Thermal comfort and HVAC: In air-conditioning practice, the term ‘‘air conditioning’’ includes cooling, heating, and moisture control (dehumidifying/humidifying) as required to achieve desired indoor conditions.

Introduction / Context:
Air conditioning is broader than just cooling. The objective is to deliver thermal comfort and acceptable indoor air quality year-round, which requires control of temperature, humidity, cleanliness, and air movement.

Given Data / Assumptions:

• Comfort conditions vary by season and application (residential, commercial, process).
• Systems may require heating in winter, cooling in summer, and humidity control anytime.
• Ventilation and filtration are also part of complete air conditioning, though not listed here.

Concept / Approach:
An HVAC system should maintain dry-bulb temperature within limits and adjust humidity ratio to avoid discomfort such as stickiness (high humidity) or dryness (low humidity). Dehumidification often involves cooling below the dew point to condense moisture, while humidification adds water vapor to the air stream. Heating raises the dry-bulb temperature to maintain thermal balance.

Step-by-Step Solution:

Verification / Alternative check:
Psychrometric processes plotted on the chart show cooling and dehumidification (down-left toward saturation), heating (horizontal rightward), and humidification (upward toward saturation), all used by HVAC systems.

Why Other Options Are Wrong:
Choosing only one function ignores the integrated nature of HVAC design aimed at comfort and process control.

Common Pitfalls:
Equating ‘‘AC’’ strictly with cooling; many systems spend substantial time heating and controlling humidity.

Final Answer:
All of these