# Fan electricity postprocessing Ideal Loads Air System results

How to determine the total Fan energy through postprocessing the Outdoor and Supply Air Standard Density Flow Rates in output from a zone simulation with Ideal Air Loads?

The outputs that I'm referring to are:

- HVAC,Average,Zone Ideal Loads Outdoor Air Standard Density Volume Flow Rate [m3/s]
- HVAC,Average,Zone Ideal Loads Supply Air Standard Density Volume Flow Rate [m3/s]

I thought that running the simulation to get hourly values for the flow rate I could then input these values into a simple equation to obtain the fan power:
**fanPressureRise*fanFlowRate/fanEfficiency**

(fanPressureRise and fanEfficiency being constant values)

I'm working with Grasshopper Honeybee to run the EnergyPlus simulation.
I’ve done a quick test, but I’m not sure my assumptions are correct. Would the total fan power be:
**FanSupply + FanOutdoor + FanExtract**

with:

- FanSupply = Fan energy obtained postprocessing the Ideal Loads Supply Air Standard Density Volume Flow Rate
- FanOutdoor = Fan energy obtained postprocessing the Ideal Loads Outdoor Air Standard Density Volume Flow Rate
- FanExtract = same values of FanOutdoor

This forum doesn't allow me to upload files yet, but I've posted screenshots and Honeybee script of the test in the Ladybug forum as well, here the link: link text

I've been advised to post the question in Unmet, hope you can help me. Many thanks.