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Questions and Answers
What effect causes a decrease in pressure when air is accelerated to cover a greater distance?
What effect causes a decrease in pressure when air is accelerated to cover a greater distance?
The stack effect occurs because air density increases as it warms.
The stack effect occurs because air density increases as it warms.
False
What is required for effective cross ventilation?
What is required for effective cross ventilation?
An inlet and an outlet
The __________ effect causes acceleration when laminar airflow is constricted.
The __________ effect causes acceleration when laminar airflow is constricted.
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Match the airflow concepts with their descriptions:
Match the airflow concepts with their descriptions:
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What is the purpose of introducing a ventilated air space between the roof and the ceiling?
What is the purpose of introducing a ventilated air space between the roof and the ceiling?
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Repositioning the inlet to a more diagonal location can decrease airflow in a building.
Repositioning the inlet to a more diagonal location can decrease airflow in a building.
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The _____ location has little effect on flow within the room, while the low inlet is best for cooling.
The _____ location has little effect on flow within the room, while the low inlet is best for cooling.
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Which of the following is an advantage of natural ventilation?
Which of the following is an advantage of natural ventilation?
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Mechanical ventilation relies solely on natural airflow to cool buildings.
Mechanical ventilation relies solely on natural airflow to cool buildings.
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Name two sources of natural ventilation.
Name two sources of natural ventilation.
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Natural ventilation is effective for cooling buildings from ______ to ______.
Natural ventilation is effective for cooling buildings from ______ to ______.
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Match the type of ventilation with its characteristics:
Match the type of ventilation with its characteristics:
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What is a disadvantage of mechanical ventilation?
What is a disadvantage of mechanical ventilation?
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Airflow is smooth when adjacent air moves in opposite directions.
Airflow is smooth when adjacent air moves in opposite directions.
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During which months is mechanical cooling required in Bahrain?
During which months is mechanical cooling required in Bahrain?
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Study Notes
Cooling Methods
- Two main cooling strategies exist: passive natural ventilation and active mechanical ventilation.
Passive Natural Ventilation
- Methods include openings such as doors, windows, and shafts.
- Advantages of natural ventilation: inexpensive, energy-efficient and healthy.
Active Mechanical Ventilation
- Methods include air conditioning, fans, and air coolers.
- Disadvantages of mechanical ventilation: expensive and requires energy.
Natural Ventilation Principle
- Natural ventilation involves the exchange of air between the inside and outside of a building.
Natural Ventilation Use in Bahrain
- Hourly effective temperature (ET) data for Bahrain indicates optimal natural ventilation use from October to April.
Comfort Zone
- The comfortable temperature range in Bahrain is 22-27°C.
Airflow Principles
- Air always flows from high to low pressure.
- Air has mass and continues in its path until obstructed.
- Smooth airflow (laminar flow) occurs when adjacent air moves similarly; opposed currents become separated by intermittent eddies.
- Sharp changes in airflow produce turbulent flow.
- Bernoulli effect: accelerated air causes decreased pressure; greater distance covered compared to adjacent airflow.
- Venturi effect: constricted airflow increases speed.
Stack Effect
- Building air warms, density decreases, and the warmer air rises, which creates a pressure difference and encourages airflow toward open high points.
Cross Ventilation
- Cross ventilation requires an inlet and an outlet.
Factors Affecting Airflow
- Low-pressure regions form along windward construction sides and the leeward side of buildings.
- Tall structures in the wind path cause turbulence near them.
- Multiple low-pressure regions occur along linearly arranged buildings, resulting in ventilation shadow.
- High-pressure regions on windward sides are reduced when structures allow air to pass underneath.
- Airflow and ventilation improve when structures have openings on opposing sides.
Window Placement
- Best airflow arises when openings are on opposite walls.
- Ventilation can improve with openings on adjacent walls via wing walls.
Effective Window Open Area
- Measurements exist showing open area effectiveness of different window types (single-hung, double-hung, sliding, awning, casement, jalousie, hopper).
Inlet and Outlet Sizing
- A smaller inlet compared to the outlet enhances airflow. If the inlet is larger, the velocity of air within the building decreases.
Double Roof Strategies
- Roofs are primary sources of unwanted heat gain.
- Introducing a ventilated air space between the roof and the ceiling can reduce that gain.
Inlet Centering
- Inlets positioned centrally in walls restrict side airflow, making the direction of flow more linear.
Inlet Positioning
- Lower inlets maximize airflow across the occupied portion of a building.
- Outlet placement has minimal influence on airflow within the structure.
Interior Partitions
- Partition sizes affect airflow velocity near the inlet; larger partitions can increase the speed of air entering the building.
Case Study: Center Zion National Park (ZNP)
- The visitor center is located in Utah, 150 miles outside Las Vegas.
- Cooling primarily relies on natural ventilation via operable clerestory windows.
- Passive cooling is augmented by evaporative cool towers.
- Cool towers operate through natural convection primarily driven by buoyancy.
Cool Tower Operation
- Water is pumped to pads at the tower top.
- Cool air descends the tower through openings.
- Cool air enters the building, and hot air rises and exits via the clerestory windows.
- Energy requirements for the pumps are 249W per tower.
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Description
Test your knowledge on key airflow concepts and their effects on building ventilation. This quiz covers the stack effect, cross ventilation requirements, and cooling systems. Perfect for those studying architectural design or environmental engineering.
