May 2021 EnergyWise Tip: Polar Vortex Heat Pump Operation

May 2021 EnergyWiseSM Tip: Polar Vortex Heat Pump Operation

By: Energy Efficiency Supervisor Steve Zach

During the February polar vortex, the cost of certain heating fuels increased significantly. In some cases throughout the nation, this extra fuel cost will be passed on to customers for years. But those in Nebraska with the most efficient electric heat pumps (air-source and geothermal) stayed warm, with only a blip in extra costs caused by the extremely cold weather, not by exorbitant fuel escalation.

Heat pumps have advantages when compared with fossil-fuel heat (natural gas, propane, fuel oil), including high overall efficiency (i.e., higher energy output for the same energy input) and reduced local emissions such as carbon dioxide.

With geothermal heat pumps, even if it’s -25 or +105˚Fahrenheit outside, your house will stay conditioned. That’s because geothermal heat pumps make use of transferring heat into and out of the earth. At 12 feet or more beneath the earth, the ground temperature is a constant 55 to 60˚F in Nebraska. A geothermal heat pump capitalizes on this to provide heating efficiencies that exceed 400%, as compared to natural gas and propane, which cannot exceed 100%. As an added benefit, a geothermal heat pump is 25 to 50% more efficient than a typical air-conditioner.

Electric Power Research Institute field testing has demonstrated that certain models of variable-speed air-source heat pumps meet a home’s entire heating load without supplemental heating down to 0°F outdoors, with continued heat pump compressor operation providing energy savings down to -20°F.

These variable capacity air-source heat pumps are gaining traction in the marketplace. They continuously adjust compressor and fan speeds to meet a home’s required heating and cooling loads, resulting in high energy efficiency and excellent occupant comfort. Though heating capacity of standard-efficiency, single-speed heat pumps is greatly reduced as outdoor temperatures decline, variable-speed systems still provide a higher proportion of their heating capacity at low outdoor temperatures. The end result is a significant reduction in electricity demand during winter by reducing dependence on supplemental heating.

Results from actual variable capacity heat pump installations during the February 2021 polar vortex substantiate this, proving they can handle the heating needs of an entire home at zero to -5˚F. At extremely low temperatures below that, the heat pump is simply boosted by a small amount of electric resistance strip heat (five to 10 kilowatts (kW)) to keep your home comfortable. Contrast this to standard single-speed heat pumps in typical residential applications, where 15 to 20 kW of electric resistance strip heat is needed during the coldest periods, depending on the size of home. These new heat pumps also provide quiet operation and higher air temperatures coming out of your registers.

It should be noted that variable capacity technology has also been applied to geothermal heat pumps for a number years, which results in ultra-efficient heating and cooling of your home.

Both the geothermal and variable capacity air-source heat pumps are especially viable options for rural living where a back-up generator is desired. A 10 kW generator may very well handle the electric heating load during even the most severe conditions.

NPPD and its wholesale partners have incentives up to $3,300 for the installation of these very efficient heat pumps. In addition, federal tax credits are available for geothermal installations made in 2021. For more ideas on how you can make your home or business EnergyWiseSM, along with information about energy efficiency financial incentives, contact your local utility or visit www.nppd.com.