Comparing Energy Use and Emissions in Multifamily and Office Buildings

Multifamily and office buildings represent the vast majority of high-rise buildings in NYC. Of all building floor 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. In addition, multifamily and office buildings account for 90% of energy consumption in properties subject to LL84, so improving their performance can greatly help towards the NYC emissions reduction goal - 80% by 2050.

An important difference between both building types is that the main energy source in the multifamily sector is natural gas, while that of the office sector is electricity. In great part, this can be explained by the higher usage of domestic hot water in the multifamily sector, in contrast to the increased role of plug loads 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, K-12 public schools also represent an important fraction of NYC floor space 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 area, 380 million ft2 of office area, and 140 million ft2 of K-12 public school area. All other private properties add up 330 million ft2, and all other public properties account for 90 million ft2.

Breakdown of Energy Consumption for Each Type of Building

In its 2017 Energy and Water Use Report, the NYC Urban Green Council carried out a detailed breakdown of energy consumption by both source and application. The latest benchmarking data available is for 2015, and the energy sources are broken down as follows:

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

Although there are always exceptions, most space heating and domestic hot water systems run with 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 NYC. The table above provides energy use breakdown by source, but the analysis has also been carried out by application:

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

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

Carbon Dioxide Emissions for Each Building Sector

Since multifamily and office buildings account for the largest share of benchmarked floor area and energy consumption, it should come as no surprise that they are also a key source of emissions in NYC. In particular, most emissions come from fossil fuel combustion for space heating and domestic hot water applications. Given the sheer floor area of multifamily buildings and the ample use of heating appliances, they accounted for 5,970,000 metric tons of CO2 according to the latest benchmarking data available (2015). The commercial sector accounted for 4,599,000 metric tons of CO2.

With respect to 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. Just like with energy usage, natural gas accounts for the largest share of emissions in the multifamily sector (46%), while electricity accounts for most emissions in the commercial sector (63%). Although heating oils produce less emissions than both 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.

The data gathered thanks to the Greener, Greater Buildings Plan (Local Laws 84 & 87) has provided unique insights on how NYC uses energy, allowing a breakdown of energy consumption and emissions that had not been possible before. It is very likely that future version of the NYC Energy Conservation Code will introduce editions and amendments based on the results on benchmarking (LL84) and energy audits (LL87).