Quiz 3 Flashcards
Define Condensing Unit
-Outside portion of a split system
-Contains compressor, condensing coils, and condenser fan
-Purpose is to reject the space heat to the outside by condensing the refrigerant vapor from the evaporator (AHU cooling coil) back to a liquid
Define Direct Digital Controls
-DDC is an advanced form of conventional pneumatic or electronic controls. Pneumatic or electric controls may be found in old buildings
-Uses microprocessors and digital data to make decisions
-Receives signals from various inputs (temp, humidity, fan status), makes decisions through programming, and sends signals as output to directly control equipment.
-Examples: Honeywell WiFi stats and Distech
Define Inlet Valves
-Vary the volume of air flowing through an air handlerfan by pre-spinning the air entering the fan
-Changes the angle at which the air contacts the fan blades thus increasing/decreasing volume of air the fan moves.
-Often found in older VAV systems
-Reduction in VOLUME reduces fan motor ENERGY used.
Define Plenum
-Enclosed space within a building used for air flow by the HVAC system
-Typically the space between the ceiling tile and the structural ceiling used fro RA ductwork
-In ducted systems, plenum refers to a sheet metal box at the supply and return ends of the air handler where ductwork is connected
Define Economizer
-Add on feature to an air handler that uses “free cooling” by drawing in cool outside air to satisfy the call for cooling and turning off mechanical cooling
-Systems can chose to economize based on dry bulb only or enthalpy
-If local humidity sensor is present, we will choose to use the dry bulb of the OAT, becuase of the lack of long-term reliability of humidity sensors. (OAT 55º or below in HOU or 60º and below in DFW)
-If EMS can access a reliable humidity sensor from the weather service, we choose to economize based on enthalpy setpoint of 25 BTU/lb.
Define Refrigerant Cycle
-Used in a split system
-Heat is absorbed with air handler evaporator coil and rejecting that heat through the condenser coil outside.
-Evaporator absorbs heat by evaporating liquid refrigerant into vapor
-Condenser rejects heat outside by condensing refrigerant vapor back to a liquid
Define Barometric Damper
-Damper that does not rely on a damper motor to open and close it
-Essentially is either blown open when pressure is greater on one side as in a system with an economizer when outside air being brought in for cooling over-pressurizes the building (relief or exhaust air)
-OR may be sucked open as in a fan powered VAV box when the box supply air damper is in minimm position and the box fan comes on causing the barometric damper to suck inward and allow return air into the box and out into the space for heating
Define Double Duct Unit
-Similar to MZU becuase it serves multiple zones
-Two separate ducts which are run around the building floor above the ceiling tile supplying hot air in one and cold air in the other
-At each zone, a mixing box blends the hot and cold air to satisfy the zone
-Each zone has one thermostat controlling its mixing box
Define Vent Fan
-Used to draw OA through the attic of a building which reduces the temp in the attic to help cool the building
-Also found in mechanical rooms and some gyms where they draw in cooler OA by exhausting room air from one side of the room which causes cooler OA to be drawn through an OA damper on the opposite end of the room
Define Exhaust Fan
-Various forms
-Toilet exhaust fans, kitchens, science classrooms
-Removes air pollutants from the building to improve the indoor environment
Define Package Terminal Air Conditioner (PTAC)
-Type of self contained heating and air conditioning system commonly found in hotels, motels, senior housing facilities, hospitals, condos, apartment buildings, and add-on rooms.
-Designed to be installed through a wall.
-Often electric heat or heat pump
Define Reciprocating Chiller
-Uses reciprocating compresser(s) in refrigeration cycle
-Contain reciprocating pistons to compress refrigerant vapor in order to raise its pressure/temp so it can be condense by either an air cooled condenser or by water from a cooling tower where the space heat is rejected
-Operates similarly to a car engine
Define Scroll Chiller
-Scroll compressor tech
-A fixed and moving scroll that compresses the refrigerant gas as it is moved to the center of the scrolls to compress the refrigerant vapor in order to raise its pressure/temp
-USed in many split systems condensing units and are said to be more durable than older reciprocating tech
Define Screw Chiller
-A screw chiller uses screw compressor tech
-Rotary-screw compressors use two meshing helical screws, known as rotors, to compress the refrigerant vapor in order to raise its pressure/temp so it can then be condensed by either type of cooling
Define Centrifugal Chiller
-Centrifugal compressors to increase speed of the refrigerant gas then convert that speed to pressure energy thus compressing it
Define Input
-Signal that the controller uses to either make decisions or provide feedback.
-Can be analog, meaning numerical value, or digital, meaning binary.
-Examples fan on/off (binary), space temp (analog). and outside air temp (analog).
Define Output
-Command signal from the controller and being sent to the unit to tell it what to do
-Can be analog or digital
- Examples: turn the fan on or off (digital), engage DX cooling (digital), engage CHW valve (analog)
Define Variable
-Process the inputs to help determine the outputs
-Where inputs and outputs are typically wired to and from the devices, variables live in the software of the “brains” of the controller
-Help decide what the output will be based on the inputs it has received
-Examples: set points and setbacks, occupancy, and heat call or cool call.
Define Supervisory Controller
-The central controller for a building
-Provides integrated control, supervision and network management services to all unit controllers.
-Examples: Jace (Tridium) and the MACH2 (RC Studio)
Define JACE
-Java Applet Control Engine
-Supervisory controller made by Tridium
-i3 uses this supervisory controller when installing an EMS at a client site
