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Learn How to Calculate Your Household Power Consumption







Households should approach electrical power consumption as if it were a business, dividing their costs into two categories: fixed and variable.

Fixed costs represent items that can’t be shut off or eliminated, such as the refrigerator, stove, furnace fan, etc. You must be as objective as possible when listing fixed items, as there isn’t any room for the personal comforts on this list, only the necessities. This list will become your baseline, or better yet, your power consumption goal for the household.

All of the other power-consuming items in your home--lights, computers, hair dryer, etc--are your variable costs. To start reducing your monthly energy bills, focus on this list of items.

Once you’ve created your two lists, you must then calculate the amount of power that each item uses. Start with the fixed costs, as these should be the easiest to calculate because their consumption should be based on a cycle. For example, a fridge may cycle an average of 4 times an hour for 5 minutes, 24 hours a day, 30 days a month, and, therefore, the calculation:

Watt hours = (4 x (5/60)) x 24 x 30 x 700 (running wattage) = 168 000 Wh or 168 KWh

Refer to the table and the calculation samples if you need any further help. For the purpose of filling out your list, do not use or attempt to use the starting wattage. Starting wattage will be explained and used in a different context in a future article.

Don’t concern yourself with being 100 per cent accurate with this calculation. You can refine this calculation as you get more familiar with your power usage. Having gone through each item on your ‘fixed’ list, you should now have your household’s total fixed power usage. Total all of the items and you now have your household power usage GOAL.

NOTE: Resist the temptation to put a dollar figure to this baseline as power costs per KWh can fluctuate, and it could skew your household GOAL. The ultimate goal should be to reduce power consumption and the dollar savings will follow.
Secondly, variable costs can be calculated in exactly the same manner, however, you must determine the amount of time per month that you use each particular item. Once you’ve tallied up the power usage of each item on your ‘variable’ list, you can evaluate your household energy consumption, and either eliminate some of these variable items completely or at least limit their power usage.

Appliance / Tool	Running Watts	Starting Watts
Cordless Phone	5	5
Printer	8	5
Laptop	20	20
Desk Top Computer	250	250
Incandescent light bulb	60	60
Alarm / Radio Clock	100	100
Humidifier	100	100
LCD 40" TV (TYP.)	200	200
Plasma 40" TV (TYP.)	300	300
Dehumidifier	350	350
Blender	385	385
Home Alarm System	500	500
Coffee Maker	800	800
Furnace Fan (1/3 hp)	700	1400
Fridge / Freezer	700	2200
Garage Door Opener (1/2 hp)	875	2350
Microwave	1000	1000
Iron	1000	1000
Washer	1150	2250
Toaster Oven	1200	1200
800 PSI Pressure Washer	1200	1200
7.25" Circular Saw	1400	2300
Dishwasher	1500	1500
Table Saw	2000	2000
Oven	2400	2400
Central Air Conditioner	3500	4700

*NOTE: This is the typical wattage for these items, however, you can check wattage on the appliance / tool for higher accuracy.

A Starting Watt is best described as the amount of energy that's needed to overcome inertia. The best example of an appliance which requires a large starting wattage is a central air conditioning unit. In an unpowered state, the fan blades within the central air unit have high inertial forces, meaning they tend to want to stay at rest (static). To overcome these inertial forces, your A/C unit must draw large amounts of power to free the fan from its static position. This high wattage, however, is only temporary and will drop its power consumption as the fan reaches steady operation.


A Running Watt is best described as the amount of energy that's needed to operate an appliance or tool. Typically, appliances and tools will be labelled with their running watts.

NOTE: If you are unable to find the power consumption labelled on your appliance or tool, you can calculate the approximate power usage by multiplying the unit's voltage by the current (amps) that it draws.

Example: Corded 1/2" Drill

110 volt (drill plugged into home (North America) wall socket)

10 amps (labelled on drill)

Power (watts) = 110 volts x 10 amps

Power = 1100 watts

Now, the most important of the calculations: we can figure out how much money it will cost you to run an appliance, tool, etc. by calculating the KWh, which is the unit of measure that hydro companies use to figure out your monthly bills.

KWh (Kilo watt hour)

Example continued....

Drill used for 1/2 an hour

Power = 1100 watts = 1.1 KW

KWh = 1.1 x 0.5

KWh = 0.55 KWh

These simple calculations can be used to approximate your monthly electrical bill. Use the table above to help you calculate the power usage in your home. NOTE: once you've calculated each appliance's KWh, sum all values and multiply by your region's (i.e. Durham Region) average electrical cost to reveal your approximate monthly electrical cost.

Example

Total KWh = 0.55 + 1.1 + 4.5 + 2.1 = 8.25 KWh

Durham Region Average cost per KWh = $0.08

Cost = 8.25 KWh x $0.08 = $0.66



This isn't the best example of a monthly bill, but it shows the calculation. Also, there's a product that you can buy and use with each appliance or tool to find its actual power usage, however, it does require investment dollars, probably in the neighbourhood of $50 or $60. To note, the starting watts are more of a concern for people who are aiming to go off the grid (i.e. solar/wind), because they must keep in mind that there's a spike in power during initial appliance and tool usage. We could talk about that further, in another article

[justify]Three-phase circuits distribute electrical power along multiple conductors in the same power line. The current waveform of each conductor is offset in time from the others. This allows more power to be transmitted on one line at a lower voltage, increasing efficiency without sacrificing safety. For three-phase motors, there is an added advantage: the three-phase power supply provides a smoother waveform (in effect, a more balanced supply of electricity).

Difficulty: Moderate
Instructions

things you'll need:
Ammeter
Calculator
1
Understand the difference in how power consumption is calculated for conventional and three-phase power circuits. In a conventional electric circuit, power (in watts) is equal to the voltage multiplied by the amperage. For a three-phase circuit, watts equal volts times amperes times the square root of 3.

2
Determine the voltage and amperage when the motor is running. Most three-phase motors are large devices and have their own readouts. However, you can measure the current (amperes) in some cases. An ammeter rated for three-phase applications will do the job and works much like an ordinary ammeter. You plug the motor into the ammeter and the ammeter into the power line. Be extremely careful in following manufacturer's instructions, because three-phase applications generally draw a great deal of power.

3
Calculate three-phase motor power consumption by multiplying amps by volts by the square root of three (W = AV(sqrt 3). For example, if the motor is drawing 30 amps at 250 volts, you have 30 x 250 x sqrt 3 (about 1.73) = 12,975 watts).

4
Convert watts to kilowatts by dividing the number of watts by 1,000. Thus, a three-phase electric motor drawing 12,975 watts is consuming 12.975 kilowatts. For one hour, this equals 12.975 kilowatt/hours