Ask Energenie

June 2000

Table of Contents

1. What is the heat index?
2. What is the proper humidity to maintain in a basement?
3. One disadvantage of living in the city is that it is always a few degrees hotter in the summer than the adjacent countryside. Is there anything we city dwellers can do to help reduce the summer heat?
4. What should I do to prepare my home for vinyl siding?
5. What is evaporative coolin?
6. Why does electricity cost more during the summer?
7. I can't afford to make major investments for insulation or other home improvements. What energy-saving steps can I take that don't cost anything that will help reduce my summer cooling costs?
8. How much energy do I save by omitting the drying cycle on my dishwasher?

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1. What is the heat index?

"In many ways 'heat index' is like the wind chill index," said Richard Hayter, director of Engineering Extension at Kansas State University.

"Both are temperature indices representing multiple factors which affect your thermal sensation in a particular environment or set of conditions," Hayter said.

A number of indices show the potential heat stress level using such factors as drybulb temperature (air temperature), air movement, humidity levels, and exposure to direct sunlight.

"The heat stress index, which seems most popular in media weather reports, is more commonly referred to as the heat index," Hayter said. "This index combines air temperature and dewpoint into a single unit called the apparent temperature, " he said.

Developed by R.G. Steadman of Colorado State University and first published in 1979, the index measures what hot weather "feels like" to the average person for various temperatures and relative humidities.

For example, at an air temperature of 90 degrees with 60 percent relative humidity, it feels like 100 degrees, so the heat index would be 100. The comparison is based on the thermal sensation you would experience at a constant dewpoint of approximately 55 degrees.

In addition to thermal sensation, heat stress categories have been developed based on apparent temperatures.

"The lowest would be a category IV, which includes apparent temperatures from 80 to 90 degrees," Hayter said. "Fatigue is possible with prolonged exposure or physical activity, or a combination of the two, in category IV weather."

The most severe category is I, which is an apparent temperature of 130 degrees or higher.

"Heat or sunstroke is likely to develop from continued exposure under these conditions," he said.

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2. What is the proper humidity to maintain in a basement?

"The ideal humidity depends on how you use your basement and why you want to control the humidity," said Doug Walter, president of Kansas Building Science Institute, Manhattan.

"At a minimum, you will want to keep humidity low enough to prevent condensation on walls and floors," Walter said. "Condensation leads to mildew and musty odors."

Assuming the basement air temperature is 80 degrees, relative humidity must be 70 percent or lower to prevent condensation. Reducing humidity to 60 percent or less will prevent condensation on cold water pipes. If the basement is used as living space, you will want to maintain a relative humidity of 55 percent or less for optimum comfort.

"Controlling humidity in a basement is most important during spring months because relative humidity is high as a result of frequent rains, and basement walls are still cold," he said.

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3. One disadvantage of living in the city is that it is always a few degrees hotter in the summer than the adjacent countryside. Is there anything we city dwellers can do to help reduce the summer heat?

"City temperatures can be from 5 to 8 degrees hotter in the summer as a result of the large amount of solar energy absorbed and the increase energy consumed for cooling," said Gene Meyer, extension mechanical engineer at Kansas State University. "Dark-colored roofs and pavement absorb solar energy. There are several reflective roof treatments that reduce the energy absorbed while reducing the cooling load of the building."

Reducing heat absorbed from pavements is more difficult. The pavement surface should be reflective to reduce energy absorption while providing a tough, durable surface. The reflectivity should not reduce a driver's ability to locate and identify objects in the roadway. Improved roadway surfaces are under investigation.

"Trees and other vegetation also help control summer temperatures," Meyer said. "Shading buildings helps reduce their surface temperature and the transpiration of vegetation helps actually lower air temperature. Green spaces offer a pleasant respite from the heat and actually help cool the area."

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4. What should I do to prepare my home for vinyl siding?

"Although vinyl, aluminum and steel siding are frequently advertised and sold as energy conservation improvements for homes, they are primarily a maintenance investment," said Bruce Snead, extension specialist in residential energy at Kansas State University.

He added that you probably will not recover the cost of the siding through energy savings within the lifetime of the house or the siding.

"But, before the siding is put on, you can make significant improvements to the walls that will help you save energy," Snead said.

Caulk and seal any large cracks or holes in the walls.

"Probably the most effective improvement you can make would be to blow insulation into the wall cavity."

Most older homes that are candidates for new siding were built during a period when insulation was not placed in walls. Thus, walls had an average R-value of only four. Snead said you can raise a wall's R-value to 15 by blowing three and a half inches of cellulose insulation into the wall cavity.

"You can insulate your walls this way for 35 to 75 cents a square foot, depending on whether you do it yourself or pay a contractor," he said "In addition to raising the R-value, the insulation will reduce infiltration through the walls."

Insulating walls before siding goes on is the ideal arrangement because it eliminates the need to plug and repaint the holes through which insulating materials would be blown.

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5. What is evaporative cooling?

"Evaporative cooling is the process of cooling air by the evaporation of water," said Richard B. Hayter, director of Engineering Extension at Kansas State University. "In hot, dry climates, evaporative coolers are often used as an inexpensive substitute for air conditioning."

Under proper conditions, evaporative cooling can provide comfort with lower energy costs than air conditioning. In addition, the purchase price of an evaporative cooler is less than a conventional unit.

The cooler is usually a cabinet containing wetted pads through which outdoor air is drawn. When air passes through the pads, its temperature drops as the water evaporates.

"After passing through the evaporative cooler, air entering a home or business has a lower temperatures and higher relative humidity than outside air," Hayter said.

He said the process does not reduce total energy content of the air, but the lower temperature may improve comfort if humidity is not excessive.

"The humidity that these coolers generate makes them suited to drier climates," Hayter said.

A building that is cooled by an evaporative system must have enough openings to exhaust the air that is drawn inside. Generally, the size of the open area should be equal to blower capacity, in cubic feet per minute (cfm), divided by 200.

"For example, a 30-inch by 48-inch window provides 10 square feet of open area per minute," he said. "A 6,000 cfm cooler would require the open area of three windows of this size."

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6. Why does electricity cost more during the summer?

"Most electric utilities have separate summer and winter rates," said Gene Meyer, extension mechanical engineer at Kansas State University. "The rates are higher in the summer when the utility experiences its maximum demand, due to the need for air conditioning."

This high demand requires the utility to use less efficient generating capacity. In some cases they may have to buy electricity from other utilities that have excess capacity at that time.

"The utility usually passes the higher cost to you through an increased energy charge during these months," Meyer said. For commercial and industrial customers, there may also be an increase in the capacity charges.

For more information, contact your utility or Engineering Extension Programs, 800-KSU-8898.

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7. I can't afford to make major investments for insulation or other home improvements. What energy-saving steps can I take that don't cost anything that will help reduce my summer cooling costs?

"You can make a significant savings on utility bills, even without making those major changes to your house," said Gene Meyer, extension mechanical engineer at Kansas State University.

Meyer recommended these low- or no-cost energy-saving measures.

• Set the thermostat at 75 to 76 degrees rather than 72 degrees.
• Use portable fans to provide air movements in the room you occupy. Air movement from a fan will help the room feel several degrees cooler.
• Turn up your thermostat five to ten degrees when you are gone for over six hours.
• Keep supply and return registers clear of furniture and drapes, and clean them on a regular basis.
• Check and replace furnace filters regularly.
• Have your air conditioning unit serviced at least once a year to help assure it is operating efficiently.
• Keep the sun out. Close drapes and shades during the day and open them at night.
• Plant trees to help shade your home, especially the east and west sides.
• Plan your cooking early in the day, when it is cool outside, and use the vent above the range or stove to exhaust heat and humidity.
• Turn your water heater thermostat down to 120 degrees.

"This may not be desirable if you have special laundry or dishwashing requirements," Meyer said. "Follow the appliance manufacturer's suggestions."

• Use energy-efficient light bulbs, such as compact fluorescent lamps. Compact fluorescents screw directly into the lamp socket of many fixtures and have been shown to be cost-effective even though they cost more initially.
• Take a short shower instead of a bath. Install a low-flow showerhead.
• Make sure doors and windows stay tightly closed and locked.
• Make sure storm windows are closed.
• Wash clothes in cold water and hand them outside to dry when possible.

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8. How much energy do I save by omitting the drying cycle on my dishwasher?

The drying cycle of a dishwasher consumes less than one-half to about one kilowatt-hour (kwh) of electricity, depending on the age and model of the dishwasher.

"If you wash 30 loads of dishes a month, you will save from 75 cents to $2.30 each month by omitting this cycle," said Doug Walter, president of Kansas Building Science Institute, Manhattan.

This figure is based on an electricity rate of 7.7 cents per kwh.

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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.