Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
The language of G2.4 in 90.1-2007 was not the best so we tried to clean it up some in 90.1-2013 (although reading the revised language it may not be the clearest either).
In my opinion, this is that paragraph means:
The energy costs for the proposed do NOT include any energy generated by PV. That makes sense, no energy cost for electricity generated by the PV. So if your building needs 100,000 kWh and the PV generates 30,000 kWh. You would only have the proposed building performance energy cost based on 70,000 kWh.
The baseline does not include PV in the model, so what energy source is used to satisfy the electric load for the building. Well the "backup" energy source for PV would be the electric utility. So this means that the entire baseline building performance energy cost is based on the building without PV. So using the same numbers as above, if the building needs 100,000 kWh, since there is no PV in the baseline model, the energy cost for the baseline should be based on 100,000 kWh.
Just like always, the difference between the baseline and proposed is the credit received.
For a non PV case, the "backup" concept may be more logical, for site recovered heat used to preheat water going into a gas boiler, if the site recovery was not available, more gas would be consumed so the "backup" source would be gas.
Please keep in mind that this is just my opinion and not anything official from ASHRAE.
| | 2 | No.2 Revision |
The language of G2.4 in 90.1-2007 was not the best so we tried to clean it up some in 90.1-2013 (although reading the revised language it may not be the clearest either).
In my opinion, this is that what paragraph means:
The energy costs for the proposed do NOT include any energy generated by PV. That makes sense, no energy cost for electricity generated by the PV. So if your building needs 100,000 kWh and the PV generates 30,000 kWh. You would only have the proposed building performance energy cost based on 70,000 kWh.
The baseline does not include PV in the model, so what energy source is used to satisfy the electric load for the building. Well the "backup" energy source for PV would be the electric utility. So this means that the entire baseline building performance energy cost is based on the building without PV. So using the same numbers as above, if the building needs 100,000 kWh, since there is no PV in the baseline model, the energy cost for the baseline should be based on 100,000 kWh.
Just like always, the difference between the baseline and proposed is the credit received.
For a non PV case, the "backup" concept may be more logical, for site recovered heat used to preheat water going into a gas boiler, if the site recovery was not available, more gas would be consumed so the "backup" source would be gas.
Please keep in mind that this is just my opinion and not anything official from ASHRAE.
