AirloopHVAC:UnitarySystem Heating & Fan EMS

asked 2020-03-08 23:56:19 -0500

tenna031 gravatar image

updated 2020-03-09 10:35:28 -0500

Hi all,

I'm overriding the heating energy delivered by a unitary HVAC system (DXCool,CoilHeatingGas) via EMS by setting discrete stages of the "Sensible Heating Load" actuator for the CoilHeatingGas and setting the mass flow rate of a draw-through FanOnOff module for each stage. The supply fan's flow rate gets set as expected, but the heating coil starts cycling between 0 and the requested heating load:

Fig 1

However, when I disable the actuator for setting the supply fan's mass flow rate and let E+ turn it on/off, I get this:

Fig 2

Why does the heating energy of the heating coil cycle when the mass flow rate of the supply fan is actuated (Fig 1)? and why do we see the peaks at the beginning of each step when the fan is not actuated (Fig. 2)? Is this related to the Runtime Fraction?

Thanks!

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