MF MSHP Cost bug in BEopt, scope of impact?

asked 2023-04-04 14:30:28 -0600

jpierce
375 ●5 ●6

updated 2023-04-06 08:13:27 -0600

Aaron Boranian

14155 ●83 ●24 http://bigladdersoftware.com/

It seems BEopt (v2.8) has an egregious bug in the reported costs for mini-splits in multifamily buildings. Unlike other measures such as water heaters or mechanical ventilation in which the fixed materials costs are multiplied by the number of housing units (like one might expect), the MSHP fixed cost is not scaled by the number of apartments in BEopt's calculated cost.

Does this only affect the options panel of the results screen, or does it affect the internals as well e.g; the costs used in optimization, or to determine AERC? (Looking at the initial costs in the export suggests this affects more than just the results screen)

This can be accounted for with custom measures where one pre-scales this cost, but it's not obvious one would need to, nor should it be necessary...

Clarifying Update: Three unit MF, 36 kBTU HP type A capacity. 3 × 1,100 Cost/unit labor + 36 × 56 Cost/kBTUh + 1 × 415 "fixed" cost material= 5,731, as shown at the top of the right pane. However, it should be 3 × 415 for a total of 6,561. Afterall, the heat pump for each apartment will need its own lineset, etc. image description

answered 2023-04-04 16:02:08 -0600

shorowit

11891 ●201 ●9 https://www.nrel.gov/b...

I ran two MF buildings, one with a single unit and one with 3 units, and the MSHP costs were approximately 3 times higher in the latter case. In addition, you can clearly see in the Options input screen that MSHP costs include a "$/unit" component. And the detailed output report correctly shows a cost multiplier of 3 for that MSHP cost component.

image description

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The correct multipliers are used for the Cost ($/unit; fixed labor cost, unit=# MSHPs) and Cost ($/kbTUh, variable materials), but I am referring to housing units * the penultimate column: Cost ($; fixed materials). I am modelling a 26 apartment building, where the discrepancy is more clear. If I manually calculate 26 MSHP * Cost ($/unit) + capacity * Cost ($/kBTUh) + 1 * Cost ($) I get BEopt's costs. But the fixed material costs should be 26 * Cost ($) as with DHW and mechanical ventilation.

jpierce ( 2023-04-04 16:08:54 -0600 )edit

See amendment to question for image clarification.

jpierce ( 2023-04-04 16:26:10 -0600 )edit

Thanks for clarifying, that was not clear from your original question. I agree with you that it seems wrong. You can fix this by editing your, e.g., C:\Program Files (x86)\NREL\BEopt_2.8.0\Modeling\costMultipliers.py file and changing the line self.add_cost_multiplier(431, "$", 1) to self.add_cost_multiplier(431, "$", self.num_units). I haven't tested it but it should work.

shorowit ( 2023-04-05 18:59:00 -0600 )edit

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MF MSHP Cost bug in BEopt, scope of impact?

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MF MSHP Cost bug in BEopt, scope of impact?