What does a Building Automation System do?
A Controls systems or Building Automation System (BAS) control building functions and equipment. It holds everything together.
For example, in your building, a wall thermostat connects all the signal wiring for your HVAC equipment together to tell it what to do. You typically tell the thermostat at what temperature you want the cooling to come one, and if the space temperature rises about that number, the cooling starts. This is the same process that takes place with the heat, if the space temperature falls below the number.
Input values are calculated against an active setpoint and turn on an output to make it better.
What can a Building Automation System Control?
The following list displays the items in a commercial building that a Building Automation System can typically control by using set points for adjustments and by monitoring basic inputs.
- Space Temperature
- Humidity
- Fan speed
- Duct pressure
- Water flow
- Digital on/off outputs
- Analog outputs VAV Boxes
- Fan powered boxes
- Lighting controls
- Sprinkler controls
- Alarm notifications
- History and trending lists
- Exhaust fans
- Make-up air fans
- Stairwell pressurization and smoke evac
- Occupied and unoccupied schedules
- Monitor power demand and consumption
- Generator run times
- Water demand and consumption
VAV System Controls
A Variable Air Volume System (VAV System) is a type of HVAC system. Unlike a typical HVAC system which supplies a constant airflow at a variable temperature, VAV systems vary the air flow at a constant temperature.
Advantages of a VAV System include:
- More precise temperature control
- Reduced compressor wear
- Lower energy consumption by system fans
- Less noise
- Additional passive dehumidification
- Relatively inexpensive individual room control
- Reduced operating costs
Types of VAV boxes:
There are three types of VAV boxes: Parallel Fan Powered VAV, Series Fan Powered VAV and Series Box VAV.
Parallel Fan Powered VAV
In these systems, a fan-powered variable air volume box reduces the volume of the primary 55 degree air stream; if the space requires additional heat, the fan in the box is energized. This allows any warm air above the ceiling to be used to heat the space. If this does not adequately heat the area, a heating coil in the box is energized to provide the required heat. This system is designed to power the fan only when heat is required. Running the fan when heat is required keeps the room air exchange rate constant and at a sufficient volume to maintain good air circulation. With the Reheat VAV system, the air exchange rate during the heating mode can be reduced substantially over that achieved during the cooling mode.
Series Fan Powered VAV
The series fan-powered variable air volume box operates much like the parallel box except the fan runs in both the heating and cooling modes. This always provides a constant volume of air, even though the box is varying the volume of the primary 55 degrees supplied by the air handler. Series fan-powered boxes are typically used in low temperature ice storage applications where the air leaving the air handler is maintained at temperatures below the normal 55 degrees. This ensures that the air entering the room is still at 55 degrees even though the primary air stream might be much colder.
Series Box VAV
Modulates air flow from the air handler and sometimes has reheat in the box.
Why VAV boxes?
If you have a 10 story, 500,000 sq ft office building with one air handler per floor, how do you make it work with more that one controls sensor?
Install VAV boxes! VAV boxes can modulate the air flow coming from an air handler and provide a small miniature unit for a single room, a few rooms, or big open spaces.
If you have 5 offices on the perimeter of a building, and a conference room beside the office, what would happen if all those rooms shared the same thermostat or temperature sensor? It would be okay if the duct system and airflow were designed and balanced properly, but when everyone leaves their office for a meeting in the conference room, it’s going to get tough. The thermostat or temperature sensor is not going to pick up in the conference room because it is not in there!
Instead of installing too many units or air handlers in a space to provide better control, VAV boxes can regulate temperature control in a much more affordable and efficient manner.