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Your local energy efficiency experts      

Building Services

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Calculating savings from replaced products

You can manually calculate energy cost of any product using the following formula

$$$ = W * H * T * 365 / 1000, where 

W = appliance or product wattage.

H = average hours of usage per day

T = current electrical tariff (from your electricity bill)

365 = to calculate cost per year (use any period required)

1000 = divide by 1000 to convert result to kWh.

Globes, downlights

To calculate savings from replacing 100W incandescent globe with 20W equivalent CFL, used approximately 2 hours/day on a 25c per kWh tariff,

Saving = (100W-20W) * 2 * $0.25 * 365 / 1000 = $14.60 per year 

Repeat the formula for all other incandescent lights to calculate total savings of light replacement. For downlights, use 50W for existing halogen lights and 6W for LED replacement.


To calculate savings from installing standby power controllers you must know your appliances' standby energy usage in Watts. If you don;t have this information, you can use the average values to approximate the saving:

TV (large) = 20W

TV(other) = 10W

VCR = 9W

DVD = 5W

gaming = 15W

Set top box = 7W 

For example, to calculate savings from standby power controller installed with TV, set top box and a dvd player, used approximately 3 hours/day (21hr standby), and 25c per kWh tariff, using the same formula, 

Saving = (20W+7W+5W) * 21 * $0.25 * 365 / 1000 = $61.32 / year   

Shower heads

The savings from low-flow showerheads are measured by the amount of saved hot water, for which the energy used to heat up the extra water can be calculated. A shower head with flow rating of 9L per minute or less is considered low-flow. By comparison, old shower heads can use as much as 30L per minute.   

Assuming 4 min shower is taken every day, with hot and cold water mixed 1:1, the amount of hot water saved by using low-flow shower head is

Saving = (30L-9L) * 4min / 2 = 42L per shower.

With an average 135L hot water tank this means saving of approx 1/3rd of the tank. To calculate $ saving, we use pre-calculated costs of heating 1L of water at 1$/kWh tariff. These values are 

c = $0.05305 for average electric HWS, and

c = $0.02685 for average gas HWS

Thus, the saving in our example

$$$ = 0.05305 * 42L * $0.25 = $0.28 per shower, or $102.20 per year