Search Results (29)

Hospitals are the most energy-intensive buildings in the tertiary sector because they have continuous and high demand for heating and cooling (to meet strict thermal comfort conditions), hot water, kitchen facilities, electricity, etc. Investigation of the energy performance of hospital buildings is crucial for defining energy savings and developing benchmarks and design guidelines for nearly Zero-Energy Hospitals (nZenHs). This study investigates the energy efficiency of hospital buildings in Greece and the necessary retrofit strategies to transform them to nearly Zero-Energy Buildings (nZEBs). Six building typologies were recognized, based on the building’s floor plan, and energy upgrade scenarios were investigated for each typology. The first scenarios aimed at improving the building’s energy efficiency, and the last one exploited the use of renewable energy source (RES) systems to minimize energy consumption. More specifically, a rooftop photovoltaic system was examined. The results showed differences in hospitals’ energy performance according to typology and climatic zone. They strongly confirm that hospitals can be transformed into buildings with nearly zero-energy consumption, irrespective of their design. The significant energy savings achieved by transforming hospitals into NZEBs highlight the crucial role in enhancing energy efficiency in tertiary sector buildings. Full article

Radiative cooling (RC) offers a passive pathway to reduce surface and system temperatures by emitting thermal radiation through the atmospheric window, yet its daytime effectiveness is often constrained by geometry, angular solar exposure, and practical integration limits. This work experimentally investigates the use of passive non-imaging optics, specifically compound parabolic concentrators (CPCs), as enhancers of RC performance under realistic conditions. A three-tier experimental methodology is followed. First, controlled indoor screening using an infrared lamp quantifies the intrinsic heat gain suppression of a commercial RC film, showing a temperature reduction of nearly 88 °C relative to a black-painted reference. Second, outdoor rooftop experiments on aluminum plates assess partial RC coverage, with and without CPCs, under varying orientations and tilt angles, revealing peak daytime temperature reductions close to 8 °C when CPCs are integrated. Third, system-level validation is conducted using a modified GUNT ET-202 solar thermal unit to evaluate the transfer of RC effects to a water circuit absorber. While RC strips alone produce modest reductions in water temperature, the addition of CPC optics amplifies the effect by factors of approximately three for ambient water and nine for water at 70 °C. Across all configurations, statistical analysis confirms stable, repeatable measurements. These results demonstrate that coupling commercially available RC materials with non-imaging optics provides consistent and measurable performance gains, supporting CPC-assisted RC as a scalable and retrofit-friendly strategy for urban and building energy applications while calling for longer-term experiments, durability assessments, and techno-economic analysis before deriving definitive deployment guidelines. Full article

Cool roof and green roof have been acknowledged as effective heat mitigation strategies for fighting against the urban heat island (UHI). However, empirical data in hot–humid climate are still insufficient. Experimental conventional, cool and green roofs (three types) were established to comprehensively investigate the thermal performances in Hong Kong under typical summer conditions, as retrofitting strategies for an office building. The holistic vertical thermal behavior was investigated. The comparative cooling potentials were assessed. The results reveal a “vertical thermal sequence” in peak temperatures of each substrate layer for the conventional, cool and green roofs on a sunny day. However, local reversion in the thermal sequence may occur on a rainy day. Green roof-plot C (GR_C) demonstrates the highest thermal damping effect, followed by plot B (GR_B), A (GR_A) and the cool roof (CR) in summer. On a sunny day, the thermal dampening effectiveness of the substrates in the three green roofs is consistent: drainage > soil > water reservoir > root barrier. The holistic vertical thermal profiling was constructed in a high-rise office context in Hong Kong. The diurnal temperature profiles indicate all roof systems could effectively attenuate the temperature fluctuations. The daily maximum surface temperature reduction (SDMR) was introduced for cooling potential characterization of the cool roof and green roofs with multiple vegetation types. On a sunny day, the cool roof and green roofs all showed significant cooling potential. SDMR on the concrete tile of the best performing system was GR_C (26 °C), followed by GR_B (22.4 °C), GR_A (20.7 °C) and CR (13.3 °C), respectively. The SDMR on the ceiling ranked as GR_C, GR_B, GR_A and CR, with 2.9 °C, 2.4 °C, 2.1 °C and 2.1 °C, separately. On a rainy day, the cooling effect was still present but greatly diminished. A critical insight of a “warming effect at the ceiling” of the green roof was revealed. This research offers critical insights for unlocking rooftop cooling potential, endorsing cool roof and green roof as pivotal solutions for sustainable urban environments. Full article

The building sector accounts for nearly 40% of total energy consumption in Europe, with heritage buildings posing a critical challenge due to conservation constraints. This study investigates two protected heritage sites—Palazzo Ruspoli in Cerveteri and Palazzo Vitelleschi in Tarquinia—to identify effective energy retrofit strategies integrating high-efficiency windows, HVAC and lighting systems, and photovoltaic (PV) solutions for both on-site and virtual self-consumption within Renewable Energy Communities (RECs). Energy surveys, modeling, and simulations were performed to evaluate technical, environmental, and economic impacts. The results show contrasting outcomes between the two cases: at Palazzo Vitelleschi, the combination of efficient systems and rooftop PV reduced non-renewable primary energy demand and CO₂ emissions by 73.5%, with a 10.7-year payback period; at Palazzo Ruspoli, REC-based virtual self-consumption achieved net-negative carbon emissions (−240%), a 95% reduction in non-renewable energy demand, and a 19.4-year payback period. These findings demonstrate that heritage buildings can move beyond carbon neutrality and actively offset emissions through shared renewable generation. The proposed simulation-based framework provides a replicable method to balance conservation and sustainability, supporting the decarbonization of the historical built environment. Full article

To reduce the carbon emissions of existing residential buildings while pursuing maximum cost benefits, a multi-optimization design method for the existing residential building rooftops, retrofitted by attaching the solar photovoltaic panels and thermal collectors, was proposed in the study. At first, the life cycle carbon emission and cost benefit of the retrofitted buildings were assigned as the optimization objectives, and the models of carbon emission and cost benefit were developed. Furthermore, a typical existing residential community located in the cold zone of China was selected to perform the multi-optimization based on the Grasshopper platform. Meanwhile, the laying area, laying angle, and allocation ratio of the solar photovoltaic panels and thermal collectors were selected as the design parameters. And then the best retrofitting solution suitable for the existing residential buildings was proposed. The results show that the weightings of the carbon emission of retrofitting life cycle are 42.68%, and that for the cost benefit is 57.32%. Significantly, there is a 31% reduction in carbon emissions compared to the building before retrofitting, and a 24.7% reduction in cost benefit. Full article

Integrating photovoltaic (PV) systems with green roofs presents a synergistic approach to urban sustainability. Many existing flat-roof PV installations, often east–west oriented with limited elevation, present integration challenges for green roofs and are therefore understudied. This study addresses this by investigating the microclimatic effects of retrofitting an extensive green roof beneath such an existing PV array. Over a two-year period, continuous measurements of sub-panel air temperature, relative humidity, and module surface temperature were conducted. Results show that the green roof reduced average midday sub-panel air temperatures by 1.7–2.2 °C, with peak reductions up to 8 °C during summer, while nighttime temperatures were higher above the green roof. Relative humidity increased by up to 8.1 percentage points and module surface temperatures beneath the green roof were lowered by 0.4–1.5 °C, though with greater variability. Computational fluid dynamics simulations confirmed that evaporative cooling was spatially confined beneath the panels and highlighted the influence of structural features on airflow and convective cooling. Despite limited vegetation beneath the panels, the green roof retained moisture longer than the gravel roof, resulting in particularly strong cooling effects in the days following rainfall. The study highlights the retrofitting potential for improving rooftop climates, while showing key design recommendations for enhanced system performance. Full article

Enhancing the real-world performance of sustainably designed and certified green buildings remains a significant challenge, particularly in hot climates where efforts to improve thermal comfort often conflict with energy efficiency goals. In the United Arab Emirates (UAE), even newly constructed facilities with green building certifications present opportunities for retrofitting and performance optimization. This study investigates the energy and thermal comfort performance of a LEED Gold-certified, mixed-use university campus in Dubai through a calibrated digital twin developed using IES thermal modelling software. The analysis evaluated existing sustainable design strategies alongside three retrofit energy conservation measures (ECMs): (1) improved building envelope U-values, (2) installation of additional daylight sensors, and (3) optimization of fan coil unit efficiency. Simulation results demonstrated that the three ECMs collectively achieved a total reduction of 15% in annual energy consumption. Thermal comfort was assessed using operative temperature distributions, Predicted Mean Vote (PMV), and Predicted Percentage of Dissatisfaction (PPD) metrics. While fan coil optimization yielded the highest energy savings, it led to less favorable comfort outcomes. In contrast, enhancing envelope U-values maintained indoor conditions consistently within ASHRAE-recommended comfort zones. To further support energy reduction and progress toward Net Zero targets, the study also evaluated the integration of a 228.87 kW rooftop solar photovoltaic (PV) system, which offset 8.09% of the campus’s annual energy demand. By applying data-driven thermal modelling to assess retrofit impacts on both energy performance and occupant comfort in a certified green building, this study addresses a critical gap in the literature and offers a replicable framework for advancing building performance in hot climate regions. Full article

Nearly zero-energy buildings (nZEBs) are central to global carbon reduction strategies, and Taiwan is actively promoting their adoption through building energy performance labeling, particularly in the retrofit of existing buildings. Under Taiwan’s nZEB framework, qualification requires both an A⁺ energy performance label and over 50% energy savings from retrofit technologies. This study proposes an integrated assessment framework for retrofitting small- to medium-sized office buildings into nZEBs, incorporating diagnostics, technical evaluation, policy alignment, and resource integration. A case study of a bank branch in Kaohsiung involved on-site energy monitoring and EnergyPlus V22.2 simulations to calibrate and assess the retrofit impacts. Lighting improvements and two HVAC scenarios—upgrading the existing fan coil unit (FCU) system and adopting a completely new variable refrigerant flow (VRF) system—were evaluated. The FCU and VRF scenarios reduced the energy use intensity from 141.3 to 82.9 and 72.9 kWh/m²·yr, respectively. Combined with rooftop photovoltaics and green power procurement, both scenarios met Taiwan’s nZEB criteria. The proposed framework demonstrates practical and scalable strategies for decarbonizing existing office buildings, supporting Taiwan’s 2050 net-zero target. Full article

The integration of tilted photovoltaic strings on large, flat roofs, typical of industrial and commercial buildings, raises complex design challenges, particularly regarding wind-induced loads. This study presents a comprehensive wind tunnel investigation aimed at evaluating the aerodynamic effects on rooftop PV strings under various representative configurations and the correlation between characteristic geometric parameters such as tilt angle, bottom clearance, row spacing, and wind direction. Following a literature review, a detailed 1:10 scaled model with geometric adjustment capabilities was developed and eventually tested in a boundary-layer wind tunnel. High-resolution pressure measurements were processed to derive force and moment resultants normalised by reference wind pressure. Envelopes of force/moment resultants are presented for each representative geometric configuration and for each wind exposure angle. The results present severe variations in local wind actions, particularly significant at the strings’ free ends and for oblique wind angles. The severe underestimation of local wind loads by standard codes is discussed. The findings underline the importance of detailed wind-load assessment for both new constructions and retrofits, suggesting that reliance solely on code provisions might result in unsafe designs. Full article

In the context of global decarbonization goals and increasing urban electricity demand, the green transformation of power industry buildings to enhance the utilization of renewable energy represents a significant contribution to sustainable social development. Rooftop photovoltaic (PV) systems can reduce unnecessary radiative heat gain and generate clean electricity to support this transition; however, they also alter the rooftop wind environment. Deploying rooftop PV systems requires well-planned design strategies to optimize renewable energy production while ensuring adequate natural ventilation, particularly for semi-outdoor main transformer rooms where ventilation and heat dissipation are crucial for safe substation operations. This concept was tested at a 220 kV substation in Guangzhou, China, using Computational Fluid Dynamics (CFD) and PVSYST to assess the impact of different rooftop PV systems on natural ventilation and power generation. The analysis showed that while the horizontal PV system achieved the highest energy output, it also resulted in a wind speed reduction of 13.2% or 11.8%. In contrast, the 10° symmetrical PV system offers the most balanced solution, with only a 0.6% decrease in ventilation performance but at the cost of a 13.87% reduction in PV output. The unilateral pitched PV system results in ventilation losses of less than 4%, and the power generation loss is also kept below 4%. However, this configuration may lead to increased wind loads. This approach can be developed into a practical design tool to further support the integration of PV systems in substation green retrofitting projects. Full article

Green roofs and photovoltaic (PV) roofs are important forms of roof retrofitting, and unused rural roofs provide favorable conditions for the development of green roofs and PV roofs. Here, this study proposes a new method for assessing the potential of multifunctional retrofitting of rural roofs. Firstly, rural roof types were classified into three categories based on GF-2 imagery: flat roofs, east–west pitched roofs, and north–south pitched roofs. The roof types were extracted based on the revised U-Net model, which aims to enhance the extracted features of the buildings and improve the perception of the buildings. Secondly, three types of retrofits—PV roofs, green roofs, and PV-green roofs—were designed taking into account the type, orientation, and area of the roofs. Finally, the potential electricity and carbon benefits of the different retrofit types of roofs were calculated separately, with the aim of realizing an assessment of the potential for roof retrofitting in the rural areas of Mentougou, Beijing. The results of the study showed that 35,407 (281.97 ha) roofs could be used for multifunctional retrofitting. If rural roofs are retrofitted with multifunctionality according to the methodology of this paper, they can absorb an additional 4.66 × 10⁴ kg/yr of CO₂ and increase biomass production by 0.99 × 10⁴ kg/yr compared to retrofitting only PV roofs, and they can generate an additional 34.1 GWh/yr of electricity and reduce CO₂ emissions by an additional 3.3 × 10⁷ kg/yr compared to retrofitting to both PV roofs and green roofs. The assessment methodology of this study provides decision makers with data references on the multifunctional potential of rural rooftops for retrofitting, which can optimize the use of rural rooftops, and at the same time is important for promoting the energy transition in rural areas. Full article

This study examines existing buildings in Haikou in China under tropical island climate conditions. It presents three retrofit design models for greenhouses roofs (GHR), green roofs (GR) and photovoltaic roofs (PVR). The carbon cost of each retrofit roof model is calculated in the production and transportation phases of building materials, construction, and demolition. The changes in electricity consumption, water consumption, and plant carbon reduction are coupled to calculate the carbon reduction generated by each phase of the use of the retrofitted roofs. The carbon reduction per unit area for GHR, GR and PVR over the life cycle (20 years) is then comprehensively calculated. The life cycle carbon reduction per unit area is 262.57 kg·m⁻² for GHR, 127.41 kg·m⁻² for GR and 2567.12 kg·m⁻² for PVR. Among the three retrofit methods, PVR has the greatest potential for reducing carbon emissions. The study can as a guide for implementing carbon reduction measures in tropical island areas. Domestic research on rooftop greenhouses also focuses on technology, yield, and energy consumption, mostly for northern regions with cold winters, and less research on rooftop greenhouses applied to regions with hot summers and warm winters. But domestic and foreign studies on the potential of rooftop greenhouses to reduce emissions have not yet been combined with plant cultivation of hydroelectric carbon emissions and plant carbon sequestration. Full article

Considering the ambitious climate goals defined by the European Union, the significant share of energy demand represented by buildings, the slow process of their renovation due to challenges such as a need for majority consent from residents and limited available space in dense urban areas, this study aims to foster retrofitting of energy supply systems of multi-storey apartment buildings, improving their sustainability. This entails making the transition to sustainable energy systems more socially acceptable and practical in urban contexts by proposition and demonstration of the potential of a power and heat supply system retrofit that minimises disruptions felt by residents. It integrates rooftop renewable power sources, heat storage with an electric heater, heat pumps, and existing connections to public utility networks. Furthermore, simulation results of both single- and multi-objective optimisation (performed by the genetic algorithm) for equipment selection, as well as conventional and smart control (implemented as a gradient-based optimisation) for daily scheduling, are compared, defining the main scientific contribution of the study. It is found possible to achieve a net present value of up to almost twice the annual energy expenses of the unrenovated building or self-sufficiency rate of up to 41.6% while using conventional control. These benefits can reach 2.6 times or 49.8% if the smart control is applied, demonstrating both the profitability and improved self-sufficiency achievable with the proposed approach in Latvian conditions. Full article

The present study investigates the incorporation of renewable rooftop photovoltaic systems in fully electrified residential buildings and estimates the zero-energy demand building potential in relation to the climatic data of Greece. Specifically, the aim of the analysis is to calculate the maximum possible number of stories and therefore the total building height for a complete transformation to zero-net-energy building. The energy analysis, which is conducted using the DesignBuilder software, focuses on single-floor up to seven-story buildings. The importance of the present work lies in the acknowledgment of the diversity of the Greek residential sector, the adherence to national energy policies, and the European goal of fully electrified buildings. The examined case studies are equipped with electrically driven air-to-air heat pumps serving the space heating and cooling demands and with an air-to-water heat pump covering the domestic hot water requirements. The investigated locations are the four main cities of Greece, Athens, Thessaloniki, Chania, and Kastoria, which represent the country’s four climatic categories. The conducted analysis allows for the mapping of the zero-energy building potential for the climatic data of Greece, demonstrating the possibility of striking a positive building energy balance through the integration of on-site renewable energy sources and the production of necessary electrical energy. The novelty of the present work lies in the identification of a key factor, namely, the building height, which determines the feasibility of transforming multifamily buildings into zero-energy buildings. According to the analysis results, the critical number of stories is calculated at six for Chania, five for Athens, four for Thessaloniki, and two for Kastoria. Regarding a three-story residential building, the incorporation of a renewable photovoltaic system can result in an annual surplus electricity production of 13,741 kWh (Chania), 10,424 kWh (Athens), and 6931 kWh (Thessaloniki), and a corresponding coverage of 100% (Chania), 69.0% (Athens), 38.9% (Thessaloniki) and 0% (Kastoria). Full article

Energy saving in buildings is essential as buildings’ operational energy use constitutes 30% of global energy consumption. Urban building energy modeling (UBEM) effectively understands urban energy consumption. This paper applied UBEM to assess the potential of peak demand reduction and energy saving in a mixed-use community, using 955 residential buildings, 35 office buildings and 7 hotels in Shenzhen, China, as a case study. The building type and period were collected based on the GIS dataset. Then, the baseline models were generated by the UBEM tool—AutoBPS. Five scenarios were analyzed: retrofit-window, retrofit-air conditioner (AC), retrofit-lighting, rooftop photovoltaic (PV), and demand response. The five scenarios replaced the windows, enhanced the AC, upgraded the lighting, covered 60% of the roof area with PV, and had a temperature reset from 17:00 to 23:00, respectively. The results show that using retrofit-windows is the most effective scenario for reducing peak demand at 19.09%, and PV reduces energy use intensity (EUI) best at 29.96%. Demand response is recommended when further investment is not desired. Retrofit-lighting is suggested for its low-cost, low-risk investment, with the payback period (PBP) not exceeding 4.54 years. When the investment is abundant, retrofit-windows are recommended for public buildings, while PV is recommended for residential buildings. The research might provide practical insights into energy policy formulation. Full article