On Friday, the Department of Energy (DOE) issued a new test procedure for residential and some commercial water heaters. The new procedure addresses a number of longstanding testing issues in order to better replicate real-world usage and to more accurately measure energy consumption across various technologies. Unfortunately, DOE missed an opportunity to ensure that one of the most energy-efficient technologies, the electric heat pump water heater (HPWH), performs as expected in cold temperatures. Regional efforts are underway to address variations in cold temperature performance, but DOE should address this issue soon so that HPWH performance can be accurately measured across the board.
The good news
The new test procedure is designed to more accurately measure the energy consumption of technologies that are becoming increasingly popular, such as tankless, heat pump and gas condensing water heaters. To better simulate consumer use, manufacturers will now be required to test their units using water usage patterns based on water-heater capacity and to heat the water to 125°F (the temperature setting at which units are commonly shipped). These new requirements have been largely derived from extensive field studies (e.g. 2011 LBNL report ).
The HPWH offers one of the largest energy saving opportunities available. A 2012 ACEEE/ASAP study estimates that savings from potential HPWH standards could reach more than 400 billion kWh in cumulative electricity savings through 2035, enough to power over 37 million homes for one year. Individually, EPA estimates that units save $250 a year in electricity bills when compared to standard electric-storage water heaters and that the higher purchase price can be recouped in about 3 years.
The not-so-good news
The new test procedure does not test HPWH performance at low ambient temperatures. HPWHs work by extracting heat from the surrounding air and transferring that heat to the water. But during hours when the ambient temperature is too cold, the heat pump’s compressor will shut down. When it shuts down, the water is heated by built-in resistance elements, which use about 3 times as much energy. Because of this sensitivity to low ambient temperature, performance can vary depending on where in the house the unit is installed and what region of the country the house is located in. This means that a unit installed in an unconditioned basement in northern Minnesota is likely to perform very differently from one installed in a garage in Florida.
Some HPWHs perform very efficiently in low ambient temperatures, but not all of them do. Heat pump compressors on some models shut down at temperatures as high as 57°F, while others continue to work down to 30°F. But instead of acknowledging and accounting for these performance variations, the new DOE test procedure requires only that water heaters be tested at an ambient temperature between 66.5-68.5°F, making no distinction between the best and worst cold temperature performers. DOE should address this problem by requiring manufacturers to test HPWHs in lower ambient temperatures and, if possible, by setting a minimum temperature requirement at which the heat pump compressor must still be able to perform. Until this issue is addressed, serious doubts will remain as to whether HPWH efficiency results achieved in the lab will be realized in cold-climate homes.
Efforts underway to address cold-temperature performance
EPA has begun to recognize the importance of cold-temperature performance by proposing that manufacturers report the compressor cutoff temperature as part of ENERGY STAR® qualification. The Northwest Energy Efficiency Alliance (NEEA) has gone even further by introducing its Northern Climate Heat Pump Water Heater Specification. It measures unit performance over a range of different ambient and inlet water temperatures. Through its research in the northwest, NEEA has found water-heater ambient temperatures ranging from as low as 34°F all the way up to 97°F. People can buy water heaters that meet the Northern Climate Specification knowing that the products have been tested under the full range of expected operating conditions. NEEA’s work provides DOE with a blueprint for future changes to the federal test procedure.
New water heating technologies offer enormous energy savings potential, and the new DOE test procedure goes part of the way to ensure that all water heaters are tested fairly and accurately. We hope and expect that it will not be long before DOE revises its test method again to better reflect how HPWHs perform in colder temperatures. In the meantime, NEEA, ASAP, and the Northeast Energy Efficiency Partnerships (NEEP) are encouraging wider use and adoption of the Northern Climate Specification. Our coalition plans to reach out to utilities to provide performance data, best practices information, and ways to integrate the Northern Climate Specification into current and future HPWH programming.