Physiological Principles in Air Conditioning

Definition

Physiological principles in air conditioning refer to the study of how environmental factors—such as temperature, humidity, air velocity, and radiation—interact with the human body’s thermal regulatory system to maintain comfort and health. It focuses on the heat exchange processes between the human body and the surrounding indoor environment.

Main Content

1. Thermal Balance (Heat Equilibrium)

• The human body acts as a heat engine that produces metabolic heat; to remain comfortable, this heat must be dissipated into the environment at the same rate it is produced.
• The heat balance equation is represented as: Metabolic Heat = Heat Loss (convection + radiation + evaporation).

2. Psychrometric Variables and Human Comfort

• Dry-bulb temperature and relative humidity significantly dictate the effectiveness of sweat evaporation, which is the body's primary cooling mechanism.
• If humidity is too high, the body cannot effectively evaporate sweat, leading to discomfort despite adequate air movement.

3. Mean Radiant Temperature (MRT)

• MRT represents the uniform surface temperature of an imaginary enclosure in which an occupant would exchange the same amount of radiant heat as in the actual non-uniform environment.
• High surface temperatures (like a sunlit wall) can cause heat gain even if the air temperature is cool, affecting the perceived comfort level.

Working / Process

1. Metabolic Heat Production

• The body constantly generates heat through digestion, movement, and vital organ function.
• In an air-conditioned space, the system must account for this baseline heat load (the number of occupants and their activity level) to prevent the room from warming up.

2. Heat Dissipation through Convection and Radiation

• Sensible heat loss occurs when the air surrounding the body is cooler than the skin temperature.
• This process is visually represented by the heat flow away from the body:

       [BODY HEAT]
           |
           v
    (Convection/Radiation)
           |
    [SURROUNDING AIR]

3. Evaporative Cooling

• When sensible heat loss is insufficient, the body produces moisture on the skin.
• Air conditioning systems facilitate this by controlling humidity; dry air absorbs moisture from the skin surface, cooling the body through latent heat transfer.

Advantages / Applications

• Enhances workplace productivity by minimizing thermal stress and fatigue caused by heat buildup.
• Prevents heat-related illnesses such as heat stroke or exhaustion in high-temperature industrial environments.
• Improves indoor air quality and comfort in hospitals and residential buildings, supporting faster recovery and better sleep patterns.

Summary

Physiological principles in air conditioning focus on maintaining human thermal comfort by balancing the heat produced by the human body with the cooling capacity of an air conditioning system. By regulating temperature, humidity, and airflow, these principles ensure that the environment assists the body’s natural cooling processes.

Important terms to remember: Metabolic Heat, Latent Heat, Sensible Heat, Mean Radiant Temperature, and Thermal Equilibrium.