Nibe CLIMATEMASTER TRT Series Installation Operation & Maintenance page 26

C l i m at e M a s t e r WAT E R - S O U R C E H E AT P U M P S
Rooftop ( TRT ) Series
R e v . : N o v e m b e r 2 1 , 2 0 2 2
ClimaDry II – Sequence of Operation, Cont'd.
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1st Stage Heating: A simultaneous call from (G) and (Y1)
to the (G) and (Y1) terminals of the DXM2.5 control
board will bring the unit on in 1st Stage Heating.
2nd Stage Heating: A simultaneous call from (G), (Y1),
and (Y2) to the (G), (Y1), and (Y2) terminals of the
DXM2.5 control board will bring the unit on in 2nd
Stage Heating. When the call is satisfied at the
thermostat the unit will continue to run in 1st Stage
Heating until the call is removed or satisfied, shutting
down the unit. NOTE: Not all units have two-stage
heating functionality (e.g. TRE036-072 units).
Reheat Mode: A call from the Humidistat/Dehumidistat
to the (H) terminal of the DXM2.5 control board will
bring the unit on in Reheat Mode if there is no call
for cooling at the thermostat. When the Humidistat/
Dehumidification call is removed or satisfied
the unit will shut down. NOTE: Cooling always
overrides Reheat Mode. In the Cooling mode,
the unit cools and dehumidifies. If the cooling
thermostat is satisfied but there is still a call for
dehumidification, the unit will continue to operate
in Reheat Mode.
NOTE: Care must be taken when using a humidistat
to operate ClimaDry II. When the DIP Switch on the
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DXM2.5 controller is set for 'humidistat' it reverses
the control logic so that an "open" control circuit
initiates a ClimaDry II run cycle. If a humidistat is not
connected, or if a manual switch on the humidistat is
set to "off", ClimaDry II will see the open circuit and
call for dehumidification.
TRT ClimaDry® II Component Functions
The ClimaDry II option consists of the following
®
components:
• Motorized Valve/Proportional Controller
• Supply Air Sensor
• Loop Pump
• Hydronic Coil
• Low Pressure Switch
The Proportional Controller operates on 24 VAC power
supply and automatically adjusts the water valve based
upon the Supply Air Sensor. The Supply Air Sensor
senses supply air temperature at the blower inlet
providing the input signal necessary for the proportional
control to drive the motorized valve during the reheat
mode of operation.
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The Motorized Valve is a proportional actuator/three-way
valve combination used to divert the condenser water
from the coax to the hydronic reheat coil during the reheat
mode of operation. The proportional controller signals the
motorized valve based on the supply air temperature of
the supply air sensor.
The Loop Pump circulates condenser water through the
hydronic reheat coil during the reheat mode of operation.
In this application, the loop pump is only energized during
the reheat mode of operation. The Hydronic Coil is utilized
during the reheat mode of operation to reheat the air to
the setpoint of the proportional controller. Condenser
water is diverted by the motorized valve and pumped
through the hydronic coil by the loop pump in proportion
to the control setpoint. The amount of reheating is
dependent on the setpoint and how far from setpoint the
supply air temperature is. The factory setpoint is 72°F
[22°C], generally considered "neutral" air.
ClimaDry® II Application Considerations
The reheat coil adds a small amount of resistance to the
air stream. In some cases the high static option may be
required for applications with higher static ductwork.
Consult the submittal data or the Installation/Operation/
Maintenance (I.O.M.) manual for the specific heat pump to
review blower tables.
Unlike most hot gas reheat options, the ClimaDry
option will operate over a wide range of EWTs. Special
flow regulation (water regulating valve) is not required for
low EWT conditions.
TRT units with the ClimaDry II option shall have an
antifreeze solution to protect the coil in low ambient
conditions. ASHRAE minimums for the region shall be
considered during the calculation of the antifreeze solution.
In applications where antifreeze is not specified, a
secondary heat exchanger can be used to isolate the TRT
from the water loop, thus requiring less antifreeze to be
used with the TRT Secondary brazed plate heat exchanger.
Figure 9 shows the heat exchanger connections.
Water-source heat pumps with ClimaDry II should
not be used as make-up air units. These applications
should use equipment specifically designed for make-
up air.
C l i m a t e M a s t e r Wa t e r - S o u r c e H e a t P u m p s
II
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