WaterFurnace Envision Hydronic (NDW) - Manual (Page 21)

21
NDW INSTALLATION MANUAL
Power Fail Restart
When the controller is first powered up, the outputs will be
disabled for a random start delay time (See Random Start
Delay). The delay is provided to prevent simultaneous starting
of multiple heat pumps. Once the timer expires, the controller
will operate in the occupied mode until it is commanded
to another mode by a remote thermostat. A restart status
variable is available for indication of this occurrence.
Random Start Delay
This delay will be used after every power failure, as well as the
first time the compressor(s) is started after the control exits
the emergency shutdown mode. The default time period for
the start delay will be random between 1 and 120 seconds.
Compressor Fixed On Delay Time
The Compressor Fixed On Delay Time will ensure that the
compressor output is not enabled for (90) seconds after
the control receives a call to start the compressor.
Compressor Minimum On Delay
The compressor minimum on delay will ensure that the
compressor output(s) are enabled for a minimum of (2)
minute each time the compressor output is enabled. This
will apply in every instance except in the event the high-
pressure switch is tripped or emergency shutdown, then the
compressor output will be disabled immediately.
Compressor Short Cycle Delay Time
The compressor short cycle time delay will ensure that
the compressor output will not be enabled for a minimum
of five (5) minutes after it is disabled. This allows for
the system refrigerant pressures to equalize after the
compressor is disabled.
Compressor Lead/Lag
Compressor lead/lag is a standard part of the FX10 control
system. The unit is shipped from the factory with lead/
lag enabled. Lead/lag can be deactivated through the
unit mounted user interface. Lead/lag will always start the
compressor with the least amount of run time and stop the
compressor with the longest run time.
Sequence of Operation
Heating Cycle
During the heating cycle, the reversing valves will be
positioned for heating operation. The thermostat or
aquastat will command the reversing valves “Off” for
heating. If the compressor short cycle time delay has
been satisfied, the lead compressor will turn on after the
accessory output has been enabled, the low pressure
switches have been verified, and the fixed compressor start
delay timer has been satisfied. When heating is no longer
required, the compressor will be turned off immediately
after the compressor minimum on delay has been satisfied.
After the compressor output is turned off, it will remain off
for the time specified in the compressor short cycle time
delay. If the first stage compressor is not able to satisfy
the heating demand, the second stage compressor will be
activated by the thermostat or aquastat. The controller is
allowed to operate the heat pump in the heating mode
regardless of the outdoor air temperature.
Cooling Cycle
During the cooling cycle, the reversing valves will be
positioned for cooling operation. The thermostat or
aquastat will command the reversing valves “On” for
cooling. If the compressor short cycle time delay has
been satisfied, the lead compressor will turn on after the
accessory output has been enabled, the low pressure
switches have been verified, and the fixed compressor start
delay timer has been satisfied. When cooling is no longer
required, the compressor will be turned off immediately
after the compressor minimum on delay has been satisfied.
After the compressor output is turned off, it will remain off
for the time specified in the compressor short cycle time
delay. If the first stage compressor is not able to satisfy
the cooling demand, the second stage compressor will be
activated by the thermostat or aquastat. The controller
is allowed to operate the heat pump in the cooling mode
regardless of the outdoor air temperature.