2. STACK VENTILATION is a passive cooling strategy which relies on TWO basic principles. - As air warms up, it becomes less dense and rises. - Fresh ambient air replaces the air that has risen.
3. STACK VENTILATION is a natural convection system which creates its own air current where warm air is evacuated through a high point , and cooler outdoor air is brought in at a lower level .
4. IN ORDER for the system to function properly, the difference between indoor and outdoor air temperature needs to be at least 1.7 degrees Celsius. A GREATER temperature difference can provide more effective air circulation and cooling.
5. Increasing the HEIGHT of a stack is one way to achieve a greater temperature difference. The higher the stack, the greater the vertical stratification of temperatures.
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7. Another way to increase the temperature difference between entering and exiting air is to use solar energy to heat the air . Stacks are glazed with a translucent material so that solar radiation heats the air in the stack, causing an increase in airflow within the building.
8. Building Research Establishment Building In the BRE building the stacks are given greater height than the rest of the building, providing an architectural feature that highlights the significance of these devices to the functioning of the building.
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10. Key Architectural Issues - A stack needs to generate a large temperature difference between exhaust air and incoming air . This can be done in several ways, including increasing stack height . A typical stack will provide effective ventilation for areas within the lower half of its total height.
11. Stacks may be integrated within the design or left exposed .
12. Implementation Considerations - Stacks provide more air movement at lower levels . Modular and separated stacks can address this problem, but an abundance of stacks is costly and requires more openings, which may not be possible for a variety of reasons; security, location, adjacencies, etc.
13. Vertical stacks may need to be integrated with HVAC and structural systems to ensure effective utilization of space.
14. Outside air is flushed through the building to provide cooling, allowing anything in the air to be introduced to the building, including undesired aspects such as noise. Therefore, careful attention should be paid to nearby noise sources.
15. Design Procedure 1. Establish a workable stack height for the project. 2. Size the stack openings which will in turn, define the system’s performance.
16. 3. Estimate the cooling capacity of the stack ventilation system on the basis of stack height and stack to floor area ratio. 4. Adjust stack openings and/or height as necessary to obtain desired cooling capacity.
