High Relative Humidity Levels Research Articles

Moisture robustness assessment of a window with integrated solar screen using numerical and experimental methods

In this study, a wood-frame window with an integrated exterior solar shading unit has been investigated.Numerical simulations have been carried out to quantify the moisture distribution and drying-out rate of the construction detail. The simulations have been compared to measured data from an ongoing experimental study.The results indicate that built-in moisture in the wall can lead to high levels of relative humidity (RH) in the detail and that design of this detail should be done considering this. Simulations showed that unfavourable RH-levels can be avoided if it is optimally designed. Preliminary measurements indicate the same trends.

Modeling of photovoltaic soiling loss as a function of environmental variables

In this study, an artificial neural network (ANN) approach was applied for modeling the relation between environmental variables and daily change in the Cleanness Index (ΔCI, a measure of performance loss due to soiling) of photovoltaic modules in the field in Doha, Qatar. The daily ΔCI was examined among a number of three-dimensional intervals of the daily mean of the environmental variables (i.e., the intervals of two environmental variables were presented on x and y dimensions, and average values of daily ΔCI on the third dimension), in order to qualitatively establish the relations that might help to develop improved PV soiling prediction models. Then, an ANN-based model was set up to simulate the relationship between daily ΔCI and environmental variables and compared with a linear regression model, both models using the same input variables, including present day and previous day environmental conditions, and cumulative exposure time. Strong interactions were observed among environmental variables PM10, relative humidity (RH) and wind speed (WS) regarding their effect on the daily ΔCI. Overall, higher PM10 resulted in more negative daily ΔCI (i.e. the module became more soiled), and this effect was more visible at low WS and RH levels, but at high WS (>4ms−1) and high RH (>65%) levels, PM10 had no significant (p>0.05, two tailed t-test) effect on daily ΔCI. Mostly, WS and RH determined how much airborne dust accumulates on the module surfaces and thereby affects the output of the PV modules. Higher WS typically favored more positive daily ΔCI when RH was low, but at higher RH levels (>50%) daily ΔCI was more likely to be negative with increasing WS. In fact, high RH levels were related to negative daily ΔCI only at higher WS levels (>2ms−1); at lower WS levels RH had no significant effect on daily ΔCI. These effects were apparently due to the deposition-resuspension mechanisms of dust accumulation on the PV panel surfaces. The ANN model performed significantly better in predicting daily ΔCIas well as cumulative CI than the linear model in term of R2 values and statistical error indexes. The previous day environmental conditions had a significant effect on the modeling outcome. The inclusion of the wind gustiness and cumulative exposure time also considerably improved the model prediction capability. The advantage of the ANN-based model is its simplicity, ease of data fitting and no requirement of an accurate mathematical model.

Volatile organic compounds (VOCs) in photochemically aged air from the eastern and western Mediterranean

Abstract. During the summertime CYPHEX campaign (CYprus PHotochemical EXperiment 2014) in the eastern Mediterranean, multiple volatile organic compounds (VOCs) were measured from a 650 m hilltop site in western Cyprus (34° 57′ N/32° 23′ E). Periodic shifts in the northerly Etesian winds resulted in the site being alternately impacted by photochemically processed emissions from western (Spain, France, Italy) and eastern (Turkey, Greece) Europe. Furthermore, the site was situated within the residual layer/free troposphere during some nights which were characterized by high ozone and low relative humidity levels. In this study we examine the temporal variation of VOCs at the site. The sparse Mediterranean scrub vegetation generated diel cycles in the reactive biogenic hydrocarbon isoprene, from very low values at night to a diurnal median level of 80–100 pptv. In contrast, the oxygenated volatile organic compounds (OVOCs) methanol and acetone exhibited weak diel cycles and were approximately an order of magnitude higher in mixing ratio (ca. 2.5–3 ppbv median level by day, range: ca. 1–8 ppbv) than the locally emitted isoprene and aromatic compounds such as benzene and toluene. Acetic acid was present at mixing ratios between 0.05 and 4 ppbv with a median level of ca. 1.2 ppbv during the daytime. When data points directly affected by the residual layer/free troposphere were excluded, the acid followed a pronounced diel cycle, which was influenced by various local effects including photochemical production and loss, direct emission, dry deposition and scavenging from advecting air in fog banks. The Lagrangian model FLEXPART was used to determine transport patterns and photochemical processing times (between 12 h and several days) of air masses originating from eastern and western Europe. Ozone and many OVOC levels were ∼ 20 and ∼ 30–60 % higher, respectively, in air arriving from the east. Using the FLEXPART calculated transport time, the contribution of photochemical processing, sea surface contact and dilution was estimated. Methanol and acetone decreased with residence time in the marine boundary layer (MBL) with loss rate constants of 0.74 and 0.53 day−1 from eastern Europe and 0.70 and 0.34 day−1 from western Europe, respectively. Simulations using the EMAC model underestimate these loss rates. The missing sink in the calculation is most probably an oceanic uptake enhanced by microbial consumption of methanol and acetone, although the temporal and spatial variability in the source strength on the continents might play a role as well. Correlations between acetone and methanol were weaker in western air masses (r2 = 0.68), but were stronger in air masses measured after the shorter transport time from the east (r2 = 0.73).

Indoor air quality measurements in Hungarian residential buildings

Indoor air quality is a major part of indoor environmental quality and plays an important role in creating sustainable and healthy indoor environments. Well-being, health and comfort are affected by indoor air quality. The measurements that are introduced in this research paper were used to record the results of three different residential interiors. These data are a part of a larger scale research project that included the evaluation of residential buildings, offices, university interiors and for instance nurseries. The reason behind conducting the measurements in these interiors was that in all of the examples inadequate indoor air quality and therefore human discomfort, illness and also building failure occurred. In this paper the theoretical background of the research and the measurement of indoor air quality (indoor air temperature, relative humidity level and carbon dioxide level) will be introduced. The poor indoor air quality in these buildings is a result of a complex system. The thermal bridges of the facade cause cold interior surfaces, the airtight solutions cause high relative humidity levels. These two combined result in mould appearance. Besides, the lack of appropriate ventilation rate can be the third part of the reason behind poor indoor air quality. Based on the results of the measurement data, different solutions are suggested in each case to improve indoor environmental and air quality, in accordance with creating healthier indoor environments.

Steady state and transient simulation of anion exchange membrane fuel cells

We present a new model for anion exchange membrane fuel cells. Validation against experimental polarization curve data is obtained for current densities ranging from zero to above 2 A cm−2. Experimental transient data is also successfully reproduced. The model is very flexible and can be used to explore the system's sensitivity to a wide range of material properties, cell design specifications, and operating parameters. We demonstrate the impact of gas inlet relative humidity (RH), operating current density, ionomer loading and ionomer ion exchange capacity (IEC) values on cell performance. In agreement with the literature, high air RH levels are shown to improve cell performance. At high current densities (>1 A cm−2) this effect is observed to be especially significant. Simulated hydration number distributions across the cell reveal the related critical dependence of cathode hydration on air RH and current density values. When exploring catalyst layer design, optimal intermediate ionomer loading values are demonstrated. The benefits of asymmetric (cathode versus anode) electrode design are revealed, showing enhanced performance using higher cathode IEC levels. Finally, electrochemical reaction profiles across the electrodes uncover inhomogeneous catalyst utilization. Specifically, at high current densities the cathodic reaction is confined to a narrow region near the membrane.

Understanding the mechanisms of oxygen diffusion through surface functionalized nanocellulose films

A concept for direct surface modification on self-standing films of cellulose nanofibrils (CNF) is demonstrated using an aminosilane group in cellulose compatible solvent (dimethyl acetamide, DMA). The chemically modified structure efficiently prevents the oxygen molecules from interacting with the nanocellulose film in the presence of water molecules. Oxygen permeability values lower than 1mLmmm−2day−1atm−1 were achieved at extremely high levels of relative humidity (RH95%). The aminosilane reaction is compared to conventional hydrophobization reaction using hexamethyldisilazane. The differences with respect to interactions between cellulosic nanofibrils, water and oxygen molecules taking place with aminated and silylated CNF films correlated with the degree of surface substitution, surface hydrophilicity and permeability of the formed layer. The self-condensation reactions taking place on the film surface during aminosilane-mediated bonding were decisive for low oxygen permeability. Experimental evidence on the importance of interfacial processes that hinder the water-cellulose interactions while keeping film’s low affinity towards oxygen is demonstrated.

Influence of sheath air humidity on measurement of particle size distribution by scanning mobility particle sizer

Size distribution is a critical parameter that determines the dynamics, transport and deposition of aerosol particles in a given system. Scanning Mobility Particle Sizer (SMPS), based on the principle of particle mobility classification in an electric field is one of the commonly used instruments for measurement of size distribution. To maintain laminarity of aerosol particles, a sheath air flow is generally provided annular to the sampled aerosol particle flow. Available literature suggests drying of the sheath air to avoid effect on charge neutralisation of the sampled particles and to safeguard the central high voltage electrode. However, there are certain ambiguities associated with the use of dried sheath air for SMPS measurements. This study investigates the effect of sheath air drying on particle size distribution measurements. It focuses on experiments performed with substrates of differing hydrophilic properties (e.g., NaCl, NaNO3 and nichrome) at different relative humidity (RH) levels. Results indicated a prominent effect of sheath air drying dependent on RH and material properties. For NaCl aerosol particles, a much lowered (by a factor of 2) mean size was observed at higher RH level with SMPS using a sheath air drier. The results indicate that the effect of sheath air drying on SMPS measurements should be clearly included in algorithms and protocols when interpreting the measurements.

Permeation and optical properties of YAG:Er3+ fiber membrane scintillators prepared by novel sol–gel/electrospinning method

An electrospinning method for fabrication of the YAG:Er3+ fibrous membrane is developed and the scintillation properties of the obtained membranes were examined. A homogeneous precursor YAG sol was synthesized allowing to control the sol–gel transition. The synthesized precursor allows one to achieve the 5 wt.% level of fiber doping with Er without formation of any undesired crystalline phases. It was found that the relative humidity had a strong impact on the fiber microstructure. The fibers obtained at the low relative humidity level (~30%) had almost straight cylindrical shape with an average diameter of ~590 nm, their surface was smooth. The shape of fibers obtained at the high relative humidity level (~50%) deviated from the straight cylindrical shape and the average diameter was larger, ~1.12 µm. The fluid permeability of membranes, K, obtained at the low relative humidity level was measured using an upward wicking experiment to give K~10−13 m2. The YAG:Er membrane presented a strong green photoluminescence under ultraviolet excitation and intense radioluminescence dominated by emission lines at 398 and 467 nm under the X-ray excitation. The properties of these materials make them promising candidates as porous scintillators for the detection of ionizing radiation of flowing fluids.

Human responses to high humidity in elevated temperatures for people in hot-humid climates

The impact of high humidity at high temperatures on the thermal and humid responses of people in hot-humid climates is critical for ensuring a suitable indoor environmental quality and promoting the energy efficiency of buildings. Thirty healthy young people (15 males and 15 females), who were born and raised in hot-humid areas of China, were recruited as subjects. Six experimental conditions with high levels of air temperature (Ta) and relative humidity (RH) (29°C/50%, 29°C/70%, 29°C/90%, 32°C/50%, 32°C/70%, 32°C/90%), with one extreme hot condition and two cool conditions, were tested. Both psychological and physiological responses were collected. The results indicate that the impact of humidity on human responses was not significant when the relative humidity was below 70% and was significant and increased with an increase in air temperature when the relative humidity was above 70%. The relationships between the thermal and humid responses and the ET* or RH were identified as linear or polynomial functions. The upper limit for people in hot-humid climates who engaged in sedentary activity and dressed in summer clothing (0.57 clo) was determined to be 30.3 °C in ET* for the 90% acceptable range and 32.3 °C in ET* for the 80% acceptable range. This study provides useful information for the humidity requirements of indoor environments in hot-humid climates.

Effects of relative humidity in the convective heat transfer over flat surface using ionic wind

This study investigates the effects of relative humidity (RH) on the generation of ionic wind and the subsequent convective heat transfer enhancement over a flat surface. The overall power consumption by the positive ionic wind was found to be 2.4 times lower than that of the negative ionic wind. Despite the differences in the power consumption, both positive and negative ionic wind displayed similar average velocity at low RH levels (30–50%), while the negative ionic wind showed slightly higher average velocity compared to the positive ionic wind at higher RH levels (60–70%). Besides velocity magnitude, the velocity profile of the ionic wind along the vertical axis was also seen to change with increase in RH. On a similar note, the heat transfer coefficients of both positive and negative ionic wind was seen to decrease with increase in RH, attributed to the decrease in velocity. A comparison of the heat transfer enhancement ratio showed that the negative ionic wind produced better enhancement than the positive ionic wind, being able to enhance the heat transfer by 1.6 compared to 1.43 of the latter.

Performance-based methods for masonry building rehabilitation using innovative leaching and hygrothermal risk analyses

The design and selection of a retrofitting solution can be carried out through performance-based methods (according to constructive materials behaviour, hygrothermal and occupants’ behaviour or climatic conditions) as an alternative to the deem-to-satisfy approach. The future likelihood of saturated conditions in masonry building fabrics is increased by the consequences of climatic changes, enhancing the need of selecting adequate solutions for buildings retrofitting. As it was intended to propose the optimal solutions for the preservation of a Portuguese convent, major issues such as the high level of relative humidity inside the building and the leaching phenomenon of the mortar joints between bricks masonry were taken into account as a potential degradation causes. In situ inspection was made together with the analysis of the existing documentation regarding the building. The selection of the best retrofitting measures was supported by innovative leaching and hygrothermal risk analyses using probabilistic approaches. The probability of leaching of the mortar joints is minimised if NHL5 mortars are used for re-pointing when compared to NHL2 or NHL3.5 mortars. Regarding the hygrothermal performance of the building, indoor comfort increases 10% by increasing the Moisture Buffering Value of the indoor surface using eco-efficient earth plasters.

Modulating memristive performance of hexagonal WO3 nanowire by water-oxidized hydrogen ion implantation

In a two-terminal Au/hexagonal WO3 nanowire/Au device, ions drifting or carriers self-trapping under external electrical field will modulate the Schottky barriers between the nanowire and electrodes, and then result in memristive effect. When there are water molecules adsorbed on the surface of WO3 nanowire, hydrogen ions will generate near the positively-charged electrode and transport in the condensed water film, which will enhance the memristive performance characterized by analogic resistive switching remarkably. When the bias voltage is swept repeatedly under high relative humidity level, hydrogen ions will accumulate on the surface and then implant into the lattice of the WO3 nanowire, which leads to a transition from semiconducting WO3 nanowire to metallic HxWO3 nanowire. This insulator-metal transition can be realized more easily after enough electron-hole pairs being excited by laser illumination. The concentration of hydrogen ions in HxWO3 nanowire will decrease when the device is exposed to oxygen atmosphere or the bias voltage is swept in atmosphere with low relative humidity. By modulating the concentration of hydrogen ions, conductive hydrogen tungsten bronze filament might form or rupture near electrodes when the polarity of applied voltage changes, which will endow the device with memristive performance characterized by digital resistive switching.

Efecto del método de envejecimiento artificial sobre la germinación de semillas de maíz

Some of the recommended tests to evaluate physiological quality of seed with increased accuracy cannot be commonly practiced due to the high costs of equipment From the selection of seed obtained at the “Centro de Genética del Colegio de Postgraduados in Montecillo, México”, various laboratory trials were conducted to obtain higher precision and economic efficiency that would allow for artificial ageing tests. Maize seed from the open pollinated variety “Huamantla” with 91 % germination was placed over a wire mesh in metal pots, glass jars and plastic boxes of various sizes. Distilled water was added to each of these containers leaving an open space between the water and the seeds. The air tight containers were placed In both a drying oven and a germination chamber, calibrated to 42+/- 1C for 96 hours. The Interior environment was assumed to approach high levels of relative humidity (85-100%). The results demonstrated a lowering of germination from 1 to 82% depending on treatment. In this sense the plastic box treatment (9.5 x 8.0 x 4.5 cm) placed in the germinator was more efficient with a reduction in germination of 82% and the metal pot placed In the drying oven resulted In being less efficient (1 to 5%) respectively. It was also observed that seeds placed in the plastic boxes absorbed more moisture than the metal boxes which explains the Increased deterioration found for the latter.

Composition of thin Ta2O5 films deposited by different methods and the effect of humidity on their resistive switching behavior

The resistive switching behavior of Cu/Ta2O5/Pt atomic switches, in which the Ta2O5 film was deposited by electron-beam (EB) evaporation and radio-frequency sputtering (SP), was investigated under different relative humidity (RH) levels. Fourier-transformed infrared spectroscopy and X-ray photoelectron spectroscopy measurements revealed that both films possess the oxygen-rich composition and higher water absorption capability of EB films. The Cu/Ta2O5-SP/Pt cell showed a stable, nonvolatile switching behavior in the observed RH range, whereas the Cu/Ta2O5-EB/Pt cell exhibited a similar behavior up to 50% RH, but altered from nonvolatile to volatile switching at higher RH levels. The observed volatile switching behavior of the Cu/Ta2O5-EB/Pt cell can be explained by increased ion migration, assisted by absorbed water and/or proton conduction in hydrated environments. The results indicate that the water uptake ability of the matrix film plays a crucial role in determining the resistive switching behavior of oxide-based atomic switches.

Impact of Humidity on the Biological Development of Aphidoletes aphidimyza (Diptera: Cecidomyiidae).

Aphidoletes aphidimyza Rondani (Diptera: Cecidomyiidae) is one of the most important predators used in the augmentative biological control of aphids worldwide. However, due to its particular life history, mass rearing A. aphidimyza remains difficult. Our results show that a high relative humidity level during pupation optimizes the development of A. aphidimyza . By improving humidity levels during pupae storage, we improved the production efficiency and nearly achieved a 100% adult emergence rate. These results allow us to suggest a new rearing method for the aphid predator A. aphidimyza .

Internal curing of high performance mortars with bottom ash

In Thailand, approximately 9500 tons of bottom ash are produced annually by the boilers of the SCG Paper business within the SCG conglomerate. In an effort to find high-value uses of this industrial waste and to limit landfilling, the internal curing performance of different types of bottom ash, both from stoker and circulating fluidized bed boilers was studied by means of internal relative humidity and autogenous deformation measurements on high-performance mortars. In this application, the bottom ash particles are pre-saturated with water, which is released during cement hydration and contributes to reduce self-desiccation and shrinkage of the mortars.Both bottom ash types had high open porosity and high water absorption (10–20% by mass), accompanied by steep desorption at high relative humidity levels, which are favourable because they promote water release. The addition of bottom ash was able to keep the internal relative humidity high and to almost eliminate autogenous shrinkage, with little impact on the mechanical properties of the mortars. In addition, the bottom ash is characterized by very fast absorption when immersed in water, likely due to highly interconnected pores. Thanks to this property, it can be added dry to the mixture together with surplus water, avoiding the saturation step and saving time and resources.

Mechanism of craquelure pattern formation on panel paintings

The drying shrinkage accumulation from exposure of freshly prepared gesso layers to relative humidity (RH) cycles was determined to elucidate the mechanism of craquelure pattern formation on panel paintings. The progresive drying shrinkage of the gesso is observed only under the cycles going to high RH levels which bring about transitions from brittle to ductile state of the material. The first incidence of fracture on the gesso layers occurred after a limited number of cycles ranging between a few and 100 for a range of layer thickness between 0.5 and 1 mm. The craquelure patterns stabilised also after a limited number of cycles (30 for the 1-mm thick layer). Upon increase in the gesso layer thickness, the strength of the layer is reduced and the spacing of shrinkage fractures increases. The study demonstrated that craquelure patterns, mimicking historical ones, can be realistically produced in laboratory conditions. Such studies would provide useful information for preparing specimens simulating historic panel paintings and would inform the current efforts on automatic, computer-aided classifications of crack formations on paintings.

Willow-based evapotranspiration systems for on-site wastewater effluent in areas of low permeability subsoils

Six different full-scale willow evapotranspiration systems receiving both septic tank and secondary treated domestic effluent from single houses in Ireland have been investigated as a potential solution to the problem of on-site effluent disposal in areas with very low permeability subsoils. Continuous monitoring of rainfall, reference evapotranspiration, effluent flows and water level in the sealed systems revealed varying evapotranspiration rates across the different seasons with annual rates ranging from 576 to 929mm/yr. The results showed that no system managed to achieve zero discharge in any year remaining at maximum levels for much of the winter months, indicating some loss of water by lateral exfiltration at the surface. This was attributed partly to the fact that the in-situ low permeability soil that had been excavated to form the lined basin was shown to have a much lower effective (useful) porosity when used to backfill the systems than had been assumed in the original designs. In addition, the Irish maritime climate, with its typical high relative humidity levels throughout the year (>85% on average), resulted in muted evapotranspiration performance of the systems. However, chemical and microbiological sampling of the water in the sumps and ponded water over the winter periods demonstrated that the systems were acting as excellent passive pollutant attenuation processes.

Green roofs: what can we learn from desert plants?

Green roofs in the Mediterranean region are often exposed to high levels of radiation, extreme temperatures, and an inconsistent water supply. To withstand these harsh conditions in shallow soils and poorly aerated growth media, plants must be armored with adaptations. Strategies that have evolved in desert plants can play significant roles in the use of plants for green covers. In the following, we will specifically focus on (1) heat and radiation, (2) drought, and (3) salinity. Further, we will discuss (4) interactions between neighboring plants. Finally, we will (5) propose a design for diverse green roofs that includes horticultural and medicinal products and provides diverse habitats. Many desert plants have developed morphological and anatomical features to avoid photo-inhibition, which can be advantageous for growth on green roofs. Plants exhibiting C4photosynthesis or crassulacean acid metabolism (CAM) photosynthesis have a protected hydraulic system that enables growth under dry conditions. Furthermore, dew and high levels of relative humidity can provide reliable water sources under limited precipitation. Halophytes are protected against salinity, ionic specific stress, and nutritional imbalances, characteristics that can be advantageous for green roofs. Under limited space, competition for resources becomes increasingly relevant. Allelopathy can also induce the germination and growth inhibition of neighboring plants. Many desert plants, as a result of their exposure to environmental stress, have developed unique survival adaptations based on secondary metabolites that can be used as pharmaceuticals. A systematic survey of plant strategies to withstand these extreme conditions provides a basis for increasing the number of green roof candidates.

Optical fibre Fabry–Perot relative humidity sensor based on HCPCF and chitosan film

An optical fibre Fabry–Perot interferometer (FPI) sensor for relative humidity (RH) measurement is proposed. The FPI is formed by splicing a short section of hollow-core photonic crystal fibre(HCPCF) to single mode fibre and covering a chitosan film at the end of HCPCF. The refractive index of chitosan and film thickness will change with ambient RH, leading to the change in the reflected interference spectrum of FPI. RH response of the FPI sensor is analysed theoretically and demonstrated experimentally. It shows nonlinear response to RH values from 35 to 95%RH. The interference fringe shifts to shorter wavelength as RH increases with a maximum sensitivity of 0.28 nm/%RH at high RH level. And the fringe contrast also decreases as RH increases with an available maximum sensitivity of 0.5 dB/%RH. The sensor shows good stability and fast response time less than 1 min. With its advantages of compact structure, good performance, simple and safe fabrication, the proposed optical fibre FPI sensor has great potential for RH sensing.