Building Automation System Overview
If two identical buildings were built in the same area, with the same mechanical equipment and occupancy schedule of the building, would you expect the buildings to use fairly close amounts of energy from year to year? You may be surprised. Mechanical Engineer Neal Ray explains why.
How the mechanical equipment within a building is controlled can drastically affect the overall energy consumption of the building. A building can have the most up-to-date and efficient mechanical equipment installed and without a good control system, the money to install the equipment would be wasted. Building automation systems (BAS) are a very important component in assuring that mechanical equipment installed in a building is operating properly, and in helping identifying which energy saving measures to take.
This blog will cover the basic components of a BAS and how these components control the mechanical equipment. Keep in mind how the information is transported will be different for every system depending upon how the architecture of the system is setup, but overall this is how the information is processed.
Brain, Sensors, Inputs
The BAS is the equivalent to a brain for the mechanical system which provides heating and cooling in a building. The brain receives information from components of the body through the nervous system and makes adjustments as needed to assure proper function of the body. A BAS takes information from the mechanical equipment either through the means of voltage, current, or in older cases compressed air; processes this information; and then makes adjustments as needed to assure proper function of mechanical equipment.
Gathering information and then using this information to communicate functions to the mechanical equipment is the main purpose of a BAS. How this information is gathered is typically done through measuring sensors. Some of the values these sensors can read are temperature, CO2, fan speed, humidity, and motor statuses. The sensor which measure the value and relay it back to the building automation system are called inputs. The inputs can either be analog, which can vary over a wide range of numbers such as temperature and CO2 or they can be binary, either on or off, in the case of a motor status.
The inputs are the method for gathering the information. This information which is gathered is then sent back to the controller. The controller will then take this information and process it and determine an output to send to back to a device such as a damper, valve, or variable frequency drive. From a BAS standpoint, analog and binary inputs and outputs are termed points on the system.
An example of this would be a space which has air coming to it from an air handling unit. A sensor will register the space temperature and send it back to the controller. If the space temperature is 70 ⁰F and the controller has a setpoint of 72 ⁰F programmed into it. The controller will have a sequence written to tell it to open the heat valve in the air handling unit a certain percentage based off the type of control on the heat valve to try and raise the space temperature.
Usability for Optimal Operation
Above is one of the more simple procedures. The BAS will have programs like this written in various controllers in the network to control all mechanical equipment in the building. If a building has many pieces of mechanical equipment, such as boilers, chillers, pumps, air handling units, VAV boxes, and fin tubed radiation, the programming is written for all these pieces of equipment on several controllers. Information is gathered from sensors on all this equipment, relayed back to the controllers and the controllers generate an output based off the input into the controller.
The nicest feature of building automation system for the end user is the ability to see graphics which represent equipment it is controlling. This is done with a communication device. A path is provided between devices, which is communicated to a PC. From the PC, a person can view the equipment the BAS is controlling graphically. From this point, the user can not only observe the current operation of the system, but also trend points on the system to observe how the systems operate over a period of time to help diagnose and identify areas which are not controlling properly and can be modified to save the facility energy.
It takes ingenuity to control mechanical equipment optimally. With knowledge of how mechanical equipment is controlled with a BAS, the process to help identify areas which are not controlling optimally and why they are not becomes easier. The better a person's knowledge of a BAS in a building, the better chances a person has to achieve optimal operation of the mechanical equipment which saves energy.