From Energy Efficiency to Comfort as a Service: 5 Concepts Shaping the Future of Smart Buildings in Ljubljana

Author: Javier Leiva, Innovation Expert on the EffiComfort project

Image 1: Miško Kranjec Primary School, part of the EffiComfort project

Ljubljana, the capital of Slovenia, has set an ambitious goal to reduce energy consumption in public buildings by 25% by 2030. In practice, this commitment goes beyond merely advanced energy supply contracts: Ljubljana simultaneously integrates distributed renewable energy generation, such as solar photovoltaic power plants, to increase energy self-sufficiency, and even more ambitiously develops initiatives that directly address a higher level of energy efficiency in public buildings.

Through instruments such as public-private partnerships, the City of Ljubljana has carried out energy retrofits of over 100 public buildings in recent years, introducing efficient solutions, including improved thermal insulation and upgraded ventilation systems. These investments have resulted in better thermal performance of buildings, lower heating and cooling demands, a reduced environmental footprint in terms of energy-related emissions, and at the same time, a measurable reduction in overall energy costs.

In this context, the EffiComfort project represents an opportunity to take a further step in optimizing energy management in publicly managed buildings. Energy efficiency measures are elevated to a higher level, as they are explicitly linked to ensuring adequate indoor comfort, which is treated in the project as a specific service provided by a specialized provider. The project thus addresses the challenge of implementing the Comfort as a Service (CaaS) concept in various environments, including schools and residential buildings. This dual implementation allows for the inclusion of different user groups, such as school communities and apartment tenants, creating complementary and transferable insights with great potential for replicability in other municipalities in Slovenia and Europe.

The project is supported by a balanced and connected consortium that effectively covers the entire spectrum of involved aspects - from enabling technologies and data analysis to human behavior and health aspects. The City of Ljubljana leads the project and acts as the owner of the buildings where the CaaS model is being piloted. In the residential sector, the Public Housing Fund of the City of Ljubljana plays a central role, being responsible for the development of new housing, the renovation and upgrading of the existing stock, and the management of tenancy relations, thereby ensuring the practical implementation of the model in real living environments.

At the regional level, the Regional Development Agency of the Ljubljana Urban Region provides a direct link between the City of Ljubljana and 24 municipalities in the region. Based on its experience in supporting local authorities in the fields of energy, spatial planning, and sustainable development, the agency acts as a key player for the regional scalability of the project and for the systematic collection of feedback from municipalities regarding the value of the project approach.

The company Resalta, as the energy services provider in the project, brings extensive experience from Central and Eastern Europe, with a portfolio of over 400 end-users involved in the design, implementation, and management of projects in the field of renewable energy integration, heating and cooling systems, and large-scale building energy retrofit programs. Within the EffiComfort project, Resalta is responsible for establishing the technical core of the model, including the installation of sensors, ventilation systems, and digital monitoring solutions that enable data-driven comfort management and the delivery of services tied to achieving agreed-upon results.

At the same time, the National Institute of Public Health ensures that the health and well-being of users are a central dimension of the project, not merely through compliance with regulatory health standards, but also by actively addressing indoor air quality as a key factor of comfort and the long-term well-being of users.

The Institute for Innovation and Development of the University of Ljubljana enables collaboration between industry, academia, and society by integrating technical and social science knowledge. This dual approach supports the interpretation of project results from both a scientific and user-centric perspective, which is particularly important for strengthening user engagement as a key success factor and for assessing the adaptability of the CaaS model to different types of buildings and user profiles.

Closely related to this, the Institute for Spatial Policies contributes its extensive experience in stakeholder engagement and knowledge transfer. Its role is focused on establishing structured connections with the communities involved in the pilot buildings, collecting user perceptions and qualitative feedback, and integrating these insights into the design and further development of the model. This ensures that the final CaaS framework remains truly user-centric, while also being operationally robust and efficient.

Image 2: Newly built residential building, part of the EffiComfort project

The EffiComfort project thus aims to demonstrate under real operational conditions in Ljubljana how CaaS can be implemented in public and residential buildings in a way that simultaneously ensures energy efficiency and a high level of indoor comfort. To understand how the project translates this vision into practice, it is useful to present the key concepts that form the foundation of EffiComfort and manifest it as an example of a user-centric, technology-supported, and energy-optimized service model.

Energy Efficiency in Buildings

Energy efficiency in buildings does not merely mean reducing energy consumption, but also integrating advanced ventilation systems or distributed energy sources, such as rooftop solar photovoltaics. By combining targeted energy retrofit measures, buildings can significantly reduce heating and cooling demands, improve indoor environmental quality, and approach nearly zero-energy performance, even without extensive local energy production. Accessibility is of central importance: investments and technologies must be cost-effective for public authorities or tenants, so that energy efficiency measures do not lead to higher energy costs or financial barriers to use. In this context, energy retrofits, optimized insulation, and smart energy systems form the foundation of a sustainable, resilient, and affordable building stock.

Energy Performance Contracts (EPC)

Energy Performance Contracts (EPC) offer a contractual framework in which energy savings or efficiency improvements are guaranteed, allowing flexibility in both scope and financing. This allows building owners to implement energy efficiency measures with minimal upfront investments, transferring the financial risk to the service provider. In addition to reducing costs, EPCs enable the optimization of energy consumption and the adaptation of building operations to the conditions in the local electricity grid or the availability of renewable sources. Flexible management of heating, cooling, and other systems ensures both user comfort and operational efficiency while responding to dynamic conditions in the energy markets.

Energy Service Company (ESCO)

Energy Service Companies (ESCOs) play a key role in implementing EPCs and advanced energy solutions. They typically finance, design, and install energy efficiency measures, assuming the initial capital costs that would otherwise burden the building owner. At the same time, they manage the operation and maintenance of the systems, ensuring the achievement of agreed-upon performance and measurable savings during the contract period. By integrating investments, technical expertise, and operational responsibility, ESCOs enable municipalities and building managers to achieve energy efficiency goals without additional financial or operational burden.

Occupant Comfort

Occupant comfort is a multidimensional concept measured by Indoor Environmental Quality (IEQ) indicators, including thermal, visual, and acoustic comfort, as well as air quality. Key indicators of thermal comfort, such as the Predicted Mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD), allow for a standardized assessment of user satisfaction and discomfort in various spaces. Ensuring comfort is crucial not only for well-being and productivity but also for supporting energy-efficient operation: systems that maintain the target level of indoor environmental quality without over-conditioning the spaces reduce energy losses while maintaining user satisfaction.

Comfort as a Service (CaaS)

Comfort as a Service (CaaS) transforms indoor environmental quality into a managed service provided based on a Service Level Agreement (SLA). Instead of paying for energy, users pay for guaranteed levels of comfort, which are automatically monitored and maintained by the provider. The SLA defines measurable indicators, such as temperature ranges, air quality, or CO₂ limits, thereby ensuring accountability and operational transparency. By outsourcing technical management and oversight, CaaS allows building managers to focus on their core activities, while users enjoy continuous comfort, energy efficiency, and reliable operation.

Conclusion

The EffiComfort project represents a path toward user-centric building management, where occupant comfort and energy efficiency work hand in hand, in close cooperation with energy service companies. Empowering end-users is of central importance: by actively engaging in adapting behavior related to comfort, users become part of the solution rather than merely passive observers, thereby strengthening energy awareness and encouraging the smart use of building systems. Through the combination of user engagement and data-driven management, the project can achieve a significant reduction in energy consumption while simultaneously reducing the need for upfront investments. By testing in schools—both those already energy-retrofitted and those in the process of being upgraded—as well as in private residential apartments, EffiComfort will generate transferable insights and a replicable model for ensuring comfort, energy efficiency, and user-centric building management in Ljubljana and beyond.