40 WGS 130A to 190A OM WGS-5
A separate alarm log stores the last 25 alarms to occur. When an alarm occurs, it is put into
the first slot in the alarm log and all others are moved down one, dropping the last alarm. In
the alarm log, the date and time the alarm occurred are stored, as well as a list of other
parameters. These parameters include unit state, OAT, LWT, and EWT for all alarms. If the
alarm is a circuit alarm, then the circuit state, refrigerant pressures and temperatures, EXV
control state, EXV position, slide position, slide target, number of fans, and compressor run
time on are also stored.
Event Logging
An event log similar to the alarm log holds the last 25 events to occur. When an event
occurs, it is put into the first slot in the event log and all other entries are moved down one,
dropping the last event. Each entry in the event log includes an event description as well as
the time and date of the occurrence. No additional parameters are logged for events.
The event log shall only be accessible with the Manager password.
Clearing Alarms
Alarms may be cleared at the unit controller and no password is required. The BAS can
clear evaporator flow loss, evaporator water freeze and pLAN failure regardless of what
other alarms are active.
Unit Controller Functions
Calculations
LWT Slope
LWT slope is calculated such that the slope represents the change in LWT over a time frame
of one minute.
Every 12 seconds, the current LWT is subtracted from the value 12 seconds back. This
value is added to a buffer containing values calculated at the last five intervals. The final
result is a slope value that is an average over the past 60 seconds.
Pulldown Rate
The slope value calculated above will be a negative value as the water temperature is
dropping. For use in some control functions, the negative slope is converted to a positive
value by multiplying by –1.
Unit Capacity
Unit capacity is estimated based on the slide target of each running circuit. The capacity of
a running circuit is estimated with this equation:
Circuit capacity = 0.8(slide target) + 20
A circuit that is off is assumed to be at 0% capacity. The unit capacity is then calculated by
this equation:
Unit capacity = (Circuit 1 capacity + Circuit 2 capacity)/2
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