Direct consumption of fossil fuels by buildings, which is burned in water heaters, furnaces and other heating sources, accounts for nearly 10 percent of greenhouse gas emissions in the United States. Switching to an electricity system that provides heating with renewable energy sources rather than coal, oil and natural gas – a process known as building electrification or building decarbonisation – is an important step towards achieving the global net zero climate goals.
However, most building decarbonisation models do not account for seasonal fluctuations in energy demand for heating or cooling. This makes it difficult to predict what the eventual transition to cleaner, all-electric heating in buildings could mean for the nation’s electricity grid, especially during peak energy use.
A new study by researchers at Boston University School of Public Health (BUSPH), Harvard Chan School of Public Health (Harvard Chan School), Oregon State University (OSU), and the nonprofit Home Energy Efficiency Group (HEET) examined these seasonal changes in need in energy, and found that monthly energy consumption varies significantly and is highest in the winter months.
Published in Scientific reportsjournal Nature Portfolio, the study presented new simulations of several building electrification scenarios and found that this seasonal spike in winter energy demand will be difficult to meet with today’s renewables as buildings switch to low-efficiency electrified heating.
The findings highlight the need for more efficient home heating technologies, such as ground source heat pumps, to be installed in buildings.
“Our study reveals the extent of variation in building energy demand and the benefits of using highly efficient heating technologies to electrify buildings,” says study leader and corresponding author Dr. Jonathan Buonocore, associate professor of environmental health at BUSPH. “Historically, these fluctuations in energy demand in buildings have been driven largely by gas, oil and wood, which can be stored throughout the year and used in the winter. Electrified buildings and the electrical system that supports them must provide the same service of providing reliable heating in winter. More efficient electric heating technologies will reduce the electrical load on the grid and improve the ability to meet this heating demand with non-combustion renewable energy sources.’
For the study, Buonocore and colleagues analyzed building energy data from March 2010 to February 2020 and found that the total monthly average energy use in the U.S. — based on current fossil fuel use as well as future winter electricity use — varies by 1 .6 times, the lowest demand in May, and the highest in January.
The researchers modeled these seasonal fluctuations in what they call a “Falcon curve”—because the plot of monthly energy use is shaped like a falcon. The data show that winter heating demand increases energy use to the highest levels in December and January with a secondary peak in July and August due to cooling and the lowest levels in April, May, September and October.
The researchers also calculated the amount of additional renewable energy, specifically wind and solar energy, that would need to be produced to meet this increased demand for electricity. Without storage, demand response, or other grid load management tactics, to meet winter heating peaks, buildings would need a 28-fold increase in January wind production or a 303-fold increase in January solar.
But with more efficient renewables such as air source heat pumps (ASHPs) or ground source heat pumps (GSHPs), buildings would only need 4.5 times more winter wind generation or 36 times more solar – thus “flattening” the curve Falcon as less new energy demand in the electric grid.
“This work really shows that both demand-side and supply-side technologies have an important role to play in decarbonization,” said study co-author Dr. Parichehr Salimifard, an associate professor in Oregon State University’s College of Engineering. Examples of these technologies on the energy side are geothermal technologies for heating buildings and renewable energy sources that can provide energy at any time, she says, such as renewables combined with long-term storage, distributed energy resources (DER) at all scales and geothermal power generation where possible. “They can be combined with demand-side technologies, such as in buildings, such as passive and active building energy efficiency measures, peak load reduction and building energy storage. These building-level technologies can simultaneously reduce a building’s total energy demand by reducing both baseline and peak energy demand, as well as smoothing fluctuations in building energy demand and, consequently, smoothing the Falcon curve.”
“The Falcon curve draws our attention to the key relationship between building electrification technology choices and the impact of building electrification on our power grid,” says study co-author Zeyneb Magawi, co-executive director of HEET, a nonprofit climate solutions incubator. .
Magavi cautions that this study does not yet quantify this dependence based on measured seasonal performance curves for specific technologies, or for more detailed time scales or regions, and does not evaluate the many strategies and technologies that can help address the problem. All this should be taken into account when planning decarbonisation.
Still, Magavi says, this research clearly shows that “using a strategic combination of heat pump technologies (air source, ground source and grid) and long-term energy storage will help us electrify buildings more efficiently, economically and equitably. The Falcon Curve shows us a faster path to a clean, healthy energy future.”
“Our study shows that, given the seasonal fluctuations in energy use evident in the Falcon Curve, the drive to electrify our buildings must be combined with a commitment to energy-efficient technologies to ensure that efforts to decarbonize buildings maximize climate and health benefits,” says senior author study by Dr. Joseph G. Allen, associate professor of impact assessment science and director of the Healthy Buildings Program at the Harvard Chan School.
“Our work here shows a path to electrification that avoids dependence on fossil fuels and renewable fuels that can still pollute the air and possibly perpetuate disparities in air pollution exposure despite climate neutrality,” says Buonocore. “Avoiding these kinds of problems is why it’s important for health experts to be involved in energy and climate policymaking.”
