Case Study on the Eco Light Bulbs by Denis

Reduction in household electricity consumption through the use of energy efficient CFL bulbs.

Unlike commercial buildings, the lighting load in most domestic households does not normally constitute a significant part of the total power consumption of the household. In comparison to electric space and water heating consumption.

However during winter months when significant quantities of lighting may be required for 5 to 6 hours per night, this situation can change considerably.

A CASE STUDY : THEORETICAL

In an effort to reduce their monthly power bill, Peter and Pat have replaced all of the standard incandescent bulbs in their house with 20W spiral CFLs.

The original total lighting load with 20 x 100W incandescent bulbs was. 2000W or 2kW.

Leaving all the lights on for one hour used 2 kW.hr of power.

The new total lighting load with 20 x 20W CFLs would be 400W

Leaving all the lights on for one hour would use 0.4 kW.hr of power.

This is a saving of 1.6 kW.hr

At their uncontrolled supply rate of 25.27 cents / kW.hr this equates to a saving of 40 cents an hour.

At 6 hours use this works out at $2.40 a night.

Obviously this is a worst case senario, you would not normally have every light in the house on at once.

A CASE STUDY : THE REAL WORLD?

Peter and Pat's house has a modern high efficiency wood burner installed with wet back connections to the water heating system. As such, the normal high power load in winter months associated with electric space heating and water heating has been minimised. In their case the increase in the lighting load during winter months would form a significant component of their monthly power bill.

The lounge, kitchen and dining area have a total of 10 recessed down lights. If we assume 6 hours continuous use each night in this area

Original power consumption = 10 x 100W = 1000W = 1 kW x 6 = 6 kW.hr @ 25.27 c/kW.hr = $1.51 per night.

New power consumption = 10 x 20W = 200W = 0.2 kW x 6 = 1.2 kW.hr @ 25.27 c/kW.hr = $0.303 per night

Saving $1.20 per night.

If we assume a total of 3 hours continuous use in two rooms during the night for the rest of the house.

Original power consumption = 2 x 100W = 0.2 kW x 3 = 0.6 kW.hr @ 25.27 c/kW.hr = $0.15 per night

New power consumption = 2 x 20W = 0.04kW x 3 = 0.12kW.hr @ 25.27 c/kW.hr = $0.03 per night

Saving $0.12 per night.

Total saving = $1.32 per night x 30 days = $39.60 per month.

This level of savings would probably only be achieved during 3 months of winter, with the savings falling either side to a minimum during summer.

An accurate level of real savings could only be ascertained by monitering power bills over an entire year, and comparing these with the previous years bills before the change to CFLs was made.