Page 77 - Designing for Zero Carbon-Volume 2_Case Studies of All-Electric Multifamily Residential Buildings

The energy modeling analysis shows that this representative “Other” building would improve its annual energy performance from an estimated EUI of 47.8 to an improved EUI of 19.6 (kBtu/sf per year) even with conventional retrofit measures. Again, the improvement would be greatest in the energy consumed for heating and DHW, even while eliminating the entire use of natural gas for these purposes.
Energy Performance and Operational Carbon: Post-Occupancy Measurement
Energy Use — Post-Occupancy Measurement
The REALIZE-CA team was able to obtain the aggregate total energy-use data from the electric utility company (Southern California Edison) for all the apartment units on the site. This data did not include the energy used by the community building or some exterior lighting, so the totals slightly understate the total project energy use. Nevertheless, the total energy use recorded for all the apartments in 2022 was 543,822 kWh, which translates to an EUI equal to 39.7. 140,554 kWh of this energy use was offset by that portion of the solar PV system dedicated to the apart- ments, resulting in an equivalent reduction in EUI of 10.3. Monthly totals for the aggregate en- ergy use by all the apartments in 2022 are shown in the graph on the next page.
The actual energy use data of individual apartments was also obtained for eight units, includ- ing three units in each of the four-unit Buildings 615 and 619. The relative effectiveness of the retrofit measures used for these demonstration buildings also cannot really be estimated based on this data since the retrofit of these particular buildings was ongoing while the utility bills were being reported and recorded. Furthermore, data is not yet available for these buildings for any of the post-retrofit period (after June 2022). Therefore, the measured energy performance of these buildings is not reported in this case study.
Comparison with Energy Modeling and Operational Carbon
The Phase 1 energy modeling, which includes all apartments on the site, cannot yet be com- pared with the actual performance data from 2022 as represented by the chart at the top of the next page, since the retrofit construction was ongoing for a significant part of this year. The energy performance was “in transition” to lower numbers when the retrofit work was finally com- pleted in May 2022. One year of additional energy-use data for all the apartments will provide more information about the relative effectiveness of the various retrofit measures.
The Phase 2 energy modeling was limited to two buildings, as discussed above, and the mea- sured energy performance data could only be collected for only three apartment units in one of those buildings, Building 619. The missing data for the one apartment unit is significant for any comparison of modeled versus actual energy use for Building 619. It is a large apartment unit with exposure on three sides plus the roof surface.
Energy Production versus Energy Use
The aggregate total of energy used by all the apartment units on the project site is usefully com- pared to the on-site renewable energy generated by the solar PV system. This comparison is shown in the graph at the bottom of the next page (p. 64). The solar PV system provided 35% of the energy used by the apartment buildings in 2022.
Both the actual monthly amount of electric energy provided by the solar PV system and the estimated amount modeled using the PVWatts calculation method are also shown in the graph on the next page. The system underperformed in 2022 compared to that predicted by PVWatts, primarily because of the large amount of dust generated by nearby agricultural activities.
Designing for Zero Carbon: Volume 2
63
VERA CRUZ VILLAGE
CASE STUDY NO. 3