Ask Energenie

June 1999

Table of Contents

1. Should I use a fan for attic ventilation, or will passive vents provide enough airflow?
2. Why do we add chemicals to the water in our cooling tower, and drain off water at the same time? It seems like a waste of money.
3. What are some quick checks I can do to assure that my air conditioner is working properly?
4. I’m getting ready to re-roof my house. Are the projects I should undertake at this time to reduce heating and cooling costs later?
5. Would I be better off using several window air conditioners?
6. How can I reduce cooling and electrical costs while I'm on vacation this summer?
7. I am on the board of my local church, and we are looking for ways to cut our energy bills. What suggestions do you have?
8. Will I save energy by using hot tap water for cooking rather than starting with cold water?

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1. Should I use a fan for attic ventilation, or will passive vents provide enough airflow?

"In most attics, fan-powered ventilation is unnecessary," said Gene Meyer, extension specialist in small business energy at Kansas State University. "Fan-powered ventilation is generally required only for roof designs which do not allow natural airflow into and out of the attic."

"The key to adequate ventilation is size and location of vents," Meyer said.

For passive systems, there should be one square inch of open vent for each square foot of attic floor. Half of the vent area should be low on the roof or in the soffits (overhang), the other half high or on the ridge.

"If you have a 1,000-square foot attic, you should have 1,000 square inches of vent — 500 located high and 500 low," he said.

Most attic vents have protective coverings, so they are not completely open. Insect screens and rain covers partially block incoming air, thus reducing the vent's open or effective area.

"Many vents have the effective area stamped on the product," Meyer said. "If not, assume a 60-percent open vent."

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2. Why do we add chemicals to the water in our cooling tower, and drain off water at the same time? It seems like a waste of money.

"You add chemicals to the water for two major reasons," said Gene Meyer, extension mechanical engineer at Kansas State University. "The first is to reduce scale build-up on the heat exchanger surfaces, and the second is to reduce growth of algae and bacteria."

As water evaporates during tower operation, dissolved minerals remain in the water. The concentration of these minerals increases as more water evaporates. Chemicals clean out the system, reducing the mineral, or scale, deposits.

"Periodic draining (blowdown) of the cooling water also reduces concentration of minerals by diluting them with fresh water," Meyer said.

Chemicals also kill organisms, including harmful Legionella bacteria.

The water has a high concentration of organic materials due to the "air washing" effect of the tower (as air is drawn into the tower, any airborne dirt or organic materials settle into the water). A wet environment, combined with the rich organic content of the water, allows all types of organisms to grow.

"Testing is an important part of the water treatment process," Meyer added. "This assures that the water contains only the minimum level of chemicals."

The EPA recently mandated changes in the chemicals allowed for water treatment. If you are in doubt about the chemicals your facility uses, contact a chemical supplier who will provide training and complete follow-up testing.

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3. What are some quick checks I can do to assure that my air conditioner is working properly?

"You should have a professional look at your cooling system at the beginning of each year," said Gene Meyer, extension specialist in small business energy at Kansas State University.

"However, there are also a few checks that you, the homeowner, can do," he said.

Some refrigerant lines have a sight glass, located on the small line coming from the outside condensing unit. If your unit has a sight glass, check it for bubbles.

"Bubbles should only appear when the unit starts, and should disappear in a few seconds as the sight glass fills with clear refrigerant," Meyer said.

Carefully touch both refrigerant lines. Meyer said the smaller line should be warm, but not so hot that it cannot be held. The larger line should be cool, but there should be no frost.

If you have a small thermometer, check the temperature of the air coming from the vents.

"Incoming air should be fifteen to twenty degrees cooler than room temperature," Meyer said. "If the unit has just started, or if humidity is high, the temperature difference may be less."

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4. I’m getting ready to re-roof my house. Are the projects I should undertake at this time to reduce heating and cooling costs later?

"Yes, there are two energy-saving measures that can be done easily during a roof job," said Gene Meyer, extension specialist in small business energy at Kansas State University.

The first is providing adequate attic ventilation.

"If your attic needs more ventilation, install additional vents before you complete the roof job," Meyer said. "There should be one square inch of open vent area for each square foot of attic space."

The second energy-saving measure is selecting the proper roof color.

Meyer suggested choosing a light colored roof to minimize cooling costs since light colored materials are more reflective.

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5. Would I be better off using several window air conditioners?

"Using multiple window air conditioners has both advantages and disadvantages," said Richard Hayter, director of Engineering Extension at Kansas State University.

"A distinct advantage of window units is that you can operate them individually," he said. "This flexibility allows you to cool only the occupied room rather than the entire house."

A central system is more convenient to operate when you cool your entire home continually, and possibly at a lower cost of operation.

"If sound level is a consideration in your home, keep in mind that window units are typically noisier than central air conditioning," Hayter said.

In terms of efficiency, top-of-the-line central units are generally more efficient than window units.

Look at the Seasonal Energy Efficiency Ratio (SEER) when selecting units — the higher the SEER, the higher the efficiency under similar conditions.

"Since there are positives and negatives about window units and central systems, you must consider personal needs and preferences before choosing a system," Hayter said.

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6. How can I reduce cooling and electrical costs while I'm on vacation this summer?

"Turn off all cooling equipment unless a pet or other special circumstance requires a minimum amount of cooling," said Bruce Snead, extension specialist in residential energy at Kansas State University.

Set your water heater to the "pilot" or "off" position, and check tubs, faucets and showers to make sure no water is dripping.

To reduce solar gain through windows, pull draperies and shades, and close all but a few windows.

"You could leave a couple of upstairs or secure windows partially open to allow for some air change," Snead said.

Turn off lights and disconnect electrical appliances. Snead also suggested putting one or two security lights on a timer.

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7. I am on the board of my local church, and we are looking for ways to cut our energy bills. What suggestions do you have?

"There are several ways to make your church more energy efficient," said Richard Nelson, extension specialist at Kansas State University.

"In fact, many of the same measures you take to weatherize your home can be done to churches as well, including caulking and weatherstripping doors and windows to reduce air infiltration," Nelson said.

One method of finding air leaks in your church is to use burning incense. Observe the flow of the smoke near walls, windows, doors, etc., to detect air leakage.

"Follow these simple tips to cut your church's energy bills," Nelson said.

• Replace or change furnace filters regularly.
• Use light-colored drapes or blinds.
• Turn off hot water in areas other than those where food is prepared.
• Use low-flow faucets.

"A major area of energy use and cost within a church is lighting," Nelson said. "Purchase energy-efficient lamps and bulbs to replace those that have burned out. You should also consider using timers or photo-sensors for outside lighting." If your church conditions only those areas only when they are being occupied," he said.

Install a programmable thermostat to automatically regulate temperature and turn off the heating/cooling system during times of non-use. Shutting off the system during the last quarter hour of services and meetings will help conserve energy as well without loss of comfort.

"Another way to reduce your energy bill is through effective scheduling of meetings," Nelson said. "Combine two or more meetings at the same time, if possible. If you use a programmable thermostat, this will reduce energy consumption."

Your electric bill has two parts — demand and consumption. The demand charge is based on the highest average use over a 15- or 30-minute period. Usually, demand rate is set on Sunday and is not exceeded during the week.

Nelson gave this example: "It may take the heating/cooling system one to two hours to bring the structure to the desired comfort level. If a meeting lasts only one hour, more energy may be expended to reach this temperature than was used during the meeting."

When meetings are scheduled throughout the week, energy is wasted conditioning the space on separate nights.

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8. Will I save energy by using hot tap water for cooking rather than starting with cold water?

"No, you will not save a significant amount of energy," said Doug Walter, president of Kansas Building Science Institute, Manhattan.

The only situation where you would save energy by using hot tap water is if you have a gas water heater and an electric range. Even then, the saving is small — about two-tenths of a penny for every six cups of water heated to 212 degrees.

"On the other hand, if you have a gas range or an electric water heater, always use cold water and heat it on the range," Walter said.

In all cases, it is assumed that water in the hot water pipe is cold and must be run until it is hot, wasting some water.

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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.