Utility Bills error on supplemental heating for Minisplits

1 reply [Last post]
Benjamin Zizi
Joined: 05/27/2013


I just realized after much effort trying to understand the discrepancy between my calculations and my ouputs that it seems that BeOpt doesn't calculate well the cost of energy for the Utility Bills graph (down left) for minisplits.

It seems that it doesn't count the Supplemental Heating Energy costs in the bills. My results are that : as the Supplemental Heating Consumption increase between two iterations (and the electricity costs are increasing also as logical), the Utility bills are decreasing.

The costs I find that would be far more logical are the costs indicated in the Energy related Costs, Annualized (up left).

Is it a good interpretation of the discrepancy I get? I attached the related outputs and can attach my simulation file if my description is not clear.

If I am not mistaking, and when we generate an optimization, does this one take into account the Utility bills or the Energy related Costs to make the optimization ? (and so, can we trust the results for optimum pathway for minisplits or not?)

Many thanks for your help!


Site Electricity Use.jpg26.37 KB
Annualized electricity bills.jpg16.41 KB
Energy Related Costs, Annualized.jpg16.14 KB
BEopt developer
Joined: 09/27/2011

Hi Benjamin,

Thanks for the detailed post, you are correct that heat pump supplemental heating electricity usage appears to not be included in the utility bill calculation (which is part of the optimization's Energy-Related Costs metric). This is absolutely a bug.

I have attached a file that fixes the bug for BEopt 2.7. To use it, download the file and replace your C:\Program Files (x86)\NREL\BEopt_2.7.0\Modeling\energyplus.py file. I will also make sure the bugfix is included in the next BEopt release.


energyplus.py.txt 776.86 KB

Scott Horowitz
Residential Buildings Group
National Renewable Energy Laboratory

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