Central air conditioners are expensive to install and to run. The widespread use of air conditioning all over the world is now one of the biggest sources of CO2 emissions.
The use of AC should be limited to the minimum possible, even in hot and tropical climates, where their use is more necessary.
So, whenever possible, consider alternatives to it. If you do need central AC, use it selectively.
If you do need a central AC system, before installing it...
1) upgrade your home’s insulation and air sealing (in order to install a smaller system, and reduce air conditioning cooling needs);
2) improve the effectiveness of your windows;
3) improve your roof reflectivity.
4) shade the walls, the roof, the windows as much as you can.
AC in Hot climates
In hot climates, use air conditioners as selectively as possible. Consider:1) Zoning your house (room-by-room cooling);
2) Do not air condition the entire house;
3) Protect air conditioned rooms from heat gains, by insulating them to high levels...
4) Use your air conditioner system in conjunction with ceiling fans;
5) Use natural ventilation and other cooling strategies in non-air conditioned rooms.
Zoning & Air conditioners
In very hot climates, avoid air conditioning all the rooms.
Limit the use of air conditioning to the rooms where it is most needed: bedrooms, for sleeping comfort, for instance; sleeping comfort is an important issue, especially during periods of high humidity, and air conditioners are a good way of providing comfort in hot conditions.
Use AC in small rooms highly insulated
Air-conditioned rooms should be thoroughly insulated. The insulation should involve the walls but also the ceiling and the floor of the rooms, which should be small or relatively small (in size and ceiling height): that’s important for energy savings. Consider very high levels of room insulation.
These air conditioned rooms should have reduced glass areas and be located in the coolest part in the house (in a central part of the house...); other rooms can provide a thermal buffer to the air-conditioned spaces...
Using AC in conjunction with other cooling methods
Consider the use of ceiling fans with air conditioners, for energy improvements.
Ceiling fans will allow you to decrease the air conditioner thermostat setting (each one degree increase (Fº) will decrease your air conditioner bills by about 5%). See: Using AC with Ceiling Fans.
Use ceiling fans, natural ventilation and other natural cooling strategies to improve comfort in non-air-conditioned rooms.