Clothes Drying

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Clothes dryers typically use about 2.5 kWh per load. A parameter called the energy factor, which is a measure of the pounds of clothing dried per kWh of electricity consumed, can be used to quantify the efficiency of clothes drying. The minimum EF for a standard capacity electric dryer is 3.01. In the U.S., new dryers are not required to display energy use information, so it is difficult to compare models. In fact, most electric dryers on the market are comparable in their construction and the basic heating technology. However, the actual energy consumption of the dryer varies with the types of controls it has, and how the operator uses those controls. Models with moisture-sensing capability can result in the most energy savings—savings on the order of 15% compared to conventional operation are common.

In addition, electric clothes dryers operate most efficiently when fully loaded. Operating with one-third to one-half load costs roughly 10%-15% in energy efficiency.

Locating clothes dryers in heated spaces could save 10%—20% of the energy used by reducing energy needed for heating up. Another approach is to save up loads and do several loads sequentially, so the dryer does not cool down between loads.

The heavier the clothes the greater the amount of water they hold. Mechanical water removal (pressing, spinning, wringing) generally requires less energy than electric heat. Therefore, be certain the washing machine goes through a complete spin cycle (0.1 kWh) before putting clothes in the dryer.

Solar drying, which requires a clothesline (rope) and two poles or trees, has been practiced for millennia and is very sparing of electricity. The chief limitation is, of course, inclement weather. New technologies such as microwave or heat pump clothes dryers may help reduce clothes drying energy consumption in the future.

10.2.2.7.2 Clothes Washing

The modified energy factor (MEF) can be used to compare different models of clothes washers. It is a measure of the machine energy required during washing, the water heating energy, and the dryer energy needed to remove the remaining moisture. A higher MEF value indicates a more efficient clothes washer. All new clothes washers manufactured or imported after January 1, 2004 are required to have an MEF of at least 1.04, and after January 1, 2007, an MEF of at least 1.26. In addition, as of January 2004, a minimum MEF of 1.42 is required for a clothes dryer to be qualified as an Energy star unit. A typical Energy star unit uses about 0.7 kWh per load.

Electric clothes washers are designed for typical loads of 3-7 kg. Surprisingly, most of the energy used in clothes washing is for hot water; the washer itself only requires a few percent of the total energy input. Therefore, the major opportunity for energy management in clothes washing is the use of cold or warm water for washing. Under normal household conditions it is not necessary to use hot water. Clothes are just as clean (in terms of bacteria count) after a 20°C wash as after a 50°C wash. If there is concern for sanitation (e.g., a sick person in the house), authorities recommend use of chlorine bleach. If special cleaning is required, such as removing oil or grease stains, hot water (50°C) and detergent will emulsify oil and fat. There is no benefit in a hot rinse.

A secondary savings can come from using full loads. Surveys indicate that machines are frequently operated with partial loads, even though a full load of hot water is used.

10.2.2.7.3 Dishwashers

The two major energy uses in electric dishwashers are the hot water and the dry cycle. Depending on the efficiency of the model and operation, dishwashers use between 2 and 5 kWh per load.

The water heating often accounts for 80% of the total energy requirement of a dishwasher. The volume of hot water used ranges from about 5 gal for the more efficient units to more than double that for less efficient models. The water volume can be varied on some machines depending on the load.

Some models also allow for a no-heat drying option. If not available, stop the cycle prior to the drying step and let the dishes air-dry. Operating the dishwasher with a full load and using a cold water prerinse are additional ways to minimize energy use.

10.2.2.7.4 General Suggestions for Residential Appliances and Electrical Equipment

Many electrical appliances (pool pumps, televisions, stereos, DVD and CD players, electronic gaming systems, aquariums, blenders, floor polishers, hand tools, mixers, etc.) perform unique functions that are difficult to duplicate. This is their chief value.

Attention should be focused on those appliances that use more than a few percent of annual electricity use. General techniques for energy management include:

• Reduce use of equipment where feasible (e.g., turn off entertainment systems when not in use)

• Perform maintenance to improve efficiency (e.g., clean pool filters to reduce pumping power)

• Schedule use for off-peak hours (evenings)

The last point requires further comment and applies to large electric appliances such as washers, dryers, and dishwashers. Some utilities now offer "time-of-use" rates that include a premium charge for usage occurring "on-peak" (when the greatest demand for electricity takes place), and lower energy costs for "off-peak" electricity use. By scheduling energy-intensive activities for off-peak hours (clothes washing and drying in the evening for example) the user helps the utility reduce its peaking power requirement, thereby reducing generating costs. The utility then returns the favor by providing lower rates for off-peak use.

10.2.2.8 Computers and Office Equipment

Computers are fairly ubiquitous in both the residential and commercial sectors at this point. There are significant energy savings available from going to LCD displays in place of CRT displays, and in enabling the sleep or power saver routines available with the machines. The use of laptop machines in place of desktop machines also offers substantial savings.

A wide variety of equipment in addition to computers can be found in commercial buildings, depending on the size and function. Process equipment within buildings (e.g., clothes washers in laundries, printing presses, refrigerated display cases, etc.) will not be discussed due to the great diversity of these items.

Excluding process equipment, major energy-using equipment in commercial buildings generally includes HVAC systems, lighting, and "other" equipment. Because energy management options for HVAC and lighting have already been described, the discussion here will be directed at "other" equipment, including:

• Computers, local area networks and peripherals

• Facsimile machines, electronic mail

• Vending machines and water coolers

• Copy machines

• Elevators and escalators

The energy management opportunities with these types of equipment are more restricted. One obvious strategy is to insure that all equipment is turned off when not needed or not in use. Another is to size equipment with the right capacity to do the job, avoiding overcapacity, which increases both energy and demand charges.

In general, the most likely opportunity with elevators, escalators, and similar equipment is to shut them down during off hours or other times when they are not needed.

There is a host of miscellaneous equipment in buildings that contributes only a small percentage of total energy use, is used infrequently, and is an unlikely candidate for improved efficiency.

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