Why Heat Pumps Are The Answer To Heat Waves

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

When 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 that there were predictably mild summers that they knew no longer existed. Scientists are certain that climate change will make these extreme heat events more common in the years to come, prompting people in areas like Seattle, Portland, and Northern California to equip their homes with air conditioning (AC) systems.

In Seattle, where 46 percent of single-family homes have no air conditioning, temperatures reached a scorching 108 ° F on June 28, creating dangerous conditions inside the homes. So how do we ensure safety and comfort during dangerous heat waves and cope with the increasing need for air conditioning in a climate-friendly and fair manner? Heat pumps are an attractive solution for politicians as well as residents, as they can efficiently keep a home cool and comfortable in summer and heat it without fossil fuels in 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 a heat pump), a typical air conditioner, and a higher capacity air conditioner. We found that not only does the heat pump maintain a comfortable and safe indoor air temperature in extreme heat, it also costs $ 228 less per year than a dual fuel cooling and heating system (air conditioning + gas stove).. In addition, the CO2 emissions of the entire house are reduced by around 25 percent when operated with a heat pump compared to high-performance air conditioning and the stove.

Heat pumps keep you cool and comfortable

Our results clearly show that the heat pump is superior in maintaining a comfortable and constant indoor air temperature and uses less electricity than the powerful 4 ton AC unit. We first looked at a small 2 ton AC unit – typical of Seattle’s historically mild 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 achieve the predefined set point temperature.

But even though this high-performance AC unit produces a more comfortable indoor air temperature compared to a typical AC unit, it still has difficulty getting the set temperature on the hottest day (i.e. 28. This is in contrast to the heat pump, which is safe even in extreme heat In addition, the powerful air conditioner consumes more electricity than the heat pump, which puts additional strain on the network.

Scenarios and additional insights

Using the National Renewable Energy Laboratory’s BEopt tool, we modeled the following scenarios using a typical existing Seattle single-family home with no air conditioning, a standard gas stove, and a relatively efficient envelope as the base model. The building properties of the house are based on the prototype model of the Pacific Northwest National Laboratory and the data from the Residential Energy Consumption Survey 2015. This physics-based building energy model uses current meteorological weather data from the heat wave of June 2021. Our goal was to find out which system had a target temperature of 75 ° F and investigate the impact on the home’s utility bills.


  • No air conditioning: We used a house with a gas stove with an annual fuel use efficiency of 78 percent for heating and no air conditioning. We examined the increase in indoor air temperature in relation to outdoor air temperature. In this scenario, the indoor air temperature has a lag compared to the outdoor air temperature, but follows a similar curve and is extremely uncomfortable and unsafe for residents. Indoor air temperature peaked at 100.4 ° F on June 28.

  • Typical AC: This scenario represents an AC unit with the typical capacity that we would expect for a Seattle home with the characteristics described above. Historically, AC was not a necessity in Seattle’s climate; however, there is now a need to cope with the recent heat waves and rising temperatures. We added a typical 2 ton AC unit with a 2 stage compressor and a Seasonal Energy Efficiency Ratio (SEER) of 18, with all other assumptions in the model remaining the same. The typical AC unit reduces the indoor air temperature to levels closer to the cooling target temperature of 75 ° F; however, it is unable to reach the target temperature. This scenario is therefore only partially safe and uncomfortable for the occupants.

  • High performance AC: We replaced the typical AC unit with a 4-ton, high-capacity SEER 18 AC unit with a 2-stage compressor, with all other assumptions remaining the same. This scenario creates a more comfortable indoor air temperature compared to a typical AC unit, but still reaches the set temperature on the hottest day (June 28th) and consumes a lot of power compared to a typical AC unit.

  • Heat pump: In this scenario we analyzed a SEER 22 variable speed heat pump without a gas oven. The heat pump generated the most comfortable room air temperature and was able to maintain the target temperature constantly and consumed 18.6 percent, 15.5 percent and 3.7 percent less energy than the high-performance air conditioning system from June 26th to 28th. It also performed better when compared to the high performance AC unit and oven in terms of energy consumption, CO2 emissions and operating costs for both heating and cooling.

Additional findings:

  • A heat pump provides both cooling and heating, so we studied its ability to heat the house during the winter months and compared it to a standard gas stove. The heat pump was more efficient than the gas stove in terms of energy consumption, CO2 emissions and operating costs when heating the house. Removing the stove and installing a heat pump will reduce CO2 emissions for the whole house by over 10,000 lb of CO2. reduced
  • Heat pumps are an effective and climate-friendly solution to meet the increasing cooling needs in regions such as the Pacific Northwest. Installing a heat pump that uses less energy for both heating and cooling than a high capacity AC unit is a long-term investment that can lower utility bills, but comes with higher up-front costs that can hinder a time to market.
  • The air conditioning system must be oversized to ensure acceptable indoor air temperatures during extreme heat waves. However, in temperate climates with a high heating requirement compared to cooling, a heat pump is sized appropriately to cope with the heat wave conditions.
  • Although not analyzed in this blog, studies have shown that weathering services offer improvements that reduce energy consumption and increase overall energy efficiency, and are a good starting point for poor living conditions. The combination of weathering due to efficiency gains could result in downsizing the equipment, resulting in greater savings. They also offer non-energetic benefits, such as health and safety, that are badly needed for low- and middle-income households.

An important turning point

As more and more people in the United States and around the world look for cooling for their homes, it is important to ensure that cooling equipment has a minimal impact on the climate. In hot regions with increasing access to AC power (e.g. India), advanced technologies, as demonstrated by the Global Cooling Prize, will be vital. In historically mild regions struggling with new heat waves, such as the Pacific Northwest, there is an urgent opportunity to simultaneously provide clean heating with efficient cooling.

The extreme heat events of this summer represent a clear opportunity and point of intervention for policy makers to support the use of heat pumps today, especially in more temperate to cold climates. The economic efficiency and energy consumption between the two systems suggest that heat pumps not only meet the increased demand for air conditioning, but also serve as a strategy for reducing CO2 emissions and achieving climate protection goals. Once a homeowner has installed their first central air conditioning system, it is a missed opportunity to remove polluting fossil fuels or inefficient electrical resistance heating from the home for at least 15 years.

To make this transition easier for households, lawmakers and utilities can push the adoption of modern heat pumps with new programs and incentives that make them affordable to more households and lower the upfront cost barrier. A federal law recently introduced by Senator Martin Heinrich would help consumers transition to all-electric homes by providing up to $ 10,000 in discounts or $ 14,000 for low and middle income households. This bill specifically focuses on space heating, the water heater and the electrical system.

Efficiency measures are an important counterpart to electrification and should be a priority, as should carveouts, to ensure that low- and middle-income households can adopt clean and efficient technologies early on.

Achieving our key climate goals requires eliminating emissions from all sectors, including buildings. That means policymakers across the country must prioritize the transition to efficient, modern electrical appliances like heat pumps. As climate change causes increasingly extreme and dangerous weather conditions, these devices can also play another essential role: They ensure that people feel comfortable and safe in their homes, even in the worst of conditions.

Related Story: Channelless Heat Pumps Demystified


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