Stack Effect in Building Ventilation

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Questions and Answers

What is the primary function of a wind tower?

To collect rainwater for irrigation

To provide cooling through air movement (correct)

To filter air pollutants from the environment

To generate electricity using wind energy

How does the temperature difference between the interior and exterior contribute to the operation of a wind tower?

It ensures that the interior temperature remains constant

It creates a constant airflow regardless of environmental conditions

It generates a draft that facilitates air movement through the tower (correct)

It allows heat to escape entirely without any air movement

What role does nocturnal radiation play in the functioning of a wind tower at night?

It absorbs the warm air and prevents drafts

It redistributes heat within the building

It cools the entire building structure effectively

It enhances the upward draft by warming the cool night air (correct)

Under what circumstances might wind towers need to be shut off?

When cooling is not needed for the building Signup and view all the answers

What is a significant characteristic of wind towers that influences their efficiency?

The presence of air temperature fluctuations and wind velocity Signup and view all the answers

What is the minimum recommended distance for cross ventilation between buildings of equal height?

7 times the building height Signup and view all the answers

Which factor affects the calculation of stack pressure according to the given equation?

Height of the stack Signup and view all the answers

What happens to the air in a solar chimney during the day?

It rises and draws in cooler air Signup and view all the answers

How can high-density layouts affect cross ventilation?

They reduce available cross ventilation Signup and view all the answers

Which of the following variables is part of the stack pressure equation?

Temperature difference Signup and view all the answers

What occurs during the night in a solar chimney system?

The process reverses, cool air replaces warm air Signup and view all the answers

What does the constant 0.042 represent in the stack pressure equation?

Constant for temperature difference in N/m^3 degC Signup and view all the answers

What is a potential solution to overcome reduced cross ventilation in dense urban environments?

Implementing ventilating ducts or shafts Signup and view all the answers

What effect does a gap between the building face and canopy have on airflow?

It creates a downward pressure enhancing airflow. Signup and view all the answers

In terms of ventilation, what is cross-ventilation?

Airflow channeled by multiple openings aligned with the wind. Signup and view all the answers

What is the result of placing openings directly across from each other in a building?

It can create pressure similar to that outside, increasing discomfort. Signup and view all the answers

What is often true regarding the optimum orientation for solar gain and wind?

The optimum orientations rarely align. Signup and view all the answers

Why is it generally recommended to avoid placing openings directly across from each other?

It may cause a buildup of pressure indoors. Signup and view all the answers

What happens to airflow in a building with a windward opening but no outlet?

Pressure similar to that outside will build up indoors. Signup and view all the answers

What is the primary reason for creating a broader wind shadow?

To enhance negative pressure effects indoors. Signup and view all the answers

What orientation is preferable for sun exclusion in equatorial regions?

North–south orientation. Signup and view all the answers

What effect does the presence of wind have on the operation of a wind tower?

It enhances air circulation and cooling. Signup and view all the answers

What happens to the hot ambient air when it comes into contact with the cool upper part of the tower?

It cools down and sinks into the living spaces. Signup and view all the answers

Which scenario can negatively impact the effectiveness of a wind tower?

Wind access is blocked by upwind buildings. Signup and view all the answers

What effect does nocturnal radiation have in the context of a wind tower?

It contributes additional cooling. Signup and view all the answers

What is a prerequisite for the effective operation of a wind catcher?

The winds must have a consistent speed. Signup and view all the answers

What happens to the tower's operation in the absence of wind?

It ceases to function effectively and acts as a chimney. Signup and view all the answers

Where is the cooling effect from a wind tower most effective?

In low-rise, high-density settlements. Signup and view all the answers

How does the ambient air temperature affect the performance of a wind tower?

Warm ambient air reduces the downward air flow. Signup and view all the answers

What happens to indoor air velocity when openings are placed at right angles to the wind direction?

It increases and optimizes air mixing. Signup and view all the answers

How does a wind incidence of 45° affect pressure and average indoor air velocity?

It reduces pressure by 50% and increases average air velocity. Signup and view all the answers

What can be done to improve air flow around internal obstacles like walls or furniture?

Use partition screens that are clear of the floor and ceiling. Signup and view all the answers

What is the primary goal when placing inlets and outlets in a building?

To optimize the path air follows for better ventilation. Signup and view all the answers

How can cross ventilation be increased in a building?

By placing openings across from each other. Signup and view all the answers

What effect do right-angle bends in airflow have on low velocity air flow?

They can stop low velocity air flow. Signup and view all the answers

What is a benefit of having larger openings on the leeward faces of a building?

They allow for better pressure distribution. Signup and view all the answers

What can be a consequence of having well-cooled areas in a room?

Some parts of the room might be poorly ventilated. Signup and view all the answers

Study Notes

Stack Effect

The stack effect is a natural process where warmer air rises and cooler air descends, creating air movement in enclosed spaces.
Stack effect can be used for ventilation, particularly in buildings with chimneys, courtyards, and wind towers.
Stack pressure (Ps) can be calculated using the formula: Ps = 0.042 × h × ΔT where:
- Ps is the stack pressure in N/m2
- h is the height of the stack in meters
- ΔT is the temperature difference in degrees Celsius

Applications of Stack Effect

Chimneys: Heated air rises through the chimney, creating negative pressure inside the building, drawing in cooler air.
Courtyards: During the day, solar radiation heats the courtyard air, which rises, drawing cooler outdoor air into the spaces.
Wind Towers: In windy conditions, cool night air is drawn into the tower and then forced downwards into living spaces.
Wind Tower Operation:
- Day: Hot ambient air cools when it contacts the cool upper part of the tower, becomes denser, sinks, and replaces hot air in the living spaces.
- Night: The tower walls absorb heat during the day and release it at night, warming the cool night air.
Wind Tower Considerations:
- Wind towers may need to be shut off when cooling is not required.
- Wind towers are typically used in hot and dry climates for cooling purposes.

Wind Shadow and Wind Towers

Buildings can create wind shadows that affect ventilation.
The wind shadow created by a building can be reduced by using a gap between the building face and the canopy.
This gap creates a downward pressure, directing airflow into the living zone.
Wind towers are commonly used to improve ventilation in low-rise, high-density settlements where wind access is limited.
Wind towers capture wind above the building and draw it downwards, delivering fresh air.
The orientation and position of louvers can significantly affect the indoor airflow and the wind shadow.

Cross-Ventilation

Cross-ventilation optimizes airflow by placing openings strategically to guide air through a building.
Optimal cross-ventilation is achieved with openings placed on opposite sides of a building.
To ensure effective air movement, avoid placing openings directly opposite each other.
Larger openings on the leeward faces of the building compared to the windward faces enhance cross-ventilation.
Placement of inlets at high-pressure zones and outlet at low-pressure zones improves airflow.
Obstacles like internal walls and furniture can reduce the speed of airflow through cross-ventilation.
Partition screens can be used to maintain some airflow even when internal partitions are necessary.

Orientation and Wind Direction

Buildings oriented at right angles to the wind direction experience the highest pressure and airflow.
A 45-degree wind incidence reduces pressure by 50% but increases the average indoor air velocity.
It is important to consider the wind direction and optimize the building's orientation for both wind and solar gains.
In equatorial regions, a building's north-south orientation is generally preferable for solar exclusion, but often the wind is predominantly easterly.

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Description

Explore the stack effect and its applications in building ventilation. Understand how this natural process allows for effective air movement in spaces through chimneys, courtyards, and wind towers. Learn about calculating stack pressure and the impact of temperature differences on air circulation.