AAON V12100 MHGRV-X Field Technical Manual

Contents

AAON V12100 MHGRV-X Field Technical Manual Manual pdf 9 page image

MHGRV-X Field Technical GuideINPUTS & OUTPUTS9Operation ModesAdditional FeaturesReheat Coil FlushTo assure positive oil return to the compressor, the Hot Gas ReheatCoil will be flushed 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 flush will occurwhen the unit’s flush cooling interval timer has elapsed. The timeis accumulated whenever it is in cooling mode and resets after eachflush cycle. The flush cooling interval timer is a setpoint that isconfi gurable using the keypad and display (0 to 120 minutes in 10minute increments).Reheat Mode Flush: If the unit is in dehumidification mode andthe valve is below 70% for the flush reheat interval timer value, aflush will occur. If the valve goes above 70%, the timer is reset. Theflush reheat interval timer is a setpoint that is configurable using thekeypad and display (0 to 120 minutes in 10 minute increments).Optional Second Stage ReheatOn larger systems, where more hot gas reheat capacity may be re-quired, a 2 Position Hot Gas Reheat valve can be connected to theMHGRV-X Controller to be used in conjunction with the ModulatingHot Gas Reheat valve. Any time the reheat demand moves abovethe Modulating Hot Gas Reheat valve capacity, this 2 positionvalve would be energized to supply additional hot gas to the HotGas Reheat coil. As the reheat demand is satisfied, the MHGRV-XController will de-energize the 2 position valve and control reheatwith the Modulating Hot Gas Reheat valve.Reheat Solenoid Valve ControlThe Hot Gas Reheat Solenoid valve for the Reheat Coil is activatedwhen there is a call for Dehumidification. In this mode, the Hot GasReheat Solenoid will be deactivated 2 minutes after the reheat de-mand ceases. The Hot Gas Reheat Solenoid valve will be reactivatedwhen a request for reheat is received by the MHGRV-X Controller.Communicating OperationIn this mode, the MHGRV-X Controller behaves as an expansionboard for an AAON Unit controller. The controller begins the dehu-midification process when the AAON Unit controller makes a requestto the MHGRV-X Controller for dehumidification. At that time, thecontroller will activate the “FAN” output to energize the HVAC unitfan. At the same time, the controller will initiate Cooling Mode byenergizing the “CMP” output starting the HVAC unit compressor.In addition, the controller will open the Hot Gas Reheat Coil byactivating the “VALVE” output which opens the Reheat SolenoidValve. At this time, the MHGRV-X Controller will start to modulatethe Modulating Hot Gas Reheat valve. The controller will modulatethe MHGR valve to maintain the Supply Air Temperature Setpointby activating the stepper motor outputs on the MHGR valve. TheSupply Air Setpoint is set by programming the HVAC unit control-ler. If Supply Air Temperature Reset is used, it will initiate whenthe HVAC sends a request to reset the Supply Air Temperature. TheSupply Air Temperature will be reset towards the Supply Air ResetTemperature Setpoint stored in the HVAC controller. It will send arequest to move towards the Supply Air Temperature Reset Setpointbased on its setpoints and configuration. The controller will concludethe Dehumidification process when the HVAC control sends a requestto terminate Dehumidification or a Cooling or Heating Overriderequest is made by the HVAC unit controller. Any setpoints orsignals at the inputs to the MHGRV-X Controller will be ignored.Auxiliary Mode Communicating1. Same as the Stand Alone Auxiliary Mode, but the ReheatEnable and Auxiliary Valve position will be sent using E-BUScommands.