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Heat Pumps
Published in Dorothy Gerring, Renewable Energy Systems for Building Designers, 2023
Electric clothes dryers use a lot of power by using resistance heat to make air hot enough to evaporate the water in the wet clothes. Heat pumps in clothes dryers are located at the bottom of the unit (figure 11.8). The dryer is unvented and uses the air in the room. Air is drawn into the dryer and then across the evaporator and condenser and through the clothes in the drum. Then it continues to circulate around the loop. The air is dried out by the evaporator because the cold coils cause the water vapor to condense and drip into a drained pan. The dry air then passes over the condenser coil, which is hot, so the air is warm and dry as it is reintroduced into the dryer. The coils are set up so that the refrigerant only flows one direction. The compressor and expansion valve work as they normally would in any heat pump. Heat pump clothes dryers can use 40–50% less energy than electric resistance dryers. According to EnergyStar, 6% of US residential electrical consumption is used for drying clothes.6
Efficiency limits of evaporative fabric drying methods
Published in Drying Technology, 2021
Kyle R. Gluesenkamp, Viral K. Patel, Ayyoub M. Momen
Nearly 80% of households in the United States have clothes dryers, and 30% of these dryers are at least 10 years old.[1] The most common types of clothes dryers use an evaporative thermal process to facilitate moisture removal from fabrics. Electric resistance dryers (ERDs) heat air from the ambient using an electric resistance element, and natural gas dryers (NGDs) heat air from the ambient using natural gas combustion. The heated air is directed into a rotating drum in which the wet fabric is tumbling; the air collects moisture and leaves the drum to be vented. This once-through configuration requires that a vent be installed. Much research effort has been dedicated to understanding the physical processes and characterizing the performance of these types of dryers. Researchers have focused on attempting to improve the energy efficiency of ERDs and NGDs using various techniques such as an air-to-air heat exchanger (HX) in the outgoing air stream to condense moisture,[2] an external hot water supply as an additional heat source,[3,4], or a membrane to enhance dehumidification in a condensing dryer.[5]
A rationally based model applicable for heat pump tumble dryer
Published in Drying Technology, 2019
Bing-Hung Lee, Rony A. Sian, Chi-Chuan Wang
Drying is one of the most energy consuming processes in the industry. For instance, drying accounts for up to 70% of all the energy used in wood industry and about 50% of the energy consumed in textile and food manufacturing industries.[1] In household applications, the energy consumed by tumbler dryers is also quite considerable. According to statistics of the International Energy Agency, the energy consumption of dryers in 22 member countries exceeds 3% of average annual household electricity consumption.[2] For instance, 80% of U.S. household clothes dryers consume 4.2% of the total residential primary energy. Clothes dryers normally use electrical resistance or gas heaters to heat up the air for drying process. In the United States, 90% of the energy consumed by domestic dryers is due to direct electric heating.[3] In contrast to direct electric dryers, heat pump-assisted dryers combine a typical heat pump system with an integrated air-loop dryer system and it is a highly energy-efficient alternative as compared to conventional electrical heating systems. Moreover, heat pump dryers are environmentally friendly and provide efficient control of drying conditions in terms of temperature, humidity and air velocity.