New York City research finds older buildings more energy efficient

This article was amended on February 1, 2014, 12.18 p.m. EST

One of the public presentations at the ASHRAE Winter Conference in New York City outlined some surprising findings about building energy efficiency. The findings are based on data gathered during the city’s requirement for buildings to declare their energy use.

On January 21, Constantine Kontokosta, Ph.D., P.E., deputy director with the NYU Center for Urban Science and Progress (CUSP) spoke in the concourse of the Javits Centre.

CUSP is a public-private organization that was an initiative of Michael Bloomberg, former mayor of New York. It exists to do research on “urban informatics,” using New York City as its laboratory and classroom and one of the centre’s focuses is on building energy efficiency. Thanks to New York City’s Law 84, CUSP has a lot of data to work with. Since 2011 the law has required that owners of any building in the city over 50,000 square feet have to submit data on their energy and water use every year. They use the EPA’s Energy Portfolio program to do so. Eight cities in the U.S. have some kind of building energy use disclosure policy.

Kontokosta explained that New York City’s building energy disclosure laws have now yielded three years’ of data on 18,000 properties. He noted that the city is unusual because its building stock is relatively old. Also, two-thirds of the buildings in the database are apartments and multi-family residential buildings.

Using energy unit intensity (EUI) as the measure (energy per square foot per year), Kontokosta’s team at CUSP has unearthed some factors about energy efficiency in commercial office buildings. While the research is in its early days, if borne out it will have important implications for building design.

For example, Kontokosta said, they have found from the data that buildings on “inside lots,” i.e. buildings attached to other adjacent buildings, are 9% more efficient than buildings that are freestanding or on the ends of a block.

They found that, while controlling for other factors, buildings constructed in the last 20 years are 40% less efficient than buildings constructed before the 1930s.

They found that the density of workers affects the energy use. For every person in a workplace, they found an 8% increase in EUI. However, as Kontokosta suggested, it’s complicated. Even though the EUI is higher, actually squeezing more workers in less space could overall be more energy efficient than if they were located in a larger area.

Another finding was that data centres added significantly to energy use. Every 10% of data space in a building added 34% to the building’s overall EUI.

Masonry buildings were more efficient than glass-and-steel buildings, and — surprisingly — LEED certified buildings (41 buildings in the database) — were no more energy efficient than the general stock. Energy Star-certified buildings were only 10% more energy efficient.

Kontokosta also said that that they are finding that the physical nature of buildings (i.e. their design and architecture) explain only 25% of the variations in their energy efficiency. Tenants and occupants have much more influence (50-60%) on the energy demand.

Interestingly, Kontokosta also observed that “no-one knows how big their building is.” There is a lack of standards on how to measure a building’s size, so, for example, some are including their basements, and others are not, The team is now working with LiDAR mapping technology to get a more accurate picture since in measuring energy use intensity it’s important to have accurate building size in order to make fair comparisons.

Kontokosta’s team were surprised to find that buildings with a high energy use intensity were demanding higher rents. Previously they had thought the opposite would be true (i.e. that developers and tenants would pay more to be in energy efficient buildings). He explained this by the fact that the more expensive buildings include a lot of amenities, and that these have an energy cost, such as corner offices and large fountains in their atriums.

The CUSP team is now turning its attention to studying water consumption, where they are finding a “huge variation” in multi-family residential buildings.

They also want to make the data more accessible to the public and are due to launch a program that will allow New Yorkers to log onto a web site to find out about the energy consumption of buildings in their neighbourhoods. Kontokosta said the idea is to present the information to the “consumers.” Like fast food restaurants having to declare their calorie counts, let the people decide what they want in buildings.

Surprising as many of the above results are, someone in the audience pointed out that there is a caveat to the CUSP research in that the data collected under Local Law 84 is provided by the building owners themselves, and there is no third party verification of it.

This article was amended on February 1, 2014, 12.18 a.m. EST