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GE GeoSpring Hybrid Electric Water Heater - Ambient Temperature and Energy Efficiency

How does the ambient air temperature affect the energy efficiency and energy savings performance of the GeoSpring?

The "$320 per year savings" and the "Saves up to 62% of the energy consumed by a standard electric water heater" claims are based on standard Department of Energy (DOE) water heater test procedures that are conducted at an ambient air temperature of 68F.

As the temperature of the air drops below 68F, there is less heat in the air, and the heat pump must work longer to extract the necessary heat from the air to heat the water. Since the heat pump works longer, the energy efficiency is slightly reduced. To put this in perspective, at a 68F ambient air temperature, the GeoSpring has an Energy factor of 2.35 and saves up to 62% of the energy consumed by a standard electric water heater. At 50F, the EF reduces to 1.8, and the savings is reduced from 62% to 50%. This means that even at ambient air temperatures as low as 50F, GeoSpring can still save up to 50% of the energy used by the second largest energy consuming appliance in your home. That's still a very substantial amount of energy savings. If the temperature drops below 45F, the amount of heat in the air has dropped too low for effective heat pump operation, and the GeoSpring will switch off the heat pump and operate the standard electric elements to heat the water. This occurs regardless of the operating mode that is set. When operating the standard electric elements, the unit will have the same efficiency as a standard electric water heater.

Keep in mind, that the ambient air temperature being discussed is the temperature of the air surrounding the water heater, not the outside air temperature. Many water heaters are found in garages, basements, and attics, and even when the air temperature outside is below freezing, the air temperature surrounding the water heater is still usually above 45F, and the heat pump will operate to efficiently heat the water. The opposite is also true for temperatures above 68F. Above 68F, there is more heat in the air, and the heat pump becomes more efficient at heating the water. This efficiency increases with ambient air temperature up to 120F. Above 120F, the unit again switches off the heat pump, and energizes the standard electric elements to heat the water. Air temperatures above 120F in residential settings are very rare and this is rarely expected to occur.