Pneumatics Midterm Flashcards
What are the parts of a commercial HVAC system?
Boiler, fan or pump, and heating units, ductwork or piping, and controls
What is Passive Dehumidification?
Dessicants placed in the air ways
What is Baseboard Heat and what is it used for?
Uses electrial resistance elements at the bottom of the outside walls and blows heated air back into the room. Warm rooms, heat envelope through natural convection
What is a VFD and how does it work?
Adjusts frequency to change voltage and current supply, intern adjusting speed of controlled device
What is a Controller?
A device that receives a signal from the sensor, compares it to a setpoint value, and sends an appropriate output signal to a controlled device
What are Differential Pressure Controls?
A specific pressure in the system is maintained based on a difference in pressure between two points in the system
What is a Closed Loop and Open Loop?
Closed Loop: control in which feedback occurs between the controller, sensor, and controlled device. Open Loop: control in which no feedback occurs between the controller, senor, and controlled device
What is a Self-contained Control System?
Control system that does not require external power supply. Powered by fluid-filled element with gas, liquid, or mixture
What is the purpose of a Bleed Port?
Oriface that allows small amount of air to be expelled from controller, changes via bimetallic element which covers or uncovers the port
How does a System Powered Control System work?
No electricity, air controlled system, controller operated by static pressure only from fan and ductwork
What is Spring Range?
Difference in pressure at which an actuator shaft moves and stops.
How do 2-way valves pertain to steam valves?
Steam valves are always two-way valves bexause steam does not require a return to the steam header or the boiler (goes to the DA tank)
How do Outside Air Dampers work on AHUs?
Adjust metal blade or set of blades to control air flow in response to controller signal
How do Winter/Summer T-stats work?
Pilot Bleed T-stat, changes setpoint and action between modes. 2 bimetallics, one DA, one RA.
How do Dual Duct AHUs work?
Has hot and cold air ducts connected to mixing boxes at each building space.
How do Controled Devices work?
Regulate flow of fluid in system in response to signal from controllers. Are dampers, valves, compressors, etc.
How do Open Systems work?
No feedback from controlled devices
How do Radiant Heat Panels work?
Ceiling panels with embedded electrical resistance elements. Heat is radiated to a local area, usu. 150 - 170 degrees, 120 or 240VAC
What is the common percentage for OA?
20 percent
What is the temperature for economizers?
Dry Bulb: OAT must be below 65 degrees to work. Enthalpy: OAT below 65, and humidity (mixed-air) below 60 but above 30 percent
What are the types of blades and how do they work?
Propeller: most common, large quantities of air, low static, usu. 24in. To 100 ft. Variable Pitch: 48 in. more common, propeller attached to moveable hub changes pitch. Centrifugal: similar to AHU fans, fan in housing, air enters from side of fan and expelled at outer edge of housing
What are the types of dampers?
Parallel Blade: blades are parallel. Opposed Blade: blades are adjacent and move in opposite directions. Round Blade: used in round ductwork, single damper
What are VAV systems and how do they work?
Use VFD to speed up and slow down fan speed to control static. Often with variable damper.
How do controllers work and operate?
Receive signla, compares to setpoint value, sends output to controlled device. Accuracy adjustments are Proportional Band, Gain, Throttling Range
