Achieving a High-Efficiency Electric Clothes Dryer

Grant # 96-09
Principal Investigator: G. M. Colver
Organization: Iowa State University
Other Participants: Frigidaire Co. and Center for Advanced Technology Development (CATD)
Student Support: Ashraf Bassily, Seung-Bae Hong
Technical Area: Energy Efficiency

Background and Significance
Electric clothes dryers are both energy wasteful and thermally polluting, relying on simple ohmic heating to evaporate moisture from clothes. The performance of clothes drying is further diminished by infiltration and/or exfiltration of air. This wasted energy means increased operating cost in terms of electricity, heating and air conditioning for the consumer. Waste electric energy also impacts our natural resources (coal/gas/oil) and contributes to environmental problems of thermal pollution and gas-solids emission at sites of electrical production.

The incorporation of alternate drying technologies, as well as the redesign of components and the integrated design of a conventional dryer can improve the energy efficiency of electric drying. This will reduce consumer costs and natural resources. Some improvements in dryer efficiency have been made with the introduction of the so-called condensing dryer.

Project of the Continuation:
The overall goal of this research is to increase the efficiency of the present-day electric clothes dryer by (1) improving component performance of present-day dryers and (2) the utilization of new methods of technology for dehumidification or heating. These will be demonstrated by a working prototype (year three). Another objective is to develop a computer model of a conventional dryer so that dryer performance can be optimized.
Ventless drying is being considered. The research represents a balance of experimental work, design and theoretical modeling of present-day and new dryer technologies. A range of solutions is being considered, from improving heater design to the utilization of electrostatic fields for dehumidification.

Summary of Work to Date:
A hands-on and cooperative approach with Frigidaire Co. has been utilized in which the graduate students and Professor Colver have completely disassembled and instrumented three dryers. They have participated in several visits and a training session held at Frigidaire Co. in Webster City.

To date, the low-tech aspect of our research has emphasized the instrumentation, installation of computer aided data acquisition and preliminary evaluation of data for three electric clothes dryers. One of the three dryer platforms was designed by Frigidaire Co. and allows for considerable versatility in performance testing. Additionally, the theoretical evaluation and fabrication of three high-tech components (membrane filtration, thermoelectric and electrostatic) are underway or have been completed. A complete computer model of a dryer has also been under development to support the design process. A first computer model for the heater and blower has been completed.

A considerable effort was required initially in designing and perfecting the experimental setup for each dryer. The measurements required include temperature, humidity, flow rate and separate power inputs to the dryer and to the heater. Various problems were overcome such as improving the reliability for the measurements of wet bulb temperature and coil temperatures. New data have been taken for the most recent dryer platform for evaluation and performance mapping of the dryer. As a result of studying the three platforms, we better understand the different approaches to air mixing, etc. This information supports our modeling effort. Our data show that some redesigning of the heater should prove beneficial to the overall dryer performance while the implication of leakage air into the drum should also be considered.

On the high-tech side of our research, the fabrication of an electrostatic device for dehumidification, as well as that of a thermoelectric based unit is currently underway. These first prototypes have followed a complete theoretical analysis of the three proposed technologies. Our study shows that the pumping losses and unit cost of membrane filtration present prohibitive factors in dryers. Consequently, membrane filtration is no longer being considered in our work.

Work Yet to Be Completed:
This is the second year of a three-year study to design and construct an energy efficient electric dryer incorporating high technology. For the low-tech side, our future work involves finalizing a heater design and evaluating drum and blower component performance. Incorporating a high-technology method will require the performance evaluation of our simplest designs followed by redesigning and testing. A hybrid dryer comprising more than one technology will be considered in year three.