To control energy consumption effectively it must first be measured, since that is the only way to establish energy efficiency baselines and targets. However, knowing how much energy is consumed is not enough - targeted measures can only be implemented with a detailed breakdown of energy consumption.
In 2016, the Urban Green Council (NYC Chapter of the US Green Building Council) published a detailed study on how energy is used in New York City. The data for this study could be gathered thanks to a pair of New York City laws that were published in 2009:
Local Law 84 (LL84), which requires energy and water usage reports for all buildings with at least 50,000 ft2 of floor area. In the case of properties with multiple buildings, reports are also required if total floor area is at least 100,000 ft2.
Local Law 87 (LL87), which requires that buildings subject to LL84 carry out an energy audit every 10 years. Buildings are split into groups that each contain 10% of the total number, and a different group submits their energy audit results each year.
Thanks to these laws, the NYC Mayor’s Office of Sustainability has obtained a detailed breakdown of energy consumption in city buildings. There is a wealth of information on how energy consumption is broken down by source, function and type of building.
It is important to note that LL84 only covers 2% of NYC buildings, but their total floor area represents 42% of the city’s total, equivalent to around 2.3 billion ft2 of built environment. Multifamily buildings represent most of this floor space (28%) followed followed by office buildings (10%). All other building types subject to LL84 make up the remaining 4% of floor area.
Of all energy consumption in the benchmarked buildings, 54% corresponds to multifamily buildings and 33% corresponds to office buildings. In terms of energy source, consumption is broken down as follows:
Electricity = 59%
Natural Gas = 24%
Fuel Oil = 11%
District Steam from Con Edison = 6%
The top five energy uses identified in the study were, in decreasing order: space heating, plug loads, lighting, space cooling and water heating. Together, they account for 79% of energy consumption in all NYC buildings. However, their breakdown is different for multifamily and office buildings.
1) Space Heating
Space heating represents the largest use in NYC buildings, and most consumption is concentrated in the multifamily residential sector. Steam-based distribution systems are still the most common in New York City, despite the fact that newer and more efficient technologies are normally installed in new buildings. Hot water boilers with hydronic piping are the second most common configuration after steam-based systems.
Although there are significant energy savings to achieve by upgrading from steam to hot water systems, the conversion cost is high. Property owners can take advantage of building renovations for heating system conversions, since the upgrade is much less disruptive when another major project is being carried out.
2) Plug Loads
Plug loads represent the second largest energy use in NYC buildings overall, and are the largest energy use in office buildings. Given the wide range of loads that can be connected to electrical receptacles, obtaining a detailed breakdown has proven a challenge. However, the building types where these loads consume the most energy have been identified:
Financial institutions and banks = More than 5 kWh/ft2 per year
Hospitals = 5 kWh/ft2 per year
Office buildings = 2.7 kWh/ft2 per year
In all other building types analyzed, plug loads account for less than 2 kWh/ft2 per year. The energy consumption density of plug loads can be expected to continue increasing as smart appliances reach a larger market.
There is a considerable opportunity to improve lighting efficiency in New York City. Lighting in multifamily residential properties is very inefficient: around 40% consists of incandescent and T12 fluorescent lighting. Office lighting is more efficient, composed mostly of compact fluorescent lights and higher-efficiency linear fluorescent technologies like T5 and T12.
LED lighting has not captured a large share of the market yet, and it has a significant energy saving potential: above 80% when it replaces incandescent lamps, and up to 50% when it replaces fluorescent lighting.
Lighting controls also have a high potential to save energy in NYC buildings. Energy audits carried out according to LL87 revealed that most lighting is still controlled manually, and frequently left on when not needed.
4) Space Cooling
The data collected thanks to LL84 and LL87 revealed that 40% of space cooling in NYC buildings is accomplished by window-type or through-the-wall air conditioning systems. These are the most inefficient types available, since they disrupt the building envelope by requiring an opening for their installation. The energy waste associated with these space cooling systems is estimated to cost between $130 and $180 million per year, equivalent to between 375,000 and 525,000 tons of CO2 emissions. Significant energy savings could be achieved by upgrading these units to split-type air conditioners or heat pumps, which eliminate the gap in the building envelope.
Space cooling systems in large office buildings tend to be more efficient, since they are based on water-cooled chiller plants. These normally consume less than half the energy required by window-type and packaged terminal air conditioners, assuming the total space cooling load is the same.
5) Water Heating
The main energy source for water heating is natural gas, followed by fuel oil and district steam from Con Edison. Electric heating is very rare, given the high cost of electricity in NYC.
Tankless water heaters are promising energy-saving technology, since they eliminate piping and standby losses. Electric heat pumps are also a promising alternative, since their superior efficiency offsets the high cost of electricity and allows them to compete with gas and oil in terms of cost, without the emissions. Heat pumps can also benefit from low cost off-peak electricity from Con Edison, storing hot water in an insulated tank for hours when electricity is more expensive.
Space heating, plug loads, lighting, space cooling and water heating represent almost 80% of energy consumption in New York City. Upgrades that improve heating efficiency have the highest potential to reduce energy consumption and emissions, since water and space heating add up 37% of energy consumption, and fossil fuels account for more than 90% of heating energy.
LED lighting upgrades complemented with automatic controls also represent a significant energy-saving opportunity, as well as space cooling upgrades that replace window-type air conditioners or PTACs.
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