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# Extract each heat balance term in EnergyPlus

I am using a DOE prototype residential SFH IDF. I want to extract each heat balance term. However, the default heat balance term in EnergyPlus is not exactly what I want. It provides "Zone Air Heat Balance Internal Convective Heat Gain Rate [W], Zone Air Heat Balance Surface Convection Rate [W], Zone Air Heat Balance Interzone Air Transfer Rate [W], Zone Air Heat Balance Outdoor Air Transfer Rate [W], Zone Air Heat Balance System Air Transfer Rate [W], Zone Air Heat Balance System Convective Heat Gain Rate [W]......" Take "Zone Air Heat Balance Internal Convective Heat Gain Rate [W]" for example, it looks like this term combines the convection from all surfaces, so how can I know in detail how much heat comes from windows, how much from walls, how much from roofs... So I checked "Surfaces" in EnergyPlus manual, and got lost since there are so many terms in surface heat balance calculation. Especially for windows, some solar heat the outside, then the heat comes inside via conduction; some solar comes in directly and heats up the internal surfaces, then the heat convection with space air... It is really complex... In summary, my question is how to extract these heat balance terms from EnergyPlus, which output variable should I use?

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Hi! Happy New Year to you too :)

My thesis uses heat balance in EnergyPlus as a base for understanding the thermal performance of buildings. Then, If you want the convection heat balance related to zone air (I assume this based on your question), I think this article could provide the answer that you need: https://www.researchgate.net/publicat...

In brief, for any surface, the output for convective heat exchange is Surface Inside Face Convection Heat Gain Rate [W] or Energy [J].

There are many outputs for windows, and the "right one" will depend on your analysis. However, the Surface Inside Face Convection Heat Gain is sufficient for convective heat balance. And if you have a frame/divider on your window, you also need to consider the output Surface Window Inside Face Frame and Divider Zone Heat Gain Rate [W] in your zone air heat balance.

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The Honeybee plugin for grasshopper has this capability - the simplest way to see what outputs you'll want is I think to just read through the outputs they extract here:

Your model probably won't be using all of these, so just work out which ones are relevant to you (e.g. if you aren't using the airflow network you won't need the AFN outputs etc.).

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