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I’m under the impression from the OM forum responses on how to model backup systems for solar DHW that OM requires you to model two water heaters (the solar and the backup tank) to account for the backup system…can you please confirm this? It would also be nice if OM would automatically calculate the solar DHW capacity and demand for backup based off the climate data for that area.
If you don’t already have that calculation built in, what do you recommend as a rule of thumb in Vegas for inputting the “%” for the solar and for the backup. I’ve heard anywhere from 70% solar and 30% backup to 90% solar and 10% backup, and have even heard that OM already accounts for the backup. Please clarify how OM handles this. Also, any data you can provide or a resource that shows solar thermal (in my case Las Vegas) backup needs would be very helpful for the HomeFree Nevada Program.
Modeling the solar and backup hot water sources as two separate systems is the correct method.
We do not currently have the means to automatically estimate the percent load met by the backup system. We do have a SolarThermal module in development that would allow you to model the solar collectors and estimate the annual load that they could meet. We are currently looking for beta testers for this module. If you would like to try it out, let us know.
I do not have any resources to help you determine the % backup. It would depend heavily on the size of the collectors and the scale of demand in the home. Your best bet is to use the utility base load as your guide and adjust the ratio to get the best fit between the model and utilities.
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