I'm working on a project that consists in the evaluation of various chiller replacement options for a chilled water application. Among the different options, I need to model chillers with and without inverter (i.e. variable capacity and on/off operation).
I tried to compare the two operations. In the attached plot, you can see the same chiller (same nominal power, COP, mass flow rate, performance curves) operated in the on/off mode (minimum PLR and minimum unloading ratio set to 1, blue) and continuously (minimum PLR and Unloading ratio set to 0.2, red). I came up with the odd result that the on/off chiller is more convenient than the inverter regulated one. It seems to me that the cycling ratio is somehow equivalent to the PLR, in terms of how it scales down the available capacity to the actual demand, neglecting that, in fact, inverter regulation of the compressor motors allows to smoothly follow the load, avoiding peak startup current.
Did I interpret it correctly? Is there any way to make the model more consistent, taking into account the benefits of inverter regulation? Thanks
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