6. Air Conditioning Operating Costs

If you are interested in purchasing an air conditioner, chances are that comfort is the main reason. However, cost is also a major factor. You may want to calculate the annual cost of operating an air conditioner to determine whether it is worth the investment. This section may also be valuable to you for comparing the performance and cost of equipment with identical cooling capacities before making a purchase decision.

Factors affecting cost

Many factors affect the operating cost of an air conditioner:

• geographical location of the house
  
• variance of weather conditions from year to year
  
• efficiency rating of the air conditioner (SEER or EER)
  
• size of the air conditioner relative to house cooling load
  
• thermostat setting
  
• number of occupants in the house
  
• habits of people in the house – if windows are open or closed; if window shading is used; and frequency of appliance, cooking and lighting use
  
• local cost of electricity

Method of calculating annual energy cost

Important note

The following formulas are intended to provide an estimate of the operating cost of an air conditioner. The actual energy consumption can vary depending on several factors, including those listed in the previous section entitled “Factors affecting cost.”

The annual cost of operation of an air conditioner can be calculated as shown below. The method can also be used to provide an estimate of the energy-cost savings of using a more efficient (i. e. higher SEER or EER rating) air conditioner.

Formula for calculating the yearly operating cost of central air conditioners

Formula for calculating the yearly operating cost of room air conditioners

Note that the local utility cost should be the cost per kilowatt hour based on your last monthly purchase. Most utility billing structures are such that the more energy you purchase, the less it costs per kilowatt hour.

SAMPLE CALCULATION

A Toronto resident is considering purchasing a central air conditioner. The utility rate for electricity is $0.0826/kWh. From Table 1, Toronto has 347 cooling degree-days and a summer outdoor design temperature of 31°C. The rated capacity of the unit is 36 000 Btu/h with a rated SEER of 10.0.

Substituting the values into the equation yields

The resident is also considering another unit with identical capacity but with a SEER of 12. 0. This unit sells for $250 more. To compare the two units, perform the same calculation, substituting 12.0 for the SEER.

The savings are about $36 per year. This represents a simple payback period of about seven years.

Remember that the more efficient model may also have a lower sound rating, and while there is no payback for noise reduction, it can be important to you and your neighbours.

Table 1. Cooling Degree-Days and Summer Outdoor Design Temperature

Sources: Environment Canada, ASHRAE