The high-capacity tensiometer and thermocouple psychrometer measure xylem water potential with high accuracy and adequate response time, as demonstrated by simultaneous measurements on sapling stems.
...Abstract
The pressure chamber, the most popular method used to measure xylem water potential, is a discontinuous and destructive technique and is therefore not suitable for automated monitoring. Continuous non-destructive monitoring could until very recently be achieved only by use of the thermocouple psychrometer (TP). Here we present the high-capacity tensiometer (HCT) as an alternative method for continuous non-destructive monitoring. This provided us with a unique chance to cross-validate the two instruments by installing them simultaneously on the same sapling stem. The HCT and the TP showed excellent agreement for xylem water potential less than –0.5 MPa. Response to day/night cycles and watering was remarkably in phase, indicating excellent response time of both instruments despite substantially different working principles. For xylem water potential greater than –0.5 MPa, the discrepancies sometimes observed between the HCT and TP were mainly attributed to the kaolin paste used to establish contact between the xylem and the HCT, which becomes hydraulically poorly conductive in this range of water potential once dried beyond its air-entry value and subsequently re-wetted. Notwithstanding this limitation, which can be overcome by selecting a clay paste with higher air-entry value, the HCT has been shown to represent a valid alternative to the TP.
Though power conversion efficiencies of perovskite solar cells of over 21% have been reported, the degradation of the performance of these cells in the presence of moisture still inhibits the ...commercialization of these otherwise promising devices. Herein, we decided to utilize the moisture sensitivity of perovskite materials and fabricate a moisture detector based on high-quality CH 3 NH 3 PbI 3−x Cl x nanosheet arrays. The resulting devices present a high sensitivity towards humidity with device resistance significantly dropping from 1.28 × 10 8 Ω at 30% relative humidity (RH) to 7.39 × 10 4 Ω at 90% RH and a response even faster than that of the commercial psychrometer. This response was even steeper than those of commercial psychrometers. Moreover, our device showed good reversibility and impressive specificity. Thus, the humidity sensitivity of perovskites, while disadvantageous for solar cell applications, was found to be quite applicable in a new field.
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•Proposed a data mining based method analyzing VRF energy consumptions.•72 test conditions: 3 part load ratios, 8 refrigerant charges, 3 cooling conditions.•Data clustering identifies ...3 distinct energy consumption patterns.•Association rules find undercharge, compressor frequency switch control patterns.•Domain knowledge is used to interpret VRF energy consumption patterns and rules.
Variable refrigerant flow systems account for a considerable portion of energy consumption in buildings. In order to improve the energy efficiency and estimate the energy saving potentials of variable refrigerant flow systems this study proposes a data mining based method to identify and interpret the power consumption patterns and associations. Two descriptive data mining algorithms, clustering analysis and association rules mining, are used for data partitioning and association mining. The proposed method consists of four phases: data pre-processing, data partitioning, data association mining and knowledge interpretation. Experimental data collected from a tested variable refrigerant flow system in the standard psychrometer testing room are pre-processed and prepared to examine the proposed method. Three time independent influential factors: part load ratio, refrigerant charge level and cooling condition are analyzed. Results show that the method is able to help identify energy consumption patterns and extract energy consumption rules in variable refrigerant flow systems. Three distinct energy consumption patterns are identified: undercharge fault, low and high part load ratio conditions. For compressor operation frequency switch control and refrigerant undercharge patterns, the energy saving potentials could be estimated by making comparisons between energy patterns and rules in a top-down way.
Abstract
Water stored in tree stems (i.e., trunks and branches) is an important contributor to transpiration that can improve photosynthetic carbon gain and reduce the probability of cavitation. ...However, in tall trees, the capacity to store water may decline with height because of chronically low water potentials associated with the gravitational potential gradient. We quantified the importance of elastic stem water storage in the top 5–6 m of large (4.2–5.0 m diameter at breast height, 82.1–86.3 m tall) Sequoiadendron giganteum (Lindley) J. Buchholz (giant sequoia) trees using a combination of architectural measurements and automated sensors that monitored summertime diel rhythms in sap flow, stem diameter and water potential. Stem water storage contributed 1.5–1.8% of water transpired at the tree tops, and hydraulic capacitance ranged from 2.6 to 4.1 l MPa−1 m−3. These values, which are considerably smaller than reported for shorter trees, may be associated with persistently low water potentials imposed by gravity and could indicate a trend of decreasing water storage dynamics with height in tree. Branch diameter contraction and expansion consistently and substantially lagged behind fluxes in water potential and sap flow, which occurred in sync. This lag suggests that the inner bark, which consists mostly of live secondary phloem tissue, was an important hydraulic capacitor, and that hydraulic resistance between xylem and phloem retards water transfer between these tissues. We also measured tree-base sap flux, which lagged behind that measured in trunks near the tree tops, indicating additional storage in the large trunks between these measurement positions. Whole-tree sap flow ranged from 2227 to 3752 l day−1, corroborating previous records for similar-sized giant sequoia and representing the largest yet reported for any individual tree. Despite such extraordinarily high daily water use, we estimate that water stored in tree-top stems contributes minimally to transpiration on typical summer days.
Abstract
Based on the measurement principle of psychrometer and experimental data, the influence of wind speed on humidity measurement is analyzed, and the uncertainty of humidity measured by ...psychrometer is evaluated by GUM method. The research results show that under the condition of high temperature and high humidity, the relative humidity measured by psychrometer is not sensitive to wind speed. When the relative humidity is 90%RH and air temperature is 85°C, the difference of relative humidity calculated by using different psychrometer coefficients is 0.03% RH. With the decrease of dry-bulb temperature and relative humidity, the influence of wind speed on relative humidity measurement gradually increases. When the relative humidity is 20%RH and air temperature is 20°C, the difference of relative humidity calculated by using different psychrometer coefficients is 2.64% RH. The main uncertainty of relative humidity measured by psychrometer is introduced by psychrometer coefficient which is a function of wind speed. Measurement uncertainty decreases with the increase of relative humidity while at the same dry-bulb temperature.
In recent years, environmental information monitoring in the agricultural field has become an important issue. There is an increasing demand for meteorological information in local areas such as a ...rice field, a greenhouse, etc., owned by an agricultural worker. Conventional research has been actively conducted on weather stations in local areas. However, weather stations that are inexpensive, highly accurate, and have achieved stable measurements indoors and outdoors for long periods of time (over a year) are not reported. In addition, there is a lack of research that simultaneously acquires weather information, stores weather information, and provides weather information to farmers. These three functions are important in the agricultural field. In this paper, we discuss the development of a meteorological observation device, the construction of a cloud server for storing meteorological information, and the provision of information to users. First, we develop the novel meteorological observation device (KOSEN-Weather Station), which applies a simple Aßmann's aspiration psychrometer for highly accurate temperature and humidity measurements. To evaluate the reliability of KOSEN-WS, we compare the weather information measured by KOSEN-WS with that of WXT520. As a result, it is shown that KOSEN-WS is viable. Then, KOSEN-WS is installed in the field, and the stability and durability of KOSEN-WS are examined. As a result, the KOSEN-WS has been operating stably over 19 months and provides weather information to users. Then, it is shown that the KOSEN-WS is able to operate continuously under the environment of -16.5 °C to 44.9 °C. Next, for the storage of meteorological information, we construct the cloud server. Then, a webpage is created to provide easy-to-understand weather information to farmers. Furthermore, to prevent damage to crops, if the current temperature is lower than the set temperature, or if the current temperature is higher than the set temperature, an alert is sent to the farmers. As a result, the system is highly evaluated by agricultural workers and JA staff. From the above results, the effectiveness of this system is shown.
The moisture storage curve is an important hygric property of porous building materials. It describes the moisture storage characteristic of a material via the relation between the moisture content ...and the moisture potential. Current experimental protocols for measuring moisture storage curves are not satisfactory, as they often require extensive facilities while still lacking the capability to handle the adsorption process in most of the over-hygroscopic range. This paper proposes two novel and simple methods – the semi-permeable membrane method and the psychrometer method – to solve these issues. Measurements on calcium silicate, autoclaved aerated concrete and ceramic brick are performed and validated by comparing the experimental outcomes obtained from these two novel methods and from other existing protocols. It is proven that the semi-permeable membrane method and the psychrometer method are applicable for both adsorption and desorption processes, the latter both from saturated and capillary moisture content. Limited by the accuracy of the psychrometer and the condensation caused by temperature fluctuations, these two methods show their best applicable range for capillary pressures below −1·105 Pa. The semi-permeable membrane method and the psychrometer method also feature in low cost, simple handling and application efficiency.
•Two novel methods for measuring the moisture storage curves are proposed.•They feature in wide applicable range, low cost, simple handling and efficiency.•Both adsorption and desorption in the over-hygroscopic range can be measured.•Tests on 3 representative porous building materials are performed and validated.
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