Clothes dryer Ventless dryers

Spin dryers

These centrifuges simply spin the drum much faster than a typical machine to extract more water from the load.They can remove more moisture in two minutes than a heated tumble dryer can in twenty minutes, saving a lot of time and energy.While spinning alone doesn't completely dry clothes, this extra step saves valuable time and energy for large laundromats like hospitals.

Condenser dryers

Just like in a tumble dryer, a condenser, or condensation dryer, passes heated air through the load.However, instead of exhausting this air, the dryer uses a heat exchanger to cool the air and condense the water vapor into a drain or collection box.Drier air passes through the circuit again.A heat exchanger usually uses ambient air as its coolant, so the heat generated by the dryer will go into the surrounding environment instead of outside, raising the room temperature.In some designs, the heat exchanger uses cold water, eliminating this heating at the expense of increased water usage.In terms of energy use, condenser dryers typically require around 2 kilowatt-hours (kW·h) of energy per average load.Because the heat exchange process simply uses ambient air (or in some cases cold water) to cool the interior air, it doesn't dry the air in the interior circuit to the same low humidity levels as typical fresh ambient air.This type of dryer requires more time than a tumble dryer due to the increased humidity of the air used to dry the load.Condenser dryers are an especially attractive option because of the long and complicated ductwork required to vent the dryer.

Heat pump dryers

Closed cycle heat pump dryers use a heat pump to dehumidify the process air.This type of dryer typically uses less than half the energy per load of a condenser dryer.Condenser dryers use a passive heat exchanger cooled by ambient air, whereas these dryers use a heat pump. Hot, moist air from the drum is passed through the heat pump, the cold end condenses the water vapor into a drain or collection box, and the hot end then reheats the air for reuse.In this way, not only does the dryer eliminate the need for ducts, but it also retains most of the heat inside the dryer instead of venting it to the surrounding environment.As a result, heat pump dryers require up to 50% less energy than condensing or traditional electric dryers.Heat pump dryers use about 1 kW∙h of energy to dry an average load, as opposed to the 2 kW∙h of condensation dryers, or the 3 to 9 kW∙h of traditional electric dryers.Home heat pump clothes dryers are designed to operate in typical ambient temperatures of 5 to 30 °C (41 to 86 °F). Below 5 °C (41 °F), the drying time will increase significantly.

As with condensing dryers, the heat exchanger will not dry the air inside to the low humidity levels of typical ambient air.As far as ambient air is concerned, higher humidity in the air used to dry clothes increases drying time; however, since heat pump dryers retain most of the heat from the air they use, already hot air can be dried more quickly cycle, which may result in shorter drying times than a tumble dryer, depending on the model.

Mechanical vapor compression dryers

These machines are a new type of clothes dryer in development that is a more advanced version of the heat pump dryer.Instead of using hot air to dry clothes, mechanical vapor compression dryers use water recovered from the clothes in the form of steam.First, the glass and its contents are heated to 100 °C (212 °F).The generated moist steam clears the air from the system and is the only remaining atmosphere in the drum.As the wet steam leaves the drum, it is mechanically compressed (hence the name) to extract the water vapor and transfer the heat of vaporization to the remaining gaseous steam.This pressurized gaseous steam is then allowed to expand and superheat before being reinjected into the drum, its heat causing more water to evaporate from the clothes, creating more wet steam and starting the cycle all over again.Like heat pump dryers, mechanical vapor compression dryers recover most of the heat used to dry clothes, and they operate in a very similar efficiency range to heat pump dryers.Both types are more than twice as efficient as conventional tumble dryers.The considerably higher temperatures used in mechanical vapor compression dryers result in about half the drying time of heat pump dryers.

Microwave dryers

Japan have developed highly efficient clothes dryers that use microwave radiation to dry clothes (although the vast majority of Japanese people air dry.Most of the drying is done using microwaves to evaporate the water, but the final drying is done with convection heating to avoid problems with arcing with metal parts in the garment.There are many advantages: shorter drying time (25% reduction),energy saving (17–25% reduction) and lower drying temperature.Some analysts believe arcing and fabric damage is a factor hindering the development of microwave dryers for the US market.