What is another name for stack action in HVAC systems?

Stack action, often referred to as motive power, is a phenomenon in HVAC systems that describes the movement of air caused by differences in temperature and density between warmer and cooler air. When air is heated, it expands, becomes less dense, and rises, while cooler, denser air sinks. This natural convection creates an upward draft or stack effect, which can help to circulate air within a system.

In HVAC applications, understanding stack action is crucial because it can improve the efficiency of ventilation systems. By utilizing this natural flow of air, systems can supplement mechanical means of air movement, leading to energy savings and improved indoor air quality. Motive power, as a term, encapsulates this idea of using natural forces to drive airflow within a space.

While the other terms—air flow, pressure coefficient, and thermal gradient—are related concepts in HVAC, they do not specifically describe the natural convection process that reflects how stack action operates. Air flow refers to the movement of air, but it does not denote the underlying forces that create the movement. Pressure coefficient relates to the behavior of air under various pressure conditions, and thermal gradient describes the difference in temperature over a distance, but neither captures the essence of stack action. Hence, motive power stands out as the term