Contents

1. How does a central air conditioner work?
2. Energy-Efficiency considerations
3. Noise Ratings
4. Sizing Considerations
5. Installation Considerations
6. Installation Costs
7. Thermostat Settings
8. Maintenance
9. Life Expectancy & Warranties
10. Replacing an older system
11. Operating Costs
12. Factors Affecting your Operating Costs
13. How can I select a good contractor from whom to purchase a central air conditioner?
14. When is the best time to buy an air conditioner?
15. Are there any municipal by-laws that affect the use of air conditioners?
16. Should I replace both my outdoor condensing unit (which includes the compressor) and the indoor coil on my central air conditioning system at the same time?
17. If I am buying a house, how can I make sure that the air conditioning system is in good working order?
18. Should I let the air conditioner fan run all the time (the "on" setting on the thermostat) or only periodically (the "auto" setting on the thermostat)?
19. Is there any relationship between my home air conditioning system and chlorofluorocarbon (CFC) refrigerant damage to the ozone layer?
20. Are there air conditioners other than window room air conditioners for homes without ductwork?

1. How does a Central Air Conditioner work?

A central air conditioner uses energy to take heat away. The most common type uses a compressor cycle (like a refrigerator), to transfer heat from the house to the outdoors. Using a special fluid called a refrigerant, heat is absorbed and released when refrigerant changes back and forth between a liquid and gas state: As it changes from liquid to gas, it absorbs heat; in changing back to a liquid from a gas, it releases heat.

Central air conditioners are designed to cool the entire house. The large compressor and outdoor coil are located outdoors and are connected by refrigerant lines to an indoor coil mounted in the furnace. The same duct system is used for both heating and cooling air distribution.

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2. Energy-Efficiency Considerations

Select a central air conditioner with as high a SEER as is practical within your budget. The annual cooling efficiency of a central air conditioner is affected by the manufacturers' choice of features and components. The SEER of central air conditioners ranges from a minimum of 10.0 to a maximum of about 20.0.

Advanced reciprocating, scroll, and variable-speed or two-speed compressors, when combined with the current best heat exchangers and controls, permit SEERs as high as 18. The central air conditioners with the highest SEERs always use variable-speed or two-speed high-efficiency compressors.

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3. Noise Ratings

Select a central air conditioner with an outdoor sound rating of about 7.6 B or lower, if possible. The sound rating is expressed in bels. The lower the sound rating, the lower the sound power emitted by the outdoor unit. New energy-efficient designs often have low sound ratings.

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4. Sizing Considerations

Cooling loads should be determined by a qualified air conditioning contractor. Unfortunately, these calculations rarely take place because most homeowners are not prepared to pay for the time professional contractors need to perform this service. Fortunately, most experienced professional contractors will still be able to recommend a size (with a fairly high degree of accuracy) that is appropriate for your home.

The biggest mistake you can make is having a unit installed that's too large for your home. Oversizing the unit will result in short operating cycles, which will not adequately remove humidity, resulting in an unpleasantly cold and damp home. Likewise, undersizing the unit will result in inability to attain a comfortable temperature on the hottest days.

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5. Installation Considerations

The following general guidelines should be taken into consideration when installing a central air conditioner:

• Locate the outdoor unit or condenser in a cool, shaded place where the waste heat can be readily rejected.
• Locate the outdoor unit where its noise will not be a problem for you or your neighbor. This generally means away from bedroom windows or patios and not between houses.
• In new construction, consider installing the central air conditioner outdoor unit on a frame mounted to the house. This avoids problems due to settlement of backfill around the foundation, which causes the outdoor unit to lose its level.
• The central air conditioner will generally require more airflow than the furnace needs for heating. Consider a two-speed fan motor with the correct speed automatically selected depending on whether cooling or heating is called for.
• Keep refrigerant lines as short as possible, and where the lines pass through the outside wall, ensure that the surrounding space between the lines and the wall is packed with a resilient material such as plumber's putty. This will prevent noise or vibration problems and air leakage.

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6. Installation Costs

The cost of installing a central air conditioner can vary depending on:

• The type of furnace you have
• If the existing ductwork needs to be modified
• If there is a need to upgrade the electrical service
• If the basement of your house is finished or unfinished

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7. Thermostat Settings

The indoor thermostat should be set somewhere in the range of 22°C to 25°C, depending on your comfort requirements. A setting at the higher end of the range will result in lower air-conditioning costs. If the humidity level is lower, temperature settings can be at the higher end.

Continuous indoor fan operation can keep the temperature more uniform throughout the house by eliminating temperature differences due to stratification. It can also help keep the home cleaner, especially if there is an electronic air cleaner installed.

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8. Maintenance

Proper maintenance is critical in ensuring that your central air conditioner will operate efficiently and have a long life. You should have a licensed professional do a periodic inspection of your unit. And of course, the best time to service a central air conditioner is just prior to the cooling season.

Filter and coil maintenance can have a dramatic impact on system performance and service life. Dirty filters and dirty indoor and outdoor coils and fans reduce airflow through the system. This reduction in airflow decreases system efficiency and capacity and can lead to expensive compressor damage if left for an extended period of time.

Furnace filters should be inspected and cleaned or replaced, depending on the type of furnace and the furnace manufacturer's instructions. The outdoor coil should be vacuumed or brushed clean to keep it clear of dirt, leaves, and grass clippings. It can be carefully cleaned with a garden hose after debris is vacuumed off. Consider a professional cleaning if the outdoor coil becomes badly plugged.

Using a high-efficiency air cleaner on a central cooling/heating system is one way of ensuring a clean indoor coil and a cleaner indoor environment.

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9. Life Expectancy and Warranties

The life expectancy of a central air conditioner is approximately 15 years or longer. When the air conditioner starts giving more problems than seem cost-effective to fix, particularly when major components, such as a compressor, require replacement, it may be time to replace the central air conditioner. New units offer greater efficiency and lower operating costs so it may be more cost-effective in the long run to replace rather than repair.

The warranty on your equipment will vary according to the manufacturer. Air conditioner warranties range from one year to ten years for parts, labour, and compressor coverage. Some manufacturers even offer to replace the air conditioner in the case of a major component failure. Make sure you fully understand the terms of a warranty.

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10. Replacing an Older System

If your existing air conditioner needs replacement or is more than 10 years old, chances are good that it's also inefficient. A 10-year-old air conditioner probably has a SEER rating between seven and eight, compared with some new models that are twice as efficient. The more efficient unit should pay for itself through decreased utility bills and offer improved reliability and warranty protection.

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11. Operating Costs

If you are interested in purchasing an air conditioner, chances are that comfort is the main reason. However, cost is also a major factor. You may want to calculate the annual cost of operating an air conditioner to determine whether it is worth the investment. This section may also be valuable to you for comparing the performance and cost of equipment with identical cooling capacities before making a purchase decision.

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12. Factors Affecting Your Operating Cost

Many factors affect the operating cost of an air conditioner, however the two most important are:

• SEER Rating of the air conditioner (seasonal energy efficiency ratio)
• Thermostat Setting

Others include:

• Geographical location of the house
• Variance of weather conditions from year to year
• Size of the air conditioner relative to house cooling load
• Number of occupants in the house
• Habits of people in the house-if windows are open or closed; if window shading is used; frequency of appliance, cooking, and lighting use; and
• Local cost of electricity

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13. How can I select a good contractor from whom to purchase a central air conditioner?

Selecting a reputable contractor is a key consideration in any decision to buy a central air conditioning system. The following tips should help you choose:

• Ensure that the contractor is qualified to install and maintain the equipment.
• The contractor should calculate the cooling load for the house and be prepared to explain this to you.
• The contractor should ensure that the ductwork system is designed to provide adequate airflow and distribution to all areas of the house. When the existing fan and duct-work are used, they should be examined to see if they are adequate, since an air conditioning system may require greater airflow than the system was designed to handle.
• The contractor should ensure that the electrical system is capable of accommodating the increased load of the air conditioner.
• The contractor should be willing to provide you with information on the unit, its operation, and warranty, and to offer a service contract on the installation. The contractor should be prepared to guarantee the installation work.

In addition, follow the usual process for selecting a contractor: ask friends and relatives for referrals; get firm (written) quotes from at least two contractors; check with previous clients to see if they were satisfied with the equipment, installation, and service provided; and follow up with the Better Business Bureau to find out if there are any outstanding claims against the contractor. If you know which brand you want to have installed, the manufacturer may recommend a contractor in your area.

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14. When is the best time to buy an air conditioner?

Like many other things, the best time to buy is during the off-season. Contractors will have more time to spend with you to consider your particular needs and to help determine exactly what system is most suitable.

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15. Are there any municipal by-laws that affect the use of air conditioners?

Some municipalities have enacted by-laws that limit the permissible noise level from such equipment. Generally, maximum noise levels are specified at the lot line. Check with your local municipal office to find out if such by-laws are in effect or if there are any additional requirements you will need to satisfy.

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16. Should I replace both my outdoor condensing unit (which includes the compressor) and the indoor coil on my central air conditioning system at the same time?

Yes, under most circumstances. The indoor and outdoor components of central air conditioners are intended to operate together, and the rated SEER is based on tests of these components working together. Matching a new high-SEER condensing unit with an old indoor coil would result in an unknown SEER and probably suboptimum efficiency.

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17. If I am buying a house, how can I make sure that the air conditioning system is in good working order?

You can check the system yourself. Turn the system on and listen for unusual sounds. Feel how cool the air is and how much airflow is coming from the vents. Listen to both the indoor and outdoor sections of the system. Within a few minutes of start-up, air from the vents should be considerably cooler than the rest of the air in the house. Although this personal inspection will provide a good indication of normal operation, the best way is to hire an air-conditioning contractor to inspect the system.

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18. Should I let the air conditioner fan run all the time (the "on" setting on the thermostat) or only periodically (the "auto" setting on the thermostat)?

Fans require a significant amount of electrical energy to operate. For indoor fans, this energy ends up in the form of heat inside the house, thus adding to the cooling requirement that the air conditioner must meet. So in addition to paying to operate the fan, you will have to pay to remove its heat as well. The SEER rating for your system was determined assuming "auto" fan operation. Continuous fan operation also reduces dehumidification. For these reasons, fan operation should be restricted to those times when it is providing some tangible benefit.

Sometimes comfort will improve with continuous fan operation by providing a more uniform temperature throughout the house. Air movement also tends to make the body feel comfortable at higher temperatures, possibly allowing you to adjust the thermostat to a higher setpoint.

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19. Is there any relationship between my home air conditioning system and chlorofluorocarbon (CFC) refrigerant damage to the ozone layer?

Both central air conditioners and room air conditioners utilize hydrochlorofluorocarbon (HCFC-22) as a refrigerant. HCFC-22 is not as damaging to the ozone layer as are CFCs. HCFC-22 does have some ozone-depletion potential, but it is only five per cent of that of CFCs, since the molecule breaks down fairly rapidly if released into the lower atmosphere.

In some provinces, it is illegal to release HCFCs into the atmosphere; soon, this will be the case nationally. Only deal with service companies that practice refrigerant recovery and recycling, and have the proper equipment and training to do so. Your air conditioner is designed to operate as a closed system and will not release refrigerant as long as it is properly maintained. Have your system checked for leaks and serviced once a year, before the cooling season.

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20. Are there air conditioners other than window room air conditioners for homes without ductwork?

There are several air conditioning system options available to meet this requirement.

• Intended for permanent installation, multi-split systems include up to three indoor evaporator units connected to a single outdoor condenser section. This permits three separate areas or zones to be cooled independently. It is generally much easier to retrofit the interconnecting refrigerant lines and control wiring than to install an air distribution system.
• One type of portable room air conditioner is not intended for window (or wall) installation. Instead, it sits on the floor and may be rolled on its casters into whichever room it is needed. Some of these portables reject condenser heat into a tank of water contained within the cabinet, which must be periodically replenished with cold water.
• Certain central air conditioning systems are specifically designed for houses without air distribution systems. These systems utilize small diameter air ducts that lend themselves to retrofit installation in walls, ceilings, and floors. The small ducts require a special high-pressure air distribution fan to overcome their large pressure drop.

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