Building automation
Building automation is a programmed, computerized, intelligent
network of electronic devices that monitor and control the mechanical and lighting systems in a building. The intent is to create an intelligent building and reduce energy and maintenance costs.
Infrastructure
Controller
The controller is normally one or more application specific controllers, often with less complex programming. These controllers come in a wide range of sizes and capabilities to control devices that are common in buildings. Usually the primary and secondary buses are chosen based on what the controllers provide.
Most PLCs provide general purpose feedback loops, as well as digital
circuits.
Occupancy sensorsOccupancy is usually based on time of day schedules. Override is possible through different means. Some buildings can sense occupancy in their internal spaces by an override switch or sensor.
Lighting Lighting can be turned on and off with a building automation system based on time of day, or the occupancy sensors and timers. One typical example is to turn the lights in a space on for a half hour since the last motion was sensed. A photocell placed outside a building can sense darkness, and the time of day, and modulate lights in outer offices and the parking lot.
Air handlersMost air handlers mix return and outside air so less temperature change is needed. This can save money by using less chilled or heated water (not all AHUs use chilled/hot water circuits). Some external air is needed to keep the building's air healthy.
Analog or digital temperature sensors may be placed in the space or room, the return and supply air ducts, and sometimes the external air. Actuators are placed on the hot and chilled water valves, the outside air and return
air dampers. The supply fan (and return if applicable) is started and stopped based on either time of day, temperatures, building pressures or a combination.
Constant Volume Air-Handling UnitsThe less efficient type of air-handler is a "Constant Volume Air Handling Unit," or CAV. The fans in CAVs do not have variable-speed controls. Instead, CAVs open and close dampers and water-supply valves to maintain temperatures in the building's spaces. They heat or cool the spaces by opening or closing chilled or hot water valves that feed their internal heat exchangers. Generally one CAV serves several spaces, but large buildings may have many CAVs.
Variable Volume Air-Handling UnitsA more efficient unit is a "Variable air volume (VAV) Air-Handling Unit," or VAV. VAVs supply pressurized air to VAV boxes, usually one box per room or area. A VAV air handler can change the pressure to the VAV boxes by changing the speed of a fan or blower with a variable frequency drive or (less efficiently) by moving inlet guide vanes to a fixed-speed fan. The amount of air is determined by the needs of the spaces served by the VAV boxes.
Each VAV box supply air to a small space, like an office. Each box has a damper that is opened or closed based on how much heating or cooling is required in its space. The more boxes are open, the more air is required, and a greater amount of air is supplied by the VAV air-handling unit.
Some VAV boxes also have hot water valves and an internal heat exchanger. The valves for hot and cold water are opened or closed based on the heat demand for the spaces it is supplying. These heated VAV boxes are sometimes used on the perimeter only and the interior zones are cooling only.
A minimum and maximum CFM must be set on VAV boxes to assure adaquate ventilation and proper air balance.
VAV Hybrid Systems
Another variation is a hybrid between VAV and CAV systems. In this system, the interior zones operate as in a VAV system. The outer zones differ in that the heating is supplied by a heating fan in a central location usually with a heating coil fed by the building boiler. The heated air is ducted to the exterior dual duct mixing boxes and dampers controlled by the zone thermostat calling for either cooled or heated air as needed.
Central plant
A central plant is needed to supply the air-handling units with water. It may supply a chilled water system, hot water system and a condenser water system, as well as
transformers and auxiliary power unit for emergency power. If well managed, these can often help each other. For example, some plants generate electric power at periods with peak demand, using a gas turbine, and then use the turbine's hot exhaust to heat water or power an absorptive chiller.
Chilled water systemChilled water is often used to cool a building's air and equipment. The chilled water system will have chiller(s) and pumps. Analog temperature sensors measure the chilled water supply and return lines. The chiller(s) are sequenced on and off to chill the chilled water supply.
Condenser water systemCooling tower(s) and pumps are used to supply cool condenser water to the chillers. The condenser water supply to the chillers has to be constant so, speed drives are commonly used on the cooling tower fans to control temperature. Proper cooling tower temperature assures the proper refrigerant head pressure in the chiller. The cooling tower set point used depends upon the refrigerant being used. Analog temperature sensors measure the condenser water supply and return lines.
Hot water system
The hot water system supplies heat to the building's air-handling units or VAV boxes. The hot water system will have a boiler(s) and pumps. Analog temperature sensors are placed in the hot water supply and return lines. Some type of mixing valve is usually used to control the heating water loop temperature. The boiler(s) and pumps are sequenced on and off to maintain supply.
Alarms and security
Many building automation systems have alarm capabilities. If an alarm is detected, it can be programmed to notify someone. Notification can be through a computer, pager, cellular phone, or audible alarm.
Common temperature alarms are Space, Supply Air, Chilled Water Supply and Hot Water Supply.
Differential pressure switches can be placed on the filter to determine if it is dirty.
Status alarms are common. If a mechanical device like a pump is requested to start, and the status input indicates it is off. This can indicate a mechanical failure.
Some valve actuators have end
switches to indicate if the valve has opened or not.
Carbon monoxide and carbon dioxide sensors can be used to alarm if levels are too high.
Refrigerant sensors can be used to indicate a possible refrigerant leak.
Amperage sensors can be used to detect low amperage conditions caused by slipping fan belts, or clogging strainers at pumps.
At sites with several buildings, momentary power failures can cause hundreds or thousands of alarms from equipment that has shut down. Some sites are programmed so that critical alarms are automatically re-sent at varying intervals. For example, a repeating critical alarm (of a uninterruptible power supply in 'by pass') might resound at 10 minutes, 30 minutes, and every 2 to 4 hours there after until the alarms are resolved.
Security systems can be interlocked to a building automation system. If occupancy sensors are present, they can also be used as burglar alarms.
Fire and smoke alarm systems can be hard-wired to override building automation. For example: if the smoke alarm is activated, all the outside air dampers close to prevent air coming into the building, and an exhaust system can isolate the alarmed area and activate an exhaust fan to move smoke out of the area. Life safety applications are normally hard-wired to a mechanical device to override building automation control.
Activities
I) Match each term with its correct definition
A
1 Building Automation
2 Controller
3 Occupancy sensors
4 Lighting
5 Air handlers
6 Central plant
7 Chilled water system
B
____ is often used to cool a building's air
and equipment.
____ mix return and outside air so less temperature change is needed.
____ is a programmed, computerized, intelligent network of electronic devices in a building.
____ can sense occupancy.
____ is needed to supply the air handling units with water.
____ can be turned on and off with a building automation system based on time of day, or the occupancy sensors and timers.
____ is normally one or more application
specific controllers, often with less complex programming.
II) Find any kind of information about the underlined words that appear in the text above. Then, create a sentence with each of them.
1 Network
2 Circuits
3 Air dumpers
4 Switches
5 Transformers
III) Select the correct idiom for each definition
1-. You are in a difficult situation with very little room for manoeuvre.
A) beneath the wall
B) behind the wall
C) back to the wall
D) in front of the wall
2-. If something happens away from the public eye.
A) behind closed doors
B) beyond closed doors
C) beside closed doors
D) behind closed windows
3-. Someone is very excited about something.
A) jump off the walls
B) bounce the walls
C) bounce off the doors
D) bounce off the walls
4-. Plans that are impractical and will never work out.
A) castles in the air
B) houses in the air
C) castles in the earth
D) castles in the beach
5-. Something that is off the wall is unconventional.
A) out the wall
B) of the wall
C) offer the wall
D) off the wall
6-. If someone hits the ceiling, they lose their temper and become very angry.
A) hit the roof
B) heat the ceiling
C) hit the seal
D) hit the ceiling
IV) Answer true or false.
___ Chilled water is often used to heat a building’s air and equipment.
___ Hot water pumps are used to supply cool condenser water to the chillers.
___ Analog temperature sensors measure the chilled water supply and return lines.
___ Speed drives are commonly used on the cooling tower fans to control temperature.
___ The hot water system will have a boiler(s) and pumps.
___ Analog temperature sensors are placed in the hot water supply and return lines.
___ Lighting can be turn on and off with a building automation system based on temperature.
V) Complete the following text with the correct idiom from exercise II.
Last saturday night I was thinking about a new invention to conquer the world and become famous and finally I got it. I was _________________________________ beacuse of thar new idea. I immediately called my husband to tell him about this revolutionary invention. Regretfully, when I told him, he said it was completely __________________ and he suggested me to stop building __________________. When I heard that I really ____________________ and I told him he was an idiot. After a while I felt very sorry about it and I decided to prepare a delicious dinner to reconcile whit him. The reconciliation was wonderful but I can not tell you more details since it happened _____________________________.
VI) Complete the following sentences with the given words.
Central plant Air handlers Occupancy Water valves Hybrid Lighting
Some buildings can sence _________________________ in their internal spaces by an overrride switch or sensor.
_____________________ can be turned on and off with a building automation system based on time of day.
Most _____________________ mix return and outside air so less temperature change is needed.
They heat or cool the spaces by opening or closing chilled or hot __________________ that feed their internal heat exchangers.
Another variation is a ___________________ between VAV and CAV systems.
A ________________ is needed to supply the air handling units with water.
VII) Answer the following questions:
What is building automation?
What are occupancy sensors used for?
What’s the function of Air handlers?
What’s the difference between CAVs and VAVs?
What’s the function of the central plant?
By Lissette Reyes and Germán Villalón
