A low energy building in a life cycle—its embodied energy, energy need for operation and recycling potential

doi:10.1016/S0360-1323(01)00033-6

Building and Environment

Volume 37, Issue 4, April 2002, Pages 429-435

https://doi.org/10.1016/S0360-1323(01)00033-6 Get rights and content

Abstract

Total energy use during the life cycle of a building is a growing research field. The embodied energy makes up a considerable part of the total energy use in low energy buildings. Recycling provides the opportunity to reduce the embodied energy by using recycled materials and reusable/recyclable materials/components. This paper presents values on embodied energy, energy needed for operation and the recycling potential of the most energy efficient apartment housing in Sweden ( $45 kWh / m^{2}$ ). In a life span of 50 years, embodied energy accounted for 45% of the total energy need. The recycling potential was between 35% and 40% of the embodied energy.

Introduction

An important goal for the building sector is to produce buildings with a minimum of environmental impact. Energy use is a central issue as energy is generally one of the most important resources used in buildings over their lifetime. Low energy houses have therefore become an important research field.

There are several reasons to include the aspects of recycling in an analysis of the energy use of buildings; for example, the increasing proportion of the total energy use attributable to materials, the benefits of recycling and a decreasing service life of buildings [1].

In the last few years, there has been an increasing interest in the energy use of buildings in a lifetime perspective. The lifetime is mostly divided into production (including all processes from extraction of raw materials up to the time the material is ready to leave the factory and feedstock), erection, operation, maintenance and demolition. Numerous studies show that the operation accounts for the main part of the energy use in the general run of dwellings. The energy for production accounts for only about 10–15% in most cases [2], [3], [4], [5], [6], [7], [8].

The energy needed for operation can be considerably decreased by improved insulation of the building envelope, technical solutions, etc. These measures will increase the energy use for the production phase. Studies of low energy houses have shown that the energy for production can account for 40–60% of the total energy use [4], [6]. However, studies have shown that even if the energy for operation was very low in one building, the total energy use (energy for production, maintenance and operation) in that building over 50 years was higher than in a building which had a higher energy need for operation [9].

In a study of recycling nationally produced building waste, the potential energy saving through recycling was about 50% of the embodied energy [10]. (Embodied energy for the waste was calculated as if the waste would have been new building materials produced today.) In a study of new buildings, the recycling potential was about 50% of the embodied energy [11]. When reused materials were used in a one-family building, the embodied energy decreased about 45% [12].

The previous sections show, that the more the energy needed for operation decreases, the more important it is to pay attention to both energy for material production and to the aspects of the recycling potential. The recycling potential, earlier presented as an example [1], [13], can be briefly defined as the potential for environmental benefits from recycling building materials after refurbishment or demolition. For comparisons, there is a great need for reference values.

This paper presents values of the energy use for production and operation, as well as the recycling potential for the most energy efficient building in Sweden today.

Section snippets

Aim of the study

The aim of this study is to analyse the recycling potential of a low-energy dwelling ( $45 kWh (162 MJ)/ m^{2}$ ) in Sweden and to relate the recycling potential to the energy used for production and operation of the building. The possibilities and problems in comparing such results from different studies will also be discussed.

Studied object

The studied object is the Swedish scheme within the CEPHEUS project (cost efficient passive houses as European standard, project number BU/0127/97) in the European Thermie-programme.

The housing consists of 20 apartments in four two-storey rows (see Fig. 1). Each apartment has a net residential floor area of $120 m^{2}$ . The buildings are under construction, in the autumn of 2000, in Gothenburg, Sweden. The energy annually needed for operation (heating, hot water, household electricity and electricity

Method

The total embodied energy over the life cycle, as well as the recycling potential, was calculated and compared with the total energy needed for operation.

The processes included in the life cycle were manufacture of building materials, transport to the building site, maintenance and operation. Energy for erection and demolition was not included. The lifetime was assumed to be 50 years in order to facilitate comparison of the result with other studies. Maintenance intervals were based on the

Definitions

The forms of recycling and energy savings are based on data and techniques of today. As mentioned above, the forms of recycling do not represent the general practice of today's recycling.

Transport

The calculation of the energy for transport to the building site was simplified in the following way. It was assumed that 75% of all materials, except crushed rock, were, on an average, transported $350 km$ with a large lorry, filled to 70%, and $90 km$ with a lorry of medium size, filled to 50%. Crushed rock was assumed to be transported $75 km$ with a lorry of medium size. With these assumptions, the total energy needed for transport was calculated as $44 kWh / m^{2}$ floor area. This result agrees well with

Results

All results are presented per m² residential floor area of an average apartment, i.e. the mean value of a middle apartment and an end section in a row.

The energy need for production and operation and the recycling potential are presented in Table 2. With the assumed production of energy for operation, the embodied energy accounted for about 40% of the total energy use over 50 years.

In the scenario material recycling/combustion, the recycling potential was about 35% of the embodied energy. In

Comparisons with other studies

The result was compared with previous studies in the Scandinavian countries.

There are numerous parameters which can vary in this kind of study. Examples assumed are lifetime, climatic conditions, assumed indoor air temperature, amount of hot water use, system boundaries of included building parts and processes, data on material production, production of electricity, rates of material spill at the building site, transport distances, assumed service life of materials, interval for maintenance,

Discussion

The study was limited to the aspect of energy use. However, recycling can have other environmental benefits, like reducing the use of natural resources and the need for space for landfill. Further, recycling can also have negative environmental impacts such as noise, dust generation, vibrations, etc [19]. Consequently, in future studies of the recycling potential aspects other than energy ought to be included.

How electricity is produced and whether electricity is accounted for as end use energy

Conclusion

The embodied energy accounted for a considerable part, 40%, of the total energy use in these low energy buildings during an assumed lifetime of 50 years. About 37–42% of the embodied energy can be recovered through recycling. The recycling potential was about 15% of the total energy use during an assumed lifetime of 50 years.

From these figures it can be concluded that it is of great importance both to pay attention to the energy intensity of materials, and to include the recycling aspects in

Acknowledgements

The work is sponsored by the Swedish Council for Building Research through its multidisciplinary programme Environment and Ecocycle in Building and Management. Part of the work is sponsored by MISTRA, the Swedish Foundation for Strategic Environmental Research. Mistra supports research, mainly through broad-based inter- and multidisciplinary programmes. One of these programmes is Sustainable Buildings—An Ecocycle System in Buildings and Construction.

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A low energy building in a life cycle—its embodied energy, energy need for operation and recycling potential

Abstract

Introduction

Section snippets

Aim of the study

Studied object

Method

Definitions

Transport

Results

Comparisons with other studies

Discussion

Conclusion

Acknowledgements

Energy use during the life cycle of single-unit dwellings: examples

Building and Environment

Solar versus green: The analysis of a Norwegian row house

Solar Energy

Life-cycle energy use in office buildings

Building and Environment