Search

At present, the energy used for air conditioning in buildings in urban areas accounts for over 36% of total global energy consumption. Energy efficiency has become a critical factor in the urban planning of cities worldwide. Courtyard buildings in hot cities are a prime example of the approach used in traditional vernacular architecture to mitigate the effects of extreme weather. However, given the challenge of guaranteeing accurate modelling of microclimates within these courtyards, their impact on energy demand in buildings has been routinely overlooked by energy certification tools. This work examines three empirical case studies selected in Seville city (Spain), where temperatures during the summer months are extreme. The case studies selected display distinct geometric variations, and the primary objective of the research is to assess the influence of this geometric factor on the cooling energy demand of the building indoors. To achieve this, a validated methodology combining experimental and numerical data was implemented to evaluate the energy performance of buildings with courtyards. Different simulations were conducted to detect the impact of individual courtyard features. The results show a reduction in cooling demand of 8–18% depending on the geometry of the courtyard. Analysis was also carried out on the influence of the floor level and the orientation of adjacent rooms, revealing differences of 15% and 22%, respectively. The main conclusion of the research is that the use of courtyards as functional devices, paying particular attention to their geometry, is a key factor in the cooling energy demand of buildings.

The objective of this paper is to present the potential of daytime radiative cooling materials as a strategy to mitigate the Urban Heat Island effect. To evaluate the cooling potential of daytime radiative cooling materials, 15 theoretical materials and seven existing materials were simulated: two radiative cooling materials, a coolmaterial, two white paints, a thermochromic paint and a construction material. The novelty of this study is that it shows that the optimal spectral characteristics of radiative cooling materials depending on the climate conditions and the type of application. A sensitivity analysis was performed to evaluate the impact of each wavelength emissivity on the ability to achieve sub-ambient radiative cooling. The sensitivity analysis comprised a total of 90 theoretical materials with 15 different wavelength combinations and 6 emissivity values. The heat transfer model, which includes conduction, convection, and radiation, was developed using a spectrally-selective sky model. Two conditions were considered: a very conductive surface and a highly insulated one. All the materials were simulated in two cities that suffer from the Urban Heat Island effect—Phoenix and Sydney. The mean surface temperature reduction achieved was 5.30 °C in Phoenix and 4.21 °C in Sydney. The results presented suggest that the type of application (active or passive) is a determinant factor in the design of radiative cooling materials. Modifying the spectra of the materials led to a substantial change in the cooling potential. A material that performs well in a dry climate as a passive solution could perform poorly as an active solution.

This study presents the results of a numerical and experimental study of the position of the baffles in a solar air heater in order to improve its thermal and hydraulic performance. The numerical study was performed on four cases corresponding to different placements of baffles with Reynolds numbers ranging from 2370 to 8340. The experimental model of the solar air heater was designed, manufactured and used for the validation of the numerical model. The new baffle placements show that effective thermo-hydraulic performance is not just a function of the shape or changes in the geometric parameters of the baffles. The correct placement of baffles dramatically improves the thermo-hydraulic performance of solar air heaters. The effect of baffle positions on local convective heat transfer coefficients has been discussed. The optimum thermo-hydraulic performance factor is achieved in the case where the baffles are located in the first part of air channel which occupies 50% of the solar air heater.

Buildings are known to be responsible for about a third of energy consumption in developed countries. This situation, together with the fact that the existing building stock is being renovated at a very slow pace, makes it crucial to focus on the energy retrofitting of buildings as the only way to reduce their contribution to these energy consumptions and the consequences derived from them in terms of pollution and climate change. The same level of insulation and the same type of windows is usually proposed for all dwellings in a building block. This article shows that since the improvements required by each dwelling in the same block are different, the proposed solution must also be different. The methodology is proposed for a practical case consisting of an apartment block in C&aacute, diz, a demonstration building of the European RECO2ST project. To achieve the optimum solution for each case, a multi-objective optimization problem is solved: to minimize the annual heating demand of the building and the standard deviation of the annual demand of the different dwellings. Thanks to the use of the proposed methodology, it is possible to bring the building to a Nearly Zero Energy Building (NZEB) level, while avoiding excessive insulation that causes overheating in summer.

Sustainable passive design strategies can reduce the energy consumption of buildings. In this regard, inner courtyards act as microclimate modifiers that enhance the perception of comfort in the surrounding environment. The present study, through a pooled analysis of experimental and numerical data, intends to assess the beneficial effect that the courtyards have in reducing the energy consumption of the buildings, especially for cooling demand. Accordingly, a new methodology allowing the use of different experimental data for facades and courtyards in software tools for the assessment of the real energy performance of buildings with courtyards is proposed. Besides, a detailed example of the application of the proposed methodology is performed for two scenarios simultaneously: a case study (considering the courtyard effect on the air temperature) and a reference one (without considering this effect). From the results, it is found that the courtyard reduces the demand for cooling in the spaces bordering it. As expected, the magnitude of the cooling demand reduction is correlated to the floor level, is increased at lower floors in the courtyard building. This relative reduction is up to 11%, being, for the case study analyzed, an average reduction of 7%., This work was supported by the Ministerio de Ciencia, Innovacion y Universidades, National Government of Spain, research projects MTM 2015-64577-C2-2-R, RTI 2018-093521-BC33 and pre-doctoral contract granted to Eduardo Diz Mellado (FPU 18/04783) . The authors gratefully acknowledge AEMET (State Meteorological Agency) for the data supplied

Radiant floor heating is becoming increasingly popular in cold climates because it delivers higher comfort levels more efficiently than conventional systems. Wood is one of the surface coverings most frequently used in radiant flooring, despite the widely held belief that in terms of thermal performance it is no match for higher conductivity materials if a high energy performance is intended. Given that the highest admissible thermal resistance for flooring finishes or coverings is generally accepted to be 0.15 m2K/W, wood would appear to be a scantly appropriate choice. Nonetheless, the evaluation of the thermal performance of wooden radiant floor heating systems in conjunction with the building in terms of energy demand, thermal comfort, and start-up period, has been insufficiently explored in research. This has led to the present knowledge gap around its potential to deliver lower energy consumption and higher thermal comfort than high-thermal-conductivity materials, depending on building characteristics. This article studies the thermal performance of wood radiant floors in terms of three parameters: energy demand, thermal comfort, and start-up lag time, analysing the effect of wood properties in conjunction with building construction on each. An experimentally validated radiant floor model was coupled to a simplified building thermal model to simulate the performance of 60 wood coverings and one reference granite covering in 216 urban dwellings differing in construction features. The average energy demand was observed to be lower in the wood than in the granite coverings in 25% of the dwellings simulated. Similarly, on average, wood lagged behind granite in thermal comfort by less than 1 h/day in 50% of the dwellings. The energy demand was minimised in a significant 18% and thermal comfort maximised in 14% of the simulations at the lowest thermal conductivity value. The vast majority of the wooden floors lengthened the start-up lag time relative to granite in only 30 min or less in all the dwellings. Wood flooring with the highest thermal resistance (even over the 0.15 m2K/W cited in standard EN 1264-2) did not significantly affect the energy demand or thermal comfort. On average, wood flooring lowered energy demand by 6.4% and daily hours of thermal comfort by a mere 1.6% relative to granite coverings. The findings showed that wood-finished flooring may deliver comparable or, in some cases, higher thermal performance than high-conductivity material coverings, even when their thermal resistance is over 0.15 m2K/W. The suggestion is that the aforementioned value, presently deemed the maximum admissible thermal resistance, may need to be revised.

Educational buildings in Europe account for around 20% of the entire non-residential floor space where good indoor comfort and air quality are essential for correct educational development. Directive 2010/31/UE upholds that the public administration should promote the transformation of its buildings towards Net Zero Energy Buildings. In Spain, it is particularly important to act on the existing building stock since the construction of new buildings has been considerably reduced as a result of the bursting of the property bubble following the frenzied building activity over the last few decades. This article proposes a method to define and assess strategies to achieve NZEB in university buildings based on student comfort analysis under real conditions. A questionnaire and monitoring campaign was conducted in a typical spring week in the Architecture Faculty in San Sebastian (Spain). User preferences have been considered as an energy saving opportunity. The analysis revealed that students prefer lower indoor temperatures (20–22.5 °C) than stated by theoretical comfort models. This was the starting point to analyze in detail strategies to reduce the energy consumption of the building and above all, to prioritize these strategies by impact and significance. The principal measures that make it possible to achieve comfort conditions work together with energy saving strategies, which can be achieved through effective interventions in the building. Retrofitting strategies for the winter period are: eliminating thermal bridges, using air-to-air heat recovery systems and improving the windows in the north facade of the building. The results show a potential energy saving of up to 62% and a reduction of two months in the heating period for the Faculty of Architecture. Furthermore, overheating problems reported by users in summer and shoulder seasons could be solved by using 4 ACH day and night time ventilative cooling, avoiding the installation of air-conditioning systems and all the associated environmental impacts. Finally, acting on the existing building stock implies necessarily understanding user needs in order to define most adequate energy saving strategies.

Night ventilation has been applied successfully to many passively-cooled or low-energy office buildings. This paper analyses the thermal comfort achievable in office buildings in Spain according to European standard EN 15251:2007. Furthermore, the comfort level is evaluated using the Degree Hours (DH) criteria and the maximum indoor temperature. Considering the high interest of architects and engineers in the evaluation of optimal comfort condition as a function of building typology (8 typologies), glazing ratio (30% and 60%) and climate (12 different Climate Zones), a total of 192 different study cases were simulated. For every case, an optimal air change per hour (ac/h) that can range from 1 to 50 ac/h was then determined. The research shows that passive night ventilation should be considered as an effective strategy for all Spanish Climates to reduce cooling demand in buildings with high daily internal gains (i.e. office buildings), improving comfort conditions and flattening peak temperatures.

The use of night cooling ventilation in addition of phase change materials (PCMs) is a very powerful strategy for reducing the cooling demand of buildings. Nevertheless, there are inherent drawbacks in the way things have been doing so far: (a) The limited area of contact between PCM and the air; (b) the very low convective heat transfer coefficients which prevents the use of significant amounts of PCM and (c) the very low utilization factor of the cool stored due to the large phase shift between the time when cool is stored and time when it is required by the building. In this paper, we present innovative solutions using PCM to overcome the above situation. Compared with existing solutions, innovative solutions proposed, increase the contact area between PCM and air by a factor of approximately 3.6, increase the convective heat transfer coefficient significantly, and improve the utilization factor due to the inclusion of active control systems which allow the cold stored be actually used when required.

This paper analyses the energy efficiency of a Ventilated Active Façade –VAF– applied to office buildings in Spain to reduce heating demand. This façade system consists of an outer layer element of 2 mm galvanized steel panels and a 3 cm air cavity where the ventilation air is preheated in winter and exhausted in summer. After defining 8 typical office typologies in Spain, 192 study cases are obtained where different parameters like the percentage of glass in façade, the orientation and the climatic zone of the buildings are considered. The energy demand of all these study cases is obtained using the official simulation tool of the Spanish Technical Building Regulation – CTE called LIDER. The results, in terms of reduction of heating demand, are presented in comparison with the minimum energetic requirements of CTE., En este artículo se analiza la eficiencia energética de una Fachada Ventilada Activa –FVA– aplicada a edificios de oficinas en España para reducir la demanda de calefacción. El sistema de fachada consiste en una hoja exterior de 2 mm de acero galvanizado y una cavidad de 3 cm donde el aire de ventilación es precalentado en invierno y extraído en verano. Tras definir 8 tipologías típicas, se han obtenido 192 casos de estudio en los que se consideran diferentes parámetros: la superficie acristalada, la orientación y la zona climática. El cálculo de la demanda energética de los casos de estudio ha sido llevado a cabo mediante el programa LIDER, el método general del Código Técnico de la Edificación – CTE. Los resultados obtenidos en términos de reducción de la demanda de calefacción, se muestran comparados con los mínimos requerimientos exigidos en el CTE.

1st International Conference on Solar Heating and Coolingfor Buildings and Industry (SHC 2012) The paper investigates experimentally the thermal performance of a ventilated double skin facade (DSF) with phase change material (PCM) in its air channel, during the heating season in the Mediterranean climate. Two identical house-like cubicles located in Puigverd de Lleida (Spain) were monitored during winter 2012, and in one of them, a ventilated facade with PCM was located in the south wall. The ventilated facade can operate under mechanical or natural ventilation mode and its thermal control depends on the weather conditions and the energetic demand of the building. The experimental results conclude that even though the use of the ventilated facade with PCM improves significantly the thermal behaviour of the whole building (working as a heat supplier in free floating tests, and reducing significantly the electrical consumption of the HVAC systems), these improvements might be increased if a thermal control is used. This work was supported by the “Corporación Tecnológica de Andalucía” by means of the project “MECLIDE-Soluciones estructurales con materiales especiales para la climatización diferida de edificios” with the colaboration of DETEA. The work was partially funded by the Spanish government (ENE2011-28269-C03-02) and the European Union (COST Action COST TU0802), and in collaboration with DETEA. The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2009 SGR 534).

This paper analyses the energy efficiency of a Ventilated Active Facade (VAF) applied to office buildings in Spain in comparison with conventional facades that comply with the minimum energy requirements of the Spanish Technical Building Regulation (Codigo Tecnico de la Edificacion – CTE). The analysis considers the climatic diversity of the 12 climatic zones of Spain. The studied VAF consists of an outer layer element of 2 mm galvanized steel panels and a 3 cm air cavity through which the ventilation air is preheated in winter and exhausted in summer. After defining 8 typical office typologies in Spain, 192 study cases are obtained where different parameters including the percentage of glass in the facade, and the orientation and the climatic zone of the buildings were considered. The energy demand of all these study cases was obtained using the official simulation tool of the CTE called LIDER.

It has been found that, among the tools and methods available for the energy calculation of double envelope elements, there are some debatable aspects such as: the selection of correlations for calculating the convective heat transfer coefficient and the procedure for calculating the temperature of the air layer. In addition, the validation of some models only refers to specific cases or no information is available whether or not a validation has been performed. This paper presents a transient model for the energy calculation of double envelope elements, using correlations for the calculations of the convective heat transfer coefficients specifically developed for this type of element. For validation, information reported by other authors has been used. This model can be applied to those elements with an opaque or semitransparent exterior envelope (usually glazing) of negligible thermal inertia, an air layer thickness less than 0.1 m, and an opaque interior envelope (usually a massive wall) with o...

The European and International Standard UNE-EN ISO 13790 presents a set of calculation methods for the evaluation and design of energy and thermal performance of buildings. These methods have diverse range of details for calculating the energy use of heating and cooling in different building zones, as well as for calculating the heat transfer and solar heat gains of special elements, such as ventilated solar walls (Trombe walls). In this article, the authors have revised the aforementioned document in order to check the proposed mathematical models and their implementation within Mediterranean climates. This assessment pinpoints the existence of some errors in the equations provided in EN ISO 13790 under steady state conditions. Concurrently, the corrected equations are shown and new correlations are proposed for the ratios δ and ω which are more suitable for Mediterranean climates.

Passive cooling techniques such as night time cross ventilation can potentially provide substantialcooling energy savings in warm climates. The efficiency of night cooling ventilation is determined by three main factors: the external airflow rate in the room, the flow pattern and the thermal mass distribution. The aim of this paper is to analyse the effect of the enclosure shape and the situation of inlet/outlet openings on the total cooling energy stored in the structure. This analysis presents a comprehensive sample of typologies to generate guidelines which can help the designer with the distribution of the thermal mass and inlet/outlet openings in the enclosure. The approach combines a theoretical analysis which characterizes the enclosure charge/discharge time constants and storage efficiencies with simulation studies based on computational fluid dynamics software (CFD).

Assessing the performance or energy efficiency of a single construction element by itself is often a futile exercise. That is not the case, however, when an element is designed, among others, to improve building energy performance by harnessing renewable energy in a process that requires a source of external energy. Harnessing renewable energy is acquiring growing interest in Mediterranean climates as a strategy for reducing the energy consumed by buildings. When such reduction is oriented to lowering demand, the strategy consists in reducing the building's energy needs with the use of construction elements able to passively absorb, dissipate, or accumulate energy. When reduction is pursued through M&E services, renewable energy enhances building performance. The efficiency of construction systems that use renewable energy but require a supplementary power supply to operate can be assessed by likening these systems to regenerative heat exchangers built into the building. The indicators needed for this purpose are particularly useful for designers, for they can be used to compare the efficiency or performance to deliver an optimal design for each building. This article proposes a series of indicators developed to that end and describes their application to façades bearing phase change materials (PCMs). © 2015 by the authors., The present paper draws from some of the findings of a project entitled “MECLIDE-Soluciones estructurales con materiales especiales para la climatización diferida de edificios” (structural solutions with special materials for deferred environmental control in buildings) co-funded by Corporación Tecnológica de Andalucía and DETEA. Luisa F. Cabeza would like to thank the Catalan Government for the quality accreditation given to her research group (2014 SGR 123)., We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).

The aim of this article is to test experimentally the thermal performance of a ventilated double skin facade (DSF) with phase change material (PCM) in its air channel, during the heating season in the Mediterranean climate. Two identical house-like cubicles located in Puigverd de Lleida (Spain) were monitored during winter 2012, and in one of them, a ventilated facade with PCM was located in the south wall. This ventilated facade can operate under mechanical or natural ventilation mode and its thermal control depends on the weather conditions and the energetic demand of the building. Hence, three different tests were performed: free floating, controlled temperature and demand profile conditions. The experimental results conclude that the use of the ventilated facade with PCM improves significantly the thermal behaviour of the whole building (working as a heat supplier in free floating tests and reducing significantly the electrical consumption of the HVAC systems). However, these improvements might be increased if thermal control is used. Moreover, the measured electrical energy consumption of the heat pumps and fans indicates that the use of mechanical ventilation in this system is not justified; unless a fast heating supply is needed. This work was supported by the “Corporacion Tecnologica de Andalucia” by means of the project “MECLIDE-Soluciones estructurales con materiales especiales para la climatizacion diferida de edificios” with the collaboration of DETEA. The work partially funded by the Spanish government (ENE2011-28269-C03-02 and ULLE10-4E-1305) and the European Union (COST Action COST TU0802). The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2009 SGR 534).

A new type of ventilated facade (VF) with macro-encapsulated phase change material (PCM) in its air cavity is presented in this paper. The thermal performance of this special building envelope is experimentally tested to analyze its potential in reducing the cooling demand during the summer season in the Continental Mediterranean climate. Two identical house-like cubicles located in Puigverd de Lleida (Spain) were monitored during summer 2012, and in one of them, a ventilated facade with PCM was located in the south wall. Six automatized gates were installed at the different openings of the channel in order to control the operational mode of the facade. This versatility allows the system to be used as a cold storage unit, as an overheating protection system or as a night free cooling application. The experimental results point out the night free cooling effect as the most promising operational sequence to reduce the cooling load of the cubicle. On the other hand, the thermal resistance of the outer skin of the facade must be increased; otherwise the cold storage system cannot be used efficiently.