CO2 Heat Pumps: A Key Piece in a Decarbonized Future

By Michael Garry, May 13, 2019, 19:34 8 minute reading

As buildings seek alternatives to fossil fuels for heating, heat pumps using CO2 are finding a growing market in North America.

Mayekawa's CO2 heat pumps at Silver Oak Cellars' winery in Healdsburg, Calif.

For the past decade, Troy Davis, energy group manager for Mayekawa USA MYCOM, has been promoting the Japanese company’s CO2- and ammonia- based heat pumps for space heating and domestic water heating in North America.

But unlike in Japan and Europe, where heat pumps using natural refrigerants have been widely used in commercial and residential applications, the North American market has been difficult to penetrate. “Ten years ago, I thought we’d have thousands [in North America] by now,” said Davis. Instead the number is about 25 CO2-based UNIMO units.

But that's beginning to change.

Over the last four to six months, Davis has been getting “a lot of phone calls and emails” about a wide variety of heat pump applications, particularly from multi-family apartment buildings on the West and East Coasts of the U.S. seeking domestic hot water heaters. One example is Stuy Town, an apartment complex in Manhattan. Multi-family buildings are considering both water-source and air-source CO2 units.

“CO2 heat pumps are great for domestic hot water heating where you take cold water and heat it to a higher temperature,” he said.

In general, Davis said he is seeing “huge potential” in the U.S. for heat pump technology using CO2, and to a lesser degree, ammonia. “The market is untapped here,” he said. “But things are starting to line up,” though he acknowledged that Mayekawa needs to “fine-tune” its large Japanese units to make them a better fit for the U.S. market.

John Miles, general manager – eco systems, Sanden International (USA), said sales of home heat pumps (still largely for units using R410A) are “booming” in Northeastern U.S. states like Maine and Vermont, which are aggressively marketing the products with rebates. But heat pumps are still a small slice of the overall market for hot water heaters in the U.S.; for example, only 1,800 were sold in Connecticut in 2017.

Miles, who is marketing Sanden’s CO2 heat pumps for domestic water heating and space heating, has been crisscrossing the U.S. to train contractors and distributors, and raise awareness about the advantages of the technology.

For Sanden, the greatest growth for its CO2 hot water heat pumps is in the commercial sector, which includes multi-family apartment buildings and restaurants, though that currently represents 40% of installed units compared to 60% for residential homes.

“Multi-family homes use more hot water and typically can see a quicker ROI than residential homes.” noted Miles, adding that apartment buildings can amortize the capital cost of the equipment. Examples of multi-family homes using the Sanden equipment include Kingway Apartments in Seattle, Wash., and Edwina Benner Plaza apartments in Sunnyvale, Calif., both low- income housing complexes.

The Decarbonization Movement

 Probably the biggest driver of the new interest in heat pumps is the growing movement toward “decarbonization” and “electrification” of building heating systems – switching from natural gas, oil or propane boilers to electric heat pumps – and the development of renewal energy sources like solar and wind energy to produce electricity for utilities.

“Utilities are interested now in electrification [of heating in buildings],” Davis said. “They’re promoting heat pump electrification and taking gas customers off natural gas or propane.”

States, he added, will be hard-pressed to achieve their carbon emission goals “unless they do a lot more with heat pumps and other technology.”

In April, Energy and Environmental Economics, a research firm based in San Francisco, Calif., issued a report, “Residential Building Electrification in California,” which analyzed the economic, environmental and electric grid impact of converting from natural gas to electricity in California homes.

The report found that building electrification – substituting electric technologies like heat pumps for gas-burning ones like furnaces – “is a relatively low-cost, low-risk way to reduce California’s building-related GHG [greenhouse gas] emissions.”

Another California-based group, the Building Decarbonization Coalition, in February issued a report called “A Roadmap to Decarbonize California’s Buildings” that lays out a plan for the state to cut building emissions 20% in the next six years and 40% by 2030. In the report, the group calls for an increase in the share of high-efficiency heat pumps for space heating from 5% of sales in 2018 to 50% in 2025 and 100% in 2030.

To make the switch to heat pumps possible, the California Public Utilities Commission is implementing SB (senate bill) 1477, which deploys $200 million in incentives for manufacturers and builders.

California is better prepared to make the transition to electrification because of its high usage of renewable energy. In 2018, California generated 34% of its electricity from renewable sources (solar, wind, geothermal, biomass and hydro), according to the California Energy Commission.

However, in the U.S. as a whole, only 17% of electricity came from renewables (and 19.3% from nuclear energy) in 2017, according to the U.S. Energy Information Administration. But even while the grid is largely linked to fossil fuels, an appliance with a COP over 3.0 is “incrementally better [in terms of emissions] than burning natural gas in the home,” said Miles.

The effort to decarbonize homes and transition to electric heat pumps is being opposed by the American Gas Association (AGA). Richard Murphy, managing director of energy marketing for AGA, argues that heat pumps are not competitive in colder parts of the U.S., according to a report in E&E News.AGA also contends that electrification of homes would raise average home energy costs up to 46%.

Miles noted that “the gas industry has to do everything it can to stop decarbonization as it threatens their very future.” He added that new technology such as inverter compressors and improved controls “are providing much better heat pump performance in lower temperatures and we are slowly seeing this technology being applied.”

The Sanden CO2 heat pump’s COP is 5.2 at an ambient temperature of 67°F, making it more efficient than other heat pumps and heating appliances. But its COP drops to 4.5 at 47°F, 3.0 at 23°F, 2.25 at 5°F and 1.6 at -20°F, which is its lowest operating temperature. Averaged over the entire winter, the COP is more favorable, noted Miles, By contrast, “the very best gas water heaters have a COP of 0.96 and can never get higher than 1.0,” he said. On the other hand, the low cost of gas makes gas water heaters overall “a wash” cost-wise compared to the Sanden heat pumps.

About 20% of Sanden’s North American installations, which number “a couple of thousand,” Miles said, are used for both radiant space heating and domestic hot water in residential homes. One homeowner in the San Francisco area who installed Sanden’s combination space heating-hot water heater system, and compared it to a previously used gas heating system, found a 74% drop in energy (kBTU/day) and a 78% decline in GHG emissions (kgCO2/day).

CO2 heat pumps are great for domestic hot water heating where you take cold water and heat it to a higher temperature.”
– Troy Davis, Mayekawa USA


In addition to providing heat, CO2 heat pumps are used for cooling in some applications. “Everybody looks at hot water and cooling as separate, but there’s a lot of potential in water source units to integrate the two,” said Davis. “It really helps with the COP [coefficient of performance].” At least 80% of Mayekawa’s water-source units produce cooling that is leveraged rather than discarded, he said.

The use of cooling also helps produce an ROI for the water-source units, which Davis acknowledged can be a “little pricey.” Compared to an electric-resistance water heater, the much more efficient CO2 heat pumps offer a payback in 1.5 years. But the payback is much longer compared to a gas water heater because of the low cost of gas, he noted.

Sanden’s heat pump water heaters, Miles acknowledged, are the most expensive water- heating products on the market, at about $3,000 per unit, compared to about $1,300 for traditional (HFC refrigerant) heat pump water heaters and $600 for gas and electric-resistance water heaters. Although Sanden’s heat pumps are 30%-40% more efficient than conventional heat pump water heaters, “we need a dedicated home owner for ours,” he said. “Water heating is a first- cost market.”

But the cost of heat pumps in the U.S. is expected to drop as the market for them grows and manufacturers achieve economies of scale, according to the Rocky Mountain Institute.

Mayekawa also makes low-charge ammonia-based heat pumps for medium or large facilities like office buildings and industrial plants. To date, most have been deployed in Europe, the Middle East and Japan but Mayekawa has installed a few in North America food processing facilities. Ammonia would not have been considered a year or two ago in North America but that has changed with the advent of low-charge systems, more robust components, and semi-hermetic components that eliminate leak points, said Davis.

Davis sees “some potential” in North America for hydrocarbon-based heat pumps, which have a significant presence in Europe but not on this side of the pond. Isobutane, he noted, “is great for hot water heaters.” But their prospects are constrained by very high costs in the U.S. where they have to be “explosion-proof,” he noted.

This is an excerpt of an article that originally appeared in the April-May 2019 issue of Accelerate America magazine. To read the complete article, click here.

By Michael Garry

May 13, 2019, 19:34




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