Air conditioners performance

Poor AC design, poor AC installation, oversized units and poor AC maintenance are the common causes of low air conditioning performance.

Oversizing causes lower AC performance

AC over-sizing is common, and a major cause of low-efficiency. Bigger, in this case, doesn't mean better cooling. On the contrary.

Over-sizing causes air conditioners to run in short cycles, wasting energy (since the unit runs some few minutes of every cycle just to cool down the coils, ducts and fins). Oversizing is the most common cause of low air conditioner performance.

See: Air Conditioners Sizing & Charts

AC duct sizing, insulation and location (Central air conditioners)

Size the duct systems properly. Undersized AC ducts (and leaky ducts) are also important causes of poor air conditioner performance. If in doubt, size the ducts upwards.

Avoid installing the AC ducts in the attic and unconditioned spaces. Whenever possible locate them within the conditioned space to minimize the effects of leaky ducts.

Ducts in unconditioned areas should be very well insulated and sealed. Their insulation value should be above R-4.

When installing or auditing the AC ducts, in new systems, make sure that the duct leakage is less than 3%; in existing systems that value should be less than 6% of coil airflow. That's crucial for energy-efficiency.

Registers (Central and split air conditioners)

Air conditioners performance depends significantly on the number and capacity of the return and supply air registers. Just make sure that supply registers deliver enough cool air and that return air registers carry enough warm air back.

Design

The efficiency of any AC system depends largely on its design.

Choose the shadiest side of your home to install room AC units or central AC condensing units. Room air conditioners should be located close to the center of the room, and AC thermostats located away from windows, supply registers or any other heat sources.

Pay attention to the design of the ducts, and to their capacity. Reduce the cooling load through passive solar techniques (including overhangs above east and west windows).

Insulation and Sealing

In the case of room air conditioners, fit the units snugly into the walls or windows openings - to minimize leaks and to higher AC performance. Use foams to seal openings and gaps.

Never forget the importance of the insulation of the walls, attic, ceiling and other parts of the building. Higher levels of insulation will reduce the cooling needs and the size of the equipment.

Refrigerant charge and airflow rate

A properly tuned AC system requires a proper air conditioner refrigerant charge and air-flow rate. It's importance is similar to the importance of tuning up a vehicle. Air conditioner performance is strictly related with them.

See:
AC Maintenance
Professional Maintenance AC
Air Conditioners Malfunction
Room and Central AC filters
Air Conditioners Refrigerant
Cleaning Air Conditioning Coils
AC Blower
Window air conditioner maintenance