Sequence of Operation
Fan Coil CARRIER CORPORATION ©2020
Integration Guide All rights reserved
25
Dehumidification
The Fan Coil provides occupied and unoccupied dehumidification, which requires an accessory space relative
humidity sensor. When using a relative humidity sensor to control dehumidification during occupied or unoccupied
times, the appropriate dehumidification setpoints are used accordingly. A request for dehumidification is
generated when the indoor relative humidity becomes greater than the dehumidification setpoint. The
dehumidification request starts the unit, if not already operating. If cooling or heating is currently operating, then
dehumidification is delayed until the cooling or heating load is satisfied. Once satisfied, dehumidification enables
cooling and the fan operates at its lowest speed.
During cooling, the unit both cools and dehumidifies. However, once the requirement for cooling is satisfied, and if
there is still a call for dehumidification, the unit continues to provide dehumidification and reheat. If a heating coil
is installed downstream of the cooling coil and REHEAT is enabled while dehumidification is active, the hydronic
heating coil maintains the supply air temperature at the configured Temper/Reheat SAT setpoint. This prevents
overcooling of the space, as long as the space temperature remains at least 1°F (-17.2°C) below the occupied
cooling setpoint. Dehumidification is disabled if the SPT falls below the Occupied Heating Setpoint.
The following conditions must be true for this algorithm to run:
• Cooling is set to Enable
• Space temperature reading is valid
• OAT is greater than the Cooling lockout temperature if OAT is available
• Condensate Overflow input is Normal
• Space temperature is above the occupied heating setpoint
• Space temperature is below the current cooling setpoint
• If unoccupied, the space RH is greater than the Unocc Relative Humidity setpoint
• If occupied, the space RH is greater than the Occ Relative Humidity setpoint
The following must also be true for the reheat to operate during dehumidification:
• A hydronic heating coil is installed in the reheat position
• Space temperature is at least 1°F (-17.2°C) below the occupied cooling setpoint
• 2-Pipe Changeover is set to no
Demand Limiting
The Fan Coil accepts 3 levels of demand limit from the network. In response to a demand limit, the unit decreases
its heating setpoint and increases its cooling setpoint to widen the range in order to immediately lower the
electrical demand. You can change the responding temperature adjustment for both heating and cooling and each
demand level. The response to a particular demand level may also be set to 0.
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