The heat pump technology is now being applied to domestic water heating.
Ground source heat pumps may now be equipped with a small heat exchanger (technically called the desuperheater) able to use superheated gases produced by their compressors to heat water for domestic uses.
But the most interesting choise for average households if not the desuperheater technology and ground-source heat pumps. Ground source heat pumps are very expensive for common single-familly homes. They do not make sense in energy-efficient houses.
That other choice is the stand-alone air heat pump water heaters, especially designed to provide hot water to bathrooms and kitchens, or to produce hot water for space heating.
Basically, heat pump water heaters work like refrigerators in reverse. They are high efficient electric units, several times more energy-efficient than common electric water heaters.
Big manufacturers like GE, Rheem, American, A. O. Smith, Aquaterm Industries, Ruud, Reliance, York or Stiebel Eltron are now offering this type of water heaters, and the Energy Star program is rating them.
Heat pump water heaters have higher initial costs than conventional gas storage water heaters. Expect prices around $1,500-$2,000 (more $300 to $700 to install) for efficient models. For cheaper prices, take a look at online stores like Amazon; see for instance: Heat Pump Water Heater, 50 Gallon.
Requirements & installation
The problem with heat pump water heaters is that they require temperatures between 40º and 90ºF (3º-32ºC) to work efficiently. In other words, they have to be installed in a room with such temperature range all year-round (installing them in a space with excess heat, like furnace rooms, is a good choice).
Besides, since they cool the space where they are installed, you should also provide at least 1.000 cubic feet (30 m3) of air space around them, and a way of exhausting the exhaust air to the outside.
Costs & Warranties
Properly installed heat pump water heaters provide low running costs - typically a third of common electric water heaters - and are cost-competitive with the best gas condensing water heaters. Warranties vary from 1 to 7 years.
Heat Pumps Water Heaters & Solar PV
Heat pump water heaters can be used in conjunction with solar photovoltaic (PV) systems.
The prices of PV solar systems have dropped sharply during the last few years, making electric solar water heating an option to consider in cold-sunny climates, in regions where the costs and the maintenance of solar thermal water heating systems are expensive.
In other cases, especially in moderate and hot climates, thermosyphon and other thermal-solar water heating systems are better options.
Disadvantages of Heat Pump Water Heaters
Air source heat pump water heaters have advantages over traditional electric resistance water heaters: they consume a fraction of the electricity. But the best units are expensive and are more prone to failure than electric-resistance water heaters (and they cool the rooms where they are installed, which is an obviously disadvantage in cold climates, during the winter).
In other words: eElectric-resistance water heaters aren’t a good fit for homes with large water heating needs, but they aren’t dead yet – at least in buildings with low water heating loads.
Electric-resistance water heaters are safe and durable, and also inexpensive to buy and to maintain, besides being easy to install (especially point-of-use water heaters). And this makes them a good choice in homes with low hot water requirements, especially in hot and moderate climates.