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
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.