Conventional room air conditioners consume a significant amount of energy, and thereby negatively affect the environment. In this perspective, passive air conditioning systems using phase change ...material (PCM) are very promising and widely investigated recently. In this study, influence of a PCM-based passive air conditioner on temperature distribution was experimentally studied in a test room under the local tropical climatic conditions. Coconut oil and water were used for latent heat storage and sensible heat storage, respectively. A storage panel was constructed with two openings—an outlet for conditioned air and an inlet for indoor air, then filled with coconut oil or water to create an additional internal thermal mass (ITM) in the room. The storage material was discharged at night in the indoor or outdoor, and stratum air circulation was utilized to provide the conditioned air into the room during diurnal period. Temperature measurements were conducted at five vertical and five horizontal points. The gained results showed that employing ITM heat storage panel in the room reduced peak temperatures and enhanced the thermal environment. Coconut oil ITM provided 0.5 °C lower peak temperature in the occupant zone while greater temperature reductions were observed in the upper zone compared to the reference case. In addition, ITM panel significantly decreased the observed temperature fluctuations throughout a day. This study revealed that ITM-based stratum air circulation can be a profound solution to the existing high energy consumption problem of conventional air conditioners used in the small urban houses under tropical climate.
•A PCM-based ITM coupled with stratum air circulation was experimentally investigated in a real-scale room.•ITM panel reduced indoor temperature fluctuation and peak temperature in all zones during diurnal period.•Coconut oil performed better than water as a heat storage material.•ITM panel provides lower amplitudes and more homogeneous distributions in the occupied zone.
Household humidification is widely practiced to combat dry indoor air. While the benefits of household humidification are widely perceived, its implications to the indoor air have not been critically ...appraised. In particular, ultrasonic humidifiers are known to generate fine particulate matter (PM). In this study, we first conducted laboratory experiments to investigate the size, quantity, and chemical composition of PM generated by an ultrasonic humidifier. The mass of PM generated showed a correlation with the total alkalinity of charge water, suggesting that CaCO3 is likely making a major contribution to PM. Ion chromatography analysis revealed a large amount of SO42− in PM, representing a previously unrecognized indoor source. Preliminary results of organic compounds being present in humidifier PM are also presented. A whole‐house experiment was further conducted at an actual residential house, with five low‐cost sensors (AirBeam) monitoring PM in real time. Operation of a single ultrasonic humidifier resulted in PM2.5 concentrations up to hundreds of μg m−3, and its influence extended across the entire household. The transport and loss of PM2.5 depended on the rate of air circulation and ventilation. This study emphasizes the need to further investigate the impact of humidifier operation, both on human health and on the indoor atmospheric chemistry, for example, partitioning of acidic and basic compounds.
Characterization of rock discontinuities and rock bridges is required to define stability conditions of fractured rock masses in both natural and engineered environments. Although remote sensing ...methods for mapping discontinuities have improved in recent years, remote detection of intact rock bridges on cliff faces remains challenging, with their existence typically confirmed only after failure. In steep exfoliating cliffs, such as El Capitan in Yosemite Valley (California, USA), rockfalls mainly occur along cliff-parallel exfoliation joints, with rock bridges playing a key role in the stability of partially detached exfoliation sheets. We employed infrared thermal imaging (i.e., thermography) as a new means of detecting intact rock bridges prior to failure. An infrared thermal panorama of El Capitan revealed cold thermal signatures for the surfaces of two granitic exfoliation sheets, consistent with the expectation that air circulation cools the back of the partially detached sheets. However, we also noted small areas of warm thermal anomalies on these same sheets, even during periods of nocturnal rock cooling. Rock attachment via rock bridges is the likely cause for the warm anomalies in the thermal data. 2-D model simulations of the thermal behavior of one of the monitored sheets reproduce the observed anomalies and explain the temperature differences detected in the rock bridge area. Based on combined thermal and ground-based lidar imaging, and using geometric and rock fracture mechanics analysis, we are able to quantify the stability of both sheets. Our analysis demonstrates that thermography can remotely detect intact rock bridges and thereby greatly improve rockfall hazard assessment.
•A solar dish receiver with the modified air-curtain system is proposed.•A validated CFD work is done for simulating the convective heat transfer process.•The convective heat loss and its fluctuation ...in the novel receiver are clearly reduced.
Here we propose a forced air circulation system to reduce the convective heat loss across the aperture of a dish concentrator. The function of the proposed system was validated with computational fluid dynamics (CFD) simulations. Compared to a concentrator without such a system, the modified solar dish cavity receiver could clearly reduce the convective heat loss and its fluctuation in the receiver. In the best case studied, the convective heat losses could be suppressed by up to 58%. In addition, two types of air circulation modes (clockwise and anticlockwise) were compared, showing that the anticlockwise mode yields better performance.
Nearly 1 billion people live without electricity at home. Energy poverty limits their ability to take autonomous actions to improve air circulation and the cooling of their homes. It is therefore ...important that electricity-access planners explicitly evaluate the current and future air circulation and cooling needs of energy-poor households, in addition to other basic energy needs. To address this issue, we combine climate, socio-economic, demographic and satellite data with scenario analysis to model spatially explicit estimates of potential cooling demand from households that currently lack access to electricity. We link these demand factors into a bottom-up electrification model for sub-Saharan Africa, the region with the world's highest concentration of energy poverty. Accounting for cooling needs on top of baseline household demand implies that the average electrification investment requirements grow robustly (a scenario mean of 65.5% more than when considering baseline household demand only), mostly due to the larger generation capacity needed. Future climate change could increase the investment requirements by an additional scenario mean of 4%. Moreover, the share of decentralised systems as the lowest-cost electrification option falls by a scenario mean 4.5 percentage points of all new connections. The crucial determinants for efficient investment pathways are the adoption and use of cooling appliances, the extent of climate change, and the baseline electricity demand. Our results call for a more explicit consideration of climate-adaptative energy needs by infrastructure planners in developing countries.
•Large unmet cooling needs among energy poor households of Africa.•Growing heat stress in the region due to climate change.•Techno-economic scenario modelling of cooling appliances uptake and use.•Estimation of potential cooling energy demand from energy poor households.•Geospatial analysis to support cooling-inclusive electrification planning.
•Two DPSAH having uniform fins and double glass cover have been experimentally analyzed.•Packed beds above absorber surface of DPSAH-1 has been added.•Experiments have been performed under natural ...and forced convection at same weather conditions.•Results display that the performance of DPSAH-1 is a considerable higher than DPSAH-2.•Natural convection has a large effect on DPSAH performance than forced convection.
This paper presents an experimental work on two trapezoidal double-pass solar air heaters (DPSAH) having double glass covers under natural and forced air circulation conditions to investigate their performances by adding packed beds above the absorber surface on one them for target of comparison. The DPSAH-1 has been operated with adding porous medium, whereas DPSAH-2 has been operated without adding porous medium. Experiments for each model have been performed in winter and compared under identical conditions. The results demonstrate that DPSAH-1 considerably enhances the system performance as compared to DPSAH-2. Results also indicate that the higher efficiency has been obtained when the systems are operated under natural convection. The peak efficiencies of DPSAH-1 and DPSAH-2 have been obtained equal to 87% and 82% for natural convection case and 81% and 67% for forced convection case for lower air mass flowrate, respectively. A considerable temperature difference has been found with natural process as compared to forced process. The advancement in performance of DPSAH-1 confirms that the adding porous medium and types of air circulation have considerable impact on heat transfer rate. Therefore, it can be concluded that DPSAH-1 is better than DPSAH-2, particularly for forced convection case including the applications that needs high temperatures and vice-verse.
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Boreal wintertime planetary-scale atmospheric circulations and their possible consequences to widespread fog occurrences over the Indo-Gangetic Plains (IGP) region of the Himalayan valley are ...investigated in this study. Among the different fog types, radiation fog type seen at night or early morning hours favored by large-scale subsidence aloft and strong near-surface inversion is focused in this study. A composite analysis reveals that upper air circulation associated with 105 fog days over the IGP region show a trail linked to circulation anomalies over the Eurasian continents and the Arctic Circle. The findings suggest that there is a footprint of the Arctic Oscillation (AO) and conventional Eurasian (EU) circulation patterns linked to anticyclonic circulation aloft over the IGP region. Although widespread IGP fog occurrences under the large-scale subsidence environment are seen to occur during both phases of AO, the negative AO phase (high pressure environment over the Arctic Circle) portends a greater likelihood for fog occurrences in the IGP region. A coupling of positive mid-tropospheric height anomalies over western Eurasia and the anticyclonic circulation anomalies over the IGP region is evident during the IGP fog periods concomitant with EU positive (height excess over Siberia) phase. Further, anomalous circulation over the IGP region during the fog periods appears to rely more on the strength of the AO negative phase than the circulation strengths over Eurasia. On the contrary, the Eurasian circulation largely appears to influence the subsidence aloft over the IGP region irrespective of the strength of the AO positive phase. It is also noted that upper-air circulation during non-foggy periods over the IGP region has conformity with positive AO phase and rapidly progressing EU pattern. These planetary-scale teleconnection pathways offer new dynamical insights into comprehending widespread IGP fog scenario, which have been hitherto perceived mostly from a regional context.
Heat pumps are widely used in many fields due to their high efficiency and energy saving potential. However, the application of single-stage vapor-compression heat pump dryer is limited due to low ...drying temperature and the decreasing reliability for hightemperaturedrying. In order to apply heat pump to high temperature drying, a heat pump drying system using a solar assisted flash tank vapor injection cycle (HPDS-SFVIC) is presented. This system allows the solar collector to absorb solar energy at a lower temperature and achieves significant improvement of heating capacity and drying temperature. The effects of component configuration and various operating conditions on the drying system with open, bypass, and closed air circulation loop are evaluated, respectively. The results show that under a typical operating condition, the proposed cycle achieves great performance improvement of 21.8% and 75.8% in both the heating coefficient of performance (COPh) and heating capacity, compared with the conventional cycle. Utilization of solar energy is advantageous to provide higher air temperature for drying. With increased solar radiation intensity and collector area, heating capacity and drying temperature can be improved, while COPh remains constant as 5.0–5.2. When the drying system provides dry air at 65 °C stably, it saves 27.8%–41.7% of power consumption, and COPh is improved by 41.2%–62.1% on average.
•The theoretical upper limit efficiency of the solar still with the optimized mass transfer is given.•The upper limit of mass transfer efficiency reaches up to 94.5% under 700 W/m2 of input power ...density.•The energy efficiency of solar still is sensitive to the inner air circulation velocity.•The upper limit is approached experimentally by using small fan power (0.2 ∼ 0.6 W) and low cost (3 $).•This work might inspire many solar desalination systems that involve latent heat recovery processes.
Solar still is an green energy, low-cost and easy-to-maintain desalination system. Enhancing the mass transfer is a very important strategy for improving solar still. However, the analysis of the upper limit performance of the solar still related to the optimized mass transfer is lacking. In this work, by assuming the most ideal heat and mass transfer condition in solar still, the theoretical upper limit performance of solar still is given. The theoretical results reveal that the mass transfer in solar still is sensitive to the inner air circulation. The mass transfer in the solar still reaches up to the upper limit quickly when the air circulation is enhanced. By enhancing the mass transfer process, the theoretical upper limit of the energy efficiency in solar still is around 87%, 91.5%, and 94.5%, respectively, for the input power density at 300 W/m2, 500 W/m2, and 700 W/m2. Experimental results show that in a solar still with the basin size at 25 cm × 25 cm, the theoretical upper limits can be approached by only using 0.2 W ∼ 0.6 W of fan power. Compared to the efficiency of conventional solar still without modification, the upper limit energy efficiency is 48%, 28%, and 20% higher, respectively, under 300 W/m2, 500 W/m2, and 700 W/m2 input power density. Meanwhile, to reach the upper limit, the total extra cost of the modification can be as low as 3 $ by using a fan in solar still. This work offers a new understanding of the mass transfer process and provides an effective and economical optimizing way not only for the solar still but other themal systems with heat and mass transfer.
Background: Since the dawn of cities, the built environment has both affected infectious disease transmission and evolved in response to infectious diseases. COVID-19 illustrates both dynamics. The ...pandemic presented an opportunity to implement health promotion and disease prevention strategies in numerous elements of the built environment. Objectives: This commentary aims to identify features of the built environment that affect the risk of COVID-19 as well as to identify elements of the pandemic response with implications for the built environment (and, therefore, for long-term public health). Discussion: Built environment risk factors for COVID-19 transmission include crowding, poverty, and racism (as they manifest in housing and neighborhood features), poor indoor air circulation, and ambient air pollution. Potential long-term implications of COVID-19 for the built environment include changes in building design, increased teleworking, reconfigured streets, changing modes of travel, provision of parks and green-space, and population shifts out of urban centers. Although it is too early to predict with confidence which of these responses may persist, identifying and monitoring them can help health professionals, architects, urban planners, and decision makers, as well as members of the public, optimize healthy built environments during and after recovery from the pandemic.
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