Different optimization methods generate a large variety of solutions that are suitable for achieving the sets of chosen objectives. The selection of appropriate design variables and objective functions are essential elements in the optimization process. However, the existing methodologies seem to be too complicated and designers seek to use simpli-fied methods in order to evaluate the overall performance of the buildings. The advancement of information technology enables the use of Building Information Modelling and energy simulation tools for the integrated building design in an early stage. Thus, this article introduces a new evaluation method for analysis of the effective solution of the building performance and aims at determining the influence of a complex criteria (construction duration, construction cost, annual bill-based costs, annual primary energy demand, annual CO2 emissions of energy use, CO2 emissions of construction materials and works, thermal comfort) for the final decision making. The findings of the article have confirmed that the high level of the building energy efficiency is not directly proportional to the overall investments, i.e. additional invest-ments do not bring benefits from economic and environmental points of view.

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Currently, such topics as improvement of energy efficiency of buildings and energy systems, development of sustainable building concepts, and promotion of renewable energy sources are in the focus of attention. The energy efficiency targets of the European Union are based on information regarding energy consumed by buildings. The amount of energy consumed by buildings depends on the main influencing factors (namely, climate parameters, building envelope, energy systems, building operation and maintenance, activities and behaviour of occupants), which have to be considered in order to identify energy efficiency potentials and opportunities. The article aims to investigate the total amount of energy consumed by a low energy house, built in Lithuania, using a combination of energy consumption data received from a simulation and measured energy consumption data. The energy performance analysis in the low energy house revealed some factors that have the main influence on the total figures of energy consumed by the house. The identified significant factors were used to find the optimal solutions for the design of low energy buildings.

This paper presents a systematic mapping (SM) study with the aim to determine how Building Information Modeling (BIM) methodologies and technologies contribute to energy-related analyses over the course of the entire building life cycle. The method adopted in the study is based on a set of seven research questions. We used a mixed technique combining co-citation analysis and bibliographic coupling in order to analyze the publications’ datasets for the period 2010–2020. The main advantage and novelty of this study are that the joint dataset from the Scopus and Web of Science databases was used to develop the keyword map. The main findings of this study indicate that many BIM-based applications can be used to analyze the building energy performance at all stages of the building life cycle. However, the applications of BIM in conjunction with other information technologies are limited and are still in the initial stage. In the future, the main improvements should be focused on process, model, system, tool, use and information modeling. The most promising long-term solution is an open BIM framework based on open standards, which allows the integration of BIM and energy simulation tools and satisfies specific data exchange requirements.

Internal heat gains from occupants, equipment and lighting contribute a significant proportion of the heat gains in an office space. Usage of ICT in offices is growing; on the other hand, their efficiency is also improving all the time. Increasing energy efficiency in buildings have led to the situation, when new, well insulated office buildings, with high internal gains within the working hours may cover low heating energy demand. Such buildings, even in heating dominated countries, such as Lithuania, often also suffer from overheating during the winter heating season. The paper presents the analysis of energy demand of the office building for various plug loads (ICT equipment) internal gains scenarios and demonstrates its influence on buildings energy performance. Simulation results enable to conclude, that when assessing sustainability and energy bills of the building, plug loads play a very important role. Meanwhile, assessing just energy performance influence is very small. Energy performance certification results show, that plug loads may influence energy performance label just for buildings corresponding A+ and A++ labels).

Researches on efficient energy supply in new buildings are significant for implementation of energy performance targets for buildings, aiming to increase energy efficiency as well as the share of renewable energy in the total balance of consumed energy and to reduce greenhouse gas emissions to the environment. Many studies suggest integrated assessment methods that combine building energy simulation and optimization methods. However, optimal solutions for case studies are based only on quantitative criteria (energy technical, environmental and economic). Therefore, such an approach is not sufficient to achieve the optimal building energy supply system in respect of the quantitative and qualitative criteria. The presented multicriteria assessment model for an energy supply system of a low energy house allows determining the optimal combination of technologies for a building energy supply system (BESS). Six variants of building constructions and fifteen combinations of BESS for each variant were analysed. Energy efficiency, environmental impact, economic rationality, comfort and system functionality were considered key criteria for optimal decision making. The results showed that the optimal solution for low energy and passive houses in Lithuania and other cold climate countries is the building envelope that corresponds to characteristics of energy efficiency class A+ and the BESS combination, consisting of a wood boiler and electricity from the national electricity grid. Mažaenergio pastato efektyvaus aprūpinimo energija tyrimai yra svarbūs įgyvendinant pastatų energinio naudingumo tikslus, siekiant padidinti energijos vartojimo efektyvumą ir atsinaujinančiųjų išteklių energijos dalį bendrajame suvartojamos energijos balanse, taip pat sumažinti šiltnamio efektą sukeliančių dujų emisijas. Atliekant tyrimus taikomi integruoto vertinimo metodai, siejantys pastato energinį modeliavimą ir optimizavimą, nustatantys racionalius sprendinius tik pagal kiekybinius kriterijus (energinius, techninius, ekologinius ir ekonominius). Tokio požiūrio nepakanka siekiant įdiegti racionalią pastato aprūpinimo energija sistemą kiekybinių ir kokybinių kriterijų atžvilgiu. Straipsnyje pateikiamas mažaenergio pastato aprūpinimo energija daugiatikslio vertinimo modelis, kuriuo remiantis iš pasirinktų šešių pastato konstrukcijų variantų ir jiems numatytų 15 PAES technologijų derinių nustatytas racionalus PAES technologijų derinys, vertinimo kriterijais imant energinį efektyvumą, poveikį aplinkai, ekonominį racionalumą, sukuriamą komfortą ir sistemos funkcionalumą. Tyrimo rezultatai parodė, kad, Lietuvoje ir panašaus klimato šalyse įgyvendinant mažaenergiams ir pasyviems vienbučiams namams keliamus reikalavimus, racionalus sprendinys yra pastato atitvaros, atitinkančios A+ energinio naudingumo klasės reikalavimus, su PAES deriniu, kurį sudaro biologinio kuro (malkų) katilas ir iš nacionalinių elektros tinklų tiekiama elektros energija.

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