Natural Ventilation: Principles and Strategies

Natural ventilation is a sustainable and efficient approach to maintaining a comfortable and healthy environment, taking advantage of available natural resources, such as fresh air and external airflows. In this article, we will explore different natural ventilation strategies, the driving forces behind this ventilation and the benefits it can bring.

There are several strategies that can be adopted to promote natural ventilation in a space. One of them is the use of openings, such as windows and doors, which allow the entry and exit of air. It is important to strategically position these openings, taking into account factors such as the direction of prevailing winds and solar incidence. In this way, it is possible to make the most of external airflows to cool the environment.

Another interesting strategy is to use architectural elements that favor cross ventilation. This means positioning openings in opposite walls to allow efficient passage of air. Cross ventilation creates a continuous air stream, renewing indoor air and reducing the feeling of stuffiness. We have a post about the use of cobogó in architecture, which is also related to the use of natural ventilation to promote more comfortable spaces. You can read it by clicking here.

In addition, it is important to consider the use of natural elements, such as vegetation, to assist in natural ventilation. Trees and plants can be strategically positioned to create shadows and mitigate the impact of external heat. In addition, the evapotranspiration of plants contributes to cooling the surrounding air.

When designing a space focused on natural ventilation, it is essential to take into account the climatic characteristics of the region. Aspects such as average temperature, humidity and wind speed must be analyzed to ensure an efficient project. Also, it is important to consider the solar orientation of the space, as this can directly influence the amount of heat received and the need for ventilation. We also have a post about the importance of air circulation for comfort and energy efficiency, here, and also a post about tools for thermal comfort analysis, which you can access by clicking here.

Principle of Driving Forces for Natural Ventilation

There are several driving forces that propel natural ventilation in an environment. These forces are influenced by external and internal factors and play an important role in air circulation. Some of the main drivers of natural ventilation are:

1. Temperature difference: The temperature difference between the interior and exterior of an environment creates a driving force for ventilation. Warm air tends to rise, while cold air tends to descend. This temperature difference creates an air stream that allows air renewal.
2. Pressure difference: The pressure difference between the interior and exterior of an environment is also a driving force for natural ventilation. If the internal pressure is higher than the external one, the air will be expelled outside. If the internal pressure is lower, the external air will be pulled inside.
3. Wind: The action of the wind is one of the main driving forces for natural ventilation. The wind creates pressure on the external surfaces of the environment, generating a pressure difference that allows the entry or exit of air.
4. Chimney effect: The chimney effect occurs when there is a temperature difference between the top and the base of an environment. The warm air rises and is expelled through openings at the top, while the cold air is pulled inside through openings at the base. This effect creates a natural circulation of air.
5. Natural convection: Natural convection is a process in which warm air expands, becoming less dense and rising, while cold air contracts, becoming denser and descending. This convection movement creates natural ventilation.

These driving forces can be used to design buildings with an efficient ventilation system, reducing dependence on mechanical ventilation systems and promoting sustainability.

System for Natural Ventilation

• Ventilation input(s): In this component of the natural ventilation system, fresh air is pulled into the system, usually through openings such as windows or specific inlets. This fresh air input is essential to ensure good circulation and renewal of air in the occupied space.
• Supply point(s): These points are where fresh air, coming from the ventilation inputs, is delivered into the occupied space. They can be strategically positioned openings to direct the air flow to areas that need ventilation, such as rooms or specific environments.
• Flow path: This is the path that fresh air takes through the occupied space, from the ventilation inputs to the exhaust point. It is important to ensure that the flow path is efficient and covers all areas that need adequate ventilation.
• Ventilation output: In this component, stale or used air is expelled from the building. This can be done through chimneys, exhaust ducts or other openings that allow the exit of stale air. The ventilation output is crucial for removing contaminated or heated air from the occupied space and maintaining indoor air quality.

Strategies for Natural Ventilation

• Unilateral ventilation (from one side): In this type of ventilation, the entry of fresh air and the exit of stale air occur on opposite sides of the occupied space. Fresh air enters through an opening, such as a window, and stale air is expelled through an outlet, such as a chimney or exhaust duct.

• Cross ventilation: In this type of ventilation, fresh air is pulled into the occupied space through an opening on one side and is expelled through an opening on the opposite side. This strategy allows air to circulate more efficiently through the environment, promoting better ventilation and air renewal.

• Atriums (single cell): Atriums are open interior spaces, usually located in the center of a building, that allow the entry of natural light and ventilation. In a single cell atrium, the space is vertically continuous, allowing air to circulate freely from one floor to another, promoting natural ventilation.

• Chimneys (multiple cells): Chimneys are vertical structures that allow natural ventilation in buildings. In multi-cell chimneys, several openings are distributed vertically, allowing fresh air to be pulled into the building and stale air to be expelled outside. These openings may be located at different levels of the building, promoting air circulation.

Use of the Wind Rose to plan Natural Ventilation

The Wind Rose is a graphical representation that plays a key role in indicating the directions and winds of a specific region. Composed of four main directions – North, South, East and West – and their respective intermediate directions, this instrument is an essential component to assist in geographic orientation.

To effectively plan the natural ventilation of a building or house using the Wind Rose, it is essential to understand and analyze the predominance of winds in the region in question. With this valuable information in hand, you can strategically plan the location and positioning of your home’s windows and other openings to make the most of natural ventilation, providing a pleasant and cool environment.

For example, if the prevailing winds in your locality come mainly from the south, you may consider placing windows or openings in this specific direction to allow the entry and circulation of wind. Similarly, it is possible to position openings on opposite sides of the house to allow air to flow freely through the house, creating an effective and natural ventilation. This type of planning can not only improve the quality of air within the house, but also contribute to energy savings, reducing the need for fans or air conditioning.

Standards and Software for Simulating Natural Ventilation in Buildings

There are several standards and software available to assist in simulating natural ventilation in buildings. Some of them are:

ISO 7730

ISO 7730 is an international standard that establishes the criteria for thermal comfort and the measurements of environmental variables. It defines parameters such as air temperature, air speed, relative humidity and thermal radiation, which are fundamental to determine a person’s thermal comfort.

In regards to natural ventilation, the standard recommends the use of strategies that allow the entry of fresh air into the environment, such as opening windows or using natural ventilation devices, such as blinds or ventilation grilles. In addition, the standard also provides guidance on the proper sizing of ventilation openings, considering factors such as the necessary air renewal rate and the uniform distribution of air flow.

It is important to note that these standards offer general guidelines and that the practical application of the recommendations may vary depending on the specific characteristics of the environment and the needs of the occupants. Therefore, it is always recommended to consult qualified experts to ensure the adequacy of natural ventilation measures in accordance with the standards.

CIBSE GUIDE A AND AM10

The Chartered Institution of Building Services Engineers (CIBSE) Guide A and AM10 are comprehensive guidelines for the design, implementation, and operation of environmental design , which also includes natural ventilation in buildings. They provide detailed criteria for various aspects of natural ventilation, including the design of ventilation openings, the arrangement of spaces to enhance airflow, and the use of architectural features to promote air movement. These guidelines are typically used during the design stage of building projects to ensure the ventilation system meets the needs of the building’s occupants and aligns with environmental sustainability goals. The importance of using these guidelines lies in their focus on enhancing the indoor air quality, promoting energy efficiency, and improving the overall comfort of the building’s occupants. Adherence to these guidelines ensures that the building’s natural ventilation system is both effective and sustainable.

ASHRAE Standard 55

ASHRAE Standard 55 is an American standard that defines the criteria for thermal comfort in buildings. It sets the limits of temperature, relative humidity, air speed and other parameters to ensure a comfortable environment for occupants.

For natural ventilation, Standard 55 recommends the use of passive strategies that allow the entry of fresh air into indoor environments. Some recommendations include the use of operable windows to promote air circulation, the use of strategically positioned openings to take advantage of external air currents and the creation of cross ventilation zones to maximize air renewal.

In addition, Standard 55 also provides calculation methods to determine the effectiveness of natural ventilation in a building, taking into account factors such as the air renewal rate, the distribution of air in the environments and the indoor air quality.

BS EN 13779

BS EN 13779 is a European standard that provides guidelines for the ventilation and air conditioning of non-residential buildings. It outlines the necessary criteria for designing and assessing the performance of ventilation systems, including natural ventilation strategies, to ensure a comfortable indoor environment. This standard is used during the design and implementation phase of building projects and is crucial in specifying the minimum air quality requirements for different areas within a building. Its importance lies in its aim to enhance occupant comfort, health, and productivity by ensuring efficient ventilation and good air quality.

Simulation Software

In addition to the standards, there are several simulation software that can be used to analyze natural ventilation in buildings. Some popular examples are:

• CFD (Computational Fluid Dynamics): Computational fluid dynamics software that enables detailed analysis of airflows in buildings.
• DesignBuilder: Software that combines 3D modeling and energy simulation features for building performance analysis.
• Optivent: Company specialized in solutions for natural ventilation in buildings. They offer products and services to optimize air flow and improve indoor air quality.

Conclusion

By adopting strategies that favor natural air circulation, it is possible to create more pleasant, economical and sustainable spaces. Therefore, when designing or renovating an environment, consider the importance of natural ventilation and take advantage of the benefits it can provide.

Remember to use appropriate standards and software to simulate and analyze natural ventilation in your projects. This will ensure that the measures adopted are efficient and in compliance with best practices.

In addition, also consider the climatic characteristics of the region and the needs of the occupants when designing spaces with natural ventilation. Thus, you will ensure maximum thermal comfort and energy efficiency of the environment.