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  • 1.
    Li, Haimeng
    et al.
    School of Building Services Science and Engineering, Xi'an University of Architecture and Technology, Shaanxi, Xi'an, China.
    Zhang, Ying
    School of Building Services Science and Engineering, Xi'an University of Architecture and Technology, Shaanxi, Xi'an, China.
    Yang, Changqing
    School of Building Services Science and Engineering, Xi'an University of Architecture and Technology, Shaanxi, Xi'an, China.
    Gao, Ran
    School of Building Services Science and Engineering, Xi'an University of Architecture and Technology, Shaanxi, Xi'an, China.
    Ding, Feng
    China Northwest Architectural Design and Research Institute Co., Ltd, Shaanixi, Xi'an, China.
    Olofsson, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Zhou, Hongxia
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Si, Pengfei
    China Southwest Architecture Design and Research Institute Co., Ltd, Sichuan, Chengdu, China.
    Shi, Lijun
    China Southwest Architecture Design and Research Institute Co., Ltd, Sichuan, Chengdu, China.
    Li, Angui
    School of Building Services Science and Engineering, Xi'an University of Architecture and Technology, Shaanxi, Xi'an, China.
    Sleep microenvironment improvement for the acute plateau entry population through a novel nasal oxygen supply system2024Inngår i: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 256, artikkel-id 111467Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Most people who have moved to high-altitude areas temporarily suffer from sleep disorders. Sleep deprivation negatively affects not only people's daytime activities but also their health. However, most of the existing nonpharmaceutical intervention methods have the problems of discomfort, restricted movement, or high cost. This study involved the use of an oxygen-rich flow of air in the breathing area during sleep to fight hypoxia and aid with altitude acclimatization when people first traveled to a highland plateau. The associated nasal breathing targeted oxygen supply system (NBTOSS) was designed and optimized by numerical simulation and full-scale experiments. Blood oxygen saturation (SaO2) and pulse rate (PR) monitoring experiments were conducted on subjects exposed to hypoxia at a high altitude (Lhasa, 3646.31 m) with or without assistance from the novel oxygen system and on a lowland plain (Xi'an, 397.5 m) as a comparison. The size of the affected area, concentration target value, and oxygen consumption were used as evaluation indices. Experiments have demonstrated the feasibility of creating an oxygen-enriched microenvironment in breathing area during sleep. The results of the testing showed that the oxygen supply area was uniformly covered and that the degree of hypoxia in subjects was effectively alleviated, with average SaO2 increasing to 95% ± 1%. Maintaining oxygen levels during sleep for temporary residents of high altitudes with less oxygen consumption and minimal oxygen supply costs is discussed to provide a healthy and comfortable oxygen-enriched environment.

  • 2.
    Zhou, Hongxia
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Andersson, André
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Olofsson, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Phase change materials influence on temperature variation in buildings2022Inngår i: E3S web of conferences / [ed] A. Li, T. Olofsson; R. Kosonen, EDP Sciences, 2022, Vol. 356, artikkel-id 01044Konferansepaper (Fagfellevurdert)
    Abstract [en]

    For the design of sustainable buildings, it is crucial with accurate methods to evaluate how alternative constructions will influence thermal comfort, as well as energy efficiency. This study introduces a model to investigate how the use of phase change materials (PCM)in building envelopes can influence the temperature stratification, which also influences the indoor thermal comfort. PCM is characterized by large latent heat in the melting/solidifying process during phase transition. Applications with PCM have been recognized as possible alternatives in building envelopes to improve thermal comfort as well as energy efficiency. The selection of the properties of the PCM, as well as how and where the PCM was installed in the building envelope, are crucial factors to be considered before application in practice. In this study, a simplified experimental set-up including a hot-box was used. The PCM material Climsel28 with different layers thicknesses was installed in the sidewall of a hot-box. Extruded polystyrene (XPS) foam boards were used as wall insulation material in the study. XPS was installed as a reference case and in different layer combinations with the PCM. The sequence of the XPS and PCM was varied. Temperature and heat flux were measured in different positions of the hot-box and on the tested walls. A 3D COMSOL model was developed to study the thermal performance of the system. The model was validated in the study using the collected experimental data. The results indicated that the developed COMSOL model can reasonably predict the performance of the system, both with and without the incorporation of PCM. Additionally, the measured temperature stratification were theoretically validated by the COMSOL model. The study gives indicative guidance of how PCMs can be installed in building constructions elements to reduce temperature peak loads and thus also contributing to an improvement of the indoor thermal comfort.

    Fulltekst (pdf)
    fulltext
  • 3.
    Zhou, Hongxia
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Fransson, Åke
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Olofsson, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    An explicit finite element method for thermal simulations of buildings with phase change materials2021Inngår i: Energies, E-ISSN 1996-1073, Vol. 14, nr 19, artikkel-id 6194Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermal performance of building envelopes is essential for building thermal comfort and the reduction of building energy requirements. Phase change materials (PCMs) implemented in building envelopes can improve thermal performance. An explicit finite element method (ex-FEM) has been developed based on a previous study to investigate the heat transfer performance through building walls with installed PCMs. For verification, we introduce an electrical circuit analogy (ECA) method. For model validation, at first, COMSOL is used. For comparison, data were collected from experiments using a small hotbox, part of the sides are covered by PCMs with different configurations. This work shows how the ex-FEM model can predict the wall's temperature profile with and without incorporated PCM. With the implementation of PCMs, the work problematizes unpredictable influences for modeling. In addition, the study introduces results from simulations of sequencing of PCM layers in wall construction.

    Fulltekst (pdf)
    fulltext
  • 4.
    Zhou, Hongxia
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Fransson, Åke
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Olofsson, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Influence of Phase Change Materials (PCMs) on the thermal performance of building envelopes2020Inngår i: 12th Nordic Symposium on Building Physics (NSB 2020) / [ed] Kurnitski, J Kalamees, T, EDP Sciences, 2020, artikkel-id 21002Konferansepaper (Fagfellevurdert)
    Abstract [en]

    To understand the influence of PCM wall configurations on the thermal performance of building envelopes, an explicit finite element model of heat transfer from indoor to outdoor (or vice versa) is developed. The accuracy of this model is first validated against the electrical circuit analogy model, and then compared with the experimental data measured in a Hot-Box device. A good agreement between the simulation results and experimental results is obtained. The results of this study show that the PCM configuration layer sequence significantly will affect the thermal performance of building envelopes and that the FEM model developed is a promising tool, which after some more development may be used for optimising PCM wall configurations.

    Fulltekst (pdf)
    fulltext
  • 5.
    Zhou, Hongxia
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Fransson, Åke
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Olofsson, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Investigation of phase change materials (PCMs) on the heat transfer performance of building systems2021Inngår i: Journal of Physics: Conference Series, Institute of Physics (IOP), 2021, Vol. 2069, artikkel-id 012020Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The energy use of building systems contributes to a large percentage of total energy consumption, which requires consideration. Solutions of improvement to save energy are crucial. Phase change materials have been proved to be good candidates to be used in building envelopes for energy save. In this paper, an extended Explicit Finite Element Method (ex-FEM), which has been previously introduced and improved, is taken for simulation of temperatures and heat transfer in simplified multilayer wall constructions, consisting of PCM and insulation. The method has been validated against experimental data measured in a so-called Hot-Box. Temperature data are measured at different positions in a number of simplified multilayer walls. Our results show a reasonable good agreement between the simulations and the experiments, at both heating and cooling considering the temperature hysteresis effect in the PCM. The temperature stabilization ability of the PCM is clear, in both the simulations and the experiments, and particularly in the data when the transition range of the PCM is fully activated and matching the temperature variation in the wall at that particular PCM position. Our ex-FEM tool has here been proved to be able to predict the thermal performance of simplified wall constructions of multiple layers with PCMs incorporated.

    Fulltekst (pdf)
    fulltext
  • 6.
    Zhou, Hongxia
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Puttige, Anjan Rao
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Nair, Gireesh
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Olofsson, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Experimental study of micro-encapsulated phase change materials’ influence on indoor temperature2023Inngår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 2654, nr 1, artikkel-id 012064Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The energy use of buildings is almost one-third of the global final energy use. Phase change Materials (PCMs) are substances that undergo phase transition when the surrounding temperature reaches their phase transition temperature. PCMs are reported to be a good candidate as a thermal storage buffer in building systems. Accordingly, PCMs may be able to regulate the indoor temperature while using less energy and thereby contributing in improving the energy performance of the building. In this project a trail to analyse the effect of PCMs in indoor temperature was carried out, in an experimental set-up, using a climate chamber. The chamber temperature is regulated as a sinusoidal profile with a cycle of 24 hours, with a maximum of 40 °C and a minimum of -10 °C. A cubic-box, is placed at the centre of the chamber, and is used as a representation of “building”. A board was made by encapsulating PCMs, with a melting temperature of 24 °C, to gypsum with a fraction of 20 wt%. The influence of PCM added gypsum board on inside temperature of the box is studied. Temperatures at different locations have been measured by thermocouples. The results indicated that the presence of PCM resulted in less temperature variation inside the box with the temperature holding close to the PCM transition temperature for a long period. Also, the PCM boards shifted the temperature profile. Further results are expected to determine the location of the PCM board that is most suitable to reduce the temperature variation inside the building.

    Fulltekst (pdf)
    fulltext
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