Direct evaporative cooling from wetted surfaces: Challenges for a clean air conditioning solution

Producción CientíficaEvaporative cooling has a major role to play in fighting climate change and in achieving a low-carbon economy. As it helps to reduce energy demand for air conditioning, it is gaining attention in terms of improving energy efficiency in buildings. Evaporative cooling from wetted media can enhance water–air contact, thereby improving heat and mass transfer further and avoiding aerosols. Wetted media are commonly called evaporative cooling pads and are widely used in greenhouses, intensive livestock farming, and industrial facilities. However, a deep understanding of evaporative cooling pad performance can enhance their application to indoor occupied spaces such as residential or commercial cooling, or in hybrid air conditioning systems. Most studies analyze pad performance mainly in terms of pressure drop and saturation effectiveness. However, some studies propose alternative cooling efficiency parameters and others provide insights into key aspects such as power requirements and the coefficient of performance, water consumption, risk of water entrainment, material decay, and air quality, as well as the effect of water temperature and salinity, solar radiation, or wind speed. Existing results on these less studied performance issues are reviewed, and we identify the gaps in the literature in addition to highlighting the main challenges encountered, in an effort to guide future researchers in the field and enhance the application of direct evaporative cooling.Junta de Castilla y León - Fondo Europeo de Desarrollo Regional (grant VA272P18

Reducción del consumo energético y emisiones de anhídrido carbónico en edificios combinando enfriamiento evaporativo, enfriamiento gratuito y recuperación de energía en sistemas todo aire.

El objetivo de la tesis es estudiar alternativas de acondicionamiento de aire de bajo consumo energético, desarrollando el diseño y construcción de varios de estos sistemas, buscando reducir la demanda energética de climatización de los edificios en verano cumpliendo los requisitos de Calidad de Aire Interior IAQ; para su posterior caracterización experimental a fin de modelar su comportamiento ante las diversas condiciones de funcionamiento esperables. Para ello se constituye un banco de ensayos en el laboratorio que permita la regulación y control de los factores de ensayo considerados en un diseño de experimentos previo. Los resultados se interpretan en función de parámetros de eficiencia que permitan describir su funcionamiento. La relevancia relativa de los factores considerados se evalúa mediante un análisis de varianza ANOVA. Finalmente, se analizan conjuntamente según su aplicabilidad a un caso práctico sencillo de un local, determinándose el ahorro energético y la reducción de emisiones alcanzados.Departamento de Ingeniería Energética y Fluidomecánic

Personalized evaporative cooler to reduce energy consumption and improve thermal comfort in free-running spaces

Producción CientíficaThe need to reduce energy consumption in buildings is imperative, but we must maintain individual thermal comfort of the occupants to ensure their well-being and productivity. Personal conditioning systems (PCS) have been suggested as a strategy to achieve both energy efficiency and thermal comfort, as they are considered to be low-energy consumers, allow increasing set-point temperatures, and give occupants the chance to control their own personal environment. While most warm-environment PCS are based on air-movement devices, the potential of using desk direct evaporative coolers (dDEC) has been scarcely explored. This work presents the results of the characterization of a dDEC and its potential for improving the indoor temperature and thermal comfort in a free-running office space. The study proposes adapted corrective power (CPa) and cooling fan efficiency for evaporative systems (CFEe) indexes. Results show that the dDEC achieves thermal comfort with a local effect, and it is recommended to be positioned directly on the desk surface, orientated to the occupant, and at a certain distance. Under these conditions, the CPa reaches −2.8 °C, involving better CFEe than the desk fans studied in the literature. Speed has little effect on the local air conditions, though it does improve the perception of thermal comfort. The relative humidity of the air does not exceed the recommendable limits, but renovation of the indoor air enables better conditions.Junta de Castilla y León - Fondo Europeo de Desarrollo Regional (project VA272P18

Alternative for summer use of solar air heaters in existing buildings

Producción CientíficaAmong solar thermal technologies for indoor heating, solar air heaters (SAH) are appealing for implementation on existing buildings due to their simplicity, fewer risks related to the working fluid, and possible independence from the building structure. However, existing research work mainly focuses on winter use and still fails in providing effective solutions for yearly operation, which would enhance their interest. With the aim of analysing an alternative summer use, this work firstly characterises a double channel-single pass solar air collector through experimentation. From the obtained results, modelling and simulation tasks have been conducted to evaluate the possibilities of using hot air, provided by the SAH, while operating under summer conditions within a closed loop, to feed an air-to-water heat exchanger for domestic hot water (DHW) production. The system is studied through simulation under two different configurations for a case study in Valladolid (Spain), during the period from May to September for different airflows in the closed loop. Results show that daily savings can vary from 27% to 85% among the different operating conditions; a configuration where make-up water is fed to the heat exchanger being preferable, with a dedicated water tank for the solar heated water storage of the minimum possible volume. The more favourable results for the harshest months highlight the interest of extending the use of the solar air heaters to the summer period

Estudio experimental del comportamiento de distintos materiales textiles como medio para enfriamiento evaporativo

Los sistemas de enfriamiento evaporativo son reconocidos por su elevada efectividad, respaldada por su gran sencillez y casi nulo consumo energético. La simplicidad de su funcionamiento lo constituye como el método de climatización en verano más antiguo, a la vez que el interés de su uso no caduca dentro de un contexto actual de concienciación sobre la eficiencia energética en las instalaciones edificatorias. Los equipos actuales de enfriamiento adiabático desde superficie húmeda deben afrontar unas severas restricciones en cuanto a seguridad frente a riesgo de Legionelosis, respecto a lo cual los medios comercializados más extendidos de relleno rígido presentan buenas prestaciones, pero con elevadas pérdidas de carga y relativamente elevado coste de adquisición. Estudios previos han demostrado que la utilización de materiales textiles proporciona resultados semejantes, pudiendo además reducir costos, permitiendo buenas opciones de mantenimiento [1]. A pesar de su interés energético y económico, para salvar la problemática asociada a la Legionella es interesante estudiar configuraciones alternativas de estos sistemas evaporativos textiles, que permitan trabajar sin acumulación de agua y optimizar el mantenimiento favoreciendo la limpieza y sustitución de materiales. Con este objeto, en este trabajo se caracterizan de forma comparativa tejidos de distinta naturaleza, para su selección en cuanto a su comportamiento frente a distintas opciones de humidificación sin pulverización (capilaridad y gravedad). Asimismo se estudia la tasa de evaporación de agua desde estas superficies para determinar la efectividad previsible del sistema, con el fin último de proponer el diseño de una configuración optimizada.Manuel Andrés Chicote desea agradecer la contribución del Ministerio de Educación, Cultura y Deporte del Gobierno de España a través del Programa de Formación de Profesorado Universitario (FPU). Referencia: AP2010-2449

Experimental characterisation of an indirect evaporative cooling prototype in two operating modes

Producción CientíficaThe present paper aims to describe the experimental study developed to characterize an indirect evaporative cooling system made of polycarbonate, designed and manufactured by the Thermal Engineering Group of the University of Valladolid; as well as to introduce the main results obtained. The prototype is characterized by a total heat exchange area of 6 m2 and is installed in a heat recovery cycle in the experimental setup constructed in the laboratory. This setup mainly consists of: an AHU that enables the reproduction of the different climatic conditions to be tested; a climatic chamber where comfort conditions are to be achieved; a circuit to supply water during one of the operating modes; and the due ducts and measurement probes to properly connect the whole system and register the evolution of the interesting parameters. Two operating modes are performed. In the first one, exhaust air from the climate chamber, in comfort conditions, goes through one side of the heat exchanger, producing heat transfer from the outdoor air stream through the plastic walls of the system. In the second case, an evaporative cooling mode is implemented by supplying water to the exhaust airstream. Results obtained show that heat transfer through the heat exchanger polycarbonate wall improves in the evaporative cooling mode. Furthermore, both cooling capacity and thermal effectiveness of the system also increase in the second case. Moreover, global heat transfer coefficient and cooling capacity are improved by higher outdoor air volume flow rates. Finally, higher outdoor air temperatures imply better cooling capacities and thermal effectiveness.This work forms part of the research being carried out within the framework of the “Reduction of energy consumption and carbon dioxide emission in buildings combining evaporative cooling, free cooling and energy recovery in all-air systems”, project supported by the Ministry of Science and Technology through the call for scientific research and technological development research projects. Reference number ENE2008-02274/CON. Ana Tejero wants to thank the Consejería de Educación of the Junta de Castilla y León for the support provided through the Regional Strategy of Scientific Research and Technological Development of the European Social Fund

Improved performance of a PV integrated ventilated façade at an existing nZEB

Producción CientíficaVentilated façades are among the existing measures to reduce the energy demand in buildings. The combination of this passive heating and cooling strategy with photovoltaics (PV) can drive new buildings towards the current European targets for near or even net zero-energy buildings (nZEB). The present work aims at studying the PV integrated ventilated façade of the nZEB known as “LUCIA” at the University of Valladolid, Spain. First, the transmissivity of the PV façade is measured. Then, the monitoring of the available solar radiation is presented together with the air-dry bulb temperatures indoors, outdoors and inside the ventilated façade. The experimental results permit the validation of a mathematical model that describes the behaviour of the ventilated façade in its current operating modes. The results show that dampers should be closed during winter to let the façade act as a further insulation for outdoor temperatures below 18.4 C to improve energy efficiency. Indoor air recirculation would be helpful during 10% of the winter period.Junta de Castilla y Leon - Fondo Europeo de Desarrollo Regional (project VA272P18)VIPSKILLS (project 2016-1-PL01-KA203-026152 Erasmus +

Experimental characterisation of the operation and comparative study of two semi-indirect evaporative systems

Producción CientíficaThe study described in this paper aims to present the fundamentals in which the operation of two different evaporative cooling systems is based, as well as the experimental results developed to characterise their behaviour in different conditions of outside air. These results will permit to define, according to the ideas of the systems’ operation, appropriate parameters to characterise the heat and mass exchange processes that take place as well as to compare them, like cooling capacity, thermal or energetic effectiveness; and afterwards developing this comparative analysis. The first system consists of a bank of ceramic pipes arranged vertically and staggered acting as a heat exchanger (SIERCP). In the second case an evaporative cooler has been manufactured with hollow bricks filled with still water (SIECHB). Both systems are called “semi-indirect” because they are designed to act as either direct or indirect evaporative systems depending on the relative humidity of the outdoor and return air streams. Results show that parameters related to the air humidity should be considered; and that the second system behaves generally as a direct evaporative cooler and provides a better performance.Dr. Francisco Javier Rey would like to thank the Consejería de Educación, Dirección General de Universidades e Investigación of Junta de Castilla y León for the support given to the Excellence Research Group GR181 within whose framework is being carried out the project “Design, manufacturing and characterisation of a combined system of high energetic effectiveness climatization: semi-indirect ceramic evaporative cooler, air solar thermal colectors, and heat pump”.Ana Tejero would like to thank the support given by the Consejería de Educación through the Regional Strategy of Scientific Research, Technologic Development and Innovation, supported by the European Social Fund

Energy use optimization in ventilation of operating rooms during inactivity periods

Producción CientíficaHospitals are highly energy demanding buildings, where simple actuations can involve large savings. However, energy efficiency actions must comply with the high safety standards. Operating rooms demand continuous ventilation despite the short activity periods. Setback during non-occupation of the operating rooms can reduce ventilation loads but must not hinder indoor overpressure to avoid infiltrations. Besides, it prevents any existing heat recovery system from operation. This work evaluates setback ventilation in operating rooms at a case study in Spain, from two approaches: its effect on indoor overpressure and its preference to an existing coil heat recovery (runaround) loop. It bases on monitored data of two operating rooms under setback and normal ventilation with operation of the heat recovery system. Seven tests are performed throughout the year, whose comparison to estimated results enables extrapolation to yearly operation. Results show that indoor overpressure maintain at 15 Pa under setback, thus meeting current and coming standards. Setback turned to be always preferable to hear recovery under cooling needs. Estimated heating and electric yearly supply energy savings reach 29 MWht and 262 MWhe, the latter accounting for 2% of the total electric energy consumption of the hospital during 2019.Junta de Castilla y León (grant EREN_2019_L2_UVA

IAQ improvement by smart ventilation combined with geothermal renewable energy at nZEB

Producción CientíficaThe building sector has the responsibility of being a generator of high carbon emissions, due to inefficient energy consumption in the last decades. For the European Union (EU) and the building sector, this pollution has generated a great impact and concern, establishing objectives in sustainability and energy efficiency in the short term. The EU, committed to energy sustainability, has established several guidelines, aiming at reducing carbon emissions. For this reason, European directives have been published to increase energy efficiency and sustainability in buildings, with EPBD 2018/844/EU being the most up-to-date regulation. This directive mainly focuses on reducing carbon emissions and increasing the efficiency of energy systems in buildings, but it also refers to the importance of establishing indoor air quality indices and smart management of ventilation systems. Before this directive was published, many of the implemented ventilation strategies did not consider the indoor air quality (IAQ) in their scope of established comfort parameters. Therefore, this study analyses the performance of the ventilation system, controlled smartly to cover the demand and the established IAQ rates via CO2 ppm, through renewable geothermal energy systems. This study has been carried out at the LUCIA building, a near Zero Energy Building (nZEB), which belongs to the University of Valladolid, Spain. This building stands out for being one of the most sustainable buildings in the world, according to LEED certification, ranking as the most sustainable building in the northern hemisphere. This building to study is equipped with cutting-edge energy systems, with zero carbon emissions. Several parameters have been analysed (air speed, enthalpy, air flow, temperature, humidity, kWh, climate data, etc.) enabling an energy optimisation of the combined systems. All the monitoring data obtained by the smart management have been analysed, providing favourable outcomes, due to the establishment of IAQ levels, according to the EPBD 2018/844/EU. After this study, the smart management of ventilation combined with removable geothermal energy can be exported as a strategy to reach the established IAQ levels through zero carbon systems.Junta de Castilla y León - FEDER (VA272P18