CD

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).