Sufficient natural lighting and ventilation are basic necessities of any building. Cross ventilation is one of the common terms we come across while discussing air ventilation in homes and it plays an important role in maintaining the wellbeing of occupants and their buildings. Read on to understand the cross ventilation meaning, why it is important and explore strategies to optimise room ventilation design.
What is Cross Ventilation?
There are two types of ventilation systems for buildings– natural and mechanical. While mechanical ventilation relies on induced energy to work, natural cross ventilation is an eco-friendly and energy efficient mechanism. In simple terms, the natural movement of air from one location to another can be referred to as cross ventilation. This movement occurs due to air pressure differences between different locations- air moves from areas with high pressure to lower pressure areas. Temperature differences can also cause air movement- hot air rises up to be replaced by cool air at lower levels.
Importance and Purpose of Ventilation
Cross ventilation is vital in buildings for several reasons, the most important ones of which are:
- Thermal Comfort: A natural air ventilation system removes hot and stale air from enclosed spaces and replaces it with fresh, cool air. Cross ventilation ensures the thermal comfort of occupants, which has several positive effects, such as upliftment of moods, a general increase in productivity and regulated sleep cycles.
- Indoor Air Quality: Stale air can often accumulate bacteria which cause air-borne diseases, allergies and breathing issues like asthma. Passive ventilation replaces such air with clean and fresh air, which prevents these problems and ensures that good indoor air quality is maintained constantly.
- Building Health: The build-up of moisture in enclosed spaces can cause issues like water seepage, cracking and concrete corrosion, which can lead to building damage and eventual collapse through structural failures. Cross ventilation prevents moisture accumulation by bringing in cool breezes, thus helping maintain the structural integrity of buildings.
Techniques to Enhance Cross Ventilation in Homes
Some techniques and types of natural ventilation enhancement are:
Building Orientation
The design of buildings and their orientation must consider the movement patterns and directions of wind in the local region. Facades that face the wind (windward side) at right angles experience the highest wind pressures, while a 45-degree inclination against the wind direction can reduce the wind pressure by half. However, it has been studied that a 45-degree inclination against the wind can improve indoor air velocity and provide better air distribution in a room. Therefore, in warm and humid climates, it is ideal to have the larger building facades and openings on the windward side, while in hot and dry climates—where it is important to avoid dry and dusty winds—it may be more preferable to have openings on the leeward side (the side facing away from winds).
Stack Effect or Chimney Effect
The stack effect is caused by differences in air density and temperature in a room. Hot air with a higher density moves upwards, while low-density, cooler air moves downwards. This effect can be observed when windows are placed at lower levels on windward-facing facades, with higher-level windows on the opposite side. The stack effect can also be compounded through the use of vertical stacks such as double-height spaces or specially designed ventilating shafts with openings at the top. Here, air stacking caused by differential densities will lead to natural air movement and cross ventilation.
Venturi Effect in Architecture
The size, number and position of openings in a room play a major role in the quantity and quality of cross ventilation. The largest air velocity can be obtained through small openings, where air will flow at a higher pressure than with bigger openings- this is called the Venturi effect. The Venturi effect can be optimised by providing small openings on the windward side and large openings on the leeward side to have effective air flow in warm and humid climates. However, if multiple openings are located on the windward side without any openings on other sides, it can create an increased air pressure with no outlets and make a room uncomfortable.
Humidity Control
Apart from ensuring that air flows inside a room, it is also important to remove the existing air along with excess humidity or to bring in humidity in dry areas. Humidity control can be achieved through natural means such as:
- Wind Scoops/ Wind Catcher: These consist of shafts with openings at the top on the windward side. Cool wind enters this shaft, passes through water-filled pots and moves into rooms through lower level openings on the leeward side. This system acts like a reverse stack effect and introduces humidity into rooms.
- Curtains/ Screens: Screens made of natural materials like cascas grass can be hung against windows. These are kept wet by sprinkling water periodically and when wind passes through them, it carries humidity inside. This method is effective in hot and dry regions.
External Devices and Controls
Many external features can be added to existing buildings to ensure adequate cross ventilation. Some of these are:
- Louvres/ Window Sashes/ Chajjas: These devices can be used to block or direct breezes along certain directions into a room as required.
- Barriers: External elements like trees that are on the windward side and very close to a building can obstruct air flowing inside. However, if trees are planted on the leeward side, they can help with better air flow and distribution.
- Evaporative Cooling: Evaporation of water causes cooling, resulting in the movement of cool winds. Therefore, including small water bodies in or near buildings can be an effective way of increasing cross ventilation, especially in areas with hot and dry climates.
Apart from these popular methods, a modern house ventilation system can also incorporate more advanced components like kinetic facades with automated controls to ensure sufficient cross ventilation.
Getting the Best Ventilation Design for Home
The amount and efficiency of cross ventilation in a room are largely dependent on good architectural design and its accurate execution. These aspects require careful analysis of cross ventilation diagrams, local climatic conditions and appropriate design measures to accommodate them along with individual requirements. Brick & Bolt is a company that provides end-to-end construction services aided by a team of architects and professionals who are experts in house ventilation design. With customised designs provided for every project, the company has completed 7000+ homes and gained a reputation as a dominating force in the construction industry. To get your dream home built with assured expertise and optimised cross ventilation, contact Brick & Bolt today!