6
BAS-PRC006-EN
The Tracer ZN521 zone controller
provides digital control of fan coils, unit
ventilators, and blower coils. The Tracer
ZN521 improves comfort control and
provides stand-alone or networked
building automation.
Inputs and outputs
Tracer ZN521 inputs and outputs
include:
•
Analog inputs
: zone temperature,
space setpoint, fan speed, entering
water temperature, discharge air tem-
perature, outside air temperature,
zone relative humidity
•
Binary inputs
: occupancy, low coil
temperature detection, fan status,
condensate overflow detection
•
Outputs
: Fan high, fan medium, fan
low, exhaust fan on/of, cooling valve,
heating valve, face and bypass
damper, economizer damper, electric
heat (two stages)
•
Generic points
for use with a Tracer
Summit building automation system:
binary input (shared with occupancy),
binary output (shared with baseboard
heat), two analog inputs (one shared
with humidity sensor and often used
with the optional carbon dioxide
sensor, and the second shared with
outdoor air temperature)
The generic inputs pass information to
the building automation system. They do
not affect the operation of the unit. The
generic binary output is controlled by
the building automation system and its
state is not changed by unit operation,
even under a diagnostic shutdown.
Features
Easy installation
The controller can be installed in existing
Trane and competitive HVAC equipment
without major wiring changes, and
clearly labeled screw terminals ensure
that wires are connected quickly and
accurately. A compact enclosure design
simplifies installation in minimal space.
Modulating control
The Tracer ZN521 provides exceptional
comfort control through hydronic valve
and damper tri-state modulation and a
proportional-integral control algorithm.
Cascade control
Cascade control differs from zone
temperature control in that the unit
resets the discharge air temperature to
control the zone. Cascade control
manages zone temperature more
effectively than zone temperature
control, in which the discharge air
temperature can exceed comfort levels.
Entering water temperature sampling
Traditional equipment using a two-way
control valve might not sense the
correct entering water temperature
during long periods when the control
valve is closed. The Tracer ZN521 solves
this problem by opening the valve for
three minutes to allow the water
temperature to stabilize before the
temperature is taken. This feature allows
the use of two-way control valves to
provide accurate two-pipe system
changeover for 1heat/1 cool applications.
Automatic heat/cool mode
determination
The Tracer ZN521 automatically
determines whether heating or cooling
is needed to maintain comfort levels,
without the need to manually adjust unit
controls. The controller measures the
zone temperature and setpoint
temperature, then uses a proportional/
integral algorithm to maintain zone
temperature at the setpoint.
Occupied and unoccupied operation
The occupancy input works with a
motion (occupancy) sensor or time
clock. A communicated value from a
building automation system through the
LonTalk communication link can also be
used. The input allows the controllers to
use unoccupied (setback) temperature
setpoints.
Random start
This feature randomly staggers multiple-
unit start-up to reduce electrical demand
spikes.
Warm-up and cool-down
This feature is available with the
installation of an outside air damper. If
the room temperature drifts too far from
the setpoint, the controller temporarily
closes the damper to bring the
temperature to the desired setpoint as
quickly as possible.
Manual output test
Pressing the test button on the
controller exercises all binary outputs in
sequence. This feature is an invaluable
troubleshooting tool.
Peer-to-peer communication
Multiple controllers can share data if
they are bound together. Shared data
can include setpoint, zone temperature,
mode, and fan status. Applications
having more than one unit serving a
single large space can benefit from this
feature, which prevents multiple units
from simultaneously heating and
cooling.
Interoperability
The Tracer ZN521 conforms to the
LonMark
®
Space Comfort Controller
(SCC) profile and communicates via the
LonTalk protocol. This allows it to work
with other control systems that support
LonTalk and the SCC profile.
Equipment protection
The Tracer ZN521 includes inputs that
allow for the following equipment
protection:
• A condensate overflow switch to pre-
vent water damage to the building
• Low-temperature detection to help
prevent coil freeze-up
• Discharge air temperature limiting to
help prevent the coil from freezing
Automatic fan speed reset
Units set to
AUTO
operate at the default
fan speeds (cooling and heating may
have different default speeds). If the
default fan speed is high, medium, or
low, the unit operates accordingly.
If the default fan speed is set to
AUTO
,
the fan operates at low speed most of
the time. If the temperature exceeds the
setpoint by more than 2°F (1°C), the
controller changes the fan speed to
medium or high. This allows the unit to
operate at low speed whenever
possible.
Tracer ZN521 zone controller
