Orion System MHGRV-X - Manual (Page 8)

OPERATION MODES
MHGRV-X Field Technical Guide 8
Initialization
The MHGRV-X Controller uses on-board LEDs to indicate various
diagnostic conditions during power-up and operation. It also uses the
LCD Display to show initialization. Please review this information
for a complete description of the controller initialization sequence.
Modulating Hot Gas Valves
The MHGRV-X Controller utilizes two modulating valves to control
the fl ow of Hot Gas through the Hot Gas Reheat Coil. One of these
valves is the Condenser Hot Gas Valve and the other is the Reheat
Hot Gas Valve. The valves are wired to the MHGRV-X Controller
Modulating Hot Gas Valve Output terminals on the controller. These
valves work in concert with each other to create a “three-way valve”
confi guration. As one closes, the other opens, etc. All modes of opera-
tion that follow referring to the Hot Gas Reheat Valve are actually
a combination of these two valves working together to achieve the
specifi ed sequence of operation.
Modes of Operation
The MHGRV-X Controller can be used in two different modes of op-
eration. These modes behave in a similar manner; the main difference
is the way they receive information to control the dehumidifi cation
process. The following is a description of these modes:
Stand-Alone Operation
As the name implies, in this mode the controller behaves as an in-
dependent unit. The controller begins the dehumidifi cation process
when the Dehumidifi cation Input “H1” receives a 24 VAC signal
from an outside source. When the signal is received, the controller
will activate the “FAN” output to energize the HVAC unit fan. At the
same time, the controller will initiate Cooling Mode by energizing
the “CMP” output starting the HVAC unit compressor. In addition,
the controller will open the Hot Gas Reheat Coil by activating the
“VALVE” output. At this time, the MHGRV-X Controller will start
to modulate the Modulating Hot Gas Reheat valve. The control-
ler will modulate the MHGR valve to maintain the Supply Air
Temperature Setpoint by activating the stepper motor outputs on
the MHGR valve. The Supply Air Setpoint is confi gured with the
Setpoint Screen in the LCD Display. If Supply Air Temperature
Reset is used, it will initiate when a 0-10 VDC signal is supplied to
the “RESET IN” input. As the voltage increases from 0 to 10 Volts
at the “RESET IN” input, the Supply Air Temperature will be reset
towards the Supply Air Reset Temperature Setpoint. This setpoint
is confi gured with the Setpoint Screen in the LCD Display. When
a 10 Volt input signal is received at the “RESET IN” input, it will
be controlling at the Supply Air Temperature Reset Setpoint. The
controller will conclude the Dehumidifi cation process when input
“H1” is deactivated, the input “Cool Override” is activated, or the
input “Heat Override” is activated.
Operation in Communicating Mode
In this mode, the MHGRV-X Controller behaves as an expansion
board for an AAON Unit controller. The controller begins the dehu-
midifi cation process when the AAON Unit controller makes a request
to the MHGRV-X Controller for dehumidifi cation. At that time, the
controller will activate the “FAN” output to energize the HVAC unit
fan. At the same time, the controller will initiate Cooling Mode by
energizing the “CMP” output starting the HVAC unit compressor.
In addition, the controller will open the Hot Gas Reheat Coil by
activating the “VALVE” output which opens the Reheat Solenoid
Valve. At this time, the MHGRV-X Controller will start to modulate
the Modulating Hot Gas Reheat valve. The controller will modulate
the MHGR valve to maintain the Supply Air Temperature Setpoint
by activating the stepper motor outputs on the MHGR valve. The
Supply Air Setpoint is set by programming the HVAC unit control-
ler. If Supply Air Temperature Reset is used, it will initiate when
the HVAC sends a request to reset the Supply Air Temperature. The
Supply Air Temperature will be reset towards the Supply Air Reset
Temperature Setpoint stored in the HVAC controller. It will send a
request to move towards the Supply Air Temperature Reset Setpoint
based on its setpoints and confi guration. The controller will conclude
the Dehumidifi cation process when the HVAC control sends a request
to terminate Dehumidifi cation or a Cooling or Heating Override
request is made by the HVAC unit controller. Any setpoints or
signals at the inputs to the MHGRV-X Controller will be ignored.
Additional Features
Reheat Coil Flush
To assure positive oil return to the compressor, the Hot Gas Reheat
Coil will be fl ushed of liquid refrigerant by moving the Modulat-
ing Gas Reheat Valve to its maximum position for a short interval.
Cooling Flush: If the unit is in cooling mode, a fl ush will occur
when the unit’s fl ush cooling interval timer has elapsed. The time
is accumulated whenever it is in cooling mode and resets after each
fl ush cycle. The fl ush cooling interval timer is a setpoint that is
confi gurable using the keypad and display (0 to 120 minutes in 10
minute increments).
Reheat Mode Flush: If the unit is in dehumidifi cation mode and
the valve is below 70% for the fl ush reheat interval timer value, a
fl ush will occur. If the valve goes above 70%, the timer is reset. The
fl ush reheat interval timer is a setpoint that is confi gurable using the
keypad and display (0 to 120 minutes in 10 minute increments).
Optional Second Stage Reheat
On larger systems, where more hot gas reheat capacity may be re-
quired, a 2 Position Hot Gas Reheat valve can be connected to the
MHGRV-X Controller to be used in conjunction with the Modulating
Hot Gas Reheat valve. Any time the reheat demand moves above
the Modulating Hot Gas Reheat valve capacity, this 2 position
valve would be energized to supply additional hot gas to the Hot
Gas Reheat coil. As the reheat demand is satisfi ed, the MHGRV-X
Controller will de-energize the 2 position valve and control reheat
with the Modulating Hot Gas Reheat valve.
Reheat Solenoid Valve Control
The Hot Gas Reheat Solenoid valve for the Reheat Coil is activated
when there is a call for Dehumidifi cation. In this mode, the Hot Gas
Reheat Solenoid will be deactivated 2 minutes after the reheat de-
mand ceases. The Hot Gas Reheat Solenoid valve will be reactivated
when a request for reheat is received by the MHGRV-X Controller.
Operation Modes