Carrier RTU Open v3 Integration Manual

Contents

Sequence of OperationRTU Open v3 Carrier Proprietary and Confidential CARRIER CORPORATION ©2016Integration Guide All rights reserved25DehumidificationThe RTU Open provides occupied and unoccupied dehumidification on units that are equipped with the CarrierHumidi-MiZer™ option from the factory. This requires a space relative humidity sensor or a humidistat for control.The following conditions must be true for the dehumidification control to operate:• The Outside Air Temperature is greater than the Cooling Lockout Temperature setpoint• The Indoor Fan has been on for at least 30 seconds• The unit has a valid Supply Air Temperature input• The unit has a valid Space Temperature input• The unit has a valid Space Relative Humidity Sensor or Humidistat input• Heat mode is not active and the time guard between modes has expiredWhen using a relative humidity sensor to control dehumidification, occupied and unoccupied dehumidificationsetpoints are used.When using a humidistat, the setpoints are not used. The humidistat indicates a high-humidity condition.When a high indoor relative humidity condition is indicated and the above conditions are satisfied, the RTU Openenters the dehumidification mode, energizing the Humidi-MiZer™ output.The mode continues until the space relative humidity falls below the active setpoint by a 5% fixed Hysteresis whena humidity sensor is used, or when there is no longer a call for dehumidification where a humidistat is used.See the base unit / Humidi-MiZer™ operations manual for additional information.Demand LimitingThe RTU Open may employ a demand limit strategy. Demand limiting in the RTU Open works through setpointexpansion. The controller’s heating and cooling setpoints are expanded in steps or levels. The degree to which thesetpoints are expanded is defined by the Demand Level Setpoints.Each Demand Level (1 through 3) adjusts the heating and cooling setpoints outwards. By default, Demand 1yields a 1 °F (.5 °C) expansion, Demand 2 yields a 2 °F (1.1 °C) expansion, and Demand 3 yields a 4 °F(2.2 °C) expansion.The BACnet Demand Limit variable sets the desired level of setpoint expansion in the receiving controller. Level 0leaves the standard occupied and unoccupied heating and cooling setpoints in effect. Levels 1 through 3 expandsoccupied heating and cooling setpoints.Door switchA Door Contact may be configured on any unused binary input. A typical application is a door or window contactmounted within the space served by a single zone rooftop. The Door Contact disables mechanical cooling and anyheating, when active (an open door or window is detected). Economizer cooling, if available, continues to operate.The input provides a configurable alarm delay (60 second default) before heating and cooling is disabled.