Air conditioners are expensive to operate; in a hot month, they can easily consume $500 worth of electricity. That's common.
Unfortunately some of the alternatives to AC are expensive or impractical in existing buildings. Yet you should consider them; some may not be impractical, after all...
Do you really need a central AC? That's the first question you should ask yourself. Do you really need a system that will cost you several thousands of dollars to buy and install, and many thousands more in maintenance and running costs during its lifespan?
A couple of room (window) air conditioners - with a cost of some few hundred dollars each - can do a good job, in many homes.
And the same can be said of ductless AC. They are a lot less expensive to buy, install, size and maintain than central AC. They can make a lot of sense in low-energy homes, with very high levels of insulation and air sealing.
There are several good cooling strategies that can be used to reduce or replace traditional AC.
If you live in a region with cool nights, or with cooling breezes in the early morning or late afternoon, it’s important to bring them inside, and to close up the house during the daytime. That’s easy to get cool air by opening the windows, or by using window fans, whole-house fans, casement windows (to deflect breezes into rooms) or other means.
Do not undervalue the impact of these cooling strategies; they can save you many hundreds of dollars in air-conditioning.
See: Natural Cooling
Ceiling fans – and other circulation fans - are great for increasing comfort and to reduce or eliminate the use of air conditioners.
Fans do not lower the actual temperature of the rooms where they are; but they increase comfort by evaporating moisture from our skin. The airflow generated by fans increases human thermal comfort from about 75ºF/24ºC to 80-82ºF (26-29ºC).
And you can use fans in conjunction with AC. Instead of setting your air conditioner to 74-76 ºF, you can raise that setting to, say, 80-82ºF; each degree increase in your AC thermostat can reduce your cooling bills by 3-5%. With the fans working, you will not notice the difference.
Also consider whole-house fans. They are great to bring outside fresher air into the house, and to drive inside warmer air out.
Whole-house fans draw outside air in through open windows while exhausting inside hotter air through the attic, using ducts, or by simply pushing it out through roof vents and other openings.
See: Whole House Fans
If you live in a dry climate, consider evaporative coolers (swamp coolers). They are an excellent alternative to air conditioners. They use a small fraction of the electricity used by air conditioners. Their secret is on the tiny droplets of water that they evaporate.
Be aware anyway: they are not effective in humid weather conditions.
See: Evaporative Coolers
AC ENVIRONMENTAL IMPACT: A MYTH OR A FACT?
AC creates peak demand loads during hot summer afternoons, when everybody uses it. And to respond to that demand utilities have to build dozens of polluting power plants, otherwise unnecessary.
Do not forget that any alternative to air conditioners should be used in conjunction with other cooling improvements; otherwise the alternatives may not be effective enough.
Cooling improvements include...
window films (to reduce heat gains through old or inadequate glazed windows to a small fraction);
fans (which can be used in conjunction with AC);
sun protection, by using shading devices like awnings, blinds, shades, shutters; or the shade of trees, trellis and shrubs: plants will also create evapotranspiration, leading to lower temperatures around the house and ultimately in house.
roof reflective materials, to reduce heat gains through the ceiling;
the control of internal sources of heat, coming from food preparation, baths or laundry...
See: AC Savings
In new construction, consider carefully your home's orientation and shape; and also the materials used in the walls, the type of window glazing and the size of the windows and their orientation and location, or elements like air sealing and insulation. See: Cooling and Design and AC in Hot Climates
A poorly shaded home will need more air-conditioning; some types of trees and structures like trellis on east and west-facing windows can also help reduce cooling needs. That's critical for energy improvements.
When painting your home or improving or replacing your roof, use light colors and "cool" roofing techniques. Roof coatings are excellent to cut down unwanted heat gains.