Simulation Technology of Environmental Impacts by Zero-energy Residential Buildings Based on Emergy Analysis Method

Hong Zhou，Xiao-Long Xue，Wang-Shu Yang

(1.School of Architecture and Civil Engineering，Xiamen University，Xiamen 361005，China; 2.School of Management，Harbin Institute of Technology，Harbin 150001，China)

1 Introduction

The building interacts with the external environment throughout life cycle，consuming resources and energy.There have been two challengesin engineering assessment:1)measuring the absolute value of building resources and energy consumption.2)the dynamic expression environmentimpact throughout the building’s life cycle.At present，the discussions of zero-energy building and energy saving are primarily focused on the theme of energy consumption during construction phase.Green building has been studied for nearly 30 years.Some countries have launched a flurry of evaluation criteria［1］.Judging from current practical situation，one reason why those criteria cannot be the basis for evaluating design schemes is that most of the current evaluation indexes are more qualitative in nature，so the results do not precisely reflect the energy consumption and environmental impact of a building throughout its life cycle.In addition，there is no feasible technical tool that we can implement which shows how construction projects impact the surrounding environment throughout their entire life cycle.

One practical problem is that the life cycle of architecture involves all aspects of social material production due to its inherentheterogeneity and dimensional inconsistency.Therefore，a building’s energy consumption just can be measured at some stage but not cumulatively throughout its entire life cycle.Currently，the price setting of construction product follows the monetization method determined by compensation of relative value，which presents the transaction price without taking total cumulative energy consumption into account.

Therefore，in order to calculate and perform the substance energy expenditure and environmental impact ofconstruction projects effectively，three specific problems should be solved:1)a scale，which unifies social， economic and natural environment heterogeneous systems;2)a kind of technology，which can be employed to design and simulate buildings’environmental behavior;3)the tools，which can construct and express the environmental space.

2 Theoretical Defects of Construction Products Cost Accounting

With the research and application of‘whole lifecycle theory’，the concept of life cycle cost(LCC)of construction output has become popular.In practice however，there exists some drawbacks in current building cost accounting system and method.Because of this decision-making process of constructional project is adversely affected，as the pros and cons can not be determined.1)The system of analyzing building products is not complete.In fact，the existing cost system of building product includes those from only demolition and construction but not from environment and society.2)Beyond that，the present valuation pattern of construction products is based on monetization which merely reflects the relative value of consumed resources and energy at a certain stage，and use value only(for example land-transferring fees).Calculating the resource value of construction products is on the basis of benefit regression analysis and pursues economic output. In building energy consumption analysis，power consumption is converted to standard coal equivalent.Most researchers adopt environmental management accounting to mainly quantify the environmental cost with currency，and physical unit as dual purpose，as well as text captions for measurement attribution.Moreover，social cost seems to still be a problem，which is difficult to solve［2］.All methods mentioned above indicate that the difficulties arise from the disunity of the aforementioned heterogeneous dimensions.Bakshi and Fiksel put forward an idea that developing"ecocentric"method is of great importance due to the environmental problems which belong to the interaction of multi-disciplinary and interdisciplinary fields［3］.

3 Cost and Calculation of Building Products Emergy

All energy on the earth comes from the solar［4］.Theconceptand analysisofemergy have been gradually extended to civil engineering research［5］.Emergy provides a new scaling parameter for analyzing and evaluating environmental resources， human services，information acquisition and the development of decision-making［6］.

3.1 Emergy Theory

Based on the perspective of the overall economy，emergy theory strives to build up a new value theory in which emergy acts as a unified measurement units in comprehensive consideration of ecosystem and economic system.By tracing the retrospective study，any kind of energy can be represented by one identical energy form emergy.In 1996，emergy was firstly defined by Odum as one kind of flow or stored energy means the quantity of another certain type of energy contained within the previous one，also，the amount of an efficient available energy which is applied directly or indirectly in the process of forming a product or service［4］.All different types of energy are converted from solar energy.These transformational relations are known as emergy transformity，which can convert a variety of energy to uniform emergy(such as solar emergy).Hence，emergy can effectively measure the quality discrepancy among different forms of energy.

The obvious benefit of emergy dimension comes from itspresentation ofthe relationship between artificial structure and nature and it is hailed as a bridge between ecology and economics［7］.This scale is no longer a rigid，hypothetical equivalent，such as electrical degree or standard coral neither is CO2applied to greenhouse effect measurement，but derived from solar energy，the source of all energy on planet earth.Consequently，as a way of measuring the absolute value of construction products and complementing the simulation of interaction between buildings and ambience throughout the total life cycle，emergy is definitely the best way that we know of so far.

3.2 Emergy Analysis

3.2.1 Emergy analysis method

In emergy analysis，emergy is a benchmark for conversion reference，different species of incomparable energy from ecological system，and ecological economic system.The whole nature and human social economic system are changed into emergy with the same standard to further quantitatively study on the real value of resource，environmental， economic activities and relationship among them［7］.The merits of emergy analysis method are that it is able to simulate material and energy fluxion that flow between nature environment and social-economic systems，via the unified criterion of emergy，as well as the measure contribution of the surroundings to economic development.As part of the man-made environment，single building and building groups have to meet requirements and follow ecological principles so as to ensure a harmonious coexistence［8］.For this reason，emergy and emergy analysis can be adopted as an effective quantitative method for ecological economics.Domestic and foreign research results have proved the feasibility of this approach.

3.2.2 Emergy analysis model

Emergy analysisprimarily involvesmodeling，charting energy system diagram and emergy summary diagram.Most of emergy transformity and indexes can be completed in accordance with Odum’s research outlets，specific research object and content.The general computing model(as shown in Fig.1)，which is suitable for construction work in the whole lifecycle，can be applied to emergy analysis and the calculation of the single building［5］.

Fig.1 Emergy calculation model for construction projects

3.3 Calculation of Construction Products Emergy Cost

Throughouta building’s entire life， the architecture constantly interacts with both external physical environment and the social-economic system，which are followed with substance metabolism and the cycling of energy.Emergy is capable of connecting construction and economic product， to natural environment，and consequently makes it possible to simulate the building’s dynamic interaction with environment.Interaction above is defined as emergy cost and divided into three parts:engineering cost，environment cost and social cost.Engineering cost refers to the consumed natural resources(land，wood，etc.)and energy(electricity)for the construction of architecture itself，which actually means the relative currency value of substance and power accounted within the monetized valuation system.Environmental cost stands for the price of environmental influence in the process of architecture production and can be computed by the reductions in the number of species and organisms number in a population.Social cost is related to human society，for example，relocation，and labor expenditure in engineering construction.As the following expression shows:

And，

Waste emergy represent the residual value of the waste stream that is unable to be recycled or reused due to.(PS.:because of limited space，pricing calculation of emergy cost will not be illustrated here.)

4 Dynamic Simulative Design of Environmental Effects from Buildings

4.1 Multi-Agent Technology and GIS

Interaction involves ontology of architecture and external environment and requires the simulation of time，space and behavior.GIS technology has been widely used in analysis of some factors，such as land，district，river basin and city in the fields of ecological，social，economic system［9］.Multi-agent technology (ABM，Agent-based Model)offers a pathway to complete the expression of building-environment interaction［10］.As a consequence，via integrated GIS and multi-agent technology the simulation mentioned above can be achieved.For a single building，the interaction is conducted between an individual agent and exterior circumstance.In this paper，analogue test about interaction of single building and environment is realized and the difficult points in this whole simulation are the influence path of construction’s environmental behavior and to find the responding threshold，as shown in Fig.2.

Fig.2 Technical route of how simulating environmental impact from construction engineering by integrated GIS-Repast

4.2 Judging Criterion System

4.2.1 Maximum power principle in emergy theory

In order for a system to survive and obtain the sustainable development in competition with other system，it must acquire more external energy with low emergy and at the same time reflect more stored energy with high emergy spontaneously to intensify the external environment.In this way，internal system will be mutually beneficial and co-existence with the external environment and gain energy continually to produce maximum power［11］.The systematic maximum power principle is named as self-organization.It is a criterion for systematic behavior as well.Researchers are able to observe the state of its system during the study period.

4.2.2 Environmental self-purification ability

Environmental self-purification capability is a special function for this system，and can be selfregulating and self-protection， and related to environmental carrying capacity.On the basis of Feng’s research［12］，the environmental self-purification ability of all environments in our earth are smaller than level 10，that of Shanxi province probably are level 4，which means the probability of environmental renewability is 40%.

4.3 Muilt-agent Modeling Tool and Fundamentals

There are many multi-agent modeling tools，for example， SWARM， Repast， Mason， StarLogo，NetLogo，OBEUS，AgentSheets，AnyLogic.Repast is an Open source Multi-agent modeling tools developed by David Sallach who came from Social Sciences Computing Center at the University of Chicago.Repast has the advantage of being able to introduce the data into the GIS simulation directly，so it is chosen as the simulation tool in this article.In the multi-agent model，the grid is the bridge between the simulated space and the highly structured agent.A basic repast model includes the following elements:1)a model object that is used as the model itself was the file which the model runs from;2)a space object which controls the behavior of the environment;3)an agent object.

5 Multi-agent Model Experiment Cased of SD Building

5.1 Empirical Research Objects—SD Buildings and NSD Buildings

For reflecting the differences of life cycle cost of building better，the entity experiment of zero-energy building—the entries works“Sunny Inside”of Xiamen university for 2013 China international solar decathlon and an ordinary residential building with the same building area were selected to make a comparison.The 2013 Solar decathlon，which was sponsored by the U.S.Department of Energy and hosted by the China National Energy Administration，was held in Datong，Shanxi，and featured 22 international teams.The annual sunshine time of Datong is about 2800 h，which means that the potential of light use is considerable.The red line of the project covered 72532.2 square meters(as shown in Fig.3).In order to obtain the environmental impact of life circle of zero-energy buildings［13］and non-zero-energy buildings， one sample of the comparative simulation experiment was a set of“Sunny Inside”buildings(as shown in Fig.4) where 22 entries works of SD were homogenized.The othersample wasthe same numberofordinary residential buildings(called NSD buildings)with the same number，the same land area，the same building interval and gross floor area，which were built in the most common brick-concrete structure.The emergy costofcomputing environmentofSD residential building took Datong’s environmental conditions as the emergy calculation basis.

Fig.3 Overview of the SD construction project site

Fig.4 Effect picture of the entries works of Xiamen University—Sunny Inside

5.2 Analog Technology Program

Due to the environmental impact of the project being very complex， only the impactofwaste discharged by the buildingsinto the surrounding environment was considered.Using the Multi-agent simulation based on grid data and idealclosed environmental impact， this paper implements environmental response by defining life and death of agent.Emergy cost aggregate-value of environmental impact means emergy cost aggregate-value of environmental impact by waste streams.

1)Agentbehaviordesign.There were two assumptions in the multi-agent simulation:(1)The simulation environment was idealized closed and based on grid data.In the idealized model，the system is closed.Waste stream did not flow out quickly in the short term，and it always increased.Therefore，the environment always resisted.The grid was used to simulate the space and create a highly structured relationship between the agents.The case of Predator prey［14］and NetLogo model［15］in Repast Simphony for reference to analyze the agent in the construction process system was considered.In the model，the construction micro-system was identified by the grid.There were only the waste streams of the building agent and the environmental agent.(2)The movement of waste streams was non vectorized random diffusion.Since in reality the diffusion direction of the waste stream was affected by many factors and was difficult to determine，the building agent and the environment agent were prescribed for random interaction.The waste streams agent was randomly spread to the outside world.Environment in the diffusion radius was the building engineering systems microenvironment.Waste stream would lose some energy through the system (represented by emergy cost).When meeting the environment agent，the waste agent eliminated it and occupied the land.The environment agent died when the waste stream it received was overload.In the closed system，the waste stream flowed continuously into the external environment at a certain rate until the demise of the building.

2)The self-purification ability ofDatong’s environment.Based on the side of the square venue－side length is 152.6 m，extend upwardly 3 m and extend down 0.8 m and extend horizontally 200 m to get the micro system of project and its environment.According to Ref.［7］，the solar transformity of the atmosphere in Datong was 8.8×104 sej，and the solar transformity of topsoil was 7.40×104 sej.

Therefore，

3)Model implementation.There were two kinds of agent(waste agent and environmental agent)in the sub-environment of the model.Initialize the geographic information was created a two-dimensional grid by using Object2DGrid in Repast.The waste agent was stipulated to generate a random distribution in any grid and the environment agent was stipulated to tile the entire grid.When the two agents，the environment agent would be killed when they met，but it would regenerate randomly with small probability in other place to reflect the environment’s self-purification capacity.It is to create simple agent and stipulate the random behavior of all agent.Then all the subenvironments are added to the main environment.The impact ofwaste agentto environmentagentwas measured by the number of environment agents which were killed.The environment impact(blue curve in Figs.5 and 6)is set to represent the number of killed environment agent in the display and set one tick to represent one day when outputting the image.The red line represented environmental self-purification capacity.The value of 40%meant that 40%of system emergy is regenerated in other place.

Fig.5 Cumulative curve of environmental impact emergy cost of NSD building on the 87th day

Fig.6 Cumulative curve of environmental impact emergy cost of SD building on the 87th day

6 Results and Discussion

As shown in Figs.5 and 6.

1)The environmental impact emergy cost of SD building is rising faster，and the numbers are larger than the SD building.As the environmental impact emergy costofboth NSD and SD buildingsare consistent incremental with construction time，the fact that the construction phase has a larger environmental impact has been confirmed.The cumulative maximum point of environmental impacts of the project is related the environmental self-purification capacity，the size of the waste stream and the construction schedule of the project.

2)On the 78th day，the cumulative value of environmental impact emergy cost of NSD building rose over the environmental self-purification capacity(red line)and continued rising.In contrast，SD building in the 78th days also reaches the cumulative maximum point of environmental impact emergy cost，but the value does not exceed the environmental selfpurification capacity.Therefore，in the design process，even if the building design does not meet the standard zero-energy，we should ensure that the cumulative maximum point of environmental impact emergy cost does not exceed the maximum point of self-purification capacity of the environment，otherwise it will greatly damage the environment.

3)The cumulative maximum point of environmental impact emergy cost also proves the Odum＇s energy supply system and the system＇s maximum power，which claims that there will be fast growth in the system which will then quickly weaken.From the perspective of the waste flow，the cumulative maximum point of environmental impact emergy cost is the pointin which waste flow willdamage the environment，and also is the maximum rate of building micro systems destroyed.

From Figs.7 and 8，it can be found that the curves of both NSD and SD building decline rapidly after the cumulative maximum point of environmental impact emergy cost，which is because of the limit of a closed system，and is verified via the theory of the maximum power of Odum.

Fig.7 Cumulative curve of environmental impact emergy cost of NSD building on the 120th day

4)As shown in Figs.9 and 10，after a period of decline， the environmental impact emergy cost generates fluctuations.And we can find a rule from the fluctuation，which as long as the building exists，the waste flow will continue to be produced，and will continue fluctuating.This also confirms the fluctuations of Odum ecosystems.Fluctuation is a function of stabilization，and the more complex the system is，the more stable the fluctuation is.

Fig.8 Cumulative curve of environmental impact emergy cost of SD building on the 120th day

Fig.9 Cumulative curve of environmental impact emergy cost of NSD building on the 600th day

Fig.10 Cumulative curve of environmental impact emergy cost of SD building on the 600th day

5)In Figs.11and 12，the black units are waste agents，and the green units are environment agents，and the brown area is land which fails to update because of the death of environment agent.The larger brown area is，the worse the environmental impact is. The impact of NSD building reach the maximum value on the 120th day，and SD is the 87th day.The impact on both the types of buildings stabilizes on the 600th day，and as long as the operation period has been sustained，the impact remains steady.If the waste stream in a closed system environment is far greater than the self-purification capacity，the environment will not regenerate in the simulation，even if we modify the program in parameters.xml.

Fig.11 The environmental impact of two types of bulidings on 120th days

Fig.12 The environmental impact of two types of buildings on 600th days(white units are waste agent)

7 Conclusions

Simulating the environmental impact of material energy metabolism of building throughout the life cycle of buildings has been a problem，because it requires an integration of a variety of techniques and methods to quantitatively calculate and empirically demonstrate.Based on the calculation of the building life cycle emergy costs using the emergy analysis method，this paper integrates the GIS and ABS technologyto complete an environmental impact simulation of two types ofconstruction，which is a bold attemptand a breakthroughs.Though different types of agents designed in GIS stillneed continuously expanding behavior description along with constantly development.

1)The technology route applied in this paper is feasible.The grid model applied in this paper has been widely used in various types of multi-agent simulations.To achieve the environmental impact simulation of buildings，the dimensionless of building and natural systemsmustbe unified.Afterthe quantitative calculation，the specific technical design is completed using ABS technology.The results also confirm that the model assumptions and technical design presented in this paper are feasible，scientific，and credible.

2)Some buildings program in SD contest project can supply energy，which is one of Odum＇s ideal energy models.This paper confirms Odum＇s energy supply system，the system’s maximum power and volatility model technically.However，Odum＇s theories above have not been visual reproduced in a practice project.

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