Why Heat Pumps Are The Answer To Heat Waves

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Article courtesy of RMI.By Lacey Tan & Mohammad Hassan Fathollahzadeh

As a record-breaking heat wave scorched the Pacific Northwest earlier this summer and again this week, killing hundreds of people in the United States and Canada, many residents realized the predictably mild summers they knew no longer exist. Scientists are clear that climate change will make these extreme heat events more common in the coming years, prompting people in areas like Seattle, Portland, and Northern California to add air conditioning (AC) to their homes.

In Seattle, where 46 percent of single-family homes do not have air conditioning, temperatures reached a scorching 108°F on June 28, creating hazardous conditions inside homes. So how do we keep people safe and comfortable during dangerous heat waves and manage the increasing need for air conditioning in a climate-friendly and equitable way? Heat pumps are an attractive solution for both policymakers and residents alike, as they can keep a home cool and comfortable in an efficient manner in the summer while also heating the home without fossil fuels in the winter.

RMI modeled the performance of several cooling options for a Seattle home during the three-day heat wave in June 2021: an air-source heat pump (hereafter heat pump), a typical AC unit and a higher capacity AC unit. We found that the heat pump was not only capable of maintaining a comfortable and safe indoor air temperature during extreme heat, but it also costs $228 less per year to operate than a dual fuel cooling and heating system (AC unit + gas furnace). In addition, CO2 emissions are reduced by around 25 percent for the entire home when it operates with the heat pump compared to the high-capacity AC and furnace.

Our results clearly show the heat pump is superior at maintaining a comfortable and consistent indoor air temperature and consumes less electricity than the high-capacity 4-ton AC unit. We first looked at a small 2-ton AC unit — typical for the historically mild Seattle climate — but it failed to maintain a safe indoor environment (cooling setpoint of 75°F) during the extreme heat event. This implies that a high-capacity AC unit is needed to meet the predefined setpoint temperature.

But even while this high-capacity AC unit generates a more pleasant indoor air temperature compared to the typical AC unit, it still struggles to meet the setpoint temperature on the hottest day (i.e., June 28), as shown in the temperature figure below. This is in contrast to the heat pump, which was able to maintain a safe temperature even in extreme heat. The high-capacity AC unit also consumes more electricity than the heat pump, adding additional strain to the grid.

Using the National Renewable Energy Laboratory's BEopt tool, we modeled the following scenarios using a typical existing single-family home in Seattle with no air conditioning, a standard gas furnace and a relatively efficient envelope characteristics as the baseline. The home's building characteristics are based on the Pacific Northwest National Laboratory's prototype model and the Residential Energy Consumption Survey 2015 data. This physics-based building energy model uses actual meteorological year weather data from the June 2021 heat wave. Our objective was to see which system could meet a setpoint temperature of 75°F and examine the impacts on the home's utility bills.

Scenarios:

Additional findings:

While more and more people in the United States and around the world look to add cooling to their homes, it's important to ensure that cooling equipment has minimal climate impact. In hot regions with growing access to AC, (e.g., India), advanced technologies like those demonstrated through the Global Cooling Prize will be critical. In historically mild regions grappling with new heat waves, like the US Pacific Northwest, there is an urgent opportunity to provide clean heating simultaneously with efficient cooling.

This summer's extreme heat events present a clear opportunity and an intervention point for policy makers to support the deployment of heat pumps today, especially in more temperate to cold climates. The economics and energy use between the two systems make the case for incentivizing heat pumps to not only meet the increased demand for AC, but as a strategy for reducing carbon emissions and meeting climate action goals. Once a homeowner installs their first central AC unit, it's a missed opportunity to get polluting fossil fuel or inefficient electric resistance heating out of the home for at least 15 years.

To make this transition easier for households, lawmakers and utilities can drive adoption of modern heat pumps with new programs and incentives that make them affordable for more homes and reduce the upfront cost barrier. A recent piece of federal legislation introduced by Senator Martin Heinrich would help consumers transition to all-electric homes by providing up to $10,000 in rebates, or $14,000 in the case of low-and-moderate income households. This bill has a particular focus on the space heater, water heater, and electric system.

Efficiency measures are a key counterpart to electrification and should also be prioritized, along with carveouts to ensure low and middle-income households can be early adopters of clean and efficient technologies.

Meeting our essential climate targets requires eliminating emissions from every sector, including buildings. That means policymakers across the country need to be prioritizing the transition to efficient, modern, electric appliances like heat pumps. As climate change drives increasingly extreme and dangerous weather conditions, these devices can also play another essential role: keeping people comfortable and safe in their homes, even under the worst conditions.

Related story: Ductless Heat Pumps Demystified

Since 1982, RMI (previously Rocky Mountain Institute) has advanced market-based solutions that transform global energy use to create a clean, prosperous and secure future. An independent, nonprofit think-and-do tank, RMI engages with businesses, communities and institutions to accelerate and scale replicable solutions that drive the cost-effective shift from fossil fuels to efficiency and renewables. Please visit http://www.rmi.org for more information.

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