Ultra-Efficient Clothes Dryer Wins Design Competition

Ultra-efficient two-stage heat pump clothes dryer (HPCD) prototype
Hybrid air/water conditioner (HAWC).
The winning University of Maryland team
Runner-up Ohio State University's team
September 2013

An ultra-efficient two-stage heat pump clothes dryer (HPCD) prototype brought home the gold for the University of Maryland (UMD) design team who developed it during a spirited, year-long competition. The Max Tech and Beyond Design Competition, a project of the Energy Efficiency Standards group at Lawrence Berkeley National Laboratory that is funded by the Emerging Technologies Program of the U.S. Department of Energy (DOE), promotes the rapid development of energy-efficient appliances that outperform currently available models and supports the education of the next generation of U.S. clean energy engineers. The UMD team was one of eight college teams that participated.

At the end of the 2012/2013 academic year expert judges awarded the UMD team for its outstanding technological engineering achievement in the advancement of energy-saving appliances. A close runner-up, Ohio State University won an honorary mention for educational impact and business plan development for their hybrid air/water conditioner (HAWC).

The UMD team will showcase their winning prototype at the 2013 Solar Decathlon XPO sponsored by DOE, which will be held this October in Irvine, California. The Solar Decathlon challenges collegiate teams to design, build, and operate solar-powered houses that are cost-effective, energy-efficient, and attractive.

Both of the Max Tech winning teams will have the opportunity to participate in an entrepreneur workshop at UC Davis in September, which helps to bring new technologies to market by connecting student entrepreneurs with leaders in the business and investment communities.

The support provided by the Max Tech and Beyond Design Competition was critical for the development of these prototype technologies and, for some teams, paved the way to other prizes. The HAWC team won first place in a college-wide engineering capstone design showcase and took the top clean energy prize in a local business plan competition. "Our success in these activities can be traced back to the resources, advice, and structure provided by the Max Tech organizers," says Professor Mark Walter, the team's faculty advisor. "In addition to our technical achievements in building a prototype that met our coefficient of performance (COP) improvement goals, our project has exceeded our expectations for a design-build educational experience."

The student leader of the UMD team, Tao Cao, similarly praised the competition's educational experience. "Working on the UMD dryer team for the Max Tech and Beyond Design Competition was quite a rewarding experience for me," says Cao, "and it has definitely strengthened my interest in working in the eco-engineering area." The competition has sparked a growing interest in the fields of sustainability and energy efficiency enhancement at UMD, as evidenced by the now popular Ultra-Low Energy Use Appliance Design course, according to the team's faculty advisor, Dr. Yunho Hwang.

The award-winning two-stage HPCD from the UMD team takes dryer efficiency a major leap beyond what is currently available. In the United States today, an energy-efficient clothes dryer is not a readily available option. Most electric clothes dryer models consume similar amounts of energy. In Europe and Japan, such a search would be more successful, as more efficient heat pump clothes dryers can be found there. Heat pump dryers typically consume about one-third less energy than conventional electric dryers.

The two-stage HPCD goes further, combining compact heat exchangers, a brushless direct-current (DC) motor, and a vapor injection cycle to deliver energy savings of 59% compared to an existing state-of-the-art U.S. electric clothes dryer. Experimental testing of each dryer's energy use followed DOE's published clothes dryer test procedures. With an estimated 67 million U.S. households that use electric clothes dryers, nationwide energy savings could amount to 21 GWh (Gigawatt-hours), if all these households switched to using the prototype HPCD. Hwang is seeking industrial partners to bring the prototype to market.

Dr. Hwang attributes the team's success to the students' enthusiasm and perseverance. "They were really interested in improving energy efficiency, more than just taking a class," says Hwang. "Students on the team spent extra lab hours and weekends working on constructing the dryer prototype and testing."

The team at Ohio State University was also enthusiastic about reducing household energy use. According to the U.S. Energy Information Administration, in 2009, more than 65% of all energy use in U.S. homes was dedicated to space/air conditioning and water heating. Targeting both of these end-uses could achieve significant energy savings. That was the original thinking that resulted in an earlier HAWC prototype. The 2012/2013 team built upon this work to develop the HAWC 2.0 prototype. Recognizing that newer buildings tend to be better insulated and more air-tight, the team aimed to develop an air and water conditioning system that is well suited to meeting smaller loads, better controls humidity, and does all this more efficiently. In conjunction with the technical development, the team created a business plan that informed many of the decisions made regarding the features of HAWC 2.0, the physical layout, and pricing.

The HAWC 2.0 system employs an appropriately sized desiccant wheel, a sensible heat exchanger, and a variable-speed compressor. The desiccant wheel is used to control humidity, while improving efficiency by approximately 49%. Hybridization of air conditioning and water heating, which takes full advantage of the heat produced during the vapor compression cycle, results in a 30% improvement in the appliance's COP. According to the team's testing, the HAWC 2.0 provides a 73% yearly energy cost savings over a conventional central air conditioning, dehumidification, and ventilation system with a payback period of just over 3.4 years.

Max Tech and Beyond is sponsoring another competition during the academic 2013/2014 year to further encourage and support the next generation of energy engineers, with additional funding from DOE's Building Technologies Office (BTO). Twelve teams from different colleges and universities have been selected to participate—a 50% increase in the number of schools participating and the university teams funded since the competition was inaugurated in 2010. The winners will be announced in August 2014.

Those interested in obtaining more information about the competition should contact the program organizers at maxtech@dante.lbl.gov.

Mary James