iWorx® VPU2
22
505-010-2, Effective: April 29, 2014
© 2014 Taco Electronic Solutions, Inc.
The economizer can be disabled during excessively warm or cool weather by setting the outdoor air temperature econ-
omizer lockouts
Max OAT Econ
and
Min OAT Econ
. If the OAT is above the
Economizer Max OAT
, or below the
Econ-
omizer Min OAT
, the economizer is disabled. During an IAQ emergency, the
Economizer Min OAT
is lowered by the
IAQ Settings Temperature Reset
, while the
Economizer Max OAT
is raise by the same value. This feature requires a
controller that broadcasts the OAT, such as an ASM2, be installed on the network.
Heating Sequence
The controller provides support for either two stages of heating or one floating point or 0-10V modulating heating output
(valve or variable speed circulator). You can specify which type of heat you are using through configuration parameters.
Heating Stages
The heating sequence is initiated when the current operating mode calls for heat. The electric heating stages are
sequenced based on the supply air temperature, the heating setpoint and the control band. When the supply air tem-
perature drops below the heating setpoint minus the control band, a stage is turned on. If the supply air temperature
remains below the control band for an additional time-period, the next available stage is turned on. If all zone tempera-
ture readings are within 0.5
°F of their setpoints, the next stage does not cycle on. This cycle continues until all avail-
able stages have been energized.
After the supply temperature has risen above the heating setpoint, the first available stage is turned off. If the supply air
temperature remains above the heating setpoint for an additional time-period, the next available stage is turned off.
This cycle continues until all available stages have been de-energized. If the supply air temperature rises above the
heating setpoint plus control band all of the stages immediately cycle off.
Figure 8: Staged Heating Sequence (Occupied)
T1 = Stage Cycle Time
Calculated
Heating Setpoint
Heating
Control
Band
T2 = Stage Cycle Time x 2
Stage 1 On
Stage 2 On
Stage 2 Off
Stage 1 Off
T1
T2
T1
T2
Temperature
Heating with Floating Point Control
The heating stage outputs can be configured for floating point control of a heating valve. Floating point control is
enabled when
Heating Stages
are set to zero and the
Heating Valve Travel Time
is non-zero. The H1 output is the
valve open signal and the H2 output is the valve close signal.
After a reset, the floating point valve is calibrated by closing the valve for a period of the travel time. This ensures that
the valve is fully closed. When the valve is at its calculated 0% or 100% position, the valve is overdriven for 30 seconds
to ensure that the valve is fully closed or open.
