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Building a model for consumption, production and efficiency of a combined heat and power (CHP) system can bring important data for planning and management activity of such a technological system. The results of this study will show the overall efficiency of a real cogeneration plant over a year. The study is based on the information from the daily database of an economic operator, during 2012. The CHP plant, having reciprocating internal combustion engines (RICE) as prime movers, provides the thermal energy to the district heating system of a city from Romania with 129,368 habitants. RICE are operating in simultaneous mode or in partial load. The numerical model reveals the behavior of the daily thermal, electrical and global efficiency, accordingly to the partial load. The model was applied in both calculation assumptions: using the lower heating value and the higher heating value of the natural gas. A statistical analysis of efficiencies of the CHP plant was made. Was performed the statistical analysis of the database efficiency (also called real efficiency) with the global efficiency calculated by the model (also called modelled efficiency). Linear and multiple regression equations explain the variance of the real efficiency and of the modelled global efficiency.

In the paper the authors analyze the possibility of using the energy recovered from combustion gases, for air cooling. The objective is to evaluate the thermal potential of combustion gases from a cogeneration plant with a 3 MW electric power, located in Buzau. The monitoring data for the cogeneration system shows that the average flue gas temperature at the exit to the atmosphere is 125° C and the mass flow rate of the combustion gases is 18351 kg/h. The thermal potential of combustion gases isused for the preparation of hot water at 85°C for the operation of a LiBr-H2O solution absorption plant. Finally, the authors present a comparative study between the classic cooling system using chiller with mechanical vapor compression (VCM) and the absorption plant supplied by recovered energy from the cogeneration system, high lighting the advantage of the proposed trigeneration system.

Copyright of Romanian Journal of Civil Engineering / Revista Română de Inginerie Civilă is the property of Matrix Rom and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents a technical study on energy consumption and performance of a refrigeration system used for food products refrigeration and congelation. The authors compared the two-stage refrigeration system with the cascade refrigeration system. The analysis was based on the thermodynamic cycles corresponding to each one of the proposed solutions. For the booster system several refrigerants were considered in the analysis for the upper loop, respectively R717, R404A, R407C and R417A. Based on the total energy consumption of the installation (compressor, fans, recirculation pumps), the overall performance coefficient of the installation was determined. The study showed that the lowest electrical energy consumption corresponds to the cascade refrigeration system with R717-R744 and the two-stage compression refrigeration system with R717. The difference between the 2 optimal variants is only 4.6%. Therefore, it is recommended that the choice of the final scheme to be made on the basis of an LCC (Life cycle cost) analyze, which takes into account the refrigerant charge, the initial investment cost, the operating costs and the electricity cost. [ABSTRACT FROM AUTHOR]

Climate change is an increasingly important global concern at this moment. Fossil fuels meet a majority of world energy needs and because buildings are large energy consumers, they are also a major contributor to global carbon emissions and greenhouse gas (GHG) production. It's important for the European Union, including Romania to avoid these problems. Buildings are responsible for 40% of energy consumption and 36% of CO2 emissions in the EU, according to United Nations Environment Programme (UNEP). The construction sector is developing since 2013 so in the future the energy consumption will increase very fast. As a result, renewable energy sources represent one of the main directions in reducing conventional energy consumption in buildings. In this paper the authors analyze solutions for decreasing the energy consumption required by the airconditioning system in an office building of 6466 m², located in Bucharest. The current air conditioning solutions are the classical ones, based on either fan coils, supplied with chilled water of 12/7 °C, or air-coolers, as part of an Air Handling Unit (AHU). In the latter case, the cooled water is prepared by a vapor compression refrigeration unit chiller of 190kW cooling capacity, working with R22. The solutions analyzed in this paper consider each of the following alternatives: a. Heat recovery from the exhausted air by using a heat exchanger integrated in the AHU; b. Replacement of the vapor compression refrigeration unit chiller with an one stage lithium bromide/water absorption refrigeration unit driven by solar energy; c. Coupling the above mentioned solutions. All these solutions are discussed and analyzed from both technical and economical points of view. [ABSTRACT FROM AUTHOR]

Copyright of Romanian Journal of Civil Engineering / Revista Română de Inginerie Civilă is the property of Matrix Rom and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The gas-liquid two-phase flow is characterized by continuous and local change of surface separation of phases and by their mutual interactions. Due to the instability of the flow, heat transfer and mass, a precise analytical approach is difficult to achieve. Despite these difficulties, efforts are underway to progress from the more frequent empirical studies to reliable analytical models. This requires an accurate research of the processes involved in the two phase flow and how they interact with one another. This paper aims to determine the pressure drop for a two-phase flow in a horizontal pipe of a heating plant. The author would like to to compare the results obtained by numerical simulation with existing results in the domain. The mixture is air-water, at an environmental temperature of 25 C. [ABSTRACT FROM AUTHOR]

Copyright of Romanian Journal of Civil Engineering / Revista Română de Inginerie Civilă is the property of Matrix Rom and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper develops a theoretical and experimental study on convective heat transfer characteristics in a mini-channel type air-cooler, operating with ice-slurry. Although ice slurry is usually employed as a secondary fluid in air conditioning systems, this paper investigates its behaviour as a primary fluid. Furthermore, since previous investigations on ice slurry mostly referred to plate heat exchangers, little information is yet available in the literature regarding ice slurry use in mini-channel heat exchangers, this study employed several correlations recommended by the open literature for binary mediums, such as ice-slurry, in order to identify the best fitted correlation in terms of best agreement with the experimental results obtained for the given geometrical configuration of the heat exchanger, ice mass fraction, and specific operating conditions. Besides the theoretical study, the authors have also developed an experimental study and a comparative analysis of theoretical vs. experimental results with respect to the heat transfer coefficient on ice-slurry side as a function of ice mass fraction, of ice-slurry flow rate and air flow rate. [ABSTRACT FROM AUTHOR]