Tuesday, June 8, 2021

Next-Generation Heat Pumps Are Making Customers Happy

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Technology is Potentially Applicable to 90% of the U.S.

At 25 residential and commercial sites in 6 states across the continental United States, EPRI is testing advanced, electric heat pumps for replacing propane heat, natural gas systems, and older heat pumps. With respect to comfort, cost, and efficiency, results to date are promising.

This ‘next-generation’ system is potentially applicable to 90% of the U.S. population. The implications are significant: if electric heat pumps were to displace 90% of fossil fuel use for residential space heating, on-site fossil fuel consumption in the U.S. would be reduced by nearly three quads. For context, in 2020 the U.S. consumed a total of about 30 trillion cubic feet of natural gas, which is equivalent to approximately 31 quads of energy.

Heat pumps use electricity to move heat from one area to another. They can heat cold rooms or cool hot rooms and are far more efficient than heating systems that burn fossil fuels. Yet in colder climates, their use has been limited by lower heating capacity and efficiency. Below a certain outdoor temperature, the heat pump is supplanted by less efficient electric resistance heating or fossil fuel heating to provide additional warmth. As a result, most heat pumps are deployed in the Southern U.S.

For several years, EPRI has been working with manufacturers to develop a heat pump with a variable-speed compressor that operates more efficiently and can provide up to 50% more heating capacity at low outdoor temperatures than a similarly sized traditional system with a single-speed compressor. Variable-speed units run at low speeds for most of the day, then speed up during colder nighttime hours.

EPRI’s field tests have determined that in a range of climates the variable-speed units provided warmth much more evenly and cost-effectively than the systems they replaced.

“The customers’ reception has been very good,” said EPRI Program Manager Ron Domitrovic. “They are benefiting from a significant reduction in energy consumption and report superior indoor comfort compared with their older systems. At all test sites, they have told us that the comfort and temperature throughout the house are more even than they’ve ever experienced before.”

EPRI monitors the heat pumps’ performance along with numerous variables that affect their operation, including outdoor air temperature and humidity, temperature of heat pump supply air, temperatures in various rooms at each site, and more.

One collaborator in the field tests is Tri-State Generation and Transmission, which supplies electricity to 43 distribution cooperatives and public power districts in Wyoming, Colorado, Nebraska, and New Mexico. Tri-State has deployed heat pumps at five houses in its members’ service territories. The houses vary from one to three levels and from 1,160 to 3,356 square feet of heated space.

“Our primary insight is verifying that these heat pumps work in colder climates, and they do it economically and efficiently,” said Myles Jensen, Tri-State’s senior manager of member relations.

In a Nebraska farmhouse, the heat pump saved $211 in heating costs between December and April. The owner reported that the system is heating evenly and at lower outdoor temperatures more efficiently and economically than the propane furnace it replaced.

“The value of EPRI’s expertise in collecting and analyzing the heat pump data in our field tests has been immeasurable,” Jensen said. “It is essential to have rigorous data that we can use to demonstrate the effectiveness of variable-speed heat pumps to our member distributors and their customers.”

At certain test sites, researchers also are investigating advanced heat pumps’ support for demand response. Some manufacturers produce variable-speed heat pumps that can reduce compressor speed in response to utility signals during peak demand. In 2019, the Air-Conditioning, Heating and Refrigeration Institute established operating requirements for variable-capacity heat pumps with demand response capabilities, standardizing both system communication and heat pump response.

“With these variable-speed systems, even as you slow them down during peak demand on hot summer afternoons or cold winter mornings, they can provide moderate space conditioning very efficiently,” Domitrovic said. “This benefits consumers and grid operators.”

According to EPRI Senior Project Manager Don Shirey, the project’s biggest challenge has been educating local HVAC contractors about installing, maintaining, and optimizing the new heat pumps.

“Many HVAC contractors only have experience with single-speed heat pumps and don’t yet fully understand the capabilities of variable-speed systems,” Shirey said. “Selecting the proper equipment size for variable-speed systems is different than sizing conventional systems. In addition, there are numerous thermostat settings that affect performance, and it’s very important to select the settings appropriate for a particular climate.”

Shirey works with HVAC contractors to assess their sizing calculations and select proper settings. Ultimately, he plans to develop guidance for contractors.

The project also revealed a need to educate homeowners about how variable-speed heat pumps operate.

“Homeowners are used to hearing their heating system cycle on and off rather than running all the time. When the variable-speed heat pump runs most of the time, they get nervous, thinking ‘I must be using a lot of energy,’” Shirey said. “The reality is that the variable-speed units run at low speeds virtually the entire day. This mode of operation is much more efficient than a single-speed system running at full speed periodically.”

Key EPRI Technical Experts:

Ron Domitrovic, Don Shirey
For more information, contact techexpert@eprijournal.com.