Audit of Household Electricity Consumption

Student Task

Student Task

You are to do an electricity energy audit of your household. Usually most households receive a quarterly (3 monthly) electricity bill from their retailer. The aim of this task is to compare your electrical energy audit with your actual electricity bill. Your electricity consumption will vary according to the time of your year; it would be useful to compare your electricity consumption for different seasons - summer, winter, spring and autumn.

Follow the steps below:

Step 1: Make a list of all electrical appliances that are used in your household. Do not forget to include fans used in ducted heating and cooling systems as well as power tools etc.

Step 2: From the tag on the appliance, ascertain the power rating of the appliance. Note that for some appliances such as refrigerators, a kW.h rating is given for the whole year. For example, if a refrigerator has a rating of 800 kW.h per year, this would equate to 200 kW.h per quarter. If you cannot find the appliance power rating, refer to manufacturer's specifications or Google 'power ratings of electrical appliances'.

Website References:
www.rpc.com.au/products/efn/efnextracts/estima_rating/
www.howto.altenergy.com/Reference_Materials/

Step 3: Determine approximately how long each appliance would be on over a 3 month period (90 days) in terms of hours. As an example, if a clothes iron used for say 10 minutes each day, over 90 days this would be:

15 hours =

90 x 10

60

Step 4: Construct a table or spreadsheet similar to the example below. For lighting, you need to assume an average power (how many lights are on) x average time lights are on over 90 days. Make a "best estimate".

Step 5: Calculate your total electricity usage over the quarter. Compare this to a recent electricity bill, but take into account the time of year.

Step 6: Now calculate the cost of your electricity usage for the quarter. On your electricity bill will be the retail cost of electricity as a domestic consumer (usually between 15 cents and 20 cents per kW.h) Once you have calculated your cost, compare your electricity usage with others in the classroom. As a class, discuss the results and suggest reasons and factors why there may be a wide range of electricity consumption amongst your peers' households.

Example of Household Electricity Energy Audit (Over 3 months)

Column #1 Column #2 Column #3 Column #4 Column #5
Electrical Appliance Power Rating in Watts (W) Power Rating in kilowatts (kW) Estimated use in hours (h) over 90 day period Energy Use (kW.h) Columns 3 x 4
Television 250W 0.25kW 180 45
Oven 1200W 1.2kW 180 72
Refridgerator       200
Clothes Drier 600W 0.60kW 15 9
Air Conditioner 3500W 3.5kW 100 350
Microwave 800W 0.80kW 20 16
Electric Drill 600W 0.60kW 2 1.2
Lighting 400W 0.40kW (average lights) 270 (3 hours per day) 108

You may have 20 or more electrical appliances. Add all figures in Column 5 to give your total kiloWatt hours. This is the real energy consumed.

The actual energy consumption (as per your bill) is the figure you have calculated above, divided by a power factor which can be taken as 0.8. This should be close to your energy used as shown on your electricity bill.

What is the Power Factor?

In electricity, an appliance generally loses some of the power given to it due to its internal properties. Thus in order for the appliance to work at the power stipulated on its specifications, known as the Real Power, a greater power called the Actual Power is supplied to it.

Actual Power =

Real Power

Power Factor

The Power Factor is a number between 0 and 1. We will assume a Power Factor of 0.8 for all appliances (average value).

The energy consumption of a device (in kiloWatt-hours kWh) is found according to the relationship:

Daily energy consumption (kWh) = Actual Power (kW) x hours of use (h)

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