How Building Energy Efficiency Can Improve Air Quality in Cities

Topics: Energy Efficiency, green building, greenhouse gas emissions, building emissions, air quality

Chelsey Bipat
Author : Chelsey Bipat on July 28, 2020

Air pollution has been linked with many health problems, which include respiratory and cardiac illnesses. Also, a recent Harvard study found that coronavirus mortality is increased in regions with high levels of particulate matter. Air pollution is often associated with traffic, but a much larger source of emissions is overlooked. The transportation sector accounts for 28% of GHG emissions, but the building sector is responsible for 40%.

Buildings produce direct emissions when they use combustion equipment, such as diesel generators and natural gas boilers. They also produce indirect emissions when consuming electricity from power plants that burn fossil fuels. When buildings improve their energy efficiency, direct and indirect emissions are both reduced.


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Importance of an Energy Audit

Each property has a unique energy consumption profile, and the optimal combination of energy efficiency measures will vary. To identify the most suitable upgrades for a building, the best starting point is a professional energy audit. This way, building owners can know the cost and financial return of all potential upgrades before spending funds. An energy audit also helps owners avoid measures that are not effective in their building.

energyaudit-1

Since an energy audit analyzes the savings by energy source, it is possible to estimate the emissions reduction after the recommended building upgrades. The audit reveals two important pieces of information:

  • Energy savings per dollar invested.
  • Avoided GHG emissions per dollar invested.

Generally, the best results can be achieved by upgrading old furnaces and boilers that run with heating oil. This reduces not only the heating cost, but also the emissions per BTU. When many buildings upgrade their heating equipment, the cumulative effect can have a positive impact on urban air quality.

Depending on where a building is located, the estimated reduction of emissions may help qualify for a clean energy grant or low-interest loan. In New York City, properties over 25,000 square feet will be subject to an emissions reduction law starting from 2024. An energy audit can identify the most cost-effective measures to meet the target.

Switching Energy Sources to Cut Emissions

Energy efficiency measures can achieve better results when the energy sources are also optimized. For example, solar power is cost-effective in many parts of the US, and owners can claim a 26% federal tax credit for their renewable energy investment (as of 2020). Building owners can also switch from oil-fired boilers and furnaces to gas-fired units - natural gas has less emissions per BTU of heat delivered.

energysource

With high-efficiency heat pumps, building owners also have the option of going 100% electric and eliminating site emissions. Indirect emissions  remain, since fossil fuels still dominate the power grid. However, concentrating emissions at power plants is preferred over having them released directly in cities.

Building electrification has another important benefit: if the local grid starts using a larger share of renewable energy, indirect emissions are reduced automatically.

  • Assume you have a building that uses 100,000 kilowatt-hours per month, in a region where the power grid produces 0.8 kg of CO2 equivalent per kWh.
  • In this case, the indirect emissions are 80,000 kg CO2 equivalent per month.
  • However, if the grid reduces its emission intensity to 0.6 kg CO2 eq / kWh, the indirect emissions from this building are reduced to 60,000 kg per month.

Using electricity for space heating and hot water may not be viable in some buildings. However, switching from heating oil to natural gas can cut emissions by half in many cases. The following is a simplified example, where a 300,000 BTU/h boiler is upgraded from a 70% efficient oil unit, to a 90% efficient gas unit. According to the US Energy Information Administration (US EIA), heating oil releases 73.16 kg CO2 per million BTU, while natural gas releases 53.07 kg CO2 per million BTU.

Boiler Fuel

Capacity

Efficiency

Heat Input

Emissions

Heating oil

300,000 BTU/h

70%

428,571 BTU/h

31.35 kg CO2 /h

Natural gas

300.000 BTU/h

90%

333,333 BTU/h

17.69 kg CO2 /h

This example has been simplified drastically for demonstration purposes. In an actual building, it would be necessary to conduct energy modeling for each boiler to analyze emissions. However, the estimated emissions reduction is 44%, based on an hourly comparison with both boilers at full capacity.

The natural gas boiler in this example also reduces heating costs. New York pays $1.210 per therm of natural gas (100,000 BTU/therm), and 232.5 cents per gallon of heating oil (137,000 BTU/gallon). The oil boiler spends $7.27 per hour, while the gas boiler spends $4.03 per hour, which is 45% less.

This is a very simplified analysis, but it demonstrates how energy expenses and GHG emissions can be reduced simultaneously with energy efficiency. Building owners can help improve air quality by cutting emissions, while reducing their energy costs.

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