First exam

Definitions

• Sensible Heat: Heat that causes a change in temperature, measurable by a thermometer.

• Latent Heat: Heat energy absorbed or released during a change in the state of matter, without changing temperature.

• Heat Fusion: Heat required to change a solid into a liquid.

• Heat of Vaporization: Heat needed to transform liquid into gas.

• Enthalpy: Total heat content of a system.

• Radiant Heat: Heat energy transferred as electromagnetic radiation, like infrared waves; does not require a medium and can transfer through a vacuum.

Heat Transfer Mechanisms

Conduction

• Heat transfer from one particle to another in direct contact.

Convection

• Fluids expand, become less dense, and rise, depending on gravity.

Radiation

• Heat transferred by electromagnetic waves emanating from warm bodies, carrying energy to bodies in direct line of sight.

Energy Interaction Parameters

• Transmittance: Radiation passing through materials (ceilings, walls).

• Absorptance: Radiation converted into sensible heat within a material.

• Reflectance: Radiation reflected off the surface.

• Emittance: Radiation given off by the surface, reducing sensible heat.

Air Infiltration and Ventilation

• Infiltration: Cold air enters through construction joints (cracks around doors and windows).

• Blower Door Test: Measures building tightness.

• Ventilation: Controlled and purposeful infiltration of air.

Cooling Concepts

• Evaporative Cooling: Heat from vaporization cools the environment.

• Greenhouse Effect: Shortwave solar radiation passes through glass and is absorbed by indoor objects.

• Stratification: Separation of cooler and warmer layers of fluid/air as warm air rises.

• Mean Radiant Temperature: Environmental factor in human comfort.

Thermal Properties

Equilibrium Temperature

• Balance between absorptance and emittance.

Heat Sink/Transfer

• Movement of heat from one body to another.

• Heat Capacity: Amount of heat required to raise temperature.

• Thermal Resistance: Opposition to heat flow by conduction, convection, and radiation.

• Heat-flow Coefficient (U): Measure of heat flow; reciprocal of thermal resistance.

• Time Lag: Delay in heat flow phenomenon.

Dew Point Temperature

• The temperature at which air is fully saturated and can hold no more moisture.

Solar Positioning and Effects

• Altitude: Sun’s angle in the vertical plane.

• Azimuth: Sun’s angle in the horizontal plane.

• Sky Vault: Imaginary dome indicating the sun's path.

• Solar Window: Portion of the sky vault most beneficial for sunlight, typically from 9 AM to 3 PM.

• Reflected Light: Light reflected from surfaces.

Solar Heat Gain and Loss Strategies

• Passive Solar: System collecting, storing, and redistributing solar energy without mechanical systems.

• Bernoulli Effect: Velocity of fluid increases, static pressure decreases, creating negative pressure in venturi tubes.

• Stack Effect: Expels air from buildings through natural convection.

• Various methods of cooling through ventilation, such as Day and Night cooling strategies.

Behavior of Water and Phase Changes

• Sensible vs. Latent Heat: Sensible heat raises temperature; latent heat causes phase changes without temperature change.

• Heating Water Example: Heating 1 lb of water requires 1 BTU to raise by 1 °F. Latent heat required to change states (144 BTU for ice to water, 1000 BTU for water to steam).

• Energy Calculations for Ice and Water:

  • To melt 2 lbs of ice: 2 lbs × 144 BTU/lb = 288 BTU.

  • To heat 2 lbs of water from 32°F to 122°F: 2 lbs × 1 BTU/lb°F × 90°F = 180 BTU.

  • Total energy for both processes: 288 BTU + 180 BTU = 468 BTU.

Radiation and Thermal Mass

• All objects absorb and emit radiation with net flow from warm to cool.

• Different materials affect thermal properties:

  • White: Low solar absorptance; high emittance.

  • Black: High absorptance; high emittance.

  • Shiny Metal: Low absorptance; low emittance.

Climate, Comfort, and Thermal Comfort

• Wet-Bulb Temperature: Shows variation between dry and humid air.

• Climate Zones: Tropical, Temperate, Arctic, affecting design priorities for buildings.

• ASHRAE factors: temperature, relative humidity, air motion affect thermal comfort.

Regional Design Priorities

• Region 15 (Houston): Keep heat out, allow ventilation, summer sun protection.

• Region 14 (New Orleans): Natural ventilation for cooling and moisture removal.

• Region 9 (Arkansas): Keep heat in during winter, ventilation for summer cooling.

Construction Techniques and Solar Inputs

• Vapor barriers' placement varies by climate (warm exterior, cool interior).

• Sun's position (23.5 degrees tilted) affects seasonal light availability.

• Summer Solstice: 24 hours light above the Arctic Circle.

• Winter Solstice: 24 hours darkness above the Arctic Circle.

Solar Equinox

• Occurs March and September; Sun is above the equator.

• Noon solar altitude calculation: A = 90 - L (L being latitude). For Lafayette (30°), A = 60°.

Light Distribution and Building Design

Reflected Light Dynamics

• Ground is the dominant light source on sunny days; overcast skies change dynamics.

• Cloud Cover Dynamics: Varies intensity from zenith to horizon.

Light Distribution Strategies

• Increase distance from task areas to ceilings to improve light distribution.

• Side lighting effectiveness is affected by height placement of windows.

Passive Solar Strategies

• Direct Gain: Collects solar energy during the day for nighttime use.

• Trombe Walls: Store and vent heat to interior.

• Sun Spaces: Collect solar energy while sealing at night to retain heat.

Passive Cooling Techniques

• Wind Towers: Direct air into buildings; historical structures (Chickees, Trulli).

• Airflow Principles: Air takes straight routes, conservation of air is key in design considerations.

• Cross-Ventilation: Air enters windows set with respect to wind direction; effectively ventilated spaces.

Conclusion

• Effective building design requires understanding of thermal mass, shading, and solar exposure.

• Use of well-placed windows and ventilation strategies enhances energy efficiency and occupant comfort.