Daikin WGZ030DW Operating And Maintenance Manual page 34

'Active'
Heat LWT
Set Point
active heating leaving water set point is reset using the following parameters:
1. Heating Leaving Water Temperature set point (Heat LWT)
2. Heating Maximum Reset set point (Htg MaxRes)
3. Heating Start Reset Delta Temperature (Htg StrtResDT)
4. Condenser Delta Temperature (condenser leaving water temperature minus entering temperature)
Reset is accomplished by changing the Active Heating Leaving Water set point from the Heat LWT set
point to the value of [Heat LWT (-) Heating Maximum Reset set points] as the condenser delta
temperature (leaving minus entering) varies from the Heating Start Reset Delta T set point towards 0ºF
delta temperature.
Active LWT Set Point
The active LWT set point represents the current control set point based on unit mode and reset. If unit
mode is ice, then the active set point is equal to the ice set point. If the unit mode is cool, the active set
point is the cool set point plus the leaving water reset value. If the unit mode is heat, the active set point is
the heat set point minus the leaving water reset value.
LWT Error
LWT error compares the actual LWT to the active LWT set point.
The equation for cool mode is:
LWT error = LWT – active LWT set point
The equation for heat mode is:
LWT error = active LWT set point – LWT
LWT Slope
LWT slope is calculated such that the slope represents 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.
Pull Down 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.
34
Heat LWT set point
(140ºF)
Htg MaxRes set point
(range of reset action)
(10ºF)
Heat LWT (–) Htg MaxRes
(130ºF)
WGZ030D through WGZ200D
Heating Mode Return Reset
0ºF Htg StrtResDT setpoint
Condenser Delta Temperature
The
OMM 1130-2