California aims to be carbon-neutral by 2045. Any path to get there will require decarbonizing the state’s buildings.

According to a new Natural Resources Defense Council (NRDC) study, published in the Electricity Journal, electric heat pumps should be part of any long-term building decarbonization strategy in California.

“If you purchase and install a new heat pump today, you can expect emission reductions over its life of between 50 and 70 percent compared to conventional gas alternatives,” Pierre Delforge, study co-author and senior scientist, climate and clean energy program, NRDC, told Greentech Media in an interview. The other co-author, Anna Brockway, is a graduate student in the Energy & Resources Group at the University of California, Berkeley.

Delforge said the study was prompted by conversations with policymakers who wanted to know how electric heat pumps’ greenhouse gas emissions profile changed at times of peak electricity demand, when the carbon intensity of the grid increases, as well as during periods when hot water demand is high and hybrid heat pump water heaters operate in less-efficient electric resistance backup modes.

In order to compile an emissions profile accounting for those factors, Delforge and Brockway compared hourly electricity usage data for heat pump water heaters and air-source heat pump space heaters to hourly emissions intensity data for electricity generation on the California grid prepared by the consultancy Energy and Environmental Economics, Inc. (E3) for the California Public Utilities Commission.

Delforge and Brockway subsequently found that a gas-to-electricity swap reduced emissions by 50 percent to 70 percent for heat pump water heaters and by 46 percent to 54 percent for air-source heat pumps, depending on the efficiency of the gas-fired equipment replaced.

“When you combine the high efficiency with clean electricity, we get very low emissions, and that is particularly important for space heating and water heating, which are two of our biggest energy users and emissions sources in buildings and homes in particular,” said Delforge.

Savings for homeowners

In addition to the carbon savings, recent studies have found that electric heat pumps can save homeowners money, especially when installed in new buildings.

A study prepared for NRDC by the consultancy Synapse Energy Economics, Inc., published in October, found that California homeowners could save $1,500 upfront, and hundreds of dollars annually in reduced operating costs thereafter, with the installation of electric heat pumps instead of natural-gas furnaces in new construction.

A report released by the Rocky Mountain Institute in June found that homeowners could save money by opting for electric heat pumps in new construction as well as retrofits in which electricity supplants propane or heating oil, or when both a gas-fired furnace and air-conditioner need to be replaced at the same time.

“In many scenarios, notably for most new home construction, we find electrification of space and water heating and air conditioning reduces the homeowner’s costs over the lifetime of the appliances when compared with performing the same functions with fossil fuels,” the authors concluded.

Emissions reductions increase with a cleaner grid

Delforge noted that he and Brockway conducted their analysis before passage of SB 100, legislation signed into law by Governor Jerry Brown in September that increased California’s renewable electricity target to 60 percent by 2030 and mandated 100 percent carbon-free electricity by 2045.

“If we redid the analysis with that bill now in law,” he added, “the reductions would actually be even higher than they are in our analysis.”

Even greater near-term emissions reductions could be had, Delforge said, if load management technologies are used to unlock the demand flexibility capabilities of electric heat pump water heaters and air-source heat pumps.

“Pre-heating in the early afternoon to raise the home temperature before 4 p.m., could substantially reduce the contribution of ASHPs [air-source heat pumps] to peak electricity usage,” Delforge and Brockway wrote in the Electricity Journal paper.

Afternoon pre-heating or pre-cooling would also enable air-source heat pumps to provide space conditioning when the California grid is saturated with zero-carbon solar electricity.

Delforge said the rollout of time-of-use rates by California’s investor-owned utilities beginning in 2020 will provide additional opportunities to leverage the demand flexibility of heat pumps equipped with smart controls.

“Electrification plus high efficiency plus demand flexibility: That’s the magic equation we think is going to be key to reach the level of emissions reductions we need in the building sector,” he said.