iWorx® HPU3
505-035, Effective: June 30, 2015
17
© 2015 Taco Electronic Solutions, Inc.
After the space temperature has risen above the heating setpoint for a predefined time-period, the last-energized stage
is turned off. (Note that the last stage that was turned on will be the first one to be turned off.) If the space temperature
remains above the heating setpoint for an additional time-period, the next previous stage will be turned off. This cycle
continues until all stages have been de-energized.
The configurable value "stage time" determines the duration of the stage. An absolute minimum stage ON time of 2
minutes, and an absolute minimum stage OFF time of 5 minutes are enforced when the space temperature is less than
the space setpoint. If the temperature rises above the space setpoint then the minimum on and off times are ignored.
When the space temperature rises above the space setpoint, all of the compressor stages turn off immediately; the
stage time and minimum on time are ignored.
During unoccupied periods, the heating setpoint is adjusted downwards through a separate unoccupied heating set-
point.
Figure 7:
T1 = Stage Cycle Time
Occupied
Heating
Setpoint
Heating
Control
Band
T2 = Stage Cycle Time x 2
Space
Setpoint
Temperature
Stage 2 On
Stage 1 On
Stage 2 Off
Stage 1 Off
T1
T2
T1
T2
Reversing Valve = HEAT
Heat Sequence - Occupied Mode
Figure 8: Heat Sequences – Unoccupied Mode
T1 = Stage Cycle Time
Unoccupied
Heating
Setpoint
Heating
Control
Band
T2 = Stage Cycle Time x 2
Space
Setpoint
Temperature
Stage 2 On
Stage 1 On
Stage 2 Off
Stage 1 Off
T1
T2
T1
T2
Reversing Valve = HEAT
