40 AGZ 010B through 034B IOMM AGZB1
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.
Refrigerant Saturated Temperature
Methods for calculating saturated refrigerant temperature differ with each refrigerant.
R22 Saturated Temperature
Evaporator saturated temperature and condenser saturated temperature are calculated from
the pressures for each circuit. The pressure will be fitted to a curve made up of 13 straight
line segments. The points used to define these segments are as follows.
Pressure (PSI) Temperature (
o
F)
24.0 0
34.7 12.0
47.6 24.0
62.8 36.0
80.8 48.0
101.6 60.0
126.2 72.0
153.8 84.0
185.2 96.0
220.6 108.0
260.5 120.0
305.2 132.0
355.1 144.0
430.4 160.0
R407C Saturated Temperature
Evaporator dew point and condenser midpoint are calculated using 32-bit math. The
equation is as follows:
If Pressure < 120 psi Then
Saturation = [Pressure x 145/105] – [(Pressure
2
)/2000] – 250
If Pressure >= 120 psi Then
Saturation = [Pressure x 46/94] – [Pressure
2
/25000] + 145
Evaporator Approach
The evaporator approach is calculated for each circuit. The equation is as follows:
Evaporator Approach = LWT – Evaporator Saturated Temperature
Suction Superheat
Suction superheat is calculated for each circuit using the following equation:
Suction superheat = Suction Temperature – Evaporator Saturated Temperature
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