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BEGINNER'S GUIDE TO AIR CONDITIONERS

How Air Conditioners Work

By removing heat from the indoor air and transferring it outdoors, an air conditioner cools your room. A chemical refrigerant in the system absorbs the unwanted heat and pumps it through a system of piping to the outside coil. A fan located in the outside unit blows outside air over the hot coil, transferring heat from the refrigerant to the outdoor air.

Most central air conditioning units operate by means of a split system: a "hot" side (the condensing unit–including the condensing coil, the compressor and the fan–which is situated outside your home) and a "cold" side (located inside your home). The cold side consists of an expansion valve and a cold coil and is usually part of your furnace or some type of air handler. The furnace blows air through an evaporator coil, which cools the air. This cool air is then routed throughout your home by means of a series of air ducts. A window unit operates on the same principal, the only difference being that both the hot side and the cold side are located within the same housing unit.

Most air conditioning systems have the following mechanical components:

Compressor

The compressor is controlled by the thermostat and is the heart of the system. The compressor acts as the pump, causing the refrigerant to flow through the system. Its job is to draw in a low-pressure, low-temperature, refrigerant in a gaseous state and by compressing this gas, raise the pressure and temperature of the refrigerant. This high-pressure, high-temperature gas then flows to the condenser coil, which is a series of piping with a fan that draws outside air across the coil. As the refrigerant passes through the condenser coil and the cooler outside air passes across the coil, the air absorbs heat from the refrigerant which causes the refrigerant to condense from a gas to a liquid state. The high-pressure, high-temperature liquid then reaches the expansion valve.

Expansion valve or metering device

The expansion valve acts as the brain of the system. By sensing the temperature of the evaporator or cooling coil, it allows liquid to pass through a very small orifice, which causes the refrigerant to expand to a low-pressure, low-temperature gas. This "cold" refrigerant flows to the evaporator.

Evaporator coil and blower

The evaporator coil is a series of piping connected to a furnace or air handler that blows indoor air across it, causing the coil to absorb heat from the air. The cooled air is then delivered to the house through ducting, and the refrigerant then flows back to the compressor where the cycle starts over again.

Chemical refrigerant

A refrigerant is a compound used in a heat cycle that changes form a gas to a liquid and then back.

Choosing Your Air Conditioner

Air Conditioner Type

You'll first need to decide whether to purchase a window AC unit (which is mounted in a window frame) or a portable AC unit, which can be moved from room to room. Wall unit air conditioners are designed to be mounted in holes cut into exterior walls. Some prefer wall units because they do not take up window space and don't leave your home as vulnerable to burglars. Wall units generally require a great deal more effort for installation than similar window units.

Cooling Capacity

The ability of each AC unit to cool a specified area is measured in BTU's (British thermal units). Higher BTUs indicate greater cooling power. It is not smart, however, to choose a unit simply based upon its cooling capacity. The size of the room you wish to cool will play prominently into this decision. If you choose a unit with a BTU that is too high for the space, the air conditioning unit won't operate efficiently, may cycle on and off too often, and will cost you money every month on your energy bill.

Efficiency

Air conditioners use about 5% of all the electricity produced in the United States, at a cost to homeowners of over $11 billion. As a result, roughly 100 million tons of carbon dioxide is released into the air each year–an average of about two tons for each home with an air conditioner. Switching to high-efficiency air conditioners and taking other actions to keep your home cool could reduce this energy use by 20% to 50%. The most efficient air conditioners on the market are up to 70% more efficient than the typical room air conditioners found in U.S. homes today.

A room air conditioner's efficiency is measured by the energy efficiency ratio (EER). The EER is the ratio of the cooling capacity (in British thermal units [Btu] per hour) to the power input (in watts). The required cooling capacity depends on the size of the room being cooled. The higher the EER rating, the more efficient the air conditioner. Look for units with an EER of 10.0 or above, check the EnergyGuide label for the unit, and also look for room air conditioners with the ENERGY STAR label.

Installation Requirements

This may sound obvious, but make sure that the window unit you are considering purchasing is the right size for the window you plan to use it in. Some units also require special wiring, so be aware of any special requirements.

Sizing

Proper sizing is very important for efficient air conditioning. A bigger unit is not necessarily better; a unit that is too large will waste energy and will not cool an area uniformly. A small unit running for an extended period operates more efficiently and is more effective at dehumidifying than a large unit that too frequently cycles on and off. Based on size alone, an air conditioner generally needs 20 BTU's for each square foot of living space. You should also consider room height, local climate, shading, window size, etc.

Your Home's Electrical System

Verify that your home's electrical system can meet the unit's power requirements. Room units operate on 115-volt or 230-volt circuits. The standard household receptacle is a connection for a 115-volt branch circuit. Large room units rated at 115 volts may require a dedicated circuit and room units rated at 230 volts may require a special circuit.

Mounting Considerations

If you are mounting your air conditioner near the corner of a room, look for a unit that can direct its airflow in the desired direction for your room layout. If you need to mount the air conditioner at the narrow end of a long room, then look for a fan control known as "Power Thrust" or "Super Thrust" that sends the cooled air farther into the room.

Slide-out Filters

The filter should slide out easily for regular cleaning. Particles of mold and dust remain trapped in the filter, and if the filters are not cleaned, your unit's functionality will be considerably slowed.

Other features to look for:
• Logically arranged controls
• Digital readout for the thermostat setting
• Built-in timer

Air Conditioner Sizing

Many people mistakenly believe that "the bigger, the better" is the mantra to follow when it comes to air conditioners. It would seem logical that larger, more powerful AC units would translate into cooler, more comfortable rooms. In truth, if you purchase an air conditioning unit that is too large or powerful for your space, you will actually create more of a problem for yourself.

The general rule of thumb states that you should allow 35BTU for every square foot of a room. If you wish to cool a room that is 12 x 18 (or 216 square feet), multiply 216 x 35 = 7560. You should try to find an air conditioning unit that is close to 7560 BTUs as possible.

By ensuring that you are purchasing an air conditioning unit that is correctly sized for your space you will find several immediate benefits:
• After measuring your space, you will not waste any money on a unit that is too large for your space.
• Using a properly-sized air conditioning unit will keep your energy bills at their most efficient levels, as your compressor will be running constantly.
• You will find that your room will maintain more even temperatures as your AC unit will run more regularly, rather than constantly cycling on and off.
• A properly sized AC unit will not create any extra noise in your space.

Keep in mind that window-sized air conditioning units, even the larger models, are only meant to cool limited spaces. Another common mistake people make is to purchase a gigantic air conditioning unit that they hope will cool their entire house or apartment. You are always better off purchasing several smaller units for each room, rather than one large unit. This will also give you much greater control of your temperatures (and allow you to vary them room by room), as well as your energy bills.

Check the labels and tags of any air conditioning unit you wish to purchase. The recommended room size for each unit is normally listed and will allow you to make the best purchase for your space possible. A properly sized air conditioning unit will be much easier for you to install and maintain, and it will provide you with exactly the sort of cool comfort you will appreciate on a hot summer day.

BTU's

Most people think that an oversized air conditioner will cool your room better. The truth is that an oversized air conditioner wastes energy as it works to cool and is therefore less effective and efficient. Air conditioners remove both heat and humidity from the air, and if the unit is too large, it will cool the room quickly, but not remove all of the humidity. As a result, the room will be left with a dampness to it. Not good.

Here's a guideline that was designed to help you find out how many BTU's are right for you:
1. Determine square footage of the room that is to be cooled. For square and rectangular rooms, multiply the length by the width. For triangular rooms, multiply the length by the width and then divide by 2.
2. Determine cooling capacity, which is measured in BTU's, by using the helpful key below:

   Square feet	BTU's per hour
   100-150	5,000
   150-200	6,000
   200-250	7,000
   250-300	8,000
   300-350	9,000
   350-400	10,000
   400-550	12,000
   550-700	14,000
   700-1,000	18,000
   1,000-1,200	21,000
   1,200-1,400	23,000
   1,400-1,500	24,000
   1,500-2,000	30,000
   2,000-2,500	34,000

3. Make the following accommodations if necessary:
   • Reduce cooling capacity by 10% of the room is heavily shaded. Conversely, increase cooling capacity by 10% if the room is generally sunny.
   • If more than 2 people occupy a given room, increase cooling capacity by 600 BTU's for each extra person in that room.
   • Increase cooling capacity by 4,000 BTU's for kitchens.

STAY COOL!