The Building Automation System

A building is a dynamic entity; it has to provide and protect the internal environment and the whole range of support activities in a constantly changing scene. The weather and outside environment are constantly changing; the occupations and functions within a building are constantly changing along with management, security and communication systems. In this situation we require a building that can not only respond to these conditions and produce predetermined conditions, but a building that can adjust the control parameters so that it can be optimised to meet other needs. The essence of an automated building is that the systems supporting the functions of the building can change automatically to changing needs and conditions, to maximise the convenience of the users and minimise the costs associated with its operation and use. Particularly significant areas where such control is necessary are energy management, security and safety.

Building Automation Systems (BAS) are generally used for the control and optimisation of building services, which include air-conditioning, lighting, fire safety and security services, etc. There are benefits from any BAS in the reduction of operation and maintenance costs. These reductions are mainly in the areas of reduced energy consumption and reduction of personnel required for monitoring duties. These cot reductions can provide sufficient financial justification for the investment in BAS. In addition, energy savings being desirable in themselves also make the building environment friendly.

The building automation system is analogous to the nervous system in a body, and the computer can be considered as the nerve-centre or brain of the system. BAS has a number of basic functions including;

Sensing elements are used for a wide variety of functions, such as heating and cooling, monitoring of access, detection of fires, the opening of smoke dampers, starting and stopping of fans, control of lighting which can then take place according to the sensed requirements, after the information has been fed to the Automation system.
The range of applications of the BAS within a building can be divided into a number of major categories:

Environmental control

Environmental systems within a building control several important functions; heating, cooling, fresh air, air movement and cleanliness, lighting and acoustics. The devices used to control these functions are often independently designed, but integrated control over the devices is exercised by the BAS. The BAS can also provide linkage to other functions such as energy management and smoke control.

Air conditioning
The air conditioning system has to respond to a number of variables like the changing outside environment, varying degrees of occupancy in different areas, varying uses and contaminants, varying heat gains and requirements for smoke control, fire safety and escape. The powerful and flexible control functions of the BAS can enable the air conditioning system to respond to a greater range of operational needs than would otherwise be possible. For the efficient working of the BAS, the building should be divided into zones depending on occupancy load, hours of occupation, etc. so that the system can set different parameters for different zones making optimum use of the available energy and reducing wastage. The BAS can accrue energy savings through varying the start time for heating and cooling plant, so that normal environmental space temperature is reached precisely at the time of occupation. It can also vary the amount of cooling required after taking into account the internal and external dry-bulb temperature, humidity, occupancy levels in each zone thus reducing fuel wastage.

Lighting has conventionally been provided on the basis of occupancy, with the tendency to provide lighting wherever people are present. This leads to wastage of power as lighting is wasted in areas where daylight is available from windows. The provision of individual control of lighting can lead to substantial savings. In commercial buildings bulk off-switching can be employed along with the facility for the individual to put it back on if necessary. Connecting the lighting to a BAS along with photosensors, will take into account factors like lighting level, time of day, occupancy, etc. the lighting can therefore be turned off according to a series of different events during the work cycle rather than just the time of day. Dimming of lights in response to the level of daylighting in the zones is also possible when coupled with photosensors. Control of reflective blinds and sun tracking optical lighting increases the level of daylighting in the interior resulting in reducing the need for artificial lighting. Computer control of lighting will also ensure that artificial lighting is on for a minimum amount of time. Centralised control thus allows the refinement of lighting cycles towards the optimum leading to greater energy efficiency and more comfortable conditions within the building.

Energy management systems
Energy is one of the most precious commodities in the world today. The scarcity and high cost of energy as well as its effect on the environment have combined to make energy control and saving a major concern. Controlling energy saves money and precious natural resources while providing the users a high level of comfort and better working conditions, which can increase productivity and provide better quality of life.

The implementation of energy control however, is difficult due to the great number of variables that have to be individually controlled. Therefore computerised control of these many variables is a necessity. The BAS can therefore save energy by collecting data from the different sensors, processing it and calculating the exact energy requirement for certain building services in a given zone and thus minimising energy use.

Certain buildings may, however, require the development of specialised automation, which is demanding in terms of time and money. The development of standard Building Automation software will reduce costs. Also the saving in energy use and reduction in fuel costs offset the financial investment in BAS quite quickly. Computerised automation of energy control-temperatures, humidity, air flows, etc. means that even one man can monitor all the factors in one control centre, reducing staff required for monitoring and maintenance.

The Control Centre
The Control Centre is where all the information from the different sensors is collected and the BAS is commanded as to the new parameters to be set and actions to be taken for optimisation of services. The control centre should be quiet, clean and comfortable, because engineers are likely to spend long hours using the systems. Very large BAS could require 24-hour attendance in the control centre, in which case consideration must be given to providing refreshment and toilet facilities locally. Variable lighting facilities are required to create comfortable conditions for different levels of activity, such as being on watch, reading computer screens, repair and maintenance.