Sequence of Operation
84
OAU-SVX006E-EN
be used to maintain the
Discharge Air Temperature
Setpoint Active
.
Supplemental Hot Water Reheat
If the
Hot Gas Reheat Valve Command
is at 100%, the hot
water valve is energized with
Heating Capacity
at 0%. If
Heat Capacity
rises above 0%, the
Hot Gas Reheat Valve
Command
will be locked at 100% and the hot water will be
used to maintain the
Discharge Air Temperature Setpoint
Active
.
Hot Water Reheat (No Hot Gas Reheat
Installed)
During
Dehumidification Mode
, the hot water valve is
energized by enabling
Heat 1 Command, Heat Capacity
is
adjusted to maintain
Discharge Air Temperature Setpoint
Active
.
Exhaust Fan Operation
With Isolation Exhaust Fan Damper(s)
After completing the Supply Fan Starting Sequence,
Exhaust Damper Open Close Command
is enabled. Once
the
Exhaust Damper End Switch
has proven,
Exhaust Fan
Start Stop Command
is enabled.
Without Isolation Exhaust Fan Dampers
After completing the Supply Fan Starting Sequence,
Exhaust Fan Start Stop Command
is enabled.
With Modulating OA/RA Dampers
Exhaust fan speed is controlled to
Duct/Space Pressure
Setpoint
.
ECM Exhaust with 2-Position OA Damper
Using the Exhaust Air Flow Active from the exhaust fan
piezo reading, the unit controls exhaust fan speed to a
constant volume of according to the
Exhaust Air Flow
Setpoint
.
VFD Exhaust with 2-Position OA Damper
The exhaust fan controls to a constant speed using
PEVFD
Setpoint
.
Energy Recovery Wheel
Operation (ERV)
The
Energy Recovery Wheel Start Stop Command
is
enabled whenever there is a call for exhaust fan. During
Ventilation Mode
or
Economizer Mode
the ERV is disabled,
except during the cleaning cycle, which occurs for two
minutes every thirty minutes.
During cooling operation, the
Energy Recovery Exhaust
Air Bypass Position Command
is locked at 0% (closed
position) for full energy recovery. During heating
operation, the position is modulated to maintain the
Discharge Air Temperature Setpoint Active
for variable
effectiveness capacity control. Once the bypass damper
becomes fully closed, the primary heater will be engaged.
Energy Wheel Without VFD
The unit prevents frost accumulation on the ERV by
measuring the
Exhaust Leaving Temperature Local
. The
Energy Recovery Outdoor Air Bypass Position Command
is modulated open to maintain 15°F for the exhaust
temperature. Above this temperature, the bypass damper
will remain at 0% signal (closed) when the ERV is in
operation.
Energy Wheel With VFD
The unit prevents frost accumulation on the ERV by
measuring the
Exhaust Leaving Temperature Local
.
Initially the ERV speed is reduced to maintain 15°F for the
exhaust temperature. If the ERV speed is at minimum, but
the exhaust temperature remains below 15°F, the unit will
maintain the temperature by modulating the
Energy
Recovery Outdoor Air Bypass Position Command
open.
During normal operation, the VFD is at 100% (full speed)
and the bypass damper is at 0% (closed).
Additional Features
Electric Pre-Heat
Pre-Heat Enable
is engaged whenever the
Exhaust
Leaving Temperature Local
falls below 20°F, with a
deadband of 5°F. The pre-heater is shut off if the
Preheat
Leaving Temperature Local
rises above 90°F.
Space Thumbwheel Input
Space Control and Single Zone VAV
With a space thumbwheel installed, the
Occupied Heating
Setpoint
and
Occupied Cooling Setpoint
is replaced with a
single setpoint from the input
Space Temperature Setpoint
Local
. The occupancy override button will override
Occupancy Request
to Occupied for two hours from the
time it was pressed.
Split Exhaust and Return Air Path
When a unit is equipped with separate paths for the return
and exhaust air, there will be a damper separating the two,
and the powered exhaust shall not run below the
minimum required speed to ensure exhaust air does not
contaminate the supply air. A differential pressure sensor
is used across the damper to verify a negative pressure on
the exhaust side. Exhaust fan will be enabled during
unoccupied mode. During
Economizer Mode
the damper
between the two air paths will open, the return damper will
close complete, and the outdoor damper will open to
100%.
