Technologies that use renewable energy sources (RES) are crucial to achieving decarbonization goals, but a significant number of studies show their relatively high environmental impact during the production phase. Therefore, technologies need to be compared in terms of their life-cycle environmental impact. The life cycle analysis (LCA) methodology is well known and widely employed. However, problems related to the methodological choices prevent taking full advantage of the LCA, as the results of numerous studies are often incomparable. The presented review aims to critically compare the impact of different energy generation technologies—RES (as well as non-RES) energy generators and co-generators. The numeric results are structured and analyzed in terms of the global warming potential (GWP) and non-RES primary energy consumption. The results show that RES technologies are superior compared to conventional fossil-fuel-based systems in most cases, and the high impact during the production and installation phases is compensated in the operational phase. The high variations in GWP from similar technologies result from different methodological choices, but they also show that the wrong choice of the technology in a certain location might cause serious environmental drawbacks when the impact of the RES technology exceeds the impact of fossil fuel-based technologies. Cogeneration technologies using waste as a fuel may even have a negative GWP impact, thus showing even higher potential for decarbonization than RES technologies.

The main users of district heating (DH) systems are multi-apartment buildings – 53% of these buildings in Lithuania are supplied with heat from DH systems. Heating systems in buildings are the largest final consumer of energy, accounting for almost half of total energy consumption in many European countries. One of the measures planned for the Lithuanian energy policy in the heat sector of renewable energy sources (RES) until 2030 is the installation of heat pumps (HP) in the DH networks. The purpose of the study is to evaluate the technological possibilities of integrating HP into existing buildings to evaluate the low temperature heat supply. To evaluate the potential temperature lowering of the building heating system, a graph of the lowest possible building heating system temperatures is set, according to which the heat pump for the heating substation is selected, which would raise the temperature of the heat carrier supplied from DH networks to the required temperature for the heating and hot water systems of the building. Applying thermodynamic analysis, a mathematical model is developed that evaluates the ability of the HP to raise the temperature of the supplied heat carrier at the heat substation and determines the energy efficiency of such a solution. During the simulation, two alternatives of constant (regardless of outdoor air temperature) heat carrier temperatures supplied from DH networks were considered: 60 °C (alternative A) and 55 °C (alternative B). To adapt the most appropriate option for the integration of HP, it would be appropriate to combine both alternatives, i. y. to supply 60 °C from the DH network in the cold period of the year and 55 °C in the warm period of the year. Article in Lithuanian. Šilumos siurblių taikymo centralizuotai aprūpinant daugiabučius pastatus šiluma technologinių galimybių tyrimas Santrauka Pagrindiniai centralizuoto šilumos tiekimo (CŠT) sistemų vartotojai yra daugiabučiai pastatai – 53 procentai šių pastatų Lietuvoje aprūpinama šiluma iš CŠT sistemų. Pastatų šildymo sistemos yra didžiausias galutinis energijos vartotojas, kuris sudaro beveik pusę viso energijos suvartojimo daugelyje Europos šalių. Viena iš planuojamų Lietuvos energetinės politikos priemonių atsinaujinančių energijos išteklių (AEI) šilumos sektoriuje iki 2030 m. yra šilumos siurblių (ŠS) diegimas CŠT tinkluose. Tyrimo tikslas yra įvertinti technologines galimybes esamuose pastatuose integruoti ŠS, siekiant taikyti žemos temperatūros šilumos tiekimą. Siekiant įvertinti pastato šildymo sistemos temperatūrų žeminimo potencialą, nustatomas žemiausių galimų pastato šildymo sistemos temperatūrų grafikas, pagal kurį pastato šilumos punktui parenkamas ŠS, kuris pažemintą iš CŠT sistemų tiekiamą šilumnešio temperatūrą pakeltų iki reikiamos pastato šildymo ir karšto vandens sistemoms temperatūros. Taikant termodinaminę analizę sukurtas matematinis modelis, įvertinantis ŠS galimybes pakelti tiekiamo šilumnešio temperatūrą šilumos punkte ir nustatantis tokio sprendimo energinį efektyvumą. Modeliavimo metu nagrinėtos dvi tiekiamo iš CŠT tinklų pastovių (nepriklausomai nuo lauko oro temperatūros) šilumnešio temperatūrų alternatyvos – 60 °C (alternatyva A) ir 55 °C (alternatyva B). Siekiant pritaikyti tinkamiausią ŠS integravimo variantą, būtų tikslinga derinti abi alternatyvas, t. y. šaltuoju metų laikotarpiu iš CŠT tinklo tiekti 60 °C, o šiltuoju metų laikotarpiu – 55 °C šilumnešį. Reikšminiai žodžiai: centralizuotas šilumos tiekimas, daugiabutis namas, šilumos siurblys, žemos temperatūros šilumos tiekimas, šilumos nuostoliai tinkle.

The installation of heat pumps in district heating (DH) systems is one of the most promising technologies to increase the efficiency of heat supply by using renewable energy sources and reducing heat carrier temperatures in the networks. The possibilities of installing heat pumps in DH systems are very wide, but most often the main purpose of their application is to increase the temperature of the supplied heat carrier at the heat substations of individual consumers or their groups. This paper describes a study that analyzed the possibilities of integrating an individual heat pump at a heat substation in a building to reduce the temperature of the heat carrier in the return line. The results of the study revealed the dependences of the reduction of the heat demand of the building from the DH network, the power of the heat pump, the coefficient of performance (COP), and the reduction of the return temperature.

Any renovation of apartment buildings by replacing or keeping their heating devices usually means that high temperatures of the heat carrier are maintained, which restricts boosting the efficiency of a central heating supply system. This also limits the scope for a switch to more efficient systems such as low-temperature district heating systems. To assess the impact of reducing the heat carrier temperature on indoor heating with a constant radiator area, the article investigates several alternatives alongside a base case scenario. In one scenario, the modernization of a building is examined, either by retaining the current heating devices or by substituting them with devices of equal size. Another scenario explores the modernization of a building by exchanging the heating devices and adjusting the building’s heating system to accommodate ultra-low temperatures. The possibility to reduce the temperature of the heat carrier in the heating system without any renovation of the building has been addressed as well. This led to seven alternatives. The analysis of the hourly data of the heating system model for two typical months in a heating season has revealed that when the building retains its existing area of heating devices post-renovation, the temperature can be brought down to 60/40/20 °C. It was also discovered that lowering the heat transfer temperature to ultra-low parameters (45/25/20 °C) cannot be achieved by refurbishing the buildings without increasing the number of radiators, as the heating devices will fail to deliver adequate heat for space heating.

When modernizing apartment buildings, heating appliances are replaced or old ones are left, high thermal temperatures are usually maintained, thus limiting the increase in the DH system’s efficiency. In the article, in order to evaluate the impact of the reduced thermal temperature of the building on space heating when the radiator area remains constant, 3 alternatives have been analyzed. They include cases when after the building modernization old heating appliances are left, but the temperature of the heat carrier is reduced up to 60/40/20 °C in one case or even up to 45/25/20 in another alternative. There has also been examined the possibility of reducing the heat carrier temperature of the heating system without modernization of the building. An hourly data analysis of the heating system model for two typical months of the heating season has been performed. The analysis shows that after the modernization of the building, when heating device areas are left the same, the existing heating temperature can be reduced to 60/40/2020 °C.

VGTU - Vilniaus Gedimino Technikos Universitetas, Mokomojoje knygoje supažindinama su energijos vartojimo auditų atlikimo pastatuose modeliais šalyje ir užsienyje, apžvelgti kai kurie energijos vartojimo audito modeliai, atskleistos jų ypatybės, pateikti šių modelių taikymo Lietuvoje siūlymai. Remiantis apžvelgtais modeliais suformuoti du rekomenduojamieji modeliai (apžvalginis ir išsamusis), atskleidžiamas jų...