Why some buildings still have air lines running to every thermostat — and why that doesn't necessarily mean the control logic itself is old.
Walk into the mechanical room of an older building and you may find a compressor feeding a network of small copper or plastic tubes that snake up through walls to a thermostat on every floor. That's pneumatic control — a technology where compressed air isn't just moving something, it is the control signal. Most modern buildings have replaced it with Direct Digital Control (DDC), where a microprocessor does the thinking instead. The two approaches are often described as "old vs. new," but the real distinction is more specific: it's about where the control logic physically lives, not simply what kind of actuator ends up moving a damper.