Similarly, various rapid-growing vines can be grown over windows during the summer. Varieties should be selected that will expose the windows to the sun during the winter.
"Blocking or reflecting the sun's rays before they enter the home will prove most effective," Hayter said. "Awnings, for example, will be more effective than interior drapes."
Reflective lining on the drapes will be more effective than traditional fabrics. Similarly, reflective films will reflect the sun's rays before they can enter your home.
"Permanently mounted reflective films, however, have the disadvantage of reducing the benefit of solar heating during the winter," Hayter said.
Another radiant load which adds significantly to the cooling requirements of a home is the energy radiated from a hot roof across the attic space to the ceiling. Reflective films have recently become available which reduce the radiation load in the attic.
"Typically, the film is attached below the rafters, although other installation positions do exist," Hayter said.
Maximum radiation shielding can occur only when there is an air space on the reflective side.
"If the reflective side is in direct contact with a solid material, a significant amount of heat will transfer and reduce the benefit of the radiant barrier," Hayter said.
When buying a new central air conditioner, what should I look for to ensure a high efficiency unit that will last?
One of the best guides to the efficiency of the air conditioner unit that you are considering is the Seasonal Energy Efficiency Ratio (SEER).
"The higher the SEER, the more efficient the unit," said Gene Meyer, extension mechanical engineer at Kansas State University.
Federal legislation dictates a minimum SEER rating of 10 for central air conditioners sold in the residential marketplace.
"Air conditioning units are now available with SEER ratings as high as 16," Meyer said.
Long life and ease of service are two other important considerations when purchasing an air conditioner. One recent development in compressor design, the scroll compressor, offers long, trouble free life and low noise level. Scroll compressors are also more efficient than convention compressors. Scroll compressors are often used on units with a SEER of 12 or greater. When receiving bids, be sure to ask if the unit uses a scroll compressor.
"You should contact at least three air conditioning service companies in your area to obtain bids for comparison of features, warranties and efficiency" Meyer said.
Be sure to carefully evaluate the proposed size of the units, Meyer said. Purchasing a properly sized unit is critical to achieving good performance
August 11, 1996
How can I estimate the cost of operating my air conditioner for an hour?
"First you will need to know the size of the unit," said Gene Meyer, extension mechanical engineer at Kansas State University. "You can make a more accurate estimate if you know the Seasonal Energy Efficiency Ratio (SEER) of the unit."
"If you don't know the SEER for your unit, and it is more than 15 years old, assume it is 7. If it is between 15 and four years old, use a SEER of 8. If it was installed after 1992, use a SEER of 10," said Meyer."
Multiply the size of the unit (in Btu per hour) by the cost of electricity in dollars per kilowatt hour. Divide this by 1,000 times the SEER.
Your utility bill will show your usage and its total cost. Divide your total cost by number of kilowatt hour you use to determine the cost per kilowatt hour (kwh).
The following example should help clarify this process.
The usage from a bill shows 1,276 kwh used for a total cost of $108.56. The cost per kilowatt hour is $108.56 divided by 1,276, which equals $.085 per kwh.
If the SEER is 9, and it is 36,000 Btu per hour, the hourly cost of operation is 36,000 times 8.5 cents, divided by nine times 1,000 (36,000 X .085/9 X 1,000), which equals .34, or 34 cents an hour
"This is only an estimate for the cost of operating the unit for one hour," Meyer said. "Remember that the unit cycles off automatically and this estimate is only for actual operating time."
Our split level house is difficult to keep comfortable in the summer. When the downstairs is comfortable, the upstairs is too warm. Lowering the thermostat setting makes the downstairs too cool and requires the air conditioner to run a long time. Would a ceiling fan mounted over the open stairway and switched to blow upward help our distribution problem?
"A ceiling fan operating in any direction probably will not solve your distribution problem," said Doug Walter, extension specialist in residential energy at Kansas State University.
Ceiling fans are effective at creating air movement within rooms and can enhance comfort. They are not effective, however, at circulating air from one space to another, whether horizontally or vertically, unless they operate at a very high speed typical of industrial ceiling fans.
"Occupants of split level homes like yours have reported some success in setting the furnace fan to run continuously," Walter said. "This isn't ordinarily recommended because of the energy consumed by the fan's constant operation."
The constant mixing of the air in the furnace may help reduce the difference in temperature between levels, but it probably won't eliminate it entirely.
You can also close off some of the supply registers in the lower level, but this should be no more than 20 percent of the total supply registers in your home. Shutting off too many registers may restrict air flow too much, which could damage your air conditioner.
A good long-term solution may be to have an air conditioning contractor add several large supply registers on the upper level.
These registers would be opened in the summer and shut off in the winter. This would not only deliver more cool air to the upper level, but also allow you to shut off more registers in the lower level.
August 18, 1996
My attic seems extremely hot. With outdoor temperatures only in the 80s, I'd guess it gets to more than 110 degrees F in spite of two wind-driven rotating roof vents. Does that mean I should get a thermostatically-controlled, powered roof vent? Or should I concentrate on the other suspect, poor soffit ventilation?
Neither.
"An attic exposed to the sun in the summer will always be well above the outdoor ambient temperature because the roof functions as a giant solar collector," said Doug Walter, extension specialist in residential energy at Kansas State University.
As the roof surface heats up, it heats the attic air as well as radiating heat to the ceiling below, which absorbs it and conducts it into the house.
"Attic ventilation can help to reduce the attic air temperature," Walter said, "but it will never maintain it close to the outdoor ambient temperature, even with powered attic ventilation."
This is because the roof deck will always be much hotter than the air temperature because of the solar radiation.
"Ample attic insulation (R-38) and a light-colored roof are the best ways to reduce roof solar heat gain," Walter said. A light roof will reduce the temperature of the roof deck, and ample insulation (R-38) will greatly reduce the quantity of heat that actually reaches the interior of your house.
"The only way to have a cool attic (at ambient air temperature) is to plant trees that will completely shade your roof during the summer," Walter said.
Are heat pumps, when operating as an air conditioner, more efficient than conventional air conditioners?
"The efficiency of a heat pump during the cooling season is not necessarily greater than the efficiency of an air conditioner," said Dennis Matteson, extension specialist in small business energy at Kansas State University.
Both air conditioners and heat pumps are rated according to their seasonal energy efficiency ratio (SEER). This rating represents the seasonal cooling efficiency rather than a peak efficiency. According to the Air Conditioning and Refrigeration Institute (ARI) directory, there are air conditioners available with higher SEER ratings than heat pumps.
"The cost of purchasing a heat pump is usually higher than an air conditioner of the same size," Matteson said. "The additional cost of the heat pump may be better spent by purchasing a higher efficiency air conditioner if the primary purpose of the heat pump will be for cooling."
August 25, 1996
Are heat pumps more efficient and cheaper to operate than a conventional electric resistance forced air furnaces and air conditioners?
"Heat pumps are more efficient and will provide a savings over resistance electric heating," said Dennis Matteson, extension specialist in small business energy at Kansas State University.
The heat pump provides heat more efficiently during moderately cold weather, but for the extremely cold temperatures resistance heat may be needed to offset part of a building's energy losses.
To determine heating savings, consider both the efficiency of the unit and the cost of the energy consumed. When a heat pump replaces resistance electric heating, heating costs can be reduced by 50 to 70 percent. Exact savings can be figured only by calculating the change in efficiency and the building heat losses.
Heat pumps will also provide a savings in cooling costs when replacing older window or central air conditioning systems. Keep in mind that new air conditioners will also provide savings over older air conditioning units.
Matteson suggested that before purchasing any heating or cooling system consumers look at several alternatives and calculate their potential savings based on their individual energy costs, rather than using rules-of-thumb calculations.
I was advised by a friend that I could dramatically and inexpensively reduce cooling costs by painting my roof white. Is that true? Other than aesthetics, are there major drawbacks to cheap white paint on a roof?
"Changing your roof color from dark to light will reduce heat gain through the ceiling by about 20 percent," said Doug Walter, extension specialist in residential energy at Kansas State University.
"Depending on how much attic insulation you have," Walter said, "this may or may not be a dramatic savings in actual cooling costs."
Although paint is cheap, is it not likely to adhere well to most roofing surfaces and may wear off after a season or two. Simply plan to choose a light color of material the next time you reroof.
"A more effective immediate, yet long-term, solution would be to increase your attic insulation," Walter said. "Going from R-19 (about six inches) to R-38 (12 inches) would reduce heat gain through your ceiling by approximately 52 percent (with the added benefit of reducing winter heat loss by a similar amount)."