Dehumidification; Model Features; Special Features - Bard Q-TEC Series Literature Assembly

DEHUMIDIFICATION

MODEL FEATURES

These models provide a unique dehumidification
circuit for periods of high indoor humidity conditions.
Additionally, an "energy recovery ventilator" may be
provided to allow for outside ventilation air requirements
by eliminating excessive sensible and latent loads as a
result of the increased ventilation requirement.
Refer to Specification Sheet S3601 for the standard
features of the QW*S3D models. Electrical data for
the QW dehumidification Q-TEC models is unique and
cannot be directly compared to the electrical data for
the standard Q-TEC models.

SPECIAL FEATURES

Dehumidification Circuit
There are two events taking place to maximize the
dehumidification performance while the unit is in
dehumidification. The first event integrates a 3-way water
valve with the iSeries Smart Actuator monitoring the
supply air temperature. The second event incorporates a
refrigeration dehumidification circuit, which includes an
independent heat exchanger coil in the supply air stream
in addition to the standard evaporator coil.
The first event, featuring the 3-way water valve with
the iSeries Smart Actuator, monitors the supply air
temperature with a thermistor. The iSeries Smart
Actuator has a temperature setting adjustment located
at the top of the actuator (see Figure 30). The
temperature setting adjustment scans the temperature
communicated to the modulating water line control
from the thermistor located in the indoor blower supply
air stream. The ohm reading sent to the iSeries Smart
Actuator attached to the 3-way water valve will drive
the valve closed or open depending on the requirement
for heat exchange. To attain the required setting,
an initial adjustment will be required by the service
technician at set-up. The adjustment will allow for fine
tuning the demand for latent extraction. Typically, the
setting on the iSeries Smart Actuator should be just
above the 80°F setting indicated on the setting control.
The second event incorporating refrigeration
dehumidification circuit uses a coil to reheat the
supply air after it passes over the cooling coil, and
is sized to nominally match the sensible cooling
capacity of the evaporator coil. Extended run times
in dehumidification mode can be achieved using
waste heat from the refrigeration cycle to achieve
the reheat process, while at the same time large
amounts of moisture can be extracted from the
passing air stream. See Dehumidification Sequence
of Operation for specific operating sequences, and see
the following tables for performance on sensible and
Manual 2100-738A
Page 40 of 71
latent capacities, water removal ratings and supply air
delivery conditions.
The dehumidification refrigerant reheat circuit is
controlled by a 3-way valve in the refrigeration
circuit, directing the refrigerant gas to the normal
water condenser during periods when standard air
conditioning is required. During periods of time of
low ambient temperature (approximately 65°F to 75°F
outdoor) and high indoor humidity, a humidistat senses
the need for mechanical dehumidification. It then
energizes both the compressor circuit and the 3-way
valve, thus directing the hot refrigerant discharge gas
into a separate desuperheating condenser circuit which
reheats the conditioned air before it is delivered to
the room. The refrigerant gas is then routed from the
desuperheating condenser to the water coil for further
heat transfer. When the humidistat is satisfied, the
system automatically switches back to normal A/C
mode and either continues to operate or turns off based
on the signal from the wall thermostat. The result is
separate humidity control at minimum operating cost.
FIGURE 30
iSeries Smart Actuator Temperature Adjustment
Dehumidification Sequence of Operation
Dehumidification is controlled through a humidistat
and is independent of the thermostat. On a call for
dehumidification mode of operation, the compressor
will operate at full load (capacity) and 3-way valve that
feeds the reheat coil is energized through D terminal.
Dehumidification will continue until the humidistat is
satisfied.
Anytime there is a R-Y call for cooling, after a 45
second time delay, dehumidification is canceled. The
time delay allows the modulating water valve to open,
allowing full capacity water flow to be achieved before
cooling is initialized. The unit will then operate in
the cooling mode at part load for Stage 1 cooling
(can shift to full load if 2nd Stage cooling required)
until thermostat is satisfied. If dehumidification call
is still present when cooling call is satisfied, the unit
will continue to operate and immediately revert to
dehumidification mode, with compressor at full level.
MIS-4136