Environmental impact and life cycle assessment of heating and air conditioning systems, a simplified case study

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Environmental impact and life cycle assessment of heating and air

conditioning systems, a simplified case study

Matjaz Prek

∗

Faculty of Mechanical Engineering, University of Ljubljana, Askerceva 6, SI-1000 Ljubljana, Slovenia

Abstract

During the design process of heating and air conditioning systems, the designer must analyse various factors in order to determine the best design options. Therefore, the environmental aspects of a product should be included in the analysis and selection of design options if an environmentally aware design is to be produced or selected. The comparison between three different heating systems was made with the Eco-indicator 95 method. The study included the environmental impact at the production phase of the system, because alternative production methods have different kinds of environmental burdens. The results showed that the three different concepts of heating systems with different construction materials varied the Eco-indicator value. For radiator heating system the Eco-indicator value is far superlative than for floor or fan coil convector heating system. Copper pipes and other copper parts contribute to the greatest environmental impact. Radiator heating Eco-indicator showed three times higher value for copper pipes than for the steel pipes despite smaller dimensions. The lowest values are obtained for floor heating systems. Reasonable values are obtained for fan coil units; analysis shows up, that heat exchanger contributes the main part of the value.

Keywords: Heating system; Life cycle analysis; Environmental impact; Impact assessment

1. Introduction

Sustainability has become a global issue by increas-ing awareness that there are limits to the availability of non-renewable resources and that there are limits to the nature’s ability to adsorb wastes. Several concepts and tools for achieving a more sustainable future have been devel-oped. The tools include environmental impact assessment (EIA), strategic environmental assessment (SEA), life cycle assessment (LCA), positional analysis (PA), cost–benefit analysis (CBA), material intensity per unit service anal-ysis (MIPS), total material requirement analanal-ysis (TMR), ecological footprint (EF), exergy analysis, emergy analysis and risk assessment. Whereas the energy is used in oper-ating a building, the energy-based tools are applied, e.g.

[1–4]. Similarly, the environmental impact of building ser-vices systems and products depends on the environmental burdens from the production processes. In addition, the environmental impact depends on the influence of these installations and systems on the environmental burdens of buildings. There can be little doubt that buildings are

impor-∗_Tel.:₊_{386-1-477-1312; fax:}₊_{386-1-25185-67.}

E-mail address: matjaz.prek@fs.uni-lj.si (M. Prek).

tant contributors to environmental deterioration. Buildings contribute 15–45% of the total environmental burden for each of the eight major LCA inventory categories. In any design, trade-offs must be made among solutions aimed to optimise building performance for various objectives. Envi-ronmental objectives are diverse, complex, interconnected, and frequently conflicting. Decision-making tools such as multiple attribute decision analysis can assist designers and their clients resolve conflicting project goals that normally are part of any project. Systematic analysis based on empir-ical data has provided the tools necessary for designers and other decision-makers to evaluate the trade-offs they must make between environment-friendly building features.

A major goal of these studies is to present the conse-quences of designers’ choices during the design phase. Selecting and designing of heating and air-conditioning sys-tems affects the costs and the environmental impacts. This study dealt with effects of selecting the heating system as a part of building services systems of a dwelling in a residen-tial building. The work was carried out by studying alter-native combinations of heating systems in model building.

In the study the LCA methodology was used. It has be-come one of the most actively considered techniques for the study and analysis of strategies to meet environmen-tal challenges. The strengths of LCAs derive from their

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roots in traditional engineering and process analysis. Also vital is the technique’s recognition that the consequences of changes in technological undertakings may extend far beyond the immediate, or local, environment. A technolog-ical process or a change in process can produce a range of consequences whose impacts can only be perceived when the entire range is taken into consideration.

2. Life cycle assessment and Eco-indicator methodology

Life cycle assessment is defined by ISO 14000 series stan-dards[5–8]and is conducted by compiling an inventory of relevant inputs and outputs of a product system by evalu-ating the potential environmental impacts associated with the inputs and outputs and by interpreting the results of the inventory analysis and impact assessment phases. The LCA covers the whole life of the product; the study be-gins from the raw material acquisition through production, use and disposal. The main phases of LCA are goal and scope definition (defining aims, product system and reach of the study), inventory (extractions and emissions caused by the product system are quantified and related to the prod-uct function), impact assessment (outcome of the inventory is analysed with respect to their environmental relevance) and interpretation (results are evaluated with regard to the goal of the study). An LCA starts with a systematic inven-tory of all emissions and the resource consumption during a product’s entire life cycle. The result of this inventory is a list of emissions, consumed resources and non-material impacts like land use. This table is termed the inventory re-sult. Since usually inventory tables are very long and hard to interpret, it is common practice to sort the impacts by the impact category and calculate a score for impact categories such as greenhouse effect, ozone layer depletion, and acid-ification. Once the category indicator results are generated, additional techniques are used to analyse the category in-dicator results (normalisation) and the valuation process to

Fig. 1. Eco-indicator weighting principle to assess environmental effect of a product life cycle.

aggregate across impact categories (valuation or weighting). How these impact categories are to be weighted is much less clear. For this reasons it is frequently the case that the result of an LCA cannot be unambiguously interpreted. To solve this problem a more complete impact assessment methodol-ogy (LCIA), followed by a weighting step, is needed. LCIA normalisation implies the normalisation of the indicator re-sult by dividing by some reference value. Commonly, this reference value is the total loading for the given category. The valuation (or weighting) phase involves a formalized ranking, weighting and possibly aggregation of the indicator results across impact categories into a final score. Weight-ing in LCA is a controversial subject due to its dependence upon value judgements. There are currently several methods available for weighting within the framework of LCA: the EPS-system, the Tellus method, economic valuation based on the impact pathway analysis approach, the ecoscarcity method, the Eco-indicator 95 and other distance to target methods.

The importance of the LCA approach, including the LCIA phase, lies in LCA’s key feature—a system-wide perspec-tive and the use of inventory functional unit to normalize the data. Weighting is an optional element to be included sep-arately to better understand the ecological consequences of results from the inventory analysis. This procedure, starting with the inventory result and then trying to interpret it, is referred to as the bottom-up approach. Another possibility is a top-down approach. The top-down approach starts by defining the required result of assessment. This involves the definition of term ‘environment’ and the way for weighting the different environmental impacts. The weighting of envi-ronmental problems is usually seen as the most controversial and difficult step in an assessment.

The Eco-indicator method[9,10]has resolved these prob-lems. The LCA method has been expanded to include a weighting method. This has enabled one single score to be calculated for the total environmental impact based on the calculated effects[11,12], as is schematically shown in

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for the Eco-indicator much attention was given to defin-ing the environmental impact. The problem lies in deter-mining the weighting factors. In this method, the so-called Distance-to-Target principle was chosen. This principle has been in use for some years in the Swiss Ecopoints weighting system[13]. The underlying premise is that there is a corre-lation between the seriousness of an effect and the distance between the current level and the target level. An important advantage of the top-down approach is the ability to sepa-rate the really important issues from the not so important issues. In order to assess the overall impacts of trade-offs, the relative importance of various environmental problems must be determined. The target level still embodies a ma-jor problem—what is a good target level and how can such a level be defined? To ensure that the target level is equiv-alent for different effects, a correlation is established with the damage caused by the effect [14]. The premise is that the target level for each effect yields uniformly serious dam-age [10]. To establish a correlation between these damage levels and the effects, a detailed study was carried out of the actual state of the environment in Europe. The current status of each effect was determined and by what degree a particular effect has to be reduced to reach the damage level defined for it. These data were used to determine the cur-rent level of an environmental problem and by what factor the problem must be reduced to reach an acceptable level. The environmental problems are defined at their endpoint level in terms of damages to human health, ecosystem qual-ity and resources. Definitions at this level are much more easier to comprehend than the rather abstract definitions of greenhouse effect and acidification.

A recently developed life cycle impact assessment (LCIA) is the Eco-indicator 99[6], the successor of the Eco-indicator 95 method[2]. Eco-indicator 99 methodology assesses the impact of emissions to human beings and ecosystems. Eco-logical impact is represented by the potentially affected fraction (PAF) or potentially disappeared fraction (PDF) of species, since the environmental impact is given as the global warming potential (GWP), ozone depletion potential (ODP), etc. The impact on human well-being is measured by dis-ability adjusted life years (DALY). This represents the years of life lost and years lived disabled due to the impact of emissions and is based on a approach described in[15,16]. For a given process, the emissions data are classified in sev-eral impact categories and characterized in common units for each category based on impact factors. The improvements have been made for damage categories themselves, inclusion of land-use as an impact or impact category, inclusion of source depletion, better modelling of damage functions and inclusion of cultural theory as a tool to manage subjectivity. This approach considers the analysis of three related spheres, namely the technosphere, ecosphere and value-sphere, following the cultural theory[17]. The technosphere is the domain of technological processes and systems devel-oped by human. The ecosphere is the domain of ecological processes and systems, and incorporates the technosphere.

The valuesphere is the domain of human valuation and in-cludes both subsystems. For the valuesphere (value choices), three perspectives were developed. According to the attitude of three human archetypes (individualists, egalitarians and hierarchists), the ranking and distribution of weighting fac-tors between human health, ecosystem health and resources were determined[18]. According to the selected valuation approach, a single indicator is obtained.

3. Case study

The purpose of the analysis is to establish priorities, or in other words—where can the designer achieve the great-est possible environmental profit? In the first instance it is possible to make fairly rough calculations and simplifica-tions are permissible. In a life cycle perspective there is an optimum, where the incremental increase of impact from environmental performance and from equipment construc-tion demands equals the incremental decrease of impacts from increasing efficiency. Comparing different products by LCA is only meaningful, if these alternative products fulfil the same function.

According to the standard ISO 14040 the functional unit is generally defined as a quantified performance of a product system. The service provided by the heating was defined as the functional unit. The service was defined to be heating the dwelling in a model building to a tem-perature level of 21◦C. The functional unit is the whole technical system, which is needed to fulfil the heating de-mand. However, instead of looking at the whole system, also functionally equivalent alternative parts of the sys-tem can be studied. Thus, the functional unit (quantitative capacity of the product system) could be the heat output, provided by the heating system. If the required amount of heat with regard to heat consumption can be produced with the help of alternative heating system, the corresponding alternative product system can be dealt with as compara-ble unit. The study included the environmental impact at the production phase, because alternative production meth-ods have different kinds of environmental burdens. The environmental impact of energy production for residen-tial heating is excluded from the analysis, since it is not the environmental impact of a heating system as is, but the environmental impact, which comes from the use of building.

The model building was a single family dwelling in a residential building. The calculated total heat demand of a dwelling equipped with the heating system was 11.8 kW. Heat demand of the dwelling and heating systems were cal-culated and dimensioned according to relevant standards. In the presented case study, the computer program (Den-drit) was used for the calculations. Also the dimensioning of heating systems was done by the standardised proce-dures, e.g. DIN 4701 for heating load, EN 422 for radia-tors, EN 1264 for floor heating. The LCA study’s

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bound-Fig. 2. Example of simplified life cycle for heating and air conditioning system. The material production and processing involves all parts of a functional unit, e.g. floor heating system.

Fig. 3. Process tree of steel radiator heating with material data and assumptions.

aries were set to the materials of the heating systems, to the use of energy during production phase and to the en-vironmental burdens caused by production. The disposal or recycling of the heating systems was not included in the examination, since different scenarios for the same sys-tem yield to different results and due to the consumer’s behaviour.

Fig. 4. Eco-indicator values for steel radiator heating; pipe length 78.4 m, material for radiator 0.947 Pt, pipe 0.412 Pt, total 1.359 Pt.

The comparison between three different heating systems was made with Eco-indicator 95 method. The indicator val-ues for the materials (and processes) are derived from the design specifications, using the values from [19]. A sim-plified life cycle of heating or/and air-conditioning systems is given inFig. 2. The material and process selection cov-ers the whole range of elements, which are necessary for

Fig. 5. Eco-indicator values for aluminium radiator heating; pipe length 78.4 m, material for radiator 1.774 Pt, pipe 2.234 Pt, total 4.0 Pt.

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specific heating system. Such a process tree provides a useful insight in further analysis, since all elements of the system are analysed with the same procedure.

3.1. Radiator heating

In the case of radiator heating system, two different systems are analysed. The main difference was the cho-sen material for piping system (steel/copper) and for radiators—heating panels (steel/aluminium). In Fig. 3 is shown the process tree for the steel radiator heating system. InFig. 4is presented the result of analysis for steel radia-tor heating with steel pipes, made by Eco-indicaradia-tor method. The results reveal the great importance of radiator (greater mass of radiator than pipes), which presents the 70% of overall impact. Total Eco-indicator is 1.359 Pt.

The results of similar analysis for heating system with aluminium radiators and copper pipes are shown inFig. 5. As it is seen inFig. 5, the copper pipes for aluminium ra-diator heating are dominant among the materials for envi-ronmental impact. Copper pipes represent 56% of overall impact for the given example, despite smaller dimensions. Total Eco-indicator is 4.0 Pt, and is much more as for the steel system.

3.2. Floor heating

Eco-indicator value for polyethylene pipes, dimension 14

× 2, is 0.089 Pt and for polybuten pipes (PB), dimension 16 ×2.2, is 0.111 Pt. Pipe length was 291 m and was the same for both systems. Difference was only in pipe mate-rial, while all other parameters were the same. While the heating demand is the same regardless the heating system, analysis results are comparable to other systems, since they

Fig. 6. Process tree of floor heating with pipe material (polybuten) data and assumptions.

are expressed in the form of Eco-indicator points. Smaller (better) eco-value for floor heating system is also the conse-quence of the fact that the extra building construction was not considered. An example of process tree of floor heating is shown inFig. 6.

3.3. Fan coil convector

For the analysis, the exposed floor fan coil convector unit was chosen with average parts. The base unit is made of 1.0 mm thick galvanized steel plate. Cold panels are insulated. The fan section is composed of a cross-flow tan-gential fan and special air discharge sections that ensures a uniform distribution of the airflow. The three-speed motor is mounted on flexible supports. Cabinet is made in five sepa-rate pieces, a front panel in 1 mm thick galvanized steel and painted with a durable baked polyester powder coating. Pipe coil is a copper tube and lanced aluminium fin construction. Process tree of fan coil (convector heating/cooling) with material data and assumptions is shown inFig. 7.

The convectors were chosen in accordance with heating power. The convectors are substitute for radiators. For piping system, one could assume the same conditions as for the radiator heating system.

The performed analysis was made for different materi-als. Since the fan coil unit consists from various parts, we could determine the Eco-value for different part. InFig. 8

is shown the Eco-indicator value for different materials and inFig. 9for different parts. From these figures the influence of different materials in different parts of unit is obvious.

In Fig. 9is presented the result of analysis for fan coil units. Heat exchanger is made of aluminium plates and cop-per pipes, which contributes the greater Eco-indicator (50%). Total Eco-indicator is 3.126 Pt.

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Fig. 7. Process tree of fan coil (convector heating/cooling) with material data and assumptions.

Fig. 8. Eco-indicator value for fan coils (convector heating/cooling), by materials; total 3.126 Pt.

Fig. 9. Eco-indicator values for fan coils (convector heating/cooling), by elements.

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4. Conclusion

The Eco-indicator 95 method has been used for the analysis and optimisation of heating and air condition-ing systems. This method enables environmentally aware design and is open working method with a platform on which both industry and science can integrate the en-vironmental aspects into the design process. The result permits the user to see how much environmental im-pact of these design alternatives will have. The designer can analyse the consequences of an idea quickly and effectively and establish clear selection criteria for an idea.

Prerequisites for a fair comparison of environmental characteristics of different heating and air conditioning systems are that the systems compared are equal and ful-fil the functional requirements, the limits of the systems are drawn up by the same principles, technical character-istics and material data of the systems and equipment are reliable, environmental profiles of energies and materials used in the comparison are comparable. The weighting factors, used by the analysis, express the relation between an impact and the amount of damage either to human health or ecosystem quality. In used methodology they based on a combination of distance to target and damage function approach. Environmental impacts from produc-tion processes of products and materials are taken into account.

This research showed that three different concepts of heating systems with different construction materials vary the Eco-indicator value. We can see that for radiator heat-ing system the Eco-indicator value is far superlative than for floor or fan coil convector heating system. Copper pipes and other copper parts contribute to the greatest en-vironmental impact. Radiator heating Eco-indicator (1.359 Pt—steel pipes and 4.0 Pt—copper pipes) showed three times higher value for copper pipes than for the steel pipes despite smaller dimensions. The lowest values are obtained for floor heating systems, but no extra building construction was considered. Reasonable values are ob-tained for fan coil units (convector heating/cooling) with Eco-indicator value 3.126 Pt. Analysis show up, that heat exchanger (copper pipes) contributes the main part of the value. Nevertheless, the environmental aspect is only one of the evaluation criteria in addition to cost, aspects of use and standards.

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