A Building Automation System (BAS) is a computerized, intelligent network of electronic devices that monitor and control the mechanical and lighting systems in a building. This system keeps the building climate within a specified range, provides lighting based on an occupancy schedule and provides email and/or text notifications. What’s more, the system could be programmed to keep record of all those notifications. The BAS reduces building energy and maintenance costs. A building controlled by this type of system is called “Intelligent Building”.

Inputs and Outputs:

Inputs and outputs are either analog or digital.

Analog inputs are used to read variable measurement such as temperature, humidity and pressure sensor which could be thermistor, 4-20 mA, 0-10 volt, platinum resistance thermometer, or wireless sensors.

Digital inputs indicate if a device is either on or off. An example of a digital input would be a 24 VDC/AC signal, an air flow switch, or a volt-free relay contact.

Analog outputs control speed or position o a device, such as a variable frequency drive, an I-P (current to pneumatics), a valve or damper actuator.

Digital outputs are used to open or close relays and switches. An example would be to turn on the parking lot lights when a photocell indicates it is dark outside.

Building Automation components:

Controllers

Controllers are small, purpose-built computer with input and output capabilities. These controllers come in different range of sizes and capabilities to control devices normally found in buildings.

Inputs, allow controllers to read signals such as temperature, humidity, pressure, current and many more. In the other hand outputs allow the controller to send commands and control signal on other devices. Both, inputs and outputs can be either analog or digital.

There are 3 different categories of controllers: PLC’s, System/Network Controllers and Terminal Unit controllers. However additional devices can also exist in order to integrate more systems.

PLC’s provide more efficient solutions for building automation; however a unit cost 2 to 3 times more than a System/Network controller for building automation system applications. Terminal Units Controllers are usually the least expensive yet the least powerful. PLC’s may be used to automate high-end applications as clean rooms or hospitals where cost of the controllers is a lesser concern.

Operating modes:

Operating modes are the different configurations that the system applied. These modes are based on external facts, such as time, occupancy or any other condition. Some examples of these modes are:

Occupancy is one for many operating modes for a building automation system. It is usually based on time of day schedules.  In this mode the system aims to provide an adequate climate and lighting. Temperature sensors and thermostats provide the feed back to the system so it can control sending heat or cooling as required for the different zones.

Morning Warm Up: it occurs prior to occupancy. During the Morning Warm Up the system tries to reach all the set points just in time for the Occupancy mode. They can be many others modes depending on the need of each system.

Lighting

Lighting can be turned on and off with a building automation system based on time, occupancy and different sensors. A typical example of lighting automation is to turn on the lights of a room after certain time since the last motion was sense. Another typical example is the use of photocells to control external lights.

Air Handlers

Some air handlers mix return and outside air so less temperature change is needed. Thus more money can be save by using less chilled or heated water, the external air is needed to keep the building’s air healthy.

Temperature sensors are placed in the room, the return and the supply air ducts to sense all temperatures and the supply fan is started and stopped based on either time of day, temperatures, building pressures or a combination.

They different types of air handlers:

Constant volume air-handling units

The constant volume air handling unit (CAV) is a type of air handler where the fan does not have variable-speed controls.