Our building will have on-site (and dedicated campus) solar PV, and we're using Trane's Trace program for our ASHRAE 90.1 energy model. However, Trace doesn't seem to have one definitive solar PV modeling feature. Here are the two Trace options we found:
- https://www.youtube.com/watch?v=5xwyVfLv8ZM. This is essentially a hack where you make a fake room and wall to calculate the solar energy, then you convert it to negative electricity.
- A base utility demand can be defined in the plants tab. The demand value can be negative. We can prescribe the input demand as the maximum possible kW the PV is capable of, input as a negative value, and create a schedule that accounts for time of day and seasonal performance.
Are these acceptable methods? If not, what is a better alternative? Merge hourly output data from our Trane model and from PVWatts (https://pvwatts.nrel.gov/)?
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5867 thumbs up
January 14, 2019 - 10:36 am
Don't do either one. If Trace does not model PV directly then it makes no sense to force it into the program. A PV system has no effect on the other building systems so there is no reason you should have to model it within the modeling software. In both scenarios above you would need to calculate the system output separately anyway. Neither method would be acceptable. Just use PV Watts and report the energy production. No need to merge the data.
Bo White
Senior Project EngineerNegaWatt Consulting
5 thumbs up
January 14, 2019 - 1:02 pm
Thanks, Marcus. I have a follow up question.
Our project is in California and has the following electric utility rates:
Should we just manually create an hourly $/kWh column based on the time of use charges (#1 above); multiple it by the PVWatts hourly energy output (in kWh); and ignore the demand charges and the non-bypassable charges (#s 2 and 3 above)?
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5867 thumbs up
January 14, 2019 - 2:30 pm
The typical way to claim renewable energy savings is to determine the output of the renewable system and then apply the virtual rate from the Proposed model (Total electric cost/total kWh).
If your software was able to directly model the PV system then I suppose you could apply the rate you describe. You can't do that manually or in a spreadsheet.