This section briefly overviews the opportunities for improved efficiency in each area.

Lighting

Lighting energy use is a product of two factors: how much power your lights use and how long they run for.

• Lighting power density: As a guideline, a state-of-the-art lighting system in an open plan office can run around 8 watts of power per square metre of floor space. Average buildings use more than twice that figure at around 18-20 W/m2, and poor buildings may use over 30 W/m2. Reducing lighting power density doesn't have to mean vast expense or doing without enough light. There are various cheap and effective methods of improving lighting efficiency. This means that lighting quality can be maintained or improved while efficiency is improved.
• Hours of use. There are plenty of people that will try to sell you gadgets for dimming or switching out lights. These are often expensive and can cause disquiet amongst staff, particularly if they don't work quite as expected. Rather than using a technological solution, try getting the staff to turn out the lights at the end of the day - because this is almost inevitably part of the problem.

Office Equipment

With office equipment the basic issue is about turning it off - or enabling it to turn itself off - when not in use. The basic measures are:

• Turn off equipment when not in use. This includes most computers, personal printers, coffee machines, kitchen hot water boilers, etc.
• Enable energy saving features. Many office equipment items have energy saving features that cause them to go into a low-energy sleep mode when not in use. These need to be enabled to work.
• Buy efficient equipment. Many whiteware items are required to have Energy Star Ratings. Always buy 4-star or better.

Air Conditioning

Air-conditioning is by far the most complex of the energy uses in your building. An essential fact to understand is that you do not need more energy to produce a "better" level of comfort in a building. Indeed, many of the most energy intensive air-conditioning systems provide very poor comfort. There are a number of broad areas into which air-conditioning energy savings fall:

• Maintenance. The majority of air-conditioning systems have maintenance problems. These cause discomfort as well as additional energy use. Getting good quality maintenance systems in place can save substantial amounts of energy.
• Controls. The most important, and least well understood, component of air-conditioning systems is the control system. Out of date, poorly maintained or incorrectly set controls can cost dearly in terms of comfort and energy.
• Boilers and Chillers. There are energy savings available at the points where the hot and cold supplies for the buildings are generated, i.e. the boilers and chillers. However, these are only part of the picture and attention must always be paid to how the hot and cold supplies are used in the building.
• System types. Some air conditioning systems are more efficient than others; however, it's difficult to change from one to another except when completely refurbishing the building.

Building Envelope

The building envelope includes the walls, windows, roof and external floors. While the building envelope plays an important role in determining the performance of your building, it is rarely something that you have much control over.

In terms of the broad areas of opportunity, you should consider the following:

• Solar gains. While you may have heard of solar passive heating for houses, the primary concern for office buildings is to keep the sun's heat out. This is because the lighting, office equipment and people in an office building generate more than enough heat to keep the building warm most of the time. You can keep heat out by using external shades, making the windows smaller, and tinting or putting a reflective film on the glass. You should aim to have enough glass to allow diffuse daylight to come in but enough shading to minimise the amount of direct sunlight entering the building. Internal blinds are a last option for reducing glare from direct sunlight but they are not very effective at reducing the energy costs of the additional cooling, as the heat has already entered the room by the time it hits the blind.
• Glass type. There are plenty of exciting high technology glass types available. However these are not necessarily economic unless considered in the context of the whole building design. Economic viability depends strongly on climatic considerations. However, double glazing is often used in buildings as a means of reducing the level of noise from outside.
• Insulation. Unlike a house, insulation does not make or break the performance of a commercial building. However, it can be an economic measure. Roofs should always be insulated. Insulation under floor slabs in colder climates will also produce major benefits in terms of occupant comfort, as well as some energy efficiency improvements.