Orion System MUA II Controller - Manual (Page 15)

VAV/CAV Controller
Technical Guide
15
Condition Mode
Outside Dewpoint rises above the
Dewpoint Setpoint.
Dehumidification
OAT drops below the Cool Setpoint Vent
During this mode the controller will maintain the SAT between a ±
Cooling Deadband from the Supply Air Setpoint. This is achieved
by activating and deactivating the stages of cooling.
Cool Deadband
Cool Deadband
Supply Setpoint
(SAT) Supply Air
Temperature
Time
Staging Up
Staging Down
Figure 19: Cool Mode Staging
Vent Mode
This mode occurs when the controller reads an OAT between the Cool-
ing and Heating Deadband from the Supply Air Setpoint, and a
Dewpoint reading below the Dewpoint Setpoint. The migration table
for this mode is shown below.
Condition Mode
OAT falls below the Heat Setpoint Heat
OAT rises above the Cool Setpoint Cool
Dewpoint Temperature rises above
the Dewpoint Setpoint
Dehumidification
During this mode the controller will shut off heating and cooling, but will
allow the blower to continue its normal operation.
Dehumidification Mode
This mode occurs when the controller reads a Dewpoint Temperature
above the Dewpoint Setpoint. The migration table for this mode is
shown below.
Condition Mode
OAT falls below the Heat Setpoint and
Dewpoint Temperature falls below the
Dewpoint Setpoint
Heat
OAT rises above the Cool Setpoint
and Dewpoint Temperature falls below
the Dewpoint Setpoint
Cool
Dewpoint Temperature falls below the
Dewpoint Setpoint
Vent
In this mode the controller will use the Outside Enthalpy to calculate the
number of compressors needed to extract the moisture from the air. At
the same time the Reheat Control will be active to avoid over cooling.
Reheat Control
The control can utilize a combination of different heating methods to
reheat the supply air during dehumidification mode. The following is
the order the control will try to reheat de supply air.
1.) Unit Hot Gas Reheat
Two kinds of Hot Gas Reheat are available with the MUA II
controller, ON/OFF Hot Gas Reheat control and Modulating
Hot Gas Reheat Control. Modulating Hot Gas Reheat control
requires that the HVAC unit is equipped with the MHGRV II
controller. If the MHGRV II board is detected, the MUA II
board will send the Supply Temperature Setpoint to the
MHGRV II controller in order to modulate the Hot Gas Reheat
Valve to maintain the desired Supply Air Temperature. If the
HVAC unit does not have the MHGRV II controller installed and
is instead using an ON/OFF Hot Gas Reheat Valve for reheat
control, the user must configure a relay to activate the ON/OFF
Hot Gas Reheat Valve. The relay will cycle the ON/OFF Hot
Gas Reheat Valve to maintain the supply air temperature
between the Cooling and Heating Setpoints.
2.) Dehumidification Heat:
The user can elect to use the unit heating source to reheat the air
during dehumidification or to supplement Hot Gas Reheat
dehumidification control. If the HVAC unit is not equipped with
Hot Gas Reheat or the Hot Gas Reheat is not able to bring the
Supply Air Temperature to the desired setpoint, the MUA II
controller will activate the heat source to maintain the Supply
Air Temperature Setpoint. The heat source can be either internal
or external to the HVAC unit.