Carrier 50HCQ04---12 - Manual (Page 20)

20
Optimal Start
The RTU--OPEN may utilize Optimal Start, which adjusts
the effective setpoints to achieve the occupied setpoints
by the time scheduled occupancy begins. The Optimal
Start recovery period may begin as early as 4 hours prior
to occupancy. The algorithm works by moving the
unoccupied setpoints toward the occupied setpoints. The
rate at which the setpoints move is based on the outside
air temperature, design temperatures, and capacities. The
following conditions must be true for unoccupied free
cooling to operate:
S Under SETPOINT, Optimal Start Value must be set
greater than zero and less than or equal to four (0
disables Optimal Start.)
S The system is unoccupied
S The RTU--OPEN has a valid outside air temperature
S The RTU--OPEN is running occupancy based on a
schedule, were next time occupied is known.
Fire Shutdown
Fire Shutdown may be configured on Binary Input 5. A
typical application involves a smoke detector or fire
shutdown contact, which, when active, immediately shuts
down equipment operation.
Compressor Safety
Compressor Safety may be configured on Binary Input 3.
A compressor safety tripped indicator circuit is available
on most Carrier rooftop equipment. A Compressor Safety
Alarm indicates that the equipment requires attention.
Cooling, heating, and supply fan outputs are not
interrupted except where the RTU--OPEN is configured
for Heat Pump operation. When configured for Heat
Pump, and in the heating mode, a compressor safety fault
will cause the available stages of electric heating to be
enabled in place of mechanical heating. Normal operation
resumes when the compressor safety circuit is
de--energized.
Fan Status
Fan Status may be configured on any unused binary input
channel. A typical application would be an airflow switch,
current sensing relay, or other device that provides a
supply fan running verification. Enabling this function
displays the supply fan’s status on the equipment graphic.
If the controller loses fan status during operation, heating
and cooling are disabled, the economizer damper (if
available) is closed, and an alarm for loss of status is
indicated. If the fan status is on when the controller is
commanding the fan off, the unit remains in the off state.
An alarm is generated indicating that the fan is running
when it should be off.
Filter Status
Filter status may be configured on any unused binary
input channel. A typical application is a differential
pressure switch that senses the pressure drop across a filter
bank. When the pressure across the filter bank exceeds the
setpoint of the differential pressure switch, the Filter
status is displayed as Dirty on the controller graphic. An
alarm indicates a dirty filter.
Door Switch
A Door Contact may be configured on any unused binary
input. A typical application is an occupancy sensor
mounted within the space served by a single zone rooftop.
Door Contact disables mechanical cooling and electric or
gas heating, when active. Economizer cooling, if
available, continues to operate.
Linkage
The RTU--OPEN may serve as an air source to an OPEN
Variable Volume Terminal (VVT) system. When the
RTU--OPEN is part of a VVT system and the controllers
are wired together to form a network, the controllers may
use a method of communication known as Linkaget.
Linkage is a method by which an air source and its
subordinate zone terminals exchange data to form a
coordinated HVAC system. The system’s air source
controller, zone controllers, and bypass controller are
linked so that their data exchange can be managed by one
zone controller configured as the VVT Master. The VVT
Master gathers the following information from the slave
zone controllers:
S occupancy status
S setpoints
S zone temperature
S relative humidity
S CO
2
level
S damper position
S optimal start data
The VVT Master performs mathematical calculations and
algorithms on the data and then sends the composite
information to the air source. The VVT Master receives
information from the air source such as mode, supply air
temperature, and outside air temperature, and passes that
information to all linked controllers.
Linkage Air Source Modes
In a linked system, the air source determines its operating
mode and qualifies that mode based on its own Supply Air
Temperature (SAT). The following modes can be sent by
the air source depending on its configuration:
S Off – Air source fan is off
S Fan Only – Air source fan is on and providing
ventilation (neutral SAT) without heating or cooling
S Economizer Cooling – Air source fan is on and
providing cooling, using economizer only
S Cooling – Air source fan is on and cooling is provided
by economizer and mechanical cooling
S Heating – Air source fan is on and heating is provided
(gas or electric)
S Dehumidification – Air source fan is on and
Humidi--MiZer] is active
S Test – The RTU Open Service Test mode is active
S Shutdown – Air source fan is off due to Safety Chain,
Fire Shutdown, or invalid SAT sensor
S Unocc Free Cooling – Air source fan is on, with the
economizer providing cooling while unoccupied