3.7.5.5 Four-Pipe Fan Coil Systems

This section contains building descriptors required to model four-pipe fan coil systems. Note that this system requires an outside air ventilation source to serve the zones and that an airside economizer is not available. Note that additional HVAC components (chiller, boiler, pumps) are needed to fully define this system.

Capacity Control Method
Applicability	Four-pipe fan coil systems
Definition	The control method for the fan coil unit at the zone. The following choices are available: ConstantFanVariableFlow CyclingFan VariableFanConstantFlow VariableFanVariableFlow
Units	List (with choices above)
Input Restrictions	Not a User Input – Derived from building descriptors for fan control and chiller loop flow control
Baseline Building	Not Applicable

90.1-2019

*Capacity Control Method*
Applicability	Four-pipe fan coil systems
Definition	The control method for the fan coil unit at the zone. The following choices are available: Constant fan variable flow: The fan speed is held constant to produce a fixed airflow rate whenever the unit is scheduled on. The hot water or chilled flow rate is varied so that the unit output matches the zone heating or cooling requirement. Constant fan constant flow: The fan speed is held constant to produce a fixed flow rate whenever the unit is scheduled on. The chilled water and hot water flow rates are kept constant at full flow. Cycling fan: The fan speed is chosen so that the unit capacity is greater than or equal to the heating/cooling load and the fan is cycled to match unit output with the load. Variable fan constant flow: The water flow rate is at full flow and the fan speed varies to meet the load. Variable fan variable flow: Both air and water flow rates are varied to match the load.
Units	List (with choices above)
Input Restrictions	Not a user input – derived from building descriptors for fan control and chiller loop flow control
Baseline Building	Four pipe fan coil systems are applicable for proposed buildings with the system type defined in Table 72. The capacity control for the baseline building will be specified as “Constant Fan Constant Flow.”

Table 72. Baseline Systems Using Fan Coil Units

Proposed		Baseline System Type
Heating	Cooling	Baseline System Type
Boiler/Electric Resistance or Gas Furnace	Purchased Chilled Water	Proposed buildings qualifying for System 1 and 2 will be constant volume fan coil units
Purchased Heat	Purchased Chilled Water	Proposed buildings qualifying for System 1 will be constant volume fan coil units