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EnergyPlus Peak Gain Components Report - Opaque Surface Conduction and Other Heat Addition

asked 2019-08-29 16:08:19 -0500

updated 2020-01-26 11:42:44 -0500

I have one simple and another potentially less simple question related to the Peak Cooling Sensible Heat Gain Components report (and its Peaking Heating counterpart). I'll keep the two questions separate for good housekeeping. Here's the less simple one...

Question: Opaque Surface Conduction and Other Heat Addition [Btu/h] -- What's actually in this load component and why is it 5x greater than the next load (Window Heat Addition)?

I am trying to help someone make sense of a poorly performing 2D "simplified" CBECC-Com model. I have a hunch that there may be geometry issues and still trying to prove it. I highly doubt that opaque surface conduction is driving cooling load sizing more than window/solar gains, and thinking there might be something strange happening in the "and Other Heat Addition" part of this load component.

I read up on this report and the variable (HERE) and found that this component is calculated as the difference between the auto-sized load and the sum of the other gains. Needless to say, that's the opposite of helpful.

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answered 2019-08-30 04:42:24 -0500

It is very confusing, and this is probably not going to help much, but at least will give some documentation.

Bottom line: it's got everything that isn't in the other major heat gains/removal columns you see, and that everything does include conduction from opaque surfaces.


In the Annual Building Sensible Heat Gain Components tables as well as the Peak ones you mentioned, two columns are calculated based on the others: Opaque Surface Conduction and Other Heat Addition [GJ] and Opaque Surface Conduction and Other Heat Removal [GJ].

These two are just there to ensure that the row sums up to zero, and either Heat Addition is used (to store positive numbers), or Heat Removal is used (to store negative numbers). Here's where these are calculated in the source code:

From the I/O reference guide for Sensible Heat Gain Summary

The Sensible Heat Gain Summary (key: SensibleHeatGainSummary) provides results for each zone and the overall building for some of the major heat gain components. The first four columns show the loads satisfied by sensible air heating and cooling as well as radiant heating and cooling surfaces in the zone. The heat gains from people, lighting, equipment, windows, interzone air flow, and infiltration are shown when adding heat to the zone and separately when removing heat from the zone (for applicable components). Finally the balance is shown as “Opaque Surface Conduction and Other Heat Addition” and “Opaque Surface Conduction and Other Heat Removal” which is a term indicating the affect of the walls, floors and ceilings/roof to the zone as well as the impact of the delay between heat gains/losses and loads on the HVAC equipment serving the zone. The following shows each output variable that is used for each column. For each timestep in the simulation, positive values are shown as additions and negative values are shown as removal for most variables.

The Opaque Surface Conduction and Other Heat Addition and Opaque Surface Conduction and Other Heat Removal columns are also calculated on an timestep basis as the negative value of the other removal and gain columns so that the total for the timestep sums to zero. These columns are derived strictly from the other columns.

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Thanks @Julien Marrec - That's what I deduced, and that's also the info I found from the I/O ref guide that I linked to on Big Ladder's site. I guess I'm looking for ways to figure out what "Other" gains could be attributing to the one combined load component.

Greg Collins's avatar Greg Collins  ( 2019-08-30 14:02:54 -0500 )edit

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Asked: 2019-08-29 16:08:19 -0500

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Last updated: Aug 30 '19