Energy Myths or Simple Truths?

A number of common assumptions about saving energy are myths, while others are largely true. The following examples are based on a similar list from the National Energy Foundation.
 

1. It uses less energy if you leave fluorescent or low-energy lights switched on

MYTH – If you are out of a room even for 5 minutes it always saves energy to switch fluorescent or low-energy lights off. Very frequent switching can shorten the lifetime of some low-energy bulbs, but recent models have greatly reduced this problem.
 

2. It is wisest to leave your immersion heater on 24 hours a day

Sometimes TRUE, sometimes a MYTH – Provided your hot water tank is properly insulated, and no water is being used, the tank should only cool by about one degree every few hours. This makes very little difference to the rate of energy loss through the insulation, so the extra cost of maintaining hot water continuously for use whenever required is negligible. If your tank is poorly insulated (with thin foam or a tank jacket), then switching the heater off when no hot water is likely to be used, for example overnight, will save energy. Note that reducing the temperature setting of the thermostat controlling the immersion heater always saves significant energy.
 

3. If you have thermostatic radiator valves you don't need a room thermostat

MYTH – Thermostatic radiator valves will only switch the flow to a single radiator on or off. They do not stop the boiler from firing and so using energy. Energy is saved if the boiler runs only when it is needed for heating or for hot water. This requires a room thermostat. However, the room thermostat should not be in a room which also has thermostatic radiator valves because the room may never get hot enough to switch off the boiler.
 

4. In summer it's cheaper to use an immersion heater than a boiler to heat water

Usually a MYTH – Gas costs much less than electricity providing the same energy, so a boiler would have to be very much less efficient than an immersion heater before electricity is cheaper. If you have a modern gas boiler controlled by a hot-water tank thermostat, then it will be better to use the boiler all year. With oil boilers the benefits are less but are still likely to be significant.
 

5. Leaving your PC screen switched on during a break prolongs its life and doesn't waste much energy

Mainly a MYTH – The screen usually consumes a large fraction of the energy used by a computer.
Whilst in operation, cathode-ray tubes typically use between 30 and 200 watts. Screens do not use less energy when they are in screen-saver mode (that's just designed to stop the phosphor coating being damaged). Many personal computers go into sleep mode after about 20 minutes if they are not being used (the time delay can be varied), but even in sleep mode they still use some energy. The end of life of a cathode-ray tube is nearly always caused by obsolescence not failure.
LCD ('flat') screens typically require less energy, but unless they are recent types with LED backlights their brightness gradually fades with age the longer they are left on. Therefore it is better if they are turned off or asleep when not in use.
 

6. Use less power – take a shower!

Sometimes TRUE, sometimes a MYTH – If your shower uses the same source of hot water as your bath, and you use less hot water when taking a shower, you will use less energy. However, if your shower is heated electrically and your bath water is heated by a cheaper fuel, the shower must use considerably less water than the bath before there is any saving. If the shower is over the bath and you put the plug in, you can find out whether your shower actually uses less water than the bath you might have taken.
 

7. Strapping on a gizmo to your boiler can save you at least 10% from your heating bills

MYTH – High-pressure salesmen claim amazing improvements in boiler efficiency if a simple device is placed around the gas pipe. Such a major improvement would be very easy to prove in objective controlled tests from an independent laboratory, however the salesmen will not be able to provide such data. Instead the salesman will cite 'satisfied customers'.
A device which increased the calorific value of a fuel by 10% would be hailed as a major advance and would be installed worldwide. Think of the money this would save a power company. This cannot be claimed, so the sales pitch is that the device improves the efficiency of the domestic boiler.
Generating a 20% improvement in a condensing boiler which is already 90% efficient would clearly be impossible. Much of the lower efficiency of older boilers is for reasons such as the discharge of steam in the flue, and the need to heat the mass of the boiler, which cannot be affected by any supposed change to the way the fuel burns. How likely is it that a reasonably maintained boiler is not burning 10% of the fuel it is using? If it was operating so badly, how likely is it that the problem can be cured by any minor change to the fuel?
 

8. Big freezers cost more to run than little freezers

Usually TRUE, but not always – Small freezers are often upright models, which lose a significant amount of cold air whenever the door is opened. It can take as much as 30 minutes for a freezer to regain its temperature after a door has been opened for a minute. Chest freezers, with a lid opening – and typically thicker insulation – will often use less than half as much energy for a given volume of food storage. So a 125 litre upright freezer will often use more energy than a 250 litre chest model. If you have empty space in either type of freezer it's best to fill it, for example with empty cardboard boxes, to stop air flow when the door opens.

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Green Electricity Tariffs

Most of us are now familiar with changing our electricity supplier and many would like to sign up to a 'green' tariff (where the electricity comes from a renewable source, such as hydropower or wind turbines), but what exactly are these and are they worthwhile?

There are two types of tariffs that you can sign up for:

• Green supply – where the electricity company ensures that for every unit of electricity you use, a set proportion of green electricity is generated. However, as supply companies have a Renewables Obligation set by the government to supply a minimum level of renewable electricity (currently about 10% and gradually rising) some companies use the renewable electricity they sell as a 'green' tariff towards meeting their own Renewables Obligation or, through certificate trading, to allow other suppliers to meet theirs. The net effect of this is that although you are getting more renewable electricity, everyone on standard tariffs is getting less.
• Green fund – where the electricity company invests some of what you pay on your bill in new renewable energy projects. However, many supply companies have already made a decision to invest in renewables, to ensure they can meet their Renewables Obligation or for other commercial reasons, so signing up for their 'green' tariff might not have any real effect, except perhaps to boost their profits.

A good source of information if you wish to switch to a green tariff is Green Electricity Marketplace.

Given this confusion, if you are really concerned about making a difference we suggest that action in your own home is the best option, including anything from improved insulation or installing low-energy lighting through to installation of solar photovoltaic (PV) panels that generate electricity or heat pumps for central heating. Every action counts. Options for renewable energy generation are discussed on our domestic generation page, and grants and other financial support (such as the Feed-in Tariff and Green Deal) are described on our domestic grants page.

Reducing the Supply Voltage

The power supply in Blewbury should be a fairly steady 240 volts, but is often around 250 volts and has been even higher at times. Electrical equipment sold in the UK must be designed to work with voltages between 216 volts and 253 volts (i.e. 230 volts +10% and –6%). If the voltage could be reduced to say a steady 223 volts, with many devices this would reduce the energy used by nearly 14% compared with 240 volts and even more if it is higher. Some electrical equipment benefits from this, while other items do not:

• Heating applications will have 14% less power, thus fan heaters, clothes dryers, ovens and hot plates will take longer to be effective.
• Lighting applications will get less power. Incandescent lights (which are being phased out) will be dimmer but will last longer. Fluorescent lights, including low-energy bulbs and LEDs, will be less affected.
• Other devices such as computers, televisions, motors and freezers are likely to operate satisfactorily while taking less power.

The benefits can be a reduction in energy bills as well as a reduction in carbon emissions.

The main disadvantages are the cost of the equipment needed, the cost of installing it, and the load taken by the voltage reduction equipment when on no load. If the standby consumption is too high this would cancel out the benefits.

Apollo Enviro offers both domestic and commercial devices to optimise voltage; their website has much useful information.

The VPhase product is designed for domestic use, and is expected to be fitted only on those electrical circuits where a lower voltage provides savings. Fitting will require the services of an electrician, and possibly an extra fusebox. The suppliers claim it consumes only about 6 watts in standby and can reduce total electricity consumption by about 15%. The Initiative has not tested this device.

Energy saving transformers can be appropriate in industrial and commercial environments

The idea is clearly relevant to industrial and commercial sites. Here the load is more continuous and may be fairly constant over 24 hours so the transformer losses at low loading are very likely to be small compared with the benefits. Also, transformers applying to a three-phase supply can achieve power smoothing and other benefits.

For example it can be economic to reduce the voltage on the cooling cabinets in supermarkets. The Power Perfector is designed for such environments.

A related idea suitable for industrial and commercial applications is exemplified by the Fluoresave device. This is specific to fluorescent light installations. It maintains full mains voltage when there is no load, but reduces the voltage to the lights after they have been switched on. It increases the voltage again for a time if the load changes. The physics of this device arises as fluorescent lights require a large voltage to strike the light, but then need much less voltage to maintain the plasma.

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