Evaporation temperature setpoint determination - Johnson Controls - LIT-12011950 - Building automation software - Smart Equipment Controller - 5.0

Smart Equipment Controls Sequence of Operation Technical Bulletin

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Smart Equipment Controller
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Evaporator Leaving Air Temperature setpoint is the setpoint used to control the compressor staging while HGR is active.

There are two parts to determining OprEvapTempSp. The first part detailed below compares the space humidity to the humidity setpoint. The higher the humidity, the lower the setpoint. Setpoint1 is used below to denote the output for the first part of the OprEvapTempSp calculation.

  • If OprSHis below HGRHum-Sp – 1.5%, then Setpoint1 is SATLo-Sp -2°F
  • If OprSHis above HGRHum-Sp + 5%, then Setpoint1 is DehumEvapLowSp
  • If OprSH is in between the values above, then interpolate between SATLo-Sp – 2°Fand DehumEvapLowSp
  • For example, if HGRHum-Sp = 50%, SATLo-Sp = 55°F, DehumEvapLowSp = 40°F

      • If OprSH< 48.5%, then Setpoint1 = 53°F
      • If OprSH > 55%, then Setpoint1 = 40°F
      • If OprSH is between 48.5% and 55%, then interpolate between 53°F and 40°F

The second part of determining OprEvapTempSp looks at RAT and how far above the zone cooling septoint it is. If it is more than half a degree above setpoint, then it decreases the value that was calculated above.

  • If RAT is below Zone Cooling Setpoint + 0.5°F, then OprEvapTempSp is Setpoint1
  • If RAT is above Zone Cooling Setpoint + 2°F, then OprEvapTempSp is DehumEvapLowSp
  • If RAT is between the values above, then interpolate between Setpoint1 and DehumEvapLowSp
    • If RAT < 72.5°F, then OprEvapTempSp = Setpoint1 (calculated above)
    • If RAT > 74°F, then OprEvapTempSp = 40°F
    • See Figure 1and Figure 1 for examples
Note: the application will enforce at least a 3 degree differential between SATLo-Sp and DehumEvapLowSp
Figure 1. Evaporation temperature setpoint determination logic represented in graph form