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Proportional, Integral, Derivative (PID) with HVAC zone control

Local university upgrading systems to reduce energy consumption costs

Acme University’s building supervisor Greg has been asked to establish a plan to make the institution more energy efficient. Greg first notices that each of the rooms in a specific wing of the campus is being heated at varying temperatures, often higher than needed.

Greg contacts his mechanical contractor to determine what adjustments can be made to ensure that controlling the temperature zones in the building is at its highest efficiency level.

See Greg's story from the beginning

PID methodology of control

Some of the rooms within the university’s building require that a precise temperature is maintained at all times, with near zero variations. The building is outfitted with a zoned HVAC system to distribute heat to the different zones by running multiple ducts from a furnace or other hot air supply to the different zones.

Control dampers are used to restrict or open the flow of hot air to the zones to control the rooms to different setpoints. The position reference of the damper must be a continuously reacting signal so that the damper is always reacting to the temperature feedback. This is accomplished by applying the Proportional, Integral, Derivative (PID) methodology of control.

Figure 1: Illustration of how temperature is managed in each zone within a space using dampers

Optimizing zone control with PID

PID control works by summing scalar multiples of the error, integral of error, and derivative of error and outputting that summation as a reference to the system, or control device.

Each fundamental part of the function is used for a different reason, and adjustments can be made to the individual components to manipulate time dependent system responses like response time, decrease oscillations, reduce overshoot, etc.

Three key components of PID control

Let’s take a little closer look at the three components of PID control.

Figure 2: Theory of proportional, integral, derivative (PID) control

Proportional control

Proportional control only relies on the error between the setpoint and the feedback from the system. The larger the error, the larger the increase in output. The proportional gain, K_pscales the error that is fed back to the system. Getting the correct amount of proportional gain is critical because if there is too much of it, the system will overshoot and oscillate.

On the other hand, if there is too little gain and the system will never get close to the setpoint and have a very slow rise time. In general, proportional gain alone will always have a small amount of steady state error.

Figure 3: Impact of proportional gain

Integral control

The integral component integrates or sums, the error over time. An error can be positive or negative, therefore, even a small error term will slowly add up overtime, increasing or decreasing the output to the system until there is zero steady state error.

The integral gain, Ki is a multiplier to scale the amount of error that is summed together every cycle of the function block. Increasing the integral gain will increase the amount of correction to the point where the response may be undesirable. Therefore, using a small amount of gain is what is typically used to slowly reach a zero steady state error.

Figure 4: Impact of integral gain

Derivative control

The derivative factor is proportional to the derivative of the error, or the rate of change of the error. Increasing the derivative gain, K_d will cause the system to react more to changes in the error.

Therefore, if there is noise on the feedback signal, the system will be highly sensitive to the fluctuations. For this reason, derivative gain is not typically used.

Figure 5: Impact of derivative gain

PID control and HVAC applications

A few common HVAC applications that utilize a nano PLC’s PID control method include:

Damper position control – when temperature is controlled by adjusting the position of the damper in an HVAC system
Variable frequency drive (VFD) control – when temperature is controlled by varying the speed of a motor in an HVAC system

Explore the PID capabilities of the easyE4 Nano PLC

Download the easyE4 manual

Visit the easyE4 website

Select an application that works for you

Damper control

VFD control

Still have questions? Contact us.

Eaton is an intelligent power management company dedicated to improving the quality of life and protecting the environment for people everywhere. We are guided by our commitment to do business right, to operate sustainably and to help our customers manage power ─ today and well into the future. By capitalizing on the global growth trends of electrification and digitalization, we’re accelerating the planet’s transition to renewable energy and helping to solve the world’s most urgent power management challenges.

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Proportional, Integral, Derivative (PID) with HVAC zone control

PID methodology of control

Optimizing zone control with PID

Three key components of PID control

Proportional control

Integral control

Derivative control

PID control and HVAC applications

Explore the PID capabilities of the easyE4 Nano PLC

Damper control

VFD control

Still have questions? Contact us.

Favorites

Manage favorites

Proportional, Integral, Derivative (PID) with HVAC zone control

PID methodology of control

Optimizing zone control with PID

Three key components of PID control

Proportional control

Integral control

Derivative control

PID control and HVAC applications

Explore the PID capabilities of the easyE4 Nano PLC

Damper control

VFD control

Still have questions? Contact us.

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