Carbon dioxide, the stuff we associate with exacerbating climate change, can actually help prevent climate change and save a lot of energy when used in the right technologies for appropriate applications, such as washing machines and water heaters.
CO2 washing machines
Commercial and industrial washing machines may be the last place you would expect to use CO2. This non-flammable, non-toxic, naturally occurring gas can be pressurized to become a liquid and used to clean laundry. In liquid form, CO2 has low viscosity and acts as a surfactant, which allows proprietary detergent formula to penetrate the fabric better than detergent in hot water. Liquid CO2 also disinfects, making it a good option for hospitals and industries with clean rooms, and a single machine can clean 100 to 200 pounds of laundry per hour.
Once the clothes are clean, the CO2 is depressurized so it flashes back into a gas and the laundry is instantly dry. No dryer is needed, which greatly reduces energy use. The liquid gas does not harm delicate fabrics, and clothing lasts longer because high-temperature water and machine agitation are not needed. After each wash, the CO2 is captured, filtered, distilled, re-pressurized and reused.
CO2 washers are appropriate for large, centralized cleaning operations, such as hotels, hospitals, uniform cleaning companies, prisons, nursing homes, textile plants and industries with clean rooms.
According to a recent study by the California Energy Commission (CEC), CO2 washing machines achieved a 60-percent reduction in electrical energy use and a 46-percent reduction in natural gas use when compared with water-based cleaning. Eliminating water use completely provides users with additional savings. The CEC estimates that 8,000 facilities in California would be good candidates for this technology. Just a five-percent market penetration in that one state could save 264 million kilowatt-hours, 20 million therms, and more than 600 million gallons of water, according to the CEC. The bottom line is that an investment in CO2 washers could have a two- to four-year payback.
CO2 heat pump water heaters
Another up-and-coming CO2 technology is the CO2 heat pump water heater (HPWH). Similar to the HPWHs available at home improvement stores, CO2 models are even more efficient at generating hot water for washing and space heating (with radiant floor, radiators, etc.).
Like CO2 washing machines, these water heaters compress CO2 until it becomes a liquid (at about 1,400 pounds per square inch). CO2 is more efficient than conventional refrigerants, and it has 1,000 times less effect on climate change.
The water tank is larger than a conventional water heater—usually about 80 gallons—allowing for some stratification of the water. The coolest water at the bottom of the tank is piped to the compressor for reheating, which optimizes efficiency. The water temperature is also higher than with a conventional water heater—about 150°F. The higher temperature, combined with a bigger tank, means that more people can take showers before the hot water runs out, even if the system turns off for a while during a utility’s peak demand reduction program.
In the split system version, the compressor and condensing fan are in a separate unit outside, which eliminates noise inside. The variable-speed drives on the fan, compressor and pump (the key to making this equipment so efficient) reduce the noise from the outside unit even more, meaning CO2 HPWHs are usually much quieter than conventional models. This also means the unit does not draw conditioned air from inside the home or small commercial building to heat the water, as un-ducted, single-unit HPWHs do. A smaller (40 gallon), single-unit, ducted CO2 HPWH may be available in the U.S. in the future. Like the larger split-system version, it benefits from CO2 refrigerant, variable speed and use of outside air.
Even with a bigger tank, hotter water, a highly pressurized refrigerant and a compressor that pulls heat out of outside air during the winter, this technology uses less energy than conventional HPWHs: its efficiency is about 50 percent greater than conventional HPWHs, which are about twice as efficient as a conventional electric water heater. The delivery rate, measured by the number of back-to-back showers you can take without running out of hot water, is also about 50 percent better than a conventional HPWH. CO2 HPWHs can be especially efficient when used in applications such as a commercial kitchen where the “outside” unit can be mounted high on a wall to provide hot water and cool air.
These are not just manufacturers’ claims, either; these are independent test results from a university and a national lab. The field study Washington State University (WSU) Energy Program conducted indicates that the systems can provide both space and water heat for highly energy-efficient homes. The WSU Energy Program is working with the Next Step Home Program of the Northwest Energy Efficiency Alliance to test this concept in a number of homes. Pacific Northwest National Laboratory is documenting the equipment’s potential to help reduce peak load demand.
Right now, CO2 HPWHs are available in the U.S. only in larger sizes for commercial and industrial applications. But the largest manufacturer expects to roll out their residential version in the U.S. in early 2015. The technology has been used in Asia, Europe and Australia for many years. Learn more about these and other new and emerging technologies from Energy Efficiency Emerging Technologies.