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Questions and Answers
What is the primary benefit of having courtyards or atriums in hot and dry climates?
What is the primary benefit of having courtyards or atriums in hot and dry climates?
In what way does the Pantheon in Rome implement cooling techniques?
In what way does the Pantheon in Rome implement cooling techniques?
What is the main purpose of vents located at the top of a dome or building?
What is the main purpose of vents located at the top of a dome or building?
What material did the Navajo people use for their hogans to achieve insulation?
What material did the Navajo people use for their hogans to achieve insulation?
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What environmental factor can negatively affect the benefit of ventilation in hot and humid climates?
What environmental factor can negatively affect the benefit of ventilation in hot and humid climates?
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Why is the deep earth considered a good barrier in hot and dry climates?
Why is the deep earth considered a good barrier in hot and dry climates?
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How do Spanish settlers utilize adobe in building construction?
How do Spanish settlers utilize adobe in building construction?
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What characteristic of the overhanging cliffs in Mesa Verde enhances the thermal comfort of dwellings?
What characteristic of the overhanging cliffs in Mesa Verde enhances the thermal comfort of dwellings?
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What is one reason for the flow of air into buildings during winter?
What is one reason for the flow of air into buildings during winter?
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Which type of airflow is NOT one of the four basic types mentioned?
Which type of airflow is NOT one of the four basic types mentioned?
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In the context of airflow around a building, what does negative pressure indicate?
In the context of airflow around a building, what does negative pressure indicate?
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How does comfort ventilation function?
How does comfort ventilation function?
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Which ventilation technique cannot be used simultaneously with comfort ventilation?
Which ventilation technique cannot be used simultaneously with comfort ventilation?
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What is a possible consequence of varying airflow across a building's roof?
What is a possible consequence of varying airflow across a building's roof?
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What primarily influences the pressure areas created around a building?
What primarily influences the pressure areas created around a building?
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What mechanism is primarily responsible for air entering buildings through earth tubes?
What mechanism is primarily responsible for air entering buildings through earth tubes?
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What is a benefit of placing windows high on a wall?
What is a benefit of placing windows high on a wall?
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What should be considered regarding inlet and outlet sizes for ventilation?
What should be considered regarding inlet and outlet sizes for ventilation?
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What is one disadvantage of windows that deflect wind upward?
What is one disadvantage of windows that deflect wind upward?
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Which type of mechanical devices can be used for operating high windows?
Which type of mechanical devices can be used for operating high windows?
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What does the stack effect create in the lower part of a space?
What does the stack effect create in the lower part of a space?
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What is the main function of movable opaque louvers on shutters?
What is the main function of movable opaque louvers on shutters?
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What must be increased to raise the neutral axis in an atrium?
What must be increased to raise the neutral axis in an atrium?
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Why are mechanical devices preferred for high windows?
Why are mechanical devices preferred for high windows?
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What is one recommended design feature of jalousie windows?
What is one recommended design feature of jalousie windows?
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Which effects contribute to effective vertical ventilation in the design?
Which effects contribute to effective vertical ventilation in the design?
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What is the primary advantage of high openings for night-flush cooling?
What is the primary advantage of high openings for night-flush cooling?
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What happens to hot air in a multistory building due to the stack effect?
What happens to hot air in a multistory building due to the stack effect?
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What role do winds play in the building's airflow according to the content?
What role do winds play in the building's airflow according to the content?
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How does the design of the building affect vertical ventilation?
How does the design of the building affect vertical ventilation?
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Which method is NOT mentioned as a way to raise the neutral axis?
Which method is NOT mentioned as a way to raise the neutral axis?
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What pressure is found in between the upper and lower parts of a space affected by the stack effect?
What pressure is found in between the upper and lower parts of a space affected by the stack effect?
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How does the water flow model assist in understanding air flow in buildings?
How does the water flow model assist in understanding air flow in buildings?
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What does an air velocity of 50 fpm indicate in terms of comfort levels?
What does an air velocity of 50 fpm indicate in terms of comfort levels?
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At what air velocity is the comfort level described as 'very noticeable but acceptable in certain high-activity areas'?
At what air velocity is the comfort level described as 'very noticeable but acceptable in certain high-activity areas'?
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Which factor does NOT pertain to thermal comfort according to air velocities in the provided data?
Which factor does NOT pertain to thermal comfort according to air velocities in the provided data?
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What is indicated at an air velocity of 40 fpm?
What is indicated at an air velocity of 40 fpm?
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Which of the following velocities is characterized by having 'barely noticeable' comfort levels?
Which of the following velocities is characterized by having 'barely noticeable' comfort levels?
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What role does the addition of dye play in the water flow model?
What role does the addition of dye play in the water flow model?
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What happens to air comfort levels as air velocity increases from 10 fpm to 160 fpm?
What happens to air comfort levels as air velocity increases from 10 fpm to 160 fpm?
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What is the primary condition for the stack effect to exhaust air?
What is the primary condition for the stack effect to exhaust air?
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To optimize the stack effect, what should be done with the openings?
To optimize the stack effect, what should be done with the openings?
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Which effect causes increased air velocity above ground level?
Which effect causes increased air velocity above ground level?
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What should be minimized to allow air to flow freely in the stack effect?
What should be minimized to allow air to flow freely in the stack effect?
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How does the stack effect relate to temperature differences?
How does the stack effect relate to temperature differences?
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What structural feature is ideal for improving the stack effect?
What structural feature is ideal for improving the stack effect?
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What would be a negative impact on the stack effect?
What would be a negative impact on the stack effect?
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Which of the following best explains why the stack effect is considered a weak airflow mechanism?
Which of the following best explains why the stack effect is considered a weak airflow mechanism?
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Study Notes
Passive Cooling
- Optimizing building envelopes for climate substantially reduces mechanical system size.
- True regional character in design results from adapting to local climate conditions (e.g., California vs. Massachusetts).
Historical and Indigenous Use of Passive Cooling
- Historical and indigenous buildings offer examples of passive cooling.
- Hot and dry climates typically use buildings with few, small windows, light colors, and massive construction (adobe, brick, stone).
- This mass acts as a heat sink during the day, which aids in cooling the building at night.
- Night ventilation using small windows and light colors minimize daytime heat gain.
- Wind scoops and towers, used in regions with little wind, maximize ventilation.
- Mashrabiya (screened bay windows) provide shading, ventilation, and evaporative cooling.
- Earth sheltering and earthen walls are used in dry climates for insulation.
- Large overhangs are beneficial.
Introduction to Cooling
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Three-tier design approach to thermal comfort:
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Heat Avoidance (minimizes heat gain using shading, orientation, color, vegetation, insulation)
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Passive Cooling (uses systems to lower temperatures)
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Mechanical Cooling (used to cool what avoidance and passive cooling couldn't achieve)
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Passive cooling strategies depend on climate.
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Hot and dry climates use massive construction and few, small windows.
Comfort Ventilation vs. Night-Flush Cooling
- Ventilation is a major cooling technique in many regions.
- Comfort Ventilation, used throughout the day, uses outdoor air, often with additional fans.
- Night-Flush Cooling uses outdoor air at night to pre-cool the building's mass, which then acts as a heat sink during the day. Use of windows or fans.
Airflow Through Buildings
- Airflow is driven by temperature and pressure differences.
- Four basic types of airflow: laminar, separated, turbulent, and eddy currents.
- Airflow is conserved and is affected by buildings
- Bernoulli effect: faster airflow means lower pressure.
- Stack effect: vertical air movement due to temperature differences.
- Site conditions (adjacent buildings, vegetation, etc.) significantly influence airflow.
- Window orientation (and wind direction) affects pressure distribution.
- Window locations affect airflow patterns.
- Fin walls can improve airflow.
- Horizontal overhangs deflect airflow upward, improving conditions below.
- Window types (casement, double-hung, etc.) affect airflow.
Comfort Ventilation, Night-Flush Cooling, Types of Passive Cooling
- Comfort ventilation uses ventilation throughout the day, while night-flush cooling uses it at night to precool the building.
- Night-flush cooling requires a large amount of mass.
Radiant Cooling
- Objects emit and absorb radiant energy.
- A building cools by radiating energy to the night sky.
- This effect is enhanced by using light colors, large overhangs, and insulation to minimize heat gain.
- Direct radiant cooling uses the roof itself as the radiator.
- Indirect radiant cooling utilizes a heat-transfer fluid to cool the building's interior.
Evaporative Cooling
- Evaporative cooling results in a temperature drop as sensible heat is converted to latent heat.
- Direct evaporative cooling adds humidity to indoor air.
- Indirect evaporative cooling does not increase indoor humidity.
- Evaporative cooling is a low-energy option for dry climates.
Earth Cooling
- Earth has a low temperature fluctuation with depth.
- Deep earth temperatures are stable and can be used as a consistent heat sink.
- Direct earth coupling occurs when building walls are in direct contact with the ground, minimizing insulation.
- Indirect earth coupling uses buried tubes to transfer cool air to the building.
Dehumidification with a Desiccant
- For humid regions, dehumidifiers are useful.
- A desiccant removes moisture from air (via absorption).
- The heat of vaporization must be removed in this process.
- Desiccant dehumidification is generally used in heat exchangers.
Solar Chimneys
- Solar chimneys use the sun to increase the stack effect.
- They can be useful in situations with little wind.
- They are a passive cooling approach.
Conclusion
- Passive cooling is highly effective in hot, dry conditions.
- Comfort ventilation is appropriate in humid conditions.
- Night-flush cooling works well in many climates.
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