In late 2021, the U.S. Department of Energy challenged HVAC industry leaders to make heating and cooling homes more efficient and cost-effective by improving heat pumps, which move existing air in or out of the home rather than generating a new source of hot or cold air.
According to the DOE, space conditioning and water heating account for 46 percent of building emissions and more than 40 percent of primary energy used in American residential and commercial. They also account for 42 percent of all building energy bills and 56 percent of household energy bills annually.
The challenge objective? Create a cold-climate heat pump that could warm homes in the northern United States—where winter temperatures create high energy demands. The estimated cost savings could reach up to $500 dollars per household per year.
Nine companies have jumped to meet the challenge, and Richardson-based Lennox became the first to put out an approved prototype this summer. “The challenge focused us and made it time-bound, and the competitive spirit out, even more than we had in our DNA,” says Prakash Bedapudi, chief technology officer at Lennox. “We wanted to be the first ones to meet the challenge.”
Here, Bedapudi explains how Lennox’s new prototype attempts to solve a longstanding issue in energy, its potential impact, and the next steps in the challenge.
D CEO: What problem did the U.S. Department of Energy hope to address with this challenge?
BEDAPUDI: “In the winter, if you need heat in the house, you typically run a furnace inside your house—a gas furnace or propane furnace. You turn on the gas, burn the gas, and you heat the air inside the house. That’s how the furnace works.
“So, what is a heat pump? A heat pump is essentially an air conditioner, except there is some valving and some piping involved, where we switch the cycle 180 degrees. Instead of picking up the hot air to put it outside, in the wintertime, you pick up the heat from outside and project it inside the house. That means you can heat the house rather than cooling the house.
“Why don’t we use the heat pump in the colder climates like in Minneapolis or in North Dakota? The reason traditional heat pumps don’t work very well is that it is zero degrees outside. There’s not a lot of heat from the outside air to project inside the house. So, essentially, the heat pump’s capacity or ability to heat the house drastically reduces when you go from a 40-or 50-degree-day ambient temperature to a zero-degree-day.
“So then, how do you heat the house? Well, you can’t. You have to have a supplemental electric strip heat augment. That’s what most people commonly do. That works well If the temperature mostly stays 20 degrees and above, but there are parts of the country where for six or seven months of the year, it’s going to be zero or below zero. During that time, you can’t use a heat pump. Electric strip heaters are notoriously inefficient. It costs you a lot of money as a homeowner to heat your house with electric strip heat. That’s why heat pumps haven’t gained a lot of momentum in the colder climates.
“Today’s heat pumps stop working at zero degrees Fahrenheit, thereabout. Also, it becomes counterproductive. You’re running the compressor without getting a lot of heat. It’s a drain on energy without getting much return for it. It’s at a point of diminishing returns.
“As an alternative, what people do is burn a gas furnace. So now, given the climate change and the carbon neutrality or decarbonization push—all the electric vehicles (EVs) replacing internal combustion engines, not burning fossil fuels—given that macro trend, the U.S. Department of Energy looked at the HVAC industry and said ‘Hey, people are still burning a lot of natural gas to heat their homes. Can we incentivize? Can we challenge HVAC manufacturers to go develop this cold climate technology?’ Meaning, ‘Can you improve the efficiency and capacity of a heat pump down to -20 degrees?’”
D CEO: How have you proposed to solve this problem with your prototype?
BEDAPUDI: “Human minds and technologists’ minds are amazing. If you put that competitive spirit, rekindle it, and put a timeline, then they’ll work day and night, and then it becomes a lot more fun than just a job. So, what we did was we put it on a higher tier, and we basically accelerated overall progress on this project. We took a lot of other projects on the plates of these R&D teams and solely focused on this.
“They looked at what are the key elements of employing the core performance. It has to come from driving more compressor capacity. How do we do that? We came up with a technology called vapor injection. That is similar to getting more power out of your sportscar. What do car companies do if they want to get more power out of an engine? They supercharger it or turbocharge it. Same concept. We supersized the compressor by putting in vapor injection technology. Essentially, it puts more mass through the compressor so that we can get the overall higher mass flow and higher heat generation in a heat pump cycle. That’s what we did.
“Then, we put in a bigger heat exchanger. We put a bigger fan. Essentially, you have to scale up along with the compressor when it puts more mass flow through. We also have to put a control scheme to manage this compressor with vapor compression and the fans, expansion valves— all of those. It’s a ground-up systems design. Once we figured out what the key knobs are to improve the efficiency and capacity, then it’s a matter of us getting it all up and building the prototypes and demonstrating that we can hit the challenge—the efficiency levels and the capacity levels.”
D CEO: What kind of capacity requirements are there for the challenge?
BEDAPUDI: “Today’s conventional heat pump produces, let’s say, 100 units of heat at 50 degrees Fahrenheit ambient temperature. That’s why you need to have a gas furnace or an electric strip heat augment—to augment the loss of capacity. For the cold climate heat pumps, the goal was down to zero degrees Fahrenheit. The challenge was to maintain the capacity flat—it still needs to deal with 100 units of heat at zero.”
D CEO: What is the next step in the challenge?
BEDAPUDI: “We have a couple of prototypes running in the lab right now. For the next step, we are working closely with the DOE to identify four to six locations in very cold climates of the country. It could be South Dakota, it could be whatever is figured out between DOE and us where would make more sense to put these field test units. So, we’re going to build a minimum of four, maybe up to six, field test units over the next several months before the winter sets in and install these in those climates.
“We’ll have a lot of instrumentation on those units. We can get data remotely so that you can monitor how much heat [the test units are] putting out capacity-wise and efficiency-wise so that we can demonstrate in actual use in some consumers’ homes that this cold-climate heat pump will deliver the capacity and efficiency that is required for the challenge.”
D CEO: If all goes well, what would be the environmental impact of Lennox’s new cold-climate heat pump?
BEDAPUDI: “The field test will give us more quantifiable results at this point compared to a conventional heat pump or compared to a gas furnace and AC system running in a cold climate; it will be in the 50 to 60 for heat efficiency improvement in colder temperatures and have a corresponding reduction in carbon footprint.”
D CEO: Once testing is completed, when could Lennox launch this product formally?
BEDAPUDI: “Generally, the product development cycle lasts 12 to 18 months. Sometimes, it can be sooner, depending on the market demand.”