Why heat pumps are a cost-effective and climate-friendly solution for extreme heat waves and freezing winters.
Summer in the Northern Hemisphere is only a few weeks old, but temperature records have already been broken as heat waves have baked regions from Scandinavia to Japan to the United States. The heat came early in India and Pakistan this year, with weeks of scorching temperatures during the deadly March and April heatwaves.
As cooling becomes increasingly a necessity for comfort and safety in buildings worldwide due to climate change, 3.3 billion air conditioning units are expected to be installed in the next few decades. As our friends at Canary Media pointed out in a recent episode of the series Copy via copier podcast, 18,000 central air conditioning units are installed in American homes every week. But for the millions of homes and businesses that require cooling in the summer and heating in the winter, a heat pump can fulfill both needs very efficiently as a dual-purpose comfort machine.
These quiet and powerful all-electric devices have been in the news a lot recently, including when President Joe Biden used the Defense Production Act to accelerate production of heat pumps and other clean energy technologies in the U.S. to boost energy security, fight climate change and create jobs. In this article, we’ll discuss some of the most common types of heat pumps, how the technology works, and how heat pumps can save people money on heating and cooling, all while reducing planet-warming and pioneering greenhouse gas emissions. to healthier indoor and outdoor air quality.
Heat pumps: A two-way solution for year-round comfort
Heat pumps differ from traditional HVAC appliances in at least two major ways. First, many heat pumps can run in both heating and cooling modes – acting as both an air conditioner and a furnace. And secondly, a heat pump running in heating mode has one major advantage in terms of energy savings compared to a traditional gas or electric boiler: the heat pump simply is moving heat rather than generating it by burning fossil fuels or electrical resistance. This key differentiator allows heat pumps to achieve much higher levels of efficiency.
Example 1: Heat pump in cooling mode. Source: EPA
The basic principles of a heat pump are similar to those of a home refrigerator. Both technologies use a refrigerant to transfer heat from one side of the system to the other. When a standard residential heat pump is running in cooling mode (Exhibit 1), the low-pressure, low-temperature refrigerant absorbs heat from the indoor air, which is released to the outside when the refrigerant is compressed and passed through an outdoor heat exchanger. (This heat transfer is why your refrigerator releases some warm air into your kitchen as it chills your food and drinks.)
In heating mode, the refrigerant flow is reversed. The refrigerant absorbs heat from the outside and evaporates inside the sealed system. Crucially, the refrigerants used in heat pumps have very low boiling points and can effectively absorb heat even from cold winter air. This heat can then be transferred to the internal environment by compressing the steam and passing it through the internal coil, where it releases some of its heat.
Because a heat pump only moves heat and does not produce heat, it can produce more than four times the heat energy (in kWh) than it consumes in electricity, resulting in lower energy consumption and running costs than electric resistance heaters. As shown below, heat pumps also significantly outperform gas furnaces. Importantly, heat pumps help homeowners avoid burning gas indoors, eliminating any potential risks of carbon monoxide poisoning or dangerous gas leaks and explosions. And eliminating the burning of fossil fuels also has huge benefits for outdoor air quality and health. According to a Harvard TH Chan School of Public Health study, air pollution from fossil fuels is responsible for one in five deaths worldwide.
Exhibit 2: Heat pump efficiency versus gas furnace efficiency. Source: RMI
Types of heat pumps
Air source heat pumps (as shown in Exhibit 1) transfer heat from indoor air to outdoor air or vice versa. Ground-to-water heat pumps (Exhibit 3) work similarly, with the main difference being that the systems use the ground as the outdoor heat exchange medium, which is relatively stable in temperature, making them a great solution for very cold climates.
Exhibit 3: Horizontal ground-water heat pump. Source: Heat pump scheduler from NYSERDA, Building Energy Exchange and Steven Winters Associates
Heat pumps can be ducted (with heated or cooled air pushed through a series of ducts to reach different parts of the building) or ductless, commonly known as a mini-split system. The mini-split contains several indoor units for precise heating and cooling of specific rooms or zones.
In addition to heat pumps for heating and cooling indoor air, there are other common household appliances such as high-efficiency water heaters and dryers that use heat pump technology. By extracting thermal energy from the ambient air, such as in an insulated garage or utility room, the most efficient heat pump water heaters in the United States boast four times the efficiency of conventional water heaters.
Are heat pumps for everyone?
Heat pumps have long been popular in temperate climates, but have often been dismissed as ill-suited to cold winters. However, technological progress in recent years has made heat pumps for cold climates a practical solution even in sub-zero conditions. Heat pumps now play a significant role in climate action plans everywhere from Colorado to Maine. A recent RMI analysis of Wisconsin’s climate and energy mix shows that heat pumps in this northern state can save households hundreds of dollars a year over electric or propane furnaces. And it’s not just the United States: cold countries like Norway have some of the highest adoption of heat pumps in Europe.
Despite the fact that heat pumps are more efficient to operate, their initial cost has been a persistent barrier to wider adoption. However, there are many scenarios where a heat pump can compete with the purchase price. For example, building new all-electric homes is generally cheaper than building mixed-fuel (electricity plus gas) homes, as the infrastructure needed to bring gas to a new building can cost roughly $5,000 per single-family home. The transition to pure electric power also cushions homeowners from fluctuating fossil fuel prices that can be affected by global disasters such as Russia’s invasion of Ukraine.
Heat pumps are also a cost-effective solution for homeowners who want to add or upgrade air conditioning and heating systems at the same time. A study by the Wisconsin Public Utilities Commission found that combined furnace and air conditioning costs start at $6,600, while a heat pump system costs just $2,300 (ductless) or $4,200 (ducted). In regions like the Pacific Northwest, where the need for air conditioning used to be rare, consumers can install a heat pump to cope with increasingly hot summers while replacing an aging or inefficient furnace.
Electric utilities can help unlock the energy, cost and carbon savings of heat pumps for everyone by subsidizing or otherwise incentivizing their purchase and installation. Government leaders around the world should act quickly to protect people from intensifying heat waves and other weather extremes by promoting policies and programs that ensure efficient, healthy and fully electric homes – especially for our most vulnerable citizens and communities. We also need to invest in building and training a clean energy workforce that can do the job.
Switching to a heat pump today is a win for home energy savings, human health and comfort, and the climate, and these benefits will only increase as the electricity grid becomes greener and more residents demand clean heating and cooling solutions.
© 2021 Rocky Mountain Institute. Published with permission. Originally posted on RMI Outlet. By John Matson
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