Valent VX Series Controller
5
setpoint. When a modulating compressor is installed
(Digital or Inverter Scroll), the compressor modulates
to maintain the supply air setpoint. Mechanical
cooling is available in the following configurations:
-
Packaged DX:
Unit with compressors and
condensing section located within the same unit.
this unit may have lead standard, lead digital
scroll, or lead inverter scroll compressors.
-
Split DX:
Unit with compressors located in the
unit and utilizes a remote condenser section.
This type of unit may have lead standard, or lead
digital scroll compressors.
Air Source Heat Pump
When a unit is configured as an ASHP, compressors are
used for cooling and heat pump heating. A reversing
valve is energized when the unit is in heating mode to
reverse the flow of the refrigerant. The ASHP is only
available as a packaged unit with an inverter scroll as
the lead compressor.
•
Cooling:
Mechanical cooling operates the same as
any other unit with compressors by controlling the
compressors to maintain the supply air temperature
set point in cooling mode and to maintain the cooling
coil temperature in dehumidification mode.
•
Heat Pump Heating
:
When heat is required, the
reversing valve is switched, and the compressors
are staged to maintain the supply air temperature set
point.
•
Heat Pump Heating Lockout:
Heat pump heating
may be locked out for any of the following reasons:
- Defrost is initiated 3 times in one hour.
- Supply Air temperature is 5ºF below set point
for more than 10 minutes and secondary heat is
available as backup only.
- Outside ambient temperature is below the HP
ambient lockout set point(10ºF).
•
Resetting HP Heating Lockout
:
One of the
following conditions must occur to return to HP
heating:
- The outside temperature increases by 5ºF.
- The outside humidity decreases by 20%RH, if
humidity sensor is installed.
- The unit has been locked out for more than 2
hours when a humidity sensor is not installed and
not locked out on low ambient condition.
•
Defrost:
Periodically, the ASHP need to initiate a
defrost cycle to remove accumulated frost from the
outside coil when operating in heating mode. The
saturated suction temperature, the outside ambient
temperature and/or the outside humidity determine
when a defrost initiates and terminates.
Initiation:
One of the following must be true for a
defrost cycle to initiate:
- The saturated suction temperature is less than
-15ºF; or
- The saturated suction temperature is less than
ambient conditions (temp/dewpoint) minus an
offset (35ºF/25ºF).
Termination:
The defrost cycle is terminated when
one of the following occur:
- The saturated discharge temperatures of all
refrigerant circuits are greater than the cancel
defrost set point (80ºF); or
- The max defrost time (5 min) has been exceeded.
•
Outside Coil Fan Control:
Refrigerant pressure
control with outside coil fans will have lead EC fans
and utilize refrigerant transducers to stage fans
on and off in cooling and heating. The following
sequences are based on the current mode of
operation:
-
Cooling/Dehumidification:
The lead outside fan
turns on with the first compressor and holds for a
min of 30 seconds based on the OA temperature.
The lead fan modulates to maintain the refrigerant
pressure control set point for cooling mode. Each
additional outside fan stage turns on based on
the saturated temperature reaching set point plus
an offset and turns off when the temperature falls
below set point after a delay.
-
Heating:
The lead outside fan turns on with
the first compressor. The lead fan modulates
to maintain the refrigerant pressure control set
point for heating mode. Each additional outside
fan stage turns on based on the saturated
temperature being below set point minus an
offset and turns off when the temperature rises
above set point after a delay.
-
Defrost:
When defrost is initiated, the outside
fans turn off allowing the heat to build and defrost
the outside coil. When defrost is terminated, the
outside fans turn on to bring the pressure down
before switching back to heating mode.
•
Secondary Heat:
A secondary heating device may
be installed in the unit. This device may be electric
heat, gas furnace, or a hot water coil. The following
sequences are available for secondary heat:
-
Backup
: Secondary heat only operates when
heat pump heating is not available.
-
Supplemental
: Secondary heat will operate
simultaneously with heat pump heating when the
compressors are not producing enough heat to
stay within 2ºF of set point.
Sequence of Operation
