The recent report of the Commonwealth’s Climate Chief calls for the creation of a Climate Report Card to track progress versus climate plans. The report recommends that we track the volume of heat pump installations as a key indicator of our progress towards our emission reduction goals for the building sector.
Heat pump installations are running at a pace below the pace necessary to electrify home heating and cut emissions as required by our stated climate plans. Shining a light on that fact is important. However, we must also bear in mind that the scale of heat pump installations alone is not an indicator of material reductions in greenhouse gasses. There are three additional questions we need to ask to put our progress in proper perspective.
To what extent are heat pumps actually displacing fossil fuels in homes?
The report card should include an analysis of energy consumption for homes that have received heat pump incentives. Heat pumps only reduce residential carbon emissions to the extent they are used in place of fossil heating. Many people buy heat pumps to use as air conditioners in the summer. And we are going to need more air conditioning as the climate warms. However, unless people are also using their heat pumps for heat in the winter, we will not be cutting emissions.
Homeowners can receive partial Mass Save incentives when a heat pump is installed, but it is fully understood that the fossil system will continue to run some of the time. Even when homeowners receive the $10,000 whole home Mass Save incentive, they are allowed to keep their fossil fuel system connected based on a representation that it will only be used when the heat pumps are down. It is impossible to accurately track the use of delivered fuels (oil and propane), but for gas customers, the utilities have the meter data that would allow them to measure pre and post consumption rates. The consumption data will be influenced by many factors but if we can’t detect a strong signal of reduced gas use in the participating homes, then we are probably not making much progress.
To what extent are heat pump installations allowing the retirement of natural gas infrastructure?
The report should include the number of residential and commercial natural gas customers in the state. As some homes that use oil choose to convert to gas (a conversion which we no longer encourage with incentives but which will likely nonetheless remain attractive), the gas service universe may actually be increasing. We should know if that is happening.
Additionally, anecdotal evidence indicates that very few heat pump installations result in disconnection of gas service. The report should show the total number of heat pump installations that have been followed by disconnection of gas service.
Finally, the report should show the total footage of streets served by gas mains and track the footage of gas main that has been retired as a result of complete electrification of a system branch. We have a geographically random distribution of heat pump installations across the state — whoever meets incentive criteria can receive support. It is unlikely that any gas main at all can be retired yet as a result of our significant statewide effort, but the report might, for example, track the number of gas mains from which more than 25%, 50%, or 75% of service accounts have been disconnected.
How much climate-damaging refrigerants are heat pumps losing into the atmosphere?
Heat pumps frequently leak the refrigerant fluids that they use to pump heat. These refrigerants are potent greenhouse gases; the most common one, R-410A, is 2000 times as harmful as carbon dioxide. One small heat pump that loses its charge can do as much damage as a year of driving. Some heat pumps lose their charge repeatedly. When heat pumps are lightly used and not displacing much fossil fuel, the climate damage from the leaks can exceed the climate benefits of the heat pump operation. Additional refrigerant loss can occur during maintenance or when the heat pump is decommissioned. The federal Environmental Protection Agency is requiring a transition away from the most harmful refrigerants, but the next generation of replacements will still be about 600 times more harmful than carbon dioxide.
At a minimum, to support an assessment of leak exposure which could be compared to fuel displacement results, the report card should include the aggregate weight of each refrigerant type in heat pumps that have received Mass Save incentives. This would be based on the heat pump model number (included in incentive applications) and manufacture recommended charge (including an allowance for reasonable connecting line length). We lack good local data that would support the inclusion of an indicator of actual leaked refrigerant in the report card, but the state Department of Environmental Protection should be tasked with assessing the challenges involved in creating a valid metric of leaks based on maintenance reporting.
Heat pump costs and benefits are sensitive to a number of variables — we cannot assume that we are materially reducing greenhouse gas emissions just by putting heat pumps into homes at scale. Our climate report card should include the additional metrics that are necessary to assure that we are benefitting the climate.
Background data relevant to these metrics appears in this collection of documents.