Can Deep Renovation Turn Your Old Building Into a Net Energy Generator?

By Antonia Egli and Radhika Deorukhkar (Dublin City University) and edited by Evangelos Bellos, Petros Iliadis, Christos Papalexis, Renos Rotas, Ioannis Mamounakis, Vasileios Sougkakis, Nikos Nikolopoulos, and Elias Kosmatopoulos

Imagine an older apartment block, the kind built in the 1970s, notorious for being cold in winter and sweltering in summer, leading to massive energy bills. This is the reality for much of Europe’s existing building stock, which accounts for approximately 40% of worldwide energy consumption. To meet ambitious climate goals, we must transform these energy guzzlers into productive assets. 

RINNO’s research “Holistic renovation of a multi-family building in Greece based on dynamic simulation analysis” explores exactly this challenge through a comprehensive deep renovation study. It provides a practical blueprint for turning old, inefficient buildings into self-sufficient ‘Positive Energy Buildings’.

What Did This Holistic Deep Renovation Study Investigate?

This study investigated the potential for a holistic deep renovation of a typical multi-family building in Moschato, Athens, Greece. The eight-apartment, four-floor building was constructed in the 1970s and chosen as a case study due to its age and highly inefficient building envelope. The core research question was simple: Can this energy-intensive block be transformed into an energy provider that gives back to the grid?

To find out, the team used a dynamic simulation tool called INTEMA.building to model detailed passive and active interventions. This tool makes possible the detailed simulation of both passive and active systems in the building environment. Furthermore, it includes the control of the energy systems and can provide accurate enough results, encompassing detailed numerical models for the systems investigated, accounting for an adjustable time step of the dynamic analysis. 

Passive measures focused on the structure and included installing thick external building insulation and replacing old frames with triple-glazed windows. Active systems involved installing efficient heat pump systems, mechanical ventilation with heat recovery, and incorporating solar energy technologies. The project was then assessed based on energy savings, as well as financial and environmental benefits through a life cycle analysis (LCA).

What Were the Key Performance Insights from the Simulation?

The comprehensive simulation revealed astonishing performance improvements across all key areas, confirming the viability of the Positive Energy Building model.

• Near-Elimination of Heating Needs: The research calculated a massive 93% reduction in heating loads, dropping the total demand from 90,890 kWh to just 6,441 kWh. This dramatic reduction shows that effective envelope enhancements, particularly superior building insulation, virtually eliminate the need for traditional, high-consumption heating.
• Drastic Cooling and Hot Water Savings: Cooling loads saw a substantial 78% decrease. Furthermore, integrating highly efficient solar thermal systems across all apartments decreased the electrical demand for Domestic Hot Water (DHW) by about 79%, with solar systems achieving 86.6% solar coverage for the hot water needs.
• Achieving ‘Positive Energy’ Status: By installing Photovoltaic (PV) panels on the roof and façades, the building’s annual electricity production was 24,755 kWh. This was more than enough to cover 100% of all the building’s electrical needs including heating, cooling, DHW, and all appliances/lighting. Crucially, the system generated a net surplus of 5,282 kWh of electricity that was exported back to the grid annually.
• 88% Primary Energy Reduction: Overall, the deep renovation reduced the building’s total primary energy demand by up to 88%. This figure is a critical indicator of a building’s overall sustainability and its true impact on national energy networks.

Why Do These Deep Renovation Findings Matter for Policy and Investment?

Specific lifecycle gains comprise €1,037/m2, while specific primary energy savings are equal to around 12.3 MWh/m2. These findings move deep renovation from a theoretical ideal to a practical, measurable goal. The key takeaway for industry professionals and policymakers is that a holistic approach combining passive structural improvements like advanced building insulation with modern active and renewable energy systems is the pathway to truly transformative results.

The study’s most compelling argument for investors lies in the financial calculations. The life cycle cost analysis predicted impressive Life Cycle Cost (LCC) savings of €622,000. This figure refutes the common perception that deep renovation is financially prohibitive and instead frames it as a massive, long-term investment.

This model is particularly relevant for the European Union, which has prioritised reducing the energy consumption of its massive building stock through directives. The fact that buildings account for around 40% of worldwide energy consumption underscores the global necessity of this blueprint.

Case Scenario for Policy in Southern Europe: In Greece, where older apartment blocks like the one studied are common, this blueprint could inform a national renovation strategy. The renovation resulted in a specific CO2​ avoidance of 2.64 tons CO2​/m2 of renovated floor area, offering a clear, tangible metric for environmental policy success. By targeting inefficient 1970s buildings, policy can mandate the shift from mixed, outdated fossil fuel heating systems (such as old oil boilers) to modern heat pump systems. This would transform large sections of the urban landscape into climate-friendly generators of clean power.

What’s the Next Step for Sustainable Building in Europe?

The journey of this Athenian apartment block shows that our oldest buildings don’t have to be a liability in the energy transition; they can become powerful assets. By moving beyond piecemeal fixes, embracing holistic renovation, and deploying advanced heat pump systems, we can not only slash energy demand but also turn buildings into small, localised power stations. This is a vital step toward achieving carbon neutrality and a truly sustainable energy future for cities across Europe and the world.

Reference:

Bellos, E., Iliadis, P., Papalexis, C., Rotas, R., Mamounakis, I., Sougkakis, V., Nikolopoulos, N. and Kosmatopoulos, E. (2022) ‘Holistic renovation of a multi-family building in Greece based on dynamic simulation analysis’, Journal of Cleaner Production, 381, p. 135202. doi:10.1016/j.jclepro.2022.135202.