38 TGZ 040A through TGZ 190A OMM TGZ-1
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.
LWT Error
LWT error compares the actual LWT to the active LWT set point. The equation is:
LWT error = LWT – active LWT set point
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.
Evaporator Saturated Temperature
Evaporator saturated temperature is calculated from the circuit evaporator pressure.
R410a Evaporator Saturated Temperatures
When R410a refrigerant is selected the refrigerant pressure will be fitted to a curve made
up of 24 straight-line segments. The accuracy of calculated saturated temperatures are less
than +/- 0.5°F when compared to standard look up tables for R410a.
Condenser Saturated Temperature
Condenser saturated temperature is calculated from the condenser pressure for each circuit.
R410a Evaporator Saturated Temperatures
When R410a refrigerant is selected the refrigerant pressure will be fitted to a curve made
up of 24 straight-line segments. The accuracy of calculated saturated temperatures are less
than +/- 0.5°F when compared to standard look up tables for R410a.
Evaporator Approach
The evaporator approach shall be calculated for each circuit. For R22 and R410a refrigerant
the equation is:
Evaporator Approach = LWT – Evaporator Saturated Temperature
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