Environmental Principles Week 3 Slideshow 2

Psychrometric Chart & Thermal Comfort

Psychrometric Chart

• A graphical representation of air properties at different temperatures & moisture levels.

• Key components:

  • Relative Humidity (RH) – Amount of moisture in the air relative to maximum capacity.

  • Dry Bulb Temperature – Regular air temperature.

  • Moisture Content – Measured in pounds of water per pound of dry air.

• Example: At 80°F and 40% RH, the air contains 0.009 lb of water per pound of dry air.

Comfort Zone

• Defined by air temperature, relative humidity, air movement, and mean radiant temperature (MRT).

• Winter vs. Summer Comfort Zone – Two overlapping zones:

  • Winter Comfort Zone → Tends to be on the left of the psychrometric chart (cooler, higher humidity).

  • Summer Comfort Zone → Tends to be on the right (warmer, lower humidity).

Climate & Ventilation Strategies

Natural Ventilation

• Uses wind & pressure differences to improve indoor air quality and cooling.

• Examples:

  • Science House, Minnesota – Designed for passive ventilation.

  • British High Commission, Sri Lanka – Uses open-air strategies.

Night-Time Ventilation

• Cooling strategy where buildings store cool night air and release it during the day.

• Works best in hot-dry climates with large temperature swings.

Thermal Mass

• Definition: Materials that absorb & store heat energy (e.g., stone, concrete, adobe).

• Used in passive design to regulate indoor temperature.

• Example: Bruck Passive House Hotel – Optimized for thermal mass efficiency.

Direct Gain Systems

• Direct solar radiation heats interior surfaces for passive heating.

• Example: Rocky Mountain Institute, Colorado – Uses passive solar gain.

Climate Adaptation & Questions

Climate Zones & Characteristics

• Lechner’s 6 Climate Zones divide the U.S. based on thermal behavior.

• Hot & Dry Climates – Large diurnal temperature swings (hot days, cool nights).

• Cool Air Movement – Cold air settles in low-lying areas due to density.

• South-Facing Slopes – Receive more solar radiation than north-facing slopes.

Thermal Comfort & Heat Transfer

• Human Heat Production – Mainly depends on physical activity.

• Evaporative Cooling:

  • Sensible Heat (air temperature) → Decreases

  • Latent Heat (moisture content) → Increases

Cold Climate Design Strategies

• Best Strategy:

  • Maximize South-Facing Windows (for passive solar heating).

  • Avoid White Exterior (reflects heat).

  • Use Heavy Mass for Insulation (not lightweight materials).