Human thermal comfort and heat loss mechanisms: Which statement(s) correctly describe how the human body can lose heat to the environment?

Introduction / Context:
Human thermal comfort involves multiple heat transfer modes: conduction, convection, radiation, and evaporation. Air-conditioning design considers these pathways to maintain comfort across varying environments.

Given Data / Assumptions:

• Skin surface is moist due to perspiration, enabling evaporative cooling.
• Air motion affects convective and evaporative heat transfer coefficients.
• Radiation depends chiefly on temperature difference between the body and surrounding surfaces.

Concept / Approach:
Evaporation removes latent heat irrespective of air temperature, provided the ambient is not fully saturated and there is vapor pressure gradient. Air movement reduces boundary layer resistance, enhancing both convection and evaporation. Radiation heat exchange depends on surface temperatures, not air temperature per se.

Step-by-Step Solution:

Verification / Alternative check:
Psychrometric reasoning: latent heat flux is proportional to mass transfer rate, which increases with air velocity and vapor pressure difference.

Why Other Options Are Wrong:

• Only (a) or only (b) omits an equally valid mechanism.
• (c) contradicts the Stefan–Boltzmann relation: increasing environmental temperature generally lowers net radiative loss.

Common Pitfalls:
Confusing air temperature with mean radiant temperature; radiation exchanges with surfaces, not air directly.

Final Answer:
Both (a) and (b)