Estudio experimental y numérico de sistemas híbridos de climatización activados a baja temperatura basados en ruedas desecantes y enfriadores evaporativos indirectos

El tratamiento de aire en edificios con altas cargas latentes habitualmente requiere un alto coste energético para satisfacer las necesidades de confort térmico de los usuarios. Piscinas climatizadas o spas son algunos ejemplos de este tipo de edificios, los cuales tienen altas ganancias latentes internas, debido a la gran cantidad de agua evaporada en las áreas húmedas. Excesiva humedad del aire podría causar disconfort para los ocupantes y problemas relacionados a la calidad del aire interior de los edificios, debido a hongos y podredumbre. Los sistemas de climatización convencionales, basados en unidades de expansión directa, son ampliamente usados en la deshumectación del aire. Sin embargo, los sistemas de climatización convencionales presentan algunas limitaciones en el tratamiento combinado de las cargas sensibles y latentes. Estos sistemas usualmente solo controlan las cargas sensibles, temperatura del aire, o las cargas latentes, humedad del aire, pero no ambas cargas. Además, los caudales de aire de impulsión requeridos por los sistemas de climatización convencionales a veces son muy altos, con el fin de obtener altas capacidades desecantes. Excesivo caudal de aire también puede causar disconfort a los ocupantes. Los sistemas de climatización híbridos compuestos de ruedas desecantes y enfriadores evaporadores indirectos podrían ser una alternativa a los sistemas convencionales, debido a su alta capacidad desecante y de enfriamiento, respectivamente. El objetivo principal de esta tesis fue analizar experimentalmente y numéricamente el rendimiento de un novedoso sistema de climatización híbrido activado a baja temperatura y basado en ruedas desecantes y enfriadores evaporativos indirectos, para su uso en pequeños edificios con altas cargas latentes. En primer lugar, se analizaron experimentalmente una rueda desecante y un enfriador evaporativo indirecto, donde se obtuvieron las variables influyentes sobre los dispositivos fueron obtenidas y diversos modelos simplificados empíricos fueron ajustados. A continuación, se desarrolló una estrategia de control del calor sensible y latente, con el objetivo de controlar independientemente la temperatura y humedad del aire de impulsión. Un desacoplamiento de la temperatura y humedad del aire de impulsión pudo ser obtenido cuando el caudal del aire de proceso y la temperatura del aire de regeneración en la rueda desecante, y el caudal de agua en el enfriador evaporativo indirecto fueron variados. Finalmente, se analizó un novedoso sistema de climatización híbrido activado a baja temperatura y basado en ruedas desecantes y enfriadores evaporativos indirectos, y se comparó con un sistema de climatización convencional. Ambos sistemas de climatización fueron diseñados para servir aire en un pequeño edificio con altas cargas latentes, tales como spas. Se realizaron diversas simulaciones energéticas anuales para diferentes condiciones climáticas, las cuales estuvieron basadas en los modelos simplificados experimentales de la rueda desecante y el enfriador evaporativo indirecto., analizando la eficiencia energética de cada sistema de climatización. El sistema de climatización híbrido alcanzó mayor eficiencia energética que el sistema de climatización convencional cuando ambos sistemas servían aire a un pequeño edificio con altas cargas latentes, independientemente de las condiciones climáticas. Además, el sistema de climatización híbrido controló adecuadamente las cargas sensibles y latentes del edificio, usando reducidos caudales de aire de impulsión. Por lo tanto, esos resultados sugieren que el sistema de climatización híbrido podría ser una seria alternativa a los sistemas de climatización convencional para tratar aire en pequeños edificios con altas cargas latentes y donde reducidos caudales de aire de impulsión son requeridos.Air handling in buildings with high latent loads usually requires a high-energy cost to satisfy the user’s thermal comfort needs. Indoor swimming pools or spas are some examples of this type of buildings, which have high internal latent gains, due to the great amount of evaporated water from the wet areas. Excessive air humidity can cause discomfort for the occupants and problems related to the indoor air quality of the building due to fungus and rot. Conventional HVAC systems based on direct expansion units are widely used in dehumidifying air. However, conventional HVAC systems present some limitations in the combined treatment of sensible and latent loads. These systems usually only control sensible loads, air temperature, or latent loads, air humidity, but not both loads. Moreover, the supply air flow rates required by conventional HVAC systems are sometimes very high, in order to obtain high desiccant capacities. Excessive air flow rate can also cause discomfort to the occupants. Hybrid HVAC systems composed of desiccant wheels and indirect evaporative coolers could be an alternative to conventional HVAC systems, due to their high desiccant and cooling capacity, respectively. The main objective of this thesis was to analyse experimentally and numerically the performance of a novel hybrid HVAC system activated at low temperature based on desiccant wheels and indirect evaporative coolers for use in small buildings with high latent load. Firstly, a desiccant wheel and an indirect evaporative cooler were analysed experimentally, where the influence input variables on the devices were obtained and several empirical simplified models were fitted. Then, a sensible and latent heat control strategy was developed in order to independently control the supply air temperature and humidity ratio. A decoupling of the supply air temperature and humidity ratio can be obtained when the process air flow rate and air regeneration temperature in the desiccant wheel, and the water flow rate in the indirect evaporative cooler were varied. Finally, a novel hybrid HVAC system activated at low temperature based on desiccant wheels and indirect evaporative coolers was analysed and compared to a conventional HVAC system. Both HVAC systems were designed to serve air in a small building with high latent loads, such as spas. Several annual energy simulations for different climatic conditions were performed, which were based on the experimentally simplified models of the desiccant wheel and the indirect evaporative cooler, analysing energy efficiency of each HVAC system. The hybrid HVAC system achieved higher energy efficiency than the conventional HVAC system when both HVAC systems served air to a small building with high latent loads, regardless of the climatic conditions. Furthermore, the hybrid HVAC system suitably controlled the sensible and latent loads of the building, using reduced supply air flow rates. Therefore, these results suggest that the proposed hybrid HVAC system could be a serious alternative to conventional HVAC systems to handle air in small buildings with high latent loads and where reduced supply air flow rates are required

Experimental study of overheating of an unglazed transpired collector façade under southern European summer conditions for four modes of operation

The use of unglazed transpired collector (UTC) façades for air preheating in buildings has been proved to be an energy saving solution for refurbishing old buildings. However, not all climates are appropriate for the installation of this type of façade, and in some cases their benefits in winter can be counterbalanced by the negative effects during summer. There is a risk of overheating and façade cooling load increase if the system is not operated appropriately in summer. In this study, a UTC façade cooling load increase was measured in real weather conditions in four different operating modes. Ambient temperature and solar radiation values were monitored. Surface and air temperatures were measured in the different layers, and the heat flux through the test cell wall was registered in two cases, both with and without UTC. The four operation modes combined mechanical or natural ventilation and air flow direction. Results showed that not ventilating the façade or using natural ventilation increased the façade cooling load by around 45%, whereas outdoor mechanical ventilation produced an increase of 23%. Ventilating with indoor air reduced heat transfer compared to a non-UTC façade but only when it is integrated into an existing ventilation system. Cooling load increase due to overheating in the UTC façade was low in all four modes of operation. UTC façades must be integrated into the building ventilation system to avoid a cooling load increase during summer, or they must be ventilated with outdoor air if there is no ventilation system to reduce the impact of overheating

First and second order simplified models for the performance evaluation of low temperature activated desiccant wheels

Hybrid systems with a desiccant wheel, DW, are an alternative to heating, ventilation and air conditioning, HVAC, commonly used systems for dehumidification and humidity control in rooms with high latent loads. Currently, the experimental methodology used to study the behaviour of a DW requires a high number of tests. The aim of this study is to obtain a DW empirical model which accurately represents the behaviour of a DW activated at low temperature, values below 60 °C, by conducting a reduced number of experimental tests. For this study, the statistical Design of Experiments technique, DOE, is used. The proposed models can be used to predict the influence of the inlet process air and inlet regeneration air, on the air process outlet temperature and humidity ratio. The accuracy obtained of the experimental models is more than acceptable, with R2 values greater than 97.4% for outlet temperature and 95.1% for outlet humidity ratio. The first order model was considered to be a good option due to the balance between accuracy and the low number of experimental tests required. However, the second order model allowed a deeper understanding of the behaviour of the air outlet conditions in the DW

Energy saving potential of a hybrid HVAC system with a desiccant wheel activated at low temperatures and an indirect evaporative cooler in handling air in buildings with high latent loads

Air handling in buildings with high latent loads usually requires a high-energy cost to satisfy the user’s thermal comfort needs. Hybrid systems composed of desiccant wheels, DW, and indirect evaporative coolers, IEC, could be an alternative to direct expansion conventional systems, DX systems. The main objective of this work was to determine the annual energy consumption of a hybrid system with a DW activated at low temperatures and an IEC, DW-IEC system, compared to a DX system to serve air in a small building with high latent loads, such as spas. Several annual energy simulations for 6 climate zones were performed, analysing electric energy consumption, seasonal mean coefficient of performance, SCOP, and energy consumption per unit of dehumidified water, Econs, of each system. The simulations were based on experimentally validated models.The annual energy consumption of the DW-IEC system was lower than that of the DX system for the 6 climate zones, achieving significant energy savings, up to 46.8%. These energy savings resulted in better SCOP values for the DW-IEC system. Therefore, the proposed DW-IEC system has high potential to reduce energy costs, achieving the user’s thermal comfort

Performance of an unglazed transpire collector in the facade of a building for heating and cooling in combination with a desiccant evaporative cooler

Refurbishment of energy inefficient buildings is an effective way of reducing energy consumption in urban areas. This can be done by taking advantage of the renewable energy sources available, mainly, solar energy. Desiccant evaporative cooling combined with unglazed transpired collectors, UTC's, allows covering the heating demand in the cold season and cooling demand in the hot season. UTC's can be installed on the facades of buildings, meeting a double goal: refurbishing the building exterior and providing heating and cooling to indoor spaces. In this paper, a model of this system was implemented using TRNSYS and the energy savings obtained were evaluated in different climatic conditions, different façade orientations and different building shapes. The objective was to find the best conditions to install this system and estimating the energy savings that can be reached, and its costs. The results showed that the reduction of heating demand was possible in all climatic conditions, weakly depending on the shape and orientation of the UTC façade installed. Cooling was also possible, but it depended more on the shape of the building. The higher energy savings were found for the linear shape buildings. Therefore, refurbishment using a UTC façade could be an interesting alternative for energy saving throughout the year in these cases

Seasonal Analysis Comparison of Three Air-Cooling Systems in Terms of Thermal Comfort, Air Quality and Energy Consumption for School Buildings in Mediterranean Climates

Efficient air-cooling systems for hot climatic conditions, such as Southern Europe, are required in the context of nearly Zero Energy Buildings, nZEB. Innovative air-cooling systems such as regenerative indirect evaporative coolers, RIEC and desiccant regenerative indirect evaporative coolers, DRIEC, can be considered an interesting alternative to direct expansion air-cooling systems, DX. The main aim of the present work was to evaluate the seasonal performance of three air-cooling systems in terms of air quality, thermal comfort and energy consumption in a standard classroom. Several annual energy simulations were carried out to evaluate these indexes for four different climate zones in the Mediterranean area. The simulations were carried out with empirically validated models. The results showed that DRIEC and DX improved by 29.8% and 14.6% over RIEC regarding thermal comfort, for the warmest climatic conditions, Lampedusa and Seville. However, DX showed an energy consumption three and four times higher than DRIEC for these climatic conditions, respectively. RIEC provided the highest percentage of hours with favorable indoor air quality for all climate zones, between 46.3% and 67.5%. Therefore, the air-cooling systems DRIEC and RIEC have a significant potential to reduce energy consumption, achieving the user’s thermal comfort and improving indoor air quality

Experimental energy performance assessment of a solar desiccant cooling system in Southern Europe climates

Solar desiccant cooling systems, SDEC, could be an effective alternative to conventional cooling systems, which mainly depend on electrical energy. The main objective of this work was to determine experimentally the seasonal coefficient of performance, SCOP, of a SDEC system composed of a desiccant wheel, an indirect evaporative cooler and a thermal solar system, to control indoor conditions in a research lab room. The dependence of coefficient of performance on outdoor air conditions and percentage of renewable energy used by the SDEC system were also analysed. Experimental tests were carried out for six weeks during spring and summer seasons in Martos, Spain. The experimental results showed that the SDEC system independently adjusted the temperature and humidity of the supply air. 75% of the energy consumed by this air handling system comes from renewable sources. A seasonal coefficient of performance of the SDEC system of 2 was obtained for the period analysed. It is shown that the higher the outdoor temperature, the higher instantaneous COPs is. These results suggest that the use of SDEC systems in hot climates, such as southern European climates, could contribute to achieve the EU's energy goals within the frame of Nearly Zero Energy Buildings

Celiac Immunogenic Potential of α-Gliadin Epitope Variants from Triticum and Aegilops Species

The high global demand of wheat and its subsequent consumption arise from the physicochemical properties of bread dough and its contribution to the protein intake in the human diet. Gluten is the main structural complex of wheat proteins and subjects affected by celiac disease (CD) cannot tolerate gluten protein. Within gluten proteins, α-gliadins constitute the most immunogenic fraction since they contain the main T-cell stimulating epitopes (DQ2.5-glia-α1, DQ2.5-glia-α2, and DQ2.5-glia-α3). In this work, the celiac immunotoxic potential of α-gliadins was studied within Triticeae: diploid, tetraploid, and hexaploid species. The abundance and immunostimulatory capacity of CD canonical epitopes and variants (with one or two mismatches) in all α-gliadin sequences were determined. The results showed that the canonical epitopes DQ2.5-glia-α1 and DQ2.5-glia-α3 were more frequent than DQ2.5-glia-α2. A higher abundance of canonical DQ2.5-glia-α1 epitope was found to be associated with genomes of the BBAADD, AA, and DD types; however, the abundance of DQ2.5-glia-α3 epitope variants was very high in BBAADD and BBAA wheat despite their low abundance in the canonical epitope. The most abundant substitution was that of proline to serine, which was disposed mainly on the three canonical DQ2.5 domains on position 8. Interestingly, our results demonstrated that the natural introduction of Q to H at any position eliminates the toxicity of the three T-cell epitopes in the α-gliadins. The results provided a rational approach for the introduction of natural amino acid substitutions to eliminate the toxicity of three T-cell epitopes, while maintaining the technological properties of commercial wheats

Stimulatory Response of Celiac Disease Peripheral Blood Mononuclear Cells Induced by RNAi Wheat Lines Differing in Grain Protein Composition

Wheat gluten proteins are responsible for the bread-making properties of the dough but also for triggering important gastrointestinal disorders. Celiac disease (CD) affects approximately 1% of the population in Western countries. The only treatment available is the strict avoidance of gluten in the diet. Interference RNA (RNAi) is an excellent approach for the down-regulation of genes coding for immunogenic proteins related to celiac disease, providing an alternative for the development of cereals suitable for CD patients. In the present work, we report a comparative study of the stimulatory capacity of seven low-gluten RNAi lines differing in grain gluten and non-gluten protein composition, relevant for CD and other gluten pathologies. Peripheral blood mononuclear cells (PBMCs) of 35 patients with active CD were included in this study to assess the stimulatory response induced by protein extracts from the RNAi lines. Analysis of the proliferative response and interferon-gamma (INF-γ) release of PBMCs demonstrated impaired stimulation in response to all RNAi lines. The lower response was provided by lines with a very low content of α- and γ-gliadins, and low or almost devoid of DQ2.5 and p31–43 α-gliadin epitopes. The non-gluten protein seems not to play a key role in PBMC stimulation.Spanish Ministry of Economy, Industry and competitiveness AGL2016-80566-PEuropean Regional Development Fund (FEDER

Diseño y construcción de una planta experimental para la experimentación de ruedas desecantes

La información comercial disponible de ruedas desecantes es limitada en muchos casos. Sin embargo, el diseño de algunos sistemas de tratamiento de aire requiere un conocimiento detallado del comportamiento de las ruedas desecantes bajo distintas condiciones operativas. En este trabajo, se presenta el diseño y construcción de una planta experimental para el ensayo de ruedas desecantes. La planta experimental se compone de unidades de tratamiento de aire así como equipos humidificadores. Un sistema de monitorización permite hacer un seguimiento de los parámetros relevantes de funcionamiento, como caudal de aire, temperatura y humedad. El trabajo recoge resultados de las pruebas de servicio realizadas para la puesta en funcionamiento de todos los equipos que componen la planta experimental. Estas pruebas analizan los consumos eléctricos, los caudales de aire para diferentes situaciones de trabajo, la capacidad térmica de los equipos o el sistema de control de temperatura y humedad del aire. La planta experimental permite ensayar ruedas desecantes en distintas condiciones de funcionamiento. Los resultados experimentales permiten obtener información relevante a partir de la cual se realiza la caracterización de ruedas desecantes.El presente trabajo es parte del proyecto DESSECA Investigación en deshumectación y secado de aire, promovido por la empresa CIAT y cofinanciado por la Agencia de Innovación y Desarrollo de Andalucía Expte. IDEA 360097 y por la Corporación Tecnológica de Andalucía Expte CTA 12/612. (2012-2014