Page 119 - Designing for Zero Carbon - Case Studies of All-Electric Buildings

Energy Design Analysis and Energy Performance:
Modeling versus Post-Occupancy Measurements
Energy Use — Modeling
Energy modeling was carried out using Energy Pro, the mandated code compliance software in California. Per the District requirements for the project design process, computer modeling was done at certain stages of design to demonstrate that the new building would achieve the speci- fied target EUI. The design team also utilized the modeling for parametric studies to determine required energy efficiency characteristics of the building features necessary to meet this target EUI. A chart showing the annual modeled energy use of the final design is shown on the next page, along with a chart of the monthly modeled energy consumption broken down by category of use.
As noted above, PVWatts6 was used to estimate the annual energy produced by the high effi- ciency solar PV panels that could be fit on the two roof areas of the building. See the chart, Solar Photovoltaic System Performance, on p. 107 for the estimated monthly production as calculated using PVWatts.
Energy Use — Actual Measurement and Comparison to Modeling Results
Until August 2021, there was only one meter measuring the energy consumption of the existing building combined with that of the new middle school building. That month, a separate metering subsystem7 was installed for the new building, which measures the energy used on each circuit and stores the data in the system. Therefore, there is not yet detailed measured data available on the building performance to confirm that the ZNE design goal was achieved.
Some indication is possible, however, by using data collected by the one meter for the period 2015-2020. This meter recorded the total energy use in the existing building for four years before the middle school began occupancy in late summer of 2019. At that time, the data recorded by that one meter is the combination of the energy used by the two buildings for that school year (2019-2020) before classes were suspended in the spring of 2020.
An approximation of the energy use for the new building for that one school year can be made from this combined data by subtracting the yearly average of the energy consumption previously recorded for the existing building alone. This approximation of annual energy use by the new building totals 107,550 kWh, or 16.7 kBtu/sq.ft. These numbers are a bit higher than the modeled energy use. When detailed metered data becomes available in the next year, a more accurate comparison can be made.
Energy Production versus Energy Use: Zero Net Energy
Similarly, when the solar PV system is installed as tentatively scheduled for 2022, the recorded data will show if the measured energy use of the new building can be entirely offset by the system production. The top chart on p.107, Solar Photovoltaic System Performance, uses the estimated annual production calculated with PVWatts in the meantime. The bottom chart on that page, Cumulative Net Energy Performance, sums the net energy production each month to that of the month prior, so that the annual total would be exactly zero if the performance is zero-net- energy (ZNE). The approximations show the building theoretically performing just below ZNE. Actual data from the years 2022-2023 may be different.
6 National Renewable Energy Laboratory (NREL) calculator for estimating energy production of grid-connected solar photovoltaic (PV) energy systems. https://pvwatts.nrel.gov/
7 The eGauge unit combines an energy meter, data logger and a web server. https://www. egauge.net/commercial-energy-monitor/#overview
Designing for Zero Carbon: Volume 1
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SFUSD CLAIRE LILIENTHAL MIDDLE SCHOOL CASE STUDY NO. 5
(Opposite Page) Classroom interior showing operable win- dows for natural ventilation and daylighting.