GE calls their GeoSpring water heater a “hybrid,” which in this case means that it heats water through a mix of old and new methods. The new part consists of a heat pump — the same kind of technology you’ve seen in HVAC units for years. An evaporator pulls heat from the ambient air, transferring it to the water within. But when your use demands water too hot for the heat pump (or, more likely, too much water for it to heat effectively in time), a classic electrical element kicks on, topping off the temperature quickly.
For those who may not have thought about how HVAC works at all — bless you in your ability to remain ignorant of this, by the way, as those of us living in Texas view HVAC kind of the way astronauts think of their oxygen delivery systems when spacewalking — the best explanation I ever received was from a friend of my father’s who worked in the industry. His tip was simple: don’t ever think of your air conditioner as “cooling air,” but rather as “moving heat around.” To cool the air inside, it extracts heat and moves it outside.
I’ll try to explain it based on my layman’s understanding. If any of you Toolmongers are HVAC pros, feel free to jump in and correct me in comments. We’ll happily post updates. But here goes:
Heat pumps move heat through the concept of latent heat, “the heat release or absorbed by a body or a thermodynamic system during a process that occurs without a change in temperature.” So, for example, in an air conditioner, gaseous refrigerant enters coils where air blowing over it removes energy, causing the refrigerant to condense — to change state from gas to liquid. When it does so, it releases that energy in the form of heat into the outside environment, dispersed by the fan. The liquid refrigerant flows back into the house and eventually through another coil placed in your A/C ductwork. The ducts direct inside air over the coil. The refrigerant in the coil absorbs energy (heat) from the air, using this energy (again through the latent heat concept) to transform back into a gaseous state. The gas flows out to the outside coil. Wash. Rinse. Repeat. Bammo: You don’t die when it’s 110 degrees outside (again).
The outside coil is commonly known as a “condenser” while the inside coil is generally called an “evaporator.”
All air refrigerant-based systems are technically “heat pumps,” but a while back they started to release newer systems that actually carried the name “heat pump.” These units features the ability to reverse the system’s flow in the wintertime to condense in the home and evaporate outside, pumping from outdoors to indoors, heating the house. Since the efficiency of such systems varies based on the difference in temperature outdoors and indoors, they can’t always provide enough heating — or enough heating quickly enough — to make us happy, so most heat pump units include an electrical “emergency heat” coil which makes up the difference. They’re essentially “hybrids” — just like the GE water heater.
All GE has done here is apply the same idea to a water heater. An evaporator on top of the tank collects heat from the surrounding environment and carries it to a condenser, which releases the heat into the water. An electric “emergency heat” coil makes up the difference.
GE claims some pretty significant savings on energy bills over the cost of a standard heater — up to $3,250 over a 10-year period. (Try their calculator to find your own predicted savings.) The unit itself looks pretty sweet, too, complete with a little digital control panel where you select your water temperature and can monitor the unit’s performance Prius-style to see whether it’s operating in pure heat pump, hybrid, or electric mode. A “vacation mode” encourages you to turn the damn thing off when you’re going to be gone for a week or more — a good idea for the owner of any tank-equipped water heater.
The downside, as you probably imagine, is cost. A quick look around online shows these things starting around a grand and running upwards from there. Similar models from Rheem and others run even more, as high as $1,700 to $2k. Some states and local utility providers offer rebates, though plugging in my own zip code into GE’s rebate finder uncovered only one measly $25 rebate for me — certainly not enough to offset the $500 to $1000 difference between the hybrid’s cost and that of a standard heater. That’s optimistically a 2.5 to 5 year payoff, or about the lifespan of my last hot water heater.
(Thanks, MasterThrerm, for the great diagram above. Check out their site for another description as well.)