Page 35 - Designing for Zero Carbon-Volume 2_Case Studies of All-Electric Multifamily Residential Buildings

IVY SENIOR APARTMENTS
CASE STUDY NO. 1
Energy Performance and Operational Carbon: Post-Occupancy Measurement
Energy Use — Post-Occupancy Measurement
The project reached full occupancy in November 2021, making it possible to obtain one full year of energy performance data from the public utility. Combined with the monitored production data of the two solar energy systems, a direct comparison of the measured data with the modeled results would be possible. Unfortunately, the solar thermal system was not monitored during this first year, so the measured data of the total electric energy offset by this on-site renewable energy system is missing that one small component (likely only a 5% effect overall).
Comparison with Energy Modeling
The measured annual energy use based on the utility bills for the first year of full occupancy (December 2021- November 2022) was 185,451 kWh. This compares to the design modeling and estimation of 167,147 kWh, which includes the estimated reductions due to the two solar energy systems.
The actual performance of the building without these reductions is equal to the sum of the month- ly utility bill totals for the 12-month periood and the energy supplied by the two solar energy sys- tems, which offset a portion of the building’s energy use. During this period, the solar PV system produced 81,937 kWh, slightly higher than that predicted using PV-Watts. Therefore, the total measured energy use for the building was 267,388 kWh over that 12-month period, plus that small amount offset by the unrecorded energy supplied by the solar thermal system.
If the latter is assumed to be approximately equal to that estimated during the design phase, namely 15,000 kWh, then the building consumed close to 282,000 kWh during the 12-month period, 12/2021 - 11/2022. This converts to an actual EUI for the building of 24.4 (kBtu/sf-yr). The measured performance overall is therefore slightly higher than that predicted by the energy modeling, with the solar PV system actually providing more electric energy than estimated.
Energy Production versus Energy Use
Both the building overall net energy use (the energy use from the utility grid) and the energy produced by the solar PV system were metered on a monthly basis for the 12-month period, 12/2021 - 11/2022. The Base Building Energy Use was determined as the sum of the net energy from the utility grid, the on-site energy produced by the solar PV system plus 5% to account for the energy provided by the solar thermal system.
The results are shown in the graph on the next page.
Designing for Zero Carbon: Volume 2
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