United Trades Exclusive
pneumatic vs. electronic controls
By Dale Yelnich
In a building automation system, there are essentially two types of controls. The first is a pneumatic type, which uses air pressure to control valves, actuators and regulators, among others. These were the first types of automated control devices, and in their most basic definition, they can be compared to using a finger to manually press a switch, open up a valve or manipulate an apparatus that would influence a specific function in an HVAC system.
The second is an electronic type that is similar in some respects to a pneumatic control, but it uses an electrical current to get the job done. Servos, valves, switches and other mechanisms are generally opened, closed, or in some way activated by the use of a small motor or an actuator. Because an electronic system uses wires instead of compressed air to transmit commands, many of the mechanical problems associated with using air pressure have been eliminated.
Pneumatics were the first commercially employed automation for HVAC building systems. By the early 60’s, technology had advanced to the point that air lines and compressors were hardy and reliable enough to be used for industrial climate control designs.
Although these were simple guidance devices used to turn a specific instrument or apparatus on and off, they became the basis for the modern building automation adaptation that is prevalent today. As an example, a pneumatic system works something like this:
If an air conditioner needed to be turned on at the far end of a factory, instead of walking all the way down and flipping a switch, a button could be pressed in a central control room that would automatically activate the unit. This was especially convenient if the air conditioner was located on the roof or in a difficult space to access.
Once the button was pushed, compressed air would flow through an air line into a pneumatic device, and the resulting air pressure would flip the switch to “on.” The button could be pushed again, and the air pressure would be used to flip the switch “off.” If a timer was employed at the pneumatic control switch, it could be set to turn the air conditioner on or off at a certain time every day. Although simple, it was effective.
The main problem with pneumatics was the lag time that it would take for the switch to be activated, sometimes considerable if the air pressure had been bled off by other commands. This could be a serious handicap in an emergency situation. The fact that it also wasn’t very precise, generally limited a pneumatic system’s overall usability to basic commands.
Certainly, a pneumatic control was very good at going fully one way or the other, like when turning a switch on or off, but precision adjustments, like minutely regulating thermostats or slightly opening dampers, was beyond their initial capability.
With electronic controls, there was no time lag. Once a command was given to an electronically controlled device, it would carry it out virtually instantaneously. It didn’t matter how long the wires were, nor how many commands had been issued recently.
Further, as microprocessor and computing technology evolved over time; these systems became capable of radically complicated and involved functions. Imagine attempting to track thousands (if not millions) of variables per second, respond to them individually and instantaneously as they change, and at a whim reprogram the way an entire system functions, with pneumatics!
The size, scope, and complexity of such a system would be mind boggling (to say nothing of the cost to construct it!). For these reasons and more, if building automation is desired in large factories or industrial complexes, electronic systems have become the predominant solution.
Precision is also a hallmark of electronic controls. Tiny motors, actuators or servos can precisely dial in any temperature needed in a specific area, adjust ventilation airflow, control heating and cooling requirements for office buildings, or almost any other aspect of building automation that needs to be decisively controlled.
The biggest disadvantages of electronic BAS systems, are the costs associated with maintaining them, and the intense difficulty associated with troubleshooting them. Electronic systems are complex and need certified and skilled maintenance technicians to keep them operational.
Electronic systems can be easily damaged by fire, and issues such as power outages, voltage fluctuations, frequency shifts, programming errors, software conflicts, faulty wiring, database corruption, and user/technician “tomfoolery” abound when troubleshooting these technological behemoths.
On the contrary, pneumatic systems are reliable to a fault. They require very little upkeep, and the maintenance needed can be undertaken by virtually any trained company staff. Pneumatics are fireproof, cheap to maintain, and easy (read “easier”) to understand.
They do have problems in very cold temperatures however, and the copper pipe air lines are vulnerable to damage from contact. Some air leaks may also occur at the joints, but the simplicity of the system is its best feature.
Also, typical pneumatic valve configurations are set so upon failure, the system will default to some functional (although not necessarily ideal) mode of operation. This is simply to say, that even when we “pull the plug” on a pneumatic system; there should be some basic semblance of system functionality.
Perhaps the best way to sum things up would be this: Electronics are a viable (and desirable) method of control at many levels of the automation spectrum. They cost relatively little to install, and can perform a litany of functions which would be impractical (and costly) to attempt with pneumatics.
Pneumatics do however, possess an edge in simple (albeit large scale) systems with less demanding functions to perform. Higher rates of reliability, safer (or at least more convenient) failure modes, and lower maintenance costs are all benefits of these types of systems.
Also worth noting, is that developments in technology have allowed hybrid electro-pneumatic systems to come into play. In these type systems, the reliability of pneumatics can be combined with some of the processing features and controllability of electronic systems.
Common applications for this design are found in retrofits, where existing pneumatic systems are equipped with converters; to produce electronic control voltages from pneumatic signals. This enables the pneumatic system to operate with some of the benefits of electronic control, without a complete rebuild of the system.