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"It is not absolutely necessary to replace the evaporator coil, or cooling coil, when you replace your air conditioner, but it is recommended that you do so," said Doug Walter, president of Kansas Building Science Institute, Manhattan.
The new air conditioner likely will be more efficient than the old air conditioner. The efficiency of the new air conditioner, however , is based on the compressor/condensing unit (the outdoor unit) being matched to a particular evaporator coil.
"By using your old coil, you probably will not obtain the efficiency the new unit is capable of delivering," Walter said.
The old evaporator coil also is likely to have accumulated dirt on the heat-transfer fins.
"If you decide not to replace it, be sure to have the coil removed from your furnace for a thorough cleaning with an acid-based cleaner," Walter said.
"The development of low emissivity ("low-e") coatings for window glass in the early 1980s has meant significant improvements in window energy efficiency," said Bruce Snead extension specialist in residential energy at Kansas State University.
All major manufacturers now have windows with low-emissivity coatings and more than 60 percent of all residential windows installed during 1997 are expected to be this type.
When calculating R-values for windows, the manufacturers account for the effect of the surrounding frame material. Here are typical R-values for comparison.
Single pane — 0.9
Double pane — 1.8
Triple pane — 2.7
Low-e coated double pane — 3.1
Low-e film suspended in double pane — 4.3
Low-e coated double pane with gas-filled space — 4.5
"It's not uncommon to find estimates of cooling capacity that vary by as much as two to one because of the methods of estimation," said Doug Walter, president of Kansas Building Science Instiute, Manhattan.
Using various rules-of-thumb to estimate the required capacity is the least accurate method, Walter said. More accurate methods involve actually calculating the cooling load.
"Some contractors simply look at a house and recommend a particular size of air conditioner based on their past experience with similar houses," Walter said.
This procedure often results in an oversized air conditioner because of the tendency to guess on the safe side. Another method is to size the air conditioner based on the floor area of the house. "This method is fine if your house fits the conditions for which the rule-of-thumb holds true," Walter said. "Often this is not the case because most square foot rules-of-thumb estimate liberally. The result, again, is an oversized air conditioner."
The most accurate method is a load calculation. This process involves measuring all the various surface areas of the house and multiplying them by heat gain factors based on their resistance to heat flow. The heat gain factors for windows alone vary by orientation, number of glazings, and degree of internal and external shading.
The cooling load also is affected by the amount of outside air infiltration, the number of occupants, the number of major appliances and the location of the air conditioning ducts. The total load is then adjusted by a "swing factor" that incorporates the amount of indoor temperature variation you are willing to tolerate on extremely hot days.
"If you want to maintain a constant temperature no matter what the outdoor conditions, no swing factor will be applied," Walter said.
A load calculation is the most accurate method because it incorporates both the size and energy efficiency of the house, as well as the lifestyle of its occupants.
Since most homes today are far more energy efficient than they were when the rules-of-thumb were formulated, a load calculation usually results in a smaller estimate of cooling load than rules-of-thumb and guessing," Walter said.
Automatic or programmable thermostats can be effective in increasing comfort and decreasing heating and cooling costs. There are a wide range of options and price ranges available.
"Your savings will depend on your lifestyle, building type and construction, heating and cooling equipment, and rate schedule," said Dennis Matteson, extension specialist in small business energy at Kansas State University.
"Before installing a programmable thermostat, be sure it is designed for the equipment it will be controlling," Matteson said.
Special considerations include single- or double-stage heating and cooling, high or low voltage control, and if it is controlling a heat pump. Heat pumps require special setback controls, so before using setback for electric resistance heating or heat pumps, consider the increase in demand costs.
"By setting the temperature back during the hours when the building is unoccupied, the heating or cooling equipment will operate less frequently," Matteson said.
"If the building has large thermal mass, such as concrete and brick, the setback savings will be less than for light construction," Matteson said.
The comfort benefit is the ability of the building to recover from setback before it is occupied or activity begins. This automatic recovery makes it more feasible for larger setbacks.
"For residential setback of eight hours a night, the savings can be up to 1 percent per degree of setback," Matteson said.
"Relief valve testing will depend greatly upon the type of heating appliance on which it is installed," said Gene Meyer, extension mechanical engineer at Kansas State University.
If it is a pressure/temperature relief valve on a water heater, you should test it each month.
"This will ensure that calcium has not built up under the relief valve opening and is preventing discharge," Meyer said.
Monthly testing also is advised on low-pressure steam and hot water systems. At least once a year, you should allow the boiler to rise in pressure until the relief valve lifts because of pressure rather than simply operating the test handle.
On higher pressure boilers, you should follow the recommendations of your insurance carrier.
"Frequent lifting of the high-pressure relief valve will cause wear of the valve seat," Meyer said.
Once the valve begins to leak, it must be repaired by the factory. This may cause unnecessary expense for the repair of safety relief valves.
"At a minimum, high-pressure relief valves should be checked by pressure at least annually," Meyer said. "Again, the recommendations of your insurance carrier are the prime consideration in high-pressure relief valve testing."
"Many new window products are using low-emissivity coatings or films to conserve energy both in the summer and winter," said Bruce Snead, extension specialist in residential energy at Kansas State University.
Emissivity refers to the ability of a surface to emit, or radiate, heat. A perfect radiator would have an emissivity of 1. Ordinary window glass has an emissivity of .84, meaning a large amount of heat is transferred due to long-wave emission.
"With a low emissivity coating on the glass, the emissivity drops to between .05 and .40," Snead said. "This means it reflects between 60 and 95 percent of the radiant heat."
In summer, these windows reduce your cooling load by reflecting heat radiated from surrounding buildings, sidewalks and driveways. In the winter, the heat radiated from interior sources is reflected back into the room, thus reducing the heating load.
"Although these windows reflect a high percentage of the long-wave infrared radiation, they transmit most of the visible light, and maintain natural light and views," Snead said. "The coated windows also reflect most of the sun's ultraviolet rays, helping to reduce the fading of furniture and fabrics."
Some manufacturers have introduced low-emissivity units with bronze-tinted glass to further reduce solar heat gain.
"These units would be the most effective on west-facing windows with full exposure to the afternoon sun in the summer," Snead said.
Electrical load management is the process of controlling the operating time for different equipment. The main benefit of load management is the reduction of demand. In some applications, you can reduce your electrical consumption.
"Most businesses can benefit from electrical load management," said Dennis Matteson extension specialist in small business energy at Kansas State University. "The types of electrical loads and your rate schedule determine your financial incentive."
Most utilities calculate electrical rates for larger users by the amount of electricity used, consumption and the highest rate of use, which is called demand or capacity for each month.
"Users may have the option of more than one rate schedule and should compare the alternatives," Matteson said.
Some utilities now offer rate schedules that charge a reduced rate for electrical use during off-peak hours. These time-of-day rates can be an attractive alternative for some types of loads.
The highest electrical use rate is usually referred to as demand or capacity.
"The charge for demand will vary depending on the utility and in some instances may vary depending on the month and time of day," Matteson said.
"To effectively implement load management, it is vital you understand the rate schedule and be aware of the charges for each component of the bill," Matteson said.
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