Trane GEV - Manual (Page 23)

Features and Benefits
ZN510 & ZN524 Controls
WSHP-PRC003-EN
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More ZN524 Controller Functions:
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 (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) sam-
pling will automatically occur at power
up when the unit is equipped with a
waterside 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 controller
will take appropriate action. The isola-
tion valve will remain open regardless
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
(27.0/10.0 C) return air temperature with
45 F (7 C) entering water. The flow rate
is established at 86 F (30 C) entering
water temperature and 96 F (36 C) leav-
ing water temperature.
Low leaving air protection will be fur-
nished to protect the unit against deliv-
ering air that is cold enough to sweat
discharge air grilles. Coil icing protec-
tion 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
enabled. When these conditions are
met, the isolation valve(s) are driven
open for three minutes and the enter-
ing water temperature reading is taken.
The determination as to whether or not
to utilize electric heat will be made and
the controller will take appropriate
action. If boilerless electric heat is
enabled, then the isolation valve will be
closed, shutting down the water flow to
the unit.
When the unit is configured for concur-
rent operation of DX heating (compres-
sor in heat pump mode) and electric
heat, the electric heat will act as a sec-
ond stage of heat for single compressor
units, and a third stage of heat for dual
compressor units. Note: With concur-
rent (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 pres-
ent. Up to two isolation valves are sup-
ported by the controller (one for each
compressor circuit).
The valves are normally closed unless
DX heating, DX cooling, waterside
economizer or dehumidification is
requested. When the isolation valves
are driven open for operation, the out-
puts will be driven for 20 seconds to
ensure adequate water flow before the
compressor outputs are energized.
Once an isolation valve has been
opened, it will remain open for a 10
minute minimum to reduce excessive
cycling of the valve.
Dehumidification
Dehumidification for the single and
dual circuited water-source heat pump
is applicable with the ZN524 controller.
The controller is capable of directing
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 meas-
ure the zone’s relative humidity (RH),
then compares the zone relative humid-
ity to the relative humidity enable/dis-
able setpoint parameters. The default
values for dehumidification enable is
60% RH with the disable point at 52%
RH. These values are configurable.