Let's Run Towards Hybrid Heat Pumps - to benefit Climate, Energy Savings, Health and Equity

It’s time for all the air conditioning equipment we buy to also be a heat pump usable in winter weather. What’s very clear now, based on nascent research performed at MIT, and by organizations including CLASP, is that we can achieve energy savings with minimal cost, as well as accrue great benefits for the climate and public health, if we all take the available choice of a quality heat pump whenever we're considering replacing our air conditioning equipment (other than portable window units). But for now, most of us in colder climate areas with gas or oil heating systems should continue to use our existing systems during very cold weather. Such dual systems are now referred to as Hybrid Heat Pumps. 

Hybrid heat pumps save energy and money, and are of great benefit for our climate. The 2018 Special Report of the UN Intergovernmental Panel on Climate Change determined that we need a 50% reduction in carbon emissions by 2030 (from 2017 levels) to avert the worst effects of climate change. By simply replacing air conditioning equipment (AC) with a quality heat pump when the current system needs replacing (a thing that many of us will have the opportunity to do by 2030), we should be able to reduce our home's site carbon emissions 60-70% in colder climates. New cold weather heat pumps are plug-and-play: they look and work the same as the AC-only alternatives, but provide economic heat as well at a modest incremental expense. With high efficiency and variable speed drives, they save money for air conditioning, and can save on heating costs substantially. But since heat pump efficiency and output drift lower as temperatures drop, the highest financial savings are achieved by using heat pumps only when they have energy costs lower than the backup oil or gas system - most hours above 20 degrees Fahrenheit, and all hours above 35F. Between 20 and 35F, it is dependent on local energy pricing, and especially the electric rate structure, as to whether more or fewer of the hours will be economic for electricity. But even with a 35F cutoff, 50% site decarbonization is achieved.

Electrification matters a lot for climate. While electricity production creates carbon emissions, the amounts are much lower if we heat with efficient electric heat pumps rather than burning fossil fuels such as gas, oil or propane during milder winter weather. The New England power grid carbon intensity has dropped 50% in the last decade - as the result of coal and oil power plants being replaced by lower carbon gas and increasingly by solar, wind, and hydropower. Public policies, such as the recent Massachusetts Next-Generation Climate Roadmap Law, require progress towards a carbon-free power grid to continue rapidly. Since air conditioning equipment fails in 12-15 years, if hybrid heat pumps were the ubiquitous choice, 2/3 of air conditioned homes could economically transition 2/3 of their heat to electric by 2030 - if we start soon.

By comparison, all-winter heat pumps are less economic and more difficult to scale as much as we need for climate: in Massachusetts we would begin to stress our power grid with less than 10% of homes switching from gas or oil to all-winter heat pumps by 2030, since even the best heat pumps in peak winter draw almost four times as much power as in peak summer conditions. It would be best to focus this limited opportunity for all-winter heat pumps where they have the least impact on the grid winter peak: on new or rehabbed homes that are highly energy efficient, meeting standards like Passive House, or for homes with highly efficient (but expensive) ground-connected heat pumps.  

But what about homes without air conditioning? The market share for air conditioning in New England has been climbing in recent years: factors include the more frequent summer heat waves (like the bicoastal blast going on today), as well as the dropping costs to add air conditioning to multi-level homes made possible by the new ductless mini-split systems. Since these new AC systems are already ubiquitously cold weather heat pumps, we simply need to educate consumers and service providers to use these mini-splits most economically and effectively for heat in winter. Public state energy efficiency programs, such as the nation-leading Mass Save program conducted by the state’s utilities, can help accelerate the change with well-targeted incentives, services, and controls; some of these are in place now.

A good public policy to consider: let's make air conditioning via heat pump a right, not a privilege. For public health, and for fairness with rising summer heat especially in cities with urban heat islands, public efficiency and climate programs that promote hybrid heat pumps should help low income consumers without air conditioning to acquire them as well. Even though hybrid heat pumps provide full air conditioning to these homes for the first time - the heating bill savings should at minimum fully offset these costs.

How do we justify the public cost of this program? State/utility energy efficiency programs are deemed worthwhile when program costs are lower than the sum of utility system benefits and other forms of public value - a utility regulatory process called Integrated Resource Planning. As of last week, in Massachusetts the new Climate Roadmap state law explicitly added climate value to this calculation, and as a result it may now be cost-effective to fully subsidize and directly install ductless mini-splits in low income homes, when one puts fair value on the mini-split impact on heat decarbonization, energy savings, and hot summer public health benefits - which are considerable. A hybrid heat pump program might be somewhat unique - an economic path to help vulnerable urban communities mitigate their carbon emissions, while simultaneously helping to adapt these homes to be more comfortable and healthy in rising global temperatures. Climate mitigation and adaptation strategies are both essential now, but these rarely overlap as they would here.

For consumers of more moderate income, the winter heat economic benefits should be adequate to cover a finance cost over about 7-8 years, so perhaps a loan and sliding scale subsidy may make sense to make this a program for all.

So let’s run towards Hybrid Heat Pumps! But at the same time, we do need to think about further heat decarbonization in the 2030’s - as climate science, and now a new Massachusetts law, set a goal of 75% decarbonization by 2040 on the path to full climate neutrality by 2050. A decade from now, we will need new options - such as decarbonized peak winter fuels (advanced biofuels, green hydrogen, or ammonia); or geothermally-heated community water loops to assist our heat pumps in peak weather (often called GeoMicrodistricts). R&D and pilots of these and other next generation potential solutions should also expand today.