The global trend of organic materials application for the construction low rise residential accommodation in the context of the sustainable development concept results in growing interest towards the usage of both known natural materials and their combinations as well as the search of new technological decisions. The trend of eco-buildings is starting to play an important role. The concept of eco-buildings means construction of low-energy buildings [1] that cause less harm to the environment due to minimised value of primary energy consumption and low rate of heat losses, cost of materials, etc. As Brojan, L. et al [2] states, one of the criteria, which can be applied for the assessment of environment damage, is an index of primary energy consumption, or primary energy input (PEI) index, MJ/m 2. In fact, this is the volume of necessary energy resources for the production and maintenance of a 1 m 2 surface of enclosing structures [2].

The determinants of profitability and environmental friendliness of bioconversion are noted in the paper. As one of the major factors the reduction of thermal energy costs for the fermentation of organic wastes in their utilization is proposed to take into consideration. The expediency of using renewable energy sources for thermal stabilization of the fermentation process, especially in the thermophilic mode of organic fermentation, is emphasized. The energy efficiency biogas installation with structural and technological scheme is given as an example. It receives thermal energy to increase its efficiency from a solar collector and a heat pump. It is proposed to evaluate the energy efficiency of a biogas plant taking into account the cost of bioconversion products and the costs of providing this process. A mathematical model was proposed to substantiate the environmental-economic efficiency of a biogas installation with the minimum energy costs for the thermal stabilization of the biomass fermentation process. The model is based on fuzzy set theory which uses linguistic variables. Linguistic variables take into account the influence of quantitative and qualitative factors on the objective function.

The expediency of using heat-insulating construction products from a straw at the erecting of energy-efficient envelope constructions is considered in the paper. The hierarchical model in the form of an inference tree of the factors influencing the target function -reliability of energy efficiency of heat-insulating building products made of straw has resulted. A fuzzy matrix of knowledge is proposed which reflects the influence of thermophysical, physic-mechanical and durability parameters on the target function. The hierarchical connections between classified factors proceeded by apparatus of fuzzy logic and linguistic variables. A system of fuzzy logical equations which describes linguistic expressions of input variables according to the corresponding terms is proposed. In the research the expressions which describe the objective function -reliability of energy efficiency of heat-insulating construction products made of straw were obtained. It was made with the of membership functions following linguistic variables, by taking into account both qualitative as well as quantitative factors of influence. Represented in the paper model can be used as the design and engineering tool for the prediction of thermal performance of any multilayered wall assembly at the design stage of the project to assess complex energy efficiency parameters, which could be applied in practice during the decision-making process.

The problem of the “best” choice in terms of the ecological, durable, cheap and energy-effective material of envelope construction has been considered in the paper. For the numerical assessment of the thermal performance, the MCDA techniques as Analytical Hierarchy Process (AHP) and Criteria Importance Theory (CIT) were used. There were proposed eight types of wall assemblies from a natural material, namely: Hempcrete, Adobe, Strawbale panel, Earthbag, Cordwood, SIP (plywood+ecofiber), Hempcrete+straw and Compositional building thermo-block. As a objective function for the search of the best alternative the integral index was proposed which consist of thermo-physical and economic criteria. As the thermo-physical criteria component of the index were taken the u-value of the envelope W/m2K, the dimensionless decrement factor of the envelope f and the internal areal heat capacity of the envelope k1, kJ/m2K according to ISO 13786:2017. As economic criteria of the integral index, the authors proposed the cost of the wall material Q, UAH/m2 and the mass of the wall m, kg/m2. The analysis of the conducted research has shown, that from the one hand there is no absolute “leader” in the ranking of the wall assemblies according to the proposed criteria and MCDA technique, but from the other hand by comparison of the results, there were revealed that the top three alternatives in both AHP and CIT technique are walls of “B”, “D” and “E” type with different point order, achieved in each MCDA calculation technique.

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