Environmental Principles Week 2 Slideshow

Thermal Comfort & Heat Flow

Definition of Thermal Comfort

• A subjective state of satisfaction with the thermal environment.

• ASHRAE (1989): "Condition of mind in which satisfaction is expressed with the thermal environment."

• Olgay: "Conditions wherein the average person does not experience discomfort."

Factors Affecting Heat Loss (4 Main Environmental Factors)

1. Air Temperature – How warm or cold the surrounding air is.

2. Mean Radiant Temperature – Temperature of surrounding surfaces impacting heat exchange.

3. Relative Humidity – Moisture in the air affecting heat dissipation.

4. Air Speed – Movement of air aiding heat loss through convection and evaporation.

Body Heat Transfer Mechanisms

1. Convection – Heat lost to moving air.

2. Radiation – Heat transfer to surrounding surfaces.

3. Evaporation – Heat loss through perspiration.

4. Conduction – Direct heat transfer to objects in contact (e.g., cold water, floors).

Thermal Equilibrium – Balance between metabolic heat production and heat dissipation.

Personal & Environmental Factors

Personal Factors:

• Clothing (Clo Value) – Measures insulation provided by clothing (0 Clo = nude, 4 Clo = max practical insulation).

• Activity Levels (Met Rate) – Higher activity → More metabolic heat → Greater need for cooling.

Environmental Factors:

• Indoor Environmental Quality (IEQ) – Affects health, productivity, and well-being.

• 95% of time spent indoors – Poor indoor environments cause billions in economic losses.

Thermal Comfort Models

Predicted Mean Vote (PMV) & Predicted Percentage of Dissatisfied (PPD)

• PMV = Thermal sensation rating (-3 to +3 scale).

• PPD = Percentage of people dissatisfied with conditions.

Thermal Resistance & Insulation

• Thermal Resistance (R-Value): Resistance of materials to heat flow.

• Heat Flow Coefficient (U-Value): Measure of heat conductance (inverse of R-value).

• High R-Value → More insulation → Less heat loss.

Design Strategies for Thermal Comfort

• Building as a “Third Skin” – Provides thermal regulation alongside clothing and body heat mechanisms.

• Adaptive Comfort Models – Considering individual differences like age, gender, and psychology.

• Smart Buildings & AI – Integrating sensors for personalized comfort models.