ASHRAE 90.1-2007 G2.4

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I've asked a variation of this before, but I am still totally confused by
section G2.4 in 90.1-2007. I've asked earlier about whether Solar panels
can be used to calculate the % efficiency difference between the baseline
and proposed. I was pointed to pg 274 of green building design where it
plainly says "model systems directly in the proposed design energy model".
OK. Understood. But I am still bothered by G2.4. It SEEMS to say the exact
opposite but I can't make sense of it. I've read the user manual
explanation and it doesn't help me out at all.

The bldg will have solar panels generating about $20k worth of money a year.
ALL of it sold back to the electric company at 220% more than they are
charged per kwh. So it makes more sense to sell the energy he makes than to
use it. I've attached the two ES-D reports. Using the solar panel money I
am at 64% more efficient. Without them I am at 35%.

I know this assumes my models are accurate but can anybody help me make
sense of this?

Alan Crittendon, PE, LEED AP

Alan Crittendon's picture
Joined: 2011-09-30
Reputation: 0

I have never modeled a building that used solar panels and I have a LEED
question regarding this topic.

Can you include the utility cost savings of solar panels if you are
selling the energy instead of using it?



Otto Schwieterman's picture
Joined: 2011-09-30
Reputation: 200


The exception for G2.4 does seem to contradict itself. The phrase ?shall not be included in the proposed building performance? means the reported consumption totals for the proposed case would only reflect grid-purchased energy, thus allowing the design to take credit for renewable energy. Similar ?shall not be considered? language appears in the exceptions under Section where special lighting applications are exempted, but the intent is clearer in that context. The G2.4 language assumes the energy is produced and consumed on-site, but keep reading, you can still take LEED credit for your situation.

The G2.4 language is slightly misaligned (for lack of a better word) with the reporting options on the new EAp2 credit form. The credit form provides multiple ways to account for renewable energy, so modelers need to be sure they don?t accidentally take credit twice: directly in the model and again in the credit form. In your case where 100% of the on-site energy is sold to the grid, your BEPU report should reflect the default EM1 consumption, which should be the building?s grid-purchased energy. This is what you want.

NOTE TO ANYONE ELSE FOLLOWING ALONG: Alan set up a separate ?electric sale? meter called SEM1 to track all the PV energy sold directly to the grid; the PV array is tied only to this meter. The SEM1 meter is tied to a separate (higher) electric sale rate. Everything is itemized in the ES-D report.

For reporting purposes, here?s what to do on the LEED Form:

? Report the BEPU consumption values in Table EAp2-5.

? In Section 1.8, choose ?manual cost input?.

? Fill out Table L-1 with the values from SEM1.

NOTE: In Table EAp2-10, the credit form will deduct the Table L-1 ?annual energy generated? from the Table EAp2-5 total. Therefore, the form will report the building?s actual consumption in Table EAp2-5 and the post-PV consumption in Table EAp2-10. Calling it an ?energy use savings?, as the form does, may not seem true when the energy is sold directly to the grid, but I wouldn?t lose any sleep over it.

? Put the PV sale annual total in Table L-1 and Table EAp2-12 ? the form does not directly transfer the energy cost from L-1 to EAp2-12.

? Make sure you include a short narrative explaining the situation and the rates for purchased and renewable energy. The form does not allow you to indicate the PV sale rate, and the reviewer may attempt to verify your Table L-1 numbers using the grid-purchase virtual rate reported in EAp2-3. Reference your ES-D report since it will show all rates separately.

In short, LEED currently allows you to take credit for your project?s situation since it is based on net energy cost, not actual building consumption. Yay for capitalism, go Huskers, and long live Texas!


Dakota Kelley's picture
Joined: 2011-09-30
Reputation: 1