AAON HB-005 - Manual (Page 19)

19
Modulating Hot Gas Reheat
The modulating hot gas reheat option is used to
provide additional moisture removal capacity to the HB
unit. Hot refrigerant gas discharged from the
compressor is sent as needed to a reheat coil
mounted immediately after the cooling coil.
For this application a humidistat must also be installed
in the conditioned space to provide a signal to initiate
the dehumidification by operating the hot gas reheat to
deliver dehumidified air at a specified temperature into
the occupied space. The humidistat may be
purchased from AAON or from others. The thermostat
wiring to the control board with single or multi-stages
should be installed as listed previously.
Supply Air Temperature Sensor
A supply air temperature sensor is factory wired and
provided within the equipment at the end of a coil of
wire. This must be installed in the downstream supply
air ductwork at a sufficient distance from the
equipment to provide a correct mixed air temperature
to the unit control board.
Reheated Supply Air Temperature
The desired discharge air temperature setpoint can be
preset and later adjusted by using the DIP switch
labeled SETPOINT on the circuit board. See Figure
18a for the location and DIP switch setting instructions.
The controller will allow the user to set a Supply Air
Temperature Setpoint between 50°F and 100°F. If a
value of less than 50°F is set, then the controller will
default to a 50°F Supply Air Temperature Setpoint. A
value greater than 100° F will cause the unit to default
to a 100°F Supply Air Temperature Setpoint.
Supply Air Temperature Reset Limit
The controller will also allow a reset of the temperature
by a 0 to 10 VDC signal from an outside source to the
terminal as shown in Figure 18a. The reset range is
determined by the setting configured on the DIP switch
labeled RESET LIMIT. The controller will reset the
supply air temperature setpoint from the value set on
the SETPOINT DIP switch to the value set on the
RESET LIMIT DIP switch, as the Reset Input (MHGRV
RSET) signal is increased from 0 Volts to 10 Volts.
Example:
We want the Discharge Air Temperature Setpoint to
increase from 55°F when the Reset Input signal is at 0
Volts, to 75°F when the Reset Input signal is at 10
Volts.
• Set the SETPOINT DIP Switch to 55°F
• Set the RESET LIMIT DIP Switch to 75°F
The discharge air temperature will now increase from
55°F to 75°F as the Reset Input voltage signal ramps
from 0 Volts to 10 Volts.
Note: It is possible to create a “reverse acting” control
sequence. Using the temperatures from the example
above by setting the SETPOINT DIP Switch to 75°F
and the RESET LIMIT DIP Switch to 55°F the reset
would be reverse acting. In this case the controller will
maintain a 75°F discharge temperature when the
Reset Input signal is at 0 Volts and will reduce it to
55°F when the Reset Input signal is at 10 Volts.
Lockout Modes
Gas Heating
The heating mode will be locked out if the ignition
system safety monitors trip 3 times during a call for
heating.
Electric Heating
The heating mode will be locked out if the high
temperature limit switch trips 3 times during a call for
heating.
Cooling
The cooling mode will be locked out if the low pressure
switch safety switch trips 3 times during a call for
cooling or dehumidification.
Cooling operation will be locked out if the Outside Air
Sensor is missing or defective.
The economizer and reheat operation during
dehumidification will be locked out if the Supply Air
Sensor is missing or defective.
To reset the lockout condition, either remove the call
for heating, cooling, dehumidification, or cycle the
power to the HB unit.