In comfort cooling calculations, “sensible heat gain” of outdoor ventilation air is primarily due to which difference between the fresh air and the conditioned space air?

Introduction / Context:
Cooling load calculations split total heat gain into sensible (temperature-related) and latent (moisture-related) components. Correctly attributing each portion is essential for sizing coils and selecting equipment. This question focuses on the sensible portion from ventilation (outdoor) air.

Given Data / Assumptions:

• Sensible heat is associated with temperature change at essentially constant moisture content.
• Latent heat is associated with moisture addition/removal (change in humidity ratio).
• Ventilation air enters warmer than the indoor air in typical summer scenarios.

Concept / Approach:
Sensible heat gain depends on the dry-bulb temperature difference between the entering outdoor air and the indoor air. The formula commonly applied is Q_sensible = m_air * cp_air * (T_out − T_in), which makes temperature difference the driver for the sensible component.

Step-by-Step Solution:

Verification / Alternative check:
Psychrometric chart movements: a horizontal move represents sensible change (constant humidity ratio). This matches the temperature-difference explanation for sensible loads from outdoor air.

Why Other Options Are Wrong:

• Humidity difference: Drives latent, not sensible, load.
• Velocity / Pressure / Elevation differences: Not primary factors in sensible load calculations for standard building HVAC.

Common Pitfalls:
Confusing sensible and latent components when ventilation air is both warmer and more humid; both may occur, but sensible is strictly linked to temperature difference.

Final Answer:
Temperature difference