LX Series Unit Ventilator Controller User's Guide42
When you switch between humidification and dehumidification, the Rooftop Unit
Controller delays for a fixed time period of 45 minutes.
Cooling State
The Unit Ventilator Controller can control the following cooling types:
• free cooling
• digital cooling
• staged digital cooling
• cooling using heat pump
• floating valve cooling
• modulated valve cooling
The UVC uses free cooling or mechanical cooling. Free cooling uses the cooler
outside air to remove heat from the building. Mechanical cooling uses chiller units
and cooling coils to remove heat and humidity from the building.
Free Cooling
You can implement several strategies when using free cooling. The strategies can
be described by their following input requirements:
• economizer enable input
• outdoor enthalpy
• indoor and outdoor enthalpies
• outdoor air temperature
Economizer Enable Input: The economizer enable output follows the
economizer enable input if the input is available by network or by the hardware
input. If the economizer enable output is ON, then the fresh air damper can be used
for cooling when the mixed air temperature or the discharge air temperature is
known.
Outdoor Enthalpy: When outdoor enthalpy is available but not indoor enthalpy,
free cooling occurs if the outdoor enthalpy is below the maximum outdoor
enthalpy. A deadband of 0.43 Btu (1 kj/kg) is used in this process.
Maximum outdoor enthalpy is set on the Heating-Cooling configuration screen of
the Unit Ventilator Controller configuration wizard or by modifying
SCPToutdoorAirEnthalpySetpoint.
Outdoor and Space Enthalpies: If the outdoor and space enthalpies are available,
free cooling occurs if the outdoor enthalpy is 0.43 Btu (1 kj/kg) below the space
enthalpy. Free cooling is not available if the outdoor enthalpy exceeds the space
enthalpy.
Outdoor and space enthalpies are made available by the following methods:
• using a network input
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