18420 research outputs found
Sort by
Reducing Indoor Noise Levels Using People’s Perception on Greenery
No full textEmployees working in cubicles of open-plan offices
in Indonesia were studied in regard to their perception on the
ability of indoor greenery to reduce noise levels. Sansevieria
trifasciata and Scindapsus sp were used. Each was placed in the
cubicle and noise levels were measured without plants, with
Sansevieria, and with Scindapsus in place. The meters showed
very insignificant difference. However, responses to surveys
indicated a perception of lower noise in the presence of greenery.
This seemed to be supported by prior knowledge and
preconception and may be useful in creating a “quieter” indoor
environment
Changes in Plant Nutrients, and Microbial Biomass in Different Soil Depths After Long-Term Surface Application of Secondary Treated Wastewater
No full textChanges in Plant Nutrients, and Microbial Biomass in
Different Soil Depths After Long-Term Surface
Application of Secondary Treated Wastewate
Heat Consumption Assessment of the Domestic Hot Water Systems in the Apartment Buildings
No full textThis study presents the analysis of energy consumption for domestic hot water in apartment buildings in Riga. The aggregate data contains information about 39 apartment buildings, including heat energy consumption and domestic hot water (DHW) consumption. The analysis is focused on the heat energy consumption in the DHW system.
The analysis characterizes the DHW consumption, energy consumption for DHW and energy losses in the DHW systems in apartment buildings
Microstructural Investigations of Ultra-High Performance Concrete Obtained by Pressure Application within the First 24 Hours of Hardening
No full textIn this study, the effect of pressure application (0–50
MPa) to fresh concrete right after casting and during the first 24
hours of hardening has been examined. Supplementary
cementitious materials in a form of silica fume, nanosilica and
ground quartz sand were used. The aim of pressure application
was to reduce porosity, thus improving concrete mechanical
properties. Considerable reduction in porosity and a subsequent
increase in compressive strength reaching the level of Ultra-High
Performance Concrete (UHPC) were achieved. Mechanical and
physical properties were tested and gas sorption porosimetry,
mercury intrusion porosimetry (MIP), X-ray diffraction (XRD),
as well as scanning electron microscopy (SEM) were used for
material characterization
Development Opportunities of the Small Hydroenergetics in Latvia and Smart Operating System for Small-Scale Hydropower Plants
No full textThe possibility of usage of one of the most
conventional and affordable local renewable energy resources –
water resources of small and medium-sized rivers, in Latvian
energy sector has been analyzed. The already known material of
this issue, which has been obtained on the basis of previous
studies by other authors published in different sources that vary
in certainty and reliability, is presented. Actually the presence of
this material to some extent was the basis of further research in
this direction. Development of the algorithm of small hydropower
optimization is in fact the basis of its control system and is based
on dynamic programming. The approbation of algorithm is
performed on the example of optimization of certain
hydropower
Evaluation of the Profitability of High Temperature Low Sag Conductors
No full textThe application of High-Temperature Low Sag
conductors is one of the possible methods for improving the
existing transmission network nowadays, especially if the
transmission network requires prospective expansion of new
electrical connections.
The purpose of the study has been to evaluate conductors of
conventional core designs like AS, ACSR and composite core
designs like ACCC and ACCR on the basis of the technical and
the economic criteria, and to establish which of these conductors
would be preferable for upgrading the existing network.
The comparative evaluation was based on an existing overhead
line model of the Latvian power network. The results of the
analysis are presented in this paper
Transmission and Optical Networks Creating by Using a Cooperative Game Theory Approach
No full textThis paper is dedicated to the task of planning
energy supply systems in the market environment. The
possibilities of forming coalitions between companies are
considered. In this case, for justifying the decisions and
distributing the gains, cooperative game theory is used. The
example with the proposed strategy is based on a real project of
330 kV and 110kV high voltage lines and optical communication
line between two substations and shows the rationality and
efficiency of using the considered approach
Design of Current Source DC/DC Converter for Interfacing a 5kw PEM Fuel Cell
No full textIn domestic applications the low DC output voltage of a hydrogen fuel cell used as the main power supply or a backup power source has to be matched to the level and frequency of the AC voltage of utility grid. The interfacing power converter systems usually consist of a DC/DC converter and an inverter. In this work, a DC/DC step-up converter stage is designed for interfacing a 5kW proton exchange membrane (PEM) fuel cell. The losses of DC/DC conversion are estimated and, basing on the relevant analysis, the most appropriate configuration of converter modules is selected for a DC/DC converter stage of increased efficiency. The authors present the results of experimental analysis and simulation for the selected configuration of four double inductor step-up push-pull converter modules
