If you can't conserve energy, stay out of the kitchen

Oct. 12, 2006
Superefficient appliances are washing and drying our clothes, cleaning the dishes, and even heating our homes.

A new high-tech refrigerator from Electrolux comes with a computer and 15-in. touchscreen for surfing the Internet, sending e-mail, and shopping for groceries without leaving the kitchen. The refrigerator is connected to broadband and TV via wireless connection. And if Internet, e-mail, phone, radio, and MP3 player are not enough, there's a calendar and videomessaging system. Before you leave for work, you can check the weather and traffic, check appointments with a personal organizer, and print an electronic shopping list (printer not included). The refrigerator is accessible via a remote-access feature. Oh yeah, it keeps things cold, too.

Energy-efficient washers increasingly are adopting a front-loading format where the drum is driven directly by a specially built permanent-magnet synchronous motor with no intervening gearbox or belt drive. Wash dynamics in these new machines are such that clothes emerge clean after a wash and rinse with water levels that may not even cover the clothes. There are tough torque and speed requirements levied on the PM synchronous motors in such systems as becomes evident in a typical torque/speed graph as depicted by International Rectifier. New integrated circuits designed especially to drive PM washer motors can now synthesize such performance.

Clothes washers undergo Energy Star evaluation at Whirlpool Corp.'s Clyde, Ohio, manufacturing plant. The test panel measures total energy consumed including water usage, recently added to the Energy Star specifications.

The IRMCF341 washer-control IC recently developed by International Rectifier incorporates an 8051-style processor to run washer application code and a separate processor (MCE) dedicated to managing the PM synchronous motor. The chip implements a sensorless control algorithm that eliminates the need for feedback from Hall-effect sensors to manage commutation. A single shunt resistor is used for motor phase-current reconstruction. The chip works with a power module which generates the motor-winding currents. International Rectifier devised a reference design platform for development work. It incorporates the chip and enough ancillary circuitry to let developers check out its operation with different motor parameters and application routines.

As soon as Energy Star products reach 20% market penetration, DOE revisits the specifications for review and possible tightening. The process nudges manufacturers to create even more efficient products.

Permanent-magnet synchronous motors are beginning to replace split-phase induction motors in appliances as a means of boosting efficiency while reducing part costs. PM synchronous motors work at variable speeds and may become part of the appliance structure itself, perhaps eliminating the need for separate gearboxes and belt drives used to harness power from induction motors.

Patrick Mahoney
Associate Editor

Nobody wants to throw out — or better still, recycle — what seems like a perfectly good appliance. But if your major appliances are more than 10 years old, you could be ahead of the game by doing just that. Major strides in energy and water-use efficiency could mean it's time to haul that reliable refrigerator, dependable dishwasher, or dutiful dryer to the curb.

Refrigerator efficiency depends on features such as defrost type (manual, partial automatic, automatic), door style, and size. Topfreezer models outperform side-byside models and partial-automatic or manual-defrost models are more efficient than those with automatic defrost. Manual-defrost models use half the energy of automatic-defrost models, but they must be defrosted periodically to remain efficient. Automatic icemakers and through-the-door dispensers boost energy use somewhat. Refrigerators are becoming incrementally more efficient thanks to improved insulation and other design efficiencies. The most energy-efficient refrigerators are relatively small with manual or partial-automatic defrost. Because their initial cost is high, acceptance is largely limited to the environmentally conscious consumer.

The typical new refrigerator with automatic defrost and topmounted freezer uses less than 500 kWh/yr compared to 1,800 in 1973. According to Sr. Product Manager Greg Garavalia with Whirlpool Food Preservation, traditional defrost systems work on a timer mechanism. The timer turns the defrost heaters on approximately every 12 hr, regardless of use. New models adjust the defrost cycle depending on use. The fewer times the door opens, the less the compressor will run; the less the compressor runs, the less need for defrosting.

Improved insulation, foam (versus fiberglass) inside the doors, and high-efficiency condensers, evaporator fans, and compressors all contribute to energy efficiency. Also, pulse-defrost electronics cycle the evaporator heater on and off during the defrost cycle. This minimizes the total temperature rise in the freezer, thereby reducing the energy needed to cool it again.

The greatest potential for energy and water savings in household-appliances is found in washingclothes. Modern machines consume 14% less electricity and 87% less water, resulting in a 31% drop in operating cost as compared to a decade ago. The biggest single factor in the efficiency gain was the result of turning the machine on its side.

Front-loading models with a horizontal axis (H-Axis) use energy and water more efficiently than top-loading vertical-axis (V-Axis) machines. Some H-axis machines can be loaded from the top but they are more difficult to find.

To understand why H-axis washers use far less water and energy, consider that the tub in a conventional top-loader (V axis) fills with water to keep clothes wet. The agitator then swirls the water around to clean the clothes. H-axis washers do not fill completely with water. The tub itself rotates, tumbling the clothes into the water.

H-axis/front-loading washers also make drying more efficient. After the rinse cycle, they spin clothes faster than conventional top-loaders, lowering the remaining moisture content of the clothes. Lower moisture content lessens drying time.

Resource-efficient, H-axis washers usually have a higher sticker price than conventional models, but the significant energy and water savings promise a quick return on the investment. Field studies show H-axis washers are also gentler on clothes. Finally, less time in the dryer means less wear-and-tear on clothes.

For some consumers, however, H-axis machines may be less desirable because of the bending necessary to load and unload them. Some redesigned V-axis washers use sprayers to wet the clothes from above. In others, a moving plate in the bottom of the tub lifts and bounces clothes through the water.

A washing machine's features also affect the amount of hot water used. Models offering many wash and rinse cycles improve efficiency. Warm wash cycles sufficiently clean most clothes, and cold rinses are generally effective. "Suds-saver" (reusing slightly soiled wash water), and presoaking are energy-conserving options. Normally, washing a full load is most efficient.

Energy-efficient washers demand precise control of drum or agitator movements with high torque at speeds that can be lower than 50 rpm. And washer makers are boosting their spin speeds to 1,000 rpm and more to wring out as much moisture as possible to minimize drying time.

In the past, washers relied on split-phase induction motors and gearboxes to power the drum and agitator. But this arrangement didn't offer the kind of performance energy-efficient washers need at both ends of the speed range. In response, next-generation washers are moving toward permanent-magnet synchronous motors. These motors can generate sufficient speed and torque without necessitating an intervening gearbox. The resulting direct-drive system is more efficient than mechanical drives and takes up less space.

Dryers work by heating and aerating clothes. In terms of energy use, gas dryers are generally less expensive to operate than electric models. But the energy use of dryers currently on the market does not vary widely.

Besides fuel type, the major energy consideration is whether the dryer uses sensors to automatically switch off once clothes are dry. The best dryers have moisture sensors in the drum. Most dryers estimate dryness by sensing the temperature of the exhaust air. These thermostatcontrolled models may overdry clothes, but even these are better than timed-dry machines. Temperature-sensing controls save about 10% and moisturesensing controls save about 15% more energy than timed drying. Want a sure way to save energy? Buy a new dishwasher. In general, water use determines a dishwasher's energy efficiency. Research by Electrolux shows that dishwashers can reduce energy and water consumption by up to 60% over washing by hand. Compared to their 10-year-old counterparts, today's dishwashers consume up to 22% less electricity and 13% less water.

Dishwashers offer special features that improve energy efficiency. Virtually all dishwashers available today use booster heaters. Boosters save energy by letting the primary water heater operate at a lower temperature, about 120°F. No-heat drying is another helpful feature. It is also important to know how much water different models need and to select one that can do the job with the least amount of water. In general, European appliances are more energy (and water) efficient, durable, and expensive. Dishwashers, now considered a mature technology, are currently experiencing only minor efficiency gains.

A residential gas water-heating system can double as a space heater. The system circulates hot water from the water heater through a heat exchanger in the air handler. A blower moves the heated air through a standard duct system. In summer, an air conditioner connected to the exchanger pushes cool air through the ductwork. And these high-efficiency water heaters vent through the wall instead of the chimney.

Gas water heaters, while not the perfect environmental choice, create fewer pollutants than other conventional waterheating options, except solar. And costs are comparable to heat pumps and electric water heaters.

The process of choosing the right size combo system is more involved than that for ordinary water heaters. Minimum tank size for a combo system is 40 gallons. In most cases, a water heater sized to meet space-heating demand will satisfy the hot water needs of the household.

The two primary choices in water heaters are demand (or instantaneous) heaters and storage-tank units. Demand heaters heat water on demand near the point of use. This can be useful if there is limited space for a storage tank. However, they must be able to handle simultaneous multiple draws of hot water. Typical medium-size units raise incoming water temperatures by 60°F at a rate of 3.5 gpm (125,000-Btu input). Some units sense incoming water temperature, not turning on if the water is sufficiently warm. This is useful for solar interconnections or circulating systems. Demand heaters typically need a minimum 15 to 20 psi, mount to the wall, and vent vertically.

The most common water heater, the storage-tank unit, is usually less expensive than a demand unit. The highest efficiency storage tank units show recovery efficiencies of 85%. In energy savings, high-efficiency units compare favorably to demand units when the initial cost of the unit is considered.

The growing cost of energy and an increased awareness of shrinking natural resources has consumers looking at their appliances in a new light and the Energy Star program holds the lamp. From light bulbs to new homes, Energy Star labels identify products that help protect the environment by using energy more efficiently.

The U. S. Dept. of Energy (DOE) and the U.S. Environmental Protection Agency (EPA) jointly administer the Energy Star program, with voluntary participation by manufacturers and retailers. Appliances awarded the Star logo typically fall within the top 25% efficiency rating for the industry.

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