Valent VX Series Controller
6
Economizer
If the application requires cooling, and the OA
conditions are suitable for free cooling, the controller
will enter economizer mode. If the unit is economizing
and the discharge temperature set point is not being
met, the controller will bring on mechanical cooling.
If equipped with a modulating OA and recirculated
air damper, the dampers will modulate between the
min OA and max positions to maintain the supply
temperature set point. If equipped with an energy
wheel, Reference Energy Recovery Wheel Sequence.
•
Temperature:
The economizer will be locked out
when:
- The outside air is greater than the economizer
high lockout (65°F).
- The unit is operating in dehumidification mode.
- There is a call for heating.
•
Temperature/Enthalpy:
The economizer will be
locked out when:
- The outside air is greater than the economizer
high lockout (65°F dry-bulb).
- The outside air is greater than the economizer
high enthalpy lockout (23 btu/lb).
- The unit is operating in dehumidification mode.
- There is a call for heating.
Dehumidification
The cooling is controlled to maintain the cold coil
set point. Dehumidification is enabled when the OA
temperature is greater than the cold coil set point plus
an offset (adj. 10ºF). Dehumidification is disabled when
the OA temperature falls below the enable point by a
hysteresis (2ºF). If equipped with BMS communications,
the user can also directly set the cold coil leaving air set
point.
•
Optional Room Relative Humidity Sensor or
Thermostat:
The controller will adjust the cold coil
leaving air temperature set point between the min
(50°F) and max (55°F) set point to satisfy the desired
space relative humidity set point.
Reheat
While the unit is dehumidifying, the supply air
temperature is maintained by controlling the reheat
device to the supply air set point.
•
Hot Gas Reheat (valve):
The microprocessor
controller modulates to maintain set point.
•
Reheat Plus:
The microprocessor controller can
be configured to use the primary heat source as
secondary reheat.
Supply Fan VFD Sequence
The factory installed VFD is wired to the controller.
Supply fan speed needs to be set during test
and balance of the unit. If equipped with BMS
communications, the user can also directly command
the supply fan speed. The following sequences are
selectable for supply fan control. The fan speed in
constrained by its min and max speed set points.
•
Constant Volume:
Supply fan operates at a constant
speed based on a constant volume set point based
on occupancy.
•
0-10 VDC by Others to VFD:
The supply fan is
enabled by the unit controller. An external field-
supplied 0-10 VDC signal to the fan’s VFD is
responsible for modulating the supply fan’s speed.
The signal is linear and the speed is at min when 0V
is present and at max when 10V is present.
•
CO
2
Control:
The supply fan modulates to maintain
CO
2
set point based on a sensor located in the space
or return duct. A CO
2
sensor or BMS communicated
value is required for this sequence.
•
Duct Static Pressure Sensor:
The supply fan
modulates to maintain an adjustable duct static set
point based on a sensor located in the supply duct. A
static pressure sensor or BMS communicated value
in required for this sequence.
• Space Static Pressure:
The supply fan modulates to
maintain a space static pressure set point based on a
sensor located in the space. A space static pressure
sensor or BMS communicated value in required for
this sequence.
•
Single Zone VAV :
The controller will control the
supply air temperature and supply fan speed in order
to maintain the space temperature.
Heating Mode-
The supply temperature set point
will be increased before increasing the supply fan
speed in order to maintain the space temperature set
point. If the calculated supply temperature set point
is greater than the current space temperature, the
supply fan speed will be increased while the supply
temperature set point is increased.
Cooling Mode -
The supply temperature set
point will be decreased before increasing the supply
fan speed in order to maintain the pace temperature
set point.
Exhaust Fan VFD Sequence
The factory installed VFD is wired to the controller.
Exhaust fan speed needs to be set during test
and balance of the unit. If equipped with BMS
communications, the user can also directly command
the exhaust fan speed. The following sequences are
selectable for exhaust fan control. The fan speed
constrained by its min and max speed set points.
•
Constant Volume:
Exhaust fan operates at a
constant speed based on a constant volume set
point based on occupancy.
•
0-10 VDC by Others to VFD:
The exhaust fan is
enabled by the unit controller. An external field-
Sequence of Operation
