Page 102 - Designing for Zero Carbon-Volume 2_Case Studies of All-Electric Multifamily Residential Buildings

CASE STUDY NO. 4
THE PALO ALTO APARTMENTS
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Designing for Zero Carbon: Volume 2
Energy Performance and Operational Carbon: Post-Occupancy Measurement
Energy Use — Post-Occupancy Measurement
Palo Alto Utilities, the department that operates utility services for the City of Palo Alto, provided energy use data for a 12-month period beginning in February of 2022. The energy provided by the public utility as recorded in the bills, plus the energy provided by the on-site solar PV system, was the energy used by the project buildings and common garage, including the four EV charg- ing units that were installed and operational.
The project energy use in 2022, notably including EV charging, totaled 123,000 kWh, more than double that predicted by the energy modeling software for the two buildings alone. The actual EUI for the project in that 12-month period was 18.6 kBtu/sq.ft. per year. See the graph on the opposite page (top).
While the large difference is attributable, in some degree, to the use of the four EV charging units, it is also likely due to the fact that the tenants are not paying for the electricity used. Energy use is currently included in the rental charges. The developer, which is still managing and maintaining the property, plans to install submeters for each apartment and for the common areas in order to remedy this situation. In the future, the energy use totals for the buildings alone will be accurately totaled and can be compared to the predicted EUI in a more meaningful way. The reporting of the individual energy use to each tenant is expected to reduce the energy consumption significantly.
Energy Production versus Energy Use
For the same period of time, the solar PV system was experiencing the problems noted above with the inverter operation, which led to a sizable reduction in the output and the contribution by the solar PV system. The net result was a shortfall of about 35% from the predicted amount, causing the project to fall well short of the predicted ZNE performance. With the correction of the inverter problem, it is expected that the energy produced by the solar PV system will align with the building energy use, particularly if the energy use for EV charging, expected to be substantial in the next few years, is accounted for separately.
The graph on the opposite page (bottom) demonstrates this expectation to some extent. In this chart, the actual energy use of the project for 2022, including just four EV chargers, is plotted with the most productive year of data for the solar PV system (2019) prior to the inverter failures. In addition, a plot of the modeled energy production (the ideal expected amount) of the solar PV system is superimposed on these two data plots. As can be seen, there is a likely balance of energy production with energy use that could result in achieving the original goal of ZNE perfor- mance for the buildings.