How Air Conditioners Work

Air conditioners employ the same operating principles and basic components as your home refrigerator. An air conditioner cools your home with a cold indoor coil called the evaporator. The condenser, a hot outdoor coil, releases the collected heat outside. The evaporator and condenser coils are serpentine tubing surrounded by aluminum fins. This tubing is usually made of copper. A pump, called the compressor, moves a heat transfer fluid (or refrigerant) between the evaporator and the condenser. The pump forces the refrigerant through the circuit of tubing and fins in the coils. The liquid refrigerant evaporates in the indoor evaporator coil, pulling heat out of indoor air and thereby cooling the home. The hot refrigerant gas is pumped outdoors into the condenser where it reverts back to a liquid giving up its heat to the air flowing over the condenser's metal tubing and fins.

Types of Air Conditioners

The basic types of air conditioners are room air conditioners, split-system central air conditioners, and packaged central air conditioners.

Room Air Conditioners Room air conditioners cool rooms rather than the entire home. If they provide cooling only where they're needed, room air conditioners are less expensive to operate than central units, even though their efficiency is generally lower than that of central air conditioners.

Smaller room air conditioners (i.e., those drawing less than 7.5 amps of electricity) can be plugged into any 15- or 20-amp, 115-volt household circuit that is not shared with any other major appliances. Larger room air conditioners (i.e., those drawing more than 7.5 amps) need their own dedicated 115-volt circuit. The largest models require a dedicated 230-volt circuit.

Central Air Conditioners Central air conditioners circulate cool air through a system of supply and return ducts. Supply ducts and registers (i.e., openings in the walls, floors, or ceilings covered by grills) carry cooled air from the air conditioner to the home. This cooled air becomes warmer as it circulates through the home; then it flows back to the central air conditioner through return ducts and registers. A central air conditioner is either a split-system unit or a packaged unit.

In a split-system central air conditioner, an outdoor metal cabinet contains the condenser and compressor, and an indoor cabinet contains the evaporator. In many split-system air conditioners, this indoor cabinet also contains a furnace or the indoor part of a heat pump. The air conditioner's evaporator coil is installed in the cabinet or main supply duct of this furnace or heat pump. If your home already has a furnace but no air conditioner, a split-system is the most economical central air conditioner to install.

In a packaged central air conditioner, the evaporator, condenser, and compressor are all located in one cabinet, which usually is placed on a roof or on a concrete slab next to the house's foundation. This type of air conditioner also is used in small commercial buildings. Air supply and return ducts come from indoors through the home's exterior wall or roof to connect with the packaged air conditioner, which is usually located outdoors. Packaged air conditioners often include electric heating coils or a natural gas furnace. This combination of air conditioner and central heater eliminates the need for a separate furnace indoors.

How big should your air conditioner be? The size of an air conditioner depends on:

• how large your home (as in home, sweet home) is and how many windows it has;
• how much shade is on your home's windows, walls, and roof;
• how much insulation is in your home's ceiling and walls;
• how much air leaks into your home from the outside; and
• how much heat the occupants and appliances in your home generate.

An air conditioner's efficiency, performance, durability, and initial cost depend on matching its size to the above factors.

Make sure you buy the correct size of air conditioner. Be aware that a large air conditioner will not provide the best cooling. Buying an oversized air conditioner penalizes you in the following ways.

It costs more to buy a larger air conditioner than you need. The larger-than-necessary air conditioner cycles on and off more frequently, reducing its efficiency. Frequent cycling makes indoor temperatures fluctuate more and results in a less comfortable environment. Frequent cycling also inhibits moisture removal. In humid climates, removing moisture is essential for acceptable comfort. In addition, this cycling wears out the compressor and electrical parts more rapidly.

A larger air conditioner uses more electricity and creates added demands on electrical generation and delivery systems.

Air Conditioner Efficiency

Each air conditioner has an energy-efficiency rating that lists how many Btu per hour are removed for each watt of power it draws. For room air conditioners, this efficiency rating is the Energy Efficiency Ratio, or EER. For central air conditioners, it is the Seasonal Energy Efficiency Ratio, or SEER. These ratings are posted on an Energy Guide Label, which must be conspicuously attached to all new air conditioners. Many air conditioner manufacturers are participants in the voluntary EnergyStar® labeling program (see Source List in this publication). EnergyStar-labeled appliances mean that they have high EER and SEER ratings.

In general, new air conditioners with higher EERs or SEERs sport higher price tags. However, the higher initial cost of an energy-efficient model will be repaid to you several times during its life span. Your utility company may encourage the purchase of a more efficient air conditioner by rebating some or all of the price difference. Buy the most efficient air conditioner you (or they) can afford, especially if you use (or think you will use) an air conditioner frequently and/or if your electricity rates are high.

An air conditioner's filters, coils, and fins require regular maintenance for the unit to function effectively and efficiently throughout its years of service. Neglecting necessary maintenance ensures a steady decline in air conditioning performance while energy use steadily increases.

Air Conditioner Filters The most important maintenance task that will ensure the efficiency of your air conditioner is to routinely replace or clean its filters. Clogged, dirty filters block normal air flow and reduce a system's efficiency significantly. With normal air flow obstructed, air that bypasses the filter may carry dirt directly into the evaporator coil and impair the coil's heat-absorbing capacity. Filters are located somewhere along the return duct's length. Common filter locations are in walls, ceilings, furnaces, or in the air conditioner itself.

Some types of filters are reusable; others must be replaced. They are available in a variety of types and efficiencies. Clean or replace your air conditioning system's filter or filters every month or two during the cooling season. Filters may need more frequent attention if the air conditioner is in constant use, is subjected to dusty conditions, or you have fur-bearing pets in the house.

Air Conditioner Coils The air conditioner's evaporator coil and condenser coil collect dirt over their months and years of service. A clean filter prevents the evaporator coil from soiling quickly. In time, however, the evaporator coil will still collect dirt. This dirt reduces air flow and insulates the coil which reduces its ability to absorb heat. Therefore, your evaporator coil should be checked every year and cleaned as necessary.

Outdoor condenser coils can also become very dirty if the outdoor environment is dusty or if there is foliage nearby. You can easily see the condenser coil and notice if dirt is collecting on its fins.

You should minimize dirt and debris near the condenser unit. Your dryer vents, falling leaves, and lawn mower are all potential sources of dirt and debris. Cleaning the area around the coil, removing any debris, and trimming foliage back at least 2 feet (0.6 meters) allow for adequate air flow around the condenser.

Coil Fins The aluminum fins on evaporator and condenser coils are easily bent and can block air flow through the coil. Air conditioning wholesalers sell a tool called a "fin comb" that will comb these fins back into nearly original condition.

Buying New Air Conditioners

Today's best air conditioners use 30% to 50% less energy to produce the same amount of cooling as air conditioners made in the mid 1970s. Even if your air conditioner is only 10 years old, you may save 20% to 40% of your cooling energy costs by replacing it with a newer, more efficient model.

The Association of Home Appliance Manufacturers reports that the average EER of room air conditioners rose 47% from 1972 to 1991. If you own a 1970s-vintage room air conditioner with an EER of 5 and you replace it with a new one with an EER of 10, you will cut your air conditioning energy costs in half.

Central Air Conditioners—SEER National minimum standards for central air conditioners require a SEER of 9.7 and 10.0, for single-package and split-systems, respectively. But you do not need to settle for the minimum standard—there is a wide selection of units with SEERs reaching nearly 17.

Before 1979, the SEERs of central air conditioners ranged from 4.5 to 8.0. Replacing a 1970s-era central air conditioner with a SEER of 6 with a new unit having a SEER of 12 will cut your air conditioning costs in half.

Evaporative Coolers

An evaporative cooler (also called a "swamp cooler") is a completely different type of air conditioner that works well in hot, dry climates.

These units cool outdoor air by evaporation and blow it inside the building, causing a cooling effect much like the process when evaporating perspiration cools your body on a hot (but not overly humid) day. When operating an evaporative cooler, windows are opened part way to allow warm indoor air to escape as it is replaced by cooled air.

Evaporative coolers cost about one-half as much to install as central air conditioners and use about one-quarter as much energy. However, they require more frequent maintenance than refrigerated air conditioners and they're suitable only for areas with low humidity.

Using Your Air Conditioner

An air conditioner will cool the air in your home (where the heart is) fairly quickly. For economical operation, turn it on only when your home is occupied. You may consider installing a programmable thermostat. These allow you to set the time when the air conditioner will turn on, such as 30 minutes before you arrive home from work on a hot day. Contact EREC (see Source List) for the fact sheet Automatic and Programmable Thermostats. During the day, keep the drapes or blinds closed on windows that face east, south, and west. This will help reduce solar heat gain into your home.

Although one cannot control certain outside forces that affect the overall price of oil – the global supply and demand for crude oil or the effect of natural disasters – there is much you can personally do to pay a lower local price for your heating oil this winter.

Locked in prices have become increasingly popular with individuals, businesses and their heating oil providers. A particular price per gallon is either fixed or capped for one year. A fixed rate doesn’t go up or down, a price cap sets the highest price you will pay but if retail prices go down, you pay the lower prices. But due to the volatility of the oil market, there are fewer providers now willing to offer these programs.

Full service oil companies offer automatic delivery, service contracts, budget plans, 24 hour emergency service, and sometimes lock-in programs. A service contract pays for an annual system maintenance visit and for most repair parts and costs and can lower an annual heating bill up to 10 percent.

Many full service providers also offer discounts for loyal customers, seniors, and large deliveries. Payments made in cash or within time frame are often discounted as well.

C.O.D. discount dealers offer heavily discounted prices, but payments must be made in cash or credit card on the day of delivery. The bottom line is that you are paying for the heating oil and nothing else; no service contract, no yearly maintenance, no budget plans, and no fixed rates. If your furnace breaks down, you’ll be paying those repair costs in full. You will also need to keep track of your oil tank levels; discount dealers typically do not offer automatic delivery.

Some companies combine features of both full-service and C.O.D. companies. Fuel oil prices are discounted – but generally not as much as C.O.D. dealers – and service contracts are offered. Payment in cash or credit is due on delivery, or within five to 10 days.

www.govbenefits.gov is a great site that acts as a single source for locating assistance programs at all levels of government. You can get results by completing a questionnaire, browsing by category or locating benefits by state.

Heating assistance programs in all 50 states include the Low Income Energy Assistance Program (LIHEAP) and the Weatherization Assistance Program. LIHEAP provides assistance in paying energy bills, and the Weatherization program provides for the installation of energy efficiency improvements that reduce energy costs.

Geography, peace of mind, and the age and condition of your furnace will also place an important part in your decision making; i.e., someone with a 15-year-old furnace living in the frigid Northeast might want the security of a full-service oil company with 24-hour emergency service and a contract that will protect against unexpected repair costs. In contrast, an individual living in South Carolina with a brand new burner might be better served by paying for fuel C.O.D. and simply paying to have a yearly tune-up.

When you do choose a heating oil provider, make sure that the company and its technicians are fully certified, licensed and insured.

You may want to consider joining a heating oil buying group in your area. These oil buying cooperatives use the collective buying power of members to negotiate considerable discounts on heating oil, service and heating equipment.