Johnson Controls ZL Series Installation Manual page 64

• Local sensing, return air humidity sensor:
A relative humidity sensor is installed in the
return air section of the unit. The sensor is
wired directly to the unit's control system.
You can relocate the sensor to an in-zone
wall mounted position, if preferred. The end
user can adjust humidity control setpoints
using the MAP tool. Refer to Accessory kit :
Single Enthalpy Kit and required for reheat units
(2EC0401) for installation details of the 3 wire,
0-10V relative humidity sensor.
On/Off humidity switch: The RTU's control system
can accept a dry contact to activate or deactivate the
humidity control sequence. The 2 wire dry contacts
replaces the dirty filter switch (DFS) input on the
unit's control system, SSE Board. The customer
can choose from a dedicated humidity switch or a
thermostat with a dehumidification contact output.
Using the MAP tool, the dirty filter pressure switch
must be converted to a humidity switch by turning
software point HGR-En = ON. If enabled, the HGR
sequencer will read DFS input for a binary call
for dehumidification, the same as if RAH% were
above setpoint. A contact closure activates humidity
control sequence while an open switch deactivates
the humidity sequence.
Note: The operational space humidity (OprSH)
is only effective if an input has been present
since the last relearn system (Relearn) was
performed. The operational space humidity
(OprSH) parameter is then shown in the UCB
display. Refer to Technical Bulletin: Smart
Equipment™ Controls Sequence of Operation
Overview for details.
Reheat mode sequence
of operations for Smart
Equipment™ control only
The MagnaDRY reheat mode of operation is
designed to remove latent heat (humidity) from a
space when there are low load conditions and the
air conditioning unit is not used to cool the space.
The general sequence of operation of the patented
MagnaDRY reheat is outlined in the following
sections. The user can select three different modes
Normal reheat mode
When the UCB detects a need for dehumidification through the field installed return/space humidity sensor
and there is not a call for cooling, the UCB energizes solenoids SOL 3 (HGRH), SOL 2 and the reheat relay
64 Installation Manual ZL Series 7.5- 12.5 Ton 60 Hertz R-410A
of operation from the unit control board (UCB)
within the Smart Equipment™ controller menu. The
available modes are normal, alternate, and aux. The
following sections describe each mode.
Normal occupied operation mode
If the return humidity is greater than or equal to the
hot gas reheat humidity set point, and there is no
demand for cooling, the C1 output energizes and
the AUX-HGR output energizes.
If there is a demand for one stage of cooling and
the return humidity is greater than or equal to
the hot gas reheat (HGR) humidity set point, the
C1 output energizes but the AUX-HGR output de-
energizes.
Any additional cooling demands energize
compressor outputs, but do not change the status
of the AUX-HGR output. When the return humidity
falls to 3% or more below the set point, the C1 and
AUX-HGR outputs de-energize.
Note: If HGR is enabled for unoccupied
operation is enabled, during unoccupied mode
the control works the same as described,
except it uses the HGR unoccupied humidity set
point instead.
Normal cooling mode
When there is a call for first stage cooling, with or
without a call for dehumidification, the UCB de-
energizes the HGR relay de-energizing SOL 2, SOL
3 (HGRH) and energizes SOL 1, engaging cooling
circuit no. 1 resulting in circuit no. 1 cooling mode
operation. The unit is now in first stage cooling
without HGRH.
When there is a call for second stage cooling, the
UCB engages both circuit no. 1 and circuit no. 2
in cooling mode. The indoor blower operation is
always initiated upon a call for first stage cooling,
second stage cooling or dehumidification (HGRH).
The unit will not operate in the reheat mode if there
is any call for heating.
On units with economizers, the unit does not
operate in the reheat mode if there is a call for
cooling and the economizer is operating as first
stage of cooling. All safety devices function as
previously described.
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