Hot gas heat 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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Technical Bulletin
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There are two main modes of modulating HGR operation: dehumidification without a cooling demand and dehumidification with a cooling demand:.

Dehumidification without a Cooling Demand

In this mode, the objective is to allow minimal temp. change between the return and supply air. However, some amount of overcooling is allowed. Specifically, some cooling may happen when RAT gets within half a degree of the zone cooling setpoint. See below for more details.
  • If RAT is below ClgOcc-Sp – 1.5°F, then use ClgOcc-Sp for OprHGRTempSp
  • If RAT is above the Occupied Cooling Setpoint – 0.5°F, then use the Eff Clg DAT Sp for OprHGRTempSp
  • If RAT is between the values above, then interpolate between ClgOcc-Sp and Eff Clg DAT Sp
  • For example, if ClgOcc-Sp = 72°F
    • If RAT < 70.5°F, then OprHGRTempSp = 72°F
    • If RAT > 71.5°F, then OprHGRTempSp = Eff Clg DAT Sp
    • If RAT is between 70.5°F and 71.5°F, then interpolate between 72°F and Eff Clg DAT Sp
    • See Figure 1 and Figure 2 for examples
Figure 1. Hot gas reheat determination setpoint represented in a graph

Dehumidification with a Cooling Demand

In this mode, the modulating HGR controls the Supply Air Temperature to the Effective Cooling DAT setpoint.