AIR-CONDITIONING OPERATING COSTS |

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 ¨C 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 ¨C 18 x CAP(35ˇăC) ------------------ SEER x Cost/kW ------------- 1000 Formula for calculating the yearly operating cost of room air conditioners Cost of operation = 24 x DDC?18 --------------------- TOD ¨C 18 x CAP(35ˇăC) ------------------ 0.9 EER x Cost/kW ------------- 1000 where, DDC?18 = number of cooling degree-days (base 18ˇăC) from TOD = summer outdoor design temperature (ˇăC) for location from CAP (35ˇăC) = the capacity of the air conditioner (in Btu/h) at an entering air temperature of 35ˇăC 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 , Toronto has 347 cooling degree-days and a summer outdoor design temperature of 31ˇăC. 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 (ˇăC) 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 Montr¨¦al 236 30 Qu¨¦bec 133 29 Sept-?les 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 NewfoundlandandLabrador Gander 43 26 St. John's 32 24 Sources: Environment Canada, ASHRAE |