New Cooling Systems
 

New cooling systems use 30 to 50 percent less energy to produce the same amount of cooling as systems made in the mid-1970s.
Even if your cooling system is only 10 years old, you may save 20 to 40 percent of your cooling energy costs by replacing it with a newer, more efficient model.
When replacing an older or failed split system, be sure that the evaporator coil is replaced with a new one that exactly matches the condenser coil in the new condensing unit.
The cooling system's efficiency will likely not improve if the existing evaporator coil is left in place; in fact, the old coil could cause the new compressor to fail prematurely.
Sizing cooling systems
Cooling systems are rated by the number of British thermal units (Btu) of heat they can remove per hour. Cooling capacity is also rated in "tons." One ton equals 12,000 Btu per hour.
How large should your cooling system be? Make sure your contractor installs a cooling system that is correctly sized and takes the building conditions listed above into consideration.

The size requirements of a cooling system depends on:
The size of your building and how many windows it has.
The amount of shade on your building's windows, walls, and roof.
The amount of insulation in your building's ceiling and walls.
The number of air leaks into your building from the outside.
The amount of heat generated by building occupants and equipment.
Bigger is not always better
An oversized cooling system will not necessarily provide the best results. Oversized systems have these drawbacks:

They are more expensive to purchase.
Larger-than-necessary cooling systems cycle on and off more frequently, reducing efficiency.
Frequent cycling causes greater fluctuation of indoor temperatures and results in decreased comfort.
Frequent cycling also inhibits moisture removal. In humid climates, removing moisture is essential for comfort.
Cycling wears out the compressor and other electrical parts more rapidly.
Larger cooling systems use more electricity and create added demands on electrical generation and delivery systems.
If major installation problems are found and fixed, cooling equipment will perform efficiently for years with only minor routine maintenance.
Installing new cooling equipment
Be sure that your contractor performs the following when installing a new cooling system:

Allows adequate indoor space for the installation, maintenance, and repair and installs an access door in the furnace or duct to provide a way to clean the evaporator coil.
Installs enough supply and return registers to deliver cool air and carry warm house air back to the cooling system.
Installs duct work within the conditioned space, not in the attic, wherever possible.
Seals all ducts with duct mastic and heavily insulates attic ducts.
Locates the condensing unit where its noise will not be disruptive, if possible.
Places the condensing unit in a shady spot, if possible.
Verifies that the newly installed cooling system has the exact refrigerant charge and air flow rate specified by the manufacturer.
Locates the thermostat away from heat sources, such as windows, or supply registers.
Room air conditioners
If you install a new room air conditioner, it's best to:

Select a room unit with an energy efficiency ratio (EER) of 9.5 or greater.
Locate the air conditioner in a window or wall area near the center of the room and on the north or east side of the building; in the shade is best.
Minimize air leakage by fitting the air conditioner snugly into its opening and sealing gaps with a foam weatherstripping material.
Purchase a properly sized unit. It will remove humidity effectively as it cools. Running a smaller unit for a longer time will use less energy to completely condition a room than running a larger unit for a shorter time.
If the room is heavily shaded, reduce capacity by 10%.
If the room is very sunny, increase capacity by 10%.
If more than 2 people regularly occupy the room, add 600 Btu/hr for each additional person.
If the unit is for a kitchen, increase the capacity by 4,000 Btu/hr.