If you have an air conditioner or a refrigerator, you have a heat pump. Heat pumps use special chemicals to move heat from one place to another. The chemicals draw heat into them, just like when you sweat. When you sweat, the heat of your body is drawn into the fluids on your skin. This cooling effect is heat moving from your body into your sweat. As the sweat evaporates, the heat is released into the air, if the dew point is in the right range for evaporation to happen. So, even you are a heat pump!!
Evaporation is known as a “phase change” where the liquid changes to a vapor. As a liquid turns to vapor, it absorbs heat. The body-cooling effect of evaporation shows this. Taking all that vapor and pushing it back into a liquid phase concentrates the stored heat until it can be released again in the vapor phase.
Certain chemicals absorb heat very well, much more so than water. If we allow these chemicals to circulate in a closed loop while in the vapor state, we can pump them down into a liquid using a condenser. This liquid has stored heat that can then be released into a different place by pumping it around the loop and passing air over it with a fan. Your refrigerator moves heat out of the fridge compartment or freezer and into the house. Your air conditioner moves heat from the house and blows it outside. Heat pumps used to heat and cool a house have a reverse switch that allows them to heat in the winter and cool in the summer.
These chemicals ( for example, 1,1,1,2-Tetrafluoroethane is R-134a, carbon dioxide is R-744, and both are allowed refrigerants) have global warming potential if allowed to escape into the atmosphere. These and other manufactured chemicals almost destroyed the ozone layer which protects all living things from excessive UV radiation. We learned, and acted, to prevent the “Ozone Hole” from ruining life on Earth. Banning the really reactive chemicals such as chlorofluorocarbons (CFCs) and controlling the release of less reactive ones has been a triumph of international policy, reversing the depletion of the ozone layer (1)
Review:
1) Heat pumps move heat from one place to another
2) Heat is moved by allowing chemicals to evaporate and condense in a closed loop system
3) When you sweat, you are pumping heat!
4) Releasing some heat pump chemicals is really bad for the environment
5) Heat pumps are also used in highly efficient home heating and cooling systems
What is a heat pump water heater?
Water heaters use combustion, electric resistance or heat pumps to heat the water in the tank. A heat pump water heater has a coil wrapped around it at the base which contains a refrigerant that will move heat from the room into the coil very efficiently. This heat passes through the conductive wall of the hot water tank into the water. In a strictly heat pump water heater, there is no backup resistance heating for high usage periods. This is good because the power requirement for heat pump domestic hot water is only 120VAC, so you can just plug them in to a dedicated circuit like a refrigerator. The hot water will be made with 60% less electricity than a regular electric water heater, so if it costs $600 per year this cost should go down to about $200 per year.
Review:
1) Heat pump water heaters can be plugged into a typical 110 Volt AC wall circuit, like a fridge
2) Only the heat pump heats the water
3) Heat in the air around the heat pump is pulled into the tank, heating the water
4) Heat pump water heaters are very efficient
What is a hybrid water heater?
Electric resistance water heaters use elements that heat up when electricity is passed through them to heat the water. With a hybrid water heater, you have both a heat pump and electric resistance back up elements to maintain hot water during high usage. These units have settings that can use only the heat pump, both heat pump and resistance, or just resistance. They have the same electrical requirements as a regular electric hot water heater, 208/240 Volts AC on a dedicated circuit.
Heat pumps use about 30% of the electricity of a resistance heater. So, if your bill is $600/year with an electric hot water heater, it will be $200/year with a properly sized heat pump. Generous state and federal rebates are available as well, making it possible to get a simple pay back of around 10 years. Here in New York, Central Hudson Gas and Electric offer $1,000 rebates!
The way to think about heat pump efficiency is in comparison to an electric resistance baseboard heater. When you turn on the electric baseboard heater, the electricity runs through wires and heats up. This resistance always makes 3412 btu per hour. When a heat pump uses refrigerant to pump heat, it is able to pump 3 times that amount of heat for the same amount of electricity. So, for 1 kilowatt hour instead of 3412 btus you get 10,236 btus. That is better living through chemical engineering if we don’t destroy the ozone…
Review:
1) Electric hot water tanks use 3 times more energy than heat pumps
2) Hybrid systems have electric elements to provide hot water during higher-than-normal usage
3) Hybrid systems need a 240V electrical hookup for the electric element back up
Split systems and integrated systems
Hot water tanks that use heat pumps usually have integrated heat pumps that are part of the unit, sitting on top of the water tank. These are easy to install because the refrigerant is contained in the heat pump, all you need to do is hook it up to your water supply and power and turn it on. Homeowners that have some tools and are handy can usually install one with low difficulty. Integrated systems have the added benefit of providing dehumidification to the room they occupy, so if you have a damp basement these marvels of engineering can do double duty. The water from dehumidifying the air needs to drain to a sump or get pumped into drainage.
Integrated systems use the interior air (basement or garage) and have a limit to how low the room temperature can get before it stops being efficient—usually about 40 degrees. Hybrids resort to electric resistance when this happens, units that don’t have electric resistance will not heat water properly if the room temperature gets too cool.
There are other systems where the heat pump is not integrated, these are called “split” systems. Split systems, like an air conditioner or heat pump system, have a condenser located outdoors and a set of insulated lines that carry the refrigerant to and from the heat pump. These are more difficult to install and require someone who knows how to handle the refrigerant.
Split systems harvest heat from the outdoor air and bring it to the water tank via those insulated lines. The heat pumps that can do this are designed to work in lower temperatures and usually cost more money. Depending on the specific design of a split system, ever larger amounts of heat can be efficiently pumped from ever colder air—below zero in fact!!
Bravery is rewarded…go ahead and get a high efficiency heat pump hot water heater. They are as reliable as a window air conditioner (yes, that 25-year-old behemoth that works all summer long) or a refrigerator (is it time to replace that stinky thing??). Heat pumps are durable tools in the fight to increase efficiency.
Review:
1) Integrated hybrid hot water heaters are “all in one” and discarded when the tank fails
2) Split systems are connected to the tank via a “line set” so when the tank fails, you just get a new tank and hook it up to the same heat pump. Nice. 
Expensive.
3) This is old tech that has been perfected—start saving up to 60% on hot water heating by switching to a heat pump water heater! It will pay for itself in less than 10 years.
