Psychrometrics check: During sensible cooling of air (no moisture removed), the relative humidity of the air stream will __________.

Introduction / Context:
Sensible cooling lowers the dry-bulb temperature without intentionally removing moisture. Understanding how relative humidity (RH) responds is fundamental in HVAC design and comfort analysis.

Given Data / Assumptions:

• Cooling coil surface is above the air stream dew-point, so no condensation occurs.
• Humidity ratio (specific humidity) is constant during the process.
• Pressure approximately constant (near atmospheric).

Concept / Approach:
Relative humidity is the ratio of the partial pressure of water vapour to the saturation vapour pressure at the same temperature. During sensible cooling with constant humidity ratio, the saturation vapour pressure decreases as temperature drops; hence the ratio (RH) increases.

Step-by-Step Solution:

Verification / Alternative check:
On a psychrometric chart, the process is a horizontal move left (constant w); lines of constant RH slope upward to the left, so RH increases.

Why Other Options Are Wrong:
Decreasing or constant RH contradicts chart behavior; becoming 100% immediately or zero is nonphysical unless the coil is at or below dew-point.

Common Pitfalls:
Confusing relative humidity with humidity ratio; only when the coil temperature dips below dew-point does moisture removal begin.

Final Answer:
Yes, it increases