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Energy efficiency FR
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Energy efficiency (FR)

It is much more cost effective and less burden on the environment to use energy efficiently than to generate it. This reduces the demand on fossil fuel resources, which currently supply most of our energy needs, so enabling us to leave resources for future generations. Such actions form the basis of the sustainable use of energy.

[link to sustainable use of energy]

Our carbon footprint is a measure of how efficiently we meet our energy needs. It us generally accepted that each of us in Europe will have to reduce our footprint by 80% over the next 40 years to avoid irreversible changes in climate . In this section we consider the various options for saving energy and in the following section, options for switching from fossil fuel to renewable energy sources.

[link to carbon footprint]


For more than 100 years electricity has been used for lighting lamps. The incandescent lamp, developed commercially by Thomas Edison in the 19th century, generates light by heating a thin wire of a material with a high resistance like tungsten. Only about 10% of the energy used is converted to light while the remaining energy is given off in the form of heat.

More recently florescent lamps have been developed which produce light through excitation of a gas and so are much more efficient, typically 80 – 85%. They are in general use in shops, offices and schools as they can light up large areas due to their length, typically one or two metres.

In the past 20 years, compact florescent lamps (CFL) have been developed which have folded tubes generally either elongated or spiral (Figure 1). They can be used in the same fittings as incandescent lamps and therefore can be a like for like replacement.

Figure 1: Compact florescent lamps


Two other types of lamps have evolved –
the halogen lamp which is of the incandescent type but is brighter due to the presence of the halogen gas; the light emitting dioxide (LED) is a very efficient electronic device in which light is emitted by exciting a suitable semi-conductor material.

Brightness (luminosity)
The lumen (lm) is a measure of the brightness of the lamp. Since September 2010 all lamps sold in Europe are marked with their power consumption in watts and their brightness in lumens. A comparison between the various types is given in Table 1.

Table 1: Typical power ratings and lifetime of lamps giving a brightness of 1100 lumens

The life of non-incandescent lamps is much longer than incandescent lamps because they have electronic circuits called ballasts which are now the life limiting factor rather than the lamp itself. Some CFLs have separate ballasts and lamps and so the ballasts can be replaced until the lamp fails. Typical lifetimes for various types of lamps are listed in Table 1. Because of their much longer life, they should always be fitted where access is difficult.

EU energy label
The EU energy label (Figure 2) has a comparative efficiency classification with a rating from A (the most efficient) to G (the least efficient). These classes are listed in Table 1 for the principal types of lamps. In addition the label also contains information about the brightness of the lamp, the power it consumes and the characteristic life time.

Observe that the low energy lamps not only use less energy but also have a much longer life time.

In order to reduce the price of low energy lamps, manufacturers have tended to set the price according to the life of the lamp. Hence a Compact fluorescent lamp with 6000 hours will generally cost less than a lamp with 15,000 hours life.

Figure 2: EU energy label for lamps

Phasing out of incandescent lamps
Agreement has been reached at EU level to phase out the use of incandescent lamps over a period of three years. The phase-out dates are listed in Table 2.

Table 2: Phase out dates for incandescent lamps

Saving money and the environment
Low energy lamps, i.e. lamps with high efficiency, can save substantial amounts of electricity, money and the environment. A typical dwelling might have 8-15 lamps with average brightness 400 -1,200 lumens, a power rating of 40 – 100 watts and 800 hours usage a year. Taking the mid point of these values, annual energy consumption with incandescent lamps would be
12 x 800 x 75 = 720 kWh
With a unit price of 15 €cents/kWh, the annual cost would be 720 x 0.15 = 108€

With low energy lamps like CFLs, the annual savings per house could be 80% and the annual electricity saving 86€.

Aggregated nationally the annual electricity savings would amount to
0.576 x 20 X 106 = 11.52 TWh/year
equivalent to the output of at least four 1 GW(e) power stations.

With an EU average of 0.5 kg CO2/kWh, the annual carbon savings would be 288 kg CO<sub>2</sub>/household/year. For the UK, France, Italy and Spain which have a similar number of households (ca 20 million), this would result in CO<sub>2</sub> savings of 5.76 M tonnes per country.

More text to follow with links to various sections of the KITH website [heat loss]      [space heating]
[refrigeration]               [space cooling]
[washing and drying]     [water heating]
[cooking]                     [electronic devices]



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