[clarified and updated] is fanElectric missing in the energy balance component?

Replies to This Discussion

Permalink Reply by Chris Mackey on August 9, 2016 at 6:26am

Grasshope,

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.

-Chris

Permalink Reply by Grasshope on August 9, 2016 at 11:31am

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.

-Ji

Permalink Reply by Anton Szilasi on August 9, 2016 at 3:34pm

Ji,

My 2 cents is that it would be.

Permalink Reply by Chris Mackey on August 9, 2016 at 5:06pm

Grasshope,

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 :)

-Chris

Attachments:

• NatVentFanTest.gh, 589 KB

Permalink Reply by Grasshope on August 9, 2016 at 10:28pm

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!

-Ji

Permalink Reply by Chris Mackey on August 10, 2016 at 8:05am

Ji,

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

Attachments:

• NatVentFanTest.gh, 594 KB

Permalink Reply by Grasshope on August 13, 2016 at 8:44am

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...

-Ji