If a project installs a PV system on a multi-family building that is designed to serve both the in-unit loads but also common space loads and exterior loads - including lighting, pools, fountains, detached garages, etc. - how should the output from this PV system be counted? Should the PV output used in the EA 10 calculation be reduced? Or should the common space loads and exterior loads be included in the annual reference electric load?
For low-rise multi-family buildings, the scope of EA 10 is only meant to include the primary loads of the units. If a PV system is installed and designed to serve common spaces or exterior loads, the PV output should be discounted for the purposes of EA 10. Specifically, the project team (including the PV designer) should estimate the electricity consumption associated with both the in-unit and relevant common or exterior loads that are served by the PV system. The PV output used in EA 10 should be weighted based on the estimated percentage of the total electricity consumption in the home. For example, if the estimated in-unit electricity consumption is 80,000 kWh/year and the estimated electricity consumption of exterior loads (e.g. pool, lighting, detached garage) is 20,000 kWh/year, then only 80% of the PV output should be counted in the EA 10 calculation.
**Updated January 1, 2014
For multi-family buildings using the performance path (EA 1) and modeling the building unit-by-unit, use a pro-rated approach to assign PV to each individual unit. Use the following approach: (a) calculate the kWh output for the entire PV system; (b) calculate the kWh per square foot of conditioned spaces based on the total building square footage; (c) estimate the PV output for each unit by multiplying the unit floor area by the kWh per square foot calculated in part b.
For multi-family buildings using the performance path (EA 1) and modeling the whole building, if the PV is serving an ancillary load that is not already included in the energy model, this ancillary load must be added to the total loads in both the rated and reference building.
For multi-family buildings using the prescriptive path (EA 10) and a whole-building approach, any ancillary loads served by the PV system must be added to the annual reference electric load before doing the calculation to determining percent savings.
For multi-family buildings using the prescriptive path (EA 10) and a unit-by-unit approach, use the following approach: (a) calculate the kWh output for the entire PV system; (b) calculate the kWh per square foot of conditioned spaces based on the total building square footage; (c) estimate the PV output for each unit by multiplying the unit floor area by the kWh per square foot calculated in part b; and (d) use this pro-rated output in the calculation in EA 10.