Hello Unmethours Community,
I have been struggling to construct the simplest load balance that I can from a single-zone unconditioned box EnergyPlus model. There are no internal loads and all gains and losses are purely from the climate (solar and conduction). My reasoning is that, if I add up the values of the following two EnergyPlus outputs, the result should be zero if EnergyPlus is truly running a balanced calculation:
Surface Window Net Heat Transfer Energy
Surface Inside Face Conduction Heat Transfer Energy
When I do this for a box model without any windows, I essentially get what I'm after where the sum of these values gives me the following result for each month in kWh, which is very close to zero:
- Jan: -1.738775
- Feb: -1.122338
- Mar: -0.431097
- Apr: -1.676013
- May: -0.037371
- Jun: -0.344535
- Jul: -1.520733
- Aug: -1.758476
- Sep: -1.89579
- Oct: -2.799482
- Nov: -2.171337
- Dec: -1.434317
However, as soon as I add windows, things start becoming imbalanced such that, by the time my box model is 90% glazed, I get the following monthly kWh totals by summing those two E+ outputs across the model:
- Jan: 317.94952
- Feb: 346.767665
- Mar: 361.9911
- Apr: 338.261545
- May: 390.638818
- Jun: 378.609665
- Jul: 418.09426
- Aug: 382.281574
- Sep: 365.228805
- Oct: 356.298138
- Nov: 300.882507
- Dec: 327.779518
The full load balance of the model can be visualized with the following chart, where the "Storage" term represents the remainder after summing those two E+ outputs:
Granted, I am calling it storage because I just don't know what it is but it's not an accurate description because the average air temperature in the room is not heating up over the whole simulation.
So my question is what is it that I am missing when I use those two EnergyPlus outputs to try and construct the load balance of the room? Where are those 300-400 kWh of thermal energy going in each month if they are not leaving through the windows or the opaque surfaces? And is there a combination of E+ outputs that I could request for this model, which would actually produce a result that sums to zero for a complete balance.
Here is the IDF of the single zone box with 90% glazed walls in case anyone wants to reconstruct this experiment for themselves:
https://drive.google.com/file/d/1KD80hMVw93NIp5JXo9Gdltiv0lzkNURv/view?usp=sharing
Thank you, as always.
