This topic contains 1 reply, has 1 voice, and was last updated by  Gamaliel Lodge 2 months, 3 weeks ago.

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  • #8528
     Gamaliel Lodge 

    I modeled a measure installing a VFD on an AHU supply fan. It shows positive annual kWh savings, but the demand savings is negative. That doesn’t make sense. Please explain?

     Gamaliel Lodge 

    A VFD usually has an efficiency of 97%. This means a little bit more power has to be consumed and dissipated into heat to operate the VFD. VFD usually reduces power use at low load condition. At peak load condition, the fan is usually fully loaded. So the VFD can not bring any demand savings. On the contrary, the extra small power consumed to run the VFD would cause a small demand penalty.

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