Reducing Building Emissions: Replacing Heating Fuels with Electricity

Jahnavi Sajip
Author : Jahnavi Sajip
June 11, 2021
5 Minutes Read
  
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    Key Takeaways

    - Buildings can reduce their emissions by lowering energy consumption, but switching to cleaner energy sources is also a viable option.

    - Natural gas is cleaner than #2 fuel oil for a given heating output, and electric heating with a high-efficiency heat pump is cleaner than gas heating.

    - Resistance heating with electricity from the grid can actually be more polluting than natural gas heating, due to the high kWh consumption.

    - Space heating emissions can be minimized with high-efficiency heat pumps, especially when combined with clean onsite generation.

    Starting from 2024, NYC buildings will be forced to meet certain emission limits. Otherwise, they will be charged a penalty of $268/year for every metric ton of CO2 equivalent above the limit. Emissions can be reduced by improving energy efficiency in buildings, but switching to cleaner energy sources is also a viable strategy. For example, natural gas is a cleaner option than #2 fuel oil, and onsite solar power is cleaner than electricity from the grid.

    • All energy sources have a price, which can take the form of a utility tariff or an ownership cost.
    • For example, solar panels produce electricity with a free energy input, but they involve an initial investment and ongoing maintenance.

    Energy consultants will generally recommend energy efficiency first, and switching to cleaner sources as a second step. If a building can become more efficient first, onsite generation can cover a larger fraction of its energy needs.


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    In this article, we will discuss the potential savings when buildings use efficient electric heating instead of fossil fuel combustion. Electric resistance heaters are not viable for many building owners due to their operating cost, especially in places with high electricity tariffs like NYC. However, there are now high-efficiency heat pumps that can match the cost of gas heating.

    Calculating Building Emissions Under Local Law 97

    building emissions

    Local Law 97 of 2019 was part of the Climate Mobilization Act, which has often been called the NYC Green New Deal. The law introduces building emission limits that will be applied from 2024, and the specific limit for a building depends on its occupancy classification and square footage. For example, a 200,000-sf building classified as Business Group B will be subject to a limit of 1,692 tCO2e/year in 2024, but an equally sized building classified as Residential Group R-2 has a lower limit of 1,350 tCO2e/year.

    The law also has emission factors for the different energy sources used by buildings. For example, 100,000 kBTU of #4 fuel oil would add 7.53 tCO2e to building emissions, while 100,000 kBTU of natural gas add 5.31 tCO2e. Assuming a constant energy consumption, switching from #4 fuel oil to natural gas would reduce emissions by almost 30% in this case. 

    With a conversion to electric heating, emissions can decrease or increase depending on the technology used. For example, an electric resistance heater using electricity from the grid produces much higher emissions than a geothermal heat pump with a combination of grid electricity and solar power.

    Estimating Building Emissions with Electric Heating

    heat pump

    As an example of how electric heating can reduce building emissions, we will estimate the metric tons of CO2 equivalent for the following heating equipment, assuming an output of 500,000 kBTU in all cases. Keep in mind this is a very simplified calculation, which has the goal of demonstrating how heating emissions compare with different technologies - only energy modeling can yield accurate results.

    • An oil boiler (#2 fuel oil) with 87% efficiency.
    • A natural gas boiler with 90% efficiency.
    • An electric resistance heater.
    • An air source heat pump with a COP of 3.
    • A geothermal heat pump with a COP of 5.

    The following table calculates the energy input required to achieve 500,000 kBTU of heating in all five cases. The energy input is then multiplied by the corresponding emissions factor from LL87:

    Heating System

    Energy Input

    LL87 Emissions (tCO2e)

    Oil boiler

    574,713 kBTU

    42.65 tCO2e

    Gas boiler

    555,556 kBTU

    29.51 tCO2e

    Electric resistance heater

    146,542 kWh

    42.35 tCO2e

    Air-source heat pump

    48,847 kWh

    14.11 tCO2e

    Geothermal heat pump

    29,308 kWh

    8.47 tCO2e

    The corresponding emission factors from LL97 are 0.00005311 tCO2e/kBTU for natural gas, 0.00007421 tCO2e/kBTU for #2 fuel oil, and 0.000288962 tCO2e/kWh for grid electricity. Note how the oil boiler and the electric resistance heater have roughly the same emissions, and natural gas heating is around 30% cleaner than both. The air-source heat pump produces around 52% less emissions than the gas boiler, while the geothermal heat pump produces around 71% less.

    • In this example, we assumed that all electricity comes from the NYC grid for the three electric heaters considered.
    • Lower emissions can be achieved if a building generates electricity onsite with clean technologies like solar panels or wind turbines.
    • For example, if the air-source heat pump gets 15,000 kWh of solar electricity, the emissions are only calculated for the remaining 33,847 kWh. Instead of 14.11 tCO2e, the ASHP would be producing 9.78 tCO2e.

    Electric heating systems have the flexibility to switch from grid electricity to clean power generated onsite, while oil and gas boilers are limited to their respective fuels. High-efficiency heat pumps could play an important role in decarbonizing NYC buildings, since space heating is the top energy expense for many properties.

    Conclusion

    Building emissions can be reduced by upgrading from combustion heating to electric heating. However, this only applies for high-efficiency heat pumps, since resistance heaters can be even more polluting than gas boilers. Even if a resistance heater uses clean power generated onsite, its high energy consumption is still a disadvantage. Depending on its design, a heat pump can consume 2 to 6 times less electricity than an equivalent resistance heater, and emissions are reduced in the same proportion.

    Tags local law 97 | LL97 | building emissions law | electric heating | heat pumps

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