The main objective of the project is to develop efficient and cost-optimal solutions for the renovation of multi-apartment buildings, with a particular focus on the following challenges: the introduction of energy efficient heating, ventilation and air conditioning (HVAC) systems, the integration of renewable energy sources (RES) into building energy systems, as well as the use of prefabricated and quick-installed thermal insulation panels for the renovation of external building envelopes to upgrade existing buildings to nearly zero-energy building (nZEB) levels. The results of the project will provide a valuable insight into the parties involved in the construction industry, including architects, engineers and building managers.The initial stages of the project will focus on the analysis of the existing building stock, which will summarise the typical building designs and HVAC system drawings. This step will provide the basis for further analysis and development of solutions. In the next stage, modelling and analysis of various HVAC solutions will be carried out in order to identify the most efficient and cost-effective solutions that would meet the renovation requirements of multi-apartment buildings, paying particular attention to ensuring indoor air quality and thermal comfort. Continuing the project, RES solutions for on-site heat and electricity generation will be theoretically assessed and tested, as well as the possible integration of smart building systems in multi-apartment buildings will be explored to improve energy efficiency. In the final stage, recommendations will be developed for fast-mounted, prefabricated thermal insulation panels for the renovation of external building envelopes. To this end, existing solutions will be reviewed and tested in a laboratory-controlled environment through accurate measurements to assess their effectiveness and suitability for practical use. A specialized building energy performance calculation tool based on the existing HeatMod calculation tool (developed by the cooperation partner), aligned with the LV and EN standards, will be used to test the developed solutions. An extension of the open tool based on HeatMod will be created, specially adapted to the needs of multi-apartment (series) buildings, providing accurate and standard-compliant results, which will contribute to the development of high-quality renovation solutions for multi-apartment buildings. After all, the project will end with an optimised complex solution for the renovation of multi-apartment buildings to nZEB level. The project will use an interdisciplinary research approach, as it is necessary to approach the problem from different sciences in order to achieve the planned results. Which mainly engineering and technology (construction and transport engineering; material science; environmental engineering and energy) and includes natural sciences (computer sciences and informatics).The objective of the project is in accordance with the objectives declared in Cabinet Regulation No 407: ‘The objective of the measure is to support the implementation of practical orientation and cooperation studies, including interdisciplinary studies, which guide the development of the specialisation areas of Latvia’s smart specialisation (RIS3) strategy, anticipating an increase in the capacity and export capacity of Latvia’s economic innovation system in line with the RIS3 strategy.’ The project is of an industrial type (> 80%, TRL 2-4), but not related to economic activity. It aims to develop optimised solutions for the renovation of multi-apartment buildings to nZEB level, improving energy efficiency with modern HVAC systems, integrating RES and smart building systems. The project includes a part of experimental development (<20%, TRL 5-7) focused on the development of fast-mountable prefabricated thermal insulation panels for the renovation of external building envelopes.The classification of projects according to FORD (classification and breakdown by R&D fields) R&D can be classified as 2.11 - Other engineering sciences and technologies.According to NACE classification, the project corresponds to 72.19 Other research and experimental development in natural sciences and engineering.The scientific results obtained during the project will be reported at 6 international conferences and published in 4 scientific articles (WoS/SCOPUS) one of them in collaboration with the industry.The impact of the project is closely related to several objectives of the Latvian Smart Specialisation Strategy (RIS3), especially Smart Energy and Mobility, as well as Photonics and Smart Materials, Technologies and Engineering Systems. During the course of the project, it is planned to improve HVAC systems by integrating RES into the energy systems of buildings, creating a smart building system. These initiatives aimed at reducing energy consumption will thus contribute to solving climate challenges, which are important for incr