Annual variations of temperature in a sample of UK dwellings

The internal temperatures of 25 households in Northern Ireland were measured in each house at four locations: the bedrooms, living rooms, halls and kitchens, and analysed on seasonal, monthly and daily bases. In 80% of the homes the winter average daily temperature was between 15 °C and 20 °C and in summer between 20 °C and 23 °C, therefore maintaining a reasonably comfortable temperature throughout the year. In 14% of the homes, the daily average temperature was above 21 °C throughout the year, suggesting a higher household temperature than required for comfort, thus exhibiting wasteful energy behaviour. Three percent of the homes did not use their heating adequately and the winter average temperature was below 15 °C. For the majority of households, the highest indoor temperature was in August and the lowest in February. In general the peak temperatures of households occur in the evening after 8:00 pm. The peak bedroom temperatures occur between 10:00 pm and midnight and in the morning after 8:00 am. The peak living room temperature is generally in the evening while it is occupied. Correlations between the temperature difference between indoor and outdoor temperatures with outdoor temperature have been developed for each house and the four locations. The relationship between the fluctuations of average daily temperature with annual average temperature has been established.     

Solar radiation modelling for the simulation of photovoltaic systems

The effect of 12 different combinations of diffuse–global correlations and tilted surface radiation models on the accuracy of PV output simulation of a grid-connected photovoltaic (PV) system was studied using statistical methods. A site specific diffuse–global correlation was developed using local insolation data and the performance of this model was compared with those of two other diffuse–global correlations. The impact of diffuse–global correlations on the calculated inclined insolation for four different tilted surface radiation models was investigated on annual, seasonal and monthly basis. The accuracies of predicted 45° inclined plane insolation and PV output were improved when the site specific diffuse–global correlation was used in the main simulation model. The error between measured and predicted inclined insolation was higher in winter than summer. The prediction of PV output was improved by using an isotropic sky tilted surface radiation model instead of the anisotropic models. The accuracy of PV output was also improved when the proposed diffuse–global correlation was used.     

The effect of low insolation conditions and inverter oversizing on the long‐term performance of a grid‐connected photovoltaic system

The performance of a roof mounted grid‐connected photovoltaic (PV) system in Northern Ireland was monitored over 3 years on annual, seasonal and monthly bases. The overall system performance was adversely affected by low insolation conditions; 19% of total incident insolation was absorbed at irradiance level below 200 W/m² and 67% below 600 W/m², only 6·2% above 900 W/m². In summer and winter, the PV and system efficiencies were 9·0 and 8·5%, and 7·8 and 7·5%, respectively and inverter efficiencies were 86·8 and 85·8%, respectively. The inverter for this particular system was oversized; 77% of the total DC energy produced when inverter's operating load was 50% of its rated capacity. The annual average monthly system performance ratio (PR) was 0·61 with seasonal variation 0·59 to 0·63. The average monthly PV, system and inverter efficiencies over the whole monitored period were 8·8, 7·6 and 86·8%, respectively. The main losses of the system were inverter DC/AC conversion loss, inverter threshold loss and low insolation loss. Copyright © 2007 John Wiley & Sons, Ltd.     

The impact of array inclination and orientation on the performance of a grid-connected photovoltaic system

The impact of PV surface orientation and inclination on grid-connected photovoltaic system performance under maritime climates was investigated using validated TRNSYS simulations. Insolation, PV output, PV efficiency, inverter efficiency, system efficiency, performance ratio (PR) and PV savings were estimated annually, seasonally and on monthly bases for various surface inclinations and orientations. Incident insolation and PV output were maximum for a surface with inclination 30° facing due south and minimum for a vertical surface with orientation 90° east or west from south. The monthly optimum collection angle maximising incident insolation varied from 10° to 70°. For the particular location and system studied, the maximum annual PV efficiency, the inverter efficiency, the PR and the system efficiency were for a south-facing surface with an inclination of 20°. For a horizontal surface, the monthly variation of system parameters was significant over a year. For time-dependent tariff rates, the annual PV savings were higher for a system oriented with same orientation towards the west than east from south while for constants tariff rates, the PV savings was the same for east or west orientation from south.     

Long-term field operation of photovoltaic solar water pumps

Three-year, hourly averaged, field data have been analysed for eight installed photovoltaic (PV) systems. Correlations of PV array yield as a function of insolation have been developed using long-term field data considering PV as a part of system in which load affects its performance. Another scenario that considered infinite load like that for grid-connected PV system has been investigated and array yield correlations were obtained. Influence of ambient temperature and wind speed on PV array yield is investigated.     

矿物掺合料对混凝土徐变影响研究进展

掺加矿物掺合料是改善混凝土性能的主要措施之一,受到研究者的广泛关注。当前,已有大量研究表明矿物掺合料对混凝土徐变性能具有积极的作用,但缺少文献系统回顾和比较不同类型矿物掺合料对混凝土徐变的影响。本文从徐变机理、单掺和复掺不同类型矿物掺合料对混凝土徐变的影响等方面,对已有文献进行总结分析,以便为进一步研究提供参考和借鉴。     

Isolation of obligate anaerobic rumen bacteria capable of degrading the neurotoxin β‐ODAP (β‐N‐oxalyl‐L‐α,β‐diaminopropionic acid) as evaluated by a liquid chromatography/biosensor analysis system

Six pure strains of obligate anaerobes capable of degrading the toxin β‐N‐oxalyl‐L ‐α, β‐diaminopropionic acid (β‐ODAP) contained in grass pea (Lathyrus sativus) have been isolated from cow rumen. The new isolates were identified as Megasphaera elsdenii (five different genotypes) and Clostridium bifermentans using 16S rDNA analysis. The β‐ODAP degrading efficiency of the isolates was evaluated by measuring the amount of β‐ODAP in the growth medium, which contained β‐ODAP as the only carbon source, before and after incubation with the microbes. The method of analysis was liquid chromatography employing bioelectrochemical detection. The biosensor is based on co‐immobilising two enzymes, glutamate oxidase (GlOx) and horseradish peroxidase (HRP), on the end of a spectrographic graphite electrode. β‐ODAP is oxidised by GlOx to form H₂O₂, which in turn is bioelectrocatalytically reduced by HRP through a mediated reaction using a polymeric mediator incorporating Os^{2 + /3+} functionalities rapidly shuttling electrons with the electrode_giving rise to the analytical signal. On the basis of this analysis system, the new isolates are capable of utilising β‐ODAP as sole carbon source to a maximum of 90–95% within 5 days with concomitant increase in cell protein. Copyright © 2005 Society of Chemical Industry     

Optimal sizing of array and inverter for grid-connected photovoltaic systems

Optimum PV/inverter sizing ratios for grid-connected PV systems in selected European locations were determined in terms of total system output, system output per specific cost of a system, system output per annualised specific cost of a system, PV surface orientation, inclination, tracking system, inverter characteristics, insolation and PV/inverter cost ratio. Maximum total system output was determined for horizontal, vertical and 45° inclined surfaces for a low efficiency inverter for sizing ratios of 1.5, 1.8 and 1.3, respectively; and for a medium efficiency inverter with sizing ratios of 1.4, 1.5 and 1.2. PV surface orientation and inclination have little impact on the performance of a high efficiency inverter. For different PV tracking systems and for different inverter characteristics, the optimum sizing ratio varied from 1.1 to 1.3. The PV/inverter cost ratio and the PV and inverter lifetimes have significant impact on the optimum PV/inverter sizing ratio. A correlation relating optimum sizing ratio and PV/inverter cost ratio has been developed; the correlation coefficients were found to be functions of insolation and inverter type. The impact of PV/inverter sizing ratio on PV array performance was less when PV array has a much higher cost than the inverter. The optimum sizing ratio for PV/inverter cost ratio of 6 and low efficiency inverter system varied from 1.4 to 1.2 for low to high insolation sites. For a high efficiency inverter system, the corresponding variation was from 1.3 to 1.1.     

Operational Prediction of Groundwater Fluctuation in South Florida using Sequence Based Markovian Stochastic Model

The ecosystem of South Florida is characterized by a vast wetland system, karst surficial hydrogeology, and extended coastal boundary. The ecosystem is poised under risks of: ecological failure due to increased fragmentation by urbanization; groundwater flow disruption because of sinkhole formation; and intrusion of oceanic water with decreasing water table head because of drought or over pumping. It was found important to synthesize the spatiotemporal state of the groundwater hydrology and also develop a forecasting model to support the intensive management and monitoring in place. In this study, an objective was set to develop a stochastic sequence model capable of forecasting groundwater levels on a monthly span at a daily time scale. The groundwater level simulation was conceptualized as a sequence of daily fluctuating states of magnitudes and patterns that has a defined probability of occurrence. The model setup involved representation of daily fluctuation magnitudes in ten states and pattern changes in three states. The sequential occurrence of states of magnitudes and patterns at each time step was used for estimation of the transitional probabilities and employed in a hidden Markov model frame work for ensemble generation and estimation of posterior probabilities. A realization was chosen based on the highest maximum likelihood ratio of 90% and smallest root mean square error of 0.05–0.12 m against the historical data. A monthly forecasting at daily time step was done dynamically incorporating observed data at each time step and revising prior and posterior probability estimation in the hidden Markov model formulation. A case study was conducted at three well sites, which are situated at three different hydrogeologic settings. The model not only reproduced annual groundwater fluctuation patterns but also forecasted preceding monthly fluctuations at maximum likelihood ratio above 90% and root mean square error below 0.15 m. A further study was recommended first to analyze break point parametric estimation for seasonal analysis, and secondly to integrate the approach in other hydrological models for the purpose of synthetic groundwater fluctuation generation.     

Genetic diversity and correlation of bean caffeine content with cup quality and green bean physical characteristics in coffee (Coffea arabica L.)

BACKGROUND: Although people began to consume coffee for its stimulating effect, the demand for decaffeinated coffee is increasing and now accounts for 10% of the total amount of coffee consumed in the world. Forty‐two arabica coffee genotypes originating from Ethiopia were tested to assess caffeine content variability among them, and the correlation of caffeine content with cup quality and green bean physical characteristics. RESULTS: Green bean caffeine content was measured using high‐performance liquid chromatography, while cup quality was determined by professional coffee tasters. Caffeine content ranged from 9.1 to 13.2 g kg^?1 on dry mass basis (d.m.b.). Six genotypes—AD0291, AD0591, AD2491, AD2691, AD2791 and AD2891—had a caffeine content of less than 10.0 g kg^?1. Caffeine content showed negative and statistically significant correlations with cup quality attributes. Correlations between caffeine content and green bean physical characteristics were non‐significant. CONCLUSIONS: Simultaneous selection for low caffeine content and good cup quality is possible. Some accessions had low caffeine content, and may serve as a source of desirable genes for variety development of types with relatively low caffeine content. Copyright © 2008 Society of Chemical Industry