The results of analysis presented in the paper are related to the certification of energy performance in buildings using calculation methods, when the real energy consumption of the building is not analyzed. Energy consumption for cooling is not examined. Heat transmission losses could be less than the sum of the heat gains of a building if building thermal insulation is sufficient. Currently, the whole amount of heat gains is included into calculation without the evaluation of time parameters. No limit conditions are specified in order to define surplus heat flows and the amount of heat flows so that energy performance of building is calculated. Thus, difference between heat gains and heat flows of a building could be negative. In the paper the basic formation schemes of heat gain access and accumulation are presented due to the presence of people and the bright period of the day. The most adverse circumstances are analyzed for the composition of the proposed schemes. The composition of estimating heat gains is the same for all categories of buildings. Calculation equations have been composed for the estimation of heat gains according to the basic formation schemes. The average monthly parameters of the heating season are used for calculation. The analysis of calculation has been done for the different categories of buildings in order to compare the results of building energy consumption when limit conditions for heat gains are estimated and vice versa. The analysis of different calculation methods of energy consumption has showed that limit conditions for heat gains are important to evaluate the calculation methodology of energy performance for building certification needs. It is important that the calculation methodology of energy performance for building certification would be universal for all EU member states. The presented limit conditions of the heat gains of a building could be used for improving calculation methods of energy consumption in the building certification process. Santrauka Straipsnyje pateiktu tyrimu rezultatai susieti su tais atvejais, kai pastatu energinis naudingumas ivertinamas skaičiavimo būdu, neatsižvelgiant i realius pastato energijos suvartojimo rodiklius. Energijos sanaudos pastato vesinimui neivertintos. Jei pastatas gerai apšiltintas, jo šilumos nuostoliai gali būti mažesni už suminius pritekančios šilumos kiekius. Dabartiniu metu skaičiuojant pastato energijos sanaudas ivertinami visi pritekančios šilumos kiekiai, išsiskiriantys pastate ar i ji patenkantys iš išores. Kol kas neaptarti laikiniai pritekančios šilumos i pastata parametrai, neaptartos ribines salygos, pagal kurias turi būti nustatyti pertekline pritekanti šiluma ir pritekančios šilumos kiekiai, kuriuos būtina vertinti skaičiuojant pastato energijos sanaudas. Todel skirtumas tarp pastato šilumos nuostoliu ir pritekančios šilumos kiekiu gali būti minusinis, t. y. pastatas pradeda gaminti energija. Darbe pateiktos autoriu sudarytos principines pritekančios šilumos kiekiu i pastata schemos per para, priklausomai nuo žmoniu buvimo pastate ta para, ir šviesaus paros laikotarpio trukmes. Sudarant šias schemas, pasirinktas pats nepalankiausias pritekančios šilumos atvejis, bendras visu naudojimo paskirčiu pastatams. Pagal šias schemas sudarytos formules, apibūdinančios ribines šilumos pritekejimo salygas, ir pagal jas buvo atlikti ivairios paskirties pastatu kontroliniai energijos sanaudu skaičiavimai pagal šildymo sezono vidutinius menesio rodiklius. Šiu skaičiavimu rezultatai rodo, kad šilumos pritekejimo i pastata ribiniu salygu ivertinimas daro didele itaka pastato energijos sanaudu skaičiavimu rezultatams. Svarbu, kad pastatu energinio naudingumo sertifikavimo skaičiavimo metodikos būtu paremtos tais pačiais pastatu energijos suvartojimo vertinimo principais. Straipsnyje autoriu pateiktos šilumos pritekejimo ribines salygos galetu būti panaudotos tikslinant skaičiavimo metodikos principus pastatu energiniam naudingumui ivertinti.

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Correct evaluation of solar heat gains through fenestration into the rooms has a great impact on energy demand calculations for buildings. This article presents an hourly energy demand calculation method for heating and cooling, which considers the fact that the solar radiation flow passed through the transparent fenestration into the rooms is not adequate to the thermal energy flow. This method considers that the thermal energy flow in the rooms transformed from solar thermal radiation depends on the short-wave thermal radiation absorption coefficient of internal surfaces of the rooms. The value of short-wave thermal radiation absorption coefficient forms a considerable impact on the flow of thermal energy gains in the room. The presented method differs from others on that score that it considers additionally physical lows, according to which the solar short-wave thermal radiation energy admitted into the room is converted into the thermal energy. This hourly method enables precise calculating the hourly mean of indoor temperature and energy demand for heating and cooling of the buildings during the day.

Energy saving has become one of the foremost priorities in the European Union and a great deal of attention is directed towards the sector of sustainable building. However, the EU members that have an extensive Soviet heritage now face a great difficulty in reducing energy consumption. Since many apartment buildings are in especially poor thermal condition, and the heat supply infrastructure is morally and physically outdated, energy consumption for heating is significant. The modernization (renovation) of such old buildings is impeded not only by legal and technical factors, but also financial and social aspects in regard to the residents. Thus, this paper provides new model of investments and modernization of apartment buildings on the basis of the calculation of energy input per one degree-day of the heated floor area. The presented degree-days calculation method enables the calculation and inter-comparison of data gathered in all European Union member states without taking into account specific climate parameters of each.