• Energy Research

Abstract Thermal energy storage (TES) systems are growing to a relevant role in solar cooling applications. Hence, high energy density is a desirable property of the TES system. Phase change materials (PCM) helps to increase this characteristic. A high temperature pilot plant able to test different types of TES systems and materials was designed and built at the University of Lleida (Spain). This pilot plant is composed mainly of three parts: heating system, cooling system, and different storage tanks. Two identical storage tanks based on the shell-and-tubes heat exchanger, one of them including 196 squared fins in the bundle of the tubes and the other without, were experimentally tested. Hydroquinone was selected as the storage material, having a latent heat of 205 kJ/kg and a phase change temperature between 168 and 173 °C. The aim of this paper is to test experimentally, and compare the average effectiveness of the TES systems analyzed using PCM for solar cooling and refrigeration applications. It was found out that for the same tank configurations (shell-and-tubes) even changing drastically the dimensions of the tank or the number and the diameter of the tubes, the average effectiveness curve proposed in the literature fits well with the results showed here.

Abstract Energy consumption presents increasing trends during last decades, presenting a great challenge. The building sector contributes to a high proportion of the energy consumed and therefore efforts should be focused to improve energy efficiency of buildings. For such purpose, the use of phase change materials in building envelopes has been extensively studied and its benefits were demonstrated. However, there is a lack of simple evaluation tools to assess these benefits. In this paper a previously proposed methodology based on four indicators, which were tested through simulation only are experimentally validated using brick, concrete and timber constructions, incorporating PCM. Results show that the methodology is successful for buildings with heat gains and having low thermal inertia or insulation. However, for highly insulated buildings with significant inertia and low heat gains the method fails to assess the potential benefit of the PCM. Moreover, the ITD indicator is found to be the most accurate in assessing PCM benefits compared to other parameters studied. In this paper the ITD indicator will be modified to take into account an upper and lower comfort temperature levels rather than single set temperature.

The main objective of this paper is to demonstrate experimentally that it is possible to improve the thermal comfort and reduce the energy consumption of a building without substantial increase in the weight of the construction materials with the inclusion of phase change materials (PCM). PCM are a suitable and promising technology for this application. This paper presents an experimental setup to test PCM with various typical insulation and construction materials in real conditions in Puigverd de Lleida (Lleida, Spain). Nine small house-sized cubicles were constructed: two with concrete, five with conventional brick, and two with alveolar brick. PCM was added in one cubicle of each typology. For each type of construction specific experiments were done. In all cubicles, free-floating temperature experiments were performed to determine the benefits of using PCM. A Trombe wall was added in both concrete cubicles and its influence was investigated. All brick cubicles were equipped with domestic heat pumps as Heating, Ventilation, and Air Conditioning (HVAC) system; therefore, the energy consumption was registered, providing real information about the energy savings. Results were very good for the concrete cubicles, since temperature oscillation were reduced by up to 4°C through the use of PCM and also peak temperatures in the PCM cubicle were shifted in later hours. In the brick cubicles, the energy consumption of the HVAC system in summer was reduced by using PCM for set points higher than 20°C. During winter an insulation effect of the PCM is observed, keeping the temperatures of the cubicles warmer, especially during the cold hours of the day.

Abstract Among the research activities that aim at reducing energy consumption in buildings and their impact on the environment is an experimental set-up that has several house-shaped cubicles constructed in Puigverd de Lleida (Spain). Assessing the environmental impact through studying the manufacturing, operational and disposal phases of these cubicles have been done in previous research. The objective of this paper is to investigate the use of esters as PCM in order to estimate its environmental impact in building envelopes in comparison to the use of paraffin or salt hydrates through a theoretical study. The evaluation of the environmental impact of this type of PCM material is conducted using Life Cycle Assessment (LCA) based on the Eco-indicator 99 method. It is found that the impact of ester used as PCM presents slightly better results than the case of using salt hydrates during the manufacturing impact. On the other hand, the use of salt hydrates or ester as PCM in the cubicles results in an impact reduction of 9% and 10.5% respectively, compared to the case of using paraffin.

Abstract Thermal energy storage and conversion aims to improve the high inefficiency of the industrial processes and renewable energy systems (supply versus demand). Chemical sorption processes and chemical reactions based on solid–gas systems are a promising way to store and convert thermal energy for heating or cooling applications and, thereby to increase the efficiency of the processes and to reduce the greenhouse effect. Although more efforts are required to bring this technology to the market, some important breakthrough have been made regarding to system efficiency. Over the last two decades, the experimental research in this field has increased largely to validate these advances under practical conditions. Therefore, this paper gives a state-of-art review of performances obtained under practical conditions by the different prototypes built over the last two decades. In addition, the main advantages and disadvantages of solid–gas chemical sorption processes and chemical reactions are summarized.

Abstract It is well known that it is necessary to insulate the buildings to decrease the thermal demand and to decrease the use of heating and cooling. Due to the high cost of fossil fuels and to the necessity to reduce CO 2 emissions, and also due to the new building regulations more attention is paid to the insulation of buildings. Different insulation materials are available in the market. Usually, they are compared by their thermal conductivity and with theoretical calculations, but there are no experimental comparisons available, where the behavior of such insulation materials in a building is compared over time. This is why the authors started a comparison of three typical insulation materials, polyurethane, polystyrene, and mineral wool. For this purpose, four house-like cubicles were constructed (with a size of 2.4 m × 2.4 m × 2.4 m) and their thermal performance throughout the time was measured. The cubicles were built under a conventional Mediterranean construction system, differing only in the insulation material used. During 2008 and the first months of 2009 the performance of these cubicles was evaluated, and the results are presented in this paper.

A new research university building with a useful area of about 3000 m2 has recently been constructed in Lleida (Spain) as an example of a sustainable energy efficient institutional building. The building is provided with passive measures in the envelope as well as a wide variety of active measures in the installed energy systems. Non-conventional energy systems such as solar photovoltaic arrays, thermal collectors, an internal combustion engine cogeneration, and an absorption chiller are in place. The standard systems, namely two 320 kW condensation boilers and a 419 kW compression chiller, are also included in the building for back-up and for comparison purposes. To assess the potential energy, economic and CO2 savings of the building a simplified model is developed and the main results discussed. For nominal electricity and gas average prices about 11.5 k€ of savings are achieved. This represents energy cost reductions of 35–58%, a payback period of 20 years and about 56 tons per year of saved CO2 emissions. The presence of the absorption chiller is found essential to maximize buildings economic and CO2 emissions savings. This work also includes parametric studies for natural gas and electricity prices as well as results for other possible combinations with only one or several of the installed systems in operation.

Nearly 30% of humanity lives in earthen dwellings. Earthbag is a sustainable, cheap, feasible and comfortable option for emergency housing. A comparative monitoring-simulation analysis of the hygrothermal behavior of an Earthbag dwelling in Mediterranean continental climate, designed under bioclimatic criteria, is presented. The dome shape Earthbag dwelling has a net floor area of 7.07 m2, a glass door facing south and two confronted windows in the east and west facades. A numerical model (EnergyPlus v8.8) was designed for comparison. Twenty-four hour cross ventilation, night cross ventilation, and no ventilation in free floating mode and a controlled indoor temperature were the tested scenarios. Comparisons between experimental data and simulation show a good match in temperature behavior for the scenarios studied. Reductions of 90% in summer and 88% in winter, in the interior thermal amplitude with respect to exterior temperatures are found. Position of the glazed openings was fundamental in the direct solar gains, contributing to the increase of temperature in 1.31 °C in winter and 1.37 °C in the equinox. Night ventilation in the summer period had a good performance as a passive system. Passive solar gains made a reduction of heating energy consumption of 2.3% in winter and 8.9% in equinox.