components. Mapping signal flow helps visualize which sensors, controllers, and devices form a closed feedback loop. Signal type and communication protocols affect timing and precision within the loop.
Furnace with Thermostat
A furnace with a thermostat heats a room by first detecting when the air has dropped below a user-set temperature. When this happens, the thermostat signals the furnace to turn on. Inside the furnace, fuel (like natural gas or oil) is burned in a combustion chamber, heating up a metal part called the heat exchanger. Cool air from the room is drawn in by a blower and passed over the hot heat exchanger, raising its temperature. The warmed air is then blown back through the home's ductwork and into the room. This cycle repeats, with the thermostat turning the furnace on and off as needed, to keep the room close to the desired temperature, while the furnace's exhaust gases are safely vented outside.
Furnace with Thermostat
A furnace with a thermostat heats a room by first detecting when the air has dropped below a user-set temperature. When this happens, the thermostat signals the furnace to turn on. Inside the furnace, fuel (like natural gas or oil) is burned in a combustion chamber, heating up a metal part called the heat exchanger. Cool air from the room is drawn in by a blower and passed over the hot heat exchanger, raising its temperature. The warmed air is then blown back through the home's ductwork and into the room. This cycle repeats, with the thermostat turning the furnace on and off as needed, to keep the room close to the desired temperature, while the furnace's exhaust gases are safely vented outside.
Submodule 3: PID Applications in HVAC
Christine Shao
Created on November 4, 2025
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Transcript
Submodule 3: PID Applications in HVAC
Let's go!
Understanding PID through PV
From the previous submodules, you have learned that a controller uses real-time feedback to minimize the difference between the SP and the PV. Specifically, a PID controller continuously measures the error and calculates an output that adjusts system devices (such as valves, dampers, fans, etc.) to bring the PV closer to the SP. Together, proportional, integral, and derivative terms enable the controller to maintain system stability, improve accuracy, and respond effectively to disturbances or changing conditions.
Continue
Understanding PID through PV
For HVAC systems, focusing on the PV is crucial because it represents the actual environmental conditions that impact occupant comfort and energy efficiency. The controller's efficacy is judged by how well it drives the PV to remain consistently at or near the SP despite external variations. This understanding will help you interpret control responses and optimize tuning for better performance in HVAC applications.
Continue
Hint 1
PV Understanding Check
Hint 2
Drag and drop examples of PVs into the gray box. You will only complete the question once all the proper PV examples have been placed. If you are stuck, two Hint buttons will appear after 30 and 60 seconds, respectively, in the upper right corner.
Word Bank:
PV Examples:
Control Temperature (°C, °F)
Valve Position (%Open)
Pressure (psi, bar, Pa)
Liquid Flow (GPM, L/min)
Proportional Gain (unitless)
Outside Temperature (°C, °F)
Level (in a tank—%full, inches, cm)
Millivolt Signal (mV)
Incorrect/Incomplete!
Correct!
Continue
Check Answers
Back
Practical Application of PID Theory Through System Loop Identification
Having explored how PID controllers influence PV to maintain precise system control, it is essential to translate this theoretical understanding into practical skills. Recognizing how PID control manifests in real HVAC systems requires identifying individual control loops that work together to regulate environmental conditions.
Continue
Practical Application of PID Theory Through System Loop Identification
This section will demonstrate how to locate and interpret these control loops within system architectures, enabling effective monitoring, troubleshooting, and optimization baed on the impacts observed on the PV. By bridging theory with hands-on system identification, you gain the ability to apply PID concepts directly to real-world HVAC controls for improved performance and reliability.
Continue
General Principles of Finding Control Loops
Follow the flowchart and click on each general principle to learn more. Once you have completed the flowchart, please move on.
Determine Controlled Devices that Affect the Process Plant
Identify Sensors Measuring PV
Locate Controllers Comparing PVs to SPs
Recognize Independence or Interaction Among Loops
Map Signal Flow to Outline the Loop
Use Signal Labels and System Documentation
Continue
PID in Real-World Applications
Next, you will review several examples of HVAC equipment: a furnace with a residential thermostat, a variable air volume (VAV) box, and an air handling unit (AHU). For each system, identify the control loops and answer the questions by dragging and dropping the correct responses into the appropriate boxes. The Continue button will appear once all answers are correct. A Description button will be available in the upper-right corner to review the equipment details. If you get stuck on the PV identification questions, two Hint buttons will appear after 30 and 60 seconds, respectively, in the upper-right corner.
Continue
Furnace with Thermostat
A furnace with a thermostat heats a room by first detecting when the air has dropped below a user-set temperature. When this happens, the thermostat signals the furnace to turn on. Inside the furnace, fuel (like natural gas or oil) is burned in a combustion chamber, heating up a metal part called the heat exchanger. Cool air from the room is drawn in by a blower and passed over the hot heat exchanger, raising its temperature. The warmed air is then blown back through the home's ductwork and into the room. This cycle repeats, with the thermostat turning the furnace on and off as needed, to keep the room close to the desired temperature, while the furnace's exhaust gases are safely vented outside.
Continue
Description
Furnace with Thermostat
Hint 1
Hint 2
A standard home furnace represents the simplest form of a control loop.
What are the PV(s) for this system?
Room Temperature
Humidity
Outdoor Air Temperature
Fuel Flow
Position of Damper
Fan Speed
You have correctly identified the PV (room temperature); this confirms there is only one control loop in this furnace system.
Correct!
Continue
Check Answers
Incorrect!
Back
Description
Furnace with Thermostat
A standard home thermostat represents the simplest form of a closed control loop.
Which device supplies the PV in this furnace system?
Thermostat Dial
Furnace Burner
Supply Air Vent
Room Temperature Sensor
Outdoor Temperature Sensor
Blower Fan
The room temperature sensor supplies the PV and allows the thermostat to continuously monitor the space and regulate heating as needed.
Correct!
Continue
Check Answers
Incorrect!
Back
Description
Furnace with Thermostat
A standard home thermostat represents the simplest form of a closed control loop.
What happens if the PV is below the SP?
Nothing; the furnace remains off.
The thermostat lowers the SP to match the room temperature.
The furnace turns on until the SP is reached.
Only the blower turns on; the furnace remains off.
When the PV drops below the SP, the thermostat responds by signaling the furnace to turn on—raising the temperature back toward the user's desired level.
Correct!
Continue
Check Answers
Incorrect!
Back
Variable Air Volume (VAV) Box
A VAV box is a device used to control the amount of air that enters a room or zone. It operates by adjusting a damper to vary the airflow based on temperature requirements and occupant comfort. The VAV box receives cooled or heated supply air from the HVAC system, and a sensor measures the actual airflow delivered to the zone. The controller analyzes the error and moves the damper to either increase or decrease the flow. When heating is needed in the zone, a reheat coil within the VAV box can warm the supply air, keeping the space comfortable without sending extra airflow. These systems may have separate control loops for airflow and temperature, working together to provide energy-efficient climate control.
Continue
Description
Variable Air Volume (VAV) Box
Hint 1
Hint 2
A VAV box represents a more advanced form of a control loop.
What are the PV(s) for this system?
Position of Damper
Humidity
Fan Speed
Airflow
Reheat Temperature
Outdoor Air Temperature
You have correctly identified the PVs (reheat temperature and airflow); this confirms there are two control loops in this VAV system.
Correct!
Continue
Check Answers
Incorrect!
Back
Description
Variable Air Volume (VAV) Box
A VAV box represents a more advanced form of a closed control loop.
What is the function of the airflow control loop in a VAV system?
Adjusts the damper position.
Adjusts the supply air temperature.
Modules the reheat coil output.
Controls fan speed at the main HVAC unit.
Maintains constant zone humidity.
The airflow control loop continuously adjusts the damper position to keep actual airflow at the required SP.
Correct!
Continue
Check Answers
Incorrect!
Back
Description
Variable Air Volume (VAV) Box
A VAV box represents a more advanced form of a closed control loop.
If the zone temperature overshoots the SP after reheat activation, what is the most likely cause?
The damper is undersized and restricting airflow.
The reheat valve PID gain is too aggressive, causing overshoot.
The supply air temperature from the HVAC system is too cold.
The airflow loop has a sensor fault.
The proportional gain of the PID controller is set too high. This causes the reheat valve to react too strongly to temperature errors, resulting in the zone temperature rising past the SP after reheat is activated.
Correct!
Continue
Check Answers
Incorrect!
Back
Air Handling Unit (AHU)
An AHU is a central building device designed to clean, heat, cool, and move air for comfort and ventilation. It draws return air from inside rooms and often mixes it with fresh ventilation air from outside, helping to maintain good indoor air quality. That air first passes through filters that trap dust and other particles. Afterwards, the air moves over heating and cooling coils to adjust its temperature—this determines the supply air temperature, which is the temperature of the air as it leaves the unit and is delivered to rooms throughout the building. Fans then push this conditioned, temperature-controlled air through the building's ductwork. Dampers inside the AHU are used to control both the direction and amount of airflow, including regulation of relief air, which is sometimes vented to the outdoors to keep indoor air fresh. Sensors measure these PVs, and a controller compares them to their desired SPs and adjusts valves, coils, dampers, or fan speeds as needed to keep the indoor environment healthy and comfortable.
Continue
Description
Air Handling Unit (AHU)
Hint 1
Hint 2
An AHU represents a more complex form of a control loop.
What are the PV(s) for this system?
Supply Air Temperature
Ventilation Air
Humidity
Relief Air
Airflow
Fan Speed
You have correctly identified some of the PVs that appear in an AHU; this confirms there are multiple control loops in this AHU system.
Correct!
Continue
Check Answers
Incorrect!
Back
Description
Air Handling Unit (AHU)
An AHU represents a more complex form of a closed control loop.
What could happen if air filters inside the AHU become clogged?
Both heating and cooling coils stop working entirely.
The supply air temperature automatically increases.
Airflow through the AHU decreases.
Relief air is no longer needed in the system.
A clogged filter restricts airflow, making it harder for the system to condition and move air. Regularly replacing or cleaning filters helps the AHU keep indoor air quality high and the climate stable.
Correct!
Continue
Check Answers
Incorrect!
Back
Description
Air Handling Unit (AHU)
An AHU represents a more complex form of a closed control loop.
If discharge air temperature fluctuates widely around the SP, what might this suggest?
The air ducts are leaking air.
The supply fan is running too slowly.
The return air damper is stuck in an open position.
The PID loop is poorly tuned.
Someone changed the SP recently.
The temperature sensor is installed incorrectly.
Large, frequent swings in discharge air temperature often mean the controller is not responding smoothly, which can be fixed by improving the PID tuning to avoid strong or delayed reactions.
Correct!
Continue
Check Answers
Incorrect!
Back
Thank you!
You have reached the end of the slideshow. Please return to the homepage and follow the next steps.
Homepage
Determine Controlled Devices that Affect the Process Plant
Look into the mechanical or electrical devices influenced by controller outputs. Understand the operational range of responsiveness of these devices, ad device limitations often restrict control effectiveness. Also, be aware of any manual overrides or safety limits that may temporarily suspend automated control.
VAV Box
A VAV box is a device used to control the amount of air that enters a room or zone. It operates by adjusting a damper to vary the airflow based on temperature requirements and occupant comfort. The VAV box receives cooled or heated supply air from the HVAC system, and a sensor measures the actual airflow delivered to the zone. The controller analyzes the error and moves the damper to either increase or decrease the flow. When heating is needed in the zone, a reheat coil within the VAV box can warm the supply air, keeping the space comfortable without sending extra airflow. These systems may have separate control loops for airflow and temperature, working together to provide energy-efficient climate control.
Hint 1
Remember that PV is defined as the current measured value of the property being managed. What examples are properties that can be managed?
AHU
An AHU is a central building device designed to clean, heat, cool, and move air for comfort and ventilation. It draws return air from inside rooms and often mixes it with fresh ventilation air from outside, helping to maintain good indoor air quality. That air first passes through filters that trap dust and other particles. Afterwards, the air moves over heating and cooling coils to adjust its temperature—this determines the supply air temperature, which is the temperature of the air as it leaves the unit and is delivered to rooms throughout the building. Fans then push this conditioned, temperature-controlled air through the building's ductwork. Dampers inside the AHU are used to control both the direction and amount of airflow, including regulation of relief air, which is sometimes vented to the outdoors to keep indoor air fresh. Sensors measure these PVs, and a controller compares them to their desired SPs and adjusts valves, coils, dampers, or fan speeds as needed to keep the indoor environment healthy and comfortable.
AHU
An AHU is a central building device designed to clean, heat, cool, and move air for comfort and ventilation. It draws return air from inside rooms and often mixes it with fresh ventilation air from outside, helping to maintain good indoor air quality. That air first passes through filters that trap dust and other particles. Afterwards, the air moves over heating and cooling coils to adjust its temperature—this determines the supply air temperature, which is the temperature of the air as it leaves the unit and is delivered to rooms throughout the building. Fans then push this conditioned, temperature-controlled air through the building's ductwork. Dampers inside the AHU are used to control both the direction and amount of airflow, including regulation of relief air, which is sometimes vented to the outdoors to keep indoor air fresh. Sensors measure these PVs, and a controller compares them to their desired SPs and adjusts valves, coils, dampers, or fan speeds as needed to keep the indoor environment healthy and comfortable.
Hint 1
Based on the description of how a VAV box works, what are the properties that can be managed?
Hint 1
Based on the description of how an AHU box works, what are the properties that can be managed?
Hint 1
Based on the description of how a furnace with a thermostat works, what are the properties that can be managed?
Hint 2
There are five correct answers for this question!
Hint 2
There is only one correct answer for this question!
Identify Sensors Measuring PV
Focus on locating the physical sensors installed in the system. Consider their locations relative to the spaces or equipment they monitor, as this influences the accuracy and relevance of the measurement. Sensor type and quality affect the fidelity of control loops, so note whether sensors are analog or digital, and their calibration status.
Use Signal Labels and System Documentation
Cross-reference signal names and control sequences with wiring diagrams, control narratives, and software graphics. Familiarity with labeling conventions aids in quickly identifying loop components and understanding the intended function of each signal patch.
Hint 2
There are four correct answers!
Hint 2
There are two correct answers for this question!
AHU
An AHU is a central building device designed to clean, heat, cool, and move air for comfort and ventilation. It draws return air from inside rooms and often mixes it with fresh ventilation air from outside, helping to maintain good indoor air quality. That air first passes through filters that trap dust and other particles. Afterwards, the air moves over heating and cooling coils to adjust its temperature—this determines the supply air temperature, which is the temperature of the air as it leaves the unit and is delivered to rooms throughout the building. Fans then push this conditioned, temperature-controlled air through the building's ductwork. Dampers inside the AHU are used to control both the direction and amount of airflow, including regulation of relief air, which is sometimes vented to the outdoors to keep indoor air fresh. Sensors measure these PVs, and a controller compares them to their desired SPs and adjusts valves, coils, dampers, or fan speeds as needed to keep the indoor environment healthy and comfortable.
Furnace with Thermostat
A furnace with a thermostat heats a room by first detecting when the air has dropped below a user-set temperature. When this happens, the thermostat signals the furnace to turn on. Inside the furnace, fuel (like natural gas or oil) is burned in a combustion chamber, heating up a metal part called the heat exchanger. Cool air from the room is drawn in by a blower and passed over the hot heat exchanger, raising its temperature. The warmed air is then blown back through the home's ductwork and into the room. This cycle repeats, with the thermostat turning the furnace on and off as needed, to keep the room close to the desired temperature, while the furnace's exhaust gases are safely vented outside.
VAV Box
A VAV box is a device used to control the amount of air that enters a room or zone. It operates by adjusting a damper to vary the airflow based on temperature requirements and occupant comfort. The VAV box receives cooled or heated supply air from the HVAC system, and a sensor measures the actual airflow delivered to the zone. The controller analyzes the error and moves the damper to either increase or decrease the flow. When heating is needed in the zone, a reheat coil within the VAV box can warm the supply air, keeping the space comfortable without sending extra airflow. These systems may have separate control loops for airflow and temperature, working together to provide energy-efficient climate control.
VAV Box
A VAV box is a device used to control the amount of air that enters a room or zone. It operates by adjusting a damper to vary the airflow based on temperature requirements and occupant comfort. The VAV box receives cooled or heated supply air from the HVAC system, and a sensor measures the actual airflow delivered to the zone. The controller analyzes the error and moves the damper to either increase or decrease the flow. When heating is needed in the zone, a reheat coil within the VAV box can warm the supply air, keeping the space comfortable without sending extra airflow. These systems may have separate control loops for airflow and temperature, working together to provide energy-efficient climate control.
Locate Controllers Comparing PVs to SPs
Examine controller settings and logic to understand their role in control. Controllers may be part of centralized automation platforms or distributed throughout the system. Check if the controller's algorithm is PID-based or uses other control strategies, and verify how control decisions are made based on input signals.
Recognize Independence or Interaction Among Loops
Identify whether control loops operate independently, or if they have cascading or supervisory relationships. Multi-loop interactions can impact system dynamics, making it essential to understand these relationships for accurate diagnosis and tuning.
Map Signal Flow to Outline the Loop
Use system documentation and real-time monitoring tools to trace how signals move between components. Mapping signal flow helps visualize which sensors, controllers, and devices form a closed feedback loop. Signal type and communication protocols affect timing and precision within the loop.
Furnace with Thermostat
A furnace with a thermostat heats a room by first detecting when the air has dropped below a user-set temperature. When this happens, the thermostat signals the furnace to turn on. Inside the furnace, fuel (like natural gas or oil) is burned in a combustion chamber, heating up a metal part called the heat exchanger. Cool air from the room is drawn in by a blower and passed over the hot heat exchanger, raising its temperature. The warmed air is then blown back through the home's ductwork and into the room. This cycle repeats, with the thermostat turning the furnace on and off as needed, to keep the room close to the desired temperature, while the furnace's exhaust gases are safely vented outside.
Furnace with Thermostat
A furnace with a thermostat heats a room by first detecting when the air has dropped below a user-set temperature. When this happens, the thermostat signals the furnace to turn on. Inside the furnace, fuel (like natural gas or oil) is burned in a combustion chamber, heating up a metal part called the heat exchanger. Cool air from the room is drawn in by a blower and passed over the hot heat exchanger, raising its temperature. The warmed air is then blown back through the home's ductwork and into the room. This cycle repeats, with the thermostat turning the furnace on and off as needed, to keep the room close to the desired temperature, while the furnace's exhaust gases are safely vented outside.