LX Series Unit Ventilator Controller User's Guide
44
•
There must be a cooling demand. A cooling demand results from a comparison
between the space temperature and the active cooling setpoint.
•
The fresh air damper, or economizer, must be at the minimum position.
•
If a floating cooling valve is used, then one output must be
COOL_VALVE_OPEN and another output must be COOL_VALVE_CLOSE.
The water used for cooling and heating operations must be cold for any outputs,
configured as such, to work:
•
heat_cool_valve_on_off
•
heat_cool_valve_close
•
heat_cool_valve_open
•
heat_cool_valve_mod
The water is considered cold when the water temperature is colder than the room
temperature, or the nviHotWater received value or state is zero.
Note:
nviHotWater has priority over the water temperature read from either the
input sensor or nviWaterTemp.
Cooling Demand
Cooling demand results from any one of the following:
•
the error between the active cooling setpoint and the space temperature
•
nviSlave
Cooling Output Sequence
If the Economizer Enable or Fresh_Air_Damper_Mod outputs are connected, and
the outside air temperature or outside air enthalpy has reached minimum low, then
free cooling is used before mechanical cooling; however, if free cooling cannot
satisfy the cooling demand, then the outside air damper is moved to the closed or
minimum position and mechanical cooling turns on.
If a cooling valve output is configured, then cooling outputs 1–4 turn ON only
after valve outputs are 100% open. Cooling outputs 1–4 are staged outputs–see the
section.
A delay occurs between the end of free cooling and the beginning of mechanical
cooling. This delay is defined by UCPTfree2MecDelay. You can set the delay on
the Heating Cooling screen by typing a value into the Switch Over Delay field.
Ending the Cooling State
Cooling outputs shut off when the bias reaches a negligible amount. However, if
the PID loop control has accumulated bias during the cooling stage, cooling
outputs may not shut off when the space temperature reaches the setpoint.