The spread of the COVID-19 pandemic is mainly due to the direct transmission routes of SARS-CoV-2 virus-carrying aerosols in indoor environments. In this study, the effect of indoor relative humidity ...(
RH
∞
) on the number concentration, size distribution, and trajectory of sneeze droplets was studied in a confined space experimentally and numerically. Computational fluid dynamics (CFD) simulations using the renormalization group
k
-
ε
turbulence model by considering the one-way and two-way (humidity) coupling models were performed to assess the effects of humidity fields on the propagation of droplets. Number concentration profiles indicated that the
RH
∞
affected the dispersion modes of droplets differently for the puff, droplet cloud, fully-dispersed, and dilute-dispersed droplets phases identified by the shadowgraph imaging technique. The two-way (humidity) coupling model led to a close agreement with the experimental data in all phases. In particular, the two-way coupling provided better agreement with the data in the puff phase compared to the one-way coupling model. However, the one-way coupling model was sufficient for studying the motion of airborne droplets in the other phases. The velocity fields in the droplet cloud were more sensitive to
RH
∞
than the puff and fully-dispersed droplets phases. Also, the effect of
RH
∞
on the maximum spreading distance of droplets,
d
max,sp
, in the puff was insignificant, while its effect became dominant in the dilute-dispersed droplets phase. A dynamic change in the velocity profile of the sneeze jet was seen at a critical relative humidity
RH
∞,crit
of about 48%. At
RH
∞
<
RH
∞,crit
, the number concentration of aerosolized droplets increases, significantly affecting the size distribution and the velocity of droplets. At
RH
∞
≥
RH
∞,crit
, the effect of evaporation time on the number concentration, and diameter of droplets was negligible. At
RH
∞
of 24 and 64%,
d
max,sp
was 2.14 m (7 feet) and 3.05 m (10 feet), respectively. However, a dry indoor environment led to an increase in evaporation rate and more than four times number concentration of aerosolized droplets compared to a humid environment. Thus, the risk of direct transmission of Covid-19 in a humid indoor environment was higher than the dry conditions, which suggested the requirements for incorporating the
RH
∞
effect in the social distancing guideline.
Image, graphical abstract
Globally, the spread and severity of COVID-19 have been distinctly non-uniform. Seasonality was suggested as a contributor to regional variability, but the relationship between weather and COVID-19 ...remains unclear and the focus of attention has been on outdoor conditions. Because humans spend most of their time indoors and because most transmission occurs indoors, we here, instead, investigate the hypothesis that
climate-particularly
relative humidity (RH)-may be the more relevant modulator of outbreaks. To study this association, we combined population-based COVID-19 statistics and meteorological measurements from 121 countries. We rigorously processed epidemiological data to reduce bias, then developed and experimentally validated a computational workflow to estimate indoor conditions based on outdoor weather data and standard indoor comfort conditions. Our comprehensive analysis shows robust and systematic relationships between regional outbreaks and indoor RH. In particular, we found intermediate RH (40-60%) to be robustly associated with better COVID-19 outbreak outcomes (versus RH < 40% or >60%). Together, these results suggest that indoor conditions, particularly indoor RH, modulate the spread and severity of COVID-19 outbreaks.
Indoor relative humidity is an important parameter to determine indoor air quality, occupants’ thermal comfort and building energy consumption. As recommended by ASHRAE, the appropriate indoor ...relative humidity range for a healthy and comfortable indoor environment is between 40% and 65% RH. In order to meet the requirements, the most commonly used method is mechanical dehumidification/humidification system by using electricity. However, this approach is energy consuming. In this paper, a novel precise humidity control material (PHCM) based on Metal-Organic Frameworks (MOFs) is synthesized and its application in built environment is investigated. This material has an S-shape isotherm, high porosity and very high water vapor uptake of 1.62 g/g at 80% RH. It can rapidly adsorb moisture as the indoor relative humidity exceeds 60%, and release moisture as relative humidity drops below 45%. Unlike the conventional desiccants, e.g. zeolites, silica gel etc., MOF-PHCM can autonomously control indoor relative humidity within the desired comfort range at room temperature. Hygrothermal properties of the new material are measured. Numerical simulations have been carried out to study the effect of MOF-PHCM on indoor hygrothermal conditions and building energy consumption in five different climates worldwide (i.e. hot desert, semi-arid, Mediterranean, temperate, and humid subtropical). The results show that MOF-PHCM can effectively control indoor relative humidity fluctuations and reduce building energy consumption in most climates without any additional energy input. MOF-PHCM can be easily regenerated by either night ventilation (e.g. in hot desert, semi-arid, Mediterranean climates) or heating system powered by low-grade energy (e.g. in humid climates).
•The basic concept of Precise Humidity Control Material was proposed.•A new PHCM based on Metal-Organic Frames (MOFs) was synthesized.•MOF-PHCM has an operating RH range between 45% and 60%.•MOF-PHCM can effectively control indoor RH within the desired comfort range.•The regeneration temperature of MOF-PHCM is around 60 °C.
The changing climate is one of the most important factors affecting public health. Older people are particularly threatened due to their less efficient immune systems. To evaluate the potential ...benefits of short-term indoor dehumidification on their circulation and cardiopulmonary health, we conducted a random, cross-over experiment with 36 healthy residents of an aged-care center in Chongqing, China in 2020. Vapor compression dehumidifiers were used over two 48-h periods. At the end of each 48 h, we immediately measured sixteen circulatory system biomarkers of inflammation, coagulation, and oxidative stress; lung function; blood pressure; and heart rate. Indoor temperature and relative humidity were monitored throughout the study period. Linear, mixed-effect models were used to associate health endpoints with indoor relative humidity. This intervention study showed that when the indoor relative humidity decreased from 75% to 45%: (1) the coagulation indicators, sCD40l, and PAI-1, decreased significantly, by 58.82% and 23.50%, respectively; (2) the inflammatory indicators, CRP, IL-6, and TNF-α decreased significantly, by 4.09%, 25.78%, and 10.60%, respectively; (3) PEF, FEV1 and FVC were increased significantly by 20.08%, 14.54%, and 15.75% respectively. To the best of our knowledge, this is the first study to examine the impact of short-term dehumidification on clinical and biochemical measures of cardiorespiratory health in humid areas, and our study suggests that RH in the dehumidified rooms (46.9 ± 8.7%) may be healthier than that in humid rooms (75.2 ± 7.9%). Humidity may be involved in the development of atherosclerosis by activating oxidative stress and mediating the secretion of inflammatory indicators. At the same time, platelet activation induced by oxidative stress stimulates thrombosis to increase cardiovascular risk in older people. Conclusion: This intervention study shows that in a Chinese city like Chongqing with serious indoor environmental humidity, indoor short-term dehumidification has obvious cardiopulmonary benefits for the healthy elderly.
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•This is the first study to explore the cardiopulmonary health effects of indoor relative humidity by a randomized cross-trial.•Air dehumidification led to a significant decrease in inflammatory, coagulation and oxidative stress indicators.•Air dehumidification led to a significant increase in lung function indicators.•Indoor short-term dehumidification has obvious cardiopulmonary benefits for the healthy elderly.
•Air handling processes of two heat pump desiccant wheel (DW) systems are compared.•Energy performance of second-stage DW largely affects the system performance.•Two-stage system saves more energy ...for indoor relative humidity lower than 40%.•Payback period is 5.3 years for two-stage system under 30% indoor relative humidity.
Heat pump desiccant wheel hybrid systems can control indoor temperature and humidity for industrial and civil buildings. To clarify the boundary of heat pump combined single-stage desiccant wheel system and two-stage desiccant wheel system for judging the optimal system under different conditions, the performance of the two systems is analyzed with experiment and simulation method. Firstly, the fresh air process is compared for different humidity set points under typical operation conditions. Secondly, the energy moisture ratio (EMR) of desiccant wheels is analyzed. At last, based on system energy consumption and economy, the humidity boundary of the single-stage and the two-stage dehumidification system is proposed, under different conditions. It is found that the energy performance of desiccant wheel increases with the reducing of humidity set point for both systems, and higher EMR can be obtained by the desiccant wheel of the single-stage dehumidification system for all operation modes. The two-stage dehumidification system is more energy efficient when humidity for the controlled space is lower than 49%, 55% and 40% for high temperature mode, typical summer mode and typical dehumidification mode, separately. With the proposed operation boundary, the optimal system can be quickly judged according to the humidity control requirement and outdoor environment.
Balanced mechanical ventilation equipped with heat recovery has been widely adopted in cold climates to ensure an acceptable indoor environment in energy-efficient buildings. An acknowledged trend to ...achieve more energy savings is to increase the temperature efficiency of heat recovery. As one of the efficient heat recovery technologies extensively used in Nordic countries, the rotary non-hygroscopic heat wheel yields high-temperature efficiency with low frosting risk. Due to the increasing temperature efficiency to comply with the tightened energy performance requirements, moisture recovery in heat wheels may occur more frequently and intensively. Moisture transfer from the extracted air to the supply air in non-hygroscopic heat wheels is not well known and scarcely studied. The impact of the resulting moisture recovery in heat wheels on indoor humidity is unclear.
This study uses machine learning algorithms to model and predict moisture recovery in a heat wheel. The effects of this moisture recovery on the supply and extract air, and indoor moisture levels in different rooms are analytically assessed for a selected single family house. The highest moisture recovery efficiency can reach 68%, and the yearly average value is 19% for the heat wheel in this study. For the specific studied single-family house, the heat wheel's moisture recovery introduces higher peaks in the supply air, bedrooms and living room. In general, the presence of moisture recovery in the heat wheel has a relatively limited effect on indoor humidity levels for a well-insulated and airtight house with the least amount of moisture generation scheme.
•This study models moisture recovery in a heat wheel using machine learning algorithms. The moisture recovery model accounts for different possible causality leading to moisture transfer for the heat wheel.•Yearly moisture recovery efficiencies with a 95% confidence interval and indoor RH for different rooms in a high (2-min) time resolution are revealed for a single-family house.•The effects of the moisture recovery in the heat wheel on the indoor RH are assessed.
Objectives
Exposure to aerosol particles generated from tooth grinding has a negative impact on the health of dental personnel. The aim of this study was to quantitatively analyze the impact of ...indoor relative humidity (IRH) on the deposition of these suspended particles in a well-controlled dental environment.
Materials and methods
In this study, a humidity control system was employed to effectively regulate and maintain indoor relative humidity (IRH). A novel computer-assisted numerical control system was developed to pre-treat the molar specimens, and accurately simulate clinical tooth grinding procedures. Each procedure was performed in triplicate, with an online real-time particle counter (ORPC; TR-8301, TongrenCo.) measuring aerosol production. All testing devices were controlled remotely. The data obtained were statistically analyzed using descriptive statistics and non-parametric tests (Kruskal–Wallis/ Dunn’s post hoc test with Bonferroni correction, p < 0.05).
Results
The findings showed that with increasing IRH, the maximum peak concentration of aerosol particles decreased by 397% from 6.51 × 10
7
particles/m
3
at 30% to 1.64 × 10
7
particles/m
3
at 80%. The Kruskal–Wallis test results indicated a statistically significant effect of IRH on the aerosol increment (p < 0.05).
Conclusions
Increasing the IRH level can effectively promote the deposition of aerosol particles, with a return to baseline within 15 min after reaching 60% or above.
Clinical Relevance
Our study suggested that maintaining IRH above 70% during the cleaning process, allowing natural recovery to ambient humidity levels within 15 min after cleaning, and taking basic precautions, may lead to an adequate reduction in the possible health risks of aerosol contamination.
Due to financial and construction limitations, existing museum buildings often do not allow the retrofit of complex HVAC systems. Thus, an attractive way to improve the quality of the microclimates ...in the museum rooms is to improve the control of systems that are already installed. This paper presents novel proven control strategies to drastically reduce the temperature and relative humidity fluctuations in the exhibitions halls of a Polish museum in a moderate climate. The methods comprise improved control of existing indoor temperature and ventilation airflow control systems, without humidification and dehumidification devices. Simulations were performed with EnergyPlus software; the multi-zone model of the building was calibrated and verified with existing measured data. A warm period of the year was simulated, and six weeks of it were experimentally validated. The existing heating and cooling systems comprised radiators and in some areas, fan-coils. Through improved control schemes and the addition of outdoor air fans, the period with the small relative humidity fluctuations (<±5%) increased from 2% to 88% in the season.
•Control microclimate strategies in the exhibitions halls are presented.•Combination temperature control together with ventilation is analyzed.•When hybrid ventilation is used, de- and humidification devices are not needed.•The proposed methods have significantly greater impact on microclimate in summer.•The proposed systems are not expensive and easy to implement in existing museums.
The population of developed nations spends a significant amount of time indoors, and the implications of poor indoor air quality (IAQ) on human health are substantial. Many premature deaths ...attributed to exposure to indoor air pollutants result from diseases exacerbated by poor indoor air. CO2, one of these pollutants, is the most prevalent and often serves as an indicator of IAQ. Indoor CO2 concentrations can be significantly higher than outdoor levels due to human respiration and activity. The primary objective of this research was to numerically investigate the indoor relative humidity and CO2 in cob buildings through the CobBauge prototype, particularly during the first months following the building delivery. Both in situ experimental studies and numerical predictions using an artificial neural network were conducted for this purpose. The study presented the use of a piecewise autoregressive exogenous model (PWARX) for indoor relative humidity (RH) and CO2 content in a building constructed with a double walling system consisting of cob and light earth. The model was validated using experimental data collected over a 27-day period, during which indoor RH and CO2 levels were measured alongside external conditions. The results indicate that the PWARX model accurately predicted RH levels and categorized them into distinct states based on moisture content within materials and external conditions. However, while the model accurately predicted indoor CO2 levels, it faced challenges in finely classifying them due to the complex interplay of factors influencing CO2 levels in indoor environments.
Nowadays, capillary active interior insulation systems are often promoted because of their ability to avoid interstitial condensation, while a drying out remains possible. Additionally, their alleged ...performance to regulate the indoor climate is often used as a selling point. This paper compares the hygrothermal performance of a capillary active interior insulation system to this of a traditional vapour tight system. Where the previous studies on capillary active insulation systems mainly focused on historical buildings, this study investigates the applicability to standard single leaf masonry walls. Apart from the risk on interstitial condensation, also the impact on the indoor climate and the impact that wind-driven rain has on the hygrothermal behaviour of the retrofitted wall have been analysed. The capillary active system is found to be more sensitive to small modifications of the wall structure (e.g. interior finishing coat, wall thickness), while hardly any differences could be observed for the wall with a vapour tight system. In addition, wind-driven rain can hamper a good hygrothermal behaviour of a capillary active interior insulation system by inducing a lower thermal resistance or an increased indoor relative humidity. Therefore, it should be checked if the advantages of using capillary systems offset the potential disadvantages. A case-specific study is recommended to ensure the applicability of a capillary active interior insulation system.
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