As homes become more efficient, the portion of energy used for water heating is growing larger. Collectively, the amount of energy expended on this simple task is astounding and much of it is wasted. There are many options for improving the efficiency of our water heating systems, including insulating the water heater and pipes, avoiding setting the thermostat higher than necessary and using low flow faucets and showerheads.
There’s also the option of using the sun to heat water. This strategy is particular well-suited to the sunny climate of the desert southwest but has yet to become mainstream despite strong incentives. This is primarily due to unnaturally low prices for electricity and natural gas – prices that do not reflect their true cost.
Another water heating option for home owners is beginning to catch on. More manufacturers are incorporating heat pump technology into their electric water heaters, greatly improving their efficiency. Heat pump technology has been used for decades for space heating and cooling, including the common refrigerator. New federal regulations will go into effect in 2015, increasing energy efficiency standards for electric water heaters larger than 55 gallons, and heat pump technology will be the likely solution.
A traditional electric water heater uses a resistive element to directly raise the temperature in the tank and has an energy factor of 1. A heat pump transfers and concentrates thermal energy from the surrounding space into the water. The process is much more efficient, with an energy factor in excess of 2.5 for some units.
Some well-known companies that offer heat pump water heaters include A.O. Smith, Bosch, Kenmore, Rheem, RUUD and Whirlpool. Currently, the gold-standard seems to be the Stiebel Eltron with an energy factor of 2.51. The German company claims it can reduce hot water costs by up to 80%. Their heat pump runs on a puny 500 watts, making it a viable option even for PV-powered (solar electric) homes.
Regardless of where your electricity comes from, a heat pump water heater can save money. Though currently more expensive than standard units, the difference in cost is usually regained in a few years of energy savings. Most come with a ten-year warranty.
Heat pump water heaters have a backup resistive element that will kick in if necessary. Since those elements use the most energy and are no more efficient than a standard electric water heater, operating in heat pump mode as much as possible is the goal. For this reason, it seems that units with a larger tank (80 gallons for example) can actually be more efficient than smaller 55 gallon units. It is somewhat counter-intuitive but having that extra buffer during high demand makes a difference.
There are a few things to be aware of when considering a heat pump water heater. They are usually taller due to the heat pump equipment on top, so make sure you have adequate clearance. That extra equipment includes a fan and compressor and they make some noise. Some are louder than others so if noise is an issue, check the specs carefully. Since the unit draws heat from the surrounding space, it needs room to “breathe” and will lower the temperature in that space. If installed in a Southern Nevada garage this is probably not a big issue and might actually be a welcome benefit during summer. Garages in colder climates might not be warm enough for the unit to work properly. Indoor installations are another story. Be sure to carefully weigh the issues of size, noise and the thermal effects on your living space.
Heat pump water heaters will become mainstream in the near future. Now you have another option in your Green Living toolbox.