HVAC pressure control with nano PLCs

A malfunctioning boiler at a local distillery puts hundreds of thousands of dollars of product at risk.

A distillery gives Sebastian a call. They are at a critical part of completing the distillation process and require that a certain volume of steam be available for the size of the batch of the spirits being distilled. For some reason, the boiler keeps shutting down with every effort that the distiller makes to complete the process.

They also rely on the high-quality steam produced by the boiler to ensure that the taste and flavor of the spirits maintain a specific standard. They have a large order that needs to be fulfilled and are running out of time.

Sebastian suspects that there may be an issue with pressure which could cause his customer to lose money on this order. 

Pressure control is required in a variety of HVAC applications to either maintain the system at a given pressure setpoint or to prevent disasters from occurring when the system pressure moves outside of its design limits.

Without pressure control, a ventilation system, for instance, may gain too much pressure when dampers are closed causing a decrease in efficiency. 

Sebastian has some options for addressing the issue:

• Use the On/Off method if his application requires basic course control with an acceptable tolerance. This is more than sufficient and is the least expensive option 
• Apply Proportional, Integral, Derivative (PID) control where precision and accuracy are critical. This is the most expensive, but most commonly used option 
• Apply High- or Low-Pressure control where nano-PLC monitors pressure switch or transducer to see if the upper or lower pressure thresholds have been exceeded. The nano-PLC then adjusts the system accordingly

On/Off control is appropriate when course control with a marginal window of error is acceptable without negatively affecting the system's process.

In the case of the distillery, this wouldn’t work because the quality of the spirits requires a precise volume of steam for the batch in question. For other applications, on/off control may very well be all that is needed.

Some applications require a higher level of control to function properly. For instance, dampers need to have their position setpoints ramped smoothly so that they do not jerk or flutter when switching position.

In the case of the distillery, precise control is required to maintain a setpoint with little to no error or be able to adjust the response rate to a change in setpoint or a system disturbance. PID control is the methodology that will accomplish this.