Bring up the topic of heat pumps and inevitably the question comes: But do they work in the cold? A perception persists that heat pumps can’t hold up in the extreme cold of an Upper Midwest or New England winter.
Rocky Mountain Institute’s new Cold Climates Addendum, an update to The Economics of Zero-Energy Homes, a report published in October 2018, aims to dispel the notion heat pumps aren’t suited for extreme cold.
The report found that when air-source heat pumps or heat pump water heaters are installed in a new home also outfitted with a tight building envelope and rooftop solar PV panels, electrification is economical even in regions with the harshest winters.
“With today’s technology, cost-effective electrification for residential new build is possible even in these cold climates — even as cold as Duluth,” Alisa Petersen, report co-author and senior associate, buildings team, RMI, told Greentech Media in an interview.
“Electrification is possible, and it can be done in a way where the utility bill is not increased for people in those buildings,” she added.
“If you are a policymaker and you’re trying to meet your climate action goals through electrification, you want to make sure you’re also making it so that people aren’t paying more for their utility bills.”
She went on, “If you do electrification in combination with other deep energy efficiency measures such as building envelope improvements and reducing the amount of infiltration going into your building, then it actually can be more cost effective than having a natural gas code baseline home.”
Moving beyond electrifying space-heating equipment
The RMI team first modelled code-compliant all-electric homes versus natural gas homes in three cities with varying severities of winter: Chicago, Illinois; Bozeman, Montana; and Duluth, Minnesota.
They found that baseline all-electric homes cost less to build upfront but more to operate in utility costs thereafter compared to baseline natural gas homes.
But, the researchers wrote, “you can tunnel through this economic barrier by pursuing deeper levels of efficiency and adding solar PV.”
So, they added scenarios comparing natural gas baseline homes to both electric zero-energy ready (ZER) and electric zero-energy homes.
“In every instance, pursuing ZER homes was more economical than just electrifying space-heating equipment with code-compliant equipment, and in colder climate it actually changed the economics of electrification from being painful to homeowners to being beneficial,” they found.
Over 30 years, the economics of high-efficiency residential electrification look even better. Electric zero-energy homes performed better than either electric ZER homes or electric baseline homes over the life of a typical mortgage, generating added net-present value of $21,438 in Chicago, $14,072 in Bozeman, and $19,018 in Duluth.
Getting it right from the start
Heat pumps were ripe for myth-busting. Air-source heat pump technology has come a long way in the last 10 years, according to Petersen and co-author Michael Gartman, also a senior associate on RMI’s buildings team.
Technology improvements are reflected in RMI’s findings. The report noted that cold-climate heat pumps can heat homes even when outdoor temperatures dip to -12 degrees Fahrenheit and found that supplemental electric resistance heating was needed just 3 percent of the time in Bozeman and 10 percent of the time in Duluth.
The key is to buy the right equipment for your climate zone at the outset.
“The colder the climate, the more important it is to make sure you are finding the correct equipment when you are electrifying,” said Petersen. “There are specific cold-climate heat pumps that are made for cold climates. If you are just installing a typical heat pump in a cold climate, then you’re not going to have success.”
“We’re building 1 million homes every single year [in the U.S.],” she added. “It’s always easier to electrify those buildings from the start than to retrofit them later. When we build new homes, we should build them right the first time because any home we build now is going to be around in 2050.”
The importance of changing building codes
With heat pumps now a viable option in cold climates, Petersen and Gartman urged manufacturers, policymakers and utilities to take proactive measures to jumpstart the market.
“For obvious reasons,” said Petersen, “you need a bit more than manufacturer promises. That’s exactly what we’re finding. There are case studies in the real world in very cold conditions where these are working.”
Even more important, she added, is that policymakers need to adopt stricter building codes that raise the floor for electrified buildings.
“Ultimately, most builders tend to build code-compliant buildings,” she said. “If policymakers really want to drive electrified buildings or net zero energy buildings, it will come down to changing their building code. The codes are the ultimate driver.”
She went on, “If we were able to convince city policymakers to have written into their code that you can only do all-electric buildings, that’s when you’re going to see ultimate change where builders are going to have to figure out how to install all-electric buildings.”
“The smart utilities realize that electrification is where city and state policymakers are driving towards,” said Petersen. “Utilities should be planning for the future and plan for how to do building electrification the right way.”
Need for more thoughtful design
Petersen and Gartman conceded that getting electrification right might require additional pre-construction planning.
“You do need to be a little more thoughtful in how you design your buildings,” said Petersen. “The colder the climate, the more thoughtful you need to be.”
She cited as an example the installation of residential heat pump water heaters. In their modeling, Petersen and Gartman found that in cold climates heat pump water heaters should be installed inside the home, rather than the garage, for optimal performance.
Installing heat pump water heaters indoors requires the builder to set aside more space for the unit, but it also eliminates the need for less efficient backup electric resistance heating.
If care is taken to properly select and site heat pumps, it should help ensure that contractors, builders, and homeowners don’t dismiss heat pumps based on a bad experience.
“It’s seeing more of these products actually installed and having experience with it, and hearing the success stories, that would make people feel more comfortable,” said Petersen.
“We’ve hit this point where heat pumps work even in the coldest and harshest conditions in our country, and there’s no reason we shouldn’t be pushing forward on all fronts,” added Gartman.