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Stack Effect Ventilation

The stack effect describes the passive movement of air through a building resulting from differences in vertical pressure developed by thermal buoyancy. When air inside a building is warmer than the outside air, the warmer, the less dense air will rise.

Stack ventilation takes advantage of this effect by constructing openings in the building envelope high at a substantial height, allowing the warm air to escape. The negative pressure at the top of the building draws in colder, denser outside air through openings low in the building. Naturally, this effect is fairly weak, but it can be concentrated through the use of a stack. Longer stacks will typically increase airflow.

Controlled stack ventilation can allow for passive cooling in the summer with some benefits over mechanical ventilation including low maintenance and operating cost, minimal or no energy costs, and typically lower construction costs in new buildings, as passive stack ventilation is designed similarly to mechanical ventilation without the mechanical components. Passive stack ventilation is generally rare in the United States, but is fairly popular in buildings in Europe.

While stack ventilation can have cooling benefits in the summer, it can be problematic during cold winters, as the high temperature difference between the building interior and exterior can result in overventilation and unwanted building heat loss. Conversely, underventilation can occur even with large ventilation openings when temperature differences are low. Even when temperature differences are sufficient to facilitate adequate stack ventilation, upper floors in larger buildings can be underventilated. Ventilation stacks, particularly in larger buildings, should be designed with some method of flow control, such as self-regulating vents, pressure sensitive ventilators, or fans (including solar powered fans). Some systems may need backup mechanical ventilation as well.

Benefits
•Allows for building cooling and ventilation with lower maintenance and operating costs than mechanical systems. Minimal operational noise.
•Fully passive systems require no additional energy. Stacks supplemented by active flow control use less energy than equivalent mechanical systems.
•Reduces building cooling energy needs. Can be combined with passive cross-ventilation to maximize ventilation.

Drawbacks:
•Due to reliance on natural forces, overventilation and underventilation can occur frequently.
•Proper design and flow control are necessary to maintain adequate ventilation rates.
•Ventilation can be inadequate on upper floors of larger buildings, trapping heat and reducing air quality. Installation of operable windows may be necessary to facilitate ventilation.
•In winter, the high difference in temperature between the building’s interior and exterior can result in overventilation and heat loss without adequate flow control.

Source: https://santacruzarchitect.wordpress.com/2015/05/16/stack-effect-ventilation/#:~:text=The%20stack%20effect%20describes%20the,pressure%20developed%20by%20thermal%20buoyancy.&text=Stack%20ventilation%20takes%20advantage%20of,the%20warm%20air%20to%20escape.

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Buoyancy Ventilation

Buoyancy or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. Buoyancy revolves around the subject of density.

Buoyancy ventilation results from the density differences between interior and exterior air. This variance causes the warm air to rise above the cold air, and create an upward air-stream. The saying "hot air rises" stems from this. The effectiveness of the buoyancy effect increases as the temperature differences between the different sections of the building increases. Increased height between the lower and higher apertures, leads to better displacement and superior ventilation.

Reference:
https://www.wbdg.org/resources/natural-ventilation#:~:text=Buoyancy%20ventilation%20may%20be%20temperature,the%20space%20through%20a%20stack.

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Water Elements

Water is an important element in landscaping and designing a house especially in the aspects of ventilation inside the house. Water elements such as ponds, pools, or fountains act as space for transition where air can be naturally cooled off before entering the house.

Reference:
https://www.onegreenplanet.org/lifestyle/10-natural-ventilation-tips-for-your-home/

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VENTURI EFFECT,   HARMONIZING A STRUCTURE  TO THE ELEMENT OF WIND

The Venturi effect is the product of studying wind ventilation. It is a phenomenon whereas fluids such as gases flow and equalize the pressure between two zones. First, wind will enter the building through openings such as windows and doors. Much differently from cross ventilation,  the Venturi effect takes advantage of the fact that warm air rises. Instead of letting the air flow through the building and letting it exit on another side, warm air is directed to an output vent at a higher elevation for warm air to exit. This does not mean however, that cross ventilation and the venturi effect could not work together. Most of the time, Architects use this principle hand-in-hand to develop a structure that maintains a uniformly cool structure .

This practice is commonly used in tropical climates to maintain the temperature to a comfortable state.

https://www.sciencedirect.com/topics/engineering/venturi-effect

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Mechanical Ventilation
Mechanical fans drive mechanical ventilation, it supplies air into, or exhausting air from, a room.

In warmer climates, infiltration may need to be minimized to reduce interstitial condensation--done through a positive pressure system

In colder climates, exfiltration may need to be minimized to reduce interstitial condensation--done through a negative pressure system

For rooms that garner pollutants regularly (e.g bathroom, kitchen, toilet), a negative pressure system is used

*Negative pressure system - room is in negative pressure and 'sucks' air from outside
*Positive pressure system - room is in positive pressure and room air is 'leaked' outside through various openings
Reference: https://www.ncbi.nlm.nih.gov/books/NBK143277/

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HYBRID OR MIXED-MODE VENTILATION

Hybrid or mixed-mode ventilation, from the word itself means that it is a combination of both natural and mechanical ventilation. It depends on natural ventilation in determining the flow rate and it then uses mechanical ventilation when the flow rate is sub optimal. When flow rate is inadequate, exhaust fans are installed to increase ventilation rates and it should be installed in rooms where air may be directly exhausted outside either through a wall or thr roof. Advanced hybrid ventilation techniques may include intelligent controls which gives balance to indoor air qualities, thermal comfort, and energy consumption. This gives users more options when the environment outside has a more favorable condition.

https://svach.lbl.gov/hybrid-ventilation-and-adaptive-comfort/
https://www.ncbi.nlm.nih.gov/books/NBK143277/

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WIND VENTILATION

Wind driven ventilation includes harnessing the control of the wind to ventilate your home. Not only is wind ventilation a free, normal ventilation strategy, but giving that your home has been planned with wind ventilation in intellect, it can moreover be exceptionally compelling.

One frame of wind ventilation is called cross ventilation. This includes wind entering through a vent (or a window or entryway), and permitting air to stream straightforwardly through the house and out through an opening on the other side of the home. Knowing which way the wind is likely to blow is where you should plan to build as it may be a great way to plan for successful cross ventilation. Moreover, the position and estimate of your vents, windows and entryways, as well as the way between the different sides of the house, make a big difference to how effectively you'll be able cross ventilate your home.

Reference:
https://build.com.au/ventilation-methods

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Natural ventilation
Is the passive flow of wind bringing fresh air into your home without the use of mechanical systems. It provides free cooling and reduces home energy use during nighttime in summer months. The factors that affect the effectiveness of natural ventilation are dominant wind speed direction, surrounding environment, building footprint and orientation, outdoor temperature and humidity, and window sizing, location, and operable. The two common types of natural ventilation techniques are wind driven ventilation and stack ventilation.

Natural Ventilation. (n.d.). Retrieved September 17, 2020, from https://greenhome.osu.edu/natural-ventilation

Fenimore, J. (2018, August 2). Natural ventilation [Illustration]. DLR Group. https://www.dlrgroup.com/media/articles/fenimore-local-design-africa/

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Open Spaces

When looking at structures I always want to see how it has respect for open spaces and entrances. This is relative to accessibility. It shouldn't restrict people to go inside. Moreover, open spaces is a characteristic found in natural ventilation because organic cooling is applied.

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Comparison of Mechanical Ventilation and Natural Ventilation

Mechanical Ventilation
There are number of advantages if Mechanical Ventilation systems are well installed, designed, and maintained.
Pros:

Mechanical Ventilation systems are reliable in providing the flow rate regardless of the influences of the temperature and the wind. Also, it can be easily installed in air-conditioning, so indoor air temperature and humidity can also be controlled.

Filtration systems can be installed to secure the incoming air inside the structure.

It can easily work with an electricity.

The airflow path of the mechanical ventilation can be easily controlled.

Cons:

Maintenance of ventilation systems can cost high

Sometimes provide faulty operations (e.g. no electricity, equipment failure, etc.)

Natural Ventilation
There are also several advantages Natural Ventilation provides.
Pros:

It can provide a high ventilation rate more economically, it does not need electricity to provide ventilation.

Natural ventilation can be more energy efficient, particularly if heating is not required.

Great design of Natural Ventilation provides a good access of daylight and also a good sense of well-being.

Cons:

It depends solely on the climatic conditions outside, and it is also difficult to control.

It only works if the forces around are high

If not installed properly, it can cause damages and problems to the structure.

Reference:

Atkinson J, Chartier Y, Pessoa-Silva CL, et al., editors. Natural Ventilation for Infection Control in Health-Care Settings. Geneva: World Health Organization; 2009. 2, Concepts and types of ventilation. Available from: https://www.ncbi.nlm.nih.gov/books/NBK143277/

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Cross Ventilation

Cross ventilation, also known as wind effect ventilation, is a natural method of cooling. This method uses two important systems namely: inlet and outlet. The inlet (louver, open windows, etc.) forces cool exterior wind inside a structure while the outlet directs warm interior air outside through the use of roof vents or higher window openings. Modern cross ventilation systems help increase the flow of air from the exterior to the interior and vice-versa.

Essentially, cross ventilation relies heavily on natural elements to provide a beneficial and comforting atmosphere within commercial, industrial and residential buildings. This kind of ventilation excels in almost any climate and is an inexpensive method of cooling.

Advantages:

Inexpensive

No operating costs

Lack of carbon emissions

No additional energy consumption

Disadvantages:

Compared to mechanical ventilation, the cooling isn't as strong

Relies on the climatic conditions outside of the structure

Lack of air filtration

Reference:
Moffit Natural Ventilation Solutions. (n.d.). What is Cross Ventilation? Retrieved from: https://www.moffittcorp.com/wind-effect-cross-ventilation/

Designing Buildings. (2020, September 4). Cross Ventilation. Retrieved from: https://www.designingbuildings.co.uk/wiki/Cross_ventilation