An Approach to Develop the Sustainable Warehousing Assessment Model

The aim of the art icle is to present an approach to define the set of criteria applied to create the sustainable warehousing assessment model. The criteria were ident ified on the basis of expert analysis and the literature review includin g the scient ific approach as well as standards applied for the purpose of assessing the level of sustainable bui ldin gs. It allowed to include in the proposed model the broad spect rum of factors, which affect the warehousing sustainabi lity in economic, social and environmental aspect . As a solut ion ut ilized for the purpose of sustainable warehousing assessment model creat ion the COMET method (characterist ic object method) was applied. This const itutes the basis for applying the fuzzy set theory to propose the characterist ic of each criteria used for the assessment.


Introduction
However the problem of sustainable development was firstly discussed 300 years ago by Hans Carl von Carlowit z, the term became popular in 80-t ies of the last century [1]. Firstly joined with the ecology, due to conducted research was considered taking into account its interdisciplinary character, manifesting the need for integration in key areas: econo my, society and environment [2].
Nowadays, the sustainable development is more often used in logistic due to the fact that it is the human activ ity present and influencing at various areas of our life. In the mid-2000s, the concept was highly pro moted regarding to building and modern izing warehouses and distribution centers towards environmentally-friendly solutions, reducing operating costs and creating more favorable working conditions. However the global slowdown in economic gro wth slightly weakened this trend, the idea to apply in warehouses the solution, which are increasing the level of sustainability is still the focus of interest for many co mpanies [3]. More and more popular is becoming the cert ification of warehouses on the basis of existing building standards.
This article also considered the issue of assessing the level of sustainability in the context of warehousing and presents an approach for description of criteria that are taken into account as field of measurement.

Literature review
The sustainable development is today widely discussed in various areas of business activities . On the field of logistics, there are many research considered in particu lar the sustainable supply chain management or sustainable transport system. There are also some studies focusing on the context of sustainable warehousing area to create a unit equipped by appropriate technological and organizational solutions, which allows to operate maintaining the high standards of work, reduce the negative impact on the environment and achieve the lover cost of its functioning [4]. This assumptions are compatible with the considerations of sustainable warehouse given by Żuchowski, which requires "a set of organizational and technological solutions whose aim is to efficiently execute warehouse processes, with the highest social standards met, with the lowest possible environmental impact and taking financial effectiven ess into account" [1]. However this defin ition indicates different dimensions of sustainability concerning the building design, application of advanced technology to support the warehouse processes and application of social policy to ensure higher standards of work, nowadays the problem of sustainability of warehouse is measured taking into account the existing building certificat ion standards: BREEAM (Bu ild ing Research Establishment Environmental Assessment Methodology), LEED (Leadership in Energy and Environmental Design), HQE (Haute Qualité Environnementale), DGNB (Deutsche Gesellschaft für Nachhaltiges Bauen) [5][6][7]. Th is standards require that location, design, construction, maintenance and demolit ion of the building should provide the effective utilization of energy, water and materials which in consequence contribute to provide benefits for owners, higher social standards, better financial effectiveness and more environmental friendly environment. The most often applied certificat ion systems are LEED and BREEAM. LEED [6-7] (v4 version) takes into account 9 categories with specified aspects which are the basis of the assessment: an integrative processes (e.g. the ability to use innovative approaches to design and construct the building, selection of a pro ject team), location and transportation (e.g. neighborhood location, efficient transportation options), sustainable sites (e.g. minimizat ion of pollution, naturally inclusion to ecosystem), water efficiency (e.g. reduction of water consumption, application of innovative technologies to avoid wastage of water), energy and at mosphere (e.g. use of the renewable energy sources, optimizat ion of energy consumption, applicat ion the technological solutions to reduce energy consumption), material resources (e.g. utilizat ion of recycled materials, use of certified materials), indoor environ mental quality (e.g. ventilat ion system efficiency, possibility of temperature control, CO2 mon itoring), innovation in design (aspects not included in the basic criteria), reg ional priority (entering the regional strategy). BREEAM [6-7] distinguishes the following categories: management (e.g. overall management policy, site management, procedural issues), energy (e.g. CO2 emission, light energy consumption), health and wellbeing (e.g. amount of daylight in rooms, temperature and air quality, acoustics), materials (e.g. use of materials obtained fro m legal and local sources with appropriate ecological certificates ), transport (e.g. CO2 emission, location-related factors), water (e.g. applicat ion the solutions limit ing water consumption), waste (e.g. applied waste management policy), pollution (e.g. water and air pollution impact), land use and ecology (green areas management, biodiversity of flora and fauna).
The analysis of given standards lets to notice that the considered aspects affecting the sustainability are convergent in both cases. However they are focused on the construction of buildings and do not relate to specify of warehouse and the realized processes. The criteria like water and energy consumption, air quality, applicat ion of environmental friendly materials or land develop ment are required to be the core of prepared warehouse assessment model, but the way they are measure and the given scale must refer to warehouse conditions.
As indicate [4] and [8], the concept of sustainable warehousing goes beyond the building facilities.
[4] described eight sustainable warehousing constructs within wh ich there are included elements presenting various dimensions of sustainability. It allows to propose best practice activities, that can be used as a roadmap for setting future targets and goals towards achieving higher level of sustainable development.
The above remarks were the basis to elaborate a model which assesses, fro m one side, the warehouse building facilit ies in accordance with the sustainable development needs and from the other side the way of warehouse equipment and management [9]. Such a model can be applied to compare the sustainability level between different warehouses as well as can be implemented as a tool of self-assessment of the unit aiming the improve ment of various aspects of sustainable development.

An approach for identification and application of criteria for the purpose of sustainable warehousing assessment model
The final aim o f the conducted research is to propose a model, that allows to measure the level of sustainable warehousing. To create such a model it is necessary to indicate the dimensionality of the problem and for this purpose identify the set of criteria which will be the basis for the assessment. An attempt to construct a model has been taken and is presented in [9].
An applied method of model creat ion is COM ET (the Characteristic Objects Method). The COM ET method is a mult i-criteria decision-making method (M CDM ), which is an alternative approach for AHP, TOPSIS, ELECTRE or PROM ETHEE methods and allows to eliminate the phenomenon of rank reversal [10]. In accordance with the COM ET method 5 steps are required to be carried out [11]:  defining the space of the problem by determin ing the dimensionality of the problem (set of criteria) and a set of fuzzy numbers for each of the criteria,  generating characteristic objects on the basis of Cartesian product,  determining the Matrix of Expert Judgment to rank and evaluation of the characteristic objects,  conversion of each characteristic object and preference value into a fuzzy rule.  inferencing in a fuzzy model and final ranking.
Applying the COM ET method lets to create the series of indiv idual models as a result of partial aggregation and finally the group model, which allows to inference on the given problem.
The first step of the method requires to determine the set of criteria and appropriate set of fu zzy nu mbers for each criteria. The set of fu zzy nu mbers is presented in natural language. Each fu zzy nu mber is determined by a membership function. The membership function describes the membership of the elements x of the base set X in the fuzzy set A.
The functions assigns to elements of X the values fro m the interval [0,1]. In this case the membership function is a curve that defines how each point in the input space is mapped to a membership value (or degree of membership) between 0 and 1 [12]. It cause that fuzzy sets allow elements to belong to a given set with a certain degree. It is the ro le of expert to define the fuzzy nu mbers and appropriate membership functions. In case of sustainable warehousing assessment model this step is crucial for further analysis, because it creates the background for generating the characteristic objects and their ran king and evaluation. The experience and knowledge of experts engage in model creat ion, and in particular in description of the As show [12][13][14], there are many types of membership functions e.g. triangular, t rapezoidal, Gaussian, generalized bell, π-shaped and s-shaped membership function. However, the description of criteria applied to create the sustainable warehousing assessment model is based on the trapezoidal and triangular functions. In general, the use of a more co mplex function does not give increased precision, so triangular and trapezoidal where: , Application the fuzzy sets and identification the criteria using the linguistic data lets to define the space of considerations of each criteria and simultaneously reduce the dimensionality of further analysis. However, this step require the precisely description of applied measure for each criteria and a given scale as well as such assignment the linguistic values to this scale, that it will properly represent the range of applicable linguistic values.
The other issue is to guarantee the appropriate spectrum of criteria, wh ich will allow inference about the level of sustainable warehousing. Fro m the sustainable development point of view this criteria should include environmental, social and economic dimensions of sustainability. Considering it in case of warehousing, it is required to choose the element regard ing to the build ing design as it is posted in standards as well as technical issues and social policy aspects, which influence on the way the warehouse processes are organized and th e resources applied and consumed.

Results
Elaborating the model assessing the level of sustainable warehousing was made with the following steps:  analysis the sustainability in the context of warehouse organization and realization of warehouse processes,  selecting the set of factors (criteria) influencing the sustainable warehousing based on literature review and expert analysis and considering their impact on economic, environ mental and social aspects of sustainable development,  indicating the measurement scale for each criteria,  indicating the linguistic scale for each criteria,  applying the criteria for the purpose of sustainable warehousing assessment model in accordance with COMET method. The literature rev iew and expert analysis let to identify 22 criteria, wh ich should be taken into account for the purpose of model creation [9]. The spectrum of criteria is presented in Table 1.  The criteria refer to both the technologies and materials used for designing and building the warehouse as well as applied equip ment (advancements and application), procedures and standards to promote environmental friendly behaviors and better organizat ion of processes and work conditions.
In accordance with characteristic object method the scale and set of fuzzy numbers was defined. On the figure  1 and figure 2 are presented two examp les of the fuzzyfication of two criteria : 1. emp loyees' training regarding to recycling and sustainable development, 2. the level of building insulation. The presented examples concern different issues of sustainability. The first one lets to assess the element of build ing design and construction and the second one refers to increasing the awareness of people wo rking in warehouse and can be perceived as a part of human policy applied in the organization.
A scale was indicated for each criteria and expressed in natural language using a set of fuzzy numbers. There were three fuzzy nu mbers in each presented criteria. The membership functions (trapezoidal and triangular) were given in accordance with expert opin ion based on his/her knowledge and experience.  However the membership function, which determine the fuzzy set is subjective, it makes the foundation for further research. It is possible to verify and change the set of fuzzy numbers used for each criteria as well as the distribution of the membership functions. The changes in this step might be the source of improvement of the sustainable warehousing assessment model.
The method requires, to give the final grade of sustainable warehousing, the creation of successive aggregates built on the basis of selected criteria. The role of the expert is to judge the created object by determin ing the Matrix of Expert Judg ment. In sustainable warehousing assessment model there were established 19 objects. The frag ment of prepared aggregation is presented on figure 3.
The object A8, named environmental awareness, was built using the criteria emp loyees' training regarding to recycling and sustainable development (presented on figure 2) and emp loyees' train ing regarding to material handling equipment. The final ran king allows to determine the level of sustainable warehousing using the 5-elemnts scale expressed in natural language: very low level of sustainability, low level of sustainability, med iu m level of sustainability, high level of sustainability, very high level of sustainability.

Conclusions and Future Research
The growing importance of sustainable development issues causes that in the literature there are many studies which has on aim offering the solutions helping to achieve balance between environ mental, social and economic dimensions.
The article presents the original approach to apply the COM ET method for the purpose of sustainable warehousing assessment model elaboration. It is indicated, how to utilize the fuzzy set theory to describe the criteria, that are the basis of the assessment and the Matrix of Expert Judgement to reduce the mult ifurthy of conclusions. The achieved results show that COM ET method lets to provide the final model, however, because is based on the expert description of the space of the problem, it is necessary to verify the adopted assumptions of criteria description. The proposed model can be an important step towards finding the measure tool of sustainable warehousing, and the selected criteria may be utilized as indicators showing the directions of improve ments implementation to achieve the higher grade of sustainability. The next step of the research is focused to check the comp lexity of the criteria and the established scales.