·        System selection depends on three main factors including the building configuration, the climate conditions, and the owner desire [2]. 

·        The design engineer is responsible for considering various systems and recommending more than one system to meet the goal and satisfy the owner of a building. 

·         Some criteria can be considered such as climate change (e.g., temperature, humidity, and space pressure), building capacity, spatial requirements, cost such as capital cost, operating cost, and maintenance cost, life cycle analysis, and reliability and flexibility. 

·        These constraints include the available capacity according to standards 

Ø  building configuration 

Ø   available space 

Ø  construction budget 

Ø  the available utility source 

Ø  heating and cooling building    loads 

 https://www.youtube.com/watch?v=Z_2tM7KA5rQ

Group 6(C)
BAHAGIAN III (1)
-Jika pengudaraan secara mekanikal telah dicadangkan, dan pecahayaan semulajadi dari sebuah bangunan atau ruang yang mempunyai pengudaraan semulajadi, boleh diketepikan mengikut budi bahasa pihak berkuasa tempatan. 

BAHAGIAN III (2)
-sesuatu permohonan yang mempunyai pengudaraan mekanikal dan ingin bertukar ke pengudaraan semulajadi  kerana perlu melakukam beber Syarat

BAHAGIAN III (3)
-Jika sesuatu bangunan itu ingin ditukarkan dari penggunaan udara semula jadi kepada pengudaraan mekanikal maka akan terpakainya peruntukkan jadual ketiga undang-undang kecil.

BAHAGIAN III (4)
-jika sesebuah tandas itu menggunakan pengudaraan secara mekanikal dan disenggara mengikut kehendak-kehendak jadual ketiga maka undang-undang melibatkan pengudaraan semula jadi dan pencahayaaan semula jadi tidak akan terpakai
 

A building ventilation system that uses powered fans or blowers to provide fresh air to rooms when the natural forces of air pressure and gravity are not enough to circulate air through a building. Mechanical ventilation is used to control indoor air quality, excess humidity, odours, and contaminants can often be controlled via dilution or replacement with outside air. However, in humid climates specialised ventilation systems can remove excess moisture from the air.

Ceiling fans are commonly seen as ventilation systems as they are usually the most visible mechanical system in a building; however ceiling fans do not provide real ventilation, as there is no introduction of fresh air. Ceiling fans only circulate air within a room for the purpose of reducing the perceived temperature by method of evaporation of perspiration on the skin of the occupants. Also hot air rises therefore; ceiling fans may be used to keep a room warmer in the winter by circulating the warm from the ceiling to the floor. 

Picture

Rotary Heat Exchanger

 

Picture

Ceiling Fan

MAIN METHODS OF FORCED VENTILATION:

PRESSURE SYSTEM: a system which air is blown through the building by a fan or other blower placed at the inlet. The air pressure in the building is slightly greater than that of the outer atmosphere.

Picture

Pressure System

VACUUM SYSTEM: causing an inrush of fresh air. This is done by an exhaust fan placed at the outlet to the vent flue or stack. The air pressure in the building is slightly lower than that of the outer atmosphere. 

However a combination of these two methods can be used to create a BALANCED SYSTEM:

Picture

A Balanced Ventilation System

BENEFITS OF BALANCED SYSTEM:

Improved indoor air quality. Balanced ventilation systems supply fresh air to the living and sleeping areas of homes while exhausting stale air at an equal rate from the bathrooms. This proactive approach to ventilation can result in improved indoor air quality.

Improved comfort. Buildings with tight construction and balanced ventilation systems can have fewer drafts and a constant supply of outdoor air resulting in improved comfort.

Improved health. Stale air can cause health problems. It can be responsible for symptoms such as headaches, drowsiness, and respiratory problems. These symptoms are more common in homes with poor ventilation and moisture control. Continuously providing fresh air can result in the improved health and well being of the occupants.

Lower utility bills. Less energy is consumed to operate ventilation systems than to heat and cool excessive amounts of outdoor air that infiltrates leaky homes. Additional savings are captured when these systems are equipped with either a sensible or total heat exchanger. This can result in lower utility bills, making homes less expensive to operate.

Balanced ventilation systems can be equipped with a heat exchanger that recovers most of the heating and cooling energy from the exhaust air.

 

Mechanical ventilation and natural ventilation have many applications where they are used, but in most modern intelligent design both are used for the best effectiveness and efficiency. 

The acceptable air quality has to be maintained by supplying adequate air of specified quality and quantity in the space. The ventilation of the building can be done by natural ventilation by means of windows and skylights or by mechanical ventilation.

Natural ventilation is the ventilation of a building without the aid of fans or other mechanical systems. Historically all buildings were ventilated naturally with the help of windows and skylights. Natural ventilation use the pressure difference or temperature difference to allow the flow of air through the building. Natural ventilation is not very effective as humidity control is not proper, but when used in conjunction with mechanical systems they can save electricity.

Mechanical ventilation is also called forced or induced ventilation and is done by fans and other mechanical means. This means of ventilation is very effective in controlling the humidity and air quality inside an air conditioned space. As it is a positive means of ventilation it can control the odors, contaminants and humidity as well. There are many examples of mechanical ventilation like our kitchens and bathrooms that have exhaust fans.

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Naturally Ventilated Building and Ducts for Mechanical Ventilation

Natural Ventilation

Mechanical Ventilation

Mechanical Ventilation

Mechanical ventilation is a method of forced or induced ventilation by using mechanical air handling systems, commonly called HVAC systems. Mechanical ventilation is more controllable than natural ventilation.

In Mechanical Ventilation blowers, fans, filters, and ducts are used for transporting and removing air from a space. There are two types of fans used for the transmission of air. When the air enters the impellers axially and is discharged radially from the impeller, it is called a centrifugal or radial flow fan. When the air flows parallel to the axis of impeller, it is called an axial flow fan.

Centrifugal Fan: Centrifugal fans are very popular in the duct air conditioning system. The centrifugal fan has an impeller mounted in a volute casing. The fan impeller of the centrifugal fan can have the following profiles:

Radial or straight blades: It is a simple impeller construction. The blades run straight from a central point. These fans provide very high pressure at high speeds of rotation.

Forward Curved Blades: These blades are shallow in depth. These fans are efficient and have less noise.

Backward curved blades: They have to be operated at higher speeds for same pressure. Due to their higher speeds they can be directly coupled to the motors.

Axial Flow Fan: These fans are never used in duct air conditioning system as they cannot develop high pressures, however they can handle large quantities of air. The axial flow fans are of the following types:

Propeller Fan: A propeller fan consist of a propeller in a mounting ring. They are used when the resistance to air movement is small as in the ventilation of bathrooms, and attic spaces.

Tube Axial Fan: It consists of a propeller fan housed in a simple cylinder. These types of fans can be installed in round ducts. The air flow in the tube is spiral on its way out.

Vane Axial Fan: A vane axial fan has a tube axial fan along with guide vanes to stop the spiral movement of air.

Images

Centrifugal Fan

Air Changes Required

ASHRAE standard 62 states that certain amount of fresh air should always be supplied to all the areas of the building or the air conditioned spaces, which is dependent on the activity being done and the number of people present. For example dancing floors and smoking areas will require more air changes than other areas.

The air changes required by various spaces are as follows: