fanElectric in the energy balance

The following is reading the results of the natural ventilation demo file on Hydra (window based natural ventilation), in which fanElectric is one of the output variables. However, there is not such input node to read this output on the energy balance component:

May I ask how to report fan electricity consumption in this case as part of the energy balance breakdown?

Thank you!


To be honest, I didn’t include an input for the fan energy because:

  1. It’s usually VERY small in comparison to the other terms of the energy balance and I usually find that I do not want to include it just for the sake of clarity. Still, it doesn’t hurt to give people the option of including it if she/he wants.

  2. Not all EnergyPlus models have all of the fan energy going into the air stream and (consequently) not all of it goes into the zone energy balance. However, to date, all fan energy of Honeybee-generated models goes into the air stream so it’s probably safe to say that this point is moot by now.

Given that I have just argued against my own reasons, I’ll add an input for it very soon.


Thank you very much, Chris!

I wonder if fan energy use might be an import item for analysis in natural ventilation modeling scenarios as specified in your demo file on hydra, especially in hot and humid climate.



My 2 cents is that it would be.


I have added it into the component as you see in the attached file and on the github. The fan term is almost always going to be very small in relation to the nat vent term but I was at least able to see it on the chart when modeling an unconditioned building in San Francisco (unofficial capital of Natural Ventilation in the US) with the most inefficient fan that I could (0.5 total efficiency):

The fan term never seems to be much larger than 1/20th of the natural ventilation term and I think I may leave it out of my energy balance charts by disconnecting it from the energy balance component. Still, we all have a right to know how small it is and that right has now been resorted :slight_smile:

-Chris (589 KB)

Thank you very much, Chris, for implementing this!

I tested your workflow using Singapore’s weather file, and here’s the results:

Seems the fan electricity energy is a bit higher here, but still relatively lower than natural ventilation heat lost as you pointed out.

Based on the image above, one suggestion here is that: will it be better if the order of the colors in the legend bar is consistent with that of the color patches shown for each month? I.e. from top to bottom, the items in the color legend bar are people, lights, fan, equipment … cooling, storage.

Just a suggestion. Thanks, again, for your prompt assistance!



I had a feeling that your result would surprise me. The average zone air temperatures are fairly high in the middle of the day and I admittedly have not run too many simulations with this high of a temperature:

Your suggestion about the ordering is noted.You should know that you can change the order to be anything you want just by replacing the paths of the data tree. Here is one example that does so (and see attached):

I am also realizing that, when you have fan energy that is this large, the energy balance seems to be “off-balance”. This is making me think that, though the fan energy goes into the zone air, a lot of it may leave through the exhaust air of the zone and this does not seem to be accounted for in the current Nat Vent term that EnergyPlus produces. I might investigate this further when I get the chance.

-Chris (589 KB)

Thanks, Chris, for the data tree path trick!

However, the colors for the heat loss items are still in reverse order as compared to the legend…

I’ll see if there is Grasshopper way to fix this color order issue later…