Energy

Up

At the Kyoto Conference in December 1997, developed countries agreed to cut their emissions of greenhouse gases by an average of 5.2% in the period 2008 to 2012. The target for the European Union is an 8% reduction, shared out amongst Member States. The UK is likely to achieve more than the average as domestically the Government has a manifesto commitment to "aim to reduce" CO2 emissions to 20% below 1990 levels by 2010.

In buildings the government aims to achieve this mainly by improving energy efficiency. Energy use in buildings accounts for between 40% and 50% of the UK's emissions of carbon dioxide, with housing contributing about half of this. Government figures estimate that 20-30% could be saved through the widespread application of energy efficiency measures which are cost-effective. This will be achieved primarily through the Energy Saving Trust, an independent government funded body working in partnership with industry. The EST has several schemes in operation at present to help homeowners save money and energy by using simple techniques such as insulation, draught stripping etc. Their web-site includes an excellent interactive house which can be used to estimate savings.

The EST is forced to use financial savings as its main attraction, since it deals mainly direct with the public. Cost savings are very useful in helping to justify installation of more efficient energy systems but the main aim of sustainable construction in this area must be to minimise the harmful environmental effects of energy consumption. In brief, these are:

global warming
acid rain
resource depletion
habitat destruction by fuel extraction
environmental damage from processing and transportation
photochemical smog

A reduction in energy consumption leads directly and proportionately to a reduction in these harmful environmental impacts.

The now famous new Report to the Club of Rome, Factor Four (ISBN 1-85383-407-6), sets out in simple detail how it is possible, with existing technology, to reduce energy consumption by 75% or more. In the context of the environmental damage caused by energy consumption in the developed world, it seems incredible that we have not already embraced this approach. There is no need to build further power stations, no need for dirty technologies like coal and nuclear power at all. It is only the combination of a lack of awareness and a flawed economic system that allows this abosurd situation to continue.

Every one of us is paying at least four times as much as we should to heat our homes, travel to work and do all the other energy-intensive things we like to do. And of course, these costs are passed on to us in everything we buy which also has to be processed and transported. As Jonathon Porritt writes in his review, "This book should make you spit with rage – at the mainstream engineers, scientists, economists and politicians who will stand between us and a genuinely sustainable future for all the Earth’s people. As Factor Four so cogently demonstrates, most of the technological solutions to our problems are there for the taking right now. If only…"

A sustainable construction project aims to minimise environmental impacts throughout its design life. In energy terms, this means reducing the amount of energy that the development requires to operate and the amount of embodied energy required to manufacture the materials and transport them to the site. It may also mean using alternative forms of energy generation. After all, the most profligate building in the world can still be sustainable if it uses only benign, renewable energy sources. This leads on to a discussion of the relative impacts of various forms of energy generation. Once again, if there is a wealth of science to consider, there is a king’s ransom in self-interested opinion. The green lobby usually considers nuclear power to be the worst option, although if you live in an area denuded by acid rain, it is possible to argue that dirty coal combustion is a worse culprit.

Scottish Power, in their 1997-98 Environment Report, set out the following hierarchy of generation technologies, with the most sustainable first:

Energy Saving
Energy Efficiency
Renewable Energy
Waste to Energy
Gas-fuelled CHP
Gas-fuelled CCGT
Conventional Gas
Cleaner Coal Plant
Old Coal Plant
Nuclear

There are also a handful of emerging technologies, such as nuclear fusion and fuel cell CHP, which have considerable potential as sustainable energy resource but which are not quite commercially viable yet.

In the context of sustainable construction, the choice of energy source is usually more restricted. With de-regulation of domestic energy supply in particular, it is illegal to force the occupants of a building to use environmentally friendly energy, as they have the right to switch between utility suppliers with a minimum delay of two weeks. This means that it is difficult to get around the sustainability implications of energy supply simply by buying a green tariff and fitting cheap electric heating. If you then sell the building, the new owner may simply change to a cheaper, dirtier supplier.

For domestic and commercial applications, the following are usually the available options (again, set out as a sustainable hierarchy).

Energy Saving
Energy Efficiency
Renewable Energy (independent supply)
Gas-fuelled CHP
Oil-fuelled CHP
Condensing gas heating and energy-efficient lighting / appliances
Conventional gas heating and energy-efficient lighting / appliances
Oil-fired heating and energy-efficient lighting / appliances
The previous three systems with conventional lighting and appliances
Conventional electricity

It may be possible to specify more exotic systems, such as geothermal, heat pumps etc. but these tend to be used only in specialised, one-off situations. Photovoltaic cells are not recommended: at present their cost, generating capacity and longevity make them a huge waste of money, which would be far better spent on increasing insulation or upgrading window specifications.

For refurbishment projects, the cost/benefit approach is particularly useful for reducing the environmental impacts of energy use. The following figures give an indication of the relative benefits of a range of energy saving measures (these examples are for a 3-bedroom, 90m2 house):

Item Lifetime of Item Cost of Item

Cost per tonne cut in CO2 over lifetime of item*

e

g

c

Loft insulation 30 yrs 500

23

41

53

Cavity Wall Insulation 30 yrs 1000

17

30

39

Draught Stripping 10 yrs 250

60

109

130

Low Energy Lamps (60W to 10W) 8000 hrs 3.50

15

Efficient Central Heating Motor Drive (5% better on 10kW motor) (300 hrs /yr) 200

10

Photo-Voltaic Panel (2 kw, 1500Kwhrs per year) 20 yrs 10,000

625

"Green" electricity tariff (e.g. SWEB Green Electron @ 0.5p/kWhr extra, based on 0.54kg CO2 per kWhr)    

9

Small Wind Turbine (100kW, 40% utilisation) 20 yrs 70,000

20

Larger Wind Turbine (5MW, 45% utilisation) 20 yrs 4.5M

10

* the three figures given are for electric, conventional gas and condensing boiler systems respectively. Figures courtesy of Hoare Lea and Partners, M&E Engineers

This table demonstrates that pound-for-pound (or Euro-for-Euro), some measures are considerably more effective than others. The higher cost of reducing a tonne of CO2 from an installation that is already relatively efficient demonstrates the law of diminishing returns operating in energy efficiency as elsewhere. It is possible to design a near zero-impact house but this may not fulfil all the requirements of the "sustainable" project brief, including financial considerations.

Specification of efficient energy systems should be balanced against the overall demands of the development to achieve the maximum environmental benefit. It is also worth building in flexibility where possible. After all, conventional electrical heating is currently one of the most environmentally damaging energy sources but a minor change in the law to allow the specification of renewable electricity would send it almost to the top of the hierarchy. Should this happen, a sustainable development without electrical facilities would be at a significant disadvantage. Similarly, fuel prices are likely to change within the lifetime of any development, whether for market reasons or through increased taxation. Wherever possible, these considerations should be considered in the design of sustainable energy systems.

More information is available from energy@sustainableconstruction.co.uk