Optimización del control de un sistema de calefacción conjunto de suelo radiante y ventiloconvectores

Los sistemas de calefacción que utilizan suelos radiantes presentan ventajas frente a los que impulsan aire: mejor distribución espacial de temperatura, mayor rendimiento en la producción y mejor integración. Sin embargo, el suelo tiene una constante de tiempo mayor que otros sistemas que impulsan aire. Esto implica que resultan más difíciles de controlar, y los tiempos de espera hasta alcanzar el confort son mayores que en sistemas de aire. Para evitar estos inconvenientes, en algunos casos, se están acoplando sistemas que impulsan aire a la zona, por ejemplo mediante fancoils, con suelos radiantes. Cuando esto ocurre, y el sistema de producción es único, se produce agua a la temperatura requerida por el fancoil y, mediante una válvula mezcladora a la entrada del suelo, se reduce ésta hasta la requerida por el suelo. Una solución de este tipo adolece de lo siguiente: 1.-No se aprovecha la menor temperatura de producción que el suelo requiere 2.-El sistema de control implica una válvula motorizada que regula en función de la temperatura de local. 3.-Si el suelo radiante está dimensionado para combatir la carga punta de calefacción, puede prescindirse del funcionamiento del fancoil después de una fase inicial de puesta a régimen. En el estudio que se propone, se plantean estrategias de control para optimizar la operación conjunta de fancoils y suelos radiantes operando simultáneamente en el suministro de calefacción a una zona. Para alcanzar los objetivos se dispone de un modelo de simulación (planteado en TRNSYS) en el que se han probado los modos de control hasta encontrar la mejor solución. Los criterios de optimización son, además de la reducción del consumo de energía, los tiempos requeridos para alcanzar la temperatura de consigna en la zona y el coste inicial del sistema. El modelo de suelo radiante se ha validado en una instalación experimental. El trabajo se desarrolla conjuntamente con la empresa ALTRA, que desarrolla sistemas de control para sistemas de climatización.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Design under uncertainty of solar hot water systems for hospitals

Failed designs are often behind underperforming solar hot water systems and excessive fossil fuel consumption in backup units. This paper proposed a reliable and robust method to design a solar thermal system combined with boilers for hot water preparation in a medium size-hospital hospital building with an average daily demand of 8.69 m3. To start with, the conventional deterministic design, which assumes business-as-usual parameter values and overlooks their uncertainties, gives a required solar caption area of 223.0 m2 to achieve an annual solar fraction of 70%. However, if the uncertainties of input parameters are considered, the reliability of this design solution is barely 22% regarding the solar fraction target set, and a solar caption area of 326 m2 would be required to achieve a reliability of 90%. This work proposes a revised design solution which such high level of trustworthiness but with a lower solar caption area and, therefore, more attractive from an economic perspective. The strategy consists of narrowing the uncertainty bounds of those controllable parameters causing major variance on the system performance. A sensitivity analysis showed that the most significant uncertainties concerning the variance of the solar fraction are the following (in decreasing order of importance): variation of the hot water supplying set-point, insulation defects in the hot water distribution loop, wrong adjustment of thermostatic valves and dust deposition on collectors. According to the improved design proposed rooted in the revision of uncertainties through the installation of high-quality measurement and control equipment and effective maintenance, a design with a solar caption area of 257.3 m2 would be enough to reduce the probability of failure below 10%.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Domestic hot water production system in a hospital: Energy audit and evaluation of measures to boost the solar contribution

Hospitals consume large quantities of energy to produce hot water and offset the distribution and recirculation thermal losses. This paper analyses a solar thermal system combined with gas boilers for domestic hot water production in a medium-size hospital. The solar contribution to the total demand (27%) is below design expectations (75%), resulting in significant gas consumption. The energy audit conducted in the first part of the paper highlights the vast thermal loss through poorly insulated pipes as the primary cause of the poor solar fraction. This issue is endemic to hot water-intensive buildings. The second part of the paper addresses the techno-economic evaluation of energy retrofit measures to reach a solar fraction of 60%. The simulation results indicate that cost-optimised solutions generally expand the solar caption area by 43–57% and improve insulations to reduce thermal losses by 70%. Depending on carbon taxes, the cost of hot water production would be 31–41 cent-€/kWh, which represents a 15–45% reduction from the current costs. Under stringent climate policies, installing heat pumps may further enhance economic competitiveness. The indicators and charts developed in this work are helpful decision-making tools concerning the energy refurbishment of solar domestic hot water systems.The authors acknowledge the Universidad de Málaga and “Programa Operativo FEDER Andalucía 2014–2020″ the financial support of the contract UMA18-FEDERJA-247.Funding for open access charge: Universidad de Málaga / CBU

Analysis of a HVAC zoning control system with an air-to-water heat pump and a ducted fan coil unit in residential buildings

This paper presents an analysis of a thermal zoning system integrated in a Heating, Ventilation and Air- Conditioning (HVAC) system based on an air-to-water heat pump with a ducted fan coil. Zoned systems are based on independently controlling the temperature of each of the zones of a building. When a zone is not occupied or not in demand, the control board sends a control signal to the zone’s motorised damper which interrupts the airflow supply to that room. Although this control system is gaining popularity in the residential sector, the results obtained in terms of thermal comfort and energy consumptions are not evident and should be documented. Besides, the control strategy is based on an algorithm that allows acting on the heat pump, setting the set-point temperature, and on the fan-coil, setting the fan speed. Based on this, it is possible to design an algorithm to optimize the performance of the installation ensuring thermal comfort and achieving energy savings. The thermal zoning and the HVAC control system are modelled and simulated in Trnsys17 for the case of study of a residential dwelling, compared with two different configurations: a non-zoned ducted fan coil and individual fan coils. Important benefits are obtained in the evaluation of thermal comfort, with higher values of PPD in all zones. From the point of view of energy consumption, the influence of the thermal zoning on the performance of the heat pump reports important energy savings. Finally, an economic analysis results in payback periods lower than 4.9 years.Funding for open access charge: Universidad de Málaga / CBU

Influencia del sistema de control zonificado en la combinación de un suelo radiante refrescante con un fancoil de conductos

La aerotermia está siendo promovida como solución en el sector residencial tanto para la producción de agua caliente sanitaria como para la climatización con instalaciones con agua, reemplazando a la energía solar térmica y los equipos de expansión directa. Este estudio presenta el análisis, desde el punto de vista del confort térmico y el consumo de energía, de un sistema de control zonificado aplicado a una instalación de suelo radiante y fancoil de conductos, comparado con un sistema de suelo radiante y fancoils individuales. El sistema de control incluye el uso eficiente combinado de ambas unidades terminales. La capacidad de refrigeración del suelo refrescante está limitada y en climas cálidos es necesario el uso del fancoil para asegurar el confort térmico y combatir la carga latente de la zona. El sistema se ha modelado en Trnsys17 y el caso de estudio se ha aplicado a una vivienda residencial y en diferentes zonas climáticas

Exergy recovery from LNG-regasification for polygeneration of energy

El Gas Natural Liquat (GNL) és una excel·lent font d'exergia física a causa de la seva temperatura criogènica i, habitualment, elevada pressió de regasificació. Encara que aquest potencial exergètic es pot utilitzar, com a un subproducte de la regasificació, en multitud d'aplicacions, són molt poques les vegades que és aprofitat a causa d’alguns problemes com son les baixes eficiències i limitada competitivitat econòmica dels sistemes proposats. A més, les solucions proposades per augmentar l'eficiència normalment requereixen d'estructures molt complexes i elevades inversions. L'objectiu d'aquesta tesi és desenvolupar nous sistemes de poligeneració sostenibles per aprofitar l'exergia física del GNL (i altres fluids criogènics com el bio-GNL) i basats en un equilibri competitiu entre eficiència i complexitat, tant en terminals a gran escala com en plantes de regasificació satèl·lit. Les diferents configuracions propostes estan basades en sistemes sense combustió que regasifican el GNL i produeixen electricitat i/o refrigeració a diferents nivells de temperatura.Els resultats obtinguts demostren que la poligeneració és una solució tècnica viable per utilitzar la exergia física del GNL eficientment en cascada. Una conclusió destacable de la tesi és que els fluids naturals són adequats per ser utilitzats com fluids de treball o transferència de calor en aquest tipus de sistemes. Les configuracions propostes per a terminals a gran escala aconsegueixen el doble d'eficiència que les actuals plantes de potència criogèniques, i amb una producció equivalent d'electricitat de fins a 150 kWh per cada tona de GNL regasificada. Des del punt de vista econòmic, el temps de retorn de la inversió de referencia, estimat per a la configuració més eficient entre les analitzades, és de cinc anys. Finalment, en certs casos, les plantes satèl·lits constitueixen una atractiva via per integrar biocombustibles criogènics en el mix energètic i per a la recuperació de fred en el seu procés de regasificació.El Gas Natural Licuado (GNL) es una excelente fuente de exergía física debido a su temperatura criogénica y habitualmente elevada presión de regasificación. Aunque este potencial exergético se puede utilizar como subproducto de la regasificación en multitud de aplicaciones, son muy pocas las veces que es aprovechado debido a algunos problemas como las bajas eficiencias y limitada competitividad económica de los sistemas propuestos. Además, las soluciones propuestas para aumentar la eficiencia normalmente requieren de estructuras muy complejas y elevadas inversiones de capital. El objetivo de esta tesis doctoral es desarrollar nuevos sistemas de poligeneración sostenibles para aprovechar la exergía física del GNL (y otros fluidos criogénicos como el bio-GNL) y basados en un equilibrio competitivo entre eficiencia y complejidad, tanto en terminales a gran escala como en plantas de regasificación satélite. Las diferentes configuraciones propuestas están basadas en sistemas sin combustión que regasifican el GNL y producen electricidad y/o refrigeración a distintos niveles de temperatura.Los resultados obtenidos demuestran que la poligeneración es una solución técnica viable para utilizar la exergía física del GNL eficientemente en cascada. Una conclusión destacable de la tesis es que los fluidos naturales son adecuados para ser utilizados como fluidos de trabajo o transferencia de calor en este tipo de sistemas. Las configuraciones propuestas para terminales a gran escala consiguen el doble de eficiencia que las actuales plantas de potencia criogénicas, y con una producción equivalente de electricidad de hasta 150 kWh por cada tonelada de GNL regasificada. Desde el punto de vista económico, el tiempo de retorno de inversión de referencia estimado para la configuración más eficiente entre las analizadas es de cinco años. Finalmente, en ciertos casos, las plantas satélites constituyen una atractiva vía para integrar biocombustibles criogénicos en el mix energético y para la recuperación de frío en su proceso de regasificación.Liquefied Natural Gas (LNG) is a premium-quality physical exergy source because of its cryogenic temperature and usually high regasification pressure. But although this exergetic potential can be utilized as a regasification by-product for multiple applications, it is rarely used because of several barriers such as low efficiencies and limited economic competitiveness of the proposed systems. Additionally, the solutions proposed to boost efficiency generally require very complex structures and huge capital investments. The objective of this doctoral thesis is to develop innovative and sustainable polygeneration systems to harness the physical exergy of LNG (and other cryogenics fluids such as bio-LNG) with a competitive efficiency-complexity ratio both in large-scale and satellite regasification facilities. The different configurations proposed consist of non-combustion systems that regasify LNG and produce electricity and/or refrigeration at different temperatures.The results obtained showcase that polygeneration is an economically feasible technical solution to squeeze the LNG physical exergy efficiently in cascade. Besides, a remarkable finding of the thesis is the suitability of natural fluids as working fluids and heat transfer fluids for such kind of systems. The configurations proposed for large-scale receiving terminals can achieve double the efficiency of current cryogenic power plants, and an equivalent electricity production up to 150 kWh per metric tonne of LNG regasified. As for the economic performance, a base-case payback period of five years is estimated for the polygeneration configuration with the most efficient performance among the investigated in this thesis. Finally, in certain scenarios satellite plants are an attractive gateway to the integration of cryogenic biofuels in the energy mix for the recovery of the low-temperature heat from the regasification

Modeling and Dynamic Simulation of a Hybrid Liquid Desiccant System with Non-Adiabatic Falling-Film Air-Solution Contactors for Air Conditioning Applications in Buildings

This paper presents an experimentally validated, dynamic model of a hybrid liquid desiccant system. For this purpose, we developed new components for the air-solution contactors, which are of the non-adiabatic falling-film type with horizontal tubes (made of improved polypropylene) and the solution tanks. We also provide new experimental correlations for both the tube-solution heat transfer coefficient and the mass transfer coefficient on the airside as a function of the air velocity. To validate the model, the results obtained from the dynamic simulations were compared with those obtained by monitoring a demonstration unit installed in a sports center in Taipei (Taiwan). Once validated, the model was used to perform a sensitivity analysis at different operational conditions, such as the inlet water temperatures in the air-solution contactors and the LiCl mass fraction at which the system operates. The results of the sensitivity analysis were used to optimize the seasonal performance in terms of comfort and energy required by the system. Compared with a conventional air-handling unit that controls air temperature and humidity, the annual energy savings of the liquid desiccant systems are 17%

Recovery and Transport of Industrial Waste Heat for Their Use in Urban District Heating and Cooling Networks Using Absorption Systems

The use of industrial excess heat in district heating networks is very attractive. The main issue is the transport of the heat from the point of generation to the local distribution network, in a way similar to the structure of electricity transport and distribution networks. Absorption systems have been proposed to transport and distribute waste heat using two absorption stations. In one of them (step-up station), industrial heat at a low temperature is pumped to a higher temperature to facilitate its transport and at the same time increase the temperature difference between the supply and return streams, in this way reducing the hot water mass flow rate circulating through the heat transport network. Heat is then used in a second absorption system (step-down station) to provide heat to a low temperature local district network. In this paper, several absorption system configurations are analyzed for both stations. A detailed thermodynamic analysis of each configuration is performed using selected energy performance indicators to calculate its global performance. The implementation of these kind of systems could enable the use of waste heat to produce heating and cooling for smart communities located a few dozens of kilometers away from industrial sites

Predicting mortality for Covid-19 in the US using the delayed elasticity method

The evolution of the pandemic caused by COVID-19, its high reproductive number and the associated clinical needs, is overwhelming national health systems. We propose a method for predicting the number of deaths, and which will enable the health authorities of the countries involved to plan the resources needed to face the pandemic as many days in advance as possible. We employ OLS to perform the econometric estimation. Using RMSE, MSE, MAPE, and SMAPE forecast performance measures, we select the best lagged predictor of both dependent variables. Our objective is to estimate a leading indicator of clinical needs. Having a forecast model available several days in advance can enable governments to more effectively face the gap between needs and resources triggered by the outbreak and thus reduce the deaths caused by COVID-19

Colectores solares fotovoltaicos-térmicos (PV/T): Características y modelado de prestaciones // Photovoltaic-thermal (PV/T) solar collectors: Features and performance modelling

Actualmente, las células fotovoltaicas (PV) presentan eficiencias eléctricas entre un 5–25%. Uno de los parámetros más importantes que afectan a dicha eficiencia es la temperatura de sus células: mayor temperatura, peor eficiencia eléctrica. La tecnología fotovoltaica/térmica (PV/T) es una solución para garantizar una adecuada conversión de la energía solar. La tecnología PV/T genera energía eléctrica y térmica simultáneamente. Es adecuada para aplicaciones a baja temperatura (25–40oC). Además se reduce el área total con respecto a colectores individuales y la eficiencia global es mayor. Se describe la instalación en una vivienda unifamiliar donde los colectores PV/T se integran con una fuente de calor geotérmica y con una bomba de calor para producir agua caliente sanitaria y calefacción. Este trabajo tiene dos objetivos. Primero, se analizan las posibilidades de la tecnología PV/T. Segundo, // Currently, the electrical efficiency of photovoltaic (PV) solar cells ranges between 5–25% One of the most important parameters that affects the electrical efficiency of a PV collector is the temperature of its cells: the higher temperature, the lower is the efficiency Photovoltaic/thermal (PV/T) technology is a potential solution to ensure an acceptable solar energy conversion The PV/T technology produces both electrical and thermal energy simultaneously It is suitable for low temperature applications (25–40 o C) and overall efficiency increases compared to individual collectors This paper describes an installation in a single-family house where PV/T collectors are coupled with a ground heat exchanger and a heat pump for domestic hot water and space heating purposes The aim of this work is twofold First, the features of the PV/T technology are analyzed Second, a model of a flat-plate PV/T water collector was developed in TRNSYS in order to analyze collectors performance