Ahorro energético en edificios mediante el almacenamiento estructural con materiales de cambio de fase.

El almacenamiento estructural con materiales de cambio de fase es una tecnología novedosa que contribuirá decididamente al ahorro energético de los edificios. Si se quiere alcanzar el objetivo de construir edificios de consumo casi nulo no son suficientes las estrategias basadas en el aislamiento y el control de la ventilación e infiltraciones, se debe recurrir a las energías renovables como sustento del bienestar térmico. La energía renovable es eficiente en sí misma pero no siempre está disponible cuando se requiere. La idea de almacenar energía puede permitir acercar la oferta y la demanda que por naturaleza están desfasadas. Los materiales de cambio de fase son una tecnología que puede ser competitiva en el acondicionamiento de los edificios. En el caso de España se tiene un gran potencial climático suficiente para hacer viable su uso siempre que se parta de un diseño técnicamente eficiente y que sea económicamente competitivo. En esta tesis se estudia el almacenamiento estructural de energía mediante elementos de cambio de fase, se analiza el material pero sobre todo la integración en el edificio. Se trata de poder predecir el comportamiento mediante modelos abriendo la posibilidad de la evaluación a través de indicadores. Si se pretende que el edificio se convierta en un captador, intercambiador y acumulador de energía se requiere que el proyectista tenga herramientas adecuadas para evaluar el funcionamiento de los sistemas. Las herramientas deben ser sencillas y utilizables pero sobre todo se requiere disponer de indicadores de eficiencia que permitan la toma de decisiones acertadas desde la fase de proyecto. En la tesis se propone un conjunto de estos indicadores que se evalúan a través de un modelo y se aplican al caso de fachadas ventiladas con PCM en su interior para demostrar la viabilidad del método. El estudio de integración se realiza en general sobre los distintos sistemas y subsistemas que conforman el edificio y que son susceptibles de incorporar estructuralmente el material de cambio de fase.Structural storage with phase change materials is a novel technology that will contribute strongly to save energy in buildings. If the objective of Nearly Zero Energy Buildings is to be achieved, the strategies based on insulation and control of ventilation and infiltration are not sufficient therefore we must turn to renewable energy in order to maintain thermal comfort. Renewable energy in itself is efficient but is not always available when required. The idea of energy storage can balance supply and demand of energy that is, by its very nature, imbalanced. The use of phase change materials is a new technology which can be competitive in the reconditioning of buildings. Spain has great potential climate conditions, enough to make phase change materials viable but only if the design of the solution is technically efficient and economically competitive. This thesis studies the structural energy storage by using phase change materials, analysing the material and mostly their integration into the building. The intention is to be able to predict their behaviour through models, opening the possibility of assessment using indicators. If the objective is that the building becomes a solar collector, heat exchanger and an energy storage system, the designer needs the adequate tools to evaluate the performance of those systems. These tools should be simple and practical but above all, efficiency indicators are needed which will facilitate the correct decisions during the design stage. Some indicators are proposed in this thesis. Indicators are assessed through a model and applied to the case of ventilated facades with PCM to demonstrate the feasibility of the proposed method. The study of integration is done on the various systems and subsystems of the building which are suitable for incorporating phase change materials

Energy impact and CO2 emissions of a building with different façade solutions

[EN]This work uses a simplified life cycle analysis (LCA) methodology to explore the impact reduction potential in the design phase in terms of primary energy and greenhouse gas emissions for a given building using several façade solutions. This is achieved through a review of several design criteria (wall characteristics, insulation level, reposition rate and component durability) and their combinations, and analizing how they relate to the selected impacts for the production and use stages in the building life cycle. Results show that both emissions and energy embedded into the building materials or the building process are of great relevance and impact of emissions is comparable to those due to the use stage. This work concludes that, for a given building, a significant impact reduction on the selected impact indicators can be achieved by a careful selection of building solutions and durability strategies (through maintenance or refurbishment) in the design phase.[ES]El artículo emplea una simplificación de la metodología del análisis de ciclo de vida (ACV) para explorar en fase de proyecto el potencial de reducción de impactos, en términos de energía primaria y emisiones de gases de efecto invernadero, para diferentes soluciones de fachada y estrategias de durabilidad. Se evalúan a nivel de edificio varias alternativas de diseño de una fachada tipo (configuración del muro, aislamiento, frecuencia de reposición y durabilidad) y se analiza su repercusión en los impactos seleccionados para las etapas de producción y uso del edificio. Se concluye la importancia de la energía y emisiones incorporadas a los materiales y procesos de construcción en los impactos totales, siendo las emisiones en esas fases comparables a las de la fase de uso. Se concluye la posibilidad de reducir significativamente los impactos mediante una selección cuidadosa de los criterios de diseño y estrategias apropiadas de durabilidad, mantenimiento y rehabilitación.Peer reviewe

Influence of Wood Properties and Building Construction on Energy Demand, Thermal Comfort and Start-Up Lag Time of Radiant Floor Heating Systems

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 m(2)K/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 m(2)K/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 m(2)K/W. The suggestion is that the aforementioned value, presently deemed the maximum admissible thermal resistance, may need to be revised

Effect of Wood Properties and Building Construction on Thermal Performance of Radiant Floor Heating Worldwide

Due to its relatively lower thermal conductivity, the suitability of wood is called into question when selecting the flooring material best suited to radiant heating systems. The European standard EN 1264 considers floorings with a thermal resistance over 0.15 m2 K/W to be out of scope. This belief was partially disproved in a previous article that studied wooden floors for Madrid’s climate. However, the effect of climate still needs to be addressed. The present study extends the previous research to worldwide climates and aimed to answer the following questions: (1) Do the lowest thermal conductivity woods present good thermal performance when used in radiant floors? (2) Should the flooring have a maximum thermal resistance value? (3) Is the standard thermal resistance limit of 0.15 m2 K/W objectively justified? And (4) Do the answers of the preceding questions depend on the climate and the construction characteristics? To answer these questions, 28 cities were selected according to the Köppen–Geiger climate classification. In each city, 216 different dwellings were simulated with 60 wood floorings and one of low thermal resistance as a reference, comprising a total of 368,928 cases. Thermal performance was evaluated in terms of three parameters: energy demand, thermal comfort, and start-up lag time. Consequently, the answers to the previous questions were: (1) The lowest thermal conductivity woods can be used efficiently worldwide in radiant floor heating systems with start-up lag times close to that of the reference flooring; (2) There is no limit value for thermal resistance for floorings that can be applied to all dwellings and climates; (3) No objective justification was found for establishing a thermal resistance limit for flooring of 0.15 m2 K/W; and (4) Climate and construction characteristics can play an important role in the correct selection of flooring properties, especially in severe winters and dwellings with the greatest outdoor-exposed envelope and the worst insulation

Evaporative Mist Cooling as Heat Dissipation Technique: Experimental Assessment and Modelling

The severity of extreme weather conditions brought on by climate change are conditioning quality of life, economic development, and well-being in today’s cities. Conventional measures have been shown to be insu cient for tackling climate change and must be supplemented with ecofriendly approaches. Hence, the scientific community’s endeavor to develop natural cooling techniques that lower energy consumption while delivering satisfactory comfort levels. For its simplicity and low cost, evaporative cooling has gained in popularity in recent years. The substantial cooling power to be drawn from evaporative mist cooling, makes it an attractive alternative to conventional systems. Research conducted to date on the technique has focused on producing cold air, whilst cooling the water involved has been neither assessed nor experimentally validated. No readily applicable simplified model for the system able to use operating parameters as input variables has been defined either. The present study consequently aimed to experimentally assess the cooling power of the evaporation of sprayed water and experimentally validate a simplified model to assess and design such systems. The findings confirmed the cooling power of the technique, with declines in water temperature of up to 6 C, and with it the promise a orded by this natural air conditioning method. Finally, simplified model developed allows to evaluate this technique like a conventional system for producing fresh water.Urban Innovation Actions by the CartujaQanat UIA03-30

Design of the Refurbishment of Historic Buildings with a Cost-Optimal Methodology: A Case Study

The transformation of existing buildings into Near Zero Energy Buildings or even positive energy buildings remains a major challenge. In particular, historic buildings are an important cultural heritage that, in most cases, may be rehabilitated and reused for new purposes. However, achieving higher e ciencies in those buildings presents many di culties, since there is a need to preserve aesthetic values and minimize impact on the buildings’ initial construction. In this work, a roadmap that allows rehabilitating a building from the eighteenth century is developed, turning it into a landmark building, to be used as a museum in the near future. The procedure is based on 3D models using REVIT software and detailed energy simulations supported by a cost-optimal methodology. The results reveal how conventional methodologies shown in the literature may improve the energy performance of the buildings during the heating regime, but performance may deteriorate during the cooling season. For that reason, the present study includes the design of a night ventilation system which allows not only solving this problem but also to reducing the cooling demands by more than 43% with little additional costs. In conclusion, historic buildings (which traditionally have a high thermal mass) have increased thermal storage potential by using the structures of the buildings themselves as well as passive cooling techniques

Systematic Simplified Simulation Methodology for Deep Energy Retrofitting Towards Nze Targets Using Life Cycle Energy Assessment

The reduction of energy consumption in the residential sector presents substantial potential through the implementation of energy e ciency improvement measures. Current trends involve the use of simulation tools which obtain the buildings’ energy performance to support the development of possible solutions to help reduce energy consumption. However, simulation tools demand considerable amounts of data regarding the buildings’ geometry, construction, and frequency of use. Additionally, the measured values tend to be di erent from the estimated values obtained with the use of energy simulation programs, an issue known as the ‘performance gap’. The proposed methodology provides a solution for both of the aforementioned problems, since the amount of data needed is considerably reduced and the results are calibrated using measured values. This new approach allows to find an optimal retrofitting project by life cycle energy assessment, in terms of cost and energy savings, for individual buildings as well as several blocks of buildings. Furthermore, the potential for implementation of the methodology is proven by obtaining a comprehensive energy rehabilitation plan for a residential building. The developed methodology provides highly accurate estimates of energy savings, directly linked to the buildings’ real energy needs, reducing the di erence between the consumption measured and the predictions

Experimental analysis of atmospheric heat sinks as heat dissipators

Artículo premiado ETSI 1er trimestre 2020Overheating, a general problem both in urban spaces and inside buildings, calls for the deployment of passive cooling techniques to reduce energy consumption, protect the environment and institute satisfactory comfort levels. A key factor in such techniques is the capitalisation on the cooling potential of natural heat sinks. The sky, one such sink, has essentially limitless cooling power. In addition, its temperature on fair nights is lower than that of other environmental sinks (ground and air). The sky's promise in that respect prompted this exploration of the potential of nocturnal radiation cooling. A review of the state of the art revealed that in all the radiative dissipators developed and tested to date the dissipation fluid (water) transferred heat indirectly to the heat sink (the sky) by circulating water inside solar collector pipes. The highest values reported for maximum dissipation power were on the order of 100 W/m2. The present study aimed to asses night time dissipation power in a dual system in which water circulated either inside pipes or flowed down the outer surface of the collector. The two modes, one involving in-pipe circulation and the other outer surface downflow, were compared experimentally, for whereas the former has been analysed and assessed by earlier researchers, the latter has not. The empirical findings verified that downflow setups enhanced cooling, delivering up to five-fold the dissipation power obtained with the conventional arrangement.Ministerio de Economía y Competitividad BIA2016-77431-C2-2-RFondos FEDER UIA03-30

Adaptative Cover to Achieve Thermal Comfort in Open Spaces of Buildings: Experimental Assessment and Modelling

The global need for healthy and safe open spaces faces continuous temperature rise due to the heat island phenomenon and climate change. This problem requires new strategies for improving the habitability of open spaces (indoor and outdoor conditions in buildings). These techniques include reducing solar radiation, reducing the temperature of surrounding surfaces, and reducing the air temperature. The radiant solutions are essential for outdoor comfort, both in summer and in winter. They are easy to integrate into open spaces. This study explores a new concept of radiant solutions adapted for outdoor spaces. The solution was evaluated in a test cell to obtain its thermal behaviour in different operation conditions. Solutions were optimised for operating in a cooling regimen since it has been identified that the demands for comfort in open spaces in hot climates during the most severe summer months are more pronounced. Experimental results have allowed getting an inverse model to analyse the thermal behaviour of the solution. The inverse model achieved high precision in its estimations. Also, it facilitated knowing the radiant and convective effects. Only the radiant heat flux is relevant in open spaces with a low level of air confinement. Finally, the discussion describes the application of the proposed model. The model allows the replicability of the solution—creating new designs (integration) or evaluating into different operating conditions of the system. This discussion demonstrates the high level of knowledge acquired in the characterisation of the solution studied.e European Commission / European Regional Development Funds (ERDF) UIA03-301-CartujaQanat of Urban Innovative Action (UIA

CartujaQanat: Recovering the street life in a climate changing world. Bioclimatic lattices and confinement of air in exterior conditions

Article number 03205