An Introduction to Building Energy
Buildings and Energy – an introduction
This is the first in a series of guides provided for M&E Sustainability by energy expert Mike Malina.
These guides will enable you to take advantage of the developing opportunities in Sustainable and low carbon technologies, helping to keep your business profitable and saving the planet at the same time.
Buildings and Energy
1: Why do buildings need energy?
Buildings need energy to provide the services that make them useful to you - lights to work by, power for your computers, and heating and cooling to for comfort.
As a result, you should never attempt to separate energy use from energy service. Cutting back energy use by reducing energy service is unlikely to be a good idea, as the loss of service will harm the productivity of building occupants so driving up end user costs.
2: Energy use in buildings
Building energy use varies over an immense range. Think of a "typical" building and you will find examples using two or three times as much energy as similar buildings. How can this be? The answer is poor energy management.
An average office building uses around 278 kWh/m2 in total, comprising around 125 kWh/m2 for lighting and power and 153 kWh/m2 for central services such as air conditioning and lifts.
Lighting, office equipment and air conditioning together account for around 85% of total energy use, so these are the areas where the best savings can be found.
It is interesting to note that computer simulation techniques suggest that a fairly average building should be able to perform at around half this level anywhere in the UK. That means many buildings are wasting up to 50% of their energy.
3: Efficiency Opportunities – targetting our efforts
Lighting (link to M&E Sustainability Guide - Lighting) energy savings come from reducing power density - that is to say, the amount of electricity used for lights per metre squared - and reducing hours of use. Both of these can often be cut back significantly with a neutral or positive effect on service quality. Don't rush out and buy lots of fancy lighting controls - these are often the least cost-effective of all lighting measures.
Office equipment (link to M&E Sustainability Guide - Office Equipment) savings come from enabling energy saving features, turning equipment off when not in use and buying efficient appliances in the first place.
Air conditioning (link to M&E Sustainability – Air Conditioning) energy savings come from a very wide range of areas, of which maintenance, and the configuration and commissioning of controls are often the most important. Further savings are possible in terms of the efficiency of boilers (link to M&E Sustainability - Heating) and chillers (link to M&E Sustainability – Air Conditioning), but often the best savings come from reducing the waste in the way that hot and chilled water supplies are used. It's common to find one being used to cancel out the other - a very expensive and wasteful arrangement!
Building envelope (link to Building Envelope) energy savings can be a major area of activity. The main issue is reduction of solar gains through shading or special glazing types. Insulation is often very economic and can be a major source of savings in certain building types where it can be applied, if the situation affords a practical access.
3.1: Evaluating your building (link to Monitoring Metering and Targeting))
A number of free benchmarking tools exist which can be used on-line. A good example can be accessed via the Carbon Trust website, which covers a variety of different building types. http://www.carbontrust.co.uk/energy/assessyourorganisation/benchmarking.htm
It is also possible to use the following simple adjustments to estimate the effect of hours of use and equipment density on your total energy use:
Ten hours a week of additional operation above 50 hours will increase total energy consumption by approximately 7%.
One additional computer per 100 m2 above five computers per 100 m2 corresponds to an extra 9 kWh/m2 of additional energy use per annum.
4: Building Envelope
Insulate the roof
Insulating the roof will reduce the need for heating in winter and cooling in summer, and will make the building a more comfortable place to be. Radiant heat from an uninsulated roof makes the occupants feel uncomfortable, and often they will run the air conditioner at a lower temperature to counteract this problem.
The cost-effectiveness of roof insulation will depend on the roof area of your building and on the thickness and type of insulation you choose. If your building is not insulated at all, roof insulation will generally be more cost-effective than floor or wall insulation.
Insulate suspended floor
Many office buildings are built on an uninsulated, suspended slab. In cooler climates, this will probably cause occupants to suffer from cold feet. Insulating the slab will improve occupant comfort, but is generally less cost-effective than insulating the roof.
Insulate walls
Insulating the walls will also reduce the need for heating and cooling in your building. Wall insulation is not as important as roof or slab insulation for occupant comfort. The cost effectiveness on insulating the walls will depend on the external wall area, the wall-to-window ratio, and the kind of insulation you choose. Generally, wall insulation will be less cost effective than roof insulation or floor insulation.
Increase window shading
Unshaded windows can cause glare and overheating at certain times of the day. Both internal and external blinds and shutters are available as shading options. Internal shades are less effective at keeping heat out of a building than external shades. However, internal blinds give occupants some control over the light and temperature of their environment. On the east and west sides, vertical shutters may be more effective than horizontal shutters, which are most effective on the north and south.
Increase glazing insulation
When a second layer of glazing is added to a window, the air layer trapped between the two sheets of glass acts as an extra layer of insulation. This reduces solar gains and heat loss from the building. Unfortunately, retrofit glazing is expensive, and may not be cost effective as an energy conservation measure.
Increase frame insulation
Heat can be transferred into (or out of) a building through the window frame itself. Reducing the heat transfer will lead to energy savings. The rate at which heat is conducted through the frame will depend on the type of frame and the frame material. Thermally broken aluminium frames contain an insulating layer between the inside and outside layers of aluminium, and conduct less heat than standard aluminium frames. Wood is also less conductive than aluminium. Unfortunately, window replacement is expensive. However, it is important to consider the frame material when you are installing new windows or selecting new premises.
Install a reflective light shelf
This is a horizontal shelf about two-thirds of the way up the window. The shelf serves the double purpose of shading occupants close to the windows from glare, and distributing daylight to occupants seated a long way from windows. Light is reflected from the shelf, onto the ceiling and deep into the office. Installing a light shelf involves expensive modification of the building fabric, and only produces significant savings if you have automatic daylight controls for your artificial lighting.
Change the roof colour
Darker colour roofs will absorb more heat from the sun, while lighter colour roofs will reflect more light, leaving the building cooler. Keeping heat out is particularly important for office buildings, so a light coloured roof is generally better.
Change the wall colour
Light coloured external walls will reflect more sunlight than dark coloured walls, and may reduce the heat absorbed into the building. Lighter internal walls will also brighten the work areas with reflected light.