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20 WSHP-PRC001-EN
Additional Functions of the
ZN524 Controller
When the building owners choice is
Trane Tracer controls, the ZN524 con-
troller is required when any of the fol-
lowing applications are selected on a
single and dual circuited equipment.
• Waterside Economizer
• Hot Gas Reheat
(for Dehumidification)
• Boilerless Control for Electric Heat
• Water Isolation Valve Control
(for Variable Speed Pumping)
Entering Water Temperature
Sampling
The ZN524 controller will sample the
entering water temperature to deter-
mine proper control action for units
equipped with boilerless electric heat
or waterside economizer.
Waterside Economizer: Entering
water temperature (EWT) sampling
will automatically occur at power up
when the unit is equipped with a wa-
terside economizer (WSE). The EWT is
used to determine if economizing is
feasible. When the conditions are met,
the isolation valve(s) are driven open
for three minutes and the EWT reading
is taken. The determination as to
whether or not the economizer can be
enabled will be made and the control-
ler will take appropriate action. The
isolation valve will remain open re-
gardless if the WSE or the DX cooling
is enabled.
The unit’s waterside economizer will
contain a 2-position water valve wired
to the ZN524. The economizing water
coil will be optimized to provide 100%
of the unit capacity at 80.6 F/66.2 F re-
turn air temperature with 45 F entering
water. The flow rate is established at
86 F entering water temperature and
96 F leaving water temperature.
Low leaving air protection will be fur-
nished to protect the unit against de-
livering air that is cold enough to
sweat discharge air grilles. Coil icing
protection will also be provided.
Waterside economizer cooling will be
active during occupied, unoccupied
and standby cooling modes.
Boilerless Control Electric Heat
and Supplemental Electric Heat:
The ZN524 supports a single stage of
boilerless electric heat operation or
concurrent heating.
When the unit is configured for boiler-
less control, the EWT will be used to
determine whether DX heating should
be disabled and the electric heater en-
abled. When these conditions are met,
the isolation valve(s) are driven open
for three minutes and the entering wa-
ter temperature reading is taken. The
determination as to whether or not to
utilize electric heat will be made and
the controller will take appropriate ac-
tion. If boilerless electric heat is en-
abled, then the isolation valve will be
closed, shutting down the water flow
to the unit.
When the unit is configured for con-
current operation of DX heating (com-
pressor in heat pump mode) and
electric heat, the electric heat will act
as a second stage of heat for single
compressor units, and a third stage of
heat for dual compressor units. Note:
With concurrent (or supplemental)
electric heat, the electric heater is field
provided.
Water Isolation Valves
Variable speed pumping systems are
supported by the ZN524 controller
when water isolation valves are
present. Up to two isolation valves are
supported by the controller (one for
each compressor circuit).
The valves are normally closed unless
DX heating, DX cooling, waterside
economizer or dehumidification is re-
quested. When the isolation valves are
driven open for operation, the outputs
will be driven for 20 seconds to ensure
adequate water flow before the com-
pressor outputs are energized. Once
an isolation valve has been opened, it
will remain open for a 10 minute mini-
mum to reduce excessive cycling of
the valve.
Dehumidification
Dehumidification for the single and
dual circuited water-source heat pump
is applicable with the ZN524 control-
ler. The controller is capable of direct-
ing one stage of DX cooling in
conjunction with one stage of reheat
(hot gas reheat).
Dehumidification can only occur when
the controller is in the cooling mode. A
humidity transmitter is used to mea-
sure the zone’s relative humidity (RH),
then compares the zone relative hu-
midity to the relative humidity enable/
disable setpoint parameters. The de-
fault values for dehumidification en-
able is 60% RH with the disable point
at 52% RH. These values are config-
urable.
Features and Benefits
ZN510 & ZN524 Controls