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In 2022, Princeton voters supported a referendum to fund the replacement and/or repair of roofs and equipment over four years at all six district schools, as well as other structural repairs, to ensure a safe and healthy learning environment for our students.

Last summer, roof work was started at two elementary schools: Littlebrook and Community Park, with the plan to continue this effort at other school buildings in the upcoming summers. As part of the roof upgrades, insulation was increased. At Community Park and Littlebrook, the upgrades resulted in average R-values between 45 and 52 for the new roofs. These upgrades are important for a conducive learning and working environment, but an early peak at the data shows signs of another benefit: energy savings.

For each of these two elementary schools, the following graphs show natural gas usage (pink line) and electricity usage (purple line) over 2.5 years. Both schools show a markedly decreased natural gas usage in the winter of 2023, as compared to the prior two winters.

Some of this difference can be explained by the milder winter we’ve experienced in 2023. To rule out these effects, we can look at this data another way. Energy Use Intensity (EUI) allows us to observe the energy load of each building as a function of its size and is calculated by dividing the total energy consumed by the building in one year (electricity and natural gas, converted to kBtu) by the total gross floor area of the building. Weather-normalized EUI, and other metrics, are adjusted for the actual weather in our area and allow a better comparison from year to year.

Below are the graphs of weather-normalized EUI for each of these schools over the same time period. For each of these schools, a small drop in the Site EUI can be observed in the last two data points.

While this drop is mild, it is important to keep in mind that each data point in these graphs represents a year of data. To truly measure the impact of the roof and insulation upgrades on energy use with weather-normalized EUI, a year of data is necessary. Please check back to learn if this trend continues. Sustainable Princeton prepares energy reports for the district twice a year – in the Spring and Fall – and the Fall 2023 report should provide this answer.

Energy costs for the schools account for 2% of the operating budget, or approximately 1.5 million dollars a year. The District is committed to lowering energy use to reduce both the school’s carbon footprint and the District’s operating expenses.

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