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Advancing energy efficiency and IEQ through fast-track renovation of residential buildings

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Article

Advancing energy efficiency and IEQ through fast-track renovation of residential buildings

23 January 2025
This article briefly presents the H2020 SUREFIT project’s innovative solutions developed to improve residential buildings energy conservation measures and indoor air quality through retrofitting, aiming for near-zero energy buildings.
Editorial Team

Authors

Bruno Pereira, Low Carbon & Resource Efficiency, R&Di, Instituto de Soldadura e Qualidade | LinkedIn profile
Luísa Dias Pereira, Low Carbon & Resource Efficiency, R&Di, Instituto de Soldadura e Qualidade | LinkedIn & ORCID profiles
Sérgio Tadeu, Low Carbon & Resource Efficiency, R&Di, Instituto de Soldadura e Qualidade | LinkedIn & ORCID profiles

(Note: opinions in the articles are of the authors only and do not necessarily reflect the opinion of the EU).

Introduction

The built environment plays a pivotal role in shaping our energy landscape and environmental footprint. In the European Union, buildings are responsible for nearly 40% of total energy consumption and 36% of CO2 emissions. This substantial energy demand is largely driven by the need for heating, cooling, and ventilation systems, which are essential for both energy efficiency and the maintenance of optimal indoor environmental quality (IEQ). Addressing these challenges requires innovative solutions and a holistic approach to building design and operation.

The European Union has set ambitious targets for energy efficiency and building performance. The revised Energy Performance of Buildings Directive (EPBD) now mandates that all new buildings must achieve zero emission building (ZEB) standards, moving beyond the previous near-zero energy building (nZEB) requirements [1]. However, the existing building stock, much of which is energy inefficient and may have poor IEQ, presents a significant challenge.

The SUREFIT project aims to revolutionise building renovation by introducing innovative, cost-effective, and environmentally friendly prefabricated technologies. By accelerating the renovation process and improving both energy performance and indoor environmental quality, SUREFIT seeks to contribute to a more sustainable, healthy, and resilient built environment. This paper explores the key challenges and opportunities in building renovation, the specific technologies and strategies employed by the SUREFIT project, and their potential impact on energy efficiency, indoor air quality, thermal comfort, and overall occupant well-being.

Challenges of building energy efficiency and the proposed methodology

The transition towards a more sustainable built environment is hindered by several significant challenges, particularly when it comes to retrofitting existing buildings. Traditional retrofitting methods often face obstacles such as high costs, lengthy timelines, and disruptions to building occupants. One major challenge lies in the complexity of existing buildings. Historical constraints, varying construction standards, and the presence of heritage features can complicate the retrofitting process. Integrating innovative technologies into these structures often requires substantial modifications, which can further increase costs and project durations.

Financial constraints are another significant barrier. The initial investment required for energy-efficient upgrades can be substantial, and the long-term payback period may deter building owners and policymakers. Additionally, the lack of standardised procedures and financing mechanisms can hinder the adoption of energy-efficient solutions. Furthermore, the impact of poor building energy efficiency on occupant health and well-being cannot be overlooked. Inefficient buildings often suffer from poor indoor air quality, inadequate ventilation, and suboptimal thermal comfort. These factors can lead to various health issues, such as respiratory problems, allergies, and reduced cognitive performance.

It is known that the numerous possible combinations of measures and the interaction of variables used in cost-optimal calculations make it difficult to obtain best solutions for the energy retrofit of buildings, within the limits imposed by the regulations. This also hinders the action of different stakeholders: authorities, experts, suppliers of products and services and building owners.

To address these challenges, SUREFIT developed an operational tool designed to support decision-making during residential building energy renovation projects. It uses life-cycle energy estimation models and cost-benefit assessments for buildings, and it can perform combined simulations of Energy Conservation Measures (ECMs). While the proposed methodology directly incorporates economic and environmental criteria, the anticipated benefits extend to the social pillar of sustainability as well.

Figure 1. Overall approach and methodology of ©SURe3FIT tool.

Figure 1. Overall approach and methodology of ©SURe3FIT tool.

The SURe³FIT tool proposes improvements to the cost-optimality methodology, established by the Delegated Regulation 244/2012 and EN 15459, as presented in selected scientific articles [2] and [3]. Considering that the EC recommends that the global cost of efficiency measures be assessed using the Net Present Value (NPV) criterion, this tool complements this approach and proposes assessing them using other criteria, with emphasis on return on investment (ROI), as well as analyzing the environmental impact of the solutions (in kgCO2eq/m2) throughout their life cycle.

The SUREFIT project and its innovative technologies

The SUREFIT project is a pioneering initiative aimed at accelerating the adoption of energy-efficient building renovation practices. The project focuses on prefabricated and innovative technologies to address the challenges of traditional retrofitting methods. By combining cutting-edge solutions with streamlined installation processes, SUREFIT aims to reduce energy consumption, enhance indoor comfort, and minimise disruptions to building occupants.

Building envelope technologies

The SUREFIT project introduces several innovative technologies to improve the energy performance of building envelopes:

  • High-performance insulation panels:

    • Bio-Aerogel Panels: These panels offer exceptional thermal insulation properties, significantly reducing heat loss or gain. Their lightweight and flexible nature facilitate easy installation and integration into existing building structures.

    • Phase Change Material (PCM) panels: PCM panels store and release thermal energy, helping to regulate indoor temperatures and reduce peak energy demand. This technology is particularly effective in mitigating thermal fluctuations caused by external factors.

  • Advanced window systems:

    • Photovoltaic Vacuum Glazing (PV VG) windows: These innovative windows combine energy generation with high thermal insulation. The vacuum layer significantly reduces heat loss and gain, while the integrated photovoltaic cells generate clean electricity.

    • High-performance glazing systems: Advanced glazing technologies, such as low-emissivity coatings and triple-pane glazing, improve the thermal performance of windows, reducing energy consumption for heating and cooling.

Energy systems and HVAC technologies

The SUREFIT project explores a range of innovative energy systems and HVAC technologies to optimise building energy performance:

  •  Heat pumps:

    • Air-Source Heat Pumps (ASHPs): ASHPs extract heat from the ambient air, providing heating in winter and cooling in summer. These systems are highly efficient and can be integrated with renewable energy sources like solar or wind power.

    • Ground-Source Heat Pumps (GSHPs): GSHPs utilise the stable temperature of the ground to provide efficient heating and cooling. The SUREFIT project investigates the use of innovative thermal pipe technologies to facilitate the installation of GSHP systems.

  • Solar thermal systems:

    • Solar thermal systems harness solar energy to heat water for domestic use or space heating. The SUREFIT project explores the integration of solar thermal collectors with heat pumps to enhance system efficiency and reduce reliance on fossil fuels.

  • Ventilation systems:

    • Advanced ventilation systems, such as demand-controlled ventilation and heat recovery ventilation, optimize indoor air quality while minimising energy consumption. These systems can be integrated with the building's overall energy management system to achieve optimal performance.

  • Energy storage systems:

    • Energy storage technologies, such as thermal storage and battery storage, can help to balance energy supply and demand, reducing peak loads and improving system efficiency. The SUREFIT project investigates the potential of integrating energy storage systems into building renovation projects.

Figure 2. Illustration of the proposed technologies for building retrofit ©SUREFIT.

Figure 2. Illustration of the proposed technologies for building retrofit ©SUREFIT.

Figure 3. Schematic diagram of the DXSAHP System ©SUREFIT.

Figure 3. Schematic diagram of the DXSAHP System ©SUREFIT.

Impact on energy efficiency and indoor wellbeing

The SUREFIT project aims to significantly improve the energy efficiency and indoor environmental quality of buildings through the implementation of innovative technologies. By addressing key areas such as building envelope, HVAC systems, and indoor air quality, the project seeks to enhance occupant comfort, reduce energy consumption, and minimise environmental impact.

Energy efficiency

  • Reduced heat loss and gain: The integration of high-performance insulation materials, such as bio-aerogel panels and advanced window systems, significantly reduces heat loss in winter and heat gain in summer. This leads to reduced energy demand for heating and cooling, resulting in lower energy bills and decreased carbon emissions.

  • Improved HVAC system efficiency: The project's innovative HVAC technologies, including heat pumps, solar thermal systems, and energy-efficient ventilation systems, offer significant energy savings. These systems are designed to optimise energy consumption while maintaining comfortable indoor conditions.

  • Enhanced building envelope performance: The use of airtightness measures, such as insulating breather membranes and advanced sealing techniques, minimises air leakage, reducing energy losses and improving indoor air quality.

Indoor environmental quality

  • Improved indoor air quality: The project's focus on ventilation systems and air filtration technologies ensures the removal of pollutants and allergens, enhancing indoor air quality and occupant well-being.

  • Enhanced thermal comfort: The integration of advanced insulation materials, efficient HVAC systems, and energy storage solutions helps maintain optimal indoor temperatures, reducing thermal discomfort and improving occupant satisfaction.

  • Optimised daylight and lighting: The use of daylighting strategies, such as skylights and light pipes, and energy-efficient lighting systems minimises the need for artificial lighting, reducing energy consumption and creating a more pleasant indoor environment.

Table 1 presents a summary of all the sensors used for environmental monitoring across the various demo sites.    

Table 1 - Technical Specifications of all the Sensors** Used in the SUREFIT Project for Environmental Monitoring.

Table 1 - Technical Specifications of all the Sensors** Used in the SUREFIT Project for Environmental Monitoring.

Notes: * An algorithm to convert ticks to VOC index points was developed for better result analysis.
** Not all sensors were applied in all demo sites.

Monitoring and evaluation

  • To assess the real-world impact of the SUREFIT technologies, the project incorporates a comprehensive monitoring and evaluation framework. This includes:
    Pre- and post-renovation assessments: Detailed assessments of building energy performance and indoor environmental quality are conducted before and after the renovation to quantify the improvements.

  • Continuous monitoring of energy consumption: Real-time monitoring of energy consumption allows for the tracking of energy savings and the identification of optimisation opportunities.

  • Occupant surveys: Surveys are conducted to gather feedback from building occupants regarding their perceptions of indoor comfort, air quality, and overall satisfaction.

  • Indoor environmental quality modelling: Advanced computer modelling tools are used to simulate indoor environmental conditions and predict the impact of the implemented technologies.

Figure 4. Step-by-Step Overview: Comparing measurements in pilot buildings before and after refurbishment. ©SUREFIT

Figure 4. Step-by-Step Overview: Comparing measurements in pilot buildings before and after refurbishment. ©SUREFIT

Additional Considerations

  • Innovative Window Heat Recovery (WHR) systems: The SUREFIT project also explores the use of innovative WHR systems, such as those using heat pipes. These systems can significantly improve energy efficiency by recovering heat from exhaust air and transferring it to incoming fresh air.

  • Impact on occupant well-being: Improved indoor air quality and thermal comfort can have a positive impact on occupant health, productivity, and overall well-being.

  • Long-term performance and maintenance: The long-term performance and maintenance requirements of the implemented technologies should be carefully considered to ensure their continued effectiveness.

By combining innovative technologies, rigorous monitoring, and occupant feedback, the SUREFIT project aims to set new standards for energy-efficient and healthy buildings.

Quick overview of the obtained results in the Spanish pilot

The SUREFIT project includes a pilot initiative in the San Pedro Regalado neighbourhood, where various housing types have been developed, reflecting different stages of urban development. These homes typically feature a ground floor plus an upper level, with some including basements and back patios. Constructed in the 1950s, the buildings utilise load-bearing walls and vaulted ceilings made from hollow bricks, contributing to their unique architectural character. Despite their historical significance, these homes face common challenges that necessitate renovation to meet modern standards of comfort, insulation, energy efficiency, and reduced CO2 emissions. Each unit ranges from 50 to 70 m² and exhibits varying conditions; however, all require updates to enhance their structural integrity and environmental performance.

The SUREFIT project aims to address these issues by implementing innovative technologies tailored for retrofitting existing buildings. By focusing on improving energy efficiency and indoor environmental quality, the project seeks to transform these older structures into sustainable living spaces that comply with contemporary energy standards. This pilot serves as a critical step towards demonstrating the feasibility of advanced renovation techniques in similar urban contexts across Europe.


The Spanish demonstration sites revealed critical building envelope issues, including high U-values in external walls, resulting in significant thermal loss, and reduced thermal inertia.
Thermal bridges further compromised energy efficiency, leading to increased energy consumption. Indoor environmental quality was notably poor, especially during summer, with occupants experiencing thermal discomfort and elevated CO2 levels in specific rooms. These findings underscored the urgent need for comprehensive renovation strategies to enhance both energy efficiency and indoor air quality in the targeted buildings.
 


Monitoring campaign

The monitoring campaign pre-renovation for the SUREFIT project in Spain spanned 12 months, from June 2023 to May 2024. During this period, indoor environmental conditions, including pollutant levels, were assessed using wireless devices equipped with Xbee antennas. A total of ten end devices, consisting of Arduino boards with various sensors were installed across the pilot homes to gather ambient data, which was transmitted to a central coordinator device located in one of the residences. 

Figure 5. Sensor installation position in all floors in each Spanish pilot. ©SUREFIT

Figure 5. Sensor installation position in all floors in each Spanish pilot. ©SUREFIT

In addition to monitoring environmental parameters, electrical energy consumption was measured in one of the houses. Following the completion of the building renovations in July 2024, new sensors were introduced, utilising dedicated PCBs, and operating on a ZigBee network designed for low power consumption.

The sensor installation plan, illustrated in Figure 5, included placements in key areas: the living area/basement (N-1 level), kitchen (N0), and bedroom (N+1) of each building. Outdoor temperature (ºC) and relative humidity (%) data were sourced from the Valladolid weather station network, specifically from the nearest station to the pilot buildings. Other measurements included: 

  1. Heat loss: Assessed using TESTO equipment over a 24-hour period. 

  2. Thermography: Conducted using a FLIR Thermal Imaging Camera to visualise heat distribution and identify areas of energy loss.

  3. Energy use monitoring: Implemented using a Carlo Gavazzi EM111 single-phase energy analyser with Modbus communication protocol. This device enabled monitoring of voltage (V), current (A), power (kW), and other energy metrics (kWh and kvarh).

Energy monitoring

The measured U-value for the external walls of the Spanish pilot buildings was 1.4 W/m²K, indicating a significantly high average heat coefficient factor suggested inadequate insulation of the building envelope. The thermographic imaging confirmed notable thermal losses through the exterior walls. Additionally, thermal bridges were observed around the window perimeters, and tests highlighted temperature differences between walls in contact with the exterior and those adjacent to interior spaces. These findings pointed also to a low-performance building envelope, which was contributing to elevated energy demands. This conclusion was supported by simulated energy requirements for heating (89.2 kWh/m²·y), which classifies the buildings in category in category IV of the ARCAS Methodology [4]. Moreover, the energy consumption recorded in one of the Spanish pilot buildings was identified as 7,100 kWh over one year, translating to approximately 110 kWh/m²·y. This figure is substantial and deviates significantly from the current European goal of achieving near-zero energy consumption in buildings.

Indoor Environmental Quality monitoring

The temperature measurements for the three dwellings revealed significantly high values prior to renovation, exceeding the category IV thermal comfort threshold of 28°C as defined by EN 16798-1 [5]. minimum temperatures generally remained within an acceptable range. However, there were occasional instances of lower comfort levels, particularly in apartment II, where temperatures fell below the threshold.

Relative humidity (RH) levels showed satisfactory performance, with average values below 50% and 60%. These values were not low enough to raise concerns about insufficient humidification. In terms of CO2 concentrations, the highest levels were found in the basements of the buildings. Elevated CO2 levels were also recorded in the bedrooms, reaching approximately 1500 ppm in apartments I and III, and 1200 ppm in apartment II. However, average CO2 levels across all units were more reasonable.

While the airtightness results met the minimum reference values, they were still excessively high. This indicates an imbalance between the need to remove contaminants and the thermal losses that contribute to increased energy demands.

Overall, these measurement results suggest poor indoor environmental quality, primarily related to thermal discomfort during summer and elevated CO2 levels in certain areas of the buildings.

Ongoing monitoring and evaluation preliminary data

The ongoing post-renovation campaign has yielded some preliminary results and conclusions. The following data is confined to one dwelling, apartment I, and showcases the evolution of the indoor environmental conditions before and after renovation of this pilot, focusing on temperature (Temp, ºC), relative humidity (RH, %), and CO2 concentration levels (CO2, ppm) for two different months of each stage – July and September, of 2023 (pre-renovation) and 2024 (post-renovation).

To provide context, Table 2 presents the external weather conditions for the analysed months, including daily average temperatures (ºC), daily maximum temperatures (ºC) and relative humidity (RH, %).
As expected, the two climate periods analysed were not exactly the same in both years, but a seasonal patterns was observed: both years showed July being warmer than September. Additionally, some differences were observed in September:  the average temperature in 2024 was about 3°C cooler than in 2023.

Table 2 - Weather conditions present during months of July and September (2023, 2024) in the vicinity of the pilot buildings.

Table 2 - Weather conditions present during months of July and September (2023, 2024) in the vicinity of the pilot buildings.

The temperature measurements for apartment I (Table 3) showed significantly high values before renovation, with average temperatures in July and peak temperatures in September exceeding the category IV thermal comfort threshold of 28°. Post-renovation, the measured average temperatures decreased to the range of 17-21ºC.    
In fact, after renovation, all rooms experienced a substantial decrease in average temperatures, with reductions ranging from 5°C to 13°C depending on the room and month. Moreover, temperatures across all rooms were more uniform, falling within a narrower range (17.4°C to 21.4°C) compared to pre-renovation.

Within this preliminary data, it was also observed that the temperature reduction was more pronounced in July than in September, suggesting the renovation may have had a greater impact on cooling during hotter months – this observation will be confirmed within the coming years.

Table 3 - Measured average temperatures in apartment I of the Spanish pilot.

Table 3 - Measured average temperatures in apartment I of the Spanish pilot.

A synthesis of the Relative humidity (RH) levels is presented on Table 4. Pre-renovation RH levels were relatively low, ranging from 33.1% to 42.3% across different rooms and months. Post-renovation, there was a significant increase in RH levels, with values ranging from 58.8% to 76.8%. Nonetheless, 
the increase in indoor RH levels post-renovation aligns with the higher outdoor RH levels observed in 2024 compared to 2023 (as shown in Table 2).

Table 4 - Measured average relative humidity in apartment I of the Spanish pilot.

Table 4 - Measured average relative humidity in apartment I of the Spanish pilot.

Table 5 provides insights into the CO2 concentration levels in apartment I of the Spanish site. Pre-renovation CO2 levels varied across rooms, with the highest average concentration (734.1 ppm) observed in the bedroom during September 2023. Post-renovation, there was a general decrease in CO2 concentrations across most rooms and months, with one exception: the kitchen in July showed a slight increase from 456.0 ppm to 474.3 ppm – this increase is not significantly worrying in terms of IEQ. 
The CO2 concentration measurements displayed a general decrease in the average levels after renovation. Post-renovation CO2 levels were more consistent across rooms, ranging from 368.3 ppm to 584.0 ppm. 
These results suggest that the renovation generally improved ventilation and air quality in the apartment, particularly in spaces like the bedroom where CO2 levels were initially highest. Nonetheless, further observation data are needed to confirm the observed general decrease in CO2 concentration levels.

Table 5  - Measured average CO2 concentration levels in apartment I of the Spanish pilot.

Table 5 - Measured average CO2 concentration levels in apartment I of the Spanish pilot.

Replicability and future potential

The SUREFIT project demonstrates significant potential for replication across various building types and geographical contexts. The modular and prefabricated nature of the technologies developed allows for adaptability to different building structures and climates.

Replicability across building types:

  • Residential buildings: The project's focus on single-family houses and apartment buildings showcases adaptability to various residential structures.

  • Non-residential buildings: While not the primary focus, the technologies have potential applications in office buildings, schools, and other commercial structures.

Geographical adaptability:

  • Climate considerations: The project's technologies, tested in different European climates (UK, Greece, Spain, Finland), demonstrate versatility across various weather conditions.

  • Cultural and architectural diversity: The solutions respect local architectural heritage while improving energy performance, making them suitable for diverse European contexts.

Economic feasibility:

  • Cost-effectiveness: Prefabricated solutions reduce on-site labour and installation time, potentially lowering overall renovation costs.

  • Payback period: Initial assessments indicate a payback period of 7-10 years for most technologies, making them economically viable for building owners.

  • Market potential: The modular approach allows for scalability, potentially reducing costs as production increases.

Impact on building renovation:

  • Acceleration of renovation rates: SUREFIT's fast-track approach could significantly contribute to achieving the EU's goal of doubling annual energy renovation rates.

  • Energy savings: Preliminary results show potential energy savings of up to 60% in renovated buildings, aligning with EU energy efficiency targets.

  • Indoor environmental quality: The focus on IEQ improvements addresses a critical aspect often overlooked in traditional renovations.

Conclusions

The SUREFIT project demonstrates significant potential for revolutionising building renovation through innovative, prefabricated technologies. By addressing key challenges in energy efficiency and indoor environmental quality, SUREFIT offers a holistic approach to creating sustainable, healthy living spaces. The project's focus on advanced materials, HVAC systems, and comprehensive monitoring strategies promises to accelerate the transition towards near-zero energy buildings. Improvements in indoor air environmental quality were achieved alongside energy conservation measures. As pilot results emerge, SUREFIT's methodologies and technologies demonstrate potential to establish new standards for energy-efficient retrofitting across Europe, contributing to reduced energy consumption, improved occupant well-being, and progress towards EU climate goals.

References

[1] European Commission. Energy Performance of Buildings Directive. 
https://energy.ec.europa.eu/topics/energy-efficiency/energy-efficient-buildings/energy-performance-buildings-directive_en (accessed on 27/12/2024)

[2] Tadeu, Sérgio; Rodrigues, Carla; Marques, Pedro; Freire, Fausto. 2022. "Eco-efficiency to support selection of energy conservation measures for buildings: A life-cycle approach", Journal of Building Engineering, 61. doi.org/10.1016/j.jobe.2022.105142

[3] Tadeu, Sérgio. 2023. “Operational tool for selecting energy systems for small buildings based on useful energy needs”, 20th International Conference on Sustainable Energy Technologies, Nottingham, UK. 
https://surefitproject.eu/wp-content/uploads/2024/03/15.-Operational-tool-for-selecting-energy-systems-for-small-buildings-based-on-useful-energy-needs.pdf

[4] Flores-Abascal et al. 2023. “A novel multicriteria methodology to assess the renovation of social buildings”, Journal of Building Engineering, 77, 107505. doi.org/10.1016/j.jobe.2023.107505

[5] EN 16798-1 - Energy Performance of Buildings-Ventilation for Buildings-Part 1: Indoor Environmental Input Parameters for Design and Assessment of Energy Performance of Buildings Addressing Indoor Air Quality, Thermal Environment, Lighting, and Acoustics - Module M1-6. CEN: Brussels, Belgium, 2019