Heat Pump Clothes Dryer : 2012-2013
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You can learn more about the winning team and their prototype at their school's website.
The electric clothes dryer (CD) is typically the appliance that uses the most electricity in a household, after the electric water heater. According to the Energy Information Administration (EIA), 90 million households used CDs, and 0.67 quadrillion Btu were used for clothes drying in residential and commercial buildings in 2010. Unlike most other types of appliances, CDs are not listed in the ENERGY STAR®'s database, because most models consume similar amounts of energy. Electrically powered CDs were used in 79% of U.S. households, while gas-fired CDs were used in 21% of the U.S. residential market in 2010. Noticeably absent were heat pump clothes dryers (HPCDs), which consume about 33% less electric energy, but so far are used mainly in Europe and Japan.
By using a vapor injection cycle, we can increase the refrigerant flow rate through the condenser and maximize the enthalpy difference across the evaporator. In this way, the system’s cooling and heating performance will be enhanced.
By using a heat exchanger in the suction line, we can reduce the temperature of the refrigerant entering the expansion device, increase the condenser inlet refrigerant temperature, and reduce the condensing pressure. In this manner, overall system capacity and efficiency are both improved.
By splitting air streams through the evaporator and condenser, and optimizing airflow rates through each heat exchanger and its refrigerant circuitry, we can remove excess moisture in the evaporator and achieve a higher degree of subcooling in the condenser, thereby maximizing the performance of the dehumidification process and the heat exchanger.
By utilizing dynamic evaporator air ventilation, moist air discharged from the evaporator is dynamically separated from the condenser air stream and ventilated to the outdoors, when the humidity ratio is higher than a threshold value; in this way only moderately humid room air is heated by the condenser and used for capturing moisture in the drum. When the humidity ratio of the evaporator outlet air is reduced below that of the room air, it is directed to the condenser.
Potential Energy and/or Cost Saving
With project energy savings of approximately 10% to 20% compared to typical European HPCDs. These projections will result from performance enhancements achieved through the use of the previously described design concepts, as well as other new ideas conceived during the project’s brainstorming phase. When comparing our prototype to current U.S. electric CDs, these savings could be as high as 40% to 46%.
Our design is commercially attractive, due to its unique energy-saving features. After a successful demonstration, we will approach current industrial partners of the Center for Environmental Energy Engineering, which includes GE, Whirlpool, and LGE.
The final report for the UMDDryer team is attached below. In it, the results of the testing and the energy savings calculations are explained.
"Improving energy efficiency is most promising tangible solution to our energy challenges. Participating in MaxTech Competition allows me to work together with next generation engineers for addressing such important issue. I am very excited to be able to continue our effort to improve our winning prototype design to next level and keep exploring for licensing options." - Yunho Whang, Faculty Lead