Civil Engineering Reference
In-Depth Information
a great many risks and waste problems, while the renewable natural resources
are safe but difficult to harness. During recent years the threat of the increased
'greenhouse effect' has received a lot of attention. This problem relates directly to
energy, which in turn is mainly produced by the fossil fuels. This theme is dis-
cussed more thoroughly in the following chapter.
The building industry is the giant amongst energy consumers. Use of ener-
gy is divided between the production, distribution and use of building mate-
rials.
Stages of energy consumption in building materials
The manufacture, maintenance and renewal of the materials in a standard tim-
ber-framed dwelling for three people over a period of 50 years requires a total
energy supply of about 2000 MJ/m
2
(Fossdal, 1995). A house in lightweight con-
crete block construction needs over 3000 MJ/m
2
. For larger buildings in steel or
concrete the energy required is around 2500 MJ/m
2
. The amount of energy that
actually goes into the production of the building materials is between 6 per cent
and 20 per cent of the total energy consumption during these 50 years of use,
depending on the building method, climate, etc.
Energy consumption during the manufacture of building materials
The primary energy consumption (PEC) is the energy needed to manufacture the
building product. An important factor in calculating PEC is the product's com-
bustion value. This is based on the amount of energy the raw material would
have produced if burnt as a fuel. The combustion value is usually included in the
PEC when the raw material would have had a high value as an energy resource.
If this combustion value is removed or heavily reduced in the product one gets a
false picture of the energy equation.
PEC is usually about 80 per cent of the total energy input in a material and is
divided up in the following way:
•
The direct energy consumption in extraction of raw materials and the production
processes
. This can vary according to the different types of machinery for the
manufacturing process.
•
Secondary consumption in the manufacturing process
. This refers to energy con-
sumption that is part of the machinery, heating and lighting in the factory and
the maintenance of the working environment.
•
Energy in transport of the necessary raw and processed materials
. The method of
transport also plays an important role in the use of energy. The following
table shows energy consumption per ton of material transported in Norway
in 1990:
