It’s not easy doing a conversion from methane gas equipment to electric technologies,” said Rafael Reyes, Peninsula Clean Energy’s director of energy programs. Like many of California’s community choice aggregators, PCE has set aggressive decarbonization goals, aiming for a 100 percent renewable electricity mix by 2025 and a carbon-free community by 2035.

We’re looking at residential decarbonization as one of our principal focus areas,” he said. But upgrading a home to run all-electric heating and cooking — and provide power to an electric vehicle charger — can often require adding multiple 240-volt circuits to power those systems. If those new loads exceed the capacity of a home’s grid connection, that creates not only costs…for the owner but also enormous costs…for the distribution grid.”

Harvest Thermal’s architecture requires only one 240-volt circuit for the heat-pump water heater of the customer’s choice, plus a 120-volt circuit to run the Harvest Pod, Reyes said. That means lower costs to install compared to two systems and lower…costs [for the utility] because you [need] fewer service upgrades.”

Beyond these upfront cost considerations, Harvest Thermal’s load-shifting capability allows you to use energy when the cost is lower,” he said. California utilities and community choice aggregators like PCE are required to implement variable time-of-use” rates that charge less for electricity when it’s plentiful on the grid and more when it’s in short supply, which in California means during late afternoon and evening hours in summer and early fall when solar power fades away while air conditioners are still running hard.

These grid peaks are driven by air-conditioner demand rather than heating demand, but they can be exacerbated by standard heat pumps that are designed to keep using electricity at steady rates to maintain desired indoor temperatures. That means the devices will keep drawing power during peaks if they don’t have some form of digital controls to alter that behavior.

Adapting home heating for an all-electric future

Even water heaters that can store heat and then shut off may not be well suited to the load-shifting task, Reyes said. Most heat-pump water heaters and hydronic heating systems aren’t designed to be turned on and off frequently, and may not be equipped with the temperature gauges or software smarts that can track how those on-and-off commands affect their core function of providing ample hot water.

Melia highlighted this distinction between the Harvest Thermal technology and those products on offer from other companies. Retrofit options such as heat-exchanger systems that use hot water to heat air don’t have knowledge of what’s happening inside the tank — and what’s happening inside the tank is really important,” she said. That’s because it allows a system to know when it’s tapping too much heat, leaving the water in the tank too cold to meet a home’s hot water needs.

The Harvest Pod, by comparison, is continuously measuring usage, it’s monitoring flow, it’s monitoring temperature.” That allows the system to fine-tune its operations to prevent the cold-water problem, she said. But it also allows the system to use weather forecasts to preplan its heating cycles, learn from a household’s energy-use patterns to adjust operations, and detect changes in heating efficiency that might indicate failing equipment, to name some examples of what its digital intelligence can enable, she said.

Harvest Thermal's Harvest Pod installed next to a heat pump water heater tank
Harvest Thermal says its hardware and software can turn heat pump water heaters into load-shifting home thermal storage systems. (Harvest Thermal)

Ray Tam was one of the first Peninsula Clean Energy customers to participate in the Harvest Thermal pilot project. So far, he has had no issues with running out of hot water, even during bath times for his two sons, ages 2 and 4, during the same evening hours the heat pump isn’t running.

Nor did the installation require any upgrades to his Daly City, California home’s electrical panel or utility service, Tam said in an interview. He and his wife have been thinking about alternatives to fossil gas appliances for some time and are considering an induction stove as their next step, he said.

As an associate with Pyatok, an Oakland, California–based architecture firm specializing in multifamily housing, he also has a professional interest in learning about the technology and understanding the data it generates, he added.

The idea that it uses machine learning to improve over time is really exciting,” he said. The traditional heating system…just [turns] on and off.”

All of this intelligence comes at some additional cost compared to a standard heating system. But Melia said that the cost of the Harvest Pod, along with the plumbing to carry water from it to the air handler, can be made up for by the reduced costs of not having to install a second heat pump to heat air as well as water in a home.

The fact that Harvest Thermal’s system requires replacing both air and water heating with one system does present a barrier to fast adoption, Reyes said. Normally homeowners say, I want to do the water heater today, and I’ll get to the furnace when it’s time for it to go,’” he said. This is basically a whole-home upgrade, and that will require more programmatic support for people to get there.”

There’s also the question of how well hydronic systems work in colder climates where winter heating loads make up a significant portion of electricity demand. For the time being, Melia said that Harvest Thermal is very…focused on the Bay Area where we’re rolling out, making sure we have trained contractors in place. We have a long waitlist of hundreds of people who want to electrify their homes.”

Harvest Thermal has received funding from a combination of federal and state grants and a $1.9 million seed funding round in December that was led by Astia Angels and included VertueLab, Energy Labs and the Band of Angels. That investment will allow the company to expand its production capacity and improve its hardware and software.

Melia would like to see Harvest Thermal expand to handle even a small portion of the roughly 500,000 home heating retrofits that take place in California every year. There’s a long way to go on that front, but state incentives and utility load-shifting imperatives might help push the market, she said.

Wouldn’t it be nice if, in five years’ time, when your furnace breaks down, the contractor has a heat pump on the back of the truck?”

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