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OPERATION
Power Up Mode
The unit will not operate until all the inputs, terminals and safety
controls are checked for normal operation. (See Fig. 21 and 22.)
NOTE: The compressor will have a 5-minute anti-short cycle
upon power up.
Unit Protection Model (UPM)
Figure 22 shows the UPM sequence of operation for unit safeties.
All 50PSW units are equipped with a UPM.
Units with Complete C or Deluxe Controls
COOLING MODE
Energizing the "O" terminal energizes the unit reversing valve
thus placing the unit into cooling mode. When the thermostat calls
for first stage cooling (Y1) the loop pump or solenoid valve if
present is energized and the first stage of compressor capacity
starts. When the thermostat calls for second stage cooling (Y2) the
second stage (or full compressor capacity) is initiated. Once the
thermostat is satisfied, the compressor shuts down accordingly.
HEATING MODE
The first two stages of heating (Y1 and Y2) operate in the same
manner as cooling, but with the reversing valve de-energized.
Once the thermostat is satisfied, the compressor shuts down.
Units with W2W Open Controls
Units with W2W Open still feature a UPM board for unit
operation, so the operation will be similar to the sequence for the
other control packages. W2W Open features advanced
functionality, such as outdoor air reset and intelligent alarming,
which will differ from the other control packages. Below is an
overview of the different features for the W2W Open controls. For
more details of the W2W Open operation, please refer to the
W2W Open Integration Guide and the W2W Points/Properties
Manual. See Fig. 21 for W2W Open Control Board overview.
SEQUENCE OF OPERATION
WSHP Open W2W
OCCUPANCY
Scheduling
Scheduling is used to start/stop the unit based upon a time period
to control the leaving water temperature to specified heating or
cooling setpoints. By default, the modules schedule is
continuously occupied and will thus be enabled to operate as
configured to maintain the leaving water temperature and the
water supply setpoint.
Time schedules may be configured with Bacview6, Field
Assistant, or i-Vu Open. See the appropriate machine interface
User's Guide for specific instructions for setting time schedules.
NOTE: The modules' local time and date must be set for these
functions to operate properly.
System occupancy
The system occupancy function provides a means for W2W
controls installed as part of an i-Vu Open system to have their
occupancy determined by another module on the controls
network. A Binary Network input (BNI2) object is utilized to read
the present value of the Occupancy Status variable of another
module. System Occupancy requires Field Assistant, or iVu Open
Server for setup.
BAS (BUILDING AUTOMATION SYSTEM) ON/OFF
The BAS On/Off function provides a means for W2W controls
installed as part of a Third-party BACnet system to have their
occupancy determined by another device on the controls network.
A Network Visible, BACnet Multi-state Value object may be
written by the third-party device to set the controls occupied state
as required. This method of occupancy determination takes
precedence over all others. No special configuration is necessary
to utilize this function. Object address information is also
described in the W2W Integration Guide.
REMOTE OCCUPANCY CONTACT
The W2W has the capability to utilize an external dry contact
closure to determine the occupancy status of the unit. The external
contact may be normally closed or normally opened. Assuming a
normally open contact, the module will be unoccupied when the
remote contact is open, and occupied when the contact is closed.
A normally closed contact will be unoccupied when the remote
contact is closed, and occupied when the remote contact is open.
SHUTDOWN
The W2W includes a unit shutdown function. Shutdown is a
software switch that allows an operator to stop unit operation.
Shutdown is a BACnet binary value (object name "shutdown")
and is accessed in the Status expander via the Shutdown variable.
Setting Shutdown "Active" will immediately stop compressor
operation. The pump and valve outputs will remain energized until
their respective off delays have expired (see pump and valve
section).
The equipment will remain off as long as Shutdown is active.
Shutdown's default state is inactive. Shutdown may be invoked
from the UI, or accessed via the network (where the module is part
of a BACnet MSTP network).
POWER FAIL RESTART DELAY
The W2W control includes an adjustable Power Fail Restart Delay
(PFRD). The PFRD holds off the equipment startup until the
configured delay time has expired, and may be utilized to stagger
equipment starts after a power outage. The PFRD default value is
60 seconds but may be adjusted between 0 and 600 seconds.
CHANGEOVER TIMEGUARD
The W2W control utilizes a fixed 5 minute Changeover
Timeguard to protect the equipment in the event of any
immediate mode change between heating and cooling. The
timeguard stops compressor operation for 5 minutes to allow
water temperatures and refrigerant pressures to normalize before
restarting the compressor. The status (Inactive / Active) of the
Changeover Timeguard may be viewed in the module's
Maintenance expander.
LOAD PUMP
The W2W has a dedicated binary output to control a Load Pump.
The load pump output will be energized whenever the unit is
occupied.
When power is first applied to the control, or reapplied after a
power outage, the pump output will be energized after the Power
Fail Restart Delay (described previously) expires.
The pump control includes a configurable Pump Stop Delay. The
stop delay defines the time the pump will continue to operate after
heating or cooling is stopped, should the unit transition to
unoccupied. The Pump Stop Delay default value is 45 seconds and
may be adjusted between 0 and 180 seconds. NOTE: On a request
for unit shutdown (described previously), the pump will continue
to operate until all compression is disabled and then additionally
until the configured pump delay expires.
SOURCE WATER ISOLATION VALVE/SOURCE WATER
PUMP OUTPUT
The W2W has a dedicated binary output to control a Source Water
Isolation Valve or dedicated source water pump. The output will
be energized prior to starting any compression stage.
The output includes a configurable close/off delay. The delay
defines the time the isolation valve will remain open or the pump
will continue to operate after the last stage of compression stops.
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