The time it takes for a clothes dryer to dry a load of laundry is important to consumers. On a heavy laundry day, many consumers expect the drying to be completed by the time the washing is done in order to quickly run one load after another. To assess the efficiency of dryer technologies with respect to drying time, we tested a variety of North American and European dryers. Further, we modified a conventional dryer to include exhaust air-to-air heat exchanger technology. We found various energy-efficient dryer technologies can have significant impacts on drying time. Unvented heat pump dryers, which can use 50 to 60 percent less energy compared to conventional electric dryers, take two to two-and-a-half times as long to dry.
Another efficient dryer technology is an exhaust heat exchanger that uses waste heat coming out of the drum to preheat incoming air. This technology can reduce energy use by about 20 percent and actually reduces drying time. Another method of saving significant amounts of energy is running the dryer in no-heat mode much of the time, saving about 25 percent of energy use but tripling the drying time. Automatic termination saves approximately 15 percent of energy and decreases drying time. Natural gas dryers provide a cost-effective way of reducing environmental impact with fast drying, while vented heat pump and radiofrequency dryers represent promising emerging technologies. With increased network capability coming to the market, some of these energy saving options could be turned on or off through software upgrades.