Fan Coil Unit
A fan coil unit functions as a cooling and/or heating source within a specific zone, comprising essential components such as a cooling coil (mandatory), an optional heating coil, a required fan, and an optional connection to a central air handling unit. The cooling coil facilitates the cooling process, while the heating coil, if included, provides additional heating capabilities. The fan ensures air circulation, and the connection to a central air handling unit, if chosen, allows for centralized control and coordination with the overall HVAC system.
Fan
Low Speed Supply Air Flow Ratio
Specify the low-speed supply air flow ratio, which is the ratio of the low-speed flow rate to the maximum supply air flow rate. The default value is 0.33. If the capacity control method selected is not Cycling Fan or ASHRAE90 Variable Fan, leave this field blank. The suggested value is 0.5 when using the ASHRAE90VariableFan capacity control method.
Medium Speed Supply Air Flow Ratio
Specify the medium-speed supply air flow ratio, which is the ratio of the medium-speed flow rate to the maximum supply air flow rate. Its value should be greater than the low-speed supply air flow ratio but less than 1. If left blank, the default value is 0.66. Leave this field blank if the capacity control method selected is not Cycling Fan or Multi-Speed Fan.
Capacity Control Method
Specify the capacity control method from the following options:
Constant Fan / Variable Flow
Cycling Fan
Variable Fan Variable Flow
Variable Fan / Constant Flow
Multi-speed Fan
ASHRAE90 Variable Fan
If selecting Constant Fan Variable Flow, note that the fan speed is fixed, and the hot water/chilled flow rate varies to match the zone load. For Cycling Fan, the fan is cycled to match unit output with the load. In Variable Fan Variable Flow, both air and water flow rates vary to match the load. Variable Fan Constant Flow maintains the water flow rate at full flow, adjusting the fan speed to meet the load. Multi-speed Fan adjusts the supply air flow rate by varying the fan speed based on the load. ASHRAE90 Variable Fan reduces the fan air flow rate when the zone sensible load is less than the product of the zone sensible load and the low-speed supply air flow ratio.
Sizing
Sizing Method
Specify the Sizing Method as either Autosize or Manual, with the latter necessitating explicit specification of all sizing parameters.
Cooling Convergence Tolerance
Specify the Cooling Convergence Tolerance, determining the convergence tolerance for unit cooling output control. Ensure the unit aligns its output with the zone demand. For units featuring water coils, numerically invert the model to attain the specified output. The cooling convergence tolerance functions as the error threshold for concluding the numerical inversion procedure.
Heating Convergence Tolerance
Specify the Heating Convergence Tolerance to set the convergence threshold for controlling the unit's heating output. The unit aligns its output with the zone demand, and for units with water coils, numerically invert the model to achieve a specified output. The heating convergence tolerance serves as the error threshold for concluding the numerical inversion procedure.
Max. Outdoor Air Flow Rate
Specify the Max. Outdoor Air Flow Rate if the fan coil unit incorporates outdoor air. This field designates the outdoor air volumetric flow rate (m3/sec), constrained by the maximum airflow rate. A value of zero signifies no outdoor air. When the Fan Coil is linked to an Air Terminal, this field defaults to zero flow.
Max. Supply Air Flow Rate
Specify the Max. Supply Air Flow Rate as the maximum volumetric airflow rate (m3/sec) through the fan coil unit, also representing the design and rated airflow rate of the unit.
Min. Cold Water Flow Rate
Specify the Min. Cold Water Flow Rate as the minimum cold water volumetric flow rate (m3/sec) through the fan coil unit's cooling coil.
Max. Cold Water Flow Rate
Specify the Max. Cold Water Flow Rate as the maximum cold water volumetric flow rate (m3/sec) through the fan coil unit's cooling coil.
Min. Hot Water Flow Rate
Specify the Min. Hot Water Flow Rate as the minimum hot water volumetric flow rate (m3/sec) through the fan coil unit's heating coil. Note that this field is not applicable when using an electric heating coil.
Max. Hot Water Flow Rate
Specify the Max. Hot Water Flow Rate as the maximum hot water volumetric flow rate (m3/sec) through the fan coil unit's heating coil. Similar to the previous field, this is not used in conjunction with an electric heating coil.
Min. Supply Air Temp. In Cooling Mode
Specify the Min. Supply Air Temp. In Cooling Mode as an optional input used only when Capacity Control Method is set to ASHRAE90VariableFan. Here, you specify the minimum supply air temperature in cooling mode.
Max. Supply Air Temp. In Heating Mode
Specify the Max. Supply Air Temp. In Heating Mode as an optional input used only when Capacity Control Method is ASHRAE90VariableFan. In this case, specify the maximum supply air temperature in heating mode.
Last updated
