Question-and-Answer Resource for the Building Energy Modeling Community
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The inefficiency of the VFD is the only thing that should increase the pump power, which would be ~5%. If you have a load that generally requires constant volume, then a VFD would be worse performing. If it's a huge increase in energy then something else is going on in the model.
An improper schedule that wasn't active with a constant volume pump, but became active with the VFD might be a possible explanation.
