New York City has publicly posted 2011 energy benchmarking results for 2,065 large commercial properties representing more than 530 million square feet, marking the first time any US city, state or county has disclosed private-sector building energy data from a mandatory policy.
The database includes site energy use intensity (EUI), a measure of the energy used at the site on a per square foot basis; the weather-normalized source EUI, which takes into account generation and distribution losses; greenhouse gas emissions; water per square foot, and the Energy Star scores for buildings, where such a rating is applicable.
The New York City Local Law 84 Benchmarking report, which summarizes the data, found that if all comparatively inefficient large buildings were brought up to the median EUI in their category, the energy consumption in the city’s large buildings could be reduced by roughly 18 percent and greenhouse gas emissions by 20 percent. Large buildings are responsible for 45 percent of New York City’s carbon emissions, the report said.
Although many factors are at play, newer office buildings in the city tend to use more energy per square foot than older ones, the report said. The city compared buildings in 20-year stretches – 1970-1990 versus 1990-2010, for example – and found that each 20-year stretch was less efficient than the one before.
Older buildings tend to have higher Energy Star scores than newer buildings for a number of reasons, including less extensive ventilation systems, better thermal envelopes, and less dense or energy intensive tenant occupations. However, measurement per square foot doesn’t necessarily reflect efficiency in terms of energy per unit of economic activity occurring in buildings, the report said.
The report found larger office buildings tend to be more energy intensive than smaller ones. Conversely, smaller multi-family buildings tend to be more energy intensive than larger ones.
The report also found that the city’s buildings have a median Energy Star score of 64 out of 100.
The first year’s benchmarking report on 2010 data, which was released last month, showed energy intensity varies dramatically among the same types of buildings, with the worst performing buildings using three to five times more energy per square foot than the most efficient. At the time, the raw 2010 data was not disclosed to the public.
The disclosure of energy use in buildings is the cornerstone of New York’s Greener, Greater Buildings Plan, which targets energy efficiency in large existing buildings. GGBP consists of four regulations, including the Local Law 84 enacted in 2009, which requires that large buildings annually benchmark their energy and water use.