Energy Resources

On current projections, there are sufficient gas and oil resources for another 40 to 60 years. Coal reserves may last for another 150 years at current rates of use. Burning of fossil fuels is the main source of greenhouse gas emissions and the United Nations Climate Panel advises rapid reductions (IPCC, 2007). This implies a need for widespread development of renewable energy sources and/or nuclear power. Nuclear power has a great many risks as well as unresolved waste problems, whilst the renewables are safe but are seen as difficult to harness.

The building industry is a giant amongst energy consumers; its use of energy is divided between the production, operation and demolition phases of buildings, and amounts in total to no less than 40% of all energy used in society. Sustainable construction is thus one of the most important challenges we face. And the potential for improvement is huge.

1.2.1 Stages of energy consumption in building materials

Local industries create less need for transport.

The manufacture, maintenance and renewal of the materials in a conventional building over a 50-year period require energy amounting to between 2000 and 6000 MJ/m2 (Gielen, 1997; Thormark, 2007). The main reason for this very large variation lies in our choice of building materials. For example, timber structures typically require 30% lower energy than concrete ones.

Further, the part of this energy use that is directly dependent on the materials used, normally comprises between 10 and 25% of the total energy use over the whole building lifecycle (Kram, 2001). By far the largest part is therefore needed to operate the building during its lifetime. However, with today's low energy buildings, the lifetime operation takes far less energy and at the same time energy needed to produce the building is increasing. For advanced low energy buildings, this fraction can be as high as 50% of the total lifetime energy used (Nielsen, 1995; Winther, 1998; Thormark, 2007).

This implies that there is an optimum where further increases in insulation thickness and other energy-consuming product inputs into the building itself cannot be justified in terms of the added energy saving that will be achieved in the operational phase.

It is thus becoming clear that the issue of building materials is in fact as important as the issue of reducing operational energy use in buildings. This, however, is quite a new perspective and it is not yet being recognized by the majority of today's decision makers.

Local industries create less need for transport.

EMBODIED ENERGY OF BUILDING MATERIALS

The embodied energy of a product includes the energy used to manufacture it all through the process of mining or harvesting the raw materials, refining, processing, and various stages of transport, to the finished product at the factory gate. Other

Table 1.2 Energy consumption in transport

Type of transport

MJ/ton km

By air

33-36

By road, diesel

0,8-2,2

By rail, diesel

0,6-0,9

By rail, electric

0,2-0,4

By sea

0,3-0,9

inputs include, for example, the energy costs of restoring mined areas, marketing and packaging, even though they may be minor. Also included in the embodied energy isthe combustion value of the raw materialsthemselves, often called feedstock. If incinerated after subsequent demolition the energy content recovered from the product will be given as a negative value and subtracted from the total energy consumed. However, as noted above, the valuable energy content that could be recovered by combustion may be lost due to problematic non-flammable or toxic additives.

The embodied energy of materials is usually about 85 to 95% of the total energy input in the production of a building and is divided up inthefollowingway:

* The direct energy consumption in extraction of raw materials and the production processes, can vary according to the different types of machinery for the manufacturing process.

* Secondary energy consumption in the manufacturing process refers to energy consumption that is invested in the machinery, heating and lighting of the factory and the maintenance of the working environment.

* Energy in transport of the necessary raw and basic materials depending on distance, type of fuel and method oftransport.

ENERGY CONSUMPTION FOR ERECTION, MAINTENANCE AND DEMOLITION OF THE BUILDING

The remaining 5 to 15% of the total energy input consists of the construction site, transport and operational processes involved in erection, maintenance and demolition.

* Energy consumption for the transport of manufactured products from factory to site can have a large role in the total energy picture. For a time, lightweight concrete elements were exported from Norway to Korea using 3 times more energy for transport than the initial embodied energy. This illustrates the principle that heavy materials should be used locally. See also example with granite from China in Figure 2.3.

* Energy consumption on the building site, includes consumption for heating, lighting and machines. The use of human energy varies depending on construction methods but has a small impact on the overall picture. Assuming one person uses 0.36 MJ energy per hour, the erection of an average dwelling would consume 270-540 MJ.

The amount of energy used on the building site has grown considerably in recent years as a result of increased mechanization. Drying out of buildings with industrial fans - mainly in order to accelerate the building completion time - is relatively new and is responsible for a substantial part of this increase. Traditionally the main structure of the building, with the roof, was completed during the spring, so it could dry during the summer. The moisture content of the different building materials also affects the picture. For example, it takes more than twice as long to dry out a concrete wall as it does a massive timber wall.

• Energy consumption for maintenance and upgrading. Sun, frost, wind, damp and normal wear and tear lead to maintenance. At the start, materials are often chemically treated and painted. Surface treatment and repainting must then be done regularly. Then follows the replacement of decayed or defective parts. If the building is not designed adaptively for interior changes this may also lead to large added inputs (Thormark, 2007).

• Energy consumption of dismantling or removal of materials during demolition.This may amount to approximately 5% of the overall energy input, but a lot less for constructions that are designed for easy deconstruction.

1.2.2 Reduction of energy consumption in the building industry

Since energy consumption in the building industry is closely connected to the use of materials, reduced materials use is critical; see page 6. For the energy sector, the following are additionally important.

Decentralized production reduces transport and is especially appropriate with local materials. Mobile production units are also an interesting option in many cases.

Use of highly efficient sources of energy. Electricity as an energy source produced in thermal power plants from oil, coal and nuclear power utilizes only 25 to 40% of the energy available. Hydroelectricity can be over 60% - still not extremely efficient. Where possible, it is best to avoid electricity and instead use production methods based on direct heat energy or mechanical energy - rotational power being an example.

Maximum efficiency depends on the relationship between the source of energy and the manufacturing process used. This principle relates to thermodynamics and describes levels of energy quality (see Table 1.3). Where electricity is produced in thermal power plants

Table 1.3 Energy qualities from renewable sources

Energy sources

Energy qualities

Mechanical

Electricity

Heat

Above 600 °C

200-600°C

100-200°C

Below 100 °C

Sun

(x)

x

(x)

(x)

x

x

Water/wind/waves

(x)

x

x1

x1

x1

x

Biomass

(x)

(x)

x

x

x

x

Biogas/bioethanol

x

x

x

x

x

x

Geothermal

x

x

Notes: x: commercially available; (x): not commercially available; x1: via electricity.

Notes: x: commercially available; (x): not commercially available; x1: via electricity.

it should always be in a cogeneration system producing heat as well as power - but this depends on the industry being located next to other functions that have a need for heat.

The energy needed to keep a worker and her family is so small that it has little effect in the total energy calculation. Labour-intensive processes are almost without exception energy-saving processes.

Use of local sources of energy. The shorter the distance between the power station and the user, the smaller the amount of energy lost in distribution. Over larger distances these losses can be around 10-15%. Small local power stations have shown definite economic advantages over recent years.

Use of energy-efficient production technologies. It is possible to reduce energy consumption in many of today's industrial processes by using efficient heat recovery and improved production techniques. Cement burning in shaft furnaces needs 10 to 40% less energy than traditional rotational furnaces. In the steel industry one can reduce the use of energy by 50% by changing from open blast-furnaces to electric arc furnaces.

Use of low-energy products. Several studies have indicated that the embodied energy in conventional buildings can be reduced by 15 to 20% by choosing low energy products (Thormark, 2007). A comparison of beams for the new airport outside Oslo showed that the total energy consumption in the manufacturing of steel beams is two to three times higher than the manufacturing of glulam beams (Petersen, 2005).

Natural drying out of the building. There is a lot to be gained by choosing quick drying materials - brick rather than concrete, for example - and by letting the building dry out naturally during the summer season.

Use of building techniques that favour recycling. Many building materials have used a great deal of energy during manufacture. This is especially the case with metals, concrete and bricks. By re-using seven bricks one litre of oil is saved. Material recycling metals can save between 40 and 90% compared with extracting from ore. For other materials the savings achieved by material recycling are less; for example, recycling glass wool insulation saves only about 5% energy.

However, the ability to recycle fairly locally is a decisive factor -otherwise transport energy costs quickly change the picture from gains to losses. This once again is a significant argument in favour of simple materials: many advanced industrial materials have to be transported over long distances to special units for recycling. See page 27 for the reading rules for Table 1.4.

Table 1.4 Effects on resources

1

2

3a

3b

4a

4b

5

Material

Weight

Material resources

Energy resources

Water resources

[kg/m3]

Raw materials, see Table 1.1. R = renewable

Reserves, see Table 1.1. [years]

Embodied energy [MJ/kg]

Combustion value [MJ/kg]

Use of water [litres/kg]

Cast iron

From ore

7200

17-40

95

13

-

Steel

Recycled

8000

-

-

9

-

Galvanized from ore

7500

17-40-39

22

25

-

3400

Stainless from ore

7800

17-40-8-25

Appr. 25

25

-

3400

Aluminium

From ore

2700

3

141

200

-

29 000

85% recycled

2700

3

141

45

-

Copper

From ore

8930

11

31

85

-

15900

Lead

From ore

11300

19

20

22

-

1900

Concrete with Portland cement

Structure, reinforced

2400

20-1

-

1,5

-

170

Roof tiles

2200

20-1

-

2

-

Fibre reinforced slabs

1200

20-1

-

7

-

450

Terrazzo

2400

20-1

-

1,5

-

Mortar & plaster

1900

20-1

-

1

-

170

Areated concrete

Blocks and prefab units

500

20-30-16-3

141

4

-

300

Light aggregate concrete

Blocks and prefab units

750

20-9

-

5

-

190

Lime sandstone

1600

20-30

-

1

-

50

Lime mortar & plaster

1700

20-1

-

1

-

Calcium silicate sheeting

875

20-30

-

2

-

Plasterboard

900

16

-

5

-

240

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