Modern buildings need heat and electrical energy to perform their design functions. Even today, with climate change widely acknowledged as the greatest threat to human civilisation in its entire history, buildings are being designed and constructed which are, and will continue to be, totally dependent on national energy grids. These grids are still, and for a long time will continue to be, almost totally dependent on fossil fuels. Thanks to political inertia, vested interests and endemic nimbyism, it will almost certainly be several decades before large-scale wind, wave or tidal power make a majority contribution to the energy distributed through national grids.

Nuclear power - if it is to maintain or increase its current contribution - is also a long-term option, assuming uranium supplies continue to be available and the storage of radioactive waste is tolerated. Virtually all the potential sites for large-scale hydropower have already been exploited. In the meantime, therefore, Western industrialised nations are increasingly dependent on fossil fuel supplies from countries with different political agendas, conveyed through pipelines and along shipping routes difficult to protect against terrorist attack. 'Peak oil' , the point at which global oil production will begin to decline as reserves dwindle, may be just around the corner - if it has not already arrived - and dwindling supplies and rocketing demand from India and China inevitably mean soaring prices for oil-based products and the energy generated from them.

For the moment and for the immediate and medium term future, energy consumption will equate fairly accurately with carbon dioxide emissions and the greenhouse effect that at the very least is exacerbating global warming and climate change. Buildings of all sizes and types account for about one-third of the energy consumption of modern industrial nations - and up to 60% of the electricity. Of a building's total carbon footprint, up to 50% of the energy consumed during its lifetime is accounted for by the materials used in its construction - this fraction will be inversely proportional to the efficiency of the building's insulation, dropping to around 25% for a poorly insulated structure. Motivation for serious attention to minimising a building's carbon footprint can be a sincere desire to mitigate the effects of climate change - or to insulate the building as far as is practicable from the uncertainties of energy supply from national grids. Achieving total independence from national energy grids is possible - at a price. (Some projects may not have access to such grids in the first place.) Achieving total independence from fossil fuels is also possible but harder, as most buildings not connected to grids depend on fossil-fuelled standby generators. (Such standby generators should also be classified as microgeneration installations.) Significant reductions in dependence on fossil fuels are now very possible, by combining a number of complementary strategies, of which the most visible, if not always the most effective, is microgeneration.

World Renewable Energy 2005

□ Large hydro 58.23% ■ Small hydro 5.12% □ Wind power 4.58%

□ Biomass elec 3.42% □ Geothermal elec 0.72% □ Photovoltaic 0.42% ■ Other elec 0.05% ■ Biomass heat 17.08% ■ Solar heat 6.83%

□ Geothermal heat 2.17% □ Biodiesel fuel 1.21% ■ Bioethanol fuel 0.16%

Hydropower is still the biggest source of renewable energy

Generating heat and power at or close to the point of use is theoretically a more efficient use of available resources than centralised generation and the distribution of energy over long distances. Actually achieving efficiency on the micro scale is far from straightforward. A lot depends on the size and effectiveness of the energy store, without which solar and wind power in particular can never be cost effective (see Chapter 15). Retrofitted domestic scale solar water heating systems, for example, normally have only the existing hot water cylinder available as a thermal store, and consequently can never provide anything like all the domestic hot water needed throughout the year. New build homes could include larger thermal stores at ground level or in basements. However, as one moves higher up the building scale, into schools, hospitals, office blocks and the like, the numbers become more attractive. The effectiveness of thermal stores, wind turbines and biomass gasification plants, for example, increases rapidly with size. Several mature microgeneration technologies already exist, with hardware generally available, and others are moving on from the pilot plant stage. Designers now have real choice, and are able to select the technology -or combination of technologies - that will provide the most practical solution for any particular project. But before going down that route, there are two other strategies that must be deployed.

Achieving a low carbon sustainable building involves more than strapping a small wind turbine to the roof of an otherwise conventional building. This is tokenism, or

'greenwashing'. True sustainability starts with serious consideration of the materials used in the construction of the building. Some materials have much greater embedded energy than others, either because of their method of manufacture or the distance they are transported to site, or the energy needed to handle and place them. Wood, for example, usually looks superior to concrete in this respect, although determining the exact ratio is more complex than it first might appear. Recycled materials are becoming more available and more predictable in performance, and new developments, such as low energy cements and biopolymers, are offering new options. And a material such as concrete may turn out to be desirable in the longer term because of its greater thermal mass. The whole subject is complex and is not covered here, but it should be high on the agenda for any building project aspiring to a low carbon footprint.

Improved insulation is the first step (Courtesy of Passivhaus Institut)

Reducing the post-construction consumption of energy from fossil fuels starts with reducing the building's overall energy demand. Really significant reductions can be achieved by high levels of insulation, by the control of airflows in and out of the building, and by the management of solar gain. Low energy lighting coupled with light pipes to conduct natural light into dark corners, the choice of energy efficient appliances and equipment, and the installation of a sophisticated building management system, can help achieve energy demand reductions of 40% or more over conventional designs. A truly green building will also minimise its use of potable mains water, with both grey water and rainwater recycling systems.

Over recent years a number of design philosophies have emerged which all offer ways of attaining a low carbon footprint. One can be summarised as the 'light and tight' solution: developed extensively in Scandinavia, this features largely timber construction with high levels of insulation, high-performance windows, obsessive attention to sealing any potential air leakage through the building envelope and closely controlled ventilation with heat recovery from the outgoing air. In the opposite corner is the 'mass and glass' approach, which is based on a structure with high thermal mass and the intelligent use of solar gain through large windows.

Microgeneration is no longer just for remote sites, like here in the Falklands (Courtesy of Proven Energy)

Overlying both these philosophies is the difference between the low and high technology solution. Low technology design features local materials and traditional techniques, such as adobe, green oak, windcatchers, biomass boilers, recycled insulation, solar water and air heating - and a high degree of human intervention in the building's day-to-day operation. A high technology solution may achieve much the same ends by the use of phase change materials as a thermal store, a biomass gasification plant feeding a trigenera-tion installation (see Chapters 11 and 15), a solar photovoltaic (PV) roofing membrane (see Chapter 4) or a unitised regenerative fuel cell. Or it could be said that the low technology approach is based on tried and tested principles backed up by well proven technology, while the alternative means taking something of a gamble on recently developed technologies which promise much higher performance at greater initial cost.

In moderate to high latitudes, climate change means that summertime cooling in the non-residential sector is becoming as important and beginning to consume as much energy as wintertime heating. Passive, low technology space cooling techniques have been around for millennia, but are not that easy to adapt to current building design preferences. Active cooling, on the other hand, need not necessarily mean conventional vapour compression air conditioning (see Chapters 13 and 15). Part of the problem, however, is the current attitude of building occupants. Over the last 50 years, habits and expectations have changed radically in the developed world. People expect to be comfortable in relatively skimpy clothing whatever the ambient conditions outside may be. This may well be changing, but in the short- to medium-term developers and designers have to look for ways to meet these expectations that allow the carbon footprint to be significantly reduced.

That is not to say that occupant expectations will continue to rise. Public awareness of the risks of global warming is close to the point where politicians and designers alike will have to take note. Gas-guzzling 4 x 4 'Chelsea tractors' and strawberries from the other side of the world are becoming harder to justify. Doubts are being cast ever more loudly on the latest generation of energy-hungry consumer electronics, while low energy lighting and recycled paper are becoming the routine choice. There is a significant and increasing interest in alternative and renewable energy supplies, on the domestic scale at least.

Intelligent use of light pipes can slash lighting costs (Courtesy of Monodraught)

A market for truly low carbon buildings is growing amongst those who will accept some compromises on lifestyle. Commercial developers still doubt the willingness of potential tenants to pay for what is still perceived as a 'green premium' for a low carbon building, but local authorities and organisations with a green agenda are already demonstrating their appetite for the low carbon option.

Ventilation system with heat recovery

Ground heat exchanger

Light and tight - the Passivehaus approach (Courtesy of Passivhaus Institut)

This is despite the fact that some of the pioneering low carbon buildings have failed to live up to their developers' and designers' expectations. Natural ventilation, for example, can struggle to cope with cooking smells. Maintenance costs have often turned out to be much higher than expected, new technologies such as biomass gasification can run into unforeseen operational problems - and some technologies, such as small-scale wind, have simply failed to produce the energy predicted by their manufacturers. It has often been said that the most cost-effective low carbon technology for buildings is occupant behaviour modification. The argument goes that occupants should be persuaded to routinely switch off computers, printers, phone chargers and lighting when not in use. Also, by turning heating thermostats down a couple of degrees and turning cooling thermostats up a couple, there will be no need for wind turbines or PV arrays. The response, of course, is that behaviour modification is just one string to the bow - improved building design, the use of sustainable materials and microgeneration are the others.

Some clients/end users will prefer to use just one of these approaches. Others will be willing to go the whole way and do everything technically possible to achieve the lowest carbon footprint. For example, some clients will deliberately omit car parking from their projects, even when space permits, although this is more common on headquarters projects than on commercial office developments. The preferred route for most committed clients is a combination of sustainable materials, good design, and serious consideration of the microgeneration options.

Attempts to quantify the economic benefits of microgeneration by calculating payback times are often misleading, and this book will avoid the temptation. A lot of important assumptions have to be made: how prices for natural gas and electricity will change over the medium- to long-term; what support will be offered by national and local governments; how much actual energy will be available from the microgeneration technologies selected. Calculating the building's actual energy needs over a whole year on a daily basis is a major exercise, made even more unpredictable by the, as yet, unquantified effects of climate change over the next few decades. But without a reasonably accurate picture of the peaks and troughs of energy demand, it will be hard to make a sensible decision on the most appropriate microgeneration technology or combination of technologies for the project. Luckily, advanced software that can model energy flows in three dimensions, enabling a much better picture of energy needs to be obtained, is now available. Input from the developers and suppliers of particular forms of microgeneration technology should be treated with caution: there have been some spectacular examples of over-optimism, commercial naivety and scientific illiteracy in recent years.

Technologies which generate electricity - wind, hydropower, solar PV, cogeneration (combined heat and power) - will often have an output profile that is far from an exact match to the building's actual demand for electricity. There will inevitably be times, even with hydropower, the most predictable option, when there is either a surplus or deficit of power available. Storing surplus electrical energy in batteries or similar is rarely as attractive in principle as 'storing' it on a national electricity grid. In an ideal world, surplus electrical energy would be sold to the local electricity supplier when it was produced, while electrical energy would be purchased from the supplier when the on-site generation facility was unable to meet the building's demands. Net metering is the generic term used for this type of arrangement; the actual rates for sale or purchase are rarely the same, and can vary without warning as official policy changes. Sometimes only one meter is involved, which runs 'backwards' when energy is exported to the grid; sometimes two, one for incoming energy, one for outgoing.

Modern inverters and control systems ensure that any supplies offered to the grid precisely match its requirements in terms of voltage and frequency. However, the attitudes of utility suppliers and national governments to disseminated generation are both unpredictable and variable. In some countries, such as Germany, building owners are offered significant financial incentives to install particular types of microgeneration technology, principally solar PV. In others, official attitudes can be far from encouraging. Worse, these attitudes can change dramatically with time and events, so calculating the long-term economic benefits of grid connection is far from straightforward.


A commitment to a green agenda can produce very effective results (Courtesy of

The practical benefits are obvious. No technology, not even hydropower, is as reliable as national grids (at least for the moment). Back-up generators running on fossil fuels are much more rugged and reliable than they used to be, but capital costs are high, regular maintenance is essential and the installations are even more vulnerable to the vagaries of fossil fuel prices and availability than national grids - even though they will deliver much more of the fuel's chemical energy in the form of electrical power than a national grid ever can. But without a reliable back-up/top-up supply most microgeneration technologies will not be a practical option for most buildings. This is despite the fact that some ' passive' technologies using solar power for space heating and cooling can, in theory, operate without any external energy input; and others, based on biomass, for example, can be self-sufficient. It would be a brave developer who deliberately spurned the opportunity of connection to the local electricity grid.

Advancedsolar photovoltaics still need a grid connection to be effective (Courtesy of Centre for Advanced Technology)

In theory at least, a grid-connected building designed to minimise energy demands by the means outlined above, and equipped with large enough and efficient enough energy stores, could obtain its entire energy needs from microgeneration technologies, using the grid only as an emergency back-up or during maintenance periods. A tall building standing well above surrounding structures and other obstructions could, in theory again, actually become a net exporter of energy. High-level wind turbines operating in clear air are much more efficient and predictable than their small low-level cousins struggling to extract energy from a slower and more turbulent airflow. Cladding on tall buildings can become 'active', incorporating vast areas of PV panels as well as solar air and water heating collectors. A biomass fuelled cogeneration plant could also produce enough heat to supply adjoining buildings. And large, tall buildings also have the increased potential to minimise energy demands. Deep basements can accommodate large thermal stores, high atria promote natural ventilation. Going through the normally complex procedures to obtain permission to extract water from underlying aquifers for cooling purposes is more worthwhile on a large project, as are negotiations with the local electricity supplier. But in practice anything close to the overall balance between energy supply and demand is very

Action Potential Pattern For Ventilation

o" a to hard to achieve, so one of the first decisions to be made on every project is the target percentage of total energy demand that will be assigned to microgeneration technologies.

There is no morally or ethically justifiable minimum percentage, although single figure percentages will smack of greenwashing. One sensible option is to calculate how much energy would be needed to keep the building functioning at the minimum acceptable level if local or national energy grids are out of action, and to provide enough microgeneration capacity to match this. Each project's pattern of energy demand will be unique, and finding the right microgeneration solution will be a complex one-off exercise, one that may throw up some surprising results. But the exercise is usually worthwhile and should become a standard part of the project development process. Be it as a result of government initiatives or for ethical, practical or economic reasons, microgeneration is now firmly on the agenda.

Sterling Motor Solar Energy
Using a concentration mirror to focus sunlight onto a Stirling engine is still at the experimental stage (credit Schlaich Bergermann and Partner)
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