Abstract. A great part of energy produced in Europe is consumed by old residential buildings. Consequently, it is necessary to retrofit energetically non-efficient buildings. However, there is a mass financial gap between cost effective retrofitting and upgrading to nearly zero energy building levels. The efficiency of apartment building modernization under current requirements applicable in Lithuania and the requirements for 2020 was analysed, focusing on thermal insulation of external walls. Six cases of residential building modernization in Lithuania were studied estimating criteria that are among the most important for implementation of apartment building modernization, such as the total cost of the external wall modernization, simple payback period, work duration, and other parameters related to the characteristics of thermal insulation systems. The weights of the criteria were calculated after an expert survey and using integrated SWARA-TODIM multi-criteria decision-making (MCDM) method the best alternatives were ranked. After analyzing the differences between the current situation and upcoming requirements for rendered and ventilated type of façades, it can be stated that the final result depends more on price, duration of works, payback period, energy losses and water vapour diffusion than on the type of façade or insulation requirements applied at present or future.

This article raises the problem of high energy consumption stimulated by heating buildings and preparing hot water. The paper shortly revises the state of renovating public buildings in Lithuania. A number of scientists devote close attention to examining various aspects of building renovation (technical regulations on constructions, subsidies provided by the state, cost-effectiveness, factors influencing building renovation, etc.). The article presents a few studies by foreign scientists, lists factors that determine public building renovation (unsatisfactory indoor air hygiene and floor temperature, indoor relative humidity, indoor air velocity, indoor carbon dioxide concentration, physical deterioration of a large building, poor aesthetic appearance of the building, etc.) and demonstrates a few practical examples. In accordance with Lithuanian design codes, a methodology for determining heat transfer coefficients in public buildings is provided. Besides, investigations into heat transfer coefficients before and after the renovation of public buildings have been conducted. A few nursery school buildings in Lithuania have been examined applying laboratory equipment before and after renovation. It was found that the wall heat transfer coefficient of properly designed and insulated buildings falls by more than 4–5 times to reach the normal value of the heat transfer coefficient (value of the heat transfer coefficient falls from 1.12 to 0.22 W/(m2·K)). A comparison of an external thermal insulation plastering composite system with an external aeration heat-insulated system has been done. The estimation has revealed that due to lower costs, better results of thermal resistance obtained using the external thermal insulation plastering composite system can produce better wall heat transfer coefficient values. The obtained results have been determined referring to better wall insulation tightness. The paper also summarizes data on heating buildings and consumption of prepared hot water before and after renovation. On the basis of the findings acquired employing the degree-day–method, public building energy consumption for heating and hot water preparation decreased from 41.30 to 43.73%. Santrauka Straipsnyje trumpai apžvelgta pastatų energinio efektyvumo problematika, visuomeninių pastatų atnaujinimo situacija Lietuvoje, pateikiami keli užsienio valstybių mokslininkų darbų, kuriuose nagrinėjama pastatų atnaujinimo tematika, pavyzdžiai. Be praktinių pavyzdžių, nurodomi veiksniai, lemiantys visuomeninės paskirties pastatų atnaujinimą. Taip pat pateikiami visuomeninės paskirties pastatų sienų šilumos perdavimo koeficientų tyrimų, atliktų naudojant laboratorinę įrangą, rezultatai, ištyrus kelis visuomeninės paskirties pastatus Lietuvoje prieš ir po pastatų atnaujinimo. Palyginta išorinė tinkuojama sudėtinė termoizoliacinė sistema su išorine vėdinamąja termoizoliacine sistema, apibendrinta nagrinėjamų pastatų sąnaudų šildyti ir karštam vandeniui ruošti ekonominė nauda prieš ir po pastatų atnaujinimo taikant dienolaipsnių metodiką.

Santrauka. Senti pástate atnaujinimas butinas norint efektyviai vartoti silumos energij^ Siam tikslui pasickti reikia pagerinti tokiii pastatii isoriniii atitvarn termoizoliacines charakteristikas. Atnaujinant senus pastatus, vienas is svarbiausiti uzdaviniiinustatyti, koki efekt^ pastatu energiniam efektyvumui suteiks taikomos atnaujinimo priemonés. Metodikos, skirtos isodniii pastato atitvani atnaujinimo poveikio energiniam efektyvumui nustat)^i, pateikiamos galiojanciuose statybos techniniuose reglamentuose. Taciau susiduriama su problema lyginant teorinius pastatii energijos sutaupymo atvejus su faktiniais, nes gaunami dideli skirtumai tarp jn. Straipsnyje pateikiama astuoniq atnaujintii namii Vilniuje ir Siauliuose faktinio energijos suvartojimo patalpoms §ildyti prie § ir po atnaujinimo analizé, gauti rezultatai palyginami su teoriniais skaiciavimais. Palyginamas tiriamii pastatii atnaujinimo atsipirkimo laikotarpis, apskaiciuotas pagal teodnius ir faktinius duomenis. Sukuriamas pastato modelis ir, ivertinant paklaid^tarp teodniii ir faktiniti energijos sutaupjmio atvejii, apskaiciuojamas jo atnaujinimo atsipirkimo laikotarpis bei pateikiamos isvados.© Vilniaus Gedimino technikos universitetas