Energy is not an end in itself; instead it is a means to provide a number of services. Businesses and households view energy as an input, an expense of doing business or maintaining a home. They are less concerned with how many kilowatt hours they purchase than with the services such as heat, light and appliances which electricity provides. This relationship provides the basis of demand-side management (DSM).

DSM is defined as “The planning and implementation of strategies designed to encourage consumers to improve energy efficiency, reduce energy costs, change the time of usage or promote the use of a different energy source”, It is a partnership between the utility and customer with benefits to both [25].

DSM tries to reduce the peak load and change the shape of the load profile through the techniques of peak clipping, load shifting and energy conservation. Correctly implemented, it can reduce energy consumption with the associated financial and environmental benefits.

Some strategies such as energy efficiency measures, education in energy use and technical advances in control can help with DSM. Of these strategies, energy efficiency is often the easiest to carry out.

The idea behind energy efficiency is quite simple; if people consume less energy, there will be less emission of greenhouse gases as the result of the burning of fossil fuels in power stations. Energy efficiency technologies and practices can therefore play a significant role in reducing the threat of global climate change.

Energy efficiency

Energy efficiency is defined largely as cost-effective ways to reduce energy consumption through existing and improved technologies as well as through sound energy use practices. The idea behind energy efficiency is quite simple - if people consume less energy, there will be less emission of greenhouse gases as the result of the burning of fossil fuels in power stations. Energy efficiency technologies and practices can therefore play a significant role in reducing the threat of global climate change [16].

Lighting

In most homes, lighting accounts for around 10-15% of an electricity bill. In offices, the lighting may account for 25% of the electricity bill. As a result, lighting as a visible sign of energy use, is being increasingly targeted by energy efficiency measures. Over the past few years in the lighting industry, there have been advances in the development of energy efficient bulbs making them smaller and more convenient to use as direct replacements for older less efficient types. With these technological developments, lighting efficiency has improved and with it has come a reduction in energy consumption and costs.

There are a number of steps that can be taken to increase lighting efficiency. The most cost effective improvements are outlined below.

Ballasts

Fluorescent lamps produce illumination by passing a low intensity electric current through an inert gas, such as Argon or a mixture of Argon and Krypton. The ballast is a device mounted inside a fluorescent fixture which develops the proper voltage needed to start the flow of electricity through the gas. Once the lamp has been turned on, it then regulates the voltage in order to stabilize the output from the light. In the past, the conventional ballast was an electromagnetic design which was cheap and reliable but had several disadvantages. These included noise, light flicker and energy losses due to the induction of the coil and the development of eddy currents within the iron core. The energy losses were then dissipated as heat.

Within the last ten years or so, lamp manufacturers have developed a ballast of electronic design which is rapidly replacing the older, electromagnetic types in most buildings. These electronic ballasts operate at much higher frequencies. The advantage of controlling a much higher frequency current is that less electricity is needed to produce the same level of illumination. In addition the high frequency operation eliminates the problems of noise and light flicker which have been long associated with this type of lighting. The electronic start is also kinder to the lamp which results in an increased lifespan [17].

It is important to take advantage of all of the light that that has been generated by the lamp. Often if high-efficiency specular reflectors are retro fitted to light fittings, there can be a reduction in the number of lamps that are used.

Localised switching

There should be enough switches to give flexible control in the switching of lights in an array. This increased flexibility should encourage individual lamps to be turned off if they are not required.

Automatic control systems

With some control systems being integrated into the lighting circuits, further levels of efficiency can be achieved. These lighting controls save money by controlling the time that the systems are in operation, turning them off when they are not needed. When hours-of-use decrease, a decrease in utility bills follows. The installation of one, or a combination of these systems will reduce the hours of use of the system.

Timer circuits

Time controls are best suited for applications where there are predictable schedules that do not change often. They will be programmed to turn off lights during periods when the rooms have no occupants such as lunch times or at the end of the working day. Usually timer systems have a manual override switch should they be needed outside these hours. Users frequently bypass controls, usually as a result of their frustration from changes to working schedules.

Occupancy sensors

A better solution for intermittently occupied spaces is occupancy sensors that turn lights on when people are present and automatically turn lights off when the spaces are vacated. There are three technologies used for occupancy sensors, passive infrared (PIR), ultrasonic, and sound. PIR sensors react to body heat; they sense occupancy using line-of-sight sensing.

Ultrasonic sensors use volumetric detectors that transmit waves above the range of human hearing, then measure the time for the waves to return. Ultrasonic units can detect persons behind obstructions, but are sensitive to air movement. There are dual-technology models for use where no single type will do the job. Dual technology sensors can usually avoid difficult situations that can lead to lights being turned off when they are still required.

However occupancy sensors are often blamed for reducing lamp life. The recommended ballasts for switching applications are rapid-start or program-start ballasts. A reduction in lamp life can be avoided and will usually be caused by a poor ballast choice and delay setting. When instant-start ballasts are used, lamp life can be reduced, especially with short delay settings [18].

Photoelectric sensors

Photoelectric sensors detect the amount of daylight in the room to either switch lamps on or off or adjust the lamp brightness depending on whether the daylight contribution is adequate. These are more expensive to install although compared to on-off controls, dimming controls generally increase energy savings, better align lighting with human needs, and extend lamp life. Dimming controls are also useful for spaces that have more lighting than is currently needed and have the added benefit of dimming lights further when natural light from outside is available. Such systems can also be used to dim lights for other reasons, such as for presentations. Dimming fixtures by as much as 50% may be barely noticeable to building occupants, unless they are involved in tasks requiring visual acuity.

There are two methods of dimming a group of fixtures. One method, known as power reducing, uses either a transformer to reduce the voltage going to the ballasts or uses electronic controls to alter the waveform of the electricity but not necessarily the voltage. Both types achieve dimmed lighting and energy savings. The electronic control type is lighter and more compact, but may reduce the building's power quality as well as lamp and ballast performance. Voltage reducing is rapidly losing popularity because of new ballast technologies, but may be applicable in some circumstances.

Dimming systems can provide great benefits in work areas identified with specific occupants, such as offices or classrooms, while on/off switching systems will be more appropriate for common spaces, such as hallways, warehouses and reception areas [19].

Lighting placement

One approach for reducing energy involves designing a space to be lit with both task and ambient lighting. The ambient lighting provides overall illumination and is kept at a modest level, while brighter task lighting is provided in the local work areas. This approach uses less energy than only overall illumination and at the same time provides lighting variation in the work place, which can be visually attractive.

Another standard method of lighting design is the PSALI (Permanent Supplementary Artificial Lighting in Interiors) developed as early as 1959 by Hopkinson and Longmore. This provides a more balanced lighting system in an industrial space. Before this approach, most installations were designed with luminaires evenly spaced across the ceiling. PSALI places more luminaires on the interior zone (away from windows) and less luminaires in the outer zone (near windows) [3].

For refrigeration and laundry appliances the Energy Efficiency Recommended logo reinforces an existing energy labelling scheme which is the European Union Energy Label . The energy labels show estimated energy consumption and give an energy grading from A to G. An A-rated appliance will use about half the electricity of a G–rated appliance. New A+ and A++ energy labels were introduced for cooling appliances during 2004.

Refrigerators and Freezers

The energy efficiency of refrigerators and freezers has improved dramatically over the past three decades. The refrigerator is the single biggest power consumer in many households with a typical refrigerator using between 600 and 900 kilowatt hours per year, although an efficient one will use somewhat less. Refrigerators and freezers typically make up over 20% of total domestic electricity consumptio [24].

The amount of electricity consumed will depend upon how the appliance is used and where it is located. For example, a half-full fridge or freezer uses more energy than a full one and it will also use more energy if it is placed next to a heater or oven [25].

Washing machines

The standard test, which allows energy ratings to be awarded for washing machines, specifies a warm wash. This mode of operation is used because the majority of the energy used during the cycle is for heating the water. As an indicator for energy efficiency, a model that has low water consumption will save energy and water.

The two main types of clothes washers are drum type machines (front loading) and agitator or impeller machines (top loading). Each has its own advantages and disadvantages, but the drum machines are usually more energy and water efficient. They manage this because their clothes drums turn on a horizontal axis and they rely on gravity for the tumbling, so no agitator is required. They also tumble the clothes through a pool of water, rather than completely immersing them in a large vertical drum as in an impeller machine. As a result of this, less water and less detergent are needed. Both types of machines use warm or cold water during the washing part of the cycle, although some efficiencies can be made as cold water is sufficient for the rinsing part of the cycle [26].

Dishwashers

A relatively common assumption is that washing dishes by hand saves hot water. However, washing dishes by hand several times a day could be more expensive than operating some dishwashers. If properly used, an efficient dishwasher can consume less energy than washing dishes by hand, particularly if the dishwasher is only operated with full loads [27].

As with washing machines, the majority of energy required to run a dishwasher is used to heat the water. However most modern dishwashers come equipped with a good range of programs, including economy options, will allow you match the dishwasher's performance to your needs and helping you save energy and water [28].

Tumble dryer

The use of tumble dryers varies widely, with some households using them as little as once per month while others use them to dry every load that they wash. The two main types of tumble dryers are controlled by a timer or by humidity sensors. The timer controlled dryer will operate for a preset duration, with the risk of over drying the load and wasting energy in the process. The dryer with the humidity sensor is obviously more efficient because it will finish the cycle when the load is dry, avoiding using excess electricity and causing unnecessary expense.

If you are a moderate to heavy user of a tumble dryer, it may be worth considering installing a gas fired dryer. Although these types of dryers are more expensive to buy and install, they are cheaper to operate, dry clothes faster and have lower greenhouse gas emissions due to the change in fuel type. Another option is a heat pump dryer which increases its efficiency by working in a slightly different way to conventional dryers. Conventional dryers heat air, pass it over the laundry and then exhaust the hot air and moisture to the atmosphere. Heat pump dryers dehumidify the hot air after it is passed over the laundry and then recirculate the hot air back into the drum.

In general conventional domestic tumble driers are not very efficient with most dryers having an energy efficient rating of C.

In general the installation will pay for itself after approximately 3 to 7 years and the amount of heat lost from your home through the walls will fall from approximately 35% to 10% [7].

It is more difficult for solid walls to be insulated, although it is possible to do so by fixing insulation boards to the outside or inside of the walls.

To insulate the inside of a wall, one method is to use an insulating board consisting of plasterboard bonded to a layer of insulation and this is simply attached to the wall making sure that it is sealed against draughts. Another method is to attach batons to the wall and when faced with plasterboard, the space formed between the wall and plasterboard is then filled with an insulating material.

To insulate the outside of a wall, a layer of mineral fibre is usually attached to the wall and a waterproof exterior cladding secured over the top of this layer.