Is CyclingFan capacity control method of fan coil unit in Energyplus with constant water flow?

[MWaltre]

Issue overview

Originally, I'd like to perform a simulation with cycling fan and constant water flow fan coil unit. From the result with fan coil unit of cycling fan capacity control method, the water flow also varies. So I dug into the code.
FanCoilUnits.cc

Details

In FanCoilUnits.cc, for function "Sim4PipeFanCoil", there is a switch case, for "case CCM::CycFan:", the code after it is empty, followed by "case CCM::VarFanVarFlow", I think this is the reason why the water flow is variable.

Maybe the code can be improved to include capacity control option by cycling fan with constant water flow .

[rraustad]

Capacity Control Method = CyclingFan is used to meet a zone load and then turn off the fan coil when not needed. When the fan is off and water continued to flow there will be no heat transfer to the water side of the heat exchanger. This type of control would result in the water plant pumps running continuously. What type of investigation or research would need to allow water to flow through the fan coil heat exchanger when air flow is off? Does Capacity Control Method = VariableFanConstantFlow give results closer to what you expect?

[MWaltre]

Here is the link to my question on UnmetHours.
As in the the section "Room fan-coil units" of Chapter "Room air distribution" in ASHRAE Handbook: HVAC Applications, the sub section "Basic Control Sequences" said, the simplest sequence of "Three-Speed Motor with Two-Position Valves" is:
"On a call for cooling, the fan is energized at the speed (high, medium, or low) selected by the occupant or by the thermostat. The chilled-water control valve opens fully. On reaching the room set point, the fan de-energizes and the chilled-water control valve closes."
I understand that this is quite old control sequence, but when someone would like to investigate the effect of fixed/constant fan speed with constant water flow (I mean on when fan energized, off when fan de-energized), cycling fan/constant fan with constant water flow rate would be quite handy option. (Such control can be realized by Trnsys)

With the current EnergyPlus option of CyclingFan, the chilled water flow of the fan coil unit seems flucurating when energized as shown by

The shown value is in kg/s, some curve may be straight by volume. However, it does not explain all the values that are too low or too high. Other reason may be that there is an on fraction effect on the reported value (I'm not sure yet).

However, for up to date Fan coil unit, variable water flow is quite common. Constant water flow may not be that necessary.
I just dug into the code to some extent, (the code indicates for case CCM::CycFan:, the code falls through to case CCM::VarFanVarFlow) so I raised this issue. Maybe there is no need to update anything. But I'll try to use some simple projects to investigate it in the future.