Search Results (63)

Sustainable renovation is a critical aspect for designing energy-efficient buildings with reasonable cost and high indoor living standards. The objective of this paper is to investigate various renovation scenarios for an old, uninsulated building with a floor area of 100 m² located in Athens, aiming to determine the global optimal solution through a multi-criteria analysis. The multi-criteria analysis considers energy, economic, and thermal comfort criteria to perform a multi-lateral approach. Specifically, the criteria are: (i) maximization of the energy savings, (ii) minimization of the life cycle cost (LCC), and (iii) minimization of the mean annual predicted percentage of dissatisfied (PPD). These criteria are combined within a multi-criteria evaluation procedure that employs a global objective function for determining a global optimum solution. The examined retrofitting actions are the addition of external insulation, the replacement of the existing windows with triple-glazed windows, the addition of shading in the openings in the summer, the application of cool roof dyes, the use of a mechanical ventilation system with a heat recovery unit, and the installation of a highly efficient heat pump system. The interventions were examined separately, and the combined renovation scenarios were studied by including them in the external insulation because of their high importance. The present study encompassed the investigation of a baseline scenario and 26 different renovation scenarios, conducted through dynamic simulation on an annual basis. The results of the present analysis indicated that the global optimal renovation scenario, including the addition of external insulation, the installation of highly efficient heat pumps, and the use of shading in the openings in the summer, saved energy by 74% compared to the baseline scenario. The LCC was approximately EUR 33,000, the simple payback period of the renovation process was around 6 years, the annual CO₂ emissions avoidance reached 4.6 tn_CO2, and the PPD was at 9.7%. An additional sensitivity analysis for determining the optimal choice under varying weights assigned to the criteria revealed that this renovation design is the most favorable option in most cases. These results prove that the suggested renovation scenario is a feasible and viable solution that leads to a sustainable design from multiple perspectives. Full article

A large proportion of the existing building stock in northern Europe is facing energy renovation in the coming years. In this process, existing architecture in cold and temperate climates, originally designed for natural ventilation, is renovated, implementing mechanical ventilation with heat recovery, in the belief that mechanical ventilation performs better than natural ventilation. Yet, can natural ventilation outperform mechanical ventilation when comparing life cycle carbon emissions, cost, and indoor environmental parameters? This study compares two different ventilation strategies in a full-scale renovation of two identical Danish residential buildings: (1) natural ventilation with passive controlled NOTECH ventilation and two-layered high-transmittance windows vs. (2) mechanical ventilation with heat recovery and three-layered low energy windows. The study compares energy performance, life cycle carbon footprint, capital cost investments, payback period, and indoor environmental quality (IEQ). Under the observed conditions, the results show that natural ventilation outperforms mechanical ventilation when it comes to energy consumption for heating (MWh), global warming potential (t. CO₂-equivalent), and total costs, while mechanical ventilation has a slightly higher indoor environmental quality. The study shows that two-layered windows and natural ventilation, based on passive solar heating, can reduce the global warming potential and act as a viable alternative to three-layered windows and mechanical ventilation when renovating existing building stock. Full article

The COVID-19 pandemic has renewed focus on the essential role of ventilation in maintaining good indoor air quality and low airborne transmission risks in school buildings, thereby supporting occupant well-being. However, many European classrooms still depend on natural ventilation, which often proves insufficient, especially during the heating season. Consequently, the integration of Mechanical Ventilation Systems (MVSs) with heat recovery in existing classrooms has become increasingly adopted, and decentralised MVS solutions, favoured for their minimal installation impact, have gained particular traction. Yet, despite their widespread implementation, a notable gap remains in the investigations into their air distribution efficiency and overall ventilation performance. To address this gap in the literature, this study offers a systematic assessment of the ventilation effectiveness for air distribution schemes related to decentralised MVSs. Computational Fluid Dynamics simulations were performed in a standard classroom, while statistical methods were used to established significant differences among the schemes. The optimal performances were observed with a single air inlet/outlet positioned on the long side of the room, providing CO₂ ≈ 1088 ppm and a mean local air change efficiency of 1.23. Ceiling-standing units installed in the room show CO₂ levels around 1200 ppm, with mean local air change efficiency between 1.02 and 1.07, whereas the floor-standing unit yields ventilation effectiveness lower than that of ideal mixing conditions. The results deliver an actionable ranking and design trade-offs to guide school retrofits. Full article

The efficient recovery of waste heat is essential for improving sustainability in industrial and urban energy systems. This study presents the experimental evaluation of a passive heat recovery unit composed of finned thermosyphons and Bismuth Telluride (Bi₂Te₃) thermoelectric generators (TEGs). The primary objective was to characterize its simultaneous thermal recovery and electrical generation capabilities under airflow and temperature conditions simulating low-grade industrial exhaust streams. The system was tested in an open-loop wind tunnel simulating exhaust gases under air velocities of 0.6, 1.1, and 1.7 m/s. Heat was transferred to the TEGs through finned thermosyphons, enabling power generation via the Seebeck effect. The passive heat exchange mechanism successfully recovered up to 250.9 W of thermal power, preheating the inlet air by a maximum of 9.5 °C with a peak thermal effectiveness of 44.4%. Simultaneously, the system achieved a maximum temperature difference of 30.0 °C across the thermoelectric modules, generating a total electrical power of 163.7 mW (81.8 mW per TEG). This dual-purpose operation resulted in a maximum overall first-law efficiency of 9.38% and an electrical power density of 52.20 W/m² from the low-grade thermal stream. These results confirm the technical feasibility of this compact, passive, and maintenance-free design, highlighting its potential for integration into applications like district heating or industrial ventilation, where balancing thermal and electrical outputs is crucial. Full article

In most European school classrooms, ventilation rates fall far short of standard requirements due to an inefficient use of manual airing, creating an unhealthy environment and increasing the risk of airborne viral transmission among occupants. To promote proper Indoor Air Quality (IAQ) levels, the required ventilation could be achieved by considering NV-oriented measures or Mechanical Ventilation systems with Heat Recovery (MVHR) implementation. This study defines a method to evaluate the potential primary energy implications of implementing MVHR in classrooms in the Mediterranean climate in comparison with NV control, selecting the Italian public-school building stock as a case study. Dynamic energy simulations were conducted across reference building construction types, considering locations representative of the national climate variability. Results show that MVHR can reduce primary energy up to 42.31 kWh/m². At the national level, it can achieve an attainable annual primary energy saving of 227 GWh, approximately 30% of current classroom consumption, with more than 70% of this potential located in northern provinces. A regression model was also used to relate energy impact to the Heating Degree Days, offering a scalable and transferable tool to support retrofit policies within similar southern European contexts. Full article

The integration of Mechanical Ventilation with Heat Recovery (MVHR) systems into heritage buildings poses a series of challenges, largely attributable to architectural constraints and conservation requirements. The present study offers an operational campaign of an MVHR system installed during the energy retrofit of a protected residential heritage dwelling in Vitoria-Gasteiz, Spain. Although environmental monitoring was carried out throughout the year, representative spring, autumn and winter days of continuous operation were analysed, as the occupants frequently avoided using the system due to noise perception. This limitation highlights the importance of considering acoustic comfort and user acceptance as critical factors in the long-term viability of MVHR in heritage contexts. The system was assessed under real-life conditions using continuous environmental monitoring, with a focus on indoor air quality (IAQ), thermal efficiency, airflow balance, and pressure losses. Despite the acceptable mean apparent thermal effectiveness (0.74) and total useful efficiency (0.96), the system’s performance was found to be constrained by significant flow imbalance (up to 106%) and elevated pressure drops, which were attributed to the legacy of the duct geometry. The results obtained demonstrate IAQ improved overall, with mean CO₂ concentrations below ~650 ppm across the analysed dataset; however, daily means occasionally exceeded 900–1000 ppm during high-occupancy periods and in the absence of spatially distributed demand control. These exceedances are consistent with the measured outdoor baseline (~400–450 ppm) and reflect the need for post-commissioning balancing and room-level sensing to sustain Category II performance in heritage dwellings. This study provides empirical evidence on the limitations and opportunities of MVHR deployment in historic retrofits, thus informing future guidelines for sustainable interventions in heritage contexts. Full article

This study presents a detailed analysis of the energy performance and thermal comfort conditions in four existing school buildings located in Madrid, Spain. Dynamic simulations were conducted using TeKton3D—(iMventa Ingenieros, Málaga, Spain)- an open-source tool based on the EnergyPlus engine—to model four improvement scenarios: (I) current state, (II) envelope retrofitting with ETICS and high-performance glazing, (III) solar control strategies, and (IV) incorporation of mechanical ventilation with heat recovery. Each building was simulated under both current and projected 2050 climate conditions. The case studies were selected to represent different construction periods and urban contexts, including varying levels of exposure to the urban heat island effect. This approach allows the results to reflect the diversity of the existing school building stock and its different vulnerabilities to climate change. The results show that envelope retrofitting substantially reduces heating demand but may increase cooling needs, particularly under warmer future conditions. Solar control strategies effectively mitigate overheating, while mechanical ventilation with heat recovery contributes to improved comfort and overall efficiency. This study highlights the trade-offs between energy savings and indoor environmental quality, underlining the importance of integrated renovation measures. The study provides relevant data for decision-making in climate-resilient building renovation, aligned with EU goals for nearly zero and zero-emission buildings. Full article

Improving the energy efficiency of residential buildings is essential for achieving global climate goals and reducing environmental impact. This study analyzes the Total Performance approach using the example of a modern semi-detached house built by a Polish developer, as an example. The building is designed with integrated systems that minimize energy consumption while maintaining resident comfort. The building is equipped with an air-to-water heat pump, underfloor heating, mechanical ventilation with heat recovery, and automatic temperature control systems. Energy efficiency was assessed using ArCADia–TERMOCAD 8.0 software in accordance with Polish Technical Specifications (TS) and verified by monitoring real-time electricity consumption during the heating season. The results show a PED from non-renewable sources of 54.05 kWh/(m²·year), representing a 23% reduction compared to the Polish regulatory limit of 70 kWh/(m²·year). Real-time monitoring conducted from December 2024 to April 2025 confirmed these results, indicating an actual energy demand of approximately 1771 kWh/year. Domestic hot water (DHW) preparation accounted for the largest share of energy consumption. Despite its dependence on grid electricity, the building has the infrastructure to enable future photovoltaic (PV) installation, offering further potential for emissions reduction. The results confirm that Total Performance strategies are not only compliant with applicable standards, but also economically and environmentally viable. They represent a scalable model for sustainable residential construction, in line with the European Union’s (EU’s) decarbonization policy and the goals of the European Green Deal. Full article

As the demand for energy-efficient homes continues to rise, the importance of advanced mechanical ventilation systems in maintaining indoor air quality (IAQ) has become increasingly evident. However, challenges related to energy balance, IAQ, and occupant thermal comfort persist. This review examines the performance of mechanical ventilation systems in regulating indoor climate, improving air quality, and minimising energy consumption. The findings indicate that demand-controlled ventilation (DCV) can enhance energy efficiency by up to 88% while maintaining CO₂ concentrations below 1000 ppm during 76% of the occupancy period. Heat recovery systems achieve efficiencies of nearly 90%, leading to a reduction in heating energy consumption by approximately 19%. Studies also show that employing mechanical rather than natural ventilation in schools lowers CO₂ levels by 20–30%. Nevertheless, occupant misuse or poorly designed systems can result in CO₂ concentrations exceeding 1600 ppm in residential environments. Hybrid ventilation systems have demonstrated improved thermal comfort, with predicted mean vote (PMV) values ranging from –0.41 to 0.37 when radiant heating is utilized. Despite ongoing technological advancements, issues such as system durability, user acceptance, and adaptability across climate zones remain. Smart, personalized ventilation strategies supported by modern control algorithms and continuous monitoring are essential for the development of resilient and health-promoting buildings. Future research should prioritize the integration of renewable energy sources and adaptive ventilation controls to further optimise system performance. Full article

The construction sector presently consumes about 40% of global energy and generates 36% of CO₂ emissions, making facade retrofits a priority for decarbonising buildings. This review clarifies how ventilated facades (VFs), wall assemblies that interpose a ventilated air cavity between outer cladding and the insulated structure, address that challenge. First, the paper categorises VFs by structural configuration, ventilation strategy and functional control into four principal families: double-skin, rainscreen, hybrid/adaptive and active–passive systems, with further extensions such as BIPV, PCM and green-wall integrations that couple energy generation or storage with envelope performance. Heat-transfer analysis shows that the cavity interrupts conductive paths, promotes buoyancy- or wind-driven convection, and curtails radiative exchange. Key design parameters, including cavity depth, vent-area ratio, airflow velocity and surface emissivity, govern this balance, while hybrid ventilation offers the most excellent peak-load mitigation with modest energy input. A synthesis of simulation and field studies indicates that properly detailed VFs reduce envelope cooling loads by 20–55% across diverse climates and cut winter heating demand by 10–20% when vents are seasonally managed or coupled with heat-recovery devices. These thermal benefits translate into steadier interior surface temperatures, lower radiant asymmetry and fewer drafts, thereby expanding the hours occupants remain within comfort bands without mechanical conditioning. Climate-responsive guidance emerges in tropical and arid regions, favouring highly ventilated, low-absorptance cladding; temperate and continental zones gain from adaptive vents, movable insulation or PCM layers; multi-skin adaptive facades promise balanced year-round savings by re-configuring in real time. Overall, the review demonstrates that VFs constitute a versatile, passive-plus platform for low-carbon buildings, simultaneously enhancing energy efficiency, durability and indoor comfort. Future advances in smart controls, bio-based materials and integrated energy-recovery systems are poised to unlock further performance gains and accelerate the sector’s transition to net-zero. Emerging multifunctional materials such as phase-change composites, nanostructured coatings, and perovskite-integrated systems also show promise in enhancing facade adaptability and energy responsiveness. Full article

Ensuring proper indoor air quality in high-rise apartment buildings is a crucial challenge, particularly when upgrading ventilation systems during deep energy renovation of existing buildings. This study evaluates the condition of existing ventilation systems and assesses the performance, cost, and energy efficiency of different mechanical ventilation solutions with heat recovery, including centralized and decentralized balanced ventilation with heat recovery, single-room ventilation units, and mechanical extract ventilation with heat pump heat recovery or without heat recovery. An onsite survey revealed significant deficiencies in existing ventilation systems, such as airtight window installations without dedicated fresh air valves, misaligned and decayed exhaust shafts, and inadequate extract airflow in kitchens and bathrooms. SWOT analyses for each system highlighted their strengths, weaknesses, opportunities, and threats, providing valuable insights for decision-makers. The results indicate that while centralized and decentralized mechanical ventilation with heat recovery enhances energy efficiency and indoor air quality in high-rise multifamily apartment buildings, challenges such as high installation costs, maintenance complexity, and architectural constraints must be addressed. Heat recovery with exhaust air heat pumps is a viable alternative for high-rise apartment buildings when more efficient options are not feasible. Full article

Heat recovery systems are increasingly recognized as key energy conservation measures in residential buildings. But their effectiveness is highly sensitive to operational conditions. This study used a calibrated OpenStudio simulation, which is validated against monthly utility data, to investigate the feasibility of implementing a heat recovery ventilator in an existing single-detached house in Vancouver under two scenarios: existing passive ventilation without a heat recovery ventilator versus the proposed balanced mechanical ventilation with a heat recovery ventilator. The findings indicate that employing an HRV in an existing house lacking balanced ventilation would lead to higher annual space heating energy consumption (75.49 GJ electricity and 56.70 GJ natural gas with HRV compared to 73.64 GJ and 52.70 GJ, respectively, without an HRV). Therefore, for existing houses without balanced ventilation, improving the existing building envelope’s airtightness through retrofits should always be carried out before installing a heat recovery ventilator. Additionally, the heat recovery ventilator should be appropriately sized to compensate for any shortfall in natural infiltration to ensure the sufficient indoor air quality while minimizing the outdoor air-induced space heating energy usage. Furthermore, the recommended break-even point of the infiltration rate for the house studied in this work to avoid increased space heating energy use due to the retrofit with a heat recovery ventilator is 0.281 air change per hour. Full article

Indoor air quality (IAQ) plays a vital role in supporting both the physical and mental well-being of individuals in enclosed spaces, and the role of mechanical ventilation systems has gained increasing attention due to building design’s focus on energy efficiency and thus airtight constructions. This study investigated the pre–post effects of installing a heat recovery mechanical ventilation system (MVHR) on indoor air quality in a high school classroom in Ferrara, Italy. The analysis focused on experimental measurements of temperature (T), relative humidity (RH), and carbon dioxide (CO₂) both inside and outside the same classroom, which had constant occupancy (17 students) for an entire school year, allowing a comparison between natural and mechanical ventilation. With a comprehensive approach, particulate matter (PM_2.5), volatile organic compounds (VOCs), and radon levels (Rn) were monitored as well, after the installation of the MVHR. By comparing natural and mechanical ventilation, the study highlights the strengths and limitations of the ventilation system implemented, together with an evaluation of the system’s energy consumption, including a 2 kW post-heating battery. In terms of results, the MVHR demonstrated clear benefits in managing CO₂ levels and improving sensory, olfactory, and psychophysical well-being, as well as the attention levels of students. In detail, under natural ventilation, peak concentrations exceeded 4500 ppm, while mechanical ventilation kept them below 1500 ppm. The average CO₂ concentration during occupancy dropped from 2500 ppm to around 1000 ppm, achieving a 62% reduction. However, beneficial effects were not observed for other parameters, such as PM_2.5, VOCs, or radon. The latter displayed annual average values around 21 Bq/m³ and peaks reaching 56 Bq/m³. Full article

The European Union (EU) has introduced a range of policies to promote energy efficiency, including setting specific targets for energy-efficient renovations across the EU building stock. This study provides a comprehensive environmental and economic assessment of energy-efficient renovation scenarios in a large-scale multifamily building project that is district-heated, considering both the building and the broader urban energy system. A systematic framework was developed for this assessment and applied to a real case in Sweden, where emission factors from energy production are significantly lower than the EU average: 114 g CO₂e/kWh for district heating and 37 g CO₂e/kWh for electricity. The project involved the renovation of four similar district-heated multifamily buildings with comparable energy efficiency measures. The primary distinction between the measures lies in the type of HVAC system installed: (1) exhaust ventilation with air pressure control, (2) mechanical ventilation with heat recovery, (3) exhaust ventilation with an exhaust air heat pump, and (4) exhaust ventilation with an exhaust air heat pump combined with photovoltaic (PV) panels. The study’s findings show that the building with an exhaust air heat pump which operates intermittently with PV panels achieves the best environmental performance from both perspectives. A key challenge identified for future research is balancing the reduced electricity production from Combined Heat and Power (CHP) plants within the energy system. Full article

The paper analyses multi-variant energy simulations carried out in IDA ICE 4.8 software for a newly designed single-family building within the framework of the 4E Idea. This idea assumes the use of energy-saving, ecological, ergonomic, and economic solutions in construction and building operation. Energy simulations were conducted to evaluate the annual energy-saving potential of the developed architectural house concept, which incorporates ergonomic analyses and cost-effective construction solutions. Analyses were conducted to optimise the non-renewable primary energy index by selecting mechanical ventilation system (CAV or VAV) with heat recovery; the configuration of photovoltaic module installation in terms of their location and orientation; the exposure and type of solar thermal collectors (flat and vacuum); and the use of two types of heat pumps (air- and ground-source). The most favourable energy performance of the building was achieved with an HVAC system equipped with a VAV mechanical ventilation system with heat recovery, an on-grid photovoltaic installation, vacuum solar thermal collectors, and a ground-source heat pump with a horizontal heat exchanger. This configuration resulted in a primary energy index value of 2 kWh/m²/year. The results of the analyses carried out for the 4E building concept may serve as a reference point for future energy-efficient building designs aspiring to meet higher standards of sustainable development. Full article