Ask Energenie

July 1999

Table of Contents

1. I am thinking about buying a new refrigerator since ours is almost 14 years old. In shopping for a new one, I’m a little confused by the ENERGYGUIDE label. How do I make sure I am purchasing the most energy efficient model?
2. Lighting is a major expense for our office. Can we reduce this cost without reducing the performance of our office staff?
3. Should I turn up my air conditioner's thermostat when I leave home for a few hours, or am I better off just leaving it on a single setting?
4. What should I consider before purchasing a whole-house fan?
5. What refrigerants are being used in residential air conditioners?
6. Our heating service contractor has mentioned that the heating and cooling unit on our commercial building has an economizer. What does this economizer do?

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1. I am thinking about buying a new refrigerator since ours is almost 14 years old. In shopping for a new one, I’m a little confused by the ENERGYGUIDE label. How do I make sure I am purchasing the most energy efficient model

"The ENERGYGUIDE label for refrigerators shows the estimated annual cost of energy to operate the appliance," replied Richard Nelson, extension specialist at Kansas State University.

The figure is based on the national average rate for electricity, or about 8.5 cents per kilowatt-hour.

"If the electric rate you pay is higher than this, your cost to operate the refrigerator will be more than the price on the label; if the cost of electricity is lower, then your operating costs will be lower as well," Nelson said.

"When you purchase a new refrigerator, it may be advantageous to buy one that has a higher initial cost," he said.

A refrigerator costs far more in electricity throughout its life than the original purchase price. Generally, models with a high initial cost are the most energy efficient.

In many instances, buyers must decide between two different models, one of which has a higher initial cost, and the other, a higher operating cost.

Nelson gave the following example to show which is the better buy.

The first model costs $750 and has a yearly energy cost of $35. The second model costs $600 with a yearly energy cost of $55. Subtract the cost of the lower priced refrigerator from the cost of the higher priced one, and divide this, $150, by the difference in yearly energy costs, $20 a year. This figure represents the number of years it takes to pay back the extra cost of the higher priced model.

"In other words, if you plan to keep the higher priced model for more than 7.5 years, it is the better buy," Nelson said.

Once you have made the purchase, keep your refrigerator operating in top condition by vacuuming the coils on the backside or bottom once a year. The build-up of dirt reduces heat transfer and lowers efficiency.

Also, make sure the door seal is tight. Close the door on a dollar bill and try to pull the bill through the door. If it pulls easily, then cold air is leaking through the door and it is time to replace the seal.

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2. Lighting is a major expense for our office. Can we reduce this cost without reducing the performance of our office staff?

"Businesses can implement inexpensive changes without reducing overall lighting quality," said Gene Meyer, extension mechanical engineer at Kansas State University.

One approach is to use task lighting. For example, offices should have between 60 and 100 foot-candles on the work surface. Overhead area lighting can be designed to provide 50 foot-candles and task lighting the remainder.

This has the advantage of reducing lighting energy use and it may well make the office visually more comfortable. In today's office, where nearly everyone has a video display terminal, high ambient lighting levels often interfere with the visual task. Task lighting allows higher levels in the desk and lower levels where computer terminals are used.

Another option that should be considered is to retrofit existing fluorescent fixtures with modern T8 lamps and electronic ballasts. Converting from four-lamp T-12 lamps and older ballasts to T-8s with electronic ballasts reduces power draw from 175 to 112 watts per four-lamp fixture.

It may be possible to convert the fixture from four to three lamps to reduce ambient lighting levels and begin using task lighting sources.

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3. Should I turn up my air conditioner's thermostat when I leave home for a few hours, or am I better off just leaving it on a single setting?

"You should turn it up," replied Doug Walter, president of Kansas Building Science Institute, Manhattan, "You will save energy by raising your thermostat setting or by simply shutting off your air conditioner when you leave home."

"As a tradeoff for the energy savings, your house may be uncomfortably warm while the air conditioner makes up for 'off' time," he said. "Therefore, to make the savings worth any discomfort, you may want to raise the setting only when you will be gone for four or more hours."

You can also increase savings, and comfort, by closing drapes to block sunlight while you are gone.

To reduce the discomfort of returning to a warm house, Walter suggested using a fan to create air movement while the air conditioner cools the house.

"Moving air feels four degrees cooler than still air," he said.

Another option is a programmable thermostat that can automatically control your air conditioner to cool your house shortly before you return. This option works best if your day-to-day schedule is fairly consistent, though most programmable thermostats permit a different weekend schedule and some permit a different schedule for each day of the week.

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4. What should I consider before purchasing a whole-house fan?

"You must consider several factors before making such a purchase," said Doug Walter, president of Kansas Building Science Institute, Manhattan. "First, make sure a whole-house fan is appropriate for your lifestyle and climatic location."

Cooling with ventilation works best in climates with large day-night temperature differences and low relatively humidity. This type of climate is more characteristic of western Kansas than eastern Kansas. "You must also be willing to use the fan on a regular basis in lieu of air conditioning to achieve a significant savings," Walter said.

If a whole-house fan still makes sense for you, determine the size of fan your house needs.

"For a whole-house fan to ventilate effectively, it should make 40 air changes an hour," Walter said. "This means it must move two-thirds of your house volume in one minute."

Determine the volume of your house by multiplying floor area by ceiling height. Then select a fan that has a CFM (cubic feet per minute) rating of two-thirds your house volume.

"If you have a large house with several floors, you might consider sizing the fan for just one floor," Walter said.

Second, determine where you will install the fan. Whole-house fans are usually mounted horizontally in the ceiling between the attic and the top floor. However, you can mount some models vertically in a wall.

"If you plan to install the fan yourself but do not want to cut through ceiling joists, consider a model that fits between standard joists or mounts on top of them," he said. "Although some carpentry is involved, you do not have to cut joists to install one of these models."

If the model you choose discharges through the attic, allow enough vent area for the air to escape without building up pressure.

Walter recommended one square foot of open vent area for every 750 CFM of the fan's rated air-moving capacity.

"For example, a fan rated at 4,500 CFM needs six square feet of open vent area," he said. "Remember that most attic vents have insect screening, which cuts the effective area by about 50 percent."

Whole-house fans are available in direct-drive and belt-drive models.

Direct-drive models have the fan mounted directly on the motor shaft. They are usually quieter and require less maintenance than belt-drive models.

Belt-drive models often use less energy per CFM of capacity than do direct-drive because the fan motor is matched more closely to the optimum fan speed. Also, belt-drive models are usually available in larger sizes.

"When you install a whole-house fan, you may want to consider a variable-speed controller and a timer," Walter said.

The variable speed controller allows you to operate the fan at different speeds, depending on outdoor temperature. The timer lets you turn on the fan in the evening, but then automatically shuts it off after you have gone to sleep.

Finally, you will need some way to seal off the fan during the winter months to eliminate the significant amount of heated air that can be lost through the fan louvers. The simplest method is to install a whole-house fan weatherization kit available at many hardware and discount stores. The kit provides a heavy clear plastic cover and self-adhesive plastic channels to hold the plastic. The channels and plastic are applied to the house side of the fan, making seasonal installation and removal convenient.

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5. What refrigerants are being used in residential air conditioners?

"With the discovery of the damage caused to the earth's ozone layer, many popular refrigerants were taken off the market," said Gene Meyer, extension mechanical engineer at Kansas State University.

One of the most damaging refrigerants used in residential cooling systems was R-12. It was used in window and through-the-wall cooling systems and in automobile units.

"R-12 has been replaced by R-134a in most applications," Meyer said. "However, there are several other refrigerants used in these applications, especially as retrofit choices where R-12 is being replaced in an existing unit."

Central home cooling systems have used R-22.

"R-22 is not as damaging to the ozone layer and is not slated for phase out until 2020," Meyer said. "Because the phase out date is 20 years away, many manufactures still use R-22."

However, some manufacturers of central air conditioners are using alternative refrigerants that will be available beyond the R-22 phase out" Meyer said.

When buying a new residential air conditioning system, consider the added price for refrigerant options, any improved performance and the life expectancy of the unit, Meyer advised.

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6. Our heating service contractor has mentioned that the heating and cooling unit on our commercial building has an economizer. What does this economizer do?

"An economizer is designed to maximize fresh air, or free cooling whenever outside conditions are suitable," said Richard Hayter, director of Engineering Extension at Kansas State University.

"Your cooling system requires a certain amount of outside air year-round, depending on the level of activity inside the building," Hayter said. "For example, a gymnasium would require more outside air than an office building."

An economizer increases the volume of cool outside air supplied, and decreases the load on the unit's cooling equipment.

"There are two methods of controlling the volume of fresh air," Hayter said. The most common is by outside temperature, and the other is by enthalpy control."

On a system controlled by outside air temperature, the unit's outside air dampers are usually fully open between 50 and 60 degrees. When the exterior temperature is above or below this temperature range, the dampers will be partially closed. During economizer operation, the load on the unit's cooling system is reduced.

Enthalpy controls measure the total heat of the air; that is, they measure both outside air temperature and humidity level. The controller then adjusts the dampers to the optimum level.

"While enthalpy controls can save more energy, humidity sensors often require more frequent calibration to keep the controller operating properly," Hayter said. "Because of this, enthalpy control is sometimes the second choice for economizer controls."

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Ask Energenie is produced by the Kansas Energy Extension Service through Kansas State University. This material was prepared with the support of the U.S. Department of Energy (DOE) Grant No. DE-FG48-97R802102. However, any opinions, findings, conclusions, or recommendations expressed herein are those of the author(s) and do not necessarily reflect the view of DOE.