Fan Coil Units

The Fan coil unit Compact option simulates a 4 pipe fan coil unit with hot water heating coil, chilled water cooling coil, and an outside air mixer. The fan coil units are zone equipment units which are assembled from other components. Fan coils contain an outdoor air mixer, a fan, a simple heating coil and a cooling coil. The fan coil unit is connected to a hot water loop (demand side) through its hot water coil and to a chilled water loop (demand side) through its cooling coil. The unit is controlled to meet the zone (remaining) heating or cooling demand. If there is a heating demand, the cooling coil is off and the hot water flow through the heating coil is throttled to meet the demand. The hot water control node must be specified (same as the hot water coil inlet node) as well as maximum and minimum possible hot water volumetric flow rates. If there is a cooling demand from the zone, the hot water coil is off and the chilled water flow through the cooling coil is throttled to meet the load.

 

You can model Fan coil unit systems with or without outside air.  If you include Mechanical ventilation with your Fan coil unit system then heating and cooling will only operate when the Mechanical ventilation operation schedule is on.

 

If you do not want to include outside air in your system, you should uncheck the Mechanical ventilation 'On' check box. In this case heating/cooling availability is determined entirely from the heating/cooling operation schedules under the Heating and Cooling headers.

 

Unlike the Unitary multizone and CAV and VAV Compact HVAC types, Fan coil unit zone systems take all their data from the zone level.

 

 

 

Note 1: Fan coil supply fans run continuously at full speed whenever the availability schedules are > 0 so fan coil outside air flow can be 'fully on' or 'fully off' but cannot reduce to fractional values in between. You may therefore get higher outside air delivery rates than with other systems if you are using Schedules and your Mechanical ventilation operation schedule has fractional values.

Limitations

  1. Fan coil units cannot be used in the same simulation as Unitary multizone Compact HVAC type.

  2. Outside air flow rate is either off, or on at a fixed flow rate depending on the value of the Fan operation schedule..

  3. Fan coil units cannot incorporate economisers and variable speed fans.

Technical EnergyPlus

EnergyPlus needs both the heating coil and cooling coil to be defined so even if heating or cooling is not selected in the input, DesignBuilder will schedule the appropriate coil to be off to mimic a 2-pipe system.