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48 VAV-PRC003-EN
Glossary
Priority shutdown – An immediate
shutdown of the fan and heating or
cooling stages in a VariTrac changeover
bypass or Delivered VAV system
caused by either the loss of critical
system information or an external
priority shutdown input
Pulse-width modulating reheat –
Reheat that operates duct mounted
electric coils on a 0-100% duty cycle in
response to increased space heating
demand.
Reheat device – A source of heat
located downstream from a control
device such as a VAV box to add heat to
air entering a space to provide
occupant comfort
ReliaTel (RTRM) – The latest
generation Trane factory mounted
unitary controller.
Return air (RA) – Air returned to the
air handler from the conditioned space,
to be reconditioned.
Setpoint – The desired room
temperature to be achieved and
maintained by an HVAC system.
Setpoint limit – An electronic or
manual constraint imposed on a
setpoint to prevent misadjustment
SPDT – A relay with of one set of
normally-open, normally-closed
contacts
Staged electric reheat – Reheat that
operates one or more duct mounted
electric coils in a series in response to
increased space heating demand.
Staged (or perimeter) hot water
reheat – Reheat that operates duct-
mounted hot water or space-mounted
electric or hot water reheat coils in
response to increased space heating
demand
Static pressure – The difference
between the air pressure on the inside
of the duct and outside of the duct.
Static pressure is an indicator of how
much pressure the fans are creating
and how effective they will be at
distributing the supply air through the
ducts.
Supply air (SA) – air which blows out
of the air handler into the ducts. See
also “Discharge air (DA)”
Terminal unit – HVAC equipment that
provides comfort directly to a space.
Thermal requirements – The heating
or cooling load requirements for a
specific area or space in a building.
Care must be taken to not control areas
with different thermal requirements
from one air handling system
Touch-screen operator display –
The LCD panel mounted onto a VariTrac
CCP to allow direct user interface and
time of day programming for the
system
Unit control module UCM – A Trane
microelectronic circuit board that
controls individual HVAC equipment.
May link to an Integrated Comfort
System
Unitary – one or more factory-made
assemblies which normally include an
evaporator or cooling coil, an air
moving device, and a compressor and
condenser combination
Variable air volume (VAV) – an air
handling system that varies the volume
(amount) of constant temperature air to
a space to control comfort
VariTrac – The Trane changeover
bypass VAV system
VariTrane – The Trane pressure
independent VAV box
VAV box – The damper or air valve
(plus associated controller) that
controls the zone air volume in a VAV
system. Also see “Variable air volume”
Ventilation air – The outdoor air
drawn into the HVAC unit to provide
fresh air to the space. Also see
“Outdoor air (OA)”
Voting – See “Polling”
Zone sensor – The device that
measures a variable (usually
temperature) in a space and sends it to
a controller. Commonly referred to as a
thermostat.