Improving the energy efficiency of residential clothes dryers

Abstract

An experimental study on energy efficient electrical domestic clothes dryers is presented. A literature survey was performed and four basic energy saving techniques were identified: (1) reduced air flow rate and heater input, (2) recirculation of a portion of the exhaust air back into the clothes dryer, (3) heat recovery, utilizing an air-to-air heat exchanger, and (4) 100% recirculation of air through the dryer and a heat pump to condense water out of the air. Reduced air flow rate and heater input leads to energy savings around 8%, while recirculation of exhaust air reduces the energy consumption by approximately 18%. Because of the low cost of these two measures, they should be pursued by the manufacturers. When utilizing an air-to-air heat exchanger for heat recovery, two modes are considered. The first is to preheat the inlet air with heat from the exhaust air, which results in 20 to 26% energy savings depending upon the location of the dryer in the house. The second more attractive mode is 100% recirculation of air and condensation of water from this air in the heat exchanger (using indoor air as a heat sink) and represents a 100% heat recovery but leads to a 1more » to 6% increase in energy consumption. The development of a clothes dryer equipped with an air-to-air heat exchanger and a summer/winter switch (preheating mode in the summer and recirculation/condenstion mode in the winter) should be pursued by the manufacturers. Recirculation through a heat pump with condensation again gives a 100% heat recovery and can save up to 33% in energy consumption but yields long drying times due to limitations of the condenser temperature.« less