Comparing Energy Use and Emissions in Multifamily and Office Buildings

Multifamily and office buildings represent the vast majority of skyscrapers in New York. Of all the built area subject to the Benchmarking Law (Local Law 84 of 2009), 55% is in the multifamily sector and 18% is in the office sector. Therefore, by understanding energy consumption patterns in these types of properties, it is possible to determine which energy efficiency measures are effective. Additionally, multifamily and office buildings are responsible for 90% of energy consumption in properties subject to LL84, so improving their performance can greatly help meet New York's emissions reduction target – 80% by 2050.

An important difference between the two types of buildings is that the main energy source in the multifamily sector is natural gas, while in the office sector it is electricity. This can largely be explained by the increased use of domestic hot water in the multifamily sector, in contrast to the increasing role of sockets and lighting in the office sector. It is important to note that space heating is the largest load in both cases.

After multifamily and office buildings, public elementary and secondary schools also represent an important fraction of New York's floor area subject to LL84, accounting for 7% of total square footage. In its latest report, the Urban Green Council considers 1.16 billion ft2 of multifamily space, 380 million ft2 of office space and 140 million ft2 of K-12 public school space. All other private properties account for 330 million square feet and all other public properties account for 90 million square feet.

Detailed energy consumption for each type of building

In its 2017 Energy and Water Usage Report, the New York Urban Green Council conducted a detailed analysis of energy consumption by source and application. The latest benchmarking data available refers to 2015 and the energy sources are broken down as follows:

It is important to note that the use of #5 and #6 fuel oils is illegal as of 2015, and #4 is expected to be phased out by 2030. This decision was made by the New York Department of Environmental Protection after finding that only 1 % of the city's buildings used these fuels, but they were responsible for 86% of soot emissions.

While there are always exceptions, most space heating and domestic hot water systems run on natural gas or fuel oil, while other loads are typically electric. For a given amount of energy delivered, electricity is much more expensive than fossil fuels in New York. The table above presents a breakdown of energy consumption by source, but the analysis was also carried out by application:

Note how space heating and DHW represent a much smaller percentage of energy consumption in the office sector, which explains why electricity is the predominant energy source in buildings of this type.

Another key difference between the multifamily and office sectors is energy use intensity (EUI), measured in thousands of BTUs per square foot (kBTU/sf). Although the multifamily area is much larger than the office area, the EUI is about 50% higher in office buildings; New York multifamily buildings use 125 kBTU/sf, while office buildings use 186 kBTU/sf.

Carbon dioxide emissions for each building sector

Given that multifamily and office buildings represent the majority of assessed floor space and energy consumption, it should come as no surprise that they are also a major source of emissions in New York. In particular, most emissions come from the combustion of fossil fuels for space heating and domestic hot water applications. Given the large usable area of ​​multi-family buildings and the widespread use of heating appliances, these represented 5,970,000 metric tons of CO2, according to the latest available reference data (2015). The commercial sector was responsible for 4,599,000 metric tons of CO2.

Regarding emissions by energy source, electricity leads with a total of 5,543,000 metric tons of CO2, followed by natural gas with 4,204,000 metric tons of CO2. As with energy use, natural gas is responsible for the majority of emissions in the multifamily sector (46%), while electricity is responsible for the majority of emissions in the commercial sector (63%). Although heating oils produce fewer emissions than electricity and natural gas, with 2,003,000 metric tons of CO2, consider that their emissions per unit of energy delivered are much higher than those of natural gas.

Data collected through the Bigger, Greener Buildings Plan (Local Laws 84 and 87) has provided unique insights into how New York uses energy, enabling a breakdown of energy consumption and emissions that was not possible before. It is very likely that a future version of the New York Energy Conservation Code will introduce edits and changes based on the results of benchmarking (LL84) and energy audits (LL87).