Heat pumps drive rapid growth in WNC’s peak electricity demand

COLD COMFORT: Since 2006, electric heat pumps have replaced over 12,000 oil- or propane-fired furnaces in WNC. While the heat pumps can be highly efficient at moderate temperatures, engineers and energy industry experts say they are less so when the mercury drops below freezing. Data from the Energy Innovation Task Force and Duke Energy; graphic by Scott Southwick

The cold front that blew through Western North Carolina Jan. 6, leaving snow and frigid temperatures in its wake, was a poster child for peak energy demand, says energy industry consultant Brad Rouse.

As temperatures hovered below 10 degrees at 9 a.m. Jan. 8, the region was drawing 1,042 megawatts from the electrical grid, according to data from the U.S. Energy Information Administration. At that hour a week earlier, with a low temperature of 28 degrees, electrical demand sat at 546 MW, or just over half the demand for the frigid morning of Jan. 8. That comparison, Rouse wrote on Facebook, shows “what a real cold snap can do to us here in the Asheville area.”

Regardless of the day, time or outside temperature, Duke Energy is legally required to meet the region’s need for electricity. When the company sought permission from the state Utilities Commission last year to replace the aging, coal-fired Lake Julian power plant, Duke proposed building two 280-MW gas-fired generators, plus a 186-MW unit to help meet peak demand. The regulators approved the first two generators but told the company to work with the community on ways to delay or eliminate the need for the third unit.

In April, the Energy Innovation Task Force — a partnership comprising Duke Energy, the city of Asheville, Buncombe County and representatives of local businesses and nonprofits — began meeting to develop strategies to reduce peak demand. The group first looked at data provided by the company to gain a better understanding of why peak demand has more than tripled since 1970. One key factor, Rouse told the task force in December, is the number of households converting their oil- and propane-powered heating systems to electric heat pumps during that period.

It had previously been assumed that development and population growth were driving the increase in peak demand, says task force member Brownie Newman. But after analyzing the data, the task force realized that’s “not really accurate,” notes Newman, the newly elected chair of the Buncombe County Board of Commissioners. The increase in peak demand from uses other than heating (such as lighting and appliances) is relatively insignificant, the task force’s Peak Reduction Work Group concluded.

Pumpin’ it up

“What we call a heat pump is an air-conditioning unit that has been circuited to provide heat to the inside of a building, and it does that by cooling the outside,” Asheville engineer Bob Wiggins explains. Down to about 40 degrees, he says, the technology is highly efficient. But below that point, the outside air contains little heat, so cooling it gets harder, and the heat pump struggles to produce enough warmth.

For this reason, notes Wiggins, these systems also include “heat strips” inside the ductwork to generate additional heat when the outside air is very cold. The heat strips warm the air by means of electrical resistance — the same technology found in notoriously energy-hungry electric baseboard heaters. According to the website Energy.gov, resistance-type electric heaters use about twice as much energy to operate as typical air-to-air heat pumps.

Thus, precisely when the need for heat is at its greatest, electric heat pumps are at their least efficient and use the most power. Meanwhile, these systems are increasingly popular in residential buildings.

Between 2005 and 2015, 12,300 homes in Buncombe County converted to electric heat from oil or propane, according to a report prepared by the work group. During the same period, electric heat pumps were installed in 8,700 new homes, while installations of natural gas-powered heating systems fell slightly. Electric systems are often used in new construction, both because they’re the least expensive option and because natural gas service isn’t available in many new developments, says task force member Sonia Marcus, UNC Asheville’s director of sustainability.

That’s too bad, says Wiggins, because natural gas-fired furnaces are over 90 percent efficient. By comparison, he explains, a natural gas-fueled power plant loses about two-thirds of the heat energy produced. “One-third of the heat energy goes to generating electricity, while the rest goes into heating up Lake Julian.” And in transmitting the electricity over power lines, says Wiggins, an additional 1 to 10 percent is lost.

While highly efficient heat pumps (those with a higher SEER, or seasonal energy efficiency rating) do a better job at lower temperatures, Wiggins maintains that during the coldest weather, systems that include a backup unit fueled by another source, such as natural gas or propane, are more appropriate for this area’s climate.

Jason Walls, Duke Energy’s government and community relations manager for the Asheville area, says he agrees with many of the work group’s conclusions. “Electric home heating is a key driver for peak electricity demand in this area,” he confirms. And though heat pumps are “very, very efficient and effective at a certain band of temperatures, when it gets really hot and really cold, they are not as efficient. The colder it gets, the less efficient they are.”

Powering through

WNC’s highest peak electric demand (1,074 MW) was recorded on a cold Tuesday morning: Jan. 19, 2015. Weekday mornings typically register higher demand than weekends (which makes the demand seen on Sunday, Jan. 8, all the more impressive). And based on current trends, Duke Energy expects that peak to reach 1,323 MW by 2030.

To meet that need today, says Walls, Duke uses an “all of the above” strategy: generating power at its 374-MW coal facility at Lake Julian, running an existing gas-fired “peaker” unit there, transmitting power to the region via the electrical grid and running hydroelectric generation facilities. In addition, the company’s EnergyWise Home program cycles power on and off intermittently to electrical appliances like heat strips and water heaters during periods of high demand. Customers who sign up for the program receive an annual $25 credit on their electric bill for each enrolled appliance.

Another Duke program offers variable electric rates based on the time of use. During the nonsummer season (Oct. 1 to March 31), the highest rates are in effect from 6-9 a.m. on weekdays. A “shoulder peak” rate applies from 9 a.m.-noon and 5-8 p.m. All other times, including any time on weekends, are subject to lower off-peak rates.

Walls says he has no statistics on the total number of residential customers enrolled in the time-of-use program, which “requires active management by the customer.” If people sign up but don’t modify their consumption patterns, he explains, their electric bills could go up.

The task force has set a target of keeping average peak demand growth below 17 MW per year, notes Newman. “If peak continues to grow at that rate for next five to six years, then we will need the proposed peaker plant,” he points out.

The low-income link

While the electric heat pumps being installed in newly built homes do contribute to peak electricity demand in the region, their impact is limited by the fact that they heat relatively efficient buildings. To meet the current building code, new structures must be well-insulated and well-sealed against leaks. But nearly half of Buncombe County’s housing stock was built before 1980. A significant number of those homes are occupied by low-income residents who struggle with high winter heating bills and often don’t have money to invest in weatherization or insulation upgrades that would make their homes more energy-efficient.

According to a 2014 study by Appalachian Voices, a nonprofit conservation group, energy bills can represent 20 percent of these families’ household income. Vicki Heidinger, director of Community Action Opportunities, says some families in the eight-county area her organization serves bear an even higher burden, with up to 50 percent of their total income going to power bills during the heating season.

Helping those residents make their homes more energy-efficient should be one of the first strategies considered to lower peak demand, says Rouse, who volunteers with the nonprofit Energy Savers Network. “We have the opportunity to invest in these efforts and get a better payback than if we, as a community, invest $150 million in a new peaker plant,” he explains. This approach, he points out, also makes housing more affordable and benefits the environment.

Rouse cites the city of Knoxville’s Extreme Energy Makeover program as the kind of initiative that could make a significant difference in our region’s energy use. Funded by the Tennessee Valley Authority, KEEM will invest $15 million in upgrading 1,200 Knoxville homes by the time it concludes in September. The specific improvements will differ from home to home, but the program aims to increase each residence’s energy efficiency by at least 25 percent.

Optimum strategies

Armed with the new data, Newman says the task force will now turn its attention to determining the most effective strategies for reducing peak demand. “There are probably 100 different things we could decide to do as a community,” he says, “but we have finite resources and finite amounts of time.”

The trick will be to focus on a limited number of strategies that also maximize clean energy benefits and reduce the community’s carbon footprint, stresses Newman. The task force’s Programs Committee is studying Duke Energy’s existing incentive programs as well as energy efficiency initiatives targeting low-income households offered by local organizations like Green Opportunities and the Community Action Network. “We’re looking at opportunities to scale up what’s already being effective in our community,” he explains. The task force is also considering new ideas such as demand management technology and battery storage.

Newman says he hopes the community will see concrete action based on the task force’s efforts as soon as this year. And though Walls doesn’t want to put a timetable on implementing such initiatives, he says he expects the task force to “show real progress” in 2017.

And for UNCA’s Marcus, that progress can’t come soon enough. Whether increased reliance on electric heat pumps is a good idea, she maintains, is directly related to the proposed peaker plant. “If we need to build a whole new power plant to run these heating units, it isn’t worth it.”


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About Virginia Daffron
Managing editor, lover of mountains, native of WNC. Follow me @virginiadaffron

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5 thoughts on “Heat pumps drive rapid growth in WNC’s peak electricity demand

  1. luther blissett

    “That’s too bad, says Wiggins, because natural gas-fired furnaces are over 90 percent efficient.”

    The story briefly mentions this, but what’s too bad is that natural gas to the home is a luxury in Asheville, even well within the city limits. If you don’t have gas supply but want to use gas appliances, then you need the space and expense to maintain a residential propane tank, as well as the fortitude not to worry about its capacity to turn your home into a pile of splinters. Perhaps Virginia could do a follow-up with PSNC to identify the areas that remain off the grid, and ask about plans to broaden service?

    The conversion of oil furnaces to heat pumps is mostly a reflection of how large chunks of the city’s housing stock have old, inefficient furnaces (40+ years) that are finally reaching the point of no return: replacement parts aren’t available, repair requires custom fabrication and even the best custom work raises safety issues. Oil tanks also have a limited lifespan, and homeowners’ insurers hate the potential liability of a fuel oil leak. (As for backup heat, a modern wood stove will do the job on cold nights.)

  2. Dave Erb

    Two other appliance technologies bear consideration, especially for new construction or major renovations: ground source heat pumps (sometimes called geothermal) and heat pump water heaters. Both are fairly expensive up front, but they’re also so efficient that they aren’t even eligible for Duke’s $25 per appliance annual demand response rebate. Ground source heat pumps are particularly good for air conditioning and in extremely low temperatures. A heat pump water heater can easily save $200 per year, compared to a standard electric resistance heater, even for a small household with low hot water usage.

  3. Snowflake (Social Justice Worrier)

    Really surprised that no one has mentioned passive solar. It can be cheap to build and virtually free to operate.

  4. Joan Walker

    Get involved with the Energy Innovation Task Force! This is an open process that depends on input from the community to develop plans and get the word out to the broader community. You can attend and speak at meetings of the whole task force and be part of a working group! Learn more at http://www.ashevillenc.gov/Departments/CommunityRelations/EnergyInnovationTaskForce.aspx
    You can also let your City Council and County Commission know that you support them developing and funding initiatives that will help local families and businesses save money and energy, and delay the need for a new power plant!

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