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

Cost of operation

=

24 x DDC•18 --------------------- TOD – 18

x

CAP (35°C) ------------------ SEER

x

Cost/kW ------------- 1000

Formula for calculating the yearly operating cost of room air conditioners

Cost of operation

=

24 x DDC•18 --------------------- TOD – 18

x

CAP (35°C) ------------------ 0.9 EER

x

Cost/kW ------------- 1000

where,
	DDC•18	=	number of cooling degree-days (base 18°C) from Table 1
	TOD	=	summer outdoor design temperature (°C) for location from Table 1
CAP (35°C)		=	the capacity of the air conditioner (in Btu/h) at an entering air temperature of 35°C
	SEER	=	the rated seasonal energy efficiency ratio (Btu/h/W)
	EER	=	the rated energy efficiency ratio
Cost per kWh		=	local electricity cost (in $/kWh)

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

Cost of operation	=	24 x 359 --------------------- (30 -18)	x	36 000 ------------------ 10	x	0.0826 ------------- 1000
	=	$214/year

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.

Cost of operation	=	24 x 359 --------------------- 30 -18	x	36 000 ------------------ 12	x	0.0826 ------------- 1000
	=	$178/year

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

PROVINCE/CITY		DDC•18	TOD  (°C)
British Columbia
	Kamloops	261	34
	Penticton	213	32
	Prince George	22	27
	Vancouver	44	25
	Victoria	24	26
Alberta
	Calgary	40	29
	Edmonton	28	28
	Lethbridge	108	31
	Medicine Hat	187	32
Saskatchewan
	Moose Jaw	177	32
	Regina	146	32
	Saskatoon	117	31
Manitoba
	Brandon	119	31
	Winnipeg	186	31
Ontario
	London	236	30
	North Bay	119	27
	Ottawa	245	30
	Sudbury	138	29
	Thunder Bay	70	29
	Toronto	359	30
	Windsor	422	31
Quebec
	Montréal	236	30
	Québec	133	29
	Sept-Îles	9	22
	Sherbrooke	101	29
New Brunswick
	Fredericton	143	30
	Moncton	103	28
	Saint John	37	26
Nova Scotia
	Halifax	104	27
	Sydney	84	27
Prince Edward Island
	Charlottetown	100	26
	Summerside	112	26
Newfoundland and Labrador
	Gander	43	26
	St. John's	32	24

Sources: Environment Canada, ASHRAE