Building Automation Systems Flashcards
__ __ control system utilizes an actuating device to control the process directly without asking for feedback
open loop
__ __ control system utilizes feedback to compare the measured variable to the desired result
Closed Loop
Refers to data received by the controller
input
refers to data received by the controller
output
a continuous signal that varies through a range of values. proportional
analog
a time-separated signal that carries information in binary form. only two state of positions; on or off. yes or no. open of closed.
digital
value of the controlled variable that is to be maintained
set point
actual measured value of the controlled variable
measured value
the difference between the set point and the actual value of the controlled variable
error
two position controller, it is the difference between the settting at which the controller operates at one position and the setting at which it changes to the other position.
differential
a type of controller for which the output can vary infinitely over the range of the controller
modulating controller
a controller for which an increase in the level of the sensor signal vs a controller for which an increase in the level of the sensor signal results in a decrease in the level of the controller output.
direct acting controller vs reverse acting controller
minimize pressure drop across valve
control valve sizing and pressure drop
excessive pressure drop could be
poor selection (high Cv factor) Valve and/or actuator impaired
the number of US gallons of water per minute at 60 degrees that will flow through a valve with a pressure drop of one psi
Flow (GPM) = Cv * square root of change in pressure (PSI)
flow coefficient
Proportional control is __ and the corrective action often __ the target
After arriving at the set point, there will be no controller action and you can get __ target.
proportional to size of error
reactive, overshoots, off
Proportional, integral, and derivative are __ __ systems that use a feedback signal to control a certain actual
closed loop
Integral Control increases corrective action in relation not only to the error but also to the….
Integral control corrective action if results aren’t achieved as time passes
time it has persisted
Proportional + Integral control can __ the time to get to steady state
reduce
With derivative control, if sudden changes occur, the response will be related to the __ __ __
derivative control is useful when trying to stay __ __ in a precisely controlled system
rate of change
on target
__ control systems are operated by clean, dry, and oil free compressed air flow at low pressure.
includes: receiver controller, actuator and valve, damper actuator
safe and easy to operate, reliable in harsh environments
not very precise, sensitive to vibrations
pneumatic
__ control is a process that transforms one or more input signals into different output signals so as to give the desired system response
instantaneous, very little affected by normal temps
very accurate
different manufactures used different signals so inoperable
Electrical
__ __ controller received input from the sensor and then sens output signals in ‘packets’ using digital communication
Different _ _ _ can be networked together using a data bus
Direct Digital Control
ASHRAE 135
BACnet - Building Automation and Control Networking protocol
A __ typically runs HVAC systems
A __ automates the functions of a __ system and enables savings via lighting, metering, access control, and other systems
A __ system is a subset of the __
the __ will allow you to visualize and manage your building systems in such a way that you can create energy savings
control system
building automation system
control system
What is an advantage of a hot water reset?
Maintain lowest hot water supply temp that will meet needs
reduces load on the boiler as well as thermal lasses throughout the distribution
What is an advantage of a chilled water reset
Raises the temperature set point of water leaving the chiller
Most chilled water setting are designed with the heaviest anticipated cooling load
significant cost savings can result from resetting chilled water temps. in anticipation of cooling load
Before a static pressure reset, all of the VAV boxes partially open creating static pressure in the main duct, typically around 2 inches. This results in ___ fan horsepower maintaining this __ than necessary set point.
After the static pressure reset, the DDC system monitors the VAV static pressure and lowest the pressure until only __ damper is completely ___, which is a better means of determining minimum flow requirements.
wasted, higher
one, open
An economizer __ cooling energy by optimizing mixed air temperature
as the outside air allows, the outdoor air damper open __
reduces, more
A room temperature sensor supplying information/feedback to an HVAC system is an example of: __ input, __ outpout
Analog Input, Closed Loop output
An actuator mounted on a variable air volume box would be a decide that would receive an __ output signal
Output
Which approach is most likely to provide the greatest improvement in boiler combustion efficiency (assuming no change in fuel)
- Increase stack temp and increase combustion air temp
- Fix all steam leaks
- Reduce stack temp and decrease combustion air temp
- Increase boiler excess oxygen and increase stack temp
- Reduce boiler excess air and reduce stack temp.
Reducing excess air in boiler __ the oxygen in the stack and for better combustion efficiency
reduces
Reducing the stack temperature by installing an economizer or combustion air pre-heater ___ the stack temperature rise and further improves efficiency
reduces
