Which variable represents the speed of air movement that affects convective heat loss or gain?

• A. Air speed
• B. Dry bulb temperature
• C. Humidity
• D. Metabolic rate

Answer: (A)

When air moves, it carries heat between surfaces and the surrounding air. The rate of this convective heat transfer rises as air speed increases because faster moving air disrupts the thin boundary layer of still air next to a surface, lowering its thermal resistance and increasing the convective transfer coefficient. So, higher air speed directly enhances convective heat loss or gain—cooling when the ambient air is cooler than the surface, or warming when it’s warmer. The other factors don’t represent how quickly air is moving: dry bulb temperature is just ambient air temperature, humidity affects moisture and evaporative cooling, and metabolic rate is about internal heat production.