Trane Tracer ZN524, Installation Owner Diagnostics

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28 CNT-SVX11A-EN
Unit Operation
Electric Heat Operation
The Tracer ZN524 supports 1-stage elec-
tric heat in one of three ways:
Supplemental, Boilerless and Main
heat.
Supplemental
When applied, the electric heat is
cycled on as the last stage of heating.
Compressor 1 and 2 (where applicable)
will be energized and the electric heat
will operate concurrently with the com-
pressors as needed to maintain space
temperature.
Boilerless
When applied, the electric heat will be
enabled based on EWT. The compres-
sor(s) and electric heat is not allowed to
operate at the same time. Boilerless
electric heat is controlled by the EWT
and compressor heat disable setpoint.
If the unit is in the heating mode and
the EWT falls below the compressor
heat disable setpoint, then the com-
pressor will be disabled for heating and
the electric heat will be cycled to main-
tain temperature.
Boilerless control will be disabled if the
EWT rises 5 F above the compressor
heat disable setpoint. The EWT value
can be either local or communicated. In
applications where the local water sen-
sor is used, the unit may utilize the
Entering Water Temperature Sampling
function to verify water temperature.
Main Heat
The electric heat will be utilized as the
only form of heat for the unit. The com-
pressor and electric heat will not oper-
ate at the same time. When in the heat-
ing mode the electric heat cycle to
maintain space temperature.
Compressor (DX) Cooling
The ZN524 controller supports two
stages of DX cooling. The control is pro-
portional and based on an error rate of
3 F for single compressor operation
and 5 F for 2-compressor units. Zone
temperature is compared against active
setpoints for compressor operation:
O
FF
, pulse width modulation or O
N
.
Note: When the control is in the
dehumidification mode only O
FF
and O
N
are valid compressor
states.
At start-up or during mode transition, if
both compressors are requested to run,
compressor 1 will be energized first.
Compressor 2 waits until the next con-
trol cycle (10 seconds) to energize.
Water Isolation Valves
The ZN524 supports the operation of
water isolation valves for varialble
speed pumping systems. Up to 2 isola-
tion valves are supported, one for each
compressor circuit. The valves are
spring return and normally closed. The
ZN524 operates as if isolation vlalves
are present. The presence or absence of
isolation valves is not a configuration
factor.
Under normal operation, the ZN524
opens the isolation valve(s) under the
following conditions:
• DX Heating request
• DX Cooling or WSE request
• When control is in DX heat or cool
mode AND is controlling with pulse
width modulation, the valves will
remain open during the pulse width
modulation cycle.
• Dehumidification request
• EWT sampling request. Valves will
remain open for 3 minutes.
• Manual testing
• During DX operation. The valves will
open for 20 seconds to ensure
adequate water flow before
energizing the compressor outputs.
• Upon opening, the valves remain
open for a 10 minute minimum to
reduce excessive valve cycling.
Note: If only a single isolation
valve is used on a two-circuit heat
unit, it must be wired to the isola-
tion valve 1 output.
Isolation valve 1 must remain open as
long as the control is in an active cool-
ing, heating, or dehumidification. If cir-
cuit/compressor 1 is taken off-line, iso-
lation valve 1 will remain open to allow
operation of circuit 2.
Under normal operation, isolation
valves will be closed under the follow-
ing conditions:
• Compressor and WSE are controlled
O
FF
and the 10-minute minimum on
has expired. Note: If the WSE is
disabled due to economizer enable
paramenter or through BAS system
and cooling demand is still present,
the isolation valve will remain open
for compressor operation.
• Isolation valve 2 will close if
compressor 2 is taken off-line due to
a diagnostic or no capacity call and
the 10-minute minimum on has
expired
• Power is lost, valves de-energize to
the closed position
• Manual test off
There is no time delay when an isola-
tion valve is to be closed. The ouptut
will be de-energized and the valve will
spring return closed.