NATURAL VENTILATION

INTRODUCTION

Almost all historic buildings were ventilated naturally, although many of these have been compromised by the addition of partition walls and mechanical systems. With an increased awareness of the cost and environmental impacts of energy use, natural ventilation has become an increasingly attractive method for reducing energy use and cost and for providing acceptable indoor environmental quality and maintaining a healthy, comfortable, and productive indoor climate rather than the more prevailing approach of using mechanical ventilation. In favorable climates and buildings types, natural ventilation can be used as an alternative to air-conditioning plants, saving 10%-30% of total energy consumption.

Natural ventilation systems rely on pressure differences to move fresh air through buildings. Pressure differences can be caused by wind or the buoyancy effect created by temperature differences or differences in humidity. In either case, the amount of ventilation will depend critically on the size and placement of openings in the building. It is useful to think of a natural ventilation system as a circuit, with equal consideration given to supply and exhaust. Openings between rooms such as transom windows, louvers, grills, or open plans are techniques to complete the airflow circuit through a building. Code requirements regarding smoke and fire transfer present challenges to the designer of a natural ventilation system. For example, historic buildings used the stairway as the exhaust stack, a technique now prevented by code requirements in many cases.

-http://en.wikipedia.org/wiki/Natural_ventilation

-Linden, P. F. (1999). "The Fluid Mechanics of Natural Ventilation". Annual Review of Fluid Mechanics 31: 201–238. doi:10.1146/annurev.fluid.31.1.201.

DEFINITION OF NATURAL VENTILATION

Natural ventilation is the process of supplying and removing air through an indoor space without using mechanical systems. It refers to the flow of external air to an indoor space as a result of pressure or temperatures differences. There are two types of natural ventilation occurring in buildings: wind driven/cross ventilation and stack ventilation.

An example of application of Natural Ventilation in building.

    Example of Cross and Stack Ventilation.

WIND-DRIVEN NATURAL VENTILATION

Wind Driven Ventilation or Roof Mounted Ventilation design in buildings provides ventilation to occupants using the least amount of resources. Mechanical ventilation drawbacks include the use of equipment that is high in embodied energy and the consumption of energy during operation. By utilizing the design of the building, Wind Driven Ventilation takes advantage of the natural passage of air without the need for high energy consuming equipment. Wind catchers are able to aid Wind Driven Ventilation by directing air in and out of buildings.

-http://www.hbp.usm.my/ventilation/winddesign11.htm

-http://www.wind-driven-ventilation.co.uk/

STACK VENTILATION

Think of a chimney with a fire burning below. The air heated above the fire rises through the chimney and out the top. In this care, air is rising at a fairly high velocity. The same principle can be used to ventilate a space. As air increases in the temperature, its density drops. This causes it to rise past air that is at a lower temperature. A stack will concentrate this effect. Typically, the longer the stack, the more airflow you can get. The main benefit of using stack ventilation is that wind is not required.

Above diagram illustrates an airflow path driven by the stack effect. Hot air rising out the roof of the building creates a vacuum in the interior space; this vacuum is used to bring cooler air from the outside into the building. In this particular scenario, the vacuum is enhanced by wind. Note that wind is not necessary for stack ventilation and that this method can be incorporated into a building in many more ways than having just a skylight.

http://cmiserver.mit.edu/natvent/stack.htm

DESCRIPTION OF NATURAL VENTILATION

Natural ventilation, unlike fan-forced ventilation, uses the natural forces of wind and buoyancy to deliver fresh air into buildings. Fresh air is required in buildings to alleviate odors, to provide oxygen for respiration, and to increase thermal comfort. At interior air velocities of 160 feet per minute (fpm), the perceived interior temperature can be reduced by as much as 5°F. However, unlike true air-conditioning, natural ventilation is ineffective at reducing the humidity of incoming air. This places a limit on the application of natural ventilation in humid climates.

A. Types of Natural Ventilation Effects.

Wind can blow air through openings in the wall on the windward side of the building, and suck air out of openings on the leeward side and the roof. Temperature differences between warm air inside and cool air outside can cause the air in the room to rise and exit at the ceiling or ridge, and enter via lower openings in the wall. Similarly, buoyancy caused by differences in humidity can allow a pressurized column of dense, evaporative cooled air to supply a space, and lighter, warmer, humid air to exhaust near the top. 

WIND EFFECT ON BUILDING

Wind causes a positive pressure on the windward side and a negative pressure on the leeward side of buildings. To equalize pressure, fresh air will enter any windward opening and be exhausted from any leeward opening.

Sometimes wind flow prevails parallel to a building wall rather than perpendicular to it. In this case it is still possible to induce wind ventilation by architectural features or by the way a casement window opens. For example, if the wind blows from east to west along a north-facing wall, the first window (which opens out) would have hinges on the left-hand side to act as a scoop and direct wind into the room. The second window would hinge on the right-hand side so the opening is down-wind from the open glass pane and the negative pressure draws air out of the room.

General classification of wind (Malaysia)

Source: http://en.wikipedia.org/wiki/Wind

GENERAL FUNCTION OF VENTILATION IN THE BUILDING

The purpose of ventilation is not only to remove bad smells from the kitchen or the toilet, ventilation also removes or dilutes potentially hazardous and gases and it helps to control the indoor humidity and, as a consequence, limits the growth of harmful organisms.

ORIENTATION

WHAT IS WIND ORIENTATION?

Wind is the flow of gasses on a large scale. On earth, wind consists of the bulk movement of air. Wind is caused by differences in pressure. When a difference in pressure exists, the air is accelerated from higher to lower pressure.

·      Northerly wind blows from the north to the south.

·      Wind direction is usually reported in cardinal directions or in azimuth degrees. So, for example wind direction is reported by the direction from which it originates. For example, a wind coming from the south is given as 180 degrees; one from the east is 90 degrees.

Tool to determine the direction of the wind:

Wind Vine

Front view of the building:

Side view of the building:

Opinion and Justification to implement optimum ventilation into the building and its surrounding.

·      Plant small trees in front of the window. This method will help to prevent the direct sunlight to enter the building. Besides that, the photosynthesis will occurs and the plant provides oxygen and moistures into building. The plant will absorb the heat. Last but not least, the plant can beautify the environment.

·      Secondly, awning can be installed. This method also prevents the direct sunlight. The dim effect will be created. Furthermore, the through fall of the rain cannot enter through windows.

·      Bamboo scree (birai) also can be installed to replace the curtain. This is because bamboo screen is low cost and low maintenance, unlike the curtain. Bamboo screen also gives the cool effect. The gap between the bamboo can allow the light and wind to enter the building even went the screen is closed. The most important thing is, the use of bamboo screen will add the cosmetic value to the building.

Ventilation

·         Lattice can make sure the hot and cold can easily enter and exit the building. The indoor  of the building will be fresh and the temperature controlled the indirectly lighting also can seep through the lattice.

·         Add the number of windows. The minimum wind can enters the building. This method will helps to make sure perfect wind circulation in the building.