In thermal comfort assessment for HVAC design, which index combines the effects of dry-bulb temperature, relative humidity, and air velocity on the human body?

Introduction / Context:
Comfort indices help HVAC engineers quantify how occupants perceive the indoor environment. Temperature alone does not capture comfort; humidity and air movement strongly influence heat loss from the body. The traditional index that blends these effects is effective temperature (ET).

Given Data / Assumptions:

• Inputs affecting comfort: air temperature, relative humidity, and air velocity.
• Radiant effects can be included separately via mean radiant temperature, but the question asks specifically for a combined air-side index.

Concept / Approach:
Effective temperature is an empirical index representing the combined sensible and latent effects of temperature, humidity, and air movement on thermal sensation. It maps different environmental states to equivalent comfort sensations. Modern practice may use operative temperature, PMV/PPD, or SET*, but ET remains the classical term covering the trio in the question.

Step-by-Step Solution:

Verification / Alternative check:
Comfort charts and psychrometric overlays for ET demonstrate equal-comfort lines spanning combinations of T, RH, and velocity that yield the same thermal sensation.

Why Other Options Are Wrong:

• MRT concerns radiation, not humidity/velocity together.
• Dew point is purely moisture-related.
• Operative temperature traditionally blends air and mean radiant temperatures, not humidity effects.
• Sling psychrometer index is a measurement procedure, not a comfort index.

Common Pitfalls:
Confusing modern PMV/PPD with ET; while PMV is more comprehensive, the question’s classic trio aligns with ET.

Final Answer:
Effective temperature (ET)