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Additional HPWH sizes in BEopt

asked 2023-05-05 10:48:10 -0500

updated 2023-05-07 07:22:53 -0500

I am looking to match WH sizing for retrofit analysis, but BEopt only has options for 50 and 80gal HPWH units. I also checked the beta 3.0.1 version, as one of the improvements listed is expanded HPWH inputs... but that doesn't seem to be the case on size diversity, at least in this beta version.

For the homes I'm modeling, I'm estimating that 2 cases where a 40gal HPWH is the reasonable retrofit choice. I know that I can modify the options available, but I'm worried about assigning the incorrect information to the model (since things like compressor size are relevant and I'm not a WH expert by any means). Is my best bet to just go find a 40gal HPWH and match the specs? Does anyone know if I'm missing something within BEopt 2.8 or the beta 3.0.1?

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answered 2023-05-08 10:22:49 -0500

In the BEopt 3.0 beta, the inputs for HPWHs have been significantly simplified so that you no longer need to provide detailed inputs (compressor capacity, COP, SHR, airflow rate, etc.) that are nearly impossible to find. The model just needs UEF as an input. So you should find it pretty simple to create a user option in BEopt v3, whereas yes, it would be very difficult to create a user option in BEopt 2.8.

As an aside: Note that while there is a penalty for using a larger tank size for a conventional storage tank water heater (because you have increased tank surface area, and therefore increased tank standby losses), there is generally a net benefit from choosing a larger HPWH. This is because the HP has a much lower heating capacity, so you are more likely to use backup electric resistance when the tank is low on hot water remaining. If you have a larger HPWH, then you are going to be low on hot water remaining much less often. So being able to use the HP more often compared to electric backup often provides increased performance that more than offsets the additional tank losses.

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Asked: 2023-05-05 10:48:10 -0500

Seen: 18 times

Last updated: May 08