Tumble dryers
Tumble dryers continuously draw in the ambient air around them and heat it before passing it through the tumbler. The resulting hot, humid air is usually vented outside to make room for more air to continue the drying process. This design makes no effort to recycle the heat put into the load, and thus is considered environmentally wasteful. Nevertheless, it is simple and reliable, and therefore has been widely used.
Improvised methods of salvaging this heat for in-home heating, by use of inline vent boxes equipped with a flapper valve to redirect moist heated air to indoor areas, will also increase humidity within a dwelling. Although this may be beneficial in dry winter conditions, excess humidity from these devices increases likelihood of mold, mildew, and bacterial growth inside a home. Indoor venting may also be against local regulations. Gas dryers, unlike electric dryers, must always be vented outdoors, as the products of combustion are mixed with the moist air. Building codes and manufacturers' instructions usually recommended that dryers vent outdoors. An indoor lint trap kit poses a similar concern of increased humidity within the dwelling.[further explanation needed]
"Long run" dryers have an additional fan inside to boost the exiting moist air through longer sections of vent pipe, as in apartments or dwellings where the vent cannot make a short direct connection from the dryer to the outside.
Beyond issues with venting exhaust, other improvised efficiency efforts with conventional dryers attempt to harvest an input source of pre-heated air rather than using the conditioned air of the living space. One notable source of heat to pre-heat dryer air is to install ductwork allowing the device to suck hot air from a dwelling's attic.[citation needed]
Tumble dryers are often integrated with a Washing machine, in the form of laundry centers, which stacks the dryer on top of the washer and integrates the controls for both machines in a single control panel, or in the form of "washer-dryer combos" which are essentially a front loading washing machine with an integrated dryer. Often the washer and dryer functions will have a different capacity, with the dryer usually having a lower capacity than the washer. Tumble dryers can also be top loading, in which the drum is loaded from the top of the machine and the drum's ends are in the left and right sides, instead of the more conventional front and rear. They can be as thin as 40cm in width.
Lint build-up (tumble dryers)
Upper image shows a severely kinked and blocked dryer transition hose used to vent a tumble dryer. In this case, the dryer was located or pushed back too far against the wall. The lower image shows initial lint build-up in the flex transition hose.
Moisture and lint are byproducts of the tumble drying process and are pulled from the drum by a fan motor and then pushed through the remaining exhaust conduit to the exterior termination fitting. Typical exhaust conduit comprises flex transition hose found immediately behind the dryer, the 4-inch (100 mm) rigid galvanized pipe and elbow fittings found within the wall framing, and the vent duct hood found outside the house.
A clean, unobstructed dryer vent improves the safety and efficiency of the dryer. As the dryer duct pipe becomes partially obstructed and filled with lint, drying time increases and causes the dryer to overheat and waste energy. In extreme cases, a blocked vent may result in a fire. Clothes dryers are one of the more costly home appliances to operate.[16]
Several factors can contribute to or accelerate rapid lint build-up. These include long or restrictive ducts, bird or rodent nests in the termination, crushed or kinked flex transition hose, terminations with screen-like features, and condensation within the duct due to un-insulated ducts traveling through cold spaces, such as a crawl space or attic. If plastic flaps are at the outside end of the duct, one maybe able to flex, bend, and temporarily remove the plastic flaps, clean the inside surface of the flaps, clean the last foot or so of the duct, and reattach the plastic flaps. The plastic flaps keep insects and birds out of the dryer vent pipe. During cold weather, the warm wet air condenses on the plastic flaps, and minor trace amounts of lint sticks to the wet inside part of the plastic flaps at the outside of the building.[17],[18]
Home clothes dryer outside vent outlet. Flaps can be removed for cleaning of the flaps and duct.
Ventless dryers include multi-stage lint filtration systems and some even include automatic evaporator and condenser cleaning functions that can run even while the dryer is running. The evaporator and condenser are usually cleaned with running water. These systems are necessary, in order to prevent lint from building up inside the dryer and evaporator and condenser coils.
Safety
Dryers expose flammable materials to heat. Underwriters Laboratories[19] recommends cleaning the lint filter after every cycle for safety and energy efficiency, provision of adequate ventilation, and cleaning of the duct at regular intervals.[20] UL also recommends that dryers not be used for glass fiber, rubber, foam or plastic items, or any item that has had a flammable substance spilled on it.
A clothes dryer that has been damaged by fire.
In the United States, the U.S. Fire Administration[21] in a 2012 report estimated that from 2008 to 2010, fire departments responded to an estimated 2,900 clothes dryer fires in residential buildings each year across the nation. These fires resulted in an annual average loss of 5 deaths, 100 injuries, and $35 million in property loss. The Fire Administration attributes “Failure to clean” (34%) as the leading factor contributing to clothes dryer fires in residential buildings, and observed that new home construction trends place clothes dryers and washing machines in more hazardous locations away from outside walls, such as in bedrooms, second-floor hallways, bathrooms, and kitchens.
To address the problem of clothes dryer fires, a fire suppression system can be used with sensors to detect the change in temperature when a blaze starts in a dryer drum. These sensors then activate a water vapor mechanism to put out the fire.[22]
Environmental impact
The environmental impact of clothes dryers is especially severe in the US and Canada, where over 80% of all homes have a clothes dryer. According to the US Environmental Protection Agency, if all residential clothes dryers sold in the U.S. were energy efficient, "the utility cost savings would grow to more than $1.5 billion each year and more than 22 billion pounds of annual greenhouse gas emissions would be prevented”.[23]
Clothes dryers are second only to refrigerators and freezers as the largest residential electrical energy consumers in America.[24]
In the European Union, the EU energy labeling system is applied to dryers; dryers are classified with a label from A+++ (best) to G (worst) according to the amount of energy used per kilogram of clothes (kWh/kg). Sensor dryers can automatically sense that clothes are dry and switch off. This means over-drying is not as frequent. Most of the European market sells sensor dryers now, and they are normally available in condenser and vented dryers.