• Energy Research

AbstractNowadays energy consumption of buildings in different countries comprises 20–40% of total energy use. In Malta, the building sector consumes about 35% of the total energy consumption, with hotels playing a significant role in producing carbon dioxide emissions. In this scenario and taking into consideration the EPBD goal for 2020, a review of all possible measures that can be considered to attain near or net zero-energy buildings has been made.. A case study has also been adopted to design a real new small hotel in the island of Gozo, Malta with the aim of making it a low energy building. An energy analysis software Design Builder-EnergyPlus has been used to simulate and optimise the energy use of the hotel, through improvements in the building's envelope. Polysun software has also been used to evaluate the performance of sustainable energy and high efficiency systems. A number of optimum solutions combining different systems together with improved building envelope design were then proposed to make the hotel a zero net-energy building.

Malta, as a member of the European Union (EU), has pledged to become carbon neutral by the year 2050. Concurrently, the need for thermal comfort for people within places of worship has expanded tremendously in recent years. As a result, prioritizing passive methods over mechanical air-conditioning systems in such buildings is an essential step toward protecting the macroclimate while achieving a sustainable and comfortable indoor environment. Using DesignBuilder-EnergyPlus software, this paper examines the effectiveness of selective passive measures in two free-running church buildings. Results show that certain passive measures alleviate severe high and low indoor temperatures, resulting in a more comfortable environment. Environmental control, on the other hand, present difficult conservation challenges. Historic church buildings were initially built to make use of passive design features for internal comfort, and this study shows that they outperform expectations and, in general, outperform more contemporary church structures.

This paper presents the implementation of a biomass-fuelled District Heating System (DHS), as a part of a deep energy renovation exercise to achieve a climate-resilient campus with minimum carbon dioxide emissions. The case study is carried out for the University of Valladolid, an average-sized university in Spain, with a continental weather climate. Prior to renovation, the different building blocks had a wide-ranging level of fossil fuel consumption for space heating and domestic hot water ranging between 60 and 430 kWh/m2·year. The application of this centralised heating system allows to achieve the minimum threshold for near zero-energy buildings (nZEB) of 100–120 kWh/m2, in accordance with the Spanish Standards. These values correspond to the maximum European indicators for offices in continental weather conditions. Results of this comprehensive study show that 15 out of the 19 buildings reached the nZEB target, due to the proposed strategy. The overall carbon dioxide emissions have dropped by 92.69% as compared to the original fossil-fuel powered boiler, thus bringing carbon dioxide emissions down to 1.57 kgCO2/m2·y. Therefore, it is shown that deep energy renovation strategies through renewable energy DHS have the potential of achieving nZEB for universities in continental weather conditions. Funding for open access charge: Universidad de Málaga / CBUA

Abstract The cost optimal method (COM) as applied in the Energy Performance of Buildings Directive (EPBD) uses “non-calibrated deterministic reference buildings (RBs)”. Such RBs are defined with single envelope and equipment parameter values, for which calibration with actual building stock energy performance (EP) is not undertaken. Thus, it is not possible to visualise the effect of uncertainties or diversity in the input parameters on cost-optimal level benchmarks and to verify the choice of RBs. The paper proposes an update to the COM via use of “Probabilistic Bayesian calibrated RBs” to handle uncertainties and produce more realistic cost optimal levels to support policy makers in devising effective fiscal and legal support mechanisms while facilitating harmonised EP benchmarking between MS for different building categories. The process is validated by findings from Urban Building Energy Modelling studies showing that Energy Use Intensity (EUI) distributions from “probabilistic Bayesian calibrated RBs” versus “deterministic RBs” match significantly closer to the measured EUI distributions with a resulting reduction in the Kolmogorov–Smirnov (KS) test results of up to 82% when monthly calibration was performed.

AbstractThe aim of this paper was to use Computational Fluid Dynamics (CFD) to study the effectiveness of natural ventilation through a chimney, forming part of the environmentally-friendly design features of a new brewery. Different simulations were conducted in order to provide an insight on the mode of operation of window openings, to provide the best ventilation conditions and to identify any situations that may require certain remedies.

Abstract The effects of cloudiness on solar ultraviolet irradiance recorded between May and October 2012 at Marsaxlokk, Malta, are analysed. A statistical analysis of cloudiness is carried out, with clear skies (0–2 oktas) proving to be the most frequent conditions under total and low cloud cover. Hence, the dependence of erythemal UV solar irradiance (UVER) on total and low cloud cover is evaluated. In all cases, low clouds show higher attenuation. The effects of total cloud cover and low clouds on UVER are evaluated by means of the cloud modification factor (CMF) that is defined as the ratio between the measured irradiance and the estimated irradiance under cloud-free conditions. The results show that the effect on UVER is less than on global solar irradiance and that UVER transmissivity under overcast conditions can reach 50%. The effect of cloud optical thickness (COT) on UVER under all conditions shows a clear exponential dependence. The analysis shows that for fairly thick clouds with a COT of 10, the UVER reaching the Earth’s surface is about 50% of its cloud-free value. The CMF UVER is found to decrease from 0.7 for COT = 0.5 to 0.25 for COT = 30. 10-min estimated COT from global solar irradiance are then compared with the GOME2 instrument. The correlation is found to be low. The influence of COT is studied by observing the evolution of irradiance on two cloudy days. When comparing the 10-min CMF under high COT for UVER and global irradiance, the first variable is found to be slightly higher than the second. As a consequence, changes in the ultraviolet index (UVI) due to COT effects are then described. Finally, the results obtained are compared with those from previous studies performed by different authors.

Like other islands, Malta experiences great challenges to secure its energy supply and independence. Deep renovation of buildings to nearly zero energy and addressing “smart-readiness” are widely believed to contribute to solving such challenges, while meeting the exigencies of the 2018 European Union energy performance of buildings directive (EPBD). Nearly zero energy buildings benchmarks for residential buildings in Malta have been defined using established EPBD cost-optimal methodologies, however these guidelines detailing a one-step and one benchmark definition approach neglects peak loads, building-grid interaction requirements and energy storage. To counteract these inadequacies, this research proposes an innovative multi-criteria approach adapted from ISO 52000-1:2017 standard, which supports the new EPBD requirements for optimizing comfort and addressing energy poverty. This is carried out by first optimizing adaptive comfort in “free-running mode,” before switching to mechanical space heating and cooling. When implementing this approach on a case study of an existing 40-family social housing block undergoing deep renovation, it was found that the discomfort hours have been reduced drastically, while the peak demand for the remaining discomfort hours requiring mechanical heating and cooling has been halved. Despite such positive impact of passive measures, the research has quantitatively demonstrated that given Malta’s temperate climate, such measures have lower impact on the energy rating of the building, when compared to that achieved with active and renewable energy (RE) measures. Thus, the proposed multi-tier benchmarking approach ensures that each energy efficiency measure is appropriately weighted on its own merits, rather than lumping all measures under a single benchmark indicator. With regards to smartness indicators for load matching and grid interaction, a detailed analysis using system advisor model software demonstrated that battery energy storage systems have the capacity to match the RE supply to the demand, although this approach is still far away from being cost-optimal. The research concluded that RE incentives should therefore move away from feed-in tariffs and subsidize direct energy use, storage, and load matching given their high costs. Furthermore, the cost-optimal analysis should also quantify the costs of thermal discomfort, energy poverty and grid mismatch, to ensure a holistic approach to deep renovation of buildings.

Heat pumps may be coupled to shallow-ground geothermal fields and used for the purpose of space heating and cooling of buildings. However, quite often it is not possible to locate the geothermal field in cleared grounds, especially in cities where building density is high and land has a high premium. This leads to the possibility of burying the geothermal field under the basement of new building blocks, before construction of the building. In the present work, the shaded-unshaded arrangement is numerically studied by coupling the software DesignBuilder-EnergyPlus to assess the building's energy requirement with the software FEFLOW to solve the heat transfer equation in porous media. Assuming a standard residential building block, the coupling between the two software is performed by assigning the thermal energy requirement for air conditioning, as calculated by EnergyPlus, to a flat-panel typology of ground heat exchanger simplified in a 2D FEFLOW's domain. The results show that it is necessary to opt for a dual-source heat pump (air/geothermal) system to ensure that the ground is not frozen or over-heated at peak times and to improve the overall performance of the system.